Ion-Pair Extraction with Tetracyanocyclopentadienides: A Method for Estimating Extraction Efficiency

Abstract

Ion-pair extraction with tetracyanocyclopentadienides (TCCPs) is an effective method for isolating ammonium cations; however, predicting the extractability of ammonium-TCCP ion pairs is challenging. Herein, the measured extraction coefficients (LogK_ex) of ammonium-TCCP ion pairs allowed the values of A (an index for anion extractability) for the TCCP anions to be determined (–3.1 to –1.4); these values were higher than and similar to those of perchlorate and picrate anions, respectively. The correlation between LogK_ex and the sum of the values of A and the calculated Log P of ammonium cations revealed that LogK_ex can be estimated by the equation LogK_ex = A + CLOGP_NR4 + 1.6, where CLOGP_NR4 is the CLOGP value obtained using the “no-plus” ammonium structure. The LogK_ex value can be used to predict the extractability of quaternary ammonium ions.

Introduction

Solvent extraction is the principal technique used in organic synthesis. The effectiveness of the approach depends on the partition coefficient (Log P), which is a fundamental index for organic compounds and an important parameter for determining absorption, distribution, metabolism, and excretion in medicinal chemistry. Therefore, a range of methods have been developed to predict the Log P values of organic compounds.^1,2) Solvent extraction of ionic organic compounds is typically performed after neutralization; thus, the Log P for ionizable compounds indicates the distribution coefficient of the neutral form. However, when the neutralization of ions is difficult, for example, when using quaternary ammonium salts, solvent extraction is not typically suitable for their isolation. Moreover, quaternary ammonium ions are important structural motifs in biological compounds such as betaines and cholinergic compounds, which maintain the normal physiological state of living organisms. Pharmaceutical products and other useful organic compounds,^3,4) including several antimicrobial drugs approved for clinical use, also incorporate quaternary ammonium structures.^5–7) In synthetic chemistry, quaternary ammonium salts are used as starting materials in the Hofmann elimination, Stevens rearrangement,⁸⁾ and in cross-coupling reactions.⁹⁾ Many quaternary ammonium salts, owing to their ionic nature, have water-soluble properties that make their handling in synthetic chemistry troublesome. In these cases, lipophilic anions are employed as ion-pair reagents for extraction.¹⁰⁾ Traditionally, picrate (pic^–),^11,12) perchlorate (${\text{ClO}}_4^{-}$), tetrafluoroborate (${\text{BF}}_4^{-}$), alkyl sulfonates,^13,14) and alkyl phosphonates¹⁵⁾ have been used as ion-pair reagents. However, such agents have drawbacks, such as the risk of explosion, surfactant properties (leading to foaming and emulsions), lack of structural diversity, and low lipophilicity. Although tetraarylborates (${\text{BAr}}_4^{-}$), such as tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF), are often used for ion-pair extraction,¹⁶⁾ their high lipophilicity can lead to non-selective extraction of alkali metal and ammonium cations. Therefore, the development of new types of lipophilic and low-coordination anions is necessary to extend and improve the practical applications of ion-pair extractions in organic synthesis.

Tetracyanocyclopentadienides (TCCPs, [C₅R(CN)₄]^–) and pentacyanocyclopentadienide (PCCP, [C₅(CN)₅]^–) are weakly basic anions, with the former bearing a site where an R substituent can be introduced.¹⁷⁾ PCCP and TCCPs are also characterized by being mainly composed of carbon and nitrogen atoms, with no fluorine atom present. Sodium salts of PCCP and TCCPs with various substituents were readily prepared from tetracyanothiophene and sulfones,¹⁸⁾ and the application of PCCP and TCCPs has been investigated in a range of chemistry fields, including biological studies¹⁹⁾ and catalytic reactions,^20,21) the creation of ion-pairing assemblies^22–24) and TCCP polymers,²⁵⁾ and their use as dopants in organic electronics.²⁶⁾ TCCPs (including PCCP) were found to have high lipophilicity despite their ionic nature and therefore were utilized as anionic phase-transfer catalysts to enhance reactions involving reactive cations.^27,28) Recently, we reported that ion-pair extraction with TCCPs is useful for separating quaternary ammonium cations²⁹⁾ (Fig. 1A). The addition of NaTCCP to an aqueous solution of quaternary ammonium halide leads to ion exchange and the formation of ion pairs of ammonium and TCCP, which can be extracted with CH₂Cl₂. In contrast, the use of a coordinating solvent, such as ethyl acetate or 4-methyltetrahydropyran, resulted in the nonselective extraction of both quaternary ammonium and sodium cations. The key feature of ion-pair extraction with the TCCP anion in CH₂Cl₂ is thus selective and effective extraction. As shown in Fig. 1B, NaClO₄ and NaBF₄ did not exhibit sufficient lipophilicity for the extraction of tetraethylammonium cations from the CH₂Cl₂ phase (entries 1–2). Sodium lauryl sulfate was ineffective for the ion-pair extraction because of the formation of an emulsion (entry 3). Extraction with NaBArF yielded a mixture of NaBArF and Et₄NBArF when an excess of NaBArF was used (entry 4). Among the conventional reagents, sodium picrate achieved both selective and effective extraction of tetraethylammonium cations (entry 5); however, picrate anions are highly explosive. Selective extraction of tetraethylammonium cations was achieved using Na[C₅(CO₂Et)(CN)₄], with Et₄N⁺[C₅(CO₂Et)(CN)₄]^– being selectively extracted irrespective of whether excess Et₄NCl or Na[C₅(CO₂Et)(CN)₄] was used (entries 6 and 7). Thus, NaTCCP exhibited outstanding performance compared with conventional ion-pair reagents for the ion-pair extraction of ammonium ions. In a previous study, we discovered that the ease of extraction of ammonium ions was dependent on the lipophilicity of substituent R on the cyclopentadienide ring. Quaternary ammonium ions with different lipophilicities were separated by ion-pair extraction using two different NaTCCP derivatives. Ion-pair extraction using TCCPs was also useful for the synthesis of complex quaternary ammonium cations (Fig. 1C). Thus, spiroammonium 3, obtained by the spirocyclization of cyclic amine 1 and tribromide 2, was isolated using ion-pair extraction with TCCPs. Ammonium 3 was subjected to an elimination reaction to give vinylammonium TCCP 4, which was isolated using the typical workup for organic synthesis. However, the previous studies did not clarify whether the extraction efficiencies of 3 and 4 were sufficient for isolating the ammonium products.

Fig. 1. Ion-Pair Extraction of Quaternary Ammoniums Using Tetracyanocyclopentadienides (TCCPs) Reported in Ref. 29

In this study, we investigated the extraction coefficients of a range of TCCP ion pairs, including quaternary and tertiary ammonium cations, between CH₂Cl₂ and water to establish a method for predicting the extraction efficiency of ammonium ion pairs.

Results and Discussion

A Method for Predicting the Efficiency of Ion-Pair Extraction

The ion-pair extraction mechanism is complex because cations and anions can exist in equilibrium between the associated and dissociated ions. In principle, the thermodynamic model of ion-pair extraction involves the equilibrium of cation/anion association and phase transfer of ion pairs.^30,31) Despite this theoretical background, several research groups, including Brändnström,¹³⁾ Motomizu,^32–34) and Goto,^35,36) reported that the extraction coefficient (LogK_ex) has a linear relationship with the sum of the extraction constants for cations, anions, and solvents. For example, Motomizu proposed that LogK_ex between CHCl₃ and water can be estimated using Eq. (1):

  

$${\text{LogK}}_{\text{ex}}\left({\text{CHCl}}_3/{\text{H}}_{\text{2}}\text{O}\right)=C+A$$ (1)

where C and A are the extraction constants for the cations and anions, respectively. In this study, we employed Eq. (1), proposed by Motomizu, because their values were obtained based on experiments using a CHCl₃/H₂O solvent system that was similar to the CH₂Cl₂/H₂O system used in our experiments.³⁷⁾ Motomizu measured the values of LogK_ex (CHCl₃/H₂O) for many types of salts with a symmetrical tetraalkylammonium ion and determined how much LogK_ex increased for each one-carbon extension. By calculating backward from there, they defined the value of C for each quaternary ammonium ion such that the value of C would be zero if the carbon atom number of the quaternary ammonium became zero. Thus, the value of A is defined as the extraction coefficient of the ion pair of the anion and a hypothetical tetraalkylammonium species without carbon atoms.³⁸⁾ During their examination of extraction solvents, Motomizu found that the LogK_ex of CH₂Cl₂/H₂O was larger than that of CHCl₃/H₂O by 0.75.³³⁾ Although Brändström¹³⁾ reported the solvent constants for CHCl₃ and CH₂Cl₂ were almost identical, we consider that the value proposed by Motomizu is more plausible because the dielectric constant of CHCl₃ (4.81) is smaller than that of CH₂Cl₂ (9.08)³⁹⁾ and the reaction proceeded faster in CH₂Cl₂ than in CHCl₃ in our previous study on the phase-transfer reaction with oxonium TCCP.²⁷⁾ Hence, the LogK_ex between CH₂Cl₂ and H₂O can be represented by Eq. (2):

  

$${\text{LogK}}_{\text{ex}}\left({\text{CH}}_{\text{2}}{\text{Cl}}_{\text{2}}{\text{/H}}_{\text{2}}\text{O}\right)=C+A+0.75$$ (2)

First, we determined the extraction coefficients (LogK_ex) for the ion pairs R₄N⁺TCCP^– in a CH₂Cl₂/H₂O solvent system using the shake-flask method (Fig. 2). The values of A for the TCCP anions were estimated based on the LogK_ex values for the ion pairs Et₄N⁺TCCP^– (5a–10a), and C for Et₄N⁺ (3.52). The obtained values of A were compared with those of other anions reported by Motomizu (Table 1). The values of A of tetrafluoroborate, iodide, and perchlorate were found to be much lower than those of TCCP and PCCPs, whereas that of picrate was similar to that of n-propyl ester ([C₅(CO₂Pr)(CN)₄]^–). These results are consistent with the extraction yields obtained in our experiment, as shown in Fig. 1B.

Fig. 2. Extraction Coefficient of Ammonium TCCPs (LogK_ex) between CH₂Cl₂ and Water Determined by the Shake–Flask Method

Table 1.  Extractability of Anions (A) for TCCP Anions and Comparison with Other Anions

	A
Cl–	–8.08a)
Br–	–6.89a)
${\text{BF}}_4^{-}$	–5.80a)
I–	–5.32a)
ClO–4	–5.03a)
[C5(CN)5]–	–3.1
[C5(CO2Et)(CN)4]–	–2.8
[C5(CO2Pr)(CN)4]–	–2.7
Picrate (pic–)	–2.45a)
[C5Ph(CN)4]–	–2.3
[C5(CO2Bu](CN)4]–	–2.3
[C5(CO2Pentyl](CN)4]–	–2.1
[C5(CO2Octyl](CN)4]–	–1.4

a)Values of A reported by Motomizu in Ref. 33.

We then focused on the lipophilicity of the ammonium cations. Although Motomizu described a method with which to calculate the values of C from the structure of a cation in detail,³³⁾ and several programs for predicting partition coefficients are currently available,¹⁾ prediction of ion lipophilicity remains challenging. Zhao and Abraham reported that the CLOGP calculations^40,41) were not consistent with the experimental results of their study of ammonium constants.⁴²⁾ In addition, in our attempt, CLOGP calculations using the ammonium structures themselves were clearly inappropriate because tertiary ammonium cations showed much higher values than quaternary ammonium cations (for example, –3.140 for Et₄N⁺ and 2.011 for Et₃NH⁺). The partition coefficient of neutral compounds (Log P) was responsible for the inversion between quaternary and tertiary ammonium species. The CLOGP of Et₃NH⁺ was the same as that of ion-free Et₃N, whereas the ionic structure of quaternary ammonium Et₄N⁺ was calculated without change. Therefore, calculations of charge-neutral structures were examined to estimate ammonium lipophilicity. Testa et al. adapted the value obtained from the corresponding neutral form of the ammonium cation in their study on the lipophilicity of quaternary ammonium cations.⁴³⁾ Zhao and Abraham proposed that structures in which “N⁺” was replaced with a “C” atom were useful for estimating the lipophilicity of quaternary ammoniums.⁴²⁾ In our previous study,²⁹⁾ we employed the structures of the corresponding ylides in which the acidic α-C–H protons of the corresponding ammonium groups were deprotonated. Therefore, we evaluated four types of structures: the ammonium ion (Type A), the ylide formed by deprotonation of the acidic proton (Type B), the “no-plus” ammonium structures where the positive sign was removed from the ammonium (Type C), and the CiN ammonium, where the C atom was used instead of N⁺ (Type D) (Fig. 3A). A list of typical CLOGP values is shown in Fig. 3B. In addition to a representative fragmental method CLOGP, similar calculations for ammonium cations were performed using established programs, including another fragmental method MiLogP,⁴⁴⁾ atomic-based methods Ghose–Crippen model,^45,46) iLOGP,⁴⁷) WLOGP,⁴⁸⁾ and XLOGP3,⁴⁹⁾ topological methods MLOGP⁵⁰⁾ and ALOGPS,^51,52) and a hybrid approach SILICOS-IT.⁵³⁾

Fig. 3. (A) Four Structures of Types A–D Were Examined to Estimate the Lipophilicity of the Et₄N⁺ Ion; (B) CLOGP Values Obtained Using Structures of Types A–D

^aStructures with the positive charge on ammonium removed. ^bCarbon atom instead of N+.

We examined the correlation between the extraction coefficient, LogK_ex (Fig. 2), and the sum of the values of A and Log P_ammo, where Log P_ammo is the calculated Log P value of ammonium obtained using each Log P program. Based on Eq. (2), LogK_ex is expected to be proportional to the sum of A and Log P_ammo with a slope of 1. Therefore, we created a regression line with a slope of 1 and evaluated the obtained model formula using the coefficient of determination (r²) (Table 2, Fig. 4).

Table 2.  Coefficient of Determination (r²) Values^a) for the Regression Lines between LogK_ex and the Sum of A and Log P_ammo

	Type A	Type B	Type C	Type D
CLOGP	—b)	0.814	0.864	0.467
Ghose–Crippen	—c)	—c)	0.796	0.701
iLOGP	—b)	—b)	0.632	0.710
XLOGP3	—b)	—b)	—b)	0.709
WLOGP	0.744	0.756	0.842	0.848
MLOGP	0.245	0.245	0.859	0.469
SILICOS-IT	—b)	—b)	0.691	0.872
ALOGPS	0.605	—b)	—b)	0.516
MiLogP	0.515	—c)	—c)	0.796

a) Calculated using the indicated program for structure types A–D in Fig. 3. The slope of the regression lines was fixed at 1 according to Eq. (1). The r² values larger than 0.84 are set in boldface. b) LogK_ex did not correlate with the sum of A and Log P_ammo. c) Values for Log P_ammo could not be calculated.

Fig. 4. Scatter Plot for LogKex (CH₂Cl₂/H₂O) and the Sum of A and CLOGP_NR4

The blue dots represent the data from this report in Fig. 2, and the dashed blue line represents the regression line created from them. The orange dots represent the data by Motomizu in Ref. 32b, corrected by the addition of a solvent constant of 0.75 (from CHCl3 to CH2Cl2). The eight orange dots in the dashed circle that deviated significantly from the regression line were from ion pairs with dye cations.

As shown in Table 2, calculations using ammonium structures without changes (Type A) resulted in a low correlation in many programs. Only WLOGP, ALOGPS, and MiLogP exhibited moderate correlations. The Values Log P_ammo from the ylide structures (Type B) did not correlate, except for CLOGP and WLOGP. For “no-plus” ammoniums in which the positive sign was removed from the parent ammoniums (Type C), many programs indicated good correlations. Furthermore, CiN structures in which N⁺ was replaced with C (Type D) showed correlations in all the examined programs. Good correlations were obtained in the CLOGP, WLOGP, and MLOGP programs with no ammonium structure (Type C) and the WLOGP and Silicos-IT programs with CiN (C instead of N⁺) structures (Type D). We adopted the regression line obtained by the CLOGP program with no ammonium structure (Type C) because the data for tetraalkylammonium salts reported by Motomizu³³⁾ were the closest to the regression line (see Supporting Information). As a result, we consider that Eq. (2) can be modified to Eq. (3):

  

$${\text{LogK}}_{\text{ex}}\left({\text{CH}}_{\text{2}}{\text{Cl}}_{\text{2}}{\text{/H}}_{\text{2}}\text{O}\right)\text{ = }A+{\text{CLOGP}}_{\text{NR4}}+\text{1.6}$$ (3)

where CLOGP_NR4 is the CLOGP calculated with no ammonium (Type C) structures. Reviewing Fig. 1B, the trace amount of extract that was obtained by the ion-pair extraction of tetraethylammonium with NaClO₄ and NaBF₄ can be explained by considering that the predicted LogK_ex for Et₄NClO₄ and Et₄NBF₄ were –0.4 and –1.2, respectively.⁵⁴⁾

The eight dots represented by Motomozu’s data deviate from the regression lines shown in Fig. 4. These are data for the ion pair of dye cations involving azo-dye cations, methylene blue, and Hofmann’s violet. The lipophilicity of these dye cations was enhanced by the delocalization of the positive charge, which increased the ionic radius. We assume that such resonance effects were not accounted for when the structures were modified, as in Types C and D, resulting in lower Log P values than the observed values. Zhao and Abraham also classified ammonium ions into eight groups in their study of ammonium lipophilicity.⁴²⁾ Currently, we cannot find any simple programs that correctly reflect the resonance effect of ammonium in predicting ammonium Log P values. Nevertheless, we believe that Eq. (3) can be used to indicate whether ammonium ion pairs can be effectively extracted in synthetic chemistry as long as the positive charge is localized at the nitrogen atom.

Reviewing Previous Studies Using Ion-Pair Extraction with TCCPs

We reviewed previous studies on the synthesis of vinylammonium using ion-pair extraction with TCCPs²⁹⁾ (Chart 1). Tertiary amine 12 was initially methylated with methyl triflate and then subjected to ion-pair extraction with Na[C₅(CN)₅]. The predicted LogK_ex value for ion pair 13 was 1.8; thus, ion pair 13 was extracted using CH₂Cl₂. Treatment of 13 with NaOMe led to elimination, and the formation of the unstable vinylammonium 14, the extractability of which was estimated to be sufficient based on its high predicted LogK_ex value of 1.9. In fact, although 14 was extracted with CH₂Cl₂, it was very unstable and underwent a facile 3-aza-Cope–Mannich cascade at room temperature, followed by elimination to give ammonium enone 15. Enone 15 was isolated without solvent extraction, which is reasonable considering its predicted LogK_ex value of –1.0.

Chart 1. Vinylammonium Synthesis Reported in Ref. 29 and Predicted LogK_ex Values (CH₂Cl₂/H₂O) Calculated with Eq. (3)

The spiroammonium compound 16 was generated via the reaction of secondary amine 1 with tribromide 2. Spiroammonium bromide 16 was separated from excess tribromide 2 by back-extraction into the aqueous layer. The predicted LogK_ex for ammonium bromide (–1.7) is consistent with the good efficiency of the back extraction. After the addition of TCCP, the spiroammonium ions became amenable to extraction because the predicted LogK_ex of ion pair 3 (2.9) was sufficiently high for CH₂Cl₂ extraction. After elimination with NaOMe, spirovinylammonium 4 maintained sufficient lipophilicity for solvent extraction, as indicated by the LogK_ex value (2.6). Although these previous experiments were conducted without the use of prediction by Eq. (3), it goes without saying that the experimental design would be easier if we could predict the extractability of these ion pairs in advance.

Conclusion

Ion-pair extraction is an effective method for isolating ionic compounds. Although this method was first established more than 50 years ago, there remains room for improvement, especially in the synthetic studies of complex ammonium cations.

The first problem was the limited number of lipophilic and stable anions that were suitable for application in synthetic chemistry. Specifically, ${\text{ClO}}_4^{-}$ and ${\text{BF}}_4^{-}$ have been used as relatively lipophilic anions, although their lipophilicities are not high enough for ion-pair extraction of ammonium cations in many cases. Tetraarylborate anions such as BArF are too lipophilic for the selective extraction of ammonium and metal cations. TCCPs and PCCP anions were found to have a high, but not too high, ability to extract ammonium cations, as shown by their values of A ranging between –1.2 and –3.0, indicating that they are highly suitable extraction agents for use in organic chemistry.

The second issue related to ion-pair extraction is that synthetic chemists are generally not sufficiently familiar with the established methods for predicting the extractability of ion pairs in syntheses of ammonium cations. We disclosed that the extractability of the ammonium–TCCP ion pairs between CH₂Cl₂ and water can be estimated by using Eq. (3), with anion hydrophobicity parameter A, CLogP_NR4 values of “no-plus” ammoniums (calculated using ChemBioDraw), and a constant value of 1.6. When we applied Eq. (3) to our previous experiments on the synthesis of vinylammoniums, we found that the extraction efficiency of the ion pairs could be visualized as a numerical value. Strictly speaking, the extraction constant of the ion pair is not simple because of the association between anions and cations. However, Eq. (3) can be used to obtain a rough estimation of the extractability of the ion pairs during investigations involving ammonium ions.

The use of ion-pair reagent NaTCCPs together with Eq. (3) thus allows the extractability of ion pairs to be predicted and will facilitate the design and development of ammonium syntheses. We believe that the development described herein will lead to increased strategic use of ion-pair extraction and new synthetic approaches.

Experimental

General Information

All the air- and moisture-sensitive reactions were performed under an argon atmosphere in commercially available dry solvents under anhydrous conditions. NMR spectra were recorded on AVANCE III HD (600 MHz), JNM-ECA (500 MHz), or JNM-ECZS (400 MHz) spectrometers. Chemical shifts of ¹H- and ¹³C-NMR spectra are reported in ppm relative to the solvent signals in CD₃CN (δ 1.94 ppm for ¹H-NMR and δ 1.39 ppm for ¹³C-NMR). Data are reported as follows: chemical shift, integration, and multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, m = multiplet, br = broad). High-resolution mass spectra were recorded using an Exactive Plus Orbitrap mass spectrometer (Thermo Fischer Scientific, Waltham, MA, U.S.A.) (electrospray ionization [ESI]).

Preparation of NaTCCPs

Na[C₅(CO₂Et)(CN)₄], Na[C_5-(CN)₅], and Na[C₅Ph(CN)₄] were prepared according to our previous report.¹⁸⁾ Four new NaTCCPs: Na[C₅(CO₂Pr)-(CN)₄], Na[C₅(CO₂Bu)(CN)₄], Na[C₅(CO₂Pentyl)(CN)₄], and Na[C₅(CO₂Octyl)(CN)₄], were synthesized as follows:

Propyl 2-(Phenylsulfonyl)acetate

To a solution of (phenylsulfonyl)acetic acid (3.05 g, 15.2 mmol, 1.0 equivalent (equiv.)), 1-propanol (2.19 mL, 29.3 mmol, 1.9equiv.), and 4-(dimethy-lamino)pyridine (186mg, 1.52 mmol, 0.1equiv.) in CH₂Cl₂ (60 mL) was added 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI·HCl) (3.20 g, 16.7 mmol, 1.1equiv.), and the mixture was stirred at room temperature. After 2.5 h, the reaction was quenched with saturated aqueous NH₄Cl solution, and the resulting mixture was extracted with CH₂Cl₂. The organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. Flash chromatography on silica gel (40% EtOAc in n-hexane) afforded propyl (phenylsulfonyl)acetate (3.15 g, 85%) as a colorless oil; IR (KBr) 2968, 1734, 1323, 1275, 1147 cm^–1; ¹H-NMR (CDCl₃, 600 MHz) δ: 7.96 (2H, m), 7.69 (1H, m), 7.59 (2H, m), 4.13 (2H, s), 4.05 (2H, t, J = 6.7 Hz), 1.59 (2H, qt, J = 7.5, 6.7 Hz), 0.87 (3H, t, J = 7.5 Hz); ¹³C-NMR (150 MHz, CDCl₃) δ: 162.4, 138.7, 134.2, 129.2, 128.5, 67.9, 61.0, 21.6, 10.1; HRMS (ESI/Orbitrap) m/z: [M+Na]⁺ Calcd for C₁₁H₁₅O₄SNa⁺ 265.0505. Found: 265.0505.

Butyl 2-(Phenylsulfonyl)acetate

To a solution of (phenylsulfonyl)acetic acid (3.39 g, 16.9 mmol, 1.0 equiv.), 1-butanol (4.7 mL, 50.8 mmol, 3.0 equiv.), and 4-(dimethylamino)pyridine (200 mg, 1.69 mmol, 0.1 equiv.) in CH₂Cl₂ (60 mL) was added EDCI·HCl (3.57 g, 18.6 mmol, 1.1 equiv.). The mixture was stirred at room temperature. After 2 h, the second portion of EDCI·HCl (1.60 g, 8.35 mmol, 0.5 equiv.) was added, and the reaction mixture was stirred for an additional 1 h. The reaction was quenched with saturated aqueous NH₄Cl solution, and the resulting mixture was extracted with CH₂Cl₂. The organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. Flash chromatography on silica gel (30% EtOAc in n-hexane) afforded butyl (phenylsulfonyl)acetate (3.64 g, 83%) as a colorless oil; ¹H-NMR (CDCl₃, 500 MHz) δ: 7.96 (2H, m), 7.70 (1H, m), 7.59 (2H, m), 4.12 (2H, s), 4.09 (2H, t, J = 6.5 Hz), 1.54 (2H, m), 1.29 (2H, m), 0.89 (3H, t, J = 7.4 Hz); ¹³C-NMR (125 MHz, CDCl₃) δ: 162.4, 138.7, 134.2, 129.2, 128.5, 66.2, 61.0, 30.2, 18.8, 13.6. ¹H- and ¹³C-NMR spectra were identical to the literature.⁵⁵⁾

Pentyl 2-(p-Toluenesulfonyl)acetate

To a solution of 2-(p-toluenesulfonyl)acetic acid (2.50 g, 11.6 mmol, 1.0 equiv.), 1-pentanol (3.8 mL, 35.0 mmol, 3.0 equiv.), and 4-(dimethylamino)pyridine (140 mg, 1.17 mmol, 0.1 equiv.) in CH₂Cl₂ (40 mL) was added EDCI·HCl (2.46 g, 12.8 mmol, 1.1 equiv.). The mixture was stirred at room temperature. After 2 h, the second portion of EDCI·HCl (1.19 g, 6.21 mmol, 0.5 equiv.) was added, and the reaction mixture was stirred for an additional 1 h. The reaction was quenched with saturated aqueous NH₄Cl solution, and the resulting mixture was extracted with CH₂Cl₂. The organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. Flash chromatography on silica gel (30% EtOAc in n-hexane) afforded pentyl (p-toluenesulfonyl)acetate (3.19 g, 96%) as a colorless oil; IR (KBr) 2956, 1739, 1327, 1151 cm^–1; ¹H-NMR (CDCl₃, 600 MHz) δ: 7.82 (2H, d, J = 7.9 Hz), 7.37 (2H, d, J = 7.9 Hz), 4.10 (2H, s), 4.07 (2H, t, J = 6.7 Hz), 2.46 (3H, s), 1.55 (2H, m), 1.30 (2H, m), 1.24 (2H, m), 0.89 (3H, t, J = 7.2 Hz); ¹³C-NMR (150 MHz, CDCl₃) δ: 162.5, 145.3, 135.8, 129.8, 128.5, 66.4, 61.0, 27.9, 27.7, 22.1, 21.6, 13.8; HRMS (ESI/Orbitrap) m/z: [M+Na]⁺ Calcd for C₁₄H₂₁O₄SNa⁺ 307.0975. Found: 307.0974;

Octyl 2-(Phenylsulfonyl)acetate

To a solution of (phenylsulfonyl)acetic acid (2.11 g, 10.5 mmol, 1.0 equiv.), 1-octanol (5.02 mL, 31.6 mmol, 3.0 equiv.), and 4-(dimethylamino)pyridine (129 mg, 1.05 mmol, 0.1 equiv.) in CH₂Cl₂ (50 mL) was added EDCI·HCl (2.22 g, 11.6 mmol, 1.1 equiv.), and the mixture was stirred at room temperature. After 3 h, the reaction was quenched with saturated aqueous NH₄Cl solution, and the resulting mixture was extracted with CH₂Cl₂. The organic layer was washed with brine, dried over MgSO₄, filtered, and concentrated under reduced pressure. Flash chromatography on silica gel (10% EtOAc in n-hexane) afforded octyl (phenylsulfonyl)acetate (2.45 g, 74%) as a colorless oil; IR (KBr) 2927, 2856, 1739, 1329, 1282, 1155 cm^–1; ¹H-NMR (CDCl₃, 600 MHz) δ: 7.96 (2H, m), 7.69 (1H, m), 7.59 (2H, m), 4.12 (2H, s), 4.07 (2H, t, J = 6.8 Hz), 1.54 (2H, m), 1.31–1.23 (10H, m), 0.89 (3H, t, J = 7.1 Hz); ¹³C-NMR (150 MHz, CDCl₃) δ: 162.4, 138.7, 134.2, 129.2, 128.5, 66.6, 61.0, 31.7, 29.1 (x2), 28.2, 25.6, 22.6, 14.1; HRMS (ESI/Orbitrap) m/z: [M+Na]⁺ Calcd for C₁₆H₂₅O₄SNa⁺ 335.1288. Found: 335.1288.

General Procedure for Synthesis of NaTCCPs (General Procedure A)

Preparation of Sodium 1,2,3,4-Tetracyano-5-(propoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pr)(CN)₄])

To a suspension of sodium hydride (60% dispersion in mineral oil, 2.63 g, 65.9 mmol) in tetrahydrofuran (THF) (40 mL) at 0 °C was added a solution of propyl 2-(phenylsulfonyl)acetate (4.84 g, 20.0 mmol, 1.0 equiv.) in THF (20 mL). The mixture was stirred at 0 °C for 1 h and then cooled to –40 °C. A solution of tetracyanothiophene (4.04 g, 22.0 mmol, 1.1 equiv.) in THF (40 mL) was added, and the reaction mixture was stirred at –40 °C for 2 h. The reaction was quenched with brine, and the resulting mixture was extracted with EtOAc. The extract was washed with brine, dried over Na₂SO₄, filtered, and concentrated under reduced pressure. Purification with flash chromatography on silica gel (EtOAc → 5% MeOH in EtOAc) and drying under vacuum (<2 mmHg) at 120 °C overnight afforded 5.60 g (quant.) of Na[C₅(CO₂Pr)(CN)₄] as a beige solid of mp 280–300 °C (decomp.); IR (KBr) 2966, 2927, 2225, 1693, 1483, 1281, 1124 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.24 (2H, t, J = 6.4 Hz), 1.77 (2H, tq, J = 6.4, 7.4 Hz), 1.06 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 124.2, 116.0, 115.3, 103.6, 101.1, 67.3, 22.8, 11.0; HRMS (ESI/Orbitrap) m/z: [M–Na]^– Calcd for C₁₃H₇N₄O₂^– 251.0574. Found: 251.0576.

Sodium 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (Na[C₅(CO₂Bu)(CN)₄])

According to the general procedure A, Na[C₅(CO₂Bu)(CN)₄] was prepared from butyl 2-(phenylsulfonyl)acetate (3.60 g, 14.2 mmol). Na[C₅(CO₂Bu)(CN)₄] (4.09 g, quant.) was obtained as a beige solid of mp 250–270 °C (decomp.); IR (KBr) 2962, 2873, 2225, 1697, 1485, 1282, 1120 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.26 (2H, t, J = 6.4 Hz), 1.73–1.67 (2H, m), 1.53–1.46 (2H, m), 0.94 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 124.2, 116.0, 115.3, 103.6, 101.1, 65.4, 31.5, 20.0, 14.0; HRMS (ESI/Orbitrap) m/z: [M–Na]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0733.

Sodium 1,2,3,4-Tetracyano-5-(pentoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pentyl)(CN)₄])

According to the general procedure A, Na[C₅(CO₂Pentyl)(CN)₄] was prepared from pentyl 2-(p-toluenesulfonyl)acetate (3.19 g, 11.2 mmol). Na[C₅(CO₂Pentyl)(CN)₄] (2.43 g, 71%) was obtained as a beige solid of mp 270–290 °C (decomp.); IR (KBr) 2960, 2870, 2224, 1691, 1485, 1284, 1124 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.25 (2H, t, J = 6.5 Hz), 1.75–1.69 (2H, m), 1.48–1.41 (2H, m), 1.36 (2H, sextet, J = 7.3 Hz), 0.91 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 124.2, 116.0, 115.3, 103.6, 101.1, 65.4, 31.5, 20.0, 14.0; ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 124.2, 116.0, 115.3, 103.6, 101.1, 65.8, 29.1, 28.9, 23.1, 14.3; HRMS (ESI/Orbitrap) m/z: [M–Na]^– Calcd for C₁₅H₁₁N₄O₂^– 279.0887. Found: 279.0890.

Sodium 1,2,3,4-Tetracyano-5-(octyloxycarbonyl)cyclopentadienide (Na[C₅(CO₂Octyl)(CN)₄])

According to the general procedure A, Na[C₅(CO₂Octyl)(CN)₄] was prepared from pentyl 2-(p-toluenesulfonyl)acetate (2.45 g, 7.85 mmol). Na[C₅(CO₂Octyl)(CN)₄] (2.17 g, 80%) was obtained as a beige solid of mp 243–253 °C (decomp.); IR (KBr) 2925, 2856, 2224, 1695, 1485, 1284, 1124 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.24 (2H, t, J = 6.5 Hz), 1.75–1.68 (2H, m), 1.46 (2H, quintet, J = 7.4 Hz), 1.36–1.21 (8H, m), 0.89–0.85 (3H, m); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 124.2, 116.0, 115.3, 103.6, 101.1, 65.8, 32.6, 29.98, 29.96, 29.4, 26.8, 23.4, 14.4; HRMS (ESI/Orbitrap) m/z: [M–Na]^– Calcd for C₁₈H₁₇N₄O₂^– 321.1357. Found: 321.1359.

Preparation of Ammonium–TCCP Ion Pairs and Determination of LogK_ex

Tetraethylammonium 1,2,3,4-Tetracyano-5-(ethoxycarbonyl)cyclopentadienide (5a)

5a was prepared according to the literature.²⁹⁾

General Procedure for Determination of LogK_ex for R₄N⁺TCCP^– between CH₂Cl₂ and Water (General Procedure B)

A 3.3 mM solution of 5a in water-saturated CH₂Cl₂ was distributed in six centrifuging tubes. CH₂Cl₂-saturated water was added to each tube until the total volume was 10 mL, and the tubes were shaken vigorously by a hand for 5 min. The resulting emulsions were centrifuged until two phases were separated. The CH₂Cl₂ phase was diluted 200 times with 50% MeOH/water, and the aqueous phase without dilution was analyzed using HPLC (40% MeOH/H₂O, ODS (L × I. D. = 10 cm × 4.6 mm), 0.8 mL/min, 2.7 min, 254 nm). LogK_ex for 5a was determined to be 1.48 ± 0.04 (n = 6).

Trimethylvinylammonium 1,2,3,4-Tetracyano-5-(ethoxycarbonyl)cyclopentadienide (5b)

5b was prepared according to the literature.²⁹⁾

LogK_ex for 5b

According to the general procedure B, 5b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (39% MeOH/H₂O, ODS (L × I. D. = 10 cm × 4.6 mm), 0.8 mL/min, 2.7 min, 254 nm). LogK_ex for 5b was determined to be 0.12 ± 0.20 (n = 6).

Triethylammonium 1,2,3,4-Tetracyano-5-(ethoxycarbonyl)-cyclopentadienide (5c)

A mixture of sodium 1,2,3,4-tetracyano-5-(ethoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Et)(CN)₄]) (100 mg, 0.385 mmol, 1.0 equiv.) and triethylamine hydrochloride (106 mg, 0.769 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h to afford 5c (119 mg, 91%) as a beige solid of mp 181–185 °C; IR (KBr) 3137, 3070, 2991, 2218, 1703, 1678, 1485, 1269, 1115 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.61 (1H, br s), 4.30 (2H, q, J = 7.2 Hz), 3.14 (6H, q, J = 7.3 Hz), 1.33 (3H, t, J = 7.2 Hz), 1.24 (9H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.1, 116.0, 115.3, 103.6, 101.1, 61.7, 48.1, 14.5, 9.3; HRMS (ESI/Orbitrap) m/z: [Et₃NH]⁺ Calcd for C₆H₁₆N⁺ 102.1277. Found: 102.1277; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Et)(CN)₄]^– Calcd for C₁₂H₅N₄O₂^– 237.0418. Found: 237.0422.

LogK_ex for 5c

According to the general procedure B, 5c was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 20 times with 50% MeOH/water were analyzed using HPLC (35% MeOH/H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 4.3 min, 254 nm). LogK_ex for 5c was determined to be 0.45 ± 0.08 (n = 6).

Acetylcholine 1,2,3,4-Tetracyano-5-(ethoxycarbonyl)cyclopentadienide (5d)

5d was prepared according to the literature.²⁹⁾

LogK_ex for 5d

According to the general procedure B, 5d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (35% MeOH/H₂O, ODS (L ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 6.0 min, 254 nm). LogK_ex for 5d was determined to be 0.26 ± 0.14 (n = 6).

Tetramethylammonium 1,2,3,4-Tetracyano-5-(ethoxycarbonyl)cyclopentadienide (5e)

A mixture of sodium 1,2,3,4-tetracyano-5-(ethoxycarbonyl)cyclopentadienide (5e) (30.0 mg, 0.110 mmol, 1.0 equiv.) and tetramethylammonium chloride (19.0 mg, 0.256 mmol, 2.4 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (20 mL × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h to afford 5e (26.0 mg, 76%) as a beige solid of mp 225–235 °C (decomp.); IR (KBr) 2989, 2777, 2214, 1703, 1485, 1271, 1115 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.29 (2H, q, J = 7.2 Hz), 3.07 (12H, t, J_C-N = 0.6 Hz), 1.33 (3H, t, J = 7.2 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.1, 124.1, 116.0, 115.3, 103.6, 101.1, 61.7, 56.3 (t, J_C-N = 3.6 Hz), 14.5; HRMS (ESI/Orbitrap) m/z: [Me₄N]⁺ Calcd for C₄H₁₂N⁺ 74.0964. Found: 74.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Et)(CN)₄]^– Calcd for C₁₂H₅N₄O₂^– 237.0418. Found: 237.0421.

LogK_ex for 5e

According to the general procedure B, 5e was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 20 times with 50% MeOH/water and the aqueous phase diluted 20 times with 50% MeOH/water were analyzed using HPLC (35% MeOH/H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.7 min, 254 nm). LogK_ex for 5e was determined to be –0.15 ± 0.06 (n = 6).

Choline 1,2,3,4-Tetracyano-5-(ethoxycarbonyl)cyclopentadienide (5g)

5g was prepared according to the literature.²⁹⁾

LogK_ex for 5g

According to the general procedure B, 5g was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (40% MeOH/H₂O, ODS-UG (L × I. D. = 10 cm  × 4.6 mm), 0.8 mL/min, 2.7 min, 254 nm). LogK_ex for 5g was determined to be –0.96 ± 0.07 (n = 6).

Tetraethylammonium Pentacyanocyclopentadienide (6a)

6a was prepared according to the literature.²⁹⁾

LogK_ex for 6a

According to the general procedure B, 6a was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (40% MeOH/H₂O, ODS (L × I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.7 min, 254 nm). LogK_ex for 6a was determined to be 1.22 ± 0.03 (n = 6).

Trimethylvinylammonium Pentacyanocyclopentadienide (6b)

6b was prepared according to the literature.²⁹⁾

LogK_ex for 6b

According to the general procedure B, 6b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (48% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.8 min, 254 nm). LogK_ex for 6b was determined to be 0.12 ± 0.07 (n = 6).

Acetylcholine Pentacyanocyclopentadienide (6d)

6d was prepared according to the literature.²⁹⁾

LogK_ex for 6d

According to the general procedure B, 6d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (40% MeOH/H₂O, ODS-UG (L × I. D.=10 cm  ×  4.6 mm), 0.8 mL/min, 2.1 min, 254 nm). LogK_ex for 6d was determined to be –0.17 ± 0.16 (n = 6).

Tetramethylammonium Pentacyanocyclopentadienide (6e)

A mixture of silver pentacyanocyclopentadienide²¹⁾ (72.5 mg, 0.293 mmol) and tetramethylammonium chloride (18.0 mg, 0.293 mg, 1.0 equiv.) in MeOH (2 mL) was stirred under dark for 36 h. The reaction mixture was filtered through a celite pad and the filtrate was concentrated under reduced pressure. Flash chromatography on DIOL silica (5→10% MeOH/CH₂Cl₂) provided 6e (34.4 mg, 54%) as a beige solid of mp >300 °C; IR (KBr) 2239, 2218, 1487, 1471 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 3.07 (12H, s); ¹³C-NMR (150 MHz, CD₃CN) δ: 114.3, 103.3, 56.3 (t, J_C-N = 3.6 Hz); HRMS (ESI/Orbitrap) m/z: [Me₄N]⁺ Calcd for C₁₅H₂₂O₄N⁺ 74.0964. Found: 74.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CN)₅]^– Calcd for C₁₀N₅^– 190.0159. Found: 190.0164.

LogK_ex for 6e

According to the general procedure B, 6e was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (65% MeOH/H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 1.1 min, 254 nm). LogK_ex for 6e was determined to be –0.52 ± 0.15 (n = 6).

Tetraethylammonium 1,2,3,4-Tetracyano-5-(propoxycarbonyl)cyclopentadienide (7a)

A mixture of sodium 1,2,3,4-tetracyano-5-(propoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pr)(CN)₄]) (50.8 mg, 0.185 mmol, 1.0 equiv.) and tetraethylammonium chloride (61.3 mg, 0.365 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h to afford 7a (63.1 mg, 89%) as a beige solid of mp 125–128 °C; IR (KBr) 2958, 2216, 1699, 1483, 1271, 1117 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.21 (2H, t, J = 6.4 Hz), 3.16 (8H, q, J = 7.3 Hz), 1.74 (2H, tq, J = 7.4, 6.4 Hz), 1.20 (12H, tt, J = 7.3, 1.9 Hz), 1.03 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 67.3, 53.1 (t, J_C-N = 3.0 Hz), 22.8, 11.1, 7.7; HRMS (ESI/Orbitrap) m/z: [Et₄N]⁺ Calcd for C₈H₂₀N⁺ 130.1590. Found: 130.1590; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pr)(CN)₄]^– Calcd for C₁₃H₇N₄O₂^– 251.0574. Found: 251.0577.

LogK_ex for 7a

According to the general procedure B, 7a was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (40% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 4.4 min, 254 nm). LogK_ex for 5c was determined to be 1.58 ± 0.02 (n = 6).

Trimethylvinylammonium 1,2,3,4-Tetracyano-5-(propoxy-carbonyl)cyclopentadienide (7b)

A mixture of sodium 1,2,3,4-tetracyano-5-(propoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pr)(CN)₄]) (137 mg, 0.30 mmol, 1.0 equiv.) and trimethylvinylammonium bromide (83 mg, 0.50 mmol, 1.7 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, and concentrated by rotary evaporation. Flash chromatography on DIOL silica (CH₂Cl₂ → 5% MeOH in CH₂Cl₂) afforded the ion pair 7b (116 mg, 69%) as a beige solid of mp 157–161 °C; IR (KBr) 2971, 2214, 1695, 1485, 1466, 1275, 1120 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.38 (1H, ddt, J = 15.0, 8.2, 3.5 Hz), 5.69 (1H, ddt, J = 15.2, 4.2, 2.6 Hz), 5.51 (1H, dtd, J = 8.2, 5.6, 4.2 Hz), 4.21 (2H, t, J = 6.4 Hz), 3.19 (9H, s), 1.74 (2H, qt, J = 7.3, 6.6 Hz), 1.03 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 143.5 (t, J_C-N = 4.8 Hz), 124.2, 116.0, 115.3, 112.8, 103.6, 101.1, 67.3, 55.3 (t, J_C-N = 3.6 Hz), 22.8, 11.0; HRMS (ESI/Orbitrap) m/z: [CH₂ = CH₂NMe₃]⁺ Calcd for C₈H₂₀N⁺ 86.0964. Found: 86.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pr)(CN)₄]^– Calcd for C₁₃H₇N₄O₂^– 251.0574. Found: 251.0577.

LogK_ex for 7b

According to the general procedure B, 7b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 20 times with 50% MeOH/water and the aqueous phase diluted 10 times with 50% MeOH/water were analyzed using HPLC (45% MeOH / H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.5 min, 254 nm). LogK_ex for 7b was determined to be 0.40 ± 0.07 (n = 6).

Acetylcholine 1,2,3,4-Tetracyano-5-(propoxycarbonyl)-cyclopentadienide (7d)

A mixture of sodium 1,2,3,4-tetracyano-5-(propoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pr)-(CN)₄]) (50.5 mg, 0.184 mmol, 1.0 equiv.) and acetylcholine chloride (69.7 mg, 0.365 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C. The ion pair 7d (59.1 mg, 81%) was obtained as a beige solid of mp 109–112 °C; IR (KBr) 2972, 2218, 1745, 1701, 1483, 1246, 1117 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.40 (2H, m), 4.21 (2H, t, J = 6.5 Hz), 3.54 (2H, m), 3.09 (9H, s), 2.06 (3H, s), 1.74 (2H, qt, J = 7.4, 6.5 Hz), 1.03 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 171.0, 162.3, 124.2, 116.0, 115.3, 103.6, 101.1, 67.3, 65.8 (t, J_C-N = 3.6 Hz), 58.6, 54.9 (t, J_C-N = 3.6 Hz), 22.8, 21.0, 11.0; HRMS (ESI/Orbitrap) m/z: [AcOCH₂CH₂NMe₃]⁺ Calcd for C₇H₁₆NO₂⁺ 146.1176. Found: 146.1174; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pr)(CN)₄]^– Calcd for C₁₃H₇N₄O₂^– 251.0574. Found: 251.0577.

LogK_ex for 7d

According to the general procedure B, 7d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (42% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.8 min, 254 nm). LogK_ex for 7d was determined to be 0.56 ± 0.06 (n = 6).

Tetramethylammonium 1,2,3,4-Tetracyano-5-(propoxycarbonyl)cyclopentadienide (7e)

A mixture of sodium 1,2,3,4-tetracyano-5-(propoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pr)(CN)₄]) (50.1 mg, 0.184 mmol, 1.0 equiv.) and tetramethylammonium chloride (40.0 mg, 0.365 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C. The ion pair 7e (37.7 mg, 63%) was obtained as a beige solid of mp 196–200 °C; IR (KBr) 2970, 2212, 1689, 1485, 1279, 1122 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.21 (2H, t, J = 6.4 Hz), 3.07 (12 H, t, J_C-N = 0.5 Hz), 1.74 (2H, qt, J = 7.4, 6.4 Hz), 1.03 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 161.9, 123.8, 115.7, 114.9, 103.3, 100.7, 66.9, 55.9 (t, J_C-N = 4.2 Hz), 22.5, 10.7; HRMS (ESI/Orbitrap) m/z: [Me₄N]⁺ Calcd for C₄H₁₂N⁺ 74.0964. Found: 74.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pr)(CN)₄]^– Calcd for C₁₃H₇N₄O₂^– 251.0574. Found: 251.0579.

LogK_ex for 7e

According to the general procedure B, 7e was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase without dilution and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (35% MeOH/H₂O, C8-UG (L × I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 4.9 min, 254 nm). LogK_ex for 7e was determined to be –0.07 ± 0.10 (n = 6).

Choline 1,2,3,4-Tetracyano-5-(propoxycarbonyl)cyclopenta-dienide (7g)

A mixture of sodium 1,2,3,4-tetracyano-5-(propoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pr)-(CN)₄]) (52.2 mg, 0.190 mmol, 1.0 equiv.) and choline chloride (50.8 mg, 0.365 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (20 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 7g (43.2 mg, 64%) was obtained as a beige solid of mp 145–155 °C (decomp.); IR (KBr) 3446, 2966, 2214, 1695, 1483, 1275, 1122 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.21 (2H, t, J = 6.4 Hz), 3.93 (2H, m), 3.37–3.34 (3H, m), 3.09 (9H, s), 1.74 (2H, m), 1.03 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 161.8, 123.7, 115.5, 114.8, 103.2, 100.6, 68.3 (t, J_C-N = 3.0 Hz), 66.8, 56.4, 54.5 (t, J_C-N = 3.6 Hz), 22.3, 10.6; HRMS (ESI/Orbitrap) m/z: [HOCH₂CH₂NMe₃]⁺ Calcd for C₅H₁₄ON⁺ 104.1070. Found: 104.1070; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pr)(CN)₄]^– Calcd for C₁₃H₇N₄O₂^– 251.0574. Found: 251.0578.

LogK_ex for 7g

According to the general procedure B, 7g was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (42% MeOH / H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.8 min, 254 nm). LogK_ex for 7g was determined to be –0.55 ± 0.06 (n = 6).

Tetraethylammonium 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (8a)

A mixture of sodium 1-(butoxy-carbonyl)-2,3,4,5-tetracyanocyclopentadienide (Na[C₅(CO₂Bu)(CN)₄]) (50.0 mg, 0.173 mmol, 1.0 equiv.) and tetraethylammonium chloride (57.9 mg, 0.347 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 8a (62.3 mg, 91%) was obtained as a beige solid of mp 144–146 °C; IR (KBr) 2925, 2218, 1701, 1483, 1273, 1117 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.26 (2H, t, J = 6.5 Hz), 3.16 (8H, q, J = 7.3 Hz), 1.73–1.67 (2H, m), 1.53–1.46 (2H, m), 1.21 (12H, tt, J = 7.2, 1.9 Hz), 0.95 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.4, 53.1 (t, J_C-N = 3.0 Hz), 31.5, 20.0, 14.0, 7.7; HRMS (ESI/Orbitrap) m/z: [Et₄N]⁺ Calcd for C₈H₂₀N⁺ 130.1590. Found: 130.1590; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0732.

LogK_ex for 8a

According to the general procedure B, 8a was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (45% MeOH/H₂O, ODS (L  ×  I. D.=10 cm  ×  4.6 mm), 4.0 min, 254 nm). LogK_ex for 8a was determined to be 2.01 ± 0.13 (n = 6).

Trimethylvinylammonium 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (8b)

A mixture of sodium 1-(butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (Na[C₅(CO₂Bu)(CN)₄]) (144 mg, 0.30 mmol, 1.0 equiv.) and trimethylvinylammonium bromide (83 mg, 0.50 mmol, 1.7 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure. Flash chromatography on DIOL silica (CH₂Cl₂ → 5% MeOH in CH₂Cl₂) afforded the ion pair 8b (128 mg, 73%) as a beige solid of mp 115–117 °C; IR (KBr) 2964, 2218, 1701, 1483, 1277, 1117 cm^-1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.38 (1H, ddt, J = 15.2, 8.2, 3.6 Hz), 5.69 (1H, ddt, J = 15.2, 4.4, 2.5 Hz), 5.51 (1H, dtd, J = 8.2, 5.6, 4.2 Hz), 4.26 (2H, t, J = 6.5 Hz), 3.19 (9H, s), 1.70 (2H, m), 1.49 (2H, m), 0.95 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 143.5 (t, J_C-N = 4.8 Hz), 124.2, 116.0, 115.3, 112.8, 103.6, 101.1, 65.4, 55.3 (t, J_C-N = 3.6 Hz), 31.5, 20.0, 14.0; HRMS (ESI/Orbitrap) m/z: [CH₂ = CH₂NMe₃]⁺ Calcd for C₈H₂₀N⁺ 86.0964. Found: 86.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0734.

LogK_ex for 8b

According to the general procedure B, 8b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 20 times with 50% MeOH/water and the aqueous phase diluted 10 times with 50% MeOH/water were analyzed using HPLC (48% MeOH/H₂O, ODS (L × I. D.=10 cm  ×  4.6 mm), 0.8 mL/min, 2.9 min, 254 nm). LogK_ex for 8b was determined to be 0.78 ± 0.03 (n = 6).

Triethylammonium 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (8c)

A mixture of sodium 1-(butoxy-carbonyl)-2,3,4,5-tetracyanocyclopentadienide (Na[C₅(CO₂Bu)-(CN)₄]) (50.6 mg, 0.176 mmol, 1.0 equiv.) and triethylamine hydrochloride (47.3 mg, 0.345 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 8c (59.1 mg, 92%) was obtained as a beige solid of mp 144–146 °C; IR (KBr) 3132, 2964, 2216, 1684, 1483, 1279, 1119 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.61 (1H, br t, J_N-H = 52.0 Hz, NH), 4.26 (2H, t, J = 6.5 Hz), 3.14 (6H, qd, J = 7.2, 4.2 Hz), 1.70 (2H, m), 1.49 (2H, m), 1.24 (9H, t, J = 7.3 Hz), 0.95 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.4, 48.1, 31.5, 20.0, 14.0, 9.3; HRMS (ESI/Orbitrap) m/z: [Et₃NH]⁺ Calcd for C₆H₁₆N⁺ 102.1277. Found: 102.1276; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0733.

LogK_ex for 8c

According to the general procedure B, 8c was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase and the aqueous phase were analyzed using HPLC (45% MeOH/H₂O, C8-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.5 min, 254 nm). LogK_ex for 8c was determined to be 0.98 ± 0.11 (n = 6).

Acetylcholine 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (8d)

A mixture of sodium 1-(butoxy-carbonyl)-2,3,4,5-tetracyanocyclopentadienide (Na[C₅(CO₂Bu)-(CN)₄]) (51.3 mg, 0.178 mmol, 1.0 equiv.) and acetylcholine chloride (64.3 mg, 0.347 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 8d (66.3 mg, 91%) was obtained as a beige solid of mp 103–106 °C; IR (KBr) 2962, 2216, 1745, 1701, 1483, 1246, 1113 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.40 (2H, m), 4.26 (2H, t, J = 6.4 Hz), 3.54 (2H, m), 3.09 (9H, s), 2.05 (3H, s), 1.70 (2H, m), 1.49 (2H, m), 0.94 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 171.0, 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.8 (t, J_C-N = 3.0 Hz), 65.4, 58.6, 54.9 (t, J_C-N = 3.6 Hz), 31.5, 21.0, 20.0, 14.0; HRMS (ESI/Orbitrap) m/z: [AcOCH₂CH₂NMe₃]⁺ Calcd for C₇H₁₆NO₂⁺ 146.1176. Found: 146.1174; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0732.

LogK_ex for 8d

According to the general procedure B, 8d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (50% MeOH/H₂O, ODS (L × I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.0 min, 254 nm). LogK_ex for 8d was determined to be 0.83 ± 0.05 (n = 6).

Tetramethylammonium 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (8e)

A mixture of sodium 1-(butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (Na[C₅(CO₂Bu)(CN)₄]) (50.4 mg, 0.175 mmol, 1.0 equiv.) and tetramethylammonium chloride (38.4 mg, 0.347 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 8e (51.2 mg, 86%) was obtained as a beige solid of mp 159–161 °C; IR (KBr) 2964, 2218, 1699, 1485, 1279, 1119 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.29 (2H, t, J = 6.5 Hz), 3.10 (12H, t, J_C-N = 0.6 Hz), 1.73 (2H, m), 1.52 (2H, m), 0.97 (3H, t, J = 7.4 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.4, 56.3 (t, J_C-N = 4.2 Hz), 31.5, 20.0, 14.0; HRMS (ESI/Orbitrap) m/z: [Me₄N]⁺ Calcd for C₄H₁₂N⁺ 74.0964. Found: 74.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0734.

LogK_ex for 8e

According to the general procedure B, 8e was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase without dilution and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (42% MeOH/ H₂O, C8-UG (L × I. D.=10 cm  ×  4.6 mm), 0.8 mL/min, 4.3 min, 254 nm). LogK_ex for 8e was determined to be 0.23 ± 0.12 (n = 6).

Pyridinium 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyc-lopentadienide (8f)

A mixture of sodium 1,2,3,4-tetracyano-5-(butoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Bu)-(CN)₄]) (51.9 mg, 0.189 mmol, 1.0 equiv.) and pyridine hydrochloride (42.9 mg, 0.365 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (20 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h to afford 8d (54.5 mg, 87%) as a beige solid of mp 137–139 °C; IR (KBr) 3523, 3253, 3108, 2966, 2218, 1697, 1485, 1275, 1120 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 8.72 (2H, d, J = 5.3 Hz), 8.64 (1H, tt, J = 7.9, 1.5 Hz), 8.08 (2H, t, J = 6.9 Hz), 4.28 (2H, t, J = 6.4 Hz), 2.73 (1H, br s, NH), 1.73 (2H, m), 1.52 (2H, m), 0.97 (3H, t, J = 7.4 Hz), and broad singlet signal of pyridinium NH is spreading between 0.5 ppm to 5.0 ppm; ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 148.9, 142.6 (t, J_C-N = 8.3 Hz), 128.8, 124.2, 116.0, 115.3, 103.6, 101.1, 65.4, 31.5, 20.0, 14.0; HRMS (ESI/Orbitrap) m/z: [pyridinium]⁺ Calcd for C₅H₆N⁺ 80.0495. Found: 80.0495; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0734.

LogK_ex for 8f

According to the general procedure B, 8f was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (50% MeOH / H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.0 min, 254 nm). LogK_ex for 8f was determined to be –0.12 ± 0.12 (n = 6).

Choline 1-(Butoxycarbonyl)-2,3,4,5-tetracyanocyclopentadienide (8g)

A mixture of sodium 1,2,3,4-tetracyano-5-(butoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Bu)(CN)₄]) (51.4 mg, 0.178 mmol, 1.0 equiv.) and choline chloride (48.4 mg, 0.347 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (20 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h to afford 8g (53.8 mg, 82%) as a beige solid of mp 116–118 °C; IR (KBr) 3448, 2962, 2216, 1693, 1485, 1279, 1119 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.29 (2H, t, J = 6.4 Hz), 3.96 (2H, m), 3.40–3.38 (3H, m), 3.12 (s, 9H), 1.73 (2H, m), 1.52 (2H, m), 0.97 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 68.8 (t, J_C-N = 3.0 Hz), 65.4, 56.9, 55.0 (t, J_C-N = 4.2 Hz), 31.5, 20.0, 14.0; HRMS (ESI/Orbitrap) m/z: [HOCH₂CH₂NMe₃]⁺ Calcd for C₅H₁₄ON⁺ 104.1070. Found: 104.1070; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Bu)(CN)₄]^– Calcd for C₁₄H₉N₄O₂^– 265.0731. Found: 265.0734.

LogK_ex for 8g

According to the general procedure B, 8g was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (50% MeOH / H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.3 min, 254 nm). LogK_ex for 8g was determined to be –0.25 ± 0.12 (n = 6).

Tetraethylammonium 1,2,3,4-Tetracyano-5-phenylcyclo-pentadienide (9a)

9a was prepared according to the literature.²⁹⁾

LogK_ex for 9a

According to the general procedure B, 9a was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (45% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 2.5 min, 254 nm). LogK_ex for 9a was determined to be 1.99 ± 0.04 (n = 6).

Trimethylvinylammonium 1,2,3,4-Tetracyano-5-phenylcyclopentadienide (9b)

9b was prepared according to the literature.²⁹⁾

LogK_ex for 9b

According to the general procedure B, 9b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (45% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 4.1 min, 254 nm). LogK_ex for 9b was determined to be 0.94 ± 0.12 (n = 6).

Triethylammonium 1,2,3,4-Tetracyano-5-phenylcyclopentadienide (9c)

A mixture of sodium 1,2,3,4-tetracyano-5-phenylcyclopentadienide (Na[C₅Ph(CN)₄]) (102 mg, 0.385 mmol, 1.0 equiv.) and triethylamine hydrochloride (104 mg, 0.756 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  ×  3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 9c (117 mg, 88%) was obtained as a beige solid of mp 76–79 °C; IR (KBr) 3068, 2989, 2206, 1464 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 7.60 (2H, m), 7.28 (2H, m), 7.39 (1H, m), 6.63 (1H, br t, J_H-N = 48.2 Hz, NH), 3.12 (6H, q, J = 7.2 Hz), 1.23 (9H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 138.4, 134.5, 129.8, 129.1, 129.0, 117.5, 116.1, 101.9, 96.3, 48.1, 9.3; HRMS (ESI/Orbitrap) m/z: [Et₃NH]⁺ Calcd for C₆H₁₆N⁺ 102.1277. Found: 102.1276; HRMS (ESI/Orbitrap) m/z: [C₅Ph(CN)₄]^– Calcd for C₁₅H₅N₄^– 241.0520. Found: 241.0525.

LogK_ex for 9c

According to the general procedure B, 9c was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (35% MeOH/H₂O, C8-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 4.5 min, 254 nm). LogK_ex for 9c was determined to be 1.13 ± 0.06 (n = 6).

Acetylcholine 1,2,3,4-Tetracyano-5-phenylcyclopentadienide (9d)

9d was prepared according to the literature.²⁹⁾

LogK_ex for 9d

According to the general procedure B, 9d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (45% MeOH / H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 2.6 min, 254 nm). LogK_ex for 9d was determined to be 0.63 ± 0.12 (n = 6).

Tetramethylammonium 1,2,3,4-Tetracyano-5-phenylcyclopentadienide (9e)

A mixture of sodium 1,2,3,4-tetracyano-5-phenylcyclopentadienide (Na[C₅Ph(CN)₄]) (25.3 mg, 0.095 mmol, 1.0 equiv.) and tetramethylammonium chloride (30.0 mg, 0.27 mmol, 2.8 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 9e (21.7 mg, 72%) was obtained as a beige solid of mp 230–240 °C (decomp.); IR (KBr) 2202, 1485 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 7.60 (2H, m), 7.47 (2H, m), 7.38 (1H, m), 3.06 (12H, s); ¹³C-NMR (150 MHz, CD₃CN) δ: 138.3, 134.5, 129.8, 129.1, 129.0, 117.5, 116.1, 101.9, 96.3, 56.3 (t, J_C-N = 4.2 Hz); HRMS (ESI/Orbitrap) m/z: [Me₄N]⁺ Calcd for C₄H₁₂N⁺ 74.0964. Found: 74.0964; HRMS (ESI/Orbitrap) m/z: [C₅Ph(CN)₄]^– Calcd for C₁₅H₅N₄^– 241.0520. Found: 241.0524.

LogK_ex for 9e

According to the general procedure B, 9e was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (45% MeOH / H₂O, ODS-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.5 min, 254 nm). LogK_ex for 9e was determined to be 0.77 ± 0.12 (n = 6).

Tetraethylammonium 1,2,3,4-Tetracyano-5-(pentoxycarbonyl)cyclopentadienide (10a)

A mixture of sodium 1,2,3,4-tetracyano-5-(pentoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pentyl)(CN)₄]) (50.0 mg, 0.165 mmol, 1.0 equiv.) and tetraethylammonium chloride (55.0 mg, 0.331 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 10a (62.3 mg, 91%) was obtained as a beige solid of mp 131–133 °C; IR (KBr) 2958, 2216, 1701, 1483, 1267, 1115 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.25 (2H, t, J = 6.5 Hz), 3.16 (8H, q, J = 7.3 Hz), 1.72 (2H, m), 1.45 (2H, m), 1.36 (2H, m), 1.21 (12H, tt, J = 7.2, 1.8 Hz), 0.91 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.7, 53.1 (t, J_C-N = 3.0 Hz), 29.1, 28.9, 23.1, 14.3, 7.7; HRMS (ESI/Orbitrap) m/z: [Et₄N]⁺ Calcd for C₈H₂₀N⁺ 130.1590. Found: 130.1589; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pentyl)(CN)₄]^– Calcd for C₁₅H₁₁N₄O₂^– 279.0887. Found: 279.0887.

LogK_ex for 10a

According to the general procedure B, 10a was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (50% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.0 min, 254 nm). LogK_ex for 10a was determined to be 2.13 ± 0.03 (n = 6).

Tetramethylvinylammonium 1,2,3,4-Tetracyano-5-(pentoxycarbonyl) cyclopentadienide (10b)

A mixture of sodium 1,2,3,4-tetracyano-5-(pentoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pentyl)(CN)₄]) (151 mg, 0.30 mmol, 1.0 equiv.) and trimethylvinylammonium bromide (83 mg, 0.50 mmol, 1.67 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure. Flash chromatography on DIOL silica (CH₂Cl₂ → 2% MeOH in CH₂Cl₂) afforded the ion pair 10b (156 mg, 86%) as a beige solid of mp 103–107 °C; IR (KBr) 2958, 2216, 1695, 1483, 1271, 1120 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.38 (1H, ddt, J = 15.2, 8.2, 3.6 Hz), 5.69 (1H, ddt, J = 15.2, 4.4, 2.4 Hz), 5.51 (1H, dtd, J = 8.2, 5.6, 4.2 Hz), 4.25 (2H, t, J = 6.5 Hz), 3.19 (9H, s), 1.72 (2H, m), 1.45 (2H, m), 1.36 (2H, sextet, J = 7.3 Hz), 0.91 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 143.5 (t, J_C-N = 4.8 Hz), 124.2, 116.0, 115.3, 112.8, 103.6, 101.1, 65.7, 55.3 (t, J_C-N = 4.2 Hz), 29.1, 28.9, 23.1, 14.3; HRMS (ESI/Orbitrap) m/z: [CH₂ = CH₂NMe₃]⁺ Calcd for C₈H₂₀N⁺ 86.0964. Found: 86.0964; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pentyl)(CN)₄]^– Calcd for C₁₅H₁₁N₄O₂^– 279.0887. Found: 279.0890.

LogK_ex for 10b

According to the general procedure B, 10b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 40 times with 50% MeOH/water and the aqueous phase diluted 10 times with 50% MeOH/water were analyzed using HPLC (50% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.5 min, 254 nm). LogK_ex for 10b was determined to be 1.12 ± 0.02 (n = 6).

Triethylammonium 1,2,3,4-Tetracyano-5-(pentoxycar-bonyl)cyclopentadienide (10c)

A mixture of sodium 1,2,3,4-tetracyano-5-(pentoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pentyl)(CN)₄]) (50.2 mg, 0.166 mmol, 1.0 equiv.) and triethylamine hydrochloride (45.8 mg, 0.331 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 10c (58.5 mg, 92%) was obtained as a beige solid of mp 85–87 °C; IR (KBr) 3120, 2964, 2216, 1711, 1682, 1485, 1466, 1267, 1117 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.61 (1H, br t, J_N-H = 52.0 Hz, NH), 4.25 (2H, t, J = 6.5 Hz), 3.14 (6H, q, J = 7.3 Hz), 1.72 (2H, m), 1.45 (2H, m), 1.36 (2H, sextet, J = 7.3 Hz), 1.24 (9H, t, J = 7.3 Hz), 0.91 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.7, 48.1, 29.1, 28.9, 23.1, 14.3, 9.3; HRMS (ESI/Orbitrap) m/z: [Et₃NH]⁺ Calcd for C₆H₁₆N⁺ 102.1277. Found: 102.1277; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pentyl)(CN)₄]^– Calcd for C₁₅H₁₁N₄O₂^– 279.0887. Found: 279.0890.

LogK_ex for 10c

According to the general procedure B, 10c was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (50% MeOH / H₂O, C8-UG (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 4.7 min, 254 nm). LogK_ex for 10c was determined to be 1.33 ± 0.03 (n = 6).

Acetylcholine 1,2,3,4-Tetracyano-5-(pentoxycarbonyl)cyclo-pentadienide (10d)

A mixture of sodium 1,2,3,4-tetracyano-5-(pentoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pentyl)-(CN)₄]) (50.0 mg, 0.165 mmol, 1.0 equiv.) and acetylcholine chloride (60.9 mg, 0.331 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 10d (66.5 mg, 94%) was obtained as a beige solid of mp 100–102 °C; IR (KBr) 2960, 2216, 1743, 1701, 1485, 1267, 1115 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.40 (2H, m), 4.25 (2H, t, J = 6.5 Hz), 3.54 (2H, m), 3.09 (9H, s), 2.06 (3H, s), 1.72 (2H, m), 1.45 (2H, m), 1.36 (2H, m), 0.91 (3H, t, J = 7.3 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 171.0, 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.8 (t, J_C-N = 3.6 Hz), 65.7, 58.6, 54.9 (t, J_C-N = 4.2 Hz), 29.1, 28.9, 23.1, 21.0, 14.3; HRMS (ESI/Orbitrap) m/z: [AcOCH₂CH₂NMe₃]⁺ Calcd for C₇H₁₆NO₂⁺ 146.1176. Found: 146.1174; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pentyl)(CN)₄]^– Calcd for C₁₅H₁₁N₄O₂^– 279.0887. Found: 279.0889.

LogK_ex for 10d

According to the general procedure B, 10d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase was diluted 200 times with 50% MeOH/water, and the aqueous phase without dilution was analyzed using HPLC (52% MeOH/H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.3 min, 254 nm). LogK_ex for 10d was determined to be 1.18 ± 0.06 (n = 6).

Pyridinium 1,2,3,4-Tetracyano-5-(pentoxycarbonyl)-cyclopentadienide (10f)

A mixture of sodium 1,2,3,4-tetracyano-5-(pentoxycarbonyl)cyclopentadienide (Na[C₅(CO₂Pentyl)(CN)₄]) (51.3 mg, 0.170 mmol, 1.0 equiv.) and pyridine hydrochloride (38.2 mg, 0.331 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (20 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 10f (54.5 mg, 89%) was obtained as a beige solid of mp 118–121 °C. IR (KBr) 3228, 3168, 3113, 2968, 2937, 2216, 1678, 1485, 1290, 1124 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 8.72 (2H, d, J = 5.3 Hz), 8.64 (1H, tt, J = 7.9, 1.5 Hz), 8.08 (2H, t, J = 6.9 Hz), 4.28 (2H, t, J = 6.5 Hz), 2.86 (1H, br s, NH), 1.74 (2H, m), 1.47 (2H, m), 1.39 (2H, sextet, J = 7.3 Hz), 0.93 (3H, t, J = 7.3 Hz), and broad singlet signal of pyridinium NH is spreading between 0.5 ppm to 5.0 ppm; ¹³C-NMR (150 MHz, CD₃CN) δ: 162.3, 148.9, 142.6 (t, J_C-N = 8.3 Hz), 128.8, 124.2, 116.0, 115.3, 103.6, 101.1, 65.7, 29.1, 28.9, 23.1, 14.3; HRMS (ESI/Orbitrap) m/z: [pyridinium]⁺ Calcd for C₅H₆N⁺ 80.0495. Found: 80.0494; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Pentyl)(CN)₄]^– Calcd for C₁₅H₁₁N₄O₂^– 279.0887. Found: 279.0891.

LogK_ex for 10f

According to the general procedure B, 10f was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase diluted 200 times with 50% MeOH/water were analyzed using HPLC (50% MeOH / H₂O, ODS-UG (L x I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.3 min, 254 nm). LogK_ex for 10f was determined to be 0.21± 0.05 (n = 6).

Tetraethylammonium 1,2,3,4-Tetracyano-5-(octylox-ycarbonyl)cyclopentadienide (11a)

A mixture of 1,2,3,4-tetracyano-5-(octyloxycarbonyl)cyclopentadienide (Na[C₅(CO₂Octyl)(CN)₄]) (50.0 mg, 0.140 mmol, 1.0 equiv.) and tetraethylammonium chloride (36.0 mg, 0.21 mmol, 1.5 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 11a (64.2 mg, 98%) was obtained as a beige solid of mp 112–113 °C; IR (KBr) 2925, 2216, 1701, 1483, 1267, 1119 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.25 (2H, t, J = 6.4 Hz), 3.16 (9H, q, J = 7.3 Hz), 1.71 (2H, m), 1.46 (2H, quintet, J = 7.4 Hz), 1.35–1.26 (8H, m), 1.20 (12H, tt, J = 7.2, 1.8 Hz), 0.88 (3H, t, J = 7.0 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.7, 53.1 (t, J_C-N = 3.0 Hz), 32.6, 29.99, 29.96, 29.4, 26.8, 23.4, 14.4, 7.7; HRMS (ESI/Orbitrap) m/z: [Et₄N]⁺ Calcd for C₈H₂₀N⁺ 130.1590. Found: 130.1590; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Octyl)(CN)₄]^– Calcd for C₁₈H₁₇N₄O₂^– 321.1357. Found: 321.1362.

LogK_ex for 11a

According to the general procedure B, 11a was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (60% MeOH / H₂O, ODS (L × I. D. = 10 cm  ×  4.6 mm), 3.7 min, 254 nm). LogK_ex for 11a was determined to be 2.89±0.14 (n = 6).

Trimethylvinylammonium 1,2,3,4-Tetracyano-5-(octo-xycarbonyl)cyclopentadienide (11b)

A mixture of 1,2,3,4-tetra-cyano-5-(octyloxycarbonyl)cyclopentadienide (Na[C₅(CO₂Octyl)(CN)₄]) (40.0 mg, 0.116 mmol, 1.0 equiv.) and trimethylvinylammonium bromide (33.3 mg, 0.200 mmol, 1.7 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 11b (47.5 mg, quant.) was obtained as a beige solid of mp 104–107 °C; IR (KBr) 2920, 2852, 2218, 1697, 1483, 1468, 1279, 1120 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.38 (1H, ddt, J = 15.2, 8.3, 3.5 Hz), 5.69 (1H, ddt, J = 15.2, 4.0, 2.6 Hz), 5.51 (1H, dtd, J = 8.2, 5.6, 4.2 Hz), 4.25 (2H, t, J = 6.5 Hz), 3.19 (9H, s), 1.71 (2H, m), 1.46 (2H, quintet, J = 7.5 Hz), 1.36–1.25 (8H, m), 0.88 (3H, t, J = 7.0 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 143.5 (t, J_C-N = 4.8 Hz), 124.2, 116.0, 115.3, 112.8, 103.6, 101.1, 65.7, 55.3 (t, J_C-N = 3.6 Hz), 32.6, 29.98, 29.96, 29.4, 26.8, 23.4, 14.4; HRMS (ESI/Orbitrap) m/z: [CH₂ = CH₂NMe₃]⁺ Calcd for C₈H₂₀N⁺ 86.0964. Found: 86.0963; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Octyl)(CN)₄]^– Calcd for C₁₈H₁₇N₄O₂^– 321.1357. Found: 321.1360.

LogK_ex for 11b

According to the general procedure B, 11b was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (50% MeOH / H₂O, ODS (L  ×  I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 4.4 min, 254 nm). LogK_ex for 11b was determined to be 2.30 ± 0.22 (n = 6).

Triethylammonium 1,2,3,4-Tetracyano-5-(octyloxycarbonyl)cyclopentadienide (11c)

A mixture of 1,2,3,4-tetracyano-5-(octyloxycarbonyl)cyclopentadienide (Na[C₅(CO₂Octyl)(CN)₄]) (50.5 mg, 0.147 mmol, 1.0 equiv.) and triethylamine hydrochloride (41.9 mg, 0.299 mmol, 2.0 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 11c (64.9 mg, quant.) was obtained as a beige solid of mp 100–104 °C; IR (KBr) 3446, 3093, 2925, 2218, 1701, 1682, 1483, 1466, 1267, 1115 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 6.63 (1H, br t, J_N-H = 52.0 Hz, NH), 4.24 (2H, t, J = 6.5 Hz), 3.14 (6H, qd, J = 7.1, 4.1 Hz), 1.71 (2H, m), 1.46 (2H, quintet, J = 7.4 Hz), 1.36–1.25 (8H, m), 1.24 (9H, t, J = 7.2 Hz), 0.88 (3H, t, J = 7.1 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ: 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.7, 48.1, 32.6, 29.99, 29.96, 29.4, 26.8, 23.4, 14.4, 9.3; HRMS (ESI/Orbitrap) m/z: [Et₃NH]⁺ Calcd for C₆H₁₆N⁺ 102.1277. Found: 102.1277; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Octyl)(CN)₄]^– Calcd for C₁₈H₁₇N₄O₂^– 321.1357. Found: 321.1361.

LogK_ex for 11c

According to the general procedure B, 11c was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (65% MeOH/H₂O, C8-UG (L × I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 3.8 min, 254 nm). LogK_ex for 11c was determined to be 2.04 ± 0.15 (n = 6).

Acetylcholine 1,2,3,4-Tetracyano-5-(octyloxycarbonyl)-cyclopentadienide (11d)

A mixture of 1,2,3,4-tetracyano-5-(octyloxycarbonyl)cyclopentadienide (Na[C₅(CO₂Octyl)(CN)₄]) (40.0 mg, 0.110 mmol, 1.0 equiv.) and acetylcholine chloride (39.0 mg, 0.267 mmol, 2.5 equiv.) in water (10 mL) was extracted with CH₂Cl₂ (15 mL  × 3). The organic layer was dried over MgSO₄, filtered, concentrated by rotary evaporation, and dried under reduced pressure (approx. 2 mmHg) at 40 °C for 24 h. The ion pair 11d (43.7 mg, 85%) was obtained as a beige solid of mp 93–96 °C; IR (KBr) 2925, 2856, 2216, 1739, 1697, 1481, 1244 cm^–1; ¹H-NMR (CD₃CN, 600 MHz) δ: 4.40 (2H, m), 4.24 (2H, t, J = 6.5 Hz), 3.54 (2H, m), 3.09 (9H, s), 2.05 (3H, s), 1.71 (2H, m), 1.46 (2H, quintet, J = 7.4 Hz), 1.35–1.25 (8H, m), 0.88 (3H, t, J = 7.1 Hz); ¹³C-NMR (150 MHz, CD₃CN) δ:171.0, 162.2, 124.2, 116.0, 115.3, 103.6, 101.1, 65.8 (t, J_C-N = 3.6 Hz), 65.7, 58.6, 54.9 (t, J_C-N = 4.2 Hz), 32.6, 29.99, 29.96, 29.4, 26.8, 23.4, 21.0, 14.4; HRMS (ESI/Orbitrap) m/z: [AcOCH₂CH₂NMe₃]⁺ Calcd for C₇H₁₆NO₂⁺ 146.1176. Found: 146.1174; HRMS (ESI/Orbitrap) m/z: [C₅(CO₂Octyl)(CN)₄]^– Calcd for C₁₈H₁₇N₄O₂^– 321.1357. Found: 321.1362.

LogK_ex for 11d

According to the general procedure B, 11d was partitioned between CH₂Cl₂ and H₂O. The CH₂Cl₂ phase diluted 200 times with 50% MeOH/water and the aqueous phase without dilution were analyzed using HPLC (60% MeOH/H₂O, ODS (L × I. D. = 10 cm  ×  4.6 mm), 0.8 mL/min, 5.4 min, 254 nm). LogK_ex for 11d was determined to be 2.16 ± 0.15 (n = 6).

Acknowledgments

This research was partially supported by Grant-in-Aid for Scientific Research (C) (22K06539) from the Japan Society for the Promotion of Science (JSPS), a research fund from the Research Institute of Meijo University, and the Meijo Research Promotion Organization for Carbon Neutrality.

Conflict of Interest

The authors declare no conflict of interest.

Supplementary Materials

This article contains supplementary materials. Data for distribution constants (LogK_ex) of ion pairs 5–11, scatter plots between LogK_ex and A+Log P_ammo, spectral data, copies of ¹H- and ¹³C-NMR spectra (PDF). These materials are available free of charge via the Internet.

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• 54)  A reviewer raised a question whether triflimide (Tf₂N) anion is useful for the ion-pair extraction using CH₂Cl₂ as an extraction solvent. Because we could not find the value of A for the Tf₂N anion in the literature, we attempted ion-pair extraction of Et₄NCl, trimethylvinylammonium bromide, and choline chloride with KNTf₂, which resulted in 99, 82, and 15% extraction yields, respectively. These extraction yields were close to the pentacyanocyclopentadienide (PCCP) anion reported in reference 29. Therefore, we speculated that the value of A for Tf₂N anion is similar to that of PCCP.
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