¹³C-NMR Spectra of 2, 4-Pentanedione and 1-(p-Substituted phenyl)1, 3-butanediones and Their Cobalt(111) Complexes

Abstract

¹³C-NMR spectra of 2, 4-pentanedione [1] and 1-(p-substituted phenyl)-1, 3-butanediones [2]J and their cobalt(III) complexes [3], [4] were measured in benzene-d6 chloroform-d and DMSO-d6, solutions. The signals of [1] in these solvents were observed around 202, 58, 3Oppm for the Keto (K) form, and around 191, 100 and 25ppm for the enol (E) form. The signals of the K form disappeared, as the sample concentration is lowered. By cornplexation, the signals near 191 and 100 ppm for the E form shifted to the higher magnetic field side, while the signal near 25ppm, the lower magnetic field side. In chloroform-d, the signals due to the acetoacetyl group of [2] were observed around 193, 182, 96 and 25ppm for the E form. In DMSO-d₆, however, the signals for the K form were also observed around 53 and 3Oppm in addition to the signals for the E form. The ¹³C chemical shift of the acetoacetyl group for fac and mer isomers of [2] approximated to those for the E form of [2]. Each ¹³C of this group for the mer isomer was separated to the three signals with the difference of ±0.2 ppm. Linear relationships were found to exist between the 13C chemical shift for the acetoacetyl group of [2], [4] and Hammett parameters (δ_pp), Δ(the difference of chemical shift between both carbonyl carbons) of [2] and pK_d, and δof [4]and 10Dq.