Bulletin of the Chemical Society of Japan
Online ISSN : 1348-0634
Print ISSN : 0009-2673
ISSN-L : 0009-2673
Platinum(II)-Olefin Complexes Containing Amino Acids. III. Optical Inversion and Substitution of Coordinated Olefins in Optically Active trans(N)-Chloro-L-prolinato-olefinplatinum(II) Complexes in Organic Solvents
Kazuo KonyaJunnosuke FujitaHiroaki KidoKazuo Saito
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1972 Volume 45 Issue 7 Pages 2161-2165

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Abstract

Optical inversion of coordinated 2-methyl-2-butene and trans-2-butene in trans(N)-chloro-L-prolinato-olefinplatinum(II), trans(N)-[PtCl(L-prol)(olefin)] (nitrogen of L-prolinate ion is trans to the olefin), i.e. the interconversion between diastereoisomers (Fig. 1), has been kinetically studied in acetone by measuring the decrease in the intensity of circular dichroism (CD) in near ultraviolet region. The rate was measurable only in the presence of olefin, and can be expressed by the relation, Rate=k[complex][olefin]. The Ea and the ΔS\ eweq values for the two complexes are 7.8±1.0 and 9.0±1.0 kcal/mol, and −44 and −39 entropy unit, respectively. The coordinated trans-2-butene is replaced by other olefins, 2,3-dimethyl-2-butene, 2-methyl-2-butene, trans-2-butene (optical inversion), and styrene, under similar conditions to give the same rate formula. The second order rate constant increases in the given order. The inversion seems to take place via bimolecular mechanism with excessive olefin as nucleophile. The corresponding complexes containing styrene and its para derivatives give such an inversion much faster in the absence of excess of olefin. With change of para substituents, the rate increases in the order, methoxy<methyl<hydrogen<chloro<nitro. This seems to be related with their electrondrawing ability.

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