A reaction of [Pt4(CH3COO)3] (1) with an excess of diethyldithiophosphate (Et2dtpH) in CH3CN affords a tetrasubstituted derivative, [Pt4(CH3COO)4(Et2dtp)4], which is a mixture of two isomers. X-ray analyses of the isolated two isomers revealed that Et2dtp ligands in both isomers are coordinated in the pane of the Pt4 cluster core, and that coordination mode of Et2dtp is the chelate type in one isomer (2) whereas it is the bridge type in the other (3). 1H NMR studies showed that both 2 and 3 isomerize slowly in solution to give the same equilibrium mixture. The rate constants for the isomerization in CDCl3 at 40 °C were k1 = 1.2 x 10-4 s-1 (for the reaction from 2 to 3) and k2 = 1.5 x 10-4 s-1 (for the reaction from 3 to 2), respectively. Both 2 and 3 undergo the isomerization also in acetonitrile with similar reaction rate, but the mechanism is different from that in chloroform. Activation entropy for the reaction starting from 2 to 3 was -9 ± 9 J nol-1 K-1 in chloroform and -47 ± 11 J mol-1 K-1 in acetonitrile. The small |ΔS(+)| value for the reaction n chloroform suggests that the isomerization proceeds without bond cleavage through an intermediate where three sulfur atoms from two Et2dtp's are coordinated to each platinum. That is, the isomerization in chloroform is caused by rotation of the Pt4 cluster core within an array of eight S atoms arranged circularly in a single plane. On the other hand, the isomerization in acetonitrile proceeds via a Pt-S bond cleaved intermediate possibly by the solvent assisted mechanism. All the kinetic parameters for the reactions in CDCl3 and CD3Cl3 are reported.
ASJC Scopus subject areas
- 化学 (全般)