Dipalladium and diplatinum bis(µ-alkanethiolato) complexes with a planar M2S2 ring

Abstract

Mononuclear complexes of formula [M(SR)₂(dppe)](M = Pd 1 or Pt 2; R = C₅H₉NMe, dppe = Ph₂PCH₂CH₂PPh₂) are formed in reactions of [MCl₂(dppe)] with the sodium salt of 4-mercapto-1-methylpiperidine NaSR in acetonitrile–methanol solution. Subsequent reaction of 1 with [PdCl₂(dppe)] and of 2 with [PtCl₂(dppe)] in acetonitrile solution produces the bridged dinuclear cationic complexes [M₂(µ-SR)₂(dppe)₂]²⁺, which are obtained as crystalline salts with tetraphenylborate anions (M = Pd 3 or Pt 4). An apparently mixed PtPd product 5 is formed in an analogous reaction from 1 and [PtCl₂(dppe)] or from 2 and [PdCl₂(dppe)]. The structures of complexes 1–5 have been determined crystallographically. Complexes 1 and 2 are isostructural, with a slightly distorted square-planar cis-MP₂S₂ co-ordination geometry. The isostructural complexes 3–5 also show square-planar co-ordination; the two aminothiolate ligands act as bridges between the metal atoms, giving a precisely planar central M₂S₂ ring. In all five structures the MP₂C₂ chelate rings have a twist conformation. The nitrogen atoms of the aminothiolates are not co-ordinated to the metal atoms. Infrared and ¹H, ³¹P and ¹⁹⁵Pt NMR spectra are presented and discussed. The combined evidence suggests that 5 is essentially a simple solid-solution mixture of pure complexes 3 and 4 in variable proportions, with at most a minor component of a genuinely heterobimetallic complex.