DIPALLADIUM AND DIPLATINUM BIS(MU-ALKANETHIOLATO) COMPLEXES WITH A PLANAR M2S2 RING

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 rationic complexes [M2(mu-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 H-1, P-31 and Pt-195 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.