Chemistry of platinum sulphido-complexes. Part 6. Reactions of [Pt2(µ-S)2(PPh3)4] with the rhodium complexes [(RhL2Cl)2](L = CO or C2H4) and [Rh(2,6-Me2C6H3NC)4]PF6. Crystal and molecular structures of [Pt2Rh(µ-S)2(PPh3)4(CO)2][Rh(CO)2Cl2]·C3H6O and [Pt2Rh(µ-S)2(PPh3)4(2,6-Me2C6H3NC)2]PF6

Abstract

The compound [Pt2(µ-S)2(PPh3)4] reacts with the chloride-bridged rhodium dimers [{Rh(CO)2Cl}2] and [{Rh(C2H4)2Cl}2] to give [Pt2Rh(µ-S)2(PPh3)4(CO)2][Rh(CO)2Cl2](1) and [Pt2Rh(µ-S)2(PPh3)4(C2H4)2]Cl (2a) respectively. The reactions of compound (1) and the PF6– derivative of (2a) with the chelating diphosphine Ph2PCH2CH2PPh2 have also been studied and the products characterised on the basis of n.m.r. data. The reaction of [Pt2(µ-S)2(PPh3)4] with [Rh(2,6-Me2C6H3NC)4]PF6 results in the formation of [Pt2Rh(µ-S)2(PPh3)4(2,6-Me2C6H3NC)2]PF6(3). The molecular structures of compounds (1) and (3) have been determined by single-crystal X-ray techniques using diffractometer data. Compound (1) crystallises in the monoclinic space group P21/c with four units of formula [Pt2Rh(µ-S)2(PPh3)4(CO)2][Rh(CO)2Cl2][Rh(CO)2Cl2]·C3H6O in a cell of dimensions a= 16.813(3), b= 16.068(4), c= 28.342(5)Å, and β= 99.24(2)°, Least-squares refinement of the structure gave a final R value of 0.033 using 5 406 observed intensities [I 3σ(I)]. Compound (3) crystallises in the monoclinic space group C2/c with four units of formula [Pt2Rh(µ-S)2(PPh3)4(2,6-Me2C6H3NC)2]PF6 in a cell of dimensions a= 22.089(8), b= 18.141(7), c= 21.363(11)Å, and β= 105.35(4)°. Least-squares refinement of the structure led to a final R value of 0.036 using 4 867 observed intensities [I⩽ 3σ(I)]. The structures of compounds (1) and (3) both show an approximately equilateral triangular arrangement of the platinum and rhodium atoms capped by two µ3-sulphido-ligands. The metal–metal distance lie in the range 3.034(1)–3.291(1)Å which is greater than those normally associated with Pt–Pt and Pt–Rh bonding distances. The efficiency of these heterometallic platinum–rhodium compounds as homogeneous hydrogenation catalysts has also been studied.