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.