Synthesis and structural characterisation of some tetrahedral platinum–gold cluster compounds containing the sulphur dioxide ligand

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Abstract
The compound [Pt3Au(µ-CO)3{P(C6H11)3}4] PF6 has been synthesised from [Pt3(µ-CO)3{P(C6H11)3}3] and [AuCl{P(C6H11)3}] in the presence of TIPF6. It reacts with SO2 to give a tetrahedral platinum–gold cluster compound [Pt3Au(µ-CO)2(µ-SO2){P(C6H11)3}4] PF6(1) in which one of the CO ligands of the starting material has been replaced by SO2. Compound (1) crystallises in the orthorhombic space group Pn21a with four formula units in a cell of dimensions a= 18.671(4), b= 19.618(3), and c= 28.162(4)Å. The compound [Pt3(µ-SO2)3{P(C6H11)3}3] reacts with [AuCl{P(C6H4F-p)3}] to give the tetrahedral platinum–gold cluster compound [Pt3Au(µ-SO2)2(µ-Cl){P(C6H11)3}3{P(C6H4F-p)3}](2) in which one of the SO2ligands of the starting triangulo-cluster has been replaced by a bridging chloride. Compound (2) crystallises in the monoclinic space group P21/n with four formula units in a cell of dimensions a= 25.490(4), b= 25.855(6), c= 13.819(4)Å, and β= 96.98(2)°. The bonded bridging ligand atoms are approximately coplanar with the metal triangles whilst the metal–phosphine bonds point towards the centre of the metal tetrahedron. N.m.r. studies, 31P-{1H} and 195Pt-{1H}, suggest that the solid-state structures are retained in solution for both compounds. The reaction of [Pt3(µ-SO2)3{P(C6H11)3}3] with [AuCl{P(C6H11)3}] in the presence of TIPF6gives [Pt3Au(µ-SO2)3{P(C6H11)3}4] PF6 which may be converted into (1) by reaction with CO. The compound [Pt3(µ-SO2)3{P(C6H11)3}3] reacts with [AuCl{P(C6H4F-p)3}] to give [Pt3Au(µ-SO2)3{P(C6H11)3}3{P(C6H4F-p)3}] PF6 which may be converted into (2) with NMe4Cl. The compound [Pt3Au(µ-SO2)3{P(C6H11)3}3{P(C6H4F-p)3}] PF6 and its chloride-bridged derivative (2) represent the first examples of compounds formed where [Au(PR3)]+ and [AuCl(PR3)] have been added to the same cluster compound. These studies indicate the occurrence of 54- and 56-electron tetrahedral Pt3Au clusters analogous to the 42- and 44-electron triangular parent clusters.

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