Substitution chemistry of carbonyl and sulphur dioxide triangulo-platinum clusters. Crystal structure of [Pt3(µ-CO)(µ-SO2)2{P(C6H11)3}3]

Abstract

The simple substitution chemistry of the triangulo-platinum clusters [Pt₃(µ-CO)_{3 –n}(µ-SO₂)_n{P(C₆H₁₁)₃}₃](n= 0–3) with carbon monoxide and sulphur dioxide ligands is described and some mechanistic implications discussed. Different products were isolated depending on the concentration of the gaseous reactants. For example, when 1 molar equivalent of carbon monoxide was added to [Pt₃(µ-SO₂)₃{P(C₆H₁₁)₃}₃](1) the monosubstituted carbon monoxide complex [Pt₃(µ-CO)(µ-SO₂)₂{P(C₆H₁₁)₃}₃](2) was formed. However, with excess of carbon monoxide, using dichloromethane as the solvent, a relatively unstable dimer, [Pt₂(µ-SO₂)(CO)₂{P(C₆H₁₁)₃}₂](3) was isolated. This dimer was also prepared by the reaction of SO₂ with [Pt₃(µ-CO)₃{P(C₆H₁₁)₃}₃](5). With benzene as the solvent, compound (1) reacts with excess of CO to give the disubstituted cluster [Pt₃(µ-CO)₂(µ-SO₂){P(C₆H₁₁)₃}₃](4). The molecular structure of (2) has been determined by a single-crystal X-ray diffraction study. It crystallises in monoclinic space group C2/m, with four units of formula [Pt₃(µ-CO)(µ-SO₂)₂{P(C₆H₁₁)₃}₃]·0.5C₆H₆ in a cell of dimensions of a= 24.909(9), b= 21.694(4), c= 15.559(4)Å, and β= 125.41(3)°. The structure consists of an isosceles triangle of Pt atoms with Pt–Pt distances of 2.678(1) and 2.710(1)Å. The Pt–Pt edges bridged by the sulphur dioxide ligands are appreciably longer than that bridged by carbon monoxide. The substitution chemistry of the mixed substituted clusters, (2) and (4) with xylyl isocyanide has been studied. The reactivities of both clusters resemble that of (1).