Synthesis and structural characterisation of some triangulo- and binuclear clusters of platinum from the reaction of [Pt3(µ-SO2)3{P(C6H11)3}3] with 2,6-xylyl isocyanide

Abstract

The compound [Pt3(µ-SO2)3{P(C6H11)3}3] reacts with 2 mol of 2,6-xylyl isocyanide, CNC8H9, to give [Pt3(µ-SO2)2(CNC8H9)2{P(C6H11)3}3](1) and with an excess of isocyanide to give [Pt2(µ-SO2)(CNC8H9)2{P(C6H11)3}2](2). The molecular structures of both compounds have been determined by single-crystal X-ray techniques using diffractometer data. Compound (1) crystallises in the monoclinic space group P21 with two units of formula [Pt3(SO2)2(CNC8H9)2{P(C6H11)3}3]·3MeCN·CH2Cl2 in a cell of dimensions a= 14.957(5), b= 24.604(4), c= 13.035(2)A, and β= 114.28(2)° and (2) in the monoclinic space group P21/n with four units of formula [Pt2(SO2)(CNC8H9)2{P(C6H11)3}2]·1.5CH2Cl2 in a cell of dimensions a= 14.842(1), b= 25.394(3), c= 17.270(2)A, and β= 112.16(1)°. The structure of (1) is based on an isosceles triangle of platinum atoms, with the two shorter Pt–Pt edges [av. 2.727(1)A] bridged by SO2 ligands and the longer edge [2.8422(9)A] unbridged. The isocyanide ligands are co-ordinated to the platinum atoms which define this long bond. N.m.r. studies (31P-{1H} and 195Pt-{1H}) have confirmed that this structure is retained in solution. In (2) the platinum–platinum bond has a length of 2.6934(5)A and is bridged by a SO2 ligand. The co-ordination environments about each platinum atom are completed by a P(C6H11)3 ligand and a terminal CNC8H9 ligand. N.m.r. data (31P-{1H} and 195Pt-{1H}) for this compound in solution have been recorded. The formation of (1) and (2) from [Pt3(SO2)3{P(C6H11)3}3] is quite unexpected in view of earlier studies on [Pt3(µ-CO)3{P(C6H11)3}3] with the same isocyanide ligand. The 44-valence-electron structure observed for (1) has no precedent in platinum cluster chemistry and the isolation of the dimeric compound (2) underlines the importance of degradation processes in ligand-substitution reactions.