Synthesis and structural characterisation of some triangulo-platinum clusters containing lsocyanide ligands

Abstract

The compound [Pt3(µ-CO)3{P(C6H11)3}3] reacts with 3 and 5 mol of 2,6-xylyl isocyanide, CNC8H9, to give [Pt3(µ-CO)(µ-CNC8H9)2(CNC8H9){P(C6H11)3}2](1) and [Pt3(µ-CNC8H9)3(CNC8H9)2{P(C6H11)3}](2) respectively. 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/n with four units of formula [Pt3(µ-CO)(µ-CNC8H9)2(CNC8H9)-{P(C6H11)3}2]·0.5C6H6in a cell of dimensions a= 15.431(5), b= 15.810(3), c= 28.489(19)A, and β= 95.22(4)° and (2) in the monoclinic space group P21/a with four formula units in a cell of dimensions a= 16.412(2), b= 18.444(2), c= 24.383(2)A, and β= 90.155(9)°. The structures of both molecules are approximately equilateral triangles of Pt atoms with Pt–Pt distances in the range 2.618(1)–2.654(1)A. The bonded ligand atoms are approximately coplanar with the metal triangles and 31P-{1H} and 195Pt-{1H} n.m.r. studies suggest that both solid-state structures are retained in solution. When intermediate mol ratios of isocyanide were added to [Pt3(µ-CO)3{P(C6H11)3}3] then mixtures of (1), (2), and starting material only were obtained. No evidence for the formation of symmetrical products of the type [Pt3(µ-CNC8H9)3{P(C6H11)3}3] was obtained. Examination of the molecular structures of (1) and (2) has formed a basis for rationalising the observed stoicheiometries. The bridging isocyanide ligands are severely bent about the nitrogen atoms and their steric requirements are incompatible with the presence of P(C6H11)3ligands on both of the metal atoms being bridged. Consequently, replacement of bridging CO by the isocyanide labilises an adjacent terminal P(C6H11)3ligand. Compound (2) has also been synthesised by sodium-amalgam reduction of [Pt(CO)Cl2{P(C6H11)3}] in the presence of an excess of isocyanide ligand.