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)Å, 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)Å, 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)Å. 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.