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)Å, 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)Å, 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)Å] bridged by SO₂ ligands and the longer edge [2.8422(9)Å] 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)Å 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.