Interconversion of 42- and 44-electron platinum triangulo-clusters using chelating tertiary phosphine ligands and the structural characterisation of [1,3-bis(diphenylphosphino)propane]-tris(µ-sulphur dioxide)-bis(tricyclohexylphosphine)triplatinum–benzene (1/2), [Pt3(µ-SO2)3{P(C6H11)3}2(dppp)]·2C6H6

Abstract

The 42-electron triangulo-clusters [Pt₃(µ-CO)₃{P(C₆H₁₁)₃}₃] and [Pt₃(µ-SO₂)₃{P(C₆H₁₁)₃}₃] react with chelating phosphines to give 44-electron clusters of the type [Pt₃(µ-X)₃{P(C₆H₁₁)₃}₂{Ph₂P(CH₂)_nPPh₂}](X = CO or SO₂, n= 2 or 3). The molecular structure of the compound [Pt₃(µ-SO₂)₃{P(C₆H₁₁)₃}₂{Ph₂P(CH₂)₃PPh₂}] has been determined by single-crystal X-ray techniques using diffractometer data. The compound crystallises in the monoclinic space group P2₁/n with four formula units in a cell of dimensions a= 11.244(6), b= 41.746(3), c= 16.324(2)Å, and β= 98.51(3)°. Least-squares refinement of the structure has led to a final R value of 0.060 using 4 506 unique absorption-corrected reflections with I 3σ(I). The structure shows an approximately isosceles triangle of platinum atoms; Pt–Pt 2.753(1), 2.826(1), and 2.811(1)Å. The bridging SO₂ ligands are not coplanar with the Pt₃ triangle. The cluster shows indications of being sterically crowded with the Pt{Ph₂P(CH₂)₃PPh₂} moiety adopting a low-symmetry conformation with respect to the Pt₃ plane. Proton-decoupled ³¹P and ¹⁹⁵Pt n.m.r. studies have demonstrated that this low-symmetry conformation which makes the P(C₆H₁₁)₃ ligands inequivalent is maintained in solution at low temperatures.