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)A, 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)A. 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.