Dinuclear complexes of rhodium and iridium with cyanide or thiocyanate bridges: molecular structure of [(PMe2Ph)3Cl2Ir(µ-CN)IrCl2(PMe2Ph)3][ClO4]

Abstract

Reactions of the rhodium or iridium complexes [MCl₂(H₂O)(PMe₂Ph)₃][ClO₄] with [MCl₂(CN)(PMe₂Ph)₃] give the homometallic cyano-bridged compounds [(PMe₂Ph)₃Cl₂M(CN)M′Cl₂(PMe₂ Ph)₃][ClO₄](M = M′= Rh or Ir) and the corresponding heterometallic isomers which do not interconvert. The crystal structure of the complex [(PMe₂Ph)₃Cl₂Ir(CN)IrCl₂(PMe₂Ph)₃][ClO₄] revealed that the two IrCl₂(PMe₂Ph)₃ groups are symmetry related because there is a disordered distribution of IrCNIr and IrNClr orientations. Hence, though the structure is well refined (R= 0.035), the different structural influences of the C and N atoms in the bridge could not be defined. However, ¹³C, ¹⁵N, and ³¹P n.m.r. studies reveal that the trans influence of C is greater than that of the N atom. The corresponding homometallic compounds [(PMe₂Ph)₃Cl₂M(SCN)MCl₂(PMe₂Ph)₃][ClO₄](M = Rh or Ir) were obtained but attempted syntheses of the mixed Rh/Ir compounds led to a mixture of all four possible homo- and hetero-metallic species. We conclude that the thiocyanato bridges can cleave to give both S- and N- bonded mononuclear species but N-bonded cyanide monomers are inccessible.