Twisted [(R₃P)PdX] groups above dicarbaborane ligands: 4-dimethyl-sulfido-3-iodo-3-triphenylphosphine-closo-3-pallada-1, 2-dicarbadodeca-borane and 3-dimethylphenylphosphine-3-chloro-4-dimethylsulfido- closo-3-pallada-1,2-dicarbadodeca-borane

The structural analyses of [3-(PPh₃)-3-I-4-(SMe ₂)-closo-3,1,2-PdC₂B₉H₁₀] or [Pd(C₄H₁₆B₉S)I(C₁₈H₁₅P)], (I), and [3-(PPh-Me₂)-3-Cl-4-(SMe₂)-closo-3,1,2-PdC ₂B₉H₁₀) or [Pd(C₄H ₁₆-B₉S)Cl(C₈H₁₁P)], (II), show that in comparison with [3-(PR₃)₂-closo-3,1,2-PdC ₂B₉H₁₁] the presence of the 4-SMe₂ group causes the [PdAT(PR₃)] unit (X = halogen) to twist about an axis passing through the Pd atom and the directly opposite B atom of the carbaborane ligand. The halogen atoms are located almost directly above a C atom in the C₂B₃ face, and the conformations of the [PdX(PR₃)] units above the C₂B₃ faces are not those predicted from molecular orbital calculations of the closo-3,1,2-PdC ₂B₉ system. The fact that the variation from the predicted conformation is greater in the case of (I) than in (II) may be ascribed to the greater steric interactions induced by the I atom in (I) compared with the Cl atom in (II).