Progressive cage-opening in d6, d8, d10, and d10s2 metallacarbaboranes: crystal and molecular structures of 3-triphenylphosphino-3-mercura-1,2-dicarbadodecaborane and triphenylmethylphosphonium 3-thalla-1,2-dicarbadodecaborate

Abstract

X-Ray studies of the novel d¹⁰ metallacarbaborane 3-PPh₃-3,1,2-HgC₂B₉H₁₁(I) and the d¹⁰s² species [PPh₃Me]⁺[3,1,2-TlC₂B₉H₁₁]^–(II) show that in (I) the mercury atom is bonded principally only to triphenyl-phosphine and to the unique boron atom of the C₂B₃ face, whereas in the anion of (II) the position of the thallium atom suggests an ion-pair formulation [Tl⁺C₂B₉H₁₁^2–]^–; together with results for analogous d⁶ and d⁸ systems, these structures demonstrate progressive opening of the metallacarbaborane cage as electron density on the metal increases.