The syntheses and crystal and molecular structures of some ten-vertex (MCB8; M = Ru or Os) metallacarbaboranes: 9,9,9-[(CO)(PPh3)2-nido-9,6-MCB8H10-5-(PPh3)](M = Ru or Os) and [9,9,9-(η-C5H5)(H)(PPh3)-arachno-9,6-RuCB8H12]

Abstract

The reaction of [MCl(CO)(H)(PPh₃)₃](M = Ru or Os) with arachno-[CB₈H₁₃]^– yields the nido-metallacarbaboranes [9,9,9-(CO)(PPh₃)₂-9,6-MCB₈H₁₀-5-(PPh₃)][M = Ru (1) or Os (2)] in reasonable yields as red and orange crystals respectively. A phosphine ligand is transferred from the metal atom to the cage in each case, and they both show a decaborane(14)-like cage structure with the 6- and 9-positions occupied by CH and M(CO)(PPh₃)₂ fragments respectively, as confirmed by single-crystal X-ray diffraction analysis. Compounds (1) and (2) are isostructural and isomorphous with their crystals monoclinic, space group P2₁/n, with Z= 4, R= 0.087 for 2 670 observed [I/σ(I) 3.0] reflections for (1) and 0.050 for 3 525 observed reflections for (2) respectively. A similar reaction with [RuCl(η-C₅H₅)(PPh₃)₂] yields the arachno species [9,9,9-(η-C₅H₅)(H)(PPh₃)-9,6-RuCB₈H₁₂], (3). In this case the cage arrangement as determined by a single-crystal X-ray diffraction study, is similar to that in [B₁₀H₁₄]^2– with the 6- and 9-positions substituted by CH₂ and RuH(η-C₅H₅)(PPh₃) fragments respectively. The crystals are monoclinic, space group P2₁/n, with Z= 4, R= 0.046 for 3 523 observed reflections. The application of the skeletal electron counting rules to this arachno structure is discussed.