Crystal and Molecular Structure of [η⁵-C₅(CH₃)₅]₃Co₃B₄H₄, an Electron-hyperdeficient Cluster with Severe Intramolecular Ligand-ligand Crowding


An X-ray diffraction study of the title compound confirmed its structure as a closo-Co3B3 octahedron whose tricobalt face is capped by BH, analogous to the previously described complex (η5-C5H5)3Co3B 4H4. The three C5(CH3)5 ligands are η5-coordinated to cobalt and are in close proximity to each other, with interligand Cmethyl-Cmethyl contacts as short as 3.33 Å. This molecule is the first structurally characterized complex in which three mutually bonded metal atoms are each η5-coordinated to a C5(CH3)5 ligand. The methyl groups are bent out of the C5 ring planes by 0.08-0.19 Å (average deflection 0.14 Å), and the three Co-Co bond distances are increased to a mean value of 2.497 (5) Å compared to 2.441 (1) Å for the (η5-C5H5)3Co3B 4H4 analogue; both effects are ascribed to relief of steric crowding of the C5(CH3)5 ligands. The observed structure is in conformity with the 1H and 11B NMR data and with the electron-counting rules for polyhedral cluster systems. Crystal data: mol wt 630; space group P1; Z = 2; a = 8.480 (9), b = 10.747 (8), c = 17.585 (15) Å; α = 89.55 (7), β = 85.76 (6), γ = 71.59 (8)°; V = 1516 Å3; R = 0.069 for 2699 reflections for which Fo 2 > 3σ(Fo 2). © 1982 American Chemical Society.



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© 1982 American Chemical Society (ACS), All rights reserved.