Metal Atom Synthesis of Metallaboron Clusters. 6. Synthesis and Structural Characterization of a Coupled Diborane-Metallacarborane Cluster: 5:1',2'-(n-C5H5) Co2,3-(Me3Si)2C2B4H3) (B2H5)

摘要

The reaction of thermally generated cobalt atoms with hexaborane(10), bis(trimethylsilyl)acetylene, and cyclopentadiene has been found to give as major products the cobaltacarborane clusters 5:1',2'-(1-n-C5H5)Co-2,3-(Me3Si)2C2B4H3)(B2H5), I, 1-(n-C5H5)Co-4,6-(Me3Si)2C2B6H6, II, and 1-(n-C5H5)Co-4,50 (Me3Si)2C2B6H6, III, along with smaller amounts of 5-(n-C5H5)Co-1,8-(Me3Si)2C2B5H5, IV, and 1-(n-C5H5)Co-2,3-(Me3Si)2C2B4H4, V. The spectroscopic data for compounds II, III, IV, and V are consistent with their formulations as closo polyhedral cage systems in which one bis(trimethylsilyl) acetylenic unit has been inserted into the cage framework. A single-crystal X-ray study of I has revealed, however, that it has a unique bridged structure composed of a closo-1-(n-C5H5)Co-2,3-(Me3Si)2C2B4H3-sandwich complex which has an exopolyhedral-B2H5 group bound to the 5-boron cage atom by means of a boron-boron-boron three-center bond. Compound I can thus be considered a bridge substituted organometallic derivative of diborane. Crystal data for I: space group C2/c; Z=8, a=29.890 (9) A, b = 9.213 (2) A,c = 15.127 (6) A,Beta = 91.57 (3) deg; V = 4164.4 A cube. The structure was refined by full-matrix least-squares techniques to a final R of 0.033 and R subscript w of 0.042 for the 4005 unique reflections.