Synthesis, characterization and crystal structure analysis of cobaltaborane and cobaltaheteroborane clusters

Cluster expansion reactions of cobaltaboranes were carried out using mono metal-carbonyls, metal halides and dichalcogenide ligands. Thermolysis of an in situ generated intermediate, obtained from the reaction of [Cp*CoCl](2) (Cp* = C5Me5) and [LiBH4 center dot thf], with three equivalents of [Mo(CO)(3)(CH3CN)(3)] followed by the reaction with methyl iodide yielded isocloso-[(Cp*Co)(3)B6H7Co(CO)(2)] (1) and closo[(Cp*Co)(2)B2H5Mo2(CO)(6)I] (2). Cluster 1 is ascribed to the isocloso structure based on a 10-vertex bicapped square antiprism geometry. In a similar manner, the reaction of [Cp*CoCl](2) with [LiBH4 center dot thf] and the dichalcogenide ligand RS-SR (R = 1-OH-2,6-(Bu-t)(2)-C6H2) yielded nido cluster [(Cp*Co)(2)B2H2S2] (3). In parallel with the formation of the compounds 1-3, these reactions also yielded known cobaltaboranes [(Cp*Co)(2)B4H6] (4) and [(Cp*Co)(3)B4H4] in good yields. After the isolation of compound 4 in good yield, we verified its reactivity with PtBr2, which yielded closo-[(Cp*Co)(2)B4H2Br4] (5). To the best of our knowledge this is the second perhalogenated metallaborane cluster which has been recognized. All the new compounds were characterized by elemental analysis, IR, H-1, B-11, and C-13 NMR spectroscopy, and the geometric structures were unequivocally established by the X-ray diffraction analysis of compounds 1, 2, 3 and 5. Geometries obtained from the electronic structure calculations employing density functional theory (DFT) are in close agreement with the solid state X-ray structures. In addition, we analyzed the variation in the stability of the model compounds 1' (1': Cp analogue of 1, Cp = C5H5), [(CpCo)(4)B6H6] (1a) and [(CpRh)(4)B6H6] (1b).