Homocubane Chemistry: Synthesis and Structures of Mono- and Dicobaltaheteroborane Analogues of Tris- and Tetrahomocubanes

Room-temperature reactions between [Cp*CoCl]₂ (Cp* = η⁵-C₅Me₅) and large excess of [BH₂E₃]Li (E = S or Se) led to the formation of homocubane derivatives, 1–7. These species are bimetallic tetrahomocubane, [(Cp*Co)₂(μ-S)₄(μ₃-S)₄B₂H₂], 1; bimetallic trishomocubane isomers, [(Cp*Co)₂(μ-S)₃(μ₃-S)₄B₂H₂], 2 and 3; monometallic trishomocubanes, [M­(μ-E)₃(μ₃-E)₄B₃H₃] [4: M = Cp*Co, E = S; 5: M = Cp*Co, E = Se and 6: M = {(Cp*Co)₂(μ-H)­(μ₃-Se)₂}­Co, E = Se], and bimetallic homocubane, [(Cp*Co)₂(μ-Se)­(μ₃-Se)₄B₂H₂], 7. As per our knowledge, 1 is the first isolated and structurally characterized parent prototype of the 1,2,2′,4 isomer of tetrahomocubane, while 3, 4, and 5 are the analogues of parent D₃-trishomocubane. Compounds 2 and 3 are the structural isomers in which the positions of the μ-S ligands in the trishomocubane framework are altered. Compound 6 is an example of a unique vertex-fused trishomocubane derivative, in which the D₃-trishomocubane [Co­(μ-Se)₃(μ₃-Se)₄B₃H₃] moiety is fused with an exopolyhedral trigonal bipyramid (tbp) moiety [(Cp*Co)₂(μ-H)­(μ₃-Se)₂}­Co]. Multinuclear NMR and infrared spectroscopy, mass spectrometry, and single crystal X-ray diffraction analyses were employed to characterize all the compounds in solution. Bonding in these homocubane analogues has been elucidated computationally by density functional theory methods.