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

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posted on 25.09.2019, 15:46 by Kriti Pathak, Rongala Ramalakshmi, Mohammad Zafar, Sukanya Bagchi, Thierry Roisnel, Sundargopal Ghosh
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)43-S)4B2H2], 1; bimetallic trishomocubane isomers, [(Cp*Co)2(μ-S)33-S)4B2H2], 2 and 3; monometallic trishomocubanes, [M­(μ-E)33-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)33-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.