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.