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

Room-temperature reactions between [Cp*CoCl] 2 (Cp* = η 5 -C 5 Me 5 ) and large excess of [BH 2 E 3 ]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 (μ 3 -S) 4 B 2 H 2 ], 1 ; bimetallic trishomocubane isomers, [(Cp*Co) 2 (μ-S) 3 (μ 3 -S) 4 B 2 H 2 ], 2 and 3 ; monometallic trishomocubanes, [M(μ-E) 3 (μ 3 -E) 4 B 3 H 3 ] [ 4 : M = Cp*Co, E = S; 5 : M = Cp*Co, E = Se and 6 : M = {(Cp*Co) 2 (μ-H)(μ 3 -Se) 2 }Co, E = Se], and bimetallic homocubane, [(Cp*Co) 2 (μ-Se)(μ 3 -Se) 4 B 2 H 2 ], 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 D 3 -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 D 3 -trishomocubane [Co(μ-Se) 3 (μ 3 -Se) 4 B 3 H 3 ] moiety is fused with an exopolyhedral trigonal bipyramid (tbp) moiety [(Cp*Co) 2 (μ-H)(μ 3 -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.