The reaction of GeCl4 with the nido-carborane dianionic salts NaLi[(Me3Si)(R)C2B4H4] (R = SiMe3, Me, or H) in a molar ratio of 1:2 in THF produced closo-1-GeII-2,3-(SiMe3)2-2,3-C2B4H4(I), closo-1-GeII-2-(SiMe3)-3-(Me)-2,3-C2B4H4(II), and closo-1-GeII-2-(SiMe3)-2,3-C2B4H5(III) as air-sensitive, pale yellow liquids, in 36, 49, and 23% yields, respectively. In addition to the corresponding neutral nido-carborane precursors, the Ge(IV)-inserted derivatives of commo-bis(germacarborane), [(Me3Si)(R)C2B4H4]2GeIV, were also produced in 9.0, 7.4, and 9.5% yields when R = SiMe3, Me, and H, respectively. The closo-germacarboranes I, II, and III react slowly with 2,2'-bipyridine in benzene to form the electron donor-acceptor complexes l-GeII-(C10H8N2)-2,3-(SiMe3)2-2,3-C2B4H4 (IV), 1-GeII(C10H8N2)-2-(SiMe3)-3-(Me)-2,3-C2B4H4(V), and 1-GeII-(C10H8N2)-2-(SiMe3)-2,3-C2B4H5(VI) in 73, 42, and 48% yields, respectively. Both the visible/UV and 11B NMR spectroscopic results on IV-VI indicate that at least two different kinetic processes are taking place: a slow formation of the bipyridine-germacarborane adduct, followed by a rapid intraor intermolecular process which causes all the basal and apical boron atoms to become equivalent on an NMR time scale. The X-ray crystal structure of IV shows an extreme displacement of the germanium from the centroidal position above the C2B3 face in its distorted pentagonal-bipyramidal geometry with the Lewis base tilted significantly away from the cage carbons. The slippage of the apical germanium is such that it could be considered as η2-bonded to the C2B3 face of the carborane cage. Although some similarities between the closo-germacarborane and the closo-stannacarborane systems exist, the donoracceptor complexes of the two metallacarboranes seem to be quite different. Compound IV crystallizes in the monoclinic space group P21/n with a = 7.102 (5) Å, b = 34.61 (2) Å, c = 9.774 (4) Å, β = 102.55 (4)°, U = 2345 (2) Å3, and Z = 4. Full-matrix least-squares refinement converged at R = 0.040 and Rw= 0.038.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- Inorganic Chemistry