Chemistry of C-trimethylsilyl-substituted heterocarboranes.: 25.: Syntheses, structures, and reactivities of GeCl3-substituted half-sandwich germacarboranes, closo-1-Ge-2-(SiMe3)-3-(R)-5-(GeCl3)-2,3-C2B4H3 (R = SiMe3, Me, and H)

Anhydrous GeCL4 reacts with the closo-stannacarboranes 1-Sn-2-(SiMe3)-3-(R)-2,3-C2B4H4 (R = SiMe3 (I), Me (Ii), and H (III)) in the absence of solvents to give the corresponding closo-germacarboranes 1-Ge-2-(SiMe3)-3-(R)-5-(GeCL3)-2,3-C2B4H3 (R = SiMe3 (IV), Me (V), and H (VI)) in yields of 43%, 22%, and 51%, respectively. Despite the presence of two potential Lewis-acid sites, the reactions of the germacarboranes with the bases C10H8N2, C8H6N4, and C15H11N3 produced exclusively 1-(L)-2-(SiMe3)-3-(R)-5-(GeCl3)-1,2,3-GeC2B4H3 (L = C10H8N2, R = SiMe3 (VII) and Me (VIII); L = C15H11N3, R = SiMe3 (XI)) or, when L = C8H6N4, the bridged complexes 1,1'-(2,2'-C8H6N4)-[1-Ge-2-(SiMe3)-3-(R)-5-(GeCl3)-2,3-C2B4H3](2) (R = SiMe3 (IX), Me (X)). The reaction of IV with (eta(5)-C5H5)Fe(eta(5)-C5H4CH2(Me)(2)N) produced a 1:1 mixture of the salt {[eta(5)-C5H5)Fe(eta(5)-C5H4CH2](2)N(Me)(2)}(+){GeCl3}(-) (XII) and 1-Ge[(eta(5)-C5H5)Fe(eta(5)-C5H4CH2(Me)(2)N)]-2,3-(SiMe3)(2)-5-(NMe2)-2,3-C2B4H3 (XIII), a germacarborane in which a NMe2 group replaced the GeCl3 moiety on the carborane cage. All compounds were characterized by their infrared and H-1, B-11, and C-13 NMR spectra, as well as chemical analysis. In addition, IV-VII, IX, and XII were characterized by single-crystal X-ray diffraction. The structures showed IV-VT to be half-sandwich complexes in which a Ge(II) was symmetrically bound to the C2B3 faces of the carboranes, with a Ge(IV) terminally bonded to the unique borons of the cages in a GeCl3 group. The structures of the Lewis-base adducts, VII and IX, showed that the nitrogens of the bases were symmetrically bonded to the Ge(II) atoms. Coordination by the bases resulted in a slip distortion of the capping metal atoms toward the boron side of the cages. Compounds XII and XIII are the final products of a sequence of reactions, one of which involves the displacement of a [GeCl3](-) unit from the unique boron by a (eta(5)-C5H5)Fe(eta(5)-C5H4CH2(Me)(2)N) base, producing an intermediate that reacts further with another molecule of the base to give both XII and XIII. In no case was there any evidence of the Ge(IV) acting as a reactive Lewis-acid center. Ab initio molecular orbital calculations were used in rationalizing some of the synthetic and spectroscopic results obtained in this study.