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-(Si Me3)-3-(R)-5-(GeCL3)-2,3-C2B4H3 (R = SiMe3 (IV), Me (V), and H (VI)) i n yields of 43%, 22%, and 51%, respectively. Despite the presence of t wo potential Lewis-acid sites, the reactions of the germacarboranes wi th 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 N4)-[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 )-C5H5)Fe(eta(5 )-C5H4CH2](2)N(Me)(2)}(+){GeCl3}(-) (XII) and H4CH2(Me)(2)N)]-2,3-(SiM e3)(2)-5-(NMe2)-2,3-C2B4H3 (XIII), a germacarborane in which a NMe2 gr oup replaced the GeCl3 moiety on the carborane cage. All compounds wer e 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 c haracterized by single-crystal X-ray diffraction. The structures showe d IV-VT to be half-sandwich complexes in which a Ge(II) was symmetrica lly bound to the C2B3 faces of the carboranes, with a Ge(IV) terminall y bonded to the unique borons of the cages in a GeCl3 group. The struc tures of the Lewis-base adducts, VII and IX, showed that the nitrogens of the bases were symmetrically bonded to the Ge(II) atoms. Coordinat ion by the bases resulted in a slip distortion of the capping metal at oms 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)-C 5H5)Fe(eta(5)-C5H4CH2(Me)(2)N) base, producing an intermediate that re acts further with another molecule of the base to give both XII and XI II. In no case was there any evidence of the Ge(IV) acting as a reacti ve Lewis-acid center. Ab initio molecular orbital calculations were us ed in rationalizing some of the synthetic and spectroscopic results ob tained in this study.