Unexpected Formation of Ga4C2H4 Heteroadamantane Cages by the Reaction of Carbon-Bridged Bis(dichlorogallium) Compounds with tert-Butyllithium

Reactions of the carbon-bridged bis(dichlorogallium) compounds (Cl2Ga)2C(SiR2R′)-CH2-Ph (1a, R = R′ = Me; 1b, R = Ph, R′ = Me; 1c, R = Me, R′ = CMe3) with four equivalents of tert-butyllithium yielded bis[tert-butyl(hydrido)digallium] compounds {[(Me3C)(H)Ga]2C(SiR2R′)-CH2-Ph}2 (3a to 3c), via β-elimination and release of isobutene. 3a to 3c are dimeric in solution and the solid state and contain unprecedented Ga4C2H4 heteroadamantane structures in which four metal atoms are bridged by four hydrogen and two carbon atoms. In contrast, n-propyllithium gave the monomeric tetra(n-propyl)digallium compound (nPr2Ga)2C(SiMe3)-CH2-Ph (2) under similar conditions, which has two coordinatively unsaturated gallium atoms and may be applicable as a chelating Lewis acid.