Formation of Calcium–Carbon Bonds From a Lewis Acid-Base Reaction of Calcium Bis[bis(trimethylsilyl)amide] and Tris(trimethylsilylmethyl)alane

Treatment of calcium bis[bis(trimethylsilyl)amide] with two equivalents of tris(trimethylsilylmethyl)alane yields (Me3SiCH2)2Al–N(SiMe3)2 (1) and the dimer [(Me3Si)2N–Ca(μ–CH2SiMe3)2Al(CH2SiMe3)2]2 (2). The five-coordinate bridging carbon atoms show Ca–C bond lengths of 264 and 268 pm. A similar reaction with calcium bis[bis(trimethylsilyl)phosphanide] gives the dimer [(Me3SiCH2)2Al–P(SiMe3)2]2 (3) with crystallographic C2 symmetry. A calcium-containing species is not isolable, however, in the presence of DME – ether cleavage reactions and the formation of the centrosymmetric dimer [(Me3SiCH2)2Al–OCH2CH2OMe]2 (4) are observed. The central moiety is an Al2O2 cycle with fivefold coordinated aluminium centers.