Lithium trialkoxo[tris(trimethylsilyl)methyl]aluminates, analogues of intermediates in reductions of carbonyl compounds.: Crystal structures of [Li(thf)2][AlR(OEt)3] and {Li[AlR(OPri)2(OH)]}2, R = C(SiMe3)3 and thf = tetrahydrofuran

The organotrihydroaluminate [Li(thf)(2)][(Me3Si)(3)CAlH3] (thf=tetrahydrofuran) reacted with alcohols R'OH, (R'=Me, Et, Pr-i or Bu-t), PhOH, aldehydes (RCHO)-C-1 (R-1=CHO (R-1=Me, Bu-t or Ph) or ketones (RR2)-R-1=Me or Ph; R-1=Me, R-2=Ph) to give organotrialkoxoaluminates [Li(thf)(n)][(Me3Si)(3)CAl(OR')(3)] (n=1, R'=Me, Pr-i, Bu-t, Ch(2)Bu(t), Ch(2)Ph or CHPh2; n=2, R'=Et or Ph; n=4, R'=Me), analogues of the intermediates presumed to be present in the reduction of carbonyl compounds by LiAlH4. The structure of [Li(thf)(2)][(Me3Si)(3)CAl(OEt)(3)] was determined by X-ray crystallography which showed that the lithium cation and the organotriethoxoaluminate anion are linked to give a planar LiO2Al ring. The organotrialkoxoaluminates are hydrolysed by traces of water to give organoalkoxohydroxoaluminates and the structure of one of these, {Li[(Me3Si)(3)CAl(OPri)(2)(OH)]}(2), has been determined. The dimer has an Li2Al2O6 framework comprising two adjacent face-sharing cubes with missing atoms at diametrically opposite corners. Terminal and bridging alkoxo groups in solutions of some of these compounds can be distinguished by NMR measurements.