LITHIUM TRIALKOXO[TRIS(TRIMETHYLSILYL)METHYL]ALUMINATES, ANALOGS 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=tetrahy drofuran) 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 intermed iates presumed to be present in the reduction of carbonyl compounds by LiAlH4. The structure of [Li(thf)(2)][(Me3Si)(3)CAl(OEt)(3)] was dete rmined by X-ray crystallography which showed that the lithium cation a nd the organotriethoxoaluminate anion are linked to give a planar LiO2 Al ring. The organotrialkoxoaluminates are hydrolysed by traces of wat er to give organoalkoxohydroxoaluminates and the structure of one of t hese, {Li[(Me3Si)(3)CAl(OPri)(2)(OH)]}(2), has been determined. The di mer has an Li2Al2O6 framework comprising two adjacent face-sharing cub es 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.