SYNTHESIS AND SPECTROSCOPIC STUDIES OF ALKYLALUMINUM ALKOXIDES DERIVED FROM OPTICALLY-ACTIVE ALCOHOLS - CRYSTAL AND MOLECULAR-STRUCTURE OF MONOMERIC DIMETHYLALUMINUM (2S,3R)-(+)-4-(DIMETHYLAMINO)-1,2-DIPHENYL-3-METHYL-2-BUTANOXIDE

The reaction of trialkylaluminum derivatives, R(3)Al(R= Me, Et, i-Bu), with optically active alcohols quantitatively yields R(2)AlOR' (R = Me (1a), Et (1b), OR' = (S)-(-)-1-methyl-2-pyrrolidinemethanolate; R = Me (2a),- Et (2b) OR' = (2S,3S)-(+)-2-amino-3-methyl-1-pentanolate; R = Me (3a), Et (3B), OR' = (1R,2S)-(-)-alpha-(1-(methylamino)ethyl)benzyl alkoxide; R = Me (4a); Et (4b), i-Bu (4c), OR' = (2S,3R)-(+)-4-(dimethylamino)-1,2-diphenyl-3-methyl- 2-butanoxide; R = Me, OR' = cinchonine, 5; R = Me, OR' = quinidine, 6, R = Me, OR' = quinine, 7) and the corresponding alkane RH. The resulting compounds la,b, 2a,b, 3a,b, 4a-c, and 5-7, have been characterized by H-1 and C-13 NMR spectroscopy Compounds la, 2a, 3a, 5-7 undergo a dynamic process with respect to the dissociation of the Al-N dative bond. This is consistent with equilibria between four- and five-coordinate aluminum species with Arrhenius activation energies of 12.5 +/- 0.6, 13.9 +/- 0.6, 25.0 +/- 1.2, 19.3 +/- 0.9, 17.3 +/- 0.7, and 22.5 +/- 1.6 kcal mol-l, respectively. The structure of 4a was determined by single crystal X-ray diffraction techniques and found to be in the monoclinic crystal system space group P2(1) (No. 4) with cell constants a 7.368(1) Angstrom, b = 15.859(3) Angstrom, c = 17.589(5) Angstrom, beta = 92.81(2)degrees, and Z = 4 (monomers); R = 4.61% (R(w) = 4.03%) based on 2228 observed reflections with I-o greater than or equal to 3.0 sigma(I). The molecule exists as a monomer with an Al-O bond distance of 1.73 Angstrom and an Al-N bond distance of 2.03 Angstrom.