VANADIUM(III) ALPHA-AMINO-ACID HOMOLEPTIC COMPLEXES FROM NON-PROTIC SOLUTIONS - REACTIONS OF [V(MES)3(THF)] WITH ALPHA-AMINO-ACIDS AND THE STRUCTURES OF TRIS(L-PROLINATO)VANADIUM DIMETHYL-SULFOXIDE AND TRIS(D-PROLINATO) VANADIUM DIMETHYL-SULFOXIDE

The reaction of [V(Mes)3(THF)] [Mes = 2,4,6-Me3C6H2] with free alpha-amino acids in non-protic solvents led to the synthesis of homoleptic mononuclcar hexacoordinate vanadium(III) complexes VA3 [AH = L-proline, 1; AH = D-proline, 2; AH = L-phenylalanine, 3; AH = D-phenylalanine, 4; AH = D,L-phenylalanine, 5; AH = L-tryptophan, 6; AH = L-valine, 7]. The solubility of the products varies according to the nature of the amino acid. The crystalline solids contain solvents of crystallization. The structures of 1.DMSO and 2-DMSO have been elucidated by an X-ray analysis. The configuration of 1 corresponds to the mer DELTA diastereoisomeric form which is one of the four possible distereoisomers of the tris(L-prolinato)vanadium complex, while the configuration of 2 is the mer LAMBDA form which is one of the four diastereoisomers of tris(D-prolinato)vanadium(III). The optical rotations of all complexes are very high when compared with those for uncomplexed a-amino acids ([alpha]D20 = 312-degrees for 1 vs -85.0-degrees for L-proline; -318-degrees for 2 vs +81.5-degrees for D-proline), the sign of the rotation for 1 being opposite to that seen for complexes 3, 6, and 7. Crystallographic details: 1 is monoclinic, space group P2(1), a = 10.468(9) angstrom, b = 19.125(6) angstrom, c = 11.448(4) angstrom, alpha = gamma = 90-degrees, beta = 109.27(4)-degrees, Z = 4, R = 0.043; 2 is monoclinic, space group P2(1), a = 10.486(2) angstrom b = 19.130(3) angstrom, c = 11.470(2) angstrom, alpha = gamma = 90-degrees, beta = 109.31(2)-degrees, Z = 4, R = 0.040.