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 α-amino acids in non-protic solvents led to the synthesis of homoleptic mononuclear 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 Δ 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 A 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 α-amino acids ([α]D20 = 312° for 1 vs −85.0° for L-proline; −318° for 2 vs +81.5° 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 P21, a = 10.468(9) Å, b = 19.125(6) Å, c = 11.448(4) Å, α = γ = 90°, β = 109.27(4)°, Z = 4, R = 0.043; 2 is monoclinic, space group P21, a = 10.486(2) Å b = 19.130(3) Å, c = 11.470(2) Å, α = γ = 90°, β = 109.31(2)°, Z = 4, R = 0.040.