Synthesis of enantiopure oxorhenium(V) and arylimidorhenium(V) "3 + 2" Schiff base complexes. X-ray diffraction, cyclic voltammetry, UV-vis, and circular dichroism characterizations.

Two new oxorhenium(V) and two new arylimidorhenium(V) complexes of the Schiff base ligands 2-hydroxybenzaldehyde-((1R,2S)-1-amino-2-indanol)imine (1) (H(2)L(1)) and 3-(1-adamantyl)-2-hydroxy-5-methylbenzaldehyde-((1R,2S)-1-amino- 2-indanol)imine (2) (H(2)L(2)) have been prepared from the reaction of the precursor Re(O)(PPh(3))(2)Cl(3), Re(NC(6)H(5))(PPh(3))(2)Cl(3), or Re(NC(6)H(4)OCH(3))(PPh(3))(2)Cl(3) and the free ligands H(2)L(1,2). The complexes Re(O)(HL(1))(L(1)) (3), Re(O)(HL(2))(L(2)) (4), Re(NC(6)H(5))(HL(1))(L(1)) (5), and Re(NC(6)H(4)OCH(3))(HL(1))(L(1)) (6) have been isolated and fully characterized by IR, (1)H NMR, circular dichroism, LRMS-FAB, and elemental analysis. All the complexes have a chiral center at rhenium. A single enantiomer is obtained in all cases. Suitable crystals of 3 and 5 were used in X-ray structural determinations. Crystal data: (3) C(32)H(27)N(2)O(5)Re.CH(2)Cl(2), orthorhombic, P2(1)2(1)2(1), a = 9.5599(16) A, b = 9.9579(16) A, c = 31.712(5) A, V = 3018.9(9) A(3), T = 100(2) K, Z = 4. (5) C(40)H(38)N(3)O(5)Re, monoclinic, P2(1), a = 9.286(3) A, b = 18.759(6) A, c = 9.957(3) A, beta = 102.817(6) degrees, V = 1691.3(10) A(3), T = 100(2) K, Z = 2. The major characteristic of these complexes is the presence of two coordination modes for the Schiff base ligands on rhenium, a tridentate ligand (noted L(1,2)) and another bidentate ligand (noted HL(1,2)). In the latter, the -OH group of the indanol is free and tilts away from the coordination sphere. X-ray structural analyses in conjunction with circular dichroism were used to assign the absolute configuration at rhenium (C). Cyclic voltammetry, UV-vis, and circular dichroism data are presented and discussed. The complexes were found to be highly stable and to resist reduction even when treated with organic phosphanes.