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) (H2L1) and 3-(1-adamantyl)-2-hydroxy-5-methylbenzaldehyde-((1R,2S)-1-amino- 2-indanol)imine (2) (H2L2) have been prepared from the reaction of the precursor Re(O)(PPh3)2Cl3, Re(NC6H5)(PPh3)2Cl3, or Re(NC6H4OCH3)(PPh3)2Cl3 and the free ligands H2L1,2. The complexes
Re(O)(HL1)(L1) (3), Re(O)(HL2)(L2) (4), Re(NC6H5)(HL1)(L1) (5), and Re(NC6H4OCH3)(HL1)(L1) (6) have been
isolated and fully characterized by IR, 1H 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) C32H27N2O5Re·CH2Cl2, orthorhombic, P2(1)2(1)2(1), a = 9.5599(16) Å, b = 9.9579(16) Å, c = 31.712(5) Å, V = 3018.9(9) Å3, T = 100(2) K, Z = 4. (5)
C40H38N3O5Re, monoclinic, P2(1), a = 9.286(3) Å, b = 18.759(6) Å, c = 9.957(3) Å, β = 102.817(6)°, V =
1691.3(10) Å3, 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 L1,2) and another bidentate ligand (noted
HL1,2). 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.