The stereochemistry of the oxidation of diamines and of the reduction of diimines in the coordination sphere of ruthenium(II)

The syntheses of Delta/Lambda-, Delta-, and Lambda-[Ru(bpy)(2)(1R,2R-chxn)](2+) (where 1R,2R-chxn=(1R,2R)-(-)-1,2-diaminocyclohexane); rac.-, Delta-, and Lambda-[Ru(bpy)(2)(chxdiim](2+) (where chxdiim=1,2-diiminocyclohexane); rac.-, and Delta-[Ru(bpy)(2)(dmen)](2+) (where dmen=N,N'-(dimethyl)ethylenediamine), and rac.-, and Delta-[Ru(bpy)(2)(dmdiim)](2+) (where dmdiim=N,N'-(dimethyl)ethylenediimine) are described. Oxidation of the coordinated diamines with an acid solution of Ce(IV) and reduction of the coordinated diimines with NaBD4 occur under retention of the configuration at the metal center. Reduction of the diimine complexes with NaBD4 gives back the amines with a diastereomeric excess (Lambda-R,R and Delta-S,S) of 60% in case of chxn as a ligand and 80% for the dmen ligand. The latter becomes a chiral ligand upon deuteration. The reduction also yields a small amount cup to 10%) of the corresponding cis isomers (Delta-R,S/Lambda-S,R). In addition, semi-reduced coordinated amine/imine ligands are observed as intermediates. The identity of the reaction products as well as their configurations has been established by means of circular dichroism and H-1 NMR spectroscopy. (C) 1998 Elsevier Science S.A. All rights reserved.