Effects of electronic structure on chiral induction in outer-sphere electron transfer reactions of complexes with the C-3 symmetric ligand, 1,4,7-triazacyclononane-1,4,7-tris[2 '(R)-2 '-propionate](-3)

The ligand 1,4,7-triazacyclononane-1,4,7-tris[2'(R)-2'-propionate](-3)((R)- tacntp(3-)), binds stereospecifically to transition metal ions. The structu res of the complexes [Cr((R)-tacntp)]. NaBr and [Fe((R)-tacntp)]. H2O have been determined by X-ray crystallography. Both complexes have the Lambda-co nfiguration but the conformation of the chelate rings in Lambda-[Cr((R)-tac ntp)] is (lambda,lambda,lambda) with a geometry close to octahedral while i n Lambda-[Fe((R)-tacntp)] it is (delta,delta,delta) and the geometry is clo ser to that of a trigonal prism. Chiral induction in the electron transfer reactions of Lambda-[Co((R)-tacntp)], Lambda-[Fe((R)-tacntp)] and Lambda-[M n((R)-tacntp)] with [Co((RR,SS)-chxn)(3)](2+) has been investigated. All th ree reactions are outer-sphere and four isomeric [Co((RR,SS)-chxn)(3)](3+) products are identified in each case. The oxidants Lambda-[Fe((R)-tacntp)] and Lambda-[Mn((R)-tacntp)] show very similar selectivities, quite differen t from those of Lambda-[Co((R)-tacntp)]. Reasons for this behavior are disc ussed. (C) 1999 Elsevier Science S.A. All rights reserved.