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)

摘要

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 structures of the complexes [Cr((R)-tacntp)] centre dot NaBr and [Fe((R)-tacntp)] centre H_2O have been determined by X-ray crystallography. Both complexes have the #LAMBDA#-configuration but the conformation of the chelate rings in #LAMBDA#-[Cr((R)-tacntp)] is (#lambda#, #lambda#, #lambda#) with a geometry close to octahedral while in #LAMBDA#-[Fe((RR)-tacntp)] it is (#delta#, #delta#, #delta#) and the geometry is closer to that of a trigonal prism. Chiral induction in the electron transfer reactions of #LAMBDA#-[Co((R)-tacntp)], #LAMBDA#-[Fe((R)-tacntp)] and #LAMBDA#-[Mn(R)-tacntp] with [Co((RR,SS-chxn)_3)~(2+) has been investigated. All three 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 different from those of #LAMBDA#-[Co((R)-tacntp)].