Synthesis, structure and catalytic activity of low-spin dicyano iron(III) complexes of N,N-bis(quinolyl)malonamide derivatives

Two low-spin Fe(III) dicyano-dicarboxamido complexes have been prepared from N,N^′-bis(8-quinolyl)malonamide derivatives. Crystal structures show that the four nitrogen donors available to complex the metal are arranged in the equatorial plane with the two cyanides trans to each other in the axial positions when the malonyl moiety is disubstituted. In contrast, the unsubstituted malonyl results in only three nitrogens in the equatorial plane with the fourth in an apical position and the two cyanides occupying cis sites, one equatorial and the other axial. NMR analyses show that the solid state structure of both complexes is retained in solution. Both types of configurational complexes catalyze cyclic olefin oxidations with H₂O₂ but only the cis-dicyano complex catalyzes stilbene oxidation with formation of epoxides, diols and benzaldehyde.