Synthesis and Catalysis of Redox-Active Bis(imino) acenaphthene (BIAN) Iron Complexes

Reactions of various substituted bis(imino) acenaphthenes (RBIANs) with FeC1(2)(thf)(1).(5) afforded the tetrahedral complexes (RBIAN) FeCl2 (2) from bulky a-diimines and the octahedral complexes [Fe(R-BIAN)(3)][FeCl4](2) (3) from less bulky ligands. The driving force for the formation of complexes 3 is the high ligand-field stabilization of the low-spin FeII center. The two sets of complexes exhibit distinct charge-transfer band intensities and redox activities. (R-BIAN) FeCl2 complexes showed re-versible ligand-centered reductions at -0.9 V (vs. FcH/FcH(+); FcH: ferrocene); further reduction led to decomposition. Irreversible oxidations were observed at 0.2 and 0.4 V, associated with a reduction at -0.4 V, as well as a ligand-centered redox event at 1.0 V. First applications of the Fe(BIAN) complexes to hydrogenations of alkenes indicated good catalytic activity under mild conditions.