Synthesis, electronic structure and interaction of rhodium(I) and iridium(I) bisimine-acenaphthalene complexes with CO2

Abstract

The bis(arylimino)acenaphthalene (BIAN) group of α-diimine compounds has shown promising electron sink behaviour and redox non-innocent activity as ligands to main group and transition metals. Here we present a series of rhodium(I) and iridium(I) complexes of BIAN derivatives with 2,6-diisopropylphenyl (DippBIAN, DB) and 2,4,6-trimethylphenyl (MesBIAN, MB), featuring various electron withdrawing and donating ancillary ligands. The crystal structures of square planar complexes 1b [RhMB(cod)]PF6, 1d [IrMB(cod)]PF6, 2a [RhDB(CO)2]PF6, 2b [RhMB(CO)2]PF6, 2c [IrDB(CO)2]PF6 and 3a [RhDB(CO)(PEt3)]PF6 are reported, as well as the square pyramidal structure of 4c [IrDB(cod)Cl]. The C-N and C-C bond lengths within the bisimine moiety for the structures of 2a and 4c suggest that the DippBIAN ligands are present in a reduced state, however, all other data from our multi-technique analyses correspond to results for neutral BIAN ligands. These contrasting results are indicative of the DippBIAN’s non-innocent behaviour, accepting additional electron density from the metal centre due to push–pull mechanism between the ancillary and BIAN ligands. The electrochemical study in non-coordinating solvent CH2Cl2 revealed that all complexes featured at least one reversible, ligand-centred reduction event at less negative potentials (above –1.0 V vs Ag/Ag+). In addition, preliminary results from our electrocatalytic CO2 reduction study has shown a promising interaction between CO2 and complex 3a, paving the way for exploring heterogeneous catalysis on these class of compounds