(8-Amino)quinoline and (4-amino)phenanthridine complexes of Re(CO)₃ halides

In this report, we present a study on the synthesis, structure and electronics of a series of (8-amino)quinoline and (4-amino)phenanthridine complexes of Re(CO)₃X, where X = Cl and Br. In all cases, the (amino)heterocycles bind as bidentate ligands, with surprisingly symmetric modes of binding based on Re–N bond lengths. Between the complexes of (8-amino)quinolines and (4-amino)phenanthridines studied in this report, we do not observe much structural variation and remarkably similar UV–visible absorption spectra. Expansion of the π-system in the (4-amino)phenanthridine complexes does result in an increase in the intensity of the lowest energy transitions (λ_max), which computational modeling suggests are more purely MLCT in character compared with the mixed π-π∗/MLCT character of these transitions in the smaller (8-amino)quinoline-supported complexes. DFT and TDDFT modeling further showed that consideration of spin-orbit coupling (SOC) is essential; omitting SOC misses the π-π∗ contributions to λ_max and is unable to accurately model the observed electronic absorption spectra.