(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)(3)X, 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 pi-system in the (4-amino)phenanthridine complexes does result in an increase in the intensity of the lowest energy transitions (lambda(max)), which computational modeling suggests are more purely MLCT in character compared with the mixed pi-pi*/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 pi-pi* contributions to lambda(max) and is unable to accurately model the observed electronic absorption spectra. (C) 2020 Elsevier B.V. All rights reserved.