Synthesis of Unsupported d1–dx Oxido-Bridged Heterobimetallic Complexes Containing VIV: A New Direction for Metal-to-Metal Charge Transfer

Heterobimetallic complexes composed only of first-row transition metals [(TMTAA)­VIVO→MIIPy5Me2]­(OTf)2 (TMTAA = 7,16-dihydro-6,8,15,17-tetramethyldibenzo­[b,i]­[1,4,8,11]­tetraaza­cyclotetradecine; Py5Me2 = 2,6-bis­(1,1-bis­(2-pyridyl)­ethyl)­pyridine; M = MnII, FeII, CoII, NiII, CuII; OTf = trifluoromethanesulfonate) have been synthesized through a dative interaction between a terminal oxido and MII metal centers. This is the first series of VIVO→MII heterobimetallic complexes containing an unsupported oxido bridge. Among these five complexes, only VIVO→FeII (3b) has a clear new absorption band upon formation of the dinuclear species (502 nm, ε = 1700 M–1 cm–1). This feature is assigned to a metal-to-metal charge transfer (MMCT) transition from VIV to FeII, which forms a VVOFeI excited state. This assignment is supported by electrochemical data, electronic absorption profiles, and resonance Raman spectroscopy and represents the first report of visible-light induced MMCT in a heterobimetallic oxido-bridged molecule where the electron originates on a d1 metal center.