Synthesis of Unsupported d¹–d^<i>x</i> Oxido-Bridged Heterobimetallic Complexes Containing V^IV: A New Direction for Metal-to-Metal Charge Transfer

Abstract

Heterobimetallic complexes composed only of first-row transition metals [(TMTAA)­V^IVO→M^IIPy₅Me₂]­(OTf)₂ (TMTAA = 7,16-dihydro-6,8,15,17-tetramethyldibenzo­[<i>b</i>,<i>i</i>]­[1,4,8,11]­tetraaza­cyclotetradecine; Py₅Me₂ = 2,6-bis­(1,1-bis­(2-pyridyl)­ethyl)­pyridine; M = Mn^II, Fe^II, Co^II, Ni^II, Cu^II; OTf = trifluoromethanesulfonate) have been synthesized through a dative interaction between a terminal oxido and M^II metal centers. This is the first series of V^IVO→M^II heterobimetallic complexes containing an unsupported oxido bridge. Among these five complexes, only V^IVO→Fe^II (<b>3b</b>) 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 V^IV to Fe^II, which forms a V^VOFe^I 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