Multi-electron redox processes at a Zr(IV) center facilitated by an appended redox-actIVe cobalt-containing metalloligand

Abstract

The reactivity of a reduced heterobimetallic Co-I/ZrIV complex, (tBuNC)Co(iPr2PNMes)3Zr(THF) (2), with a series of azido and diazo reagents is explored to demonstrate the feasibility of facilitating two-electron redox processes at a formally d0 Zr(iv) center using the appended Co fragment exclusively as an electron-reservoir. Addition of mesityl or adamantyl azide to 2 affords the terminal (tBuNC)Co(iPr2PNMes)3ZrNMes (3) and bridging (tBuNC)Co(iPr2PNMes)2(μ-NAd)Zr(iPr2PNMes) (4) CoI/ZrIV imido products, respectively. Similarly, diphenyldiazomethane reacts with 2 to afford the terminal Ph2CN22--bound product (tBuNC)Co(iPr2PNMes)3ZrN-NCPh2 (5) via a two-electron oxidation of the Co center. Thermolysis of 5 results in a structural rearrangement to the diazomethane-bridged isomer (tBuNC)Co(iPr2PNMes)2(μ-N2CPh2)Zr(iPr2PNMes) (6). In contrast, treatment of 2 with 0.5 equivalents of the conjugated diazo reagent ethyl diazoacetate affords a tetranuclear ZrIV/Co0 complex, (tBuNC)Co(iPr2PNMes)3Zr(μ2-κ1-O-η2-N,N-OC(OEt)CHN2)Zr(MesNPiPr2)3Co(CNtBu) (7), bridged through enolate and η2-bound diazo functionalities.