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/Zr^IV 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) Co^I/Zr^IV 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 Zr^IV/Co⁰ complex, (^tBuNC)Co(ⁱPr₂PNMes)₃Zr(μ₂–κ¹-O-η²-N,N-OC(OEt)CHN₂)Zr(MesNPⁱPr₂)₃Co(CN^tBu) (7), bridged through enolate and η²-bound diazo functionalities.