Oxygen atom transfer in rhenium complexes bound to the redox-active bis(3,5-di-tert-butyl-2-phenoxo)amide (ONO) ligand could potentially involve metal-centered reduction of a cis-(ONOCat)ReVIIO2(L) complex (“classical oxygen atom transfer”) or ligand-centered reduction of trans-(ONOQ)ReVO2(L) complex (“nonclassical oxygen atom transfer”). The complex with a tightly binding N-heterocyclic carbene, (ONOCat)ReO2(IMes), exhibits an unusual fac,cis-C1 geometry, which by dynamic NMR is highly nonfluxional. In fact, the barrier to isomerization is greater than that for the reaction with PMe2Ph, indicating that oxygen atom transfer occurs via a classial pathway. The complex with pyridine, fac,cis-C1-(ONOCat)ReO2(py), is deoxygenated by PPh3 in a reaction that is first-order in phosphine and inverse first-order in pyridine, suggesting the intermediacy of the five-coordinate (ONO)ReO2. Calculations indicate that this species is best formulated as (ONOCat)ReVIIO2 and that its deoxygenation is also a classical process. Thus the (ONO)ReO2 fragment exhibits a very strong tendency to undergo classical, metal-centered oxygen atom transfer processes.

Mechanistic studies of oxygen atom transfer in [ONO]Re complexes

251st National Meeting (2016)

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