Denitrification involves the stepwise reduction of soil nitrate (NO3−) into atmospheric dinitrogen (N2), which constitutes a major portion of the nitrogen cycle. This is one of the most complicated geochemical transformations, which in one of the steps involves the reductive coupling of nitric oxide (NO) to give nitrous oxide (N2O) within the active site of bacterial nitric oxide reductase (NOR). This interconversion is thought to involve the key intermediate hyponitrite [O-N=N-O]2− resulting from N−N bond formation following NO reduction. Designing bio-inspired model systems that carry out reductive NO coupling continues to be a challenging endeavor, which can shed light on yet unclear mechanistic details of NOR. This work describes the unique copper-nitrosyl chemistry of a monomeric CuI complex bearing a tight solvent-dependency, where it mediates reductive coupling of NO in protic solvents to give a dicopper-hyponitrite adduct, while demonstrating NO disproportionation chemistry in aprotic solvents. The solid-state structure of this new hyponitrite complex reveals an η1-O-bound trans-CuII-ONNO-CuII unit, where the CuII centers employ a severely distorted coordination geometry. Intriguingly, this dicopper-hyponitrite adduct undergoes redox-facilitated decay upon redissolution in aprotic solvents, leading to CuI-mediated NO disproportionation products. The pivotal role of non-covalent interactions in stabilizing this hyponitrite complex, and their implications in governing copper-nitrosyl chemistry will be discussed.

New insights into copper-nitrosyl chemistry and isolation and characterization of a trans-hyponitrite-bridged dicopper(II) complex

254th National Meeting (2017)

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