Nitric oxide is a key biological signaling molecule in health and disease serving many functions such as vasodilation. While nitrite acts as a reservoir of nitric oxide in organisms, understanding mechanisms by which nitric oxide is released can illuminate the role of nitrite in NO signaling. We have observed direct transfer of an oxygen atom from nitrite in b-diketiminato copper(II) model complexes [CuII](k2-O2N) with nucleophiles such as phosphines PAr3 to release NO with formation of O=PAr3 and reduction to copper(I). To reveal key mechanistic features in this O-atom transfer (OAT) mechanism for NO release, we performed a kinetic study of a series of electronically varied β-diketiminato copper(II) nitrite complexes with a range of phosphines PAr3 whose second order rate constants are largest for pairs of electron-poor copper(II) centers and electron-rich phosphines. Computational analysis benchmarked with experimental activation parameters reveals the importance of nitrite isomerization at CuII from κ2-O to κ1-N to activate nitrite for O-atom transfer to form a [CuI]-NO intermediate that releases NO upon PAr3 binding at CuI. These findings illustrate important mechanistic details of NO formation from nitrite via O-atom transfer and motivate the study of other substrates that can engage in OAT with nitrites, including those that involve C-H bonds.

Nitric oxide release from nitrite at copper via O-atom transfer

ACS Spring Meeting 2021

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