NO Coupling by Nonclassical Dinuclear Dinitrosyliron Complexes to Form NO Dictated by Hemilability.

Selective coupling of NO by a nonclassical dinuclear dinitrosyliron complex (D-DNIC) to form NO is reported. The coupling is facilitated by the pyridinediimine (PDI) ligand scaffold, which enables the necessary denticity changes to produce mixed-valent, electron-deficient tethered DNICs. One-electron oxidation of the [{Fe(NO)}] complex Fe(PDI)(NO) () results in NO coupling to form NO via the mixed-valent {[Fe(NO)]} species, which possesses an electron-deficient four-coordinate {Fe(NO)} site, crucial in N-N bond formation. The hemilability of the PDI scaffold dictates the selectivity in N-N bond formation because stabilization of the five-coordinate {Fe(NO)} site in the mixed-valent [{Fe(NO)}] species, [Fe(PDI)(NO)][PF] (), does not result in an electron-deficient, four-coordinate {Fe(NO)} site, and hence no N-N coupling is observed.