Photolytic C-Diazeniumdiolate Disassembly in the β-Diketiminate Complexes [^MeLM(O₂N₂CPh₃)] (M = Fe, Co, Cu)

Abstract

The reaction of [K(18-crown-6)][O2N2CPh3] with [MeLCo(μ-Br)2Li(OEt2)] (MeL = {(2,6- i Pr2C6H3)NC(Me)}2CH) generates the trityl diazeniumdiolate complex, [MeLCo(O2N2CPh3)] (1), in moderate yield. Similar metathesis reactions result in the formation of the Fe and Cu analogues, [MeLM(O2N2CPh3)] (Fe, 2; Cu, 3), which can also be isolated in moderate yields. Complexes 1–3 were characterized by ultraviolet–visible (UV–vis) spectroscopy, and their solid-state structures were determined by X-ray crystallography. These complexes were further characterized via 1H NMR spectroscopy (in the case of 1 and 2) or EPR spectroscopy (in the case of 3). Irradiation of complexes 1 and 2 with 371 nm light generates the known dinitrosyl complexes, [MeLM(NO)2] (M = Co, 4; Fe, 5), along with Ph3CH and 9-phenylfluorene. We propose that 4 and 5 are formed via the putative hyponitrite intermediates, [MeLM(κ2-O,O-ONNO)], which are formed by photoinduced homolysis of the C–N bond of the [O2N2CPh3] ligand. In contrast, irradiation of complex 3 with 371 nm light, in the presence of 1 equiv of PPh3, led to the formation of the Cu(I) complexes, [MeLCu(PPh3)], [(ArNCMeC(NO)CMe NAr)Cu(PPh3)] (6), and [(ArNCMeC(NO)CMe NAr)Cu]2 (7), of which the latter two are products of γ-nitrosation of the β-diketiminiate ligand. Also formed in this transformation are Ph3CN(H)OCPh3, Ph3PO, and N2O, along with trace amounts of NO.