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

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.