Nitric Oxide Oxidatively Nitrosylates Ni(I) and Cu(I) C-Organonitroso Adducts

Monovalent nickel and copper β-diketiminato complexes react with ArNO (Ar = 3,5-Me2C6H3, Ph) to give C-nitroso adducts that exhibit three different modes of bonding with varying degrees of N−O bond activation. The addition of ArNO to 2 equiv of [Me2NN]Ni(2,4-lutidine) {[Me2NN]− = 2,4-bis(2,6-dimethylphenylimido)pentyl} gives {[Me2NN]Ni}2(μ-η2:η2-ONAr) (1a and 1b), which exhibit symmetrical bonding of the ArNO moiety between two [Me2NN]Ni fragments, with a N−O bond distance of 1.440(4) Å in 1a that is significantly longer than those in free C-organonitroso compounds (1.13−1.29 Å). [Me2NN]Cu(NCMe) reacts with 0.5 equiv of ArNO in ether to give the dinuclear adducts {[Me2NN]Cu}2(μ-η2:η1-ONAr) (2a and 2b), which exhibit η2 and η1 bonding of the ArNO moiety with separate [Me2NN]Cu fragments possessing N−O distances of 1.375(6) Å (2a) and 1.368(2) Å (2b). In arene solvents, one β-diketiminatocopper(I) fragment dissociates from 2 to give [Me2NN]Cu(η2-ONAr) (3a and 3b), which may be isolated by the addition of 1 equiv of ArNO to [Me2NN]Cu(NCMe). The X-ray structures of 3a and 3b are similar to those of related Cu(I) alkene adducts, with N−O distances in the narrow range 1.333(4)−1.338(5) Å. IR spectra of the nitrosobenzene adducts 1b, 2b, and 3b exhibit νNO stretching frequencies at 915, 1040, and 1113 cm−1, respectively, following the decreasing degree of NO activation observed in the X-ray structures of species 1, 2, and 3. Both 1a and 3a react with anaerobic NO(g) to give the corresponding N-aryl-N-nitrosohydroxylaminato complexes [Me2NN]M(κ2-O2N2Ar) [M = Ni (4), Cu (5)]. In the reaction of dinuclear 1a with NO, one [Me2NN]Ni fragment is trapped as the nickel nitrosyl [Me2NN]Ni(NO). Reaction of the monovalent complex [Me2NN]Cu(η2-ONAr) with NO(g) to give divalent [Me2NN]Cu(κ2-O2N2Ar) represents an example of oxidative nitrosylation.