Monovalent nickel and copper beta-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)(mu-eta(2):eta(2)-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) angstrom in 1a that is significantly longer than those in free C-organonitroso compounds (1.13-1.29 angstrom). [Me2NN]Cu(NCMe) reacts with 0.5 equiv of ArNO in ether to give the dinuclear adducts {[Me2NN]Cu}(2)(mu-eta(2):eta(1)-ONAr) (2a and 2b), which exhibit eta(2) and eta(1) bonding of the ArN=O moiety with separate [Me2NN]Cu fragments possessing N-O distances of 1.375(6) angstrom (2a) and 1.368(2) angstrom (2b). In arene solvents, one beta-diketiminatocopper(I) fragment dissociates from 2 to give [Me2NN]Cu(eta(2)-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) angstrom. IR spectra of the nitrosobenzene, adducts 1b, 2b, and 3b exhibit nu(NO) 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 la and 3a react with anaerobic NO(g) to give the corresponding N-aryl-N-nitrosohydroxylaminato complexes [Me2NN]M(kappa(2)-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(eta(2)-ONAr) with NO(g) to give divalent [Me2NN]Cu(kappa(2)-O2N2Ar) represents an example of oxidative nitrosylation.