Synthesis, Structure, and Magnetic and Electrochemical Properties of Quasi-Linear and Linear Iron(I), Cobalt(I), and Nickel(I) Amido Complexes

Three potassium crown ether salts, [K-(Et2O)(2)(18-crown-6)][Fe{N(SiMe3)Dipp}(2)] (1a; Dipp = C6H3-2,6-Pr-2(i)), [K(18-crown-6)][Fe{N(SiMe3)Dipp}(2)]center dot 0.5PhMe (1b), and [K(18-crown-6)][M{N(SiMe3)Dipp}(2)] (M = Co, 2; M = Ni, 3), of the two-coordinate linear or near-linear bis-amido monoanions [M{N(SiMe3)Dipp}(2)] (M = Fe, Co, Ni) were synthesized by one-electron reduction of the neutral precursors M{N(SiMe3)Dipp}(2) with KC8 in the presence of 18-crown-6. They were characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and magnetic measurements. The anions feature lengthened M-N bonds in comparison with their neutral precursors, with slightly bent coordination (N-Fe-N = ca. 172 degrees) for the iron(I) complex, but linear coordination for the cobalt(I) and nickel(I) complexes. Fits of the temperature dependence of chi T-M of 1 and 2 reveal that the iron(I) and cobalt(I) complexes have large negative D zero-field splittings and a substantial orbital contribution to their magnetic moments with L = 2, whereas the nickel(I) complex has at most a small orbital contribution to its magnetic moment. The magnetic results have been used to propose an ordering of the 3d orbitals in each of the complexes.