Neutral pyrazolyl-bridged nickel nitrosyl complexes. Synthesis, structure, and reactivity

Abstract

A series of neutral pyrazolyl-bridged nickel nitrosyl complexes, [LNi(NO)]2 (where L = pyrazolyl, N2C3H3; 3,5-dimethylpyrazolyl, N2C5H7; or 3,5-di-tert-butylpyrazolyl, N2C11H19), is described. The nickel atoms are susceptible to nucleophilic attack and the reactivity of the dimers with neutral donor ligands is reported. In addition to the dimeric molecules a novel trimetallic nickel compound [(ON)Ni(N2C5H7)2]2Ni has also been isolated. Crystals of [Ni(NO)(N2C5H7)]2 are monoclinic, a = 18.925(2), b = 11.012(1), c = 7.037(2) Å, β = 100.93(1)°, Z = 4, space group C2/c and crystals of [(ON)Ni(N2C5H7)2]2Ni are triclinic, a = 7.4041(7), b = 9.6331(7), c = 9.7595(8) Å, α = 85.698(9), β = 73.174(8), γ = 76.109(8)°, Z = 1, space group [Formula: see text]. Both structures were solved by Patterson and Fourier syntheses and were refined by full-matrix least-squares procedures to R = 0.035 and 0.028 for 832 and 2128 reflections with I ≥ 3σ(I) respectively. Nearly planar centrosymmetric molecules of [Ni(NO)(N2C5H7)]2 contain trigonal planar nickel atoms with Ni—N(pyrazolyl) = 1.880(3) and 1.922(3), Ni—NO = 1.616(4), and N—O = 1.158(4) Å, Ni—N—O = 178.9(4)°. This structure also contains an unusually long N—N bond in the pyrazolyl ring (1.463(4) Å). Centrosymmetric molecules of [(ON)Ni(N2C5H7)2]2Ni contain a central square-planar Ni(II) atom bonded to four pyrazolyl nitrogen atoms (mean Ni—N = 1.905(1) Å) and two trigonal planar outer nickel atoms coordinated to two pyrazolyl nitrogen atoms (mean Ni—N = 1.922(3) Å) and to a somewhat bent nitrosyl group (Ni—N = 1.625(3), N—O = 1.153(4) Å, Ni—N—O = 168.9(3)°).