Synthesis and Reactivity of Nickel Hydride Complexes of an α-Diimine Ligand

Reaction of (LNiBr2)-Ni-0 with 2 equiv of NaH yielded the Ni-II hydride complex [(L center dot-)Ni(mu-H)(2)Ni(L center dot-)] (1) (L = [(2,6-iPr(2)C(6)H(3))NC(Me)](2); L-0 represents the neutral ligand, L center dot- is its radical-anionic form, and L2- denotes the dianion) in good yield. Stepwise reduction of complex 1 led to a series of nickel hydrides. Reduction of 1 with 1 equiv of sodium metal afforded a singly reduced species [Na(DME)(3)]-[(L center dot-)Ni(mu-H)(2)Ni(L center dot-)] (2a) (DME = 1,2-dimethoxy-ethane), which contains a mixed-valent core [Ni(mu-H)(2)Ni](+)-With 2 equiv of Na a doubly reduced species [Na-(DME)](2)[L2-Ni(mu-H)(2)NiL2-] (3a) was obtained, in which each monoanion (L center dot-) in the precursor 1 has been reduced to L2-. By using potassium as the reducing agent, two analogous species [K(DME)(4)][(L center dot-)Ni(mu-H)(2)Ni(L center dot-)] (2b) and [K(DME)](2)[L2-Ni(mu-H)(2)NiL2-] (3b) were obtained. Further treatment of 3b with 2 equiv of K led to a trinuclear complex [K(DME)(THF)](2)K-2[L2-Ni(mu-H)(2)Ni(mu-H)(2)NiL2-] (4), which contains one Ni-II and two Ni-I centers with a triplet ground state. When 1 and 3a were warmed in toluene or benzene, respectively, three reverse-sandwich dinickel complexes, [(L center dot-)Ni(mu-eta(3):eta(3)-C7H8)Ni(L center dot-)] (5) and [Na(DME)](2)[L-2-Ni(mu-eta(3):eta(3)-C6H5R)NiL2-] (6: R = CH3; 7: R = H), were isolated. Reaction of 1 with Me3SiN3 gave the N-3-bridged complex [(L center dot-)Ni(mu-eta(1)-N-3)(2)Ni(L center dot-)] (8). The crystal structures of complexes 1-8 have been determined by X-ray diffraction, and their electronic structures have been fully studied by EPR/NMR spectroscopy.