A Terminal Ni(III)−Imide with Diverse Reactivity Pathways

The synthesis and structure of the β-diketiminato Ni(I) lutidine adducts [Me_xNN]Ni(2,4-lutidine) (x = 2 (2); x = 3 (3)) are described which serve as synthons to the “naked” 13-electron [Me_xNN]Ni fragments in reactions with N₃Ad to give Ni−imido complexes. The singly bridged imide {[Me₂NN]Ni}₂(μ-NAd) (4) possesses short Ni−Ni (2.506(1) Å) and Ni−N(imido) distances (1.732(4)−1.752(4) Å). Steric modification of the β-diketiminate ligand to include an additional methyl group in the N-aryl 4-position affords the Ni(III) terminal imide [Me₃NN]NiNAd (8) isolated in 52% yield. The X-ray structure of terminal imide 8 reveals a contracted Ni−N(imido) bond distance (1.662(2) Å) and an only somewhat bent imido linkage (Ni−N−C = 164.5(2)°) consistent with a significant degree of multiple bond character. Frozen glass EPR studies of 5 indicate a rhombic environment in which one of the signals exhibits strong hyperfine coupling (A = 22 G) to the imido ¹⁴N (I = 1) nucleus. The terminal imide 5 undergoes complete imido group transfer to CO and CNBu^t to give AdNCO and AdNCNBu^t, respectively, as well as with PMe₃ to afford AdNPMe₃. Exemplifying the radical character at the imido N atom, 5 adds to cobaltocene and abstracts a H atom from 1,4-cyclohexadiene to give the Ni(II)−amides [Me₃NN]Ni−NAd(η⁴-C₅H₅)CoCp (7) and [Me₃NN]Ni−NHAd (8).