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

The synthesis and structure of the β-diketiminato Ni(I) lutidine adducts [Me<i>_x</i>NN]Ni(2,4-lutidine) (<i>x</i> = 2 (<b>2</b>); <i>x</i> = 3 (<b>3</b>)) are described which serve as synthons to the “naked” 13-electron [Me<i>_x</i>NN]Ni fragments in reactions with N₃Ad to give Ni−imido complexes. The singly bridged imide {[Me₂NN]Ni}₂(μ-NAd) (<b>4</b>) 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 <i>N</i>-aryl 4-position affords the Ni(III) terminal imide [Me₃NN]NiNAd (<b>8</b>) isolated in 52% yield. The X-ray structure of terminal imide <b>8</b> 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 <b>5</b> indicate a rhombic environment in which one of the signals exhibits strong hyperfine coupling (<i>A</i> = 22 G) to the imido ¹⁴N (<i>I</i> = 1) nucleus. The terminal imide <b>5</b> undergoes complete imido group transfer to CO and CNBu<i>^t</i> to give AdNCO and AdNCNBu<i>^t</i>, respectively, as well as with PMe₃ to afford AdNPMe₃. Exemplifying the radical character at the imido N atom, <b>5</b> adds to cobaltocene and abstracts a H atom from 1,4-cyclohexadiene to give the Ni(II)−amides [Me₃NN]Ni−NAd(η⁴-C₅H₅)CoCp (<b>7</b>) and [Me₃NN]Ni−NHAd (<b>8</b>).