The synthesis and structure of the beta-diketiminato Ni(I) lutidine adducts [MexNN]Ni(2,4-lutidine) (x = 2 (2); x = 3 (3)) are described which serve as synthons to the "naked" 13-electron [MexNN]Ni fragments in reactions with N3Ad to give Ni-imido complexes. The singly bridged imide {[Me2NN]Ni}2(mu-NAd) (4) possesses short Ni-Ni (2.506(1) A) and Ni-N(imido) distances (1.732(4)-1.752(4) A). Steric modification of the beta-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) A) and an only somewhat bent imido linkage (Ni-N-C = 164.5(2) degrees ) 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 CNBut to give AdNCO and AdNCNBut, 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(eta4-C5H5)CoCp (7) and [Me3NN]Ni-NHAd (8).

Addition of BF(3).OEt(2) to ethereal solutions of the Ni(II) beta-diketiminates [Me(2)NN]Ni(R)(2,4-lutidine) (R = Et (1), Pr (2)) allows the isolation of the neutral beta-H agostic monoalkyls [Me(2)NN]Ni(R) (R = Et (3), Pr (4)). X-ray studies of primary alkyls 3 and 4a reveal acute Ni-C(alpha)-C(beta) angles with short Ni-C(beta) distances, indicating structures along the beta-H elimination pathway. Positional disorder of the alkyl group in the X-ray structure of 4 corresponds to partial (22%) occupancy by the secondary alkyl [Me(2)NN]Ni(CHMe(2)) (4b). Variable-temperature NMR spectra of 3 and 4 reveal fluxional behavior that result from beta-H elimination, in-plane rotation of the beta-CH(3) group, and a tetrahedral triplet structure for 3 that were investigated by density functional theory calculations at the Becke3LYP/6-31G level of theory without simplifications on the beta-diketiminate ancillary ligand. Calculations support low temperature NMR studies that identify the linear beta-H agostic propyl isomer 4a as the ground state with the branched beta-H agostic isomer 4b slightly higher in energy. NMR studies and calculations show that the beta-agostic 3 reluctantly coordinates ethene and that 3 is the ground state for this ethylene oligomerization catalyst. The thermodynamic isotope effect K(H)/K(D) = 1.3(2) measured for the loss of 2,4-lutidine from 1 to form beta-agostic 3 was also examined by DFT calculations.

The β-diketiminato nickel(I) species [Me 3 NN]Ni(2-picoline) (1) serves as an efficient catalyst for carbodiimide (RNCNR′) formation in the reactions of a range of organoazides N 3 R with isocyanides R′NC. [Me 3 NN]-Ni(CNR) 2 (R = t Bu, Ar (Ar = 2,6-Me 2 C 6 H 3 )) species provide carbodiimides RNCNAr′ upon reaction with Ar′N 3 (Ar′ = 3,5-Me 2 C 6 H 3 ). Nitrene transfer takes place via the intermediacy of nickel imides. Reaction of [Me x NN]Ni(2-picoline) (x = 2 or 3) with Ar′N 3 gives the new dinickel imides {[Me x NN]Ni} 2 (μ-NAr′) (4 (x = 3) and 5 (x = 2)) as deep purple, diamagnetic substances. The X-ray structure of {[Me 2 NN]Ni} 2 (μ-NAr′) (5) features short Ni−N imide distances of 1.747(2) and 1.755(2) Å along with a short Ni−Ni distance of 2.7210(3) Å. These dinickel imides 4 and 5 react stoichiometrically with t BuNC to provide the corresponding carbodiimides t BuNCNAr′ in good yield. Azide transfer takes place upon reaction of 1 with TMS-N 3 to give the square planar nickel(II) azide [Me 3 NN]Ni(N 3 )(2-picoline) (7). Stoichiometric reaction of dinickel dicarbonyl {[Me 3 NN]Ni} 2 (μ-CO) 2 with organoazides such as Ar′N 3 is sluggish, indicating that 1 is not an efficient catalyst for nitrene transfer from organoazides to CO to form isocyanates RNCO.

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An electron-rich nickel(I) beta-diketiminate cleaves the E-NO bond of O-, S-, and N-organonitroso species to give the nickel nitrosyl [Me 3NN]NiNO along with dimeric nickel(II) alkoxide or thiolate complexes {[Me 3NN]Ni} 2(mu-E) 2 or the mononuclear nickel(II) amide [Me 3NN]NiNPh 2. This diamagnetic three-coordinate amide exhibits temperature-dependent NMR spectra due to a low-lying triplet state.