Synthesis, structure and reactivity of nickel monoalkyl, imido and amido complexes supported by beta-diketiminate ligands

Later transition metal complexes are widely used as catalysts for alkene hydroamination, aziridination and polymerization. A better understanding of these important catalytic processes would involve characterization and study of species proposed to be the key intermediates, a task often difficult due to their general extreme instability at room temperature.; Later transition metal-amido species are thought to be the active species in hydroamination, the addition of a R2N-H bond across a C = C double bond to generate a new amine. By employing a pyridine diimine ancillary ligand, the rhodium anilido complex [Me2NNN]Rh(NHPh) was prepared and its reactivity towards ethylene, norbornene and carbon monoxide was explored.; A family of coordinatively and electronically unsaturated nickel alkyl complexes [Me2NN]NiR(2,4-lutidine) (R = Et, Pr) based on beta-diketiminate ligands was investigated as catalysts for olefin polymerization and found to oligomerize ethylene. Removal of the labile 2,4-lutidine from these complexes by addition of a Lewis acid allowed the isolation of the neutral beta-H agostic monoalkyls [Me2NN]Ni(R) (R = Et, Pr). Variable-temperature NMR spectra of these complexes revealed fluxional behavior that result from beta-H elimination, in-plane rotation of the beta-CH3 group, and a tetrahedral triplet structure for the ethyl derivative (suggested by a density functional theory calculations). NMR studies also showed that the beta-agostic ethyl complex reluctantly coordinated ethylene. The thermodynamic isotope effect KH/KD = 1.3(2) was measured for the loss of 2,4-lutidine from [Me2NN]NiR(2,4-lutidine) to form beta-agostic [Me2NN]Ni(R) (R = C2H5, C2D5).; Isolable Ni complexes with a terminal imido functionality bonded to a single metal center have been suggested as key intermediates in catalytic aziridination and are extremely rare. Utilizing novel beta-diketiminato Ni(I) pyridine adducts [MexNN]Ni(2,4-lutidine) (x = 2, 3) which react with organoazides, a family of imido complexes was prepared with three different modes of metal-imide binding. Most interestingly, the terminal Ni(III)-imide [Me3NN]Ni = NAd (Ad = adamantyl) was found to react with nucleophiles, radicals, electrophiles, and oxidants to exhibit a truly unique range of reactivity.