Formation\nof Ni(I) Species upon Activation of 5,6,7-Trihydroquinolin-8-imine\nNickel(II) Dihalides with MAO and MMAO

Reactions between (<i>E</i>)-<i>N</i>-(2,6-diisopropylphenyl)-2-methyl-6,7-dihydroquinolin-8(5<i>H</i>)-imine nickel(II) dihalides and organoaluminum compounds\nAlMe<sub>3</sub>, Al<sup><i>i</i></sup>Bu<sub>3</sub>, MAO,\nand MMAO were monitored using EPR spectroscopy <i>in situ</i>. It was found that rapid one-electron reduction of the Ni(II) center\nresults in formation of a variety of monovalent nickel species which\nare stable at room temperature in an oxygen-free atmosphere. On the\nbasis of the EPR data obtained, these compounds were assigned to the\nheterobinuclear nickel-aluminum complexes of the type LNi<sup>I</sup>(μ-R)<sub>2</sub>AlX<sub>2</sub>, where L = <i>N</i>,<i>N′</i>-donor ligand, R = Me, <sup><i>i</i></sup>Bu, H, Br, or Cl bridge, and X = Me, <sup><i>i</i></sup>Bu, Br or, Cl, depending on conditions. Formation of the dihydride-bridged\nLNi<sup>I</sup>(μ-H)<sub>2</sub>AlX<sub>2</sub> complex was\nconfirmed using deuterium-labeled compounds. In the presence of an\nexcess of ethylene or 1-hexene, LNi<sup>I</sup>(μ-R)<sub>2</sub>AlX<sub>2</sub> eliminates RAlX<sub>2</sub> to afford LNi<sup>I</sup>R(C<sub>2</sub>H<sub>4</sub>) or LNi<sup>I</sup>R(C<sub>6</sub>H<sub>12</sub>) species, respectively. Structural assignments of the Ni<sup>I</sup> species are supported by DFT calculations of their <i>g</i>-tensor values.