Nickel Polyene(yl)\nComplexes Synthesized from a Dinuclear\nNi(I) Compound and (Multi)cyclic Polyenes

The low-valent Ni–Ni-bonded compound [(Ni<sup>I</sup><b>L</b><sup>·</sup><sup>–</sup>)<sub>2</sub>] (<b>1</b>, <b>L</b> = [(2,6-<sup><i>i</i></sup>Pr<sub>2</sub>C<sub>6</sub>H<sub>3</sub>)NC(Me)]<sub>2</sub>) reacts with\na series of multicyclic polyenes through different redox processes,\naffording seven heteroleptic complexes (<b>2</b>–<b>8</b>) containing nickel, α-diimine <b>L</b>, and\npolyene (or polyenyl) ligands, where all three components exhibit\nvariable oxidation states. The reaction of <b>1</b> with 6-(dimethylamino)fulvene\nor 6,6-dimethylfulvene led to the reductive dimerization of two fulvene\nmolecules, yielding the dinuclear complexes <b>2</b> and <b>3</b> with a bridging bis-Cp ligand. In contrast, similar reactions\nwith 6,6-diphenylfulvene or pentamethylcyclopentadiene (C<sub>5</sub>Me<sub>5</sub>H) only gave the adducts [<b>L</b>Ni(η<sup>4</sup>-6,6-diphenylfulvene)] (<b>4</b>) or [(<b>L</b><sup>·</sup><sup>–</sup>)Ni(η<sup>4</sup>-C<sub>5</sub>Me<sub>5</sub>H)] (<b>5</b>) with a neutral polyene\nmolecule. However, the two complexes have different oxidation levels\nof the nickel center and ligand <b>L</b>, depending on the electronic\nproperty of the substrate. By using biphenylene, oxidative addition\nof a strained C–C bond to nickel occurred to form the biphenyl\nmetallacycle [<b>L</b>Ni(μ<sup>2</sup>-Ph<sub>2</sub>)]\n(<b>6</b>). Furthermore, the reaction of <b>1</b> with\nacenaphthylene or C<sub>60</sub> afforded complexes [<b>L</b>Ni(η<sup>2</sup>-acenaphthylene)] (<b>7</b>) and [<b>L</b>Ni(η<sup>2</sup>-C<sub>60</sub>)] (<b>8</b>)\nfeaturing an η<sup>2</sup>-bonded neutral polyene. The results\nprovide evidence of the facile electron transfer between the metal\nand ligands so that the nickel center can adjust its basicity to coordinate\neffectively with polyene substrates of different π-acidity.