Nickel Polyene(yl) Complexes Synthesized from a Dinuclear Ni(I) Compound and (Multi)cyclic Polyenes

The low-valent Ni-Ni-bonded compound [(Ni^IL^·-)₂] (1, L = [(2,6-ⁱPr₂C₆H₃)NC(Me)]₂) reacts with a series of multicyclic polyenes through different redox processes, affording seven heteroleptic complexes (2-8) containing nickel, α-diimine L, and polyene (or polyenyl) ligands, where all three components exhibit variable oxidation states. The reaction of 1 with 6-(dimethylamino)fulvene or 6,6-dimethylfulvene led to the reductive dimerization of two fulvene molecules, yielding the dinuclear complexes 2 and 3 with a bridging bis-Cp ligand. In contrast, similar reactions with 6,6-diphenylfulvene or pentamethylcyclopentadiene (C₅Me₅H) only gave the adducts [LNi(η⁴-6,6-diphenylfulvene)] (4) or [(L^·-)Ni(η⁴-C₅Me₅H)] (5) with a neutral polyene molecule. However, the two complexes have different oxidation levels of the nickel center and ligand L, depending on the electronic property of the substrate. By using biphenylene, oxidative addition of a strained C-C bond to nickel occurred to form the biphenyl metallacycle [LNi(μ²-Ph₂)] (6). Furthermore, the reaction of 1 with acenaphthylene or C₆₀ afforded complexes [LNi(η²-acenaphthylene)] (7) and [LNi(η²-C₆₀)] (8) featuring an η²-bonded neutral polyene. The results provide evidence of the facile electron transfer between the metal and ligands so that the nickel center can adjust its basicity to coordinate effectively with polyene substrates of different π-acidity.