Interaction of acyclic tetraenes and trienes with transition metals: Organonickel compounds

Article abstract of DOI:10.1021/om00004a049

The tetraene 3,6-dimethylene-1,7-octadiene (DMOD) reacts with zerovalent [NiPR₃] species to give (η²,η²-DMOD)NiPR₃ in which the methylene group of one 1,3-diene fragment and the vinyl group of the second interact with the metal atom. This unsymmetrical complexation of the tetraene has been confirmed by X-ray diffraction for the P(OC₆H₄-o-Ph)₃-stabilized derivative (space group P2₁/c, a = 10.057(1) A?, b = 36.196(1) A?, c = 10.944(1) A?, α = γ = 90°, β = 105.76(1)°, Z = 4, R = 0.056, R_w = 0.071) and is the result of the preferred coordination of a 1,6-heptadiene chain to the metal atom. The NMR spectra indicate that the molecule is fluxional with a pairwise exchange of the methylene groups and of the vinyl groups. The structure of the product formed in the presence of the bidentate ligands Prⁱ₂P(CH₂)_nPPrⁱ ₂ (n = 1, 2, 3) is dependent upon the length of the chain bridging the two P-atoms, and compounds have been isolated having the composition (η²,η²,η²,η ²-DMOD)Ni₂(Prⁱ₂-PCH ₂PPrⁱ₂), (η⁴,η⁴-DMOD)[Ni(Prⁱ₂PC ₂H₄FPrⁱ₂)]₂, and (η²,η²-DMOD)[Ni(Prⁱ₂PC ₃H₆PPrⁱ₂)]₂. The molecular structure of the bis(diisopropylphosphino)ethane-containing compound has been established by X-ray diffraction (space group C2/c, a = 17.535 (2) A?, b = 24.152 (1) A?, c = 11.767(1) A?, α = γ = 90°, β = 120.65(1)°, Z = 4, R = 0.034, R_w = 0.035) and confirms that the two 1,3-diene fragments of the tetraene interact with [Ni(Prⁱ₂PC₂H₄PPrⁱ ₂)] moieties. The trienes 3-methylene-1,6-heptadiene and 3-methylene-1,7-octadiene react with [NiPPrⁱ₃] species to give (η²,η²-triene)NiPPrⁱ₃ compounds in which a 1,6-heptadiene chain is complexed to the metal atom.