INTERACTION OF ACYCLIC TETRAENES AND TRIENES WITH TRANSITION-METALS - ORGANONICKEL COMPOUNDS

The tetraene 3,6-dimethylene-1,7-octadiene (DMOD) reacts with zerovalent [NiPR(3)] species to give (eta(2),eta(2)-DMOD)NiPR(3) 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 P2(1)/c, a = 10.057(1) Angstrom, b = 36.196(1) Angstrom, c = 10.944(1) Angstrom, a = y = 90 degrees, beta = 105.76(1)degrees, 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 (Pr2P)-P-i(CH2)(n)PPr2i (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 (eta(2),eta(2),eta(2),eta(2)-DMOD)Ni-2(Pr-2(i)- PCH2PPr2i), (eta(4),eta(4)-DMOD)[Ni((Pr2PC2H4PPr2i)-P-i)](2), and (eta(2),eta(2)-DMOD)[Ni((Pr2PC3H6PPr)-P-i(2)(i))](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) Angstrom, b = 24.152(1) Angstrom, c = 11.767(1) Angstrom, a = y = 90 degrees, beta = 120.65(1)degrees, Z = 4, R = 0.034, R(W) = 0.035) and confirms that the two 1,3-diene fragments of the tetraene interact with [Ni((Pr2PC2H4PPr2i)-P-i)] moieties. The trienes 3-methylene-1,6-heptadiene and 3-methylene-1,7-octadiene react with [NiPPr3i] species to give (eta(2),eta(2)-triene)NiPPr3i compounds in which a 1,6-heptadiene chain is complexed to the metal atom.