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

Article abstract of DOI:10.1021/om00004a048

The tetraene 3,6-dimethylene-1,7-octadiene (DMOD) reacts with zerovalent [FePR₃] species (prepared by reduction of FeCl₂·nTHF with active Mg in the presence of the donor ligand) to give (η⁴,η⁴ -DMOD)FePR₃ compounds. The crystal structure of the PPh₃-stabilized derivative (space group A3, a = b = c = 20.290(9) A?, α = β = γ = 117.47(3)°, Z = 6, R = 0.048, R_w = 0.052) confirms that the iron atom lies at the center of a square pyramid with the P atom at the apex and the two 1,3-diene fragments forming the base. That the products of the reaction of the trienes 3-methylene-1,6-heptadiene (MHD) and 3-methylene-1,7-octadiene (MOD) with zerovalent [Fe(Prⁱ₂P(CH₂)_nPPrⁱ ₂)] species (n = 1, 2, 3) contain a triene molecule bonded in an η²,η⁴-manner to the metal atom has been confirmed by X-ray diffraction for (η²,η⁴-MHD)Fe(Prⁱ₂PC ₂H₄PPrⁱ₂) (space group P2₁/c, a = 11.831(1) A?, b = 9.744(1) A?, c = 20.917(2) A?, β = 104.87(1)°, Z = 4, R 0.042, R_w = 0.039). Warming a red ethereal solution of (η²,η⁴-MOD)Fe(Prⁱ₂PC ₃H₆PPrⁱ₂) to room temperature causes dissociation of the nonconjugated double bond of the triene to give the green, paramagnetic compound (η⁴-MOD)Fe(Prⁱ₂-PC₃H ₆PPrⁱ₂) which reacts with CO to give the yellow, diamagnetic compound (η⁴-MOD)Fe(CO)(Prⁱ₂PC₃H ₆PPrⁱ₂.