Synthesis of conjugated diene complexes of ruthenium(0) derived from Ru(η6-naphthalene)(η4-1,5-COD): Z to E isomerisation of coordinated 1,3-pentadiene

The naphthalene complex of zerovalent ruthenium, [Ru(η6-C10H8)(η4-1,5-COD)] (1), readily reacts with 1,3-dienes in the presence of a ligand (L) to produce complexes [Ru(η4-cisoid-1,3-diene)(η4-1,5-COD)(L)] [1,3-diene = butadiene, 2,3-dimethylbutadiene, isoprene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-cyclohexadiene; L = MeCN, tBuCN, PhCN, NCC6H4CN, CO, tBuNC, pyridine, P(OMe)3, P(OPh)3, PMe3, PEt3, PPh3, PCy3]. The single-crystal X-ray structures of [Ru(η4-cisoid-1,3-butadiene)(η4-1,5-COD)(MeCN)] (2a) and [Ru{η4-(E)-cisoid-1.3-pentadiene}(η4-1,5-COD)(PPh3)}] (E-5l) show the expected, approximately square pyramidal geometry about the metal atom, with the auxiliary ligand occupying the axial site. [Ru{η4-(Z)-cisoid-1,3-pentadiene}(η4-1,5-COD)(PPh3)] (Z-5l) irreversibly isomerises to E-5l in benzene-d6 at 30 °C, the reaction obeying a first-order rate law [k = (2.89 ± 0.06) × 10−4 s−1]. This reaction is significantly retarded by addition of PPh3 suggesting that a vacant site is required for the E/Z isomerisation.