Reactions of co-ordinated ligands. Part 49. Ligand-displacement and oxidative-addition reactions of [Ru{P(OMe)3}(η4-C4Ph4)(η4-C5H6)]; crystal structures of [Ru(NCMe){P(OMe)3}(η3-C3H5)(η4-C4Ph4)][SbF6] and [Ru{C(Ph)C(Ph)C(η6-C6H5)C(Ph)CH2CHCH2}{P(OMe)3}2][BF4]

Abstract

Treatment of the ruthenium(0) complex [Ru{P(OMe)₃}(η⁴-C₄Ph₄)(η⁴-C₅H₆)] with isoprene or cyclohexa-1,3-diene results in the displacement of C₅H₆ and formation of compounds of the type [Ru{P(OMe)₃}(η⁴-1,3-diene)(η⁴-C₄Ph₄)]. Although trans-penta-1,3-diene reacts similarly to give the η⁴-trans-penta-1,3-diene complex, the corresponding reaction with cis-penta-1,3-diene affords a mixture of both the trans- and cis-penta-1,3-diene ruthenium complexes. A possible mechanism for this reaction is discussed. Cyclopenta-1,3-diene is also displaced on treatment of [Ru{P(OMe)₃}(η⁴-C₄Ph₄)(η⁴-C₅H₆)] with allyl bromide or 2-methylallyl chloride to give respectively the ruthenium(II) species [RuBr{P(OMe)₃}(η³-C₃H₅)(η⁴-C₄Ph₄)] and [RuCl{P(OMe)₃}(η³-2-MeC₃H₄)(η⁴-C₄Ph₄)]. Reaction of these species with AgBF₄ in acetonitrile affords the cations [Ru(NCMe){P(OMe)₃}(η³-C₃H₅)(η⁴-C₄Ph₄)][BF₄] and [Ru(NCMe){P(OMe)₃}(η³-2-MeC₃H₄)(η⁴-C₄Ph₄)][BF₄]. The solid-state structure of the corresponding SbF₆^–, salt of the former cation was established by X-ray crystallography. The geometry of the molecule is that of a three-legged piano-stool, the allyl group adopting an endo configuration. Instead of the expected propeller configuration for the η⁴-tetraphenylcyclobutadiene ligand, two of the phenyl rings lie roughly coplanar with the C₄ ring, while the other two are approximately perpendicular to it. Attempts to replace the acetonitrile ligand present in these species by P(OMe)₃ failed, however when AgBF₄ was added to an acetone solution of [RuBr{P(OMe)₃}(η³-C₃H₅)(η⁴-C₄Ph₄)] followed by addition of P(OMe)₃ a yellow cationic species was obtained, which was shown by X-ray crystallography to be the ring-opened compound [Ru{C(Ph)C(Ph)C(η⁶-C₆H₅)C(Ph)CH₂CHCH₂}{P(OMe)₃}₂][BF₄]. A mechanism is proposed for this unusual reaction.