Hydrophilic (η6-Arene)-Ruthenium(II) Complexes with P-OH Ligands as Catalysts for the Isomerization of Allylbenzenes and C-H Bond Arylation Reactions in Water

Half-sandwich ruthenium(II) complexes containing eta(6)-coordinated 3-phenylpropanol and phosphinous-acid-type ligands, namely, [RuCl2(eta(6)-C6H5CH2CH2CH2OH){P(OH)R-2}] (R = Me (2a), Ph (2b), 4-C6H4CF3(2c), 4-C6H4OMe (2d), OMe (2e), OEt (2f), and OPh (2g), have been synthesized in 44-88% yield by reacting [RuCl2 {eta 6:k(1) (O)-C6H5CH2CH2CH2OH}] (1) with the appropriate pentavalent phosphorus oxide R2P(=O)H. The structure of [RuCl2(eta(6)-C6H5CH2CH2CH2OH){P(OH)Me-2}] (2a) was unequivocally confirmed by X-ray diffraction methods. Compounds 2a-g proved to be catalytically active in the isomerization of allylbenzenes into the corresponding (1-propenyl)benzene derivatives employing water as the sole reaction solvent, with [RuCl2(eta(6)-C6H5CH2CH2CH2OH){P(OH)(OPh)(2)}] (2g) showing the best performance and a broad substrate scope (73-93% isolated yields with E/Z ratios around 90:10 employing 1 mol % of 2g and 3 mol % of K2CO3, and performing the catalytic reactions at 80 degrees C for 4-24 h). The results herein presented show for the first time the utility of phosphinous acids as auxiliary ligands for metal-catalyzed olefin isomerization processes, reactions in which a cooperative role for the P-OH unit is proposed. On the other hand, the utility of complexes 2a-g as catalysts for ortho-arylation reactions of 2-phenylpyridine in water is also briefly discussed.