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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

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journal contribution
posted on 26.09.2019, 17:09 by Rebeca González-Fernández, Pascale Crochet, Victorio Cadierno
Half-sandwich ruthenium­(II) complexes containing η6-coordinated 3-phenylpropanol and phosphinous-acid-type ligands, namely, [RuCl26-C6H5CH2CH2CH2OH)­{P­(OH)­R2}] (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 [RuCl261(O)-C6H5CH2CH2CH2OH}] (1) with the appropriate pentavalent phosphorus oxide R2P­(O)­H. The structure of [RuCl26-C6H5CH2CH2CH2OH)­{P­(OH)­Me2}] (2a) was unequivocally confirmed by X-ray diffraction methods. Compounds 2ag 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 [RuCl26-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 °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 2ag as catalysts for ortho-arylation reactions of 2-phenylpyridine in water is also briefly discussed.