Half-sandwich ruthenium(ii) complexes with tethered arene-phosphinite ligands: synthesis, structure and application in catalytic cross dehydrogenative coupling reactions of silanes and alcohols.

The preparation of the tethered arene-ruthenium(ii) complexes [RuCl{η:κ(P)-CH(CH)OPR}] (R = Ph, n = 1 (9a), 2 (9b), 3 (9c); R = Pr, n = 1 (10a), 2 (10b), 3 (10c)) from the corresponding phosphinite ligands RPO(CH)Ph (R = Ph, n = 1 (1a), 2 (1b), 3 (1c); R = Pr, n = 1 (2a), 2 (2b), 3 (2c)) is presented. Thus, in a first step, the treatment at room temperature of tetrahydrofuran solutions of dimers [{RuCl(μ-Cl)(η-arene)}] (arene = p-cymene (3), benzene (4)) with 1-2a-c led to the clean formation of the corresponding mononuclear derivatives [RuCl(η-p-cymene){RPO(CH)Ph}] (5-6a-c) and [RuCl(η-benzene){RPO(CH)Ph}] (7-8a-c), which were isolated in 66-99% yield. The subsequent heating of 1,2-dichloroethane solutions of these compounds at 120 °C allowed the exchange of the coordinated arene. The substitution process proceeded faster with the benzene derivatives 7-8a-c, from which complexes 9-10a-c were generated in 61-82% yield after 0.5-10 h of heating. The molecular structures of [RuCl(η-p-cymene){PrPO(CH)Ph}] (6c) and [RuCl{η:κ(P)-CH(CH)OPPr}] (n = 1 (10a), 2 (10b), 3 (10c)) were unequivocally confirmed by X-ray diffraction methods. In addition, complexes [RuCl{η:κ(P)-CH(CH)OPR}] (9-10a-c) proved to be active catalysts for the dehydrogenative coupling of hydrosilanes and alcohols under mild conditions (r.t.). The best results were obtained with [RuCl{η:κ(P)-CH(CH)OPPr}] (10c), which reached TOF and TON values up to 117 600 h and 57 000, respectively.