Regioselective nucleophilic addition of triphenylphosphine to the nitrosylruthenium alkynyl complexes having a hydrotris(pyrazol-1-yl)borate: formation of phosphonio-alkenyl, alkynyl, and allenyl species

Abstract

A nitrosylruthenium alkynyl complex of TpRuCl(CCPh)(NO) (1a) was reacted with PPh₃ in the presence of HBF₄·Et₂O at room temperature to give a β-phosphonio-alkenyl complex (E)-[TpRuCl{CHC(PPh₃)Ph}(NO)]BF₄ (2·BF₄). On the other hand, for γ-hydroxyalkynyl complexes TpRuCl{CCC(R)₂OH}(NO) (R = Me (1b), Ph (1c), H (1d)), similar treatments with PPh₃ were found to give γ-phosphonio-alkynyl [TpRuCl{CCC(Me)₂PPh₃}(NO)]BF₄ (3·BF₄), α-phosphonio-allenyl [TpRuCl{C(PPh₃)CCPh₂}(NO)]BF₄ (4·BF₄), and a novel product of γ-hydroxy-β-phosphonio-alkenyl (E)-[TpRuCl{CHC(PPh₃)CH₂OH}(NO)]BF₄ (5·BF₄), respectively. Dominant factors for the selectivity in affording 3–5 were associated with the steric congestion and electronic properties at the γ-carbons, along with those around the metal fragment. From the bis(alkynyl) complex TpRu(CCPh)₂(NO) (6), a bis(β-phosphonio-alkenyl) (E,E)-[TpRu{CHC(PPh₃)Ph}₂(NO)](BF₄)₂ {7·(BF₄)₂} was produced at room temperature. However, similar reactions at 0 °C gave an alkynyl β-phosphonio-alkenyl complex (E)-[TpRu(CCPh){CHC(PPh₃)Ph}(NO)]BF₄ (8·BF₄) as a sole product, of which additional hydration in the presence of HBF₄·Et₂O afforded a β-phosphonio-alkenyl ketonyl (E)-[TpRu{CH₂C(O)Ph}{CHC(PPh₃)Ph}(NO)]BF₄ (9·BF₄). Five complexes, 2–5 and 7 were crystallographically characterized.