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.