Catalytic Intermolecular Pauson−Khand-Type Reaction:  Strong Directing Effect of Pyridylsilyl and Pyrimidylsilyl Groups and Isolation of Ru Complexes Relevant to Catalytic Reaction

Some circumstantial evidence for the directing effect of the 2-pyridylsilyl group in the Ru-catalyzed intermolecular Pauson−Khand-type reaction (PKR) of alkenyl(2-pyridyl)silane, alkyne, and carbon monoxide has been provided. Most importantly, we have succeeded in isolating several monometallic Ru complexes relevant to the catalytic reaction: Ru(vinylsilane)(CO)3 complexes and ruthenacyclopentene. While the stoichimetric reaction of the Ru(vinylsilane)(CO)3 complex with an alkyne led to the formation of the corresponding cyclopentenone (PKR product) at 100 °C, the ruthenacyclopentene intermediate was quantitatively produced at 50 °C. This complex was also converted to a cyclopentenone upon heating at 100 °C. Moreover, it was also found that the Ru(vinylsilane)(CO)3 complex and ruthenacyclopentene serve as catalysts in intermolecular PKR.