In situ Mo(CO)₆-based catalysts for alkyne metathesis: Silanols vs phenols as co-catalysts under thermal and photochemical activation

A systematic study on the use of silanols and phenols as effective activators in Mo(CO)₆ – based catalytic systems for metathesis of 4-decyne and 1-phenyl-1-propyne is reported. In comparison with traditionally used phenols, aryl-substituted silanols exhibit high activating potential of molybdenum species even at lower concentrations (2 mol% of Mo(CO)₆ and 4–20 mol% of silanol depending on the alkyne) at toluene reflux. Silylated phenols and silanols are also suitable as co-catalysts. Additionally, Mo(CO)₆/silanol catalytic system is shown to be efficiently activated by UV-irradiation at room temperature, whereas it is less effective for metathesis reactions performed in the presence of phenols.