Recyclable palladium(0)-catalyzed addition of silylstannanes to terminal alkynes in ionic liquids

Abstract

Ionic liquids have been used as solvents for many different organic reactions, often providing rate enhancements, selectivity improvements, and affording better yields compared to conventional solvents. In this study, the palladium(0)-catalyzed addition of trimethyl(tributylstannyl)silane and diphenylmethyl(tributylstannyl)silane to terminal alkynes is investigated using two different ionic liquids, 1- n -butyl-3-methylimidazolium hexafluorophosphate and 1- n -butyl-3-methylimidazolium tetrafluoroborate, under biphasic conditions using diethyl ether as a co-solvent. Five terminal alkynes were used, phenylacetylene, 1-decyne, 5-hexyn-1-ol, 5-hexyn-1-ol THP ether, and 6-chlorohexyne. In general, reactions between the silylstannanes and alkynes proceeded efficiently in both ionic liquids to give quantitative or near quantitative yields of their addition products as a single isomer.

Ionic liquids have gained much popularity of late due to their ability to immobilize transition metal catalysts, allowing them to be recycled due to the nonvolatile nature of ionic liquids. The tetrakis(triphenylphosphine)palladium(0) catalyst used in these silylstannation reactions was immobilized in both ionic liquids and shown to be extensively recyclable without loss of activity. Ionic liquid/catalyst systems were recycled ten times in the reaction of phenylacetylene with trimethyl(tributylstannyl)silane.