In Situ Generation of ArCu from CuF2 Makes Coupling of Bulky Aryl Silanes Feasible and Highly Efficient

Abstract

A bimetallic system Pd/CuF2, catalytic in Pd and stoichiometric in Cu, is very efficient and selective for the coupling of fairly hindered aryl silanes with aryl, anisyl, phenylaldehide, or pyridyl iodides of conventional size. The reaction involves the activation of the silane by CuII followed by disproportionation and transmetalation from the CuI(aryl) to PdII, on which coupling takes place. The CuIII formed in the disproportionation is reduced to CuI(aryl) by the aryl silane in excess, so that the CuF2 used is fully converted into CuI(aryl) and used in the coupling. Moreover, no extra source of fluoride is needed. Interesting size selectivity towards coupling is found in competitive reactions of hindered aryl silanes. Easily accessible [PdCl2(IDM)(AsPh3)] is by far the best catalyst, and the isolated products are esentially free of As or Pd (< 1 ppm). The mechanistic aspects of the process are experimentally examined and discussed.