In Situ Generation of ArCu from CuF 2 Makes Coupling of Bulky Aryl Silanes Feasible and Highly Efficient

A bimetallic system of Pd/CuF 2 , catalytic in Pd and stoichiometric in Cu, is very efficient and selective for the coupling of fairly hindered aryl silanes with aryl, anisyl, phenylaldehyde, p ‐cyanophenyl, p ‐nitrophenyl, or pyridyl iodides of conventional size. The reaction involves the activation of the silane by Cu II , followed by disproportionation and transmetalation from the Cu I (aryl) to Pd II , upon which coupling takes place. Cu III formed during disproportionation is reduced to Cu I (aryl) by excess aryl silane, so that the CuF 2 system is fully converted into Cu I (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 [PdCl 2 (IDM)(AsPh 3 )] (IDM = 1,3‐dimethylimidazol‐2‐ylidene) is by far the best catalyst, and the isolated products are essentially free from As or Pd (