Solvent-less and fluoride-free hiyama reaction of arylsiloxanes with aryl bromides and chlorides promoted by sodium hydroxide:: A useful protocol for palladium recycling and product isolation

Palladium salts and oxime-derived palladacycles catalyze the cross-coupling reaction of arylsiloxanes with aryl bromides and chlorides in low catalyst loading (0.001-0.1 mol % of Pd) under fluoride-free conditions to provide biaryls and heterobiaryls. For some deactivated aryl bromides and for aryl chlorides, the corresponding cross-couplings need TBAB as additive. Concentrated aqueous sodium hydroxide (50%) promoted this Hiyama reaction in practically the absence of solvents under air in good yields. The process can be performed at 120 degrees C either under heating in a pressure tube or under microwave irradiation. This protocol allows palladium recycling and facilitates the final isolation of the products simply by ether extraction.