Carbonylation reactions catalyzed by homogeneous Pd–Co bimetallic systems

Abstract

The PdCl 2(PPh 3) 2–Co 2(CO) 8 bimetallic catalyst was found to be effective for the carbonylation of ArI with CO/HSiEt 3 to give benzyl silyl ethers as the major product, although neither PdCl 2(PPh 3) 2 nor Co 2(CO) 8 alone was catalytically active. Addition of NEt 3 to the reaction system changed the distribution of the carbonylation products, where 1,2-diaryl-1,2-disiloxyethanes were obtained predominantly. The former reaction is suggested to proceed via the aldehyde intermediate, while a mechanism involving the aroylcobalt complex (ArCO)Co(CO) 3(PPh 3) formed by way of a Pd–Co bimetallic complex is proposed for the latter reaction. On the other hand, PdCl 2(PCy 3) 2 was found to work as a selective catalyst for the hydroformylation of internal alkynes to give the corresponding α,β-unsaturated aldehydes, and the combined use of PdCl 2(PCy 3) 2 and Co 2(CO) 8 remarkably improved the catalytic activity with little change of the selectivity. Regio- and chemoselective hydroformylation of alkynes was achieved by using the PdCl 2(PCy 3) 2 and PdCl 2(PCy 3) 2–Co 2(CO) 8 catalysts.