The PdCl2(PPh3)(2)-Co-2(CO)(8) bimetallic catalyst was found to be effective for the carbonylation of ArI with CO/HSiEt3 to give benzyl silyl ethers as the major product, although neither PdCl2(PPh3)(2) nor Co-2(CO)(8) alone was catalytically active. Addition of NEt3 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)(PPh3) formed by way of a Pd-Co bimetallic complex is proposed for the latter reaction. On the other hand, PdCl2(PCy3)(2) was found to work as a selective catalyst for the hydroformylation of internal alkynes to give the corresponding alpha,beta -unsaturated aldehydes, and the combined use of PdCl2(PCy3)(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 PdCl2(PCy3)(2) and PdCl2(PCy3)(2)-Co-2(CO)(8) catalysts.