HOMOGENEOUS MULTIMETALLIC CATALYSTS .11. CARBONYLATION OF ARYL IODIDES WITH HSIET(3) CATALYZED BY PD-CO BIMETALLIC SYSTEMS

The PdCl2(PPh(3))(2)-Ru-3(CO)(12) or PdCl2(PPh(3))(2)-Co-2(CO)(8) bimetallic catalyst has been found to be effective for carbonylation of aryl iodides and HSiEt(3) to give benzyl silyl ether as the major product, although neither PdCl2(PPh(3))(2), Ru-3(CO)(12), nor Co-2(CO)(8) alone had any appreciable catalytic activity. Addition of NEt(3) to the Pd-Co mixed-metal-catalyzed carbonylation reaction remarkably changed the selectivity of the products, and 1,2-diaryl-1,2-disiloxyethane was obtained as the major product. Studies on the hydrosilylation of 4-TolCHO with HSiEt(3) under CO revealed that the formation of benzyl silyl ether in the former reaction may proceed through the formylation of aryl iodide followed by hydrosilylation of the resulting aldehyde. In contrast, the aldehyde was not included as an intermediate in the formation of 1,2-diaryl-1,2-disiloxyethane in the latter reaction. An aroylcobalt complex ArCOCo(CO)(3)(PPh(3)) was suggested as an intermediate for the 1,2-diaryl-1,2-disiloxyethane production based on the following observations: (1) the aroylcobalt complex ArCOCo(CO)(3-)(PPh(3)) can be produced from aryl iodide, [Co(CO)(4)](-), and PPh(3) with a Pd(O) catalyst; (2) hydrosilylation of the aroylcobalt complex ArCOCo(CO)(3)(PPh(3)) under 50 atm of CO pressure produced 1,2-diaryl-1,2-disiloxyethane as the major product. The detailed mechanisms are proposed for the catalytic carbonylations of aryl iodides with HSiEt(3) by using the bimetallic catalysts.