REACTIVITY OF HETEROBIMETALLIC ALKOXYSILYL AND SILOXY COMPLEXES IN THE CATALYTIC DEHYDROGENATIVE COUPLING OF TIN HYDRIDES

Heterobimetallic complexes [(OC)(3)(R3Si)Fe(mu-dppm)Pd(eta(3)-allyl)] 1 (R = OMe, Me, OSiMe3, OSi(H)Me-2) and [(OC)(3)Fe{mu-Si(OR)(2)(OR)}(m u-dppm)PdCl] 6 (R = Me, SiMe3) are effective catalyst in the dehydroge native coupling of triorganotin hydrides HSnR3' (R' = Ph, Bu-n). Altho ugh the elementary transformations during catalysis appear to take pla ce at palladium, the function of the iron fragment is to provide the p alladium center with the appropriate coordination environment through metal-metal bonding and the Si-containing ligand. Indeed, complexes 1 and 6 revealed a higher catalytic activity than mononuclear Pd catalys ts. Modifications of the substituents at silicon resulted in considera ble variations of the TON (turnover number) and TOF (turnover frequenc y) values as well as in the lifetime of the catalysts. In the case of siloxy derivatives, TON and TOF values higher than in the case of the alkoxysilyl analogs have been obtained whereas the lifetime of the cat alyst is much longer for the latter. Possible mechanisms which rationa lize the role of the silicon ligand are discussed. Solvent effects hav e also been observed. One of the key features of these systems is the retention of the bimetallic nature of the catalyst. TON and TOF higher than 2 x 10(5) and 3 x 10(7) h(-1), respectively, have been obtained in the case of (HSnBu3)-Bu-n. The catalytic activity of 1 toward the d ehydropolymerization of tin dihydrides has been tested.