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)}(mu-dppm)PdCl] 6 (R = Me, SiMe3) are effective catalyst in the dehydrogenative coupling of triorganotin hydrides HSnR3' (R' = Ph, Bu-n). Although the elementary transformations during catalysis appear to take place at palladium, the function of the iron fragment is to provide the palladium 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 catalysts. Modifications of the substituents at silicon resulted in considerable variations of the TON (turnover number) and TOF (turnover frequency) 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 catalyst is much longer for the latter. Possible mechanisms which rationalize the role of the silicon ligand are discussed. Solvent effects have 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 dehydropolymerization of tin dihydrides has been tested.