Catalytic Dehydrogenative Coupling of Stannanes by Alkoxysilyl Heterobimetallic Complexes:  Influence of the Assembling Ligand

The heterobimetallic complexes ( 1, P-Z = Ph 2 PNHPPh 2 (dppa); 2, P-Z = Ph 2 P( o -C 5 H 4 N) (Ph 2 Ppy); 3, P-Z = Ph 2 PCH 2 PPh 2 (dppm); R‘ 3 = (OMe) 3, Me(OSiMe 3 ) 2 ) are very efficient catalysts for the dehydrogenative coupling of tin hydrides R 3 SnH (R = Ph, n Bu). Besides establishing that siloxy complexes are more active catalysts than their alkoxysilyl counterparts, the present study shows that modifications in the nature of the assembling functional phosphine ligand P-Z result in variations of catalyst efficiency, expressed by the TON (overall turnover number) and TOF (maximum turnover frequency) values and lifetime. The Ph 2 Ppy-bridged complexes are the most efficient catalysts, and in the case of n Bu 3 SnH, TON and TOF values higher than 1.2 × 10 6 and 2 × 10 8, respectively, have been observed. A marked difference in reactivity is also observed between the diphosphine ligands dppa and dppm, with the dppa-bridged complexes being more active than their dppm analogues. The new complex ( 2b ) prepared in the course of this work has been structurally characterized by X-ray diffraction.