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

The heterobimetallic complexes (1, P-Z = Ph2PNHPPh2 (dppa); 2, P-Z = Ph2P(o-C5H4N) (Ph2Ppy); 3, P-Z = Ph2PCH2PPh2 (dppm); R‘3 = (OMe)3, Me(OSiMe3)2) are very efficient catalysts for the dehydrogenative coupling of tin hydrides R3SnH (R = Ph, nBu). 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 Ph2Ppy-bridged complexes are the most efficient catalysts, and in the case of nBu3SnH, TON and TOF values higher than 1.2 × 106 and 2 × 108, 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.