A DFT Study of Stannane Dehydrocoupling Catalyzed by Cp2LaH
Résumé
All the pathways leading to bis-stannane and regeneration of the catalyst Cp2LaH (Cp = 5-C5H5) for the stannane SnH4 have been computed using the DFT (B3PW91) method. In all cases, the reaction is at least a two-step process with a common first step, which is the Sn-H activation of the stannane, leading to the hydrostannyl complex Cp2LaSnH3. From a pure thermodynamic point of view, the overall process is found to be exergonic by 9.3 kcal·mol-1. Since the most stable product of the energy profile is the intermediary hydrostannyl complex, the second step, which corresponds to Sn-Sn coupling, is endergonic. This explains the relatively low turnover, found experimentally, for the homocoupling of stannane into bis-stannane. This overall process is in agreement with the experiment made on hafnium complexes, where the intermediary hydrostannyl compounds have been isolated and characterized. From a kinetic point of view, the second reaction step is proposed to occur through a direct SnH3 transfer of the hydrostannyl to the incoming stannane rather than stannylene or stannylenoide insertion into the incoming stannane.