Heterogeneously catalyzed hydrogenation imines

Brabender-van den Berg EMMD, Meijer EW (1993) Polypropylene imine) dendrimers-large-scale synthesis by heterogeneously catalyzed hydrogenations. Angew Chem Int Ed Engl 32 1308-1311... 

ATR-FTIR/UV-vis/Raman spectroscopy has been applied for mechanistic studies of the heterogeneously catalyzed hydrogenation of imines and of formal [3+3] cyclocondensation reactions catalyzed by Lewis adds [11, 33]. In the latter reaction, different products were obtained dependent on the Lewis acid used. It could be elucidated by in situ spectroscopic investigations that the intermediate complex formed between the ketene acetal component and the Lewis acid (an acid-catalyzed rearrangement reaction occurs in the case of trimethylsilyltrifluoromethanesulfonate (TM SOTf), forming a bischelate complex with TiCl4) controls the subsequent attack of the second reactant in the form of a diene, and consequently, the mechanism of product formation [33]. 

The scope of hydrogen transfer reactions is not limited to ketones. Imines, carbon-carbon double and triple bonds have also been reduced in this way, although homogeneous and heterogeneous catalyzed reductions using molecular hydrogen are generally preferred for the latter compounds. 

---