Lewis acid promoted dehydration of amides to nitriles catalyzed by [PSiP]-pincer iron hydrides

The dehydration of primary amides to their corresponding nitriles using four [PSiP]-pincer hydrido iron complexes 1-4 [(2-Ph2PC6H4)(2)MeSiFe(H)(PMe3)(2) (1), (2-Ph2PC6H4)(2)HSiFe(H)(PMe3)(2) (2), (2-(iPr)(2)PC6H4)(2)HSiFe(H)(PMe3)(2) (3) and (2-(iPr)(2)PC6H4)(2)MeSiFe(H)(PMe3)(2) (4)] as catalysts in the presence of (EtO)(3)SiH as dehydrating reagent was explored in the good to excellent yields. It was proved for the first time that Lewis acid could significantly promote this catalytic system under milder reaction conditions than other Lewis acid-promoted system, such as shorter reaction time or lower reaction temperature. This is also the first example that dehydration of primary amides to nitriles was catalyzed by silyl hydrido iron complexes bearing [PSiP]-pincer ligands with Lewis acid as additive. This catalytic system has good tolerance for many substituents. Among the four iron hydrides 1 is the best catalyst. The effects of substituents of the [PSiP]-pincer ligands on the catalytic activity of the iron hydrides were discussed. A catalytic reaction mechanism was proposed. Complex 4 is a new iron complex and was fully characterized. The molecular structure of 4 was determined by single crystal X-ray diffraction.