Selective Iron-Catalyzed Deaminative Hydrogenation of Amides

The five-coordinate iron­(II) hydride
complex (iPrPNP)­Fe­(H)­CO (iPrPNP = N­[CH2CH2(PiPr2)]2) was found to selectively
catalyze deaminative hydrogenation
of amides to the corresponding amines and primary alcohols. It is
one of the most active amide hydrogenation catalysts reported to date,
with turnover numbers (TONs) in excess of 1000 observed for multiple
substrates and TONs greater than 4000 obtained for activated formanilides.
The amide C–N cleavage reactions occur with a preference for
electron-withdrawing substituents and with greater activity for formamides
compared with acetamides and benzamides. Stoichiometric reactions
between (iPrPNP)­Fe­(H)­CO and formanilide
afforded the new iron­(II) complex (iPrPNHP)­Fe­(H)­CO­(N­(Ph)­HCO) resulting from N–H addition
across the Fe–N bond. Complexes of this type were identified
as the resting state during catalytic hydrogenation reactions containing
secondary amides. Addition of a Lewis acid cocatalyst provided further
enhancement of the productivity of catalytic amide hydrogenations.