Iron-Catalyzed Amide Formation from the Dehydrogenative Coupling of Alcohols and Secondary Amines

Abstract

The five-coordinate iron(II) hydride complex ( iPr PNP)Fe(H)(CO) ( iPr PNP = N[CH 2 CH 2 (P i Pr 2 )] 2 ) selectively catalyzes the dehydrogenative intermolecular coupling of alcohols and secondary amines to form tertiary amides. This is the most productive base-metal catalyst for dehydrogenative amidation reported to date, in some cases achieving up to 600 turnovers. The catalyst works well for sterically undemanding amines and alcohols or cyclic substrates and is particularly effective in the synthesis of formamides from methanol. However, the catalyst performance declines rapidly with the incorporation of large substituents on the amine or alcohol substrate. Variable-temperature NMR spectroscopic studies suggest that the catalyst resting state is an off-cycle iron(II) methoxide species, ( iPr PN(H)P)Fe(H)(OCH 3 )(CO), resulting from addition of methanol across the Fe−N bond of ( iPr PNP)Fe(H)(CO). This reversibly formed iron(II) methoxide complex is favored at mild temperatures but eliminates methanol upon heating.

Manganese Complexes for (De)Hydrogenation Catalysis: A Comparison to Cobalt and Iron Catalysts

“…Impressive TONs were achieved for methanol. [103] Slightly better TONs and higher yields of product could be achieved by Milstein and coworkers using Mn-10 b. [104] Gauvin and co-workers showed that using Mn-16 alcohol can be converted into the corresponding ester via H 2 evolution (Scheme 13), including the synthesis of g-butyrolactone from 1,4-butanediol.…”

Recent Advances in Catalysis with Transition‐Metal Pincer Compounds

“…The dehydrogenative coupling of alcohols with amines can be performed with catalysts based on Re, Rh, Ru, Fe, and Mn, Scheme shows some representative examples. Complexes 16 a , 16 b , and 22 a show high activity, in particular with primary amines.…”

Direct Synthesis of Amides by Dehydrogenative Coupling of Amines with either Alcohols or Esters: Manganese Pincer Complex as Catalyst

“…[8,9] Beller and co-workers have reported the synthesis of various lactams from amino alcohols using an iron pincer catalyst. [11] However,w hile efficient with methanol, the catalyst showed poor catalytic activity with alcohols higher than methanol, such as ethanol or hexanol. [11] However,w hile efficient with methanol, the catalyst showed poor catalytic activity with alcohols higher than methanol, such as ethanol or hexanol.…”