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

Abstract

The first example of base-metal-catalysed synthesis of amides from the coupling of primary amines with either alcohols or esters is reported. The reactions are catalysed by a new manganese pincer complex and generate hydrogen gas as the sole byproduct, thus making the overall process atom-economical and sustainable.

Manganese Catalyzed Hydrogenation of Organic Carbonates to Methanol and Alcohols

“…Under the same catalytic conditions,hydrogenation of diethyl carbonate resulted in the formation of ethanol and methanol in 97 %a nd 95 %y ields,r espectively.D ibenzyl carbonate, diphenyl carbonate,a nd unsymmetrical methyl carbonates ( Table 1, entries [5][6][7][8][9][10][11] were also hydrogenated to afford the corresponding alcohol and methanol in good to excellent yields.W ethen used complex 1 for the hydrogenation of the more challenging cyclic carbonates.U nder the optimized conditions used for the hydrogenation of acyclic carbonates, only 60 %c onversion of propylene carbonate was observed, forming propylene glycol and methanol in % 60 %a nd 45 % yields,r espectively.I ncreasing the hydrogen pressure to 50 bar and reaction time to 48 hr esulted in the quantitative conversion of propylene carbonate to propylene glycol and methanol. Increasing the reaction time to 30 hand the amount of base to 4mol %resulted in approximately quantitative conversion of dimethyl carbonate to methanol, which was detected in 90 % yield by 1 HNMR spectroscopy.Encouraged by this result, we explored the hydrogenation of other types of carbonates.…”

Manganese‐Catalyzed Direct Olefination of Methyl‐Substituted Heteroarenes with Primary Alcohols

“…[15] In this regard, manganese,a st he third most abundant transition metal, has appeared as an attractive alternative. [17] Subsequently,m anganese complexes were utilized for catalytic dehydrogenations of methanol to CO 2 and H 2 , [18] dehydrogenative Nformylations of amines, [19] couplings of alcohols to esters, [20] syntheses of imines, [21] quinolines, [22] pyrimidines, [22,23] pyrroles, [24] cyclic imides, [25] amides, [26] and a,bunsaturated nitriles, [27] as well as hydrogenations of polar double bonds. [17] Subsequently,m anganese complexes were utilized for catalytic dehydrogenations of methanol to CO 2 and H 2 , [18] dehydrogenative Nformylations of amines, [19] couplings of alcohols to esters, [20] syntheses of imines, [21] quinolines, [22] pyrimidines, [22,23] pyrroles, [24] cyclic imides, [25] amides, [26] and a,bunsaturated nitriles, [27] as well as hydrogenations of polar double bonds.…”

Manganese Catalyzed Acceptorless Dehydrogenative Coupling Reactions

“…A hydride complex Mn‐7 catalyzed the reaction under mild, additive, and base‐free conditions. In continuation, later in 2017, they also reported the synthesis of amides by the ADC of 2 with either 1 or ester 4 catalyzed by an Mn‐PNN complex Mn‐8 (Scheme b) . Mechanistically, the aldehyde formed by manganese catalyzed dehydrogenation of alcohols couples with the amine to give an α‐hydroxy amine, which after dehydrogenation gives the corresponding amide 5 .…”

“…In continuation, later in 2017, they also reported the synthesis of amides by the ADC of 2 with either 1 or ester 4 catalyzed by an Mn-PNN complex Mn-8 (Scheme 5b). [21] Mechanistically, the aldehyde formed by manganese catalyzed dehydrogenation of alcohols couples with the amine to give an α-hydroxy amine, which after dehydrogenation gives the corresponding amide 5. Alternatively, the formed aldehyde may couple with another molecule of alcohol to give the ester 4, vide infra, which then couples with an amine to give the corresponding amide 5, and the released alcohol is then recycled (Scheme 5).…”