Phosphine-Free Well-Defined Mn(I) Complex-Catalyzed Synthesis of Amine, Imine, and 2,3-Dihydro-1H-perimidine via Hydrogen Autotransfer or Acceptorless Dehydrogenative Coupling of Amine and Alcohol

Abstract

The application of nontoxic, earth-abundant transition metals in place of costly noble metals is a paramount goal in catalysis and is especially interesting if the air-and moisture-stable ligand scaffold is used. Herein, we report the synthesis of amines/imines directly from alcohol and amines via hydrogen autotransfer or acceptorless dehydrogenation catalyzed by welldefined phosphine-free Mn complexes. Both imines and amines can be obtained from the same set of alcohols and amines using the same catalyst, only by tuning the reaction conditions. The amount and nature of the base are found to be a highly important aspect for the observed selectivity. Both the primary and secondary amines have been employed as substrates for the Nalkylation reaction. As a highlight, we showed the chemoselective synthesis of resveratrol derivatives. Furthermore, the Mncatalyzed dehydrogenative synthesis of structurally important 2,3-dihydro-1H-perimidines has also been demonstrated. Density functional theory calculations were also carried out to model the reaction path and to calculate the reaction profile.

Manganese‐Catalysed Dehydrogenative Coupling – An Overview

“…The catalytic ability of a manganese‐NNS pincer complex 123 was demonstrated in the synthesis of imines, amines and 2,3‐dihydro‐1 H‐ perimidines by Srimani et al. through dehydrogenative coupling of alcohols and amines (Scheme ) . This was found to be the first phosphine‐free Mn‐pincer protocol that could be used for the synthesis of secondary amine as well as imine from the same alcohol and primary amine by varying the base.…”

“…2,3‐Dihydro‐1 H ‐perimidines were synthesised using a manganese‐NNS pincer‐catalysed dehydrogenative coupling strategy by Srimani et al. (Scheme ) . The coupling of various alcohols occurred with 1,8‐diaminonaphthalene by using 5 mol% of 123 along with a catalytic amount of KOH in toluene at 140 °C for 24–72 h. Substrate scope analysis reveals that the reaction provides moderate to good yields for aromatic alcohols and poor yields for aliphatic alcohols.…”

Manganese Catalyzed Acceptorless Dehydrogenative Coupling Reactions

“…It was found that a potassium base favored the alkylation of amines, whereas imine formation was observed when a sodium base was used (Scheme c) . Recently, Srivastava, Srimani, and co‐workers have disclosed a phosphine‐free manganese complex Mn‐4 for the same reaction (Scheme d) . Madsen and co‐workers have developed high valent salen manganese(III)‐complex Mn‐5 and porphyrin Mn(III)‐complex Mn‐6 for the synthesis of imines via the ADC of alcohols with amines (Scheme e,f)…”

“…[17] Recently, Srivastava, Srimani, and co-workers have disclosed a phosphine-free manganese complex Mn-4 for the same reaction (Scheme 4d). [18] Madsen and co-workers have developed high valent salen manganese(III)-complex Mn-5 and porphyrin Mn(III)-complex Mn-6 for the synthesis of imines via the ADC of alcohols with amines (Scheme 4e,f). [19]…”

“…Recently, the synthesis of 2,3‐dihydro‐1H‐perimidine derivatives 42 by dehydrogenative coupling of 1,8‐diaminonapthalene 27 with various primary alcohols 1 was developed by the Srimani group (Scheme ) . The manganese complex Mn‐4 in the presence of a catalytic amount of KOH catalyzed the reaction.…”