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Template catalysis by manganese pincer complexes: oxa- and aza-Michael additions to unsaturated nitriles.

ABSTRACT: Activation of C[triple bond, length as m-dash]N bonds by metal-ligand cooperation provides a new route for the functionalization of nitriles. Herein, we report the electrophilic activation of unsaturated nitriles by dearomatized manganese pincer complexes for the oxa- and aza-Michael addition reactions under very mild and neutral conditions. Derivatives of acrylonitrile and allyl cyanide furnished the corresponding ?-addition products by reacting with alcohols and amines. Mechanistically, the catalysis is mostly ligand based. Reaction of the dearomatized PNN-Mn complex with 2-pentenenitrile or 3-pentenenitrile furnished an enamido-Mn complex. The equilibrium between an enamido complex and a ketimido complex, and reversible C-C bond formation with the ligand are proposed to play central roles in the catalysis.

SUBMITTER: Tang S

PROVIDER: S-EPMC6855260 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Template catalysis by manganese pincer complexes: oxa- and aza-Michael additions to unsaturated nitriles.

Tang Shan S Milstein David D

Chemical science 20190807 39

Activation of C[triple bond, length as m-dash]N bonds by metal-ligand cooperation provides a new route for the functionalization of nitriles. Herein, we report the electrophilic activation of unsaturated nitriles by dearomatized manganese pincer complexes for the oxa- and aza-Michael addition reactions under very mild and neutral conditions. Derivatives of acrylonitrile and allyl cyanide furnished the corresponding β-addition products by reacting with alcohols and amines. Mechanistically, the ca ...[more]

PMID: 31762979

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Project description:Bio-based platform molecules such as itaconic, fumaric, and muconic acid offer much promise in the formation of sustainable unsaturated polyester resins upon reaction with suitable diols and polyols. The C=C bonds present in these polyester chains allows for post-polymerization modification and such moieties are conventionally utilized in curing processes during the manufacture of coatings. The C=C modification sites can also act as points to add useful pendants which can alter the polymers final properties such as glass transition temperature, biodegradability, hardness, polarity, and strength. A commonly observed modification is the addition of secondary amines via an aza-Michael addition. Conventional procedures for the addition of amines onto itaconate polyesters require reaction times of several days as a result of undesired side reactions, in particular, the formation of the less reactive mesaconate regioisomer. The slow reversion of the mesaconate back to itaconate, followed by subsequent amine addition, is the primary reason for such extended reaction times. Herein we report our efforts toward finding a suitable catalyst for the aza-Michael addition of diethylamine onto a model substrate, dimethyl itaconate, with the aim of being able to add amine onto the itaconate units without excessive regioisomerization to the inactive mesaconate. A catalyst screen showed that iodine on acidic alumina results in an effective, heterogeneous, reusable catalyst for the investigated aza-Michael addition. Extending the study further, itaconate polyester was prepared by Candida Antartica Lipase B (CaL-B) via enzymatic polytranesterification and subsequently modified with diethylamine using the iodine on acidic alumina catalyst, dramatically reducing the required length of reaction (>70% addition after 4 h). The approach represents a multidisciplinary example whereby biocatalytic polymerization is combined with chemocatalytic modification of the resultant polyester for the formation of useful bio-based polyesters.

Dataset Information

Template catalysis by manganese pincer complexes: oxa- and aza-Michael additions to unsaturated nitriles.

Publications

Template catalysis by manganese pincer complexes: oxa- and aza-Michael additions to unsaturated nitriles.

Similar Datasets

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