Metal and halide free catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide

TY - JOUR

T1 - Metal and halide free catalyst for the synthesis of cyclic carbonates from epoxides and carbon dioxide

AU - Wu, Xiao

AU - Chen, Chentuo

AU - Guo, Ziyang

AU - North, Michael

AU - Whitwood, Adrian C.

N1 - © 2019 American Chemical Society. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details.

PY - 2019/3/1

Y1 - 2019/3/1

N2 - N,N′-Phenylenebis(5-tert-butylsalicylideneimine) is shown to be an effective single-component catalyst for the metal- and halide-free synthesis of cyclic carbonates from epoxides and carbon dioxide. Using this bis-phenolic catalyst, a series of eight epoxides has been converted into the corresponding cyclic carbonates. Many closely related catalyst structures were found to be catalytically inactive, and the structural features necessary for catalytic activity have been delineated. Unusually, reactions could be carried out under solvent-free conditions or in the green solvents 2-methyl tetrahydrofuran (2-MeTHF) and propylene carbonate. Stereochemical studies showed that carbon dioxide insertion occurs exclusively at the terminal end of the epoxide and does so with loss of stereochemical purity if a 1-deutero-2-alkyl epoxide is used as substrate. On the basis of this evidence, a dual activation mechanism is proposed in which one phenol acts as a Brønsted acid to activate the epoxide, while the other reacts with carbon dioxide to form a carbonic half-ester intermediate which then ring-opens the activated epoxide. Two pathways are subsequently available for cyclization to a cyclic carbonate which have opposite stereochemical consequences. The experimental results suggest that ring-opening of the epoxide by the carbonic half-ester is the rate-determining step of the catalytic cycle.

AB - N,N′-Phenylenebis(5-tert-butylsalicylideneimine) is shown to be an effective single-component catalyst for the metal- and halide-free synthesis of cyclic carbonates from epoxides and carbon dioxide. Using this bis-phenolic catalyst, a series of eight epoxides has been converted into the corresponding cyclic carbonates. Many closely related catalyst structures were found to be catalytically inactive, and the structural features necessary for catalytic activity have been delineated. Unusually, reactions could be carried out under solvent-free conditions or in the green solvents 2-methyl tetrahydrofuran (2-MeTHF) and propylene carbonate. Stereochemical studies showed that carbon dioxide insertion occurs exclusively at the terminal end of the epoxide and does so with loss of stereochemical purity if a 1-deutero-2-alkyl epoxide is used as substrate. On the basis of this evidence, a dual activation mechanism is proposed in which one phenol acts as a Brønsted acid to activate the epoxide, while the other reacts with carbon dioxide to form a carbonic half-ester intermediate which then ring-opens the activated epoxide. Two pathways are subsequently available for cyclization to a cyclic carbonate which have opposite stereochemical consequences. The experimental results suggest that ring-opening of the epoxide by the carbonic half-ester is the rate-determining step of the catalytic cycle.

KW - carbon dioxide

KW - cyclic carbonate

KW - epoxide

KW - organocatalyzed

KW - salophen

UR - http://www.scopus.com/inward/record.url?scp=85062446029&partnerID=8YFLogxK

U2 - 10.1021/acscatal.8b04387

DO - 10.1021/acscatal.8b04387

M3 - Article

AN - SCOPUS:85062446029

SN - 2155-5435

VL - 9

SP - 1895

EP - 1906

JO - ACS Catalysis

JF - ACS Catalysis

IS - 3

ER -