title: Study on the Catalytic Behavior of Bifunctional Hydrogen-Bonding Catalysts Guided by Free Energy Relationship Analysis of Steric Parameters.
abstract: Free energy relationship (FER) studies to correlate steric parameters with the enantiocatalytic performance of bifunctional tertiary-amine hydrogen-bonding catalysts, including (S,S)-cyclohexane-1,2-diamine-derived thioureas, Cinchona alkaloid derived thioureas, and (S,S)-cyclohexane-1,2-diamine-derived squaramides, in Michael reactions revealed that the reactions are much favored by catalysts with less bulky N-substituents. The observed FERs are independent of the chiral scaffold and hydrogen-bond donor, and deepen the understanding of current bifunctional hydrogen-bonding catalysts. Moreover, DFT calculations were performed to interpret the observed high reactivities of thioureas with less bulky substituents. In particular, the computations demonstrated the advantage of a benzyl thiourea catalyst, in which an extra CH⋅⋅⋅π interaction between catalyst and substrate is the key factor.
authors.affiliation: State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, P. R. China.
authors.forename: Chen
authors.initials: C
authors.lastname: Yang
authors.affiliation: State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, P. R. China.
authors.forename: Jie
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, P. R. China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, P. R. China.
authors.forename: Xiang
authors.initials: X
authors.lastname: Ni
authors.affiliation: State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, P. R. China.|Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, 300071, P. R. China.
authors.forename: Xin
authors.identifier: http://orcid.org/0000-0001-6020-9170
authors.initials: X
authors.lastname: Li
authors.affiliation: State Key Laboratory of Elemento-organic Chemistry, College of Chemistry, Nankai University, Tianjin, 300071, P. R. China.|Collaborative Innovation Center of Chemical Science and Engineering, Tianjin, 300071, P. R. China.
authors.forename: Jin-Pei
authors.initials: JP
authors.lastname: Cheng
keywords: Michael addition; density functional calculations; organocatalysis; steric hindrance; structure-activity relationships