title: Catalyst design based on agostic interactions: synthesis, characterization, and catalytic activity of bis(pyrazolyl)borate copper complexes.
abstract: Agostic interactions are often used to activate inert C-H bonds, and thus facilitate new reactions. We report the first example of designed catalysts based on the agostic interaction. Novel copper(i) complexes [BBN(pz(x))2]Cu(PPh3)n (BBN = 9-borabicyclo[3.3.1]nonane; pz(x) = 3-substituted pyrazole; x = H, n = 2; x = Me, n = 1) and {[BBN(pz(iPr))2]Cu}2 have been synthesized and characterized. Single crystal studies of the three compounds show weak intramolecular C-HCu interactions which can be assigned as agostic or anagostic interactions. Catalytic studies of these complexes toward carbenoid insertion into N-H bonds indicate these weak interactions act as a "switch" which will be turned "on" if interacting with the substrate and "off" if eliminating the product and regenerating the weak interaction. The process of the "switch" turning "on" or "off", which is related to the catalytic effect, is found to be influenced by both steric effects and the solvent: a less sterically hindered catalyst in non-coordinating benzene results in high yield, while a more sterically hindered catalyst in coordinating THF results in relatively low yield.
authors.affiliation: School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang, Henan 453007, China. xnchen@htu.edu.cn jie.zhang@htu.edu.cn.
authors.forename: Hou-Ji
authors.initials: HJ
authors.lastname: Cao
authors.affiliation: School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang, Henan 453007, China. xnchen@htu.edu.cn jie.zhang@htu.edu.cn.
authors.forename: Qianyi
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA. lai-sheng_wang@brown.edu.
authors.forename: Qian-Fan
authors.initials: QF
authors.lastname: Zhang
authors.affiliation: School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang, Henan 453007, China. xnchen@htu.edu.cn jie.zhang@htu.edu.cn.
authors.forename: Jiaxuan
authors.initials: J
authors.lastname: Li
authors.affiliation: Department of Chemistry and Biochemistry, The Ohio State University at Lima, Lima, Ohio 45804, USA.
authors.forename: Ewan J M
authors.initials: EJ
authors.lastname: Hamilton
authors.affiliation: School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang, Henan 453007, China. xnchen@htu.edu.cn jie.zhang@htu.edu.cn.
authors.forename: Jie
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA. lai-sheng_wang@brown.edu.
authors.forename: Lai-Sheng
authors.initials: LS
authors.lastname: Wang
authors.affiliation: School of Chemistry and Chemical Engineering, Henan Key Laboratory of Boron Chemistry and Advanced Energy Materials, Henan Normal University, Xinxiang, Henan 453007, China. xnchen@htu.edu.cn jie.zhang@htu.edu.cn.
authors.forename: Xuenian
authors.initials: X
authors.lastname: Chen