title: Naked d-orbital in a centrochiral Ni(II) complex as a catalyst for asymmetric [3+2] cycloaddition.
abstract: Chiral metal catalysts have been widely applied to asymmetric transformations. However, the electronic structure of the catalyst and how it contributes to the activation of the substrate is seldom investigated. Here, we report an empirical approach for providing insights into the catalytic activation process in the distorted Ni(II)-catalysed asymmetric [3+2] cycloaddition of α-ketoesters. We quantitatively characterize the bonding nature of the catalyst by means of electron density distribution analysis, showing that the distortion around the Ni(II) centre makes the dz2orbital partially 'naked', wherein the labile acetate ligand is coordinated with electrostatic interaction. The electron-deficient dz2orbital and the acetate act together to deprotonate the α-ketoester, generating the (Λ)-Ni(II)-enolate. The solid and solution state analyses, together with theoretical calculations, strongly link the electronic structure of the centrochiral octahedral Ni(II) complex and its catalytic activity, depicting a cooperative mechanism of enolate binding and outer sphere hydrogen-bonding activation.
authors.affiliation: Synthetic Organic Chemistry Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.|RIKEN Center for Sustainable Resource Science, Wako, Saitama, 351-0198, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Sohtome
authors.affiliation: Synthetic Organic Chemistry Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.|Department of Applied Chemistry, School of Science and Technology, Meiji University, Kawasaki, Kanagawa, 214-8571, Japan.
authors.forename: Genta
authors.initials: G
authors.lastname: Nakamura
authors.affiliation: RIKEN Center for Sustainable Resource Science, Wako, Saitama, 351-0198, Japan.|Elements Chemistry Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
authors.forename: Atsuya
authors.initials: A
authors.lastname: Muranaka
authors.affiliation: RIKEN Center for Emergent Matter Science, Wako, Saitama, 351-0198, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hashizume
authors.affiliation: Synthetic Organic Chemistry Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Lectard
authors.affiliation: Department of Applied Chemistry, School of Science and Technology, Meiji University, Kawasaki, Kanagawa, 214-8571, Japan.
authors.forename: Teruhisa
authors.initials: T
authors.lastname: Tsuchimoto
authors.affiliation: RIKEN Center for Sustainable Resource Science, Wako, Saitama, 351-0198, Japan.|Elements Chemistry Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Uchiyama
authors.affiliation: Synthetic Organic Chemistry Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan.|RIKEN Center for Sustainable Resource Science, Wako, Saitama, 351-0198, Japan.
authors.forename: Mikiko
authors.initials: M
authors.lastname: Sodeoka