Enhancing Hydride Transfer in Catalytic Hydrogenation via σ-Electron-Induced Polarization of Imines
Shihan Liu, Haobo Yang, Ya-Nan Wang, Ya-Nan Wang, Qiaoqiao Zhao, Yujie Wang, Yujie Wang, Ruopeng Bai, Qiang Liu, Yu Lan
Abstract
In this study, we investigated the role of aluminum cations in facilitating hydride transfer during the hydrogenation of imines within the context of Noyori-type metal-ligand cooperative catalysis. We propose a novel model involving aluminum cations directly coordinated with imines to induce activation from the lone pair electron site, a phenomenon termed σ-induced activation. The aluminum metal-hydride amidate complex ("HMn-NAl") exhibits a higher ability of hydride transfer in the hydrogenation of imines compared to its lithium counterpart ("HMn-NLi"). Density functional theory (DFT) calculations uncover that the aluminum cation efficiently polarizes unsaturated bonds through σ-electron-induced activation in the transition state of hydride transfer, thereby enhancing substrate electrophilicity more efficiently. Additionally, upon substrate coordination, aluminum's coordination saturation improves the hydride nucleophilicity of the HMn-NAl complex via the breakage of the Al-H coordination bond.