Reaction selectivity of homochiral versus heterochiral intermolecular reactions of prochiral terminal alkynes on surfaces

Tao Wang,Lin Feng,Wenzhao Zhang,Pingwu Du,Jianmin Huang,Jinyi Wang,Steven L Tait,Dong Han,Aidi Zhao,Haifeng Lv,Junfa Zhu,Xiaojun Wu,Qian Xu,Huan Shan,Yahui Mao

doi:10.1038/s41467-019-12102-y

Abstract

Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces remains a great challenge. Here, competing reactions of a prochiral alkyne on Ag(111): two-dimensional (2D) homochiral Glaser coupling and heterochiral cross-coupling with a Bergman cyclization step have been examined. We demonstrate control strategies in steering the reactions between the homochiral and heterochiral pathways by tuning the precursor substituents and the kinetic parameters, as confirmed by high-resolution scanning probe microscopy (SPM). Control experiments and density functional theory (DFT) calculations reveal that the template effect of organometallic chains obtained under specific kinetic conditions enhances Glaser coupling between homochiral molecules. In contrast, for the reaction of free monomers, the kinetically favorable reaction pathway is the cross-coupling between two heterochiral molecules (one of them involving cyclization). This work demonstrates the application of kinetic control to steer chiral organic coupling pathways at surfaces.

Highlights

Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces remains a great challenge
The intermediate and final structures are characterized by scanning tunneling microscopy (STM), noncontact atomic force microscopy, and synchrotron radiation photoelectron spectroscopy (SRPES)
The difficulty is mainly due to side reactions, for example, polymerization of alkynyl, Ullman, and Glaser homo-couplings[20]

Summary

Introduction

Controlling selectivity between homochiral and heterochiral reaction pathways on surfaces remains a great challenge. We demonstrate control strategies in steering the reactions between the homochiral and heterochiral pathways by tuning the precursor substituents and the kinetic parameters, as confirmed by high-resolution scanning probe microscopy (SPM). This work demonstrates the application of kinetic control to steer chiral organic coupling pathways at surfaces. For reactions starting from prochiral alkyne 1 (the chirality is induced by the surface confinement), the competitive pathways of Glaser coupling or Bergman cyclization could generate different products. We report the highly selective synthesis of H-type product 4 from heterochiral intermolecular reaction on Ag(111) by tuning the substituent groups of 1 and deliberately controlling the reaction kinetics. This work offers insight into the competition between homochiral vs. heterochiral intermolecular reactions on surfaces

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Results

Conclusion