Productive C-C Bond Activation through Polymer Mechanochemistry
Selective activation of simple Csp3-Csp3 bonds is a highly desirable transformation in organic chemistry.1 Due to the high-energy barrier for the insertion into the C-C σ bond, this activation is challenging even when using highly reactive transition metals catalysts.2 Meanwhile, in polymer mechanochemistry, unstrained C-C bond scission is the most ubiquitous reaction, even in the absence of heteroatoms.3 Yet this reaction is only seen as a destructive process or the non-selective reaction when trying to induce selective mechanochemical transformations. In my talk, I will describe how unstrained C-C bond scission can be improved into a C-C bond activation process in homopolymers, using a simple ball milling protocol. These activated bonds are used to functionalize polymers with various new end groups, producing semi-telechelic polymers efficiently. In addition, I will discuss the role stereochemistry plays in the acyclic C-C bond activation rate in a new mechanophore based on a benzopinacol skeleton. Up to now, stereochemical effects in polymer mechanophore activation have always been built on cyclic mechanophores, but in this work we show that the application of force limits the degrees of freedom of the transition state, reinforcing the importance of stereochemistry in the reaction kinetics even in acyclic systems.
References
(1) Murakami, M.; Ishida, N. Fundamental Reactions to Cleave Carbon–Carbon σ-Bonds with Transition Metal Complexes. In Cleavage of Carbon-Carbon Single Bonds by Transition Metals; John Wiley & Sons, Ltd, 2015; pp 1–34. https://doi.org/10.1002/9783527680092.ch1.
(2) Jun, C.-H. Transition Metal-Catalyzed Carbon–Carbon Bond Activation. Chem. Soc. Rev. 2004, 33 (9), 610–618. https://doi.org/10.1039/B308864M.
(3) De Bo, G. Polymer Mechanochemistry and the Emergence of the Mechanophore Concept. Macromolecules 2020, 53 (18), 7615–7617. https://doi.org/10.1021/acs.macromol.0c01683