School of Chemistry, University of Manchester , Oxford Road, Manchester M13 9PL, United Kingdom.
J Am Chem Soc. 2017 Nov 22;139(46):16768-16771. doi: 10.1021/jacs.7b08895. Epub 2017 Nov 13.
Mechanical force, with its ability to distort, bend, and stretch chemical bonds, is unique in the way it activates chemical reactions. In polymer mechanochemistry, the force is transduced in a directional fashion, and the efficiency of activation depends on how well the force is transduced from the polymer to the scissile bond in the mechanophore (i.e., mechanochemical coupling). We have investigated the effects of regio- and stereochemistry on the rate of force-accelerated retro-Diels-Alder reactions of furan/maleimide adducts. Four adducts, presenting an endo or exo configuration and proximal or distal geometry, were activated in solution by ultrasound-generated elongational forces. A combination of structural (H NMR) and computational (CoGEF) analyses allowed us to interrogate the mechanochemical activation of these adducts. We found that, unlike its thermal counterpart where the reactivity is dictated by the stereochemistry, the mechanical reactivity is mainly dependent on the regiochemistry. Remarkably, the thermally active distal-exo adduct becomes inert under tension due to poor mechanochemical coupling.
机械力能够扭曲、弯曲和拉伸化学键，这使其在激活化学反应方面具有独特的能力。在聚合物机械化学中，力以定向的方式传递，而激活的效率取决于力从聚合物传递到机械试剂中的易断键（即机械化学偶联）的效果如何。我们研究了区域和立体化学对呋喃/马来酰亚胺加合物的力加速反-Diels-Alder 反应速率的影响。四个加合物呈现内型或外型构型以及近端或远端几何形状，通过超声产生的拉伸力在溶液中被激活。结构（H NMR）和计算（CoGEF）分析的结合使我们能够探究这些加合物的机械化学激活。我们发现，与热反应中立体化学决定反应性不同，机械反应性主要取决于区域化学。值得注意的是，由于机械化学偶联效果不佳，热活性的远端-外型加合物在张力下变得惰性。
