Determining structure and Zn-specific Lewis acid-base descriptors for diorganozincs in non-coordinating solvents using X-ray spectroscopy.

Abstract

Diorganozinc reagents (ZnR₂, e.g. R = Et, Ph, C₆F₅) are widely used as Lewis acid catalysts or Lewis base reagents in their own right. However, descriptors for predicting the influence of the R substituent on ZnR₂ Lewis acidity/basicity are very sparse. This is because ZnR₂ liquid-phase speciation and electronic structure are unknown to date due to zinc's 'spectroscopically quiet' nature and inability to measure 'at zinc'. Here, we identify the geometric structures of ZnR₂ in weakly coordinating solvents, demonstrating that electronic structure factors will dominate reactivity. We quantify the electronic structure properties that dictate ZnR₂ Lewis acidity/basicity using three newly developed zinc-specific descriptors by combining the results from three zinc-specific X-ray spectroscopy methods and calculations. We provide accessible methods to pre-screen ZnR₂ reactivity. Furthermore, our X-ray spectroscopy toolkit offers opportunities to develop liquid-phase descriptors that dictate reactivity for other zinc species, e.g. zinc bis-amides, battery electrolytes and enzymes.