Stopped‐Flow <sup>19</sup>F NMR Spectroscopic Analysis of a Protodeboronation Proceeding at the Sub‐Second Time‐Scale
Ran Wei, Andrew M. R. Hall, Richard Behrens, Mark S. Pritchard, Edward J. King, Guy C. Lloyd‐Jones
Abstract
Abstract In‐situ NMR spectroscopic analysis of homogeneous reactions is an essential tool for mechanistic analysis in organic and organometallic chemistry. However, rapid non‐equilibrium reactions, that are initiated by mixing, require specialized approaches. We report herein on a study of the factors that ensure quantitative results in a recently‐developed technique for stopped‐flow NMR spectroscopy. The influence of some of the key parameters on quantitation is studied by 19 F NMR spectroscopic analysis of the kinetics and activation parameters for the base‐catalyzed protodeboronation of highly‐reactive polyfluorinated arylboronic acids, with half‐lives as low as 0.1 seconds. The effects of spin relaxation, pre‐magnetization, heat‐transfer versus reaction enthalpy, and mixing‐efficiency are analyzed in detail. We also compare and contrast choice of pulse angle, interscan delay, and use of pseudo real‐time by interleaving, as means to achieve an optimal balance between temporal resolution and sensitivity.