Variable Temperature LED-NMR: Rapid Insights into a Photocatalytic Mechanism from Reaction Progress Kinetic Analysis.

A multitude of techniques are available to obtain a useful understanding of photocatalytic mechanisms. The combination of LED illumination with nuclear magnetic resonance spectroscopy (LED-NMR) provides a rapid, convenient means to directly monitor a photocatalytic reaction in situ. Herein, we describe a study of the mechanism of an enantioselective intermolecular [2 + 2] photocycloaddition catalyzed by a chiral Ir photocatalyst using LED-NMR.

Palladium-Catalyzed C-H Bond Acetoxylation via Electrochemical Oxidation.

Here we describe the development of a method for the Pd-catalyzed electrochemical acetoxylation of C-H bonds. The oxidation step of the catalytic cycle is probed through cyclic voltammetry and bulk electrolysis studies of a preformed palladacycle of 8-methylquinoline. A catalytic system for C-H acetoxylation is then developed and optimized with respect to the cell configuration, rate of oxidation, and chemistry at the counter electrode.

Progress toward reaction monitoring at variable temperatures: a new stopped-flow NMR probe design.

A stopped-flow NMR probe is described that enables fast flow rates, short transfer times, and equilibration of the reactant magnetization and temperature prior to reaction. The capabilities of the probe are demonstrated by monitoring the polymerization of lactide as catalyzed by the air-sensitive catalyst 1,3-dimesitylimidazol-2-ylidene (IMes) over the temperature range of -30 to 40 °C. The incorporation of stopped-flow capabilities into an NMR probe permits the rich information content of NMR to be accessed during the first few seconds of a fast reaction.

A detailed mechanistic investigation into the reaction of 3-methylpentanoic acid with Meldrum's acid utilizing online NMR spectroscopy.

A thorough investigation into the mechanism of the reaction of 3-methylpentanoic acid and Meldrum's acid using online NMR spectroscopy is reported. This study is an expansion of a previous analysis of this chemical transformation in the synthesis of an active pharmaceutical ingredient imagabalin. The 3-methylpentanoic acid analogue reveals similar behavior under the reaction conditions.

Reaction monitoring using online vs tube NMR spectroscopy: seriously different results.

We report findings from the qualitative evaluation of nuclear magnetic resonance (NMR) reaction monitoring techniques of how each relates to the kinetic profile of a reaction process. The study highlights key reaction rate differences observed between the various NMR reaction monitoring methods investigated: online NMR, static NMR tubes, and periodic inversion of NMR tubes. The analysis of three reaction processes reveals that rates derived from NMR analysis are highly dependent on monitoring method.