Experimental and theoretical C kinetic isotope effects (KIEs) are utilized to obtain atomistic insight into the catalytic mechanism of the Pd(PPh)-catalyzed Suzuki-Miyaura reaction of aryl halides and aryl boronic acids. Under catalytic conditions, we establish that oxidative addition of aryl bromides occurs to a 12-electron monoligated palladium complex (Pd-(PPh)). This is based on the congruence of the experimental KIE for the carbon attached to bromine (KIE = 1.
View Article and Find Full Text PDFA practical approach is introduced for the rapid determination of C kinetic isotope effects that utilizes a "designed" reactant with two identical reaction sites. The mechanism of the Buchwald-Hartwig amination of -butylbromobenzene with primary and secondary amines is investigated under synthetically relevant catalytic conditions using traditional molecular C NMR methodology at natural abundance. Switching to 1,4-dibromobenzene, a symmetric bromoarene as the designed reactant, the same experimental C KIEs are determined using an molecular KIE approach.
View Article and Find Full Text PDFWhile photoredox catalysis continues to transform modern synthetic chemistry, detailed mechanistic studies involving direct observation of reaction intermediates and rate constants are rare. By use of a combination of steady state photochemical measurements, transient laser spectroscopy, and electrochemical methods, an α-aminoarylation mechanism that is the inspiration for a large number of photoredox reactions was rigorously characterized. Despite high product yields, the external quantum yield (QY) of the reaction remained low (15-30%).
View Article and Find Full Text PDFThe demand for safer design and synthesis of gold nanoparticles (AuNPs) is on the increase with the ultimate goal of producing clean nanomaterials for biological applications. We hereby present a rapid, greener, and photochemical synthesis of gold nanoplates with sizes ranging from 10 to 200 nm using water-soluble quercetin diphosphate (QDP) macromolecules. The synthesis was achieved in water without the use of surfactants, reducing agents, or polymers.
View Article and Find Full Text PDFThe rational design and implementation of enantiodivergent enamine catalysis is reported. A simple secondary amine catalyst, 2-methyl-l-proline, and its tetrabutylammonium salt function as an enantiodivergent catalyst pair delivering the enantiomers of α-functionalized aldehyde products in excellent enantioselectivities. This novel concept of designed enantiodivergence is applied to the enantioselective α-amination, aldol, and α-aminoxylation/α-hydroxyamination reactions of aldehydes.
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