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Mechanism of Pd/Senphos-Catalyzed trans-Hydroboration of 1,3-Enynes: Experimental and Computational Evidence in Support of the Unusual Outer-Sphere Oxidative Addition Pathway.


ABSTRACT: The reaction mechanism of the Pd/Senphos-catalyzed trans-hydroboration reaction of 1,3-enynes was investigated using various experimental techniques, including deuterium and double crossover labeling experiments, X-ray crystallographic characterization of model reaction intermediates, and reaction progress kinetic analysis. Our experimental data are in support of an unusual outer-sphere oxidative addition mechanism where the catecholborane serves as a suitable electrophile to activate the Pd0-bound 1,3-enyne substrate to form a Pd-η3-π-allyl species, which has been determined to be the likely resting state of the catalytic cycle. Double crossover labeling of the catecholborane points toward a second role played by the borane as a hydride delivery shuttle. Density functional theory calculations reveal that the rate-limiting transition state of the reaction is the hydride abstraction by the catecholborane shuttle, which is consistent with the experimentally determined rate law: rate = k[enyne]0[borane]1[catalyst]1. The computed activation free energy ΔG = 17.7 kcal/mol and KIE (kH/kD = 1.3) are also in line with experimental observations. Overall, this work experimentally establishes Lewis acids such as catecholborane as viable electrophilic activators to engage in an outer-sphere oxidative addition reaction and points toward this underutilized mechanism as a general approach to activate unsaturated substrates.

SUBMITTER: Zhang Y 

PROVIDER: S-EPMC10162691 | biostudies-literature | 2023 Feb

REPOSITORIES: biostudies-literature

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Mechanism of Pd/Senphos-Catalyzed <i>trans</i>-Hydroboration of 1,3-Enynes: Experimental and Computational Evidence in Support of the Unusual Outer-Sphere Oxidative Addition Pathway.

Zhang Yuanzhe Y   Wang Ziyong Z   Lamine Walid W   Xu Senmiao S   Li Bo B   Chrostowska Anna A   Miqueu Karinne K   Liu Shih-Yuan SY  

The Journal of organic chemistry 20230208 4


The reaction mechanism of the Pd/Senphos-catalyzed <i>trans</i>-hydroboration reaction of 1,3-enynes was investigated using various experimental techniques, including deuterium and double crossover labeling experiments, X-ray crystallographic characterization of model reaction intermediates, and reaction progress kinetic analysis. Our experimental data are in support of an unusual outer-sphere oxidative addition mechanism where the catecholborane serves as a suitable electrophile to activate the  ...[more]

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