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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.
J Org Chem. 2023 Feb 17; 88(4):2415-2424.JO

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 Pd[0]-bound 1,3-enyne substrate to form a Pd-η[3]-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.

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Authors+Show Affiliations

Zhang Y
Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States.
Wang Z
Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States.
Lamine W
E2S UPPA/CNRS, Université de Pau et des Pays de l'Adour, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 avenue P. Angot, 64053 Pau Cedex 09, France.
Xu S
Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States.
Li B
Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States.
Chrostowska A
E2S UPPA/CNRS, Université de Pau et des Pays de l'Adour, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 avenue P. Angot, 64053 Pau Cedex 09, France.
Miqueu K
E2S UPPA/CNRS, Université de Pau et des Pays de l'Adour, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 avenue P. Angot, 64053 Pau Cedex 09, France.
Liu SY
Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States. E2S UPPA/CNRS, Université de Pau et des Pays de l'Adour, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 avenue P. Angot, 64053 Pau Cedex 09, France.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

36752741

Citation

Zhang, Yuanzhe, et al. "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." The Journal of Organic Chemistry, vol. 88, no. 4, 2023, pp. 2415-2424.
Zhang Y, Wang Z, Lamine W, et al. 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. J Org Chem. 2023;88(4):2415-2424.
Zhang, Y., Wang, Z., Lamine, W., Xu, S., Li, B., Chrostowska, A., Miqueu, K., & Liu, S. Y. (2023). 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. The Journal of Organic Chemistry, 88(4), 2415-2424. https://doi.org/10.1021/acs.joc.2c02841
Zhang Y, et al. 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. J Org Chem. 2023 Feb 17;88(4):2415-2424. PubMed PMID: 36752741.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - 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. AU - Zhang,Yuanzhe, AU - Wang,Ziyong, AU - Lamine,Walid, AU - Xu,Senmiao, AU - Li,Bo, AU - Chrostowska,Anna, AU - Miqueu,Karinne, AU - Liu,Shih-Yuan, Y1 - 2023/02/08/ PY - 2024/02/17/pmc-release PY - 2023/2/9/pubmed PY - 2023/2/9/medline PY - 2023/2/8/entrez SP - 2415 EP - 2424 JF - The Journal of organic chemistry JO - J Org Chem VL - 88 IS - 4 N2 - 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 Pd[0]-bound 1,3-enyne substrate to form a Pd-η[3]-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. SN - 1520-6904 UR - https://www.unboundmedicine.com/medline/citation/36752741/Mechanism_of_Pd/Senphos_Catalyzed_trans_Hydroboration_of_13_Enynes:_Experimental_and_Computational_Evidence_in_Support_of_the_Unusual_Outer_Sphere_Oxidative_Addition_Pathway_ DB - PRIME DP - Unbound Medicine ER -