![Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-phosphinetriyltripiperidine]}palladium Under Mild Reaction Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F51444.jpg&w=3840&q=50)
C-X Bond Activation by Palladium: Steric Shielding versus Steric Attraction
Thomas Hansen1,2,3, Xiaobo Sun1,3, Marco Dalla Tiezza1
1Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|April 14, 2022
Summary
This study investigated palladium-catalyzed C-X bond activation, finding that while C-X bonds weaken with increasing substitution, activation barriers do not always decrease. Steric effects and catalyst-substrate interactions dictate reactivity for C-H versus C-C bonds.
Area of Science:
- Organometallic Chemistry
- Computational Chemistry
- Catalysis
Background:
- C-X bond activation is crucial in organic synthesis and catalysis.
- Understanding the influence of steric and electronic factors on bond activation is essential for catalyst design.
- Palladium catalysis is widely employed for C-X bond cleavage.
Purpose of the Study:
- To investigate the C-X bond activation of substituted C-H and C-C bonds by palladium.
- To elucidate the effect of increasing substituent degree on bond activation barriers.
- To analyze the interplay of steric repulsion and catalyst-substrate interactions in dictating reactivity.
Main Methods:
- Relativistic dispersion-corrected density functional theory (ZORA-BLYP-D3(BJ)/TZ2P) was employed.
- Activation strain and energy decomposition analyses were performed.
- Systematic variation of substituents on C-H and C-C bonds was studied.
Main Results:
- C(n°)-X bonds weaken progressively from methyl (0°) to tertiary (3°) due to steric repulsion.
- C-H activation barriers decrease from 0° to 2° substitution, then increase for 3°, unlike C-C activation barriers which consistently increase.
- Differences in C-H and C-C activation arise from opposing steric repulsion effects (across C-X vs. catalyst-substrate).
Conclusions:
- Steric hindrance significantly impacts palladium-catalyzed C-X bond activation, but not always by lowering activation barriers.
- The degree of substitution influences C-H and C-C bond activation differently due to distinct steric interactions.
- Computational modeling provides insights into the complex factors governing reactivity in organometallic catalysis.
Keywords:
activation strain modelbond activationdensity functional calculationshomogeneous catalysisoxidative additionreactivityMore Related Videos
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