C(spⁿ )-X (n=1-3) Bond Activation by Palladium

Area of Science:

• Organometallic Chemistry
• Computational Chemistry
• Catalysis

Background:

• Palladium catalysts are crucial for activating carbon-halogen (C-X) bonds in organic synthesis.
• Understanding the factors influencing C-X bond activation is key to designing more efficient catalytic systems.

Purpose of the Study:

• To investigate the palladium-catalyzed activation of C(spn)-X bonds across different hybridization states (sp3, sp2, sp).
• To elucidate the electronic and steric factors governing the oxidative addition step in palladium catalysis.

Main Methods:

• Relativistic density functional theory (DFT) calculations using the ZORA-BLYP/TZ2P level of theory.
• Analysis of oxidative addition barriers, activation strain, and energy decomposition for model substrates and palladium catalysts (PdLn).

Main Results:

• The oxidative addition barrier decreases from C(sp3)-X to C(sp2)-X to C(sp)-X, despite increasing bond strength.
• Reduced steric (Pauli) repulsion between the palladium catalyst and substrate, due to decreasing carbon coordination number, drives this trend.
• Stabilization of the catalyst-substrate interaction counteracts increasing bond strain.

Conclusions:

• The ease of palladium-mediated C-X bond activation is primarily governed by steric factors related to the carbon hybridization state.
• Catalyst design can be optimized by considering the interplay between steric repulsion and bond strength for targeted C-X activation.