Unraveling the Role of a Flexible Tetradentate Ligand in the Aerobic Oxidative Carbon-Carbon Bond Formation with Palladium Complexes

A Computational Mechanistic Study

Qian Peng, Zengwei Wang, Snežana D. Zarić, Edward Brothers, Michael B. Hall

Research output: Contribution to journalArticle

2 Citations (Scopus)

Abstract

Mechanistic details of the aerobic oxidative coupling of methyl groups by a novel (MeL)PdII(Me)2 complex with the tetradentate ligand, MeL = N,N-dimethyl-2,11-diaza[3.3](2,6)pyridinophane, has been explored by density functional theory calculations. The calculated mechanism sheds light on the role of this ligand's flexibility in several stages of the reaction, especially as the oxidation state of the Pd changes. Ligand flexibility leads to diverse axial coordination modes, and it controls the availability of electrons by modulating the energies of high-lying molecular orbitals, particularly those with major dz 2 character. Solvent molecules, particularly water, appear essential in the aerobic oxidation of PdII by lowering the energy of the oxygen molecule's unoccupied molecular orbital and stabilizing the PdX-O2 complex. Ligand flexibility and solvent coordination to oxygen are essential to the required spin-crossover for the transformation of high-valent PdX-O2 complexes. A methyl cation pathway has been predicted by our calculations in transmetalation between PdII and PdIV intermediates to be preferred over methyl radical or methyl anion pathways. Combining an axial and equatorial methyl group is preferred in the reductive elimination pathway where roles are played by the ligand's flexibility and the fluxionality of trimethyl groups.

Original languageEnglish
Pages (from-to)3929-3939
Number of pages11
JournalJournal of the American Chemical Society
Volume140
Issue number11
DOIs
Publication statusPublished - 21 Mar 2018

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Palladium
Carbon
Ligands
Molecular orbitals
Oxidative Coupling
Oxygen
Oxidation
Molecules
Density functional theory
Anions
Cations
Negative ions
Positive ions
Availability
Electrons
Water

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Unraveling the Role of a Flexible Tetradentate Ligand in the Aerobic Oxidative Carbon-Carbon Bond Formation with Palladium Complexes : A Computational Mechanistic Study. / Peng, Qian; Wang, Zengwei; Zarić, Snežana D.; Brothers, Edward; Hall, Michael B.

In: Journal of the American Chemical Society, Vol. 140, No. 11, 21.03.2018, p. 3929-3939.

Research output: Contribution to journalArticle

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