Mechanisms for the Oxidative Addition of Palladium(0) Complexes to Arenediazonium Salts

Author(s)

Esteves, Henrique ; da Silva, Vitor H. Menezes ; Correia, Carlos R. D. ; Braga, Ataualpa A. C.

• Document type: Journal article
• Source: Organometallics; v. 42, n. 22, p. 14-pg., 2023-11-06.

Abstract

A detailed computational analysis was carried out using density functional theory (DFT) calculations to investigate the reaction between arenediazonium salts and Pd(0) complexes under "ligand-less" conditions. In the present study, three plausible mechanisms scenarios were revealed: nucleophilic substitution, intramolecular insertion, and a multistep 1,3-palladium migration. The oxidative addition of palladium to aryldiazonium cation (<bold>ArN</bold>(<bold>+</bold>)(<bold>2</bold>)) is a rapid and irreversible reaction. Additionally, <bold>ArN</bold>(<bold>+</bold>)(<bold>2</bold>) counterion BF4- does not have a significant impact on the reaction free energy profile. Based on the DFT calculations, the formation of the aryl-palladium(II) complex is identified as the thermodynamic driving force, regardless of the investigated reaction mechanism. The multistep 1,3-palladium migration mechanism is preferred, but the nucleophilic substitution and intramolecular insertion mechanisms could not be ruled out. According to the natural population analysis (NPA) of charges, the oxidation of Pd(0) takes place through the coordination of cation <bold>ArN</bold>(<bold>+</bold>)(<bold>2</bold>) to the metal specifically for the multistep 1,3-palladium migration mechanism, in contrast to the aryl halide counterpart systems, in which the oxidation of Pd(0) occurs in transition-state structures. The reaction thermodynamics is affected by the electronics of the para-substituents in the phenyl ring of <bold>ArN</bold>(<bold>+</bold>)(<bold>2</bold>). However, the overall reaction barriers are less affected by the electronics of substituents. Additionally, the computational investigation was carried out under different "ligand-less" conditions using methanol (MeOH), N,N-dimethylformamide (DMF), and acetonitrile (MeCN) as solvents. Specifically, for the MeCN solvent, the oxidative addition of Pd(0) to <bold>ArN</bold>(<bold>+</bold>)(<bold>2</bold>) was found to be less exothermic. Taken together, the strong electron acceptor capacity and high reactivity of <bold>ArN</bold>(<bold>+</bold>)(<bold>2</bold>) provide facile oxidation of Pd(0) and a strongly positively charged metal atom in all palladium-containing reaction intermediates and transition states, reflecting the low free energy barriers and high reaction exothermicity revealed by the calculations at room temperature. Furthermore, the current computational study suggests that the palladium(II) aryldiazenido complexes (<bold>int6a</bold> or <bold>int6b</bold>) are stable reaction intermediates, indicating them as promising precursor complexes for prospective experimental mechanistic investigations. (AU)

• FAPESP's process: 14/25770-6 - New frontiers in cross-coupling reactions promoted by palladium: combining enantioselective catalysis, C-H activations, new materials and in flux reactions aiming at high efficiency and sustainability in synthetic processes
• Grantee: Carlos Roque Duarte Correia
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 17/18207-1 - Evaluating new palladium chiral catalysts and application in enantioselective Heck-Matsuda reaction development in new olefinic models: computational studies
• Grantee: Vitor Hugo Menezes da Silva
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/07600-3 - CIBFar - Center for Innovation in Biodiversity and Drug Discovery
• Grantee: Glaucius Oliva
• Support Opportunities: Research Grants - Research, Innovation and Dissemination Centers - RIDC
• FAPESP's process: 15/01491-3 - Theoretical study of cross-coupling reactions: homogeneous and heterogeneous catalysis
• Grantee: Ataualpa Albert Carmo Braga
• Support Opportunities: Regular Research Grants
• FAPESP's process: 16/18061-4 - Heck-Matsuda Arylation of Alkenyl Ethers and Derivatives: Expansion, Mechanistic Studies and Synthetic Applications of the Redox-Relay Strategy
• Grantee: Henrique Esteves
• Support Opportunities: Scholarships in Brazil - Doctorate