Mechanistic studies on the oxidative addition of palladium(0) to aryldiazonium cations and on the redox-relay in the Heck-Matsuda reactions of unsaturated ethers

Author(s)

Henrique Esteves

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2021-06-28

Examining board members

Carlos Roque Duarte Correia; Ronaldo Aloise Pilli; Paulo Cesar Muniz de Lacerda Miranda; Ataualpa Albert Carmo Braga; Giovanni Wilson Amarante

• Advisor: Carlos Roque Duarte Correia

Abstract

The oxidative addition of palladium(0) to aryldiazonium cations in Heck-Matsuda reactions is a very fast step, making its study an experimental challenge. Therefore, the understanding of this mechanism remains incipient. In the present computational study, structural, electronic, vibrational and energetic parameters of various intermediates and transition states for this transformation were obtained. The data allows to propose that the oxidative addition takes place in two steps: i. Oxidative coordination, providing a palladium(II) diazenide product; and ii. Intramolecular insertion, providing an aryldinitrogenpalladium(II) complex. The oxidation of palladium in the first step is supported by natural charge and frequency calculations. The mechanism for the redox step, observed in this very same Heck-Matsuda reactions, with unsaturated silicon and carbon ethers, was also explored. Integral migration (>99%) of the carbinolic hydrogen (or equivalent in ethers) to the ? position relative to the carbonyl in the product, observed via isotopic labelling studies, confirmed that a species of carbinolic palladium(II) is achieved, regardless of the substrate. This species is equivalent to those proposed for the oxidation of alkenes in Wacker reactions. For carbon ethers, the formation of the corresponding ketone indicates that an oxonium is formed, followed by ketalisation and hydrolysis, configuring a Wacker-like oxidation (AU)

• 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