A mechanistic insights into manganese-catalyzed oxidative homocoupling reactions of Grignard reagents: A computational DFT investigation

作者：Bottoni Andrea^*; Cahiez Gerard^*; Calvaresi Matteo; Moyeux Alban; Giacinto Pietro; Miscione Gian Pietro

来源：Journal of Organometallic Chemistry, 2016, 814: 25-34.

DOI：10.1016/j.jorganchem.2016.04.029

• Manganese catalysis
• Catalytic mechanism
• Computational investigation
• Homocoupling reactions
• Oxidative coupling reactions
• Grignard reagents

We have carried out a DFT computational investigation on the mechanism of the manganese-catalyzed homocoupling reaction of aryl Grignard reagents RMgX using atmospheric oxygen as an oxidant. The oxidative addition gives an oxo-complex MnR2O2 where the oxygen molecule is eta(2)-bonded to the metal. The free energy barrier for the subsequent reductive elimination (key-step of the cycle) is 9.4 kcal mol(-1) when R = p-anisyl, which indicates a rather fast reduction step. A comparative analysis of various systems (R = p-anisyl, o- and p-nitrophenyl, pentafluorophenyl, mesityl, naphtyl and phenylethynyl) suggests that, in general, the kinetics of the reductive elimination step is the result of a complex interplay between electronic and steric effects and, in the case of aryl groups, strongly depends on the nature of the substituent and its position on the phenyl ring. The reduction is favored when the electron density on the coupling carbons is large enough to interact with the metal and form the intermediate oxo-complex. However it cannot be so large to prevent the coupling because of a too strong electron repulsion or too strong Mn-R bonds.

• 出版日期2016-7-15