Theoretical Study on the Mechanism of the Hydrogenation of Azo (N═N) Bonds to Amines Catalyzed by Manganese

Rui-Ping Huo; Kai-Xin Xie; Xiang Zhang; Cai-Feng Zhang

doi:10.1021/acs.jpca.3c03955

Theoretical Study on the Mechanism of the Hydrogenation of Azo (N═N) Bonds to Amines Catalyzed by Manganese

J Phys Chem A. 2023 Dec 21;127(50):10529-10539. doi: 10.1021/acs.jpca.3c03955. Epub 2023 Dec 6.

Authors

Rui-Ping Huo¹, Kai-Xin Xie¹, Xiang Zhang², Cai-Feng Zhang¹

Affiliations

¹ College of Chemistry and Materials, Taiyuan Normal University, Jinzhong 030619, China.
² Key Laboratory of Magnetic Molecules & Magnetic Information Materials Ministry of Education, The School of Chemical and Material Science, Shanxi Normal University, Taiyuan 030600, China.

PMID: 38054661
DOI: 10.1021/acs.jpca.3c03955

Abstract

The mechanism of the transition metal manganese complex Mn(^PhPNN)(CO)₂Br (CA-4) that catalyzed the hydrogenation of the azo (N═N) bond to amines has been investigated using the PBE0 function. The results show that the whole reaction involves three basic processes: (1) the addition of H₂ to CA gives IN2, which can hydrogenate the azo (N═N) bond at the later stage; (2) hydrogenation of azobenzene by IN2, which gives 1,2-diphenylhydrazine (PhNHNHPh); and (3) hydrogenation of 1,2-diphenylhydrazine by IN2, which affords aniline (PhNH₂). The results suggest that the hydrogenation of CA and hydrogenation of azobenzene by IN2 to afford PhNHNHPh are easy to occur due to the low barriers, and the overall rate-determining step is the formation of IN11 and PhNH₂ by breaking the N-N bond in the stage of hydrogenation of 1,2-diphenylhydrazine by IN2, with an energy barrier of 39.1 kcal/mol. The computed results are in good agreement with the experimental results. The mechanism of the azobenzene reaction catalyzed by manganese was analyzed by charge and orbital analysis in detail. The theoretical results provide a deeper understanding of the mechanism and fully explain the experimental facts.