The Mechanism of NO Bond Cleavage in Rhodium‐Catalyzed CH Bond Functionalization of Quinoline N‐oxides with Alkynes: A Computational Study

Abstract

Metal-catalyzed C-H activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N-oxide is used as an arene source in C-H activation studies, the N-O bond can act as a directing group as well as an O-atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline N-O bond and alkynes, which results in C-H activation and O-atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a Rh-C bond, a reductive elimination to form an oxazinoquinolinium-coordinated Rh(I) intermediate, an oxidative addition to break the N-O bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop-1-yn-1-ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1-phenyl-2-quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity-determining step. These calculated data are consistent with the experimental observations.

Computational Investigation of the Role Played by Rhodium(V) in the Rhodium(III)‐Catalyzed ortho‐Bromination of Arenes

“…As shown in Figure , the free energy of Rh III complex 1 , which would be the active catalyst for the catalytic bromination reaction, was set to the relative zero value. Based on previous theoretical and experimental studies, Rh III complex 1 could be formed from added [{RhCp*Cl 2 } 2 ] through dissociation and ligand‐exchange reactions in the presence of AgSbF 6 and PivOH ,. The coordination of NBS to complex 1 would lead to the formation of intermediate 2 in an exothermic process that would release 1.8 kcal mol −1 of free energy.…”

“…Furthermore, the authors proposed that the formation of the C−Br bond occurred through reductive elimination from a Rh V intermediate, which was formed by the oxidative addition of NBS to Rh III . We recently conducted an in‐depth theoretical study of a series of Rh III ‐catalyzed C−H cleavage and functionalization reactions . Although the results of this study revealed that a Rh V intermediate could be formed by oxidation in some cases, they also revealed that some of these reactions preferred a Rh III /Rh I catalytic cycle.…”

Recent advances in the C–H-functionalization of the distal positions in pyridines and quinolines

“…In 2015 Lan, Li, and co-workers reported a computation study of this Rh-catalyzed reaction, 125 using the M11L DFT method. 126 While four different pathways were ultimately evaluated, the path A in Scheme 108 was found to be the most energetically favorable one.…”

Role of Alkaline-Earth Metal-Catalyst: A Theoretical Study of Pyridines Hydroboration

“…In 2011, Nikonov's group (Gutsulyak et al, 2011) realized hydrosilylation of pyridine with ruthenium as the catalyst at room temperature and obtained a mixture of 1,2- and 1,4-borohydropyridine. However, application of these reactions in synthetic chemistry is greatly limited by the expensive transition metal catalyst (Yaroshevsky, 2006; Dobereiner and Crabtree, 2010; Osakada, 2011; Huang and Xia, 2015; Li et al, 2015; Qi et al, 2016, 2018; Yang et al, 2016; Yu et al, 2016; Xing et al, 2017; Liu et al, 2018; Luo et al, 2018; Zhu et al, 2018).…”