Mechanistic aspects of pincer nickel(II)-catalyzed C-H bond alkylation of azoles with alkyl halides

TitleMechanistic aspects of pincer nickel(II)-catalyzed C-H bond alkylation of azoles with alkyl halides
Publication TypeJournal Article
Year of Publication2018
AuthorsPatel, UN, Jain, S, Pandey, DK, Gonnade, RG, Vanka, K, Punji, B
JournalOrganometallics
Volume37
Issue6
Pagination1017-1025
Date PublishedMAR
ISSN0276-7333
Abstract

The quinolinyl-based pincer nickel complex, kappa(N),kappa(N),kappa(N)-{C9H6N-(mu-N)-C6H4-NMe2}NiCl [((NNNMe2)-N-Q)-NiCl; (1)] has recently been demonstrated to be an efficient and robust catalyst for the alkylation of azoles with alkyl halides under copper-free conditions. Herein, we report the detailed mechanistic investigation for the alkylation of azoles catalyzed by ((NNNMe2)-N-Q)NiCl (1), which highlights an iodine atom transfer (IAT) mechanism for the reaction involving a Ni-II/Ni-III process. Deuterium labeling experiments indicate reversible cleavage of the benzothiazole C-H bond, and kinetic studies underline a fractional negative rate order with the substrate benzothiazole. The involvement of an alkyl radical during the alkylation is validated by radical clock and external additive experiments. An active intermediate species ((NNNMe2)-N-Q)Ni(benzothiazolyl) (5a) has been isolated and structurally characterized. The complex ((NNNMe2)-N-Q)Ni(benzothiazoly1) (5a) is found to be the resting state of catalyst 1. Kinetic analysis of electronically different intermediates suggests that the step involving the reaction of 5a with alkyl iodide is crucial and a rate-influencing step. DFT calculations strongly support the experimental findings and corroborate an IAT process for the alkylation reaction.

DOI10.1021/acs.organomet.8b00025
Type of Journal (Indian or Foreign)

Foreign

Impact Factor (IF)

3.862

Divison category: 
Catalysis and Inorganic Chemistry
Center for Material Characterization (CMC)
Physical and Materials Chemistry