Issue 20, 2024

Nickel–PNN catalysed sustainable synthesis of polysubstituted quinolines under microwave irradiation

Abstract

In this manuscript, the synthesis of a series of cationic NiII complexes based on mixed donor triazolyl-pyridine-based aminophosphine, [(NiCl){R′PRNN}-κ3-P,N,N]OTf (R = H or Me; R′ = Ph or tBu), is described. The neutral dearomatized complexes [(NiCl){R′PNN}-κ3-P,N,N] (R′ = Ph or tBu) were prepared by deprotonation of [(NiCl){PPhN(H)N}-κ3-P,N,N]OTf (Ni1) and [(NiCl){(tBu2P)N(H)N}-κ3-P,N,N]OTf (Ni3) with 1 equiv. of tBuOK. These complexes (0.5 mol%) were employed for the synthesis of substituted quinolines at 110 °C under microwave irradiation with 20 mol% of KOH. Among these, complexes [(NiCl){tBuPHNN-κ3-P,N,N}]OTf (Ni3) and [(NiCl){tBuPNN}-κ3-P,N,N] (Ni5) were found to be highly efficient. A wide range of derivatives, including aryl, aliphatic, acyclic ketones, primary alcohols and aminobenzyl alcohols, yielded the corresponding quinolines in good to excellent yields (62 examples). A series of control experiments were carried out to establish the reaction mechanism. HR-MS spectral studies were investigated to characterize the nickel-hydride intermediate. Mechanistic studies confirmed that the reaction takes an acceptorless dehydrogenative coupling pathway.

Graphical abstract: Nickel–PNN catalysed sustainable synthesis of polysubstituted quinolines under microwave irradiation

Supplementary files

Article information

Article type
Paper
Submitted
12 Jul 2024
Accepted
19 Aug 2024
First published
20 Aug 2024

Catal. Sci. Technol., 2024,14, 5959-5969

Nickel–PNN catalysed sustainable synthesis of polysubstituted quinolines under microwave irradiation

M. A. Mohite, S. Sheokand and M. S. Balakrishna, Catal. Sci. Technol., 2024, 14, 5959 DOI: 10.1039/D4CY00863D

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