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Amination of heteroaryl chlorides: palladium catalysis or SN Ar in green solvents?

ABSTRACT: The reaction of heteroaryl chlorides in the pyrimidine, pyrazine and quinazoline series with amines in water in the presence of KF results in a facile SN Ar reaction and N-arylation. The reaction is less satisfactory with pyridines unless an additional electron-withdrawing group is present. The results showed that the transition-metal-free SN Ar reaction not only compares favourably to palladium-catalysed coupling reactions but also operates under environmentally acceptable ("green") conditions in terms of the base and solvent.

SUBMITTER: Walsh K

PROVIDER: S-EPMC3792620 | biostudies-literature | 2013 Aug

REPOSITORIES: biostudies-literature

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Amination of heteroaryl chlorides: palladium catalysis or SN Ar in green solvents?

Walsh Katie K Sneddon Helen F HF Moody Christopher J CJ

ChemSusChem 20130621 8

The reaction of heteroaryl chlorides in the pyrimidine, pyrazine and quinazoline series with amines in water in the presence of KF results in a facile SN Ar reaction and N-arylation. The reaction is less satisfactory with pyridines unless an additional electron-withdrawing group is present. The results showed that the transition-metal-free SN Ar reaction not only compares favourably to palladium-catalysed coupling reactions but also operates under environmentally acceptable ("green") conditions ...[more]

PMID: 23794470

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Project description:First-row metal complexes often undergo undesirable one-electron redox processes during two-electron steps of catalytic cycles. We report the amination of aryl chlorides and bromides with primary aliphatic amines catalyzed by a well-defined, single-component nickel precursor (BINAP)Ni(η(2)-NC-Ph) (BINAP = 2,2'-bis(biphenylphosphino)-1,1'-binaphthalene) that minimizes the formation of Ni(I) species and (BINAP)2Ni. The scope of the reaction encompasses electronically varied aryl chlorides and nitrogen-containing heteroaryl chlorides, including pyridine, quinoline, and isoquinoline derivatives. Mechanistic studies support the catalytic cycle involving a Ni(0)/Ni(II) couple for this nickel-catalyzed amination and are inconsistent with a Ni(I) halide intermediate. Monitoring the reaction mixture by (31)P NMR spectroscopy identified (BINAP)Ni(η(2)-NC-Ph) as the resting state of the catalyst in the amination of both aryl chlorides and bromides. Kinetic studies showed that the amination of aryl chlorides and bromides is first order in both catalyst and aryl halide and zero order in base and amine. The reaction of a representative aryl chloride is inverse first order in PhCN, but the reaction of a representative aryl bromide is zero order in PhCN. This difference in the order of the reaction in PhCN indicates that the aryl chloride reacts with (BINAP)Ni(0), formed by dissociation PhCN from (BINAP)Ni(η(2)-NC-Ph), but the aryl bromide directly reacts with (BINAP)Ni(η(2)-NC-Ph). The overall kinetic behavior is consistent with turnover-limiting oxidative addition of the aryl halide to Ni(0). Several pathways for catalyst decomposition were identified, such as the formation of the catalytically inactive bis(amine)-ligated arylnickel(II) chloride, (BINAP)2Ni(0), and the Ni(I) species [(BINAP)Ni(μ-Cl)]2. By using a well-defined nickel complex as catalyst, the formation of (BINAP)2Ni(0) is avoided and the formation of the Ni(I) species [(BINAP)Ni(μ-Cl)]2 is minimized.

Dataset Information

Amination of heteroaryl chlorides: palladium catalysis or SN Ar in green solvents?

Publications

Amination of heteroaryl chlorides: palladium catalysis or SN Ar in green solvents?

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