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Elsevier, Journal of Organometallic Chemistry, 2(690), p. 422-429

DOI: 10.1016/j.jorganchem.2004.07.067

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The cyclopalladation reaction of 2-phenylaniline revisited

This paper was not found in any repository, but could be made available legally by the author.
This paper was not found in any repository, but could be made available legally by the author.

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Abstract

2-Phenylaniline reacted with Pd(OAc)2 in toluene at room temperature for 24 h in a one-to-one molar ratio and with the system PdCl2, NaCl and NaOAc in a 1 (2-phenylaniline):1 (PdCl2):2 (NaCl):1 (NaOAc) molar ratio in methanol at room temperature for one week to give the dinuclear cyclopalladated compounds (μ-X)2[Pd{κ2-N2′,C1-2-(2′-NH2C6H4)C6H4}]2 [1a (X=OAc) and 1b (X=Cl)] in high yield. Moreover, the reaction between 2-phenylaniline and Pd(OAc)2 in one-to-one molar ratio in acid acetic at 60 °C for 4 h, followed by a metathesis reaction with LiBr, allowed isolation of the dinuclear cyclopalladated compound (μ-Br)2[Pd{κ2-N2′,C1-2-(2′-NH2C6H4)C6H4}]2 (1c) in moderate yield. A parallel treatment, but using monodeuterated acetic acid (DOAc) as solvent in the cyclopalladation reaction, allowed isolation of a mixture of compounds 1c, 1cd1 [Pd{κ2-N2′,C1-2-(2′-NH2C6H4)C6H4](μ-Br)2[Pd{κ2-N2′,C1-2-(2′-NH2C6H4)-3-d-C6H3] and 1cd2 (μ-Br)2[Pd{κ2-N2′,C1-2-(2′-NH2C6H4)-3-d-C6H3}]2 in moderate yield and with a deuterium content of ca. 60%. 1a and 1b reacted with pyridine and PPh3 affording the mononuclear cyclopalladated compounds [Pd{κ2-N2′,C1-2-(2′-NH2C6H4)C6H4}(X)(L)] [2a (X=OAc, L=py), 2b (X=Cl, L=py), 3a (X=OAc, L=PPh3) and 3b (X=Cl, L=PPh3)] in a yield from moderate to high. Furthermore, 1a reacted with Na(acac)·H2O to give the mononuclear cyclopalladated compound 4 [Pd{κ2-N2′,C1-2-(2′-NH2C6H4)C6H4}(acac)] in moderate yield. 1H NMR studies in CDCl3 solution of 2a, 2b, 3a, 3b and 4 showed that 2a and 3a presented an intramolecular hydrogen bond between the acetato ligand and the amino group, and were involved in a dynamic equilibrium with water present in the CDCl3 solvent; and that the enantiomeric molecules of 2b and 4 were in a fast exchange at room temperature, while they were in a slow exchange for 2a, 3a and 3b. The X-ray crystal structures of 3b and 4 were determined. 3b crystallized in the triclinic space group P1¯ with a=9.9170(10), b=10.4750(10), c=12.0890(10) Å, α=98.610(10)°, β=94.034(10)° and γ=99.000(10)° and 4 in the monoclinic space group P21/a with a=11.5900(10), b=11.2730(10), c=12.2150(10) Å, α=90°, β=107.6560(10)° and γ=90°.