Potentially Tridentate Ligands in the Synthesis of Methyl- and Acetylpalladium(II) Complexes

Abstract

The two protic tridentate ligands HNN′O (1) and HNN′S (2) were treated with [(COD)Pd(Me)Cl], and the corresponding methylpalladium(II) complexes [Pd(η2-HNN′)(Me)Cl] (1a and 2a) were isolated. The neutral ligands in these complexes coordinated the metal in an NN′ bidentate mode, through the pyridine and imine nitrogens, excluding the O or S atom from the coordination. This behavior was confirmed by X-ray diffraction analysis of the dichloro complex of 1, [Pd(η2-HNN′)Cl2] (1c). Complexes 1a and 2a easily transformed quantitatively into the corresponding three-coordinate complexes [Pd(η3-NN′X)(Me)] (1b: X = O, 2b: X = S) in basic medium, with elimination of HCl. The complexes 1a and 1b were treated with PPh3 and P(CD3)3, respectively, resulting in 1e and 1h; 1a reacted further with a double quantity of PPh3 to give rise to the diphosphane complex [trans-(PPh3)2Pd(Me)Cl] (1g) and free 1. The three-coordinate complexes 1b and 2b were subjected to CO bubbling at room temperature. In the case of 1b, acylation of the ligand on the phenolic oxygen was observed, with the formation of an organic acetate and release of palladium black. In the case of 2b, besides the acylated ligand on the thiolic sulfur, the acetylpalladium(II) complex [Pd(η3-NN′S)(MeCO)] (2c) was isolated. The X-ray structures of 1c·THF, 1b·1/2C6H6O2, 2b, 2c·1/2CH2Cl2, and 1g have been solved. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)