δ-Bonded 2-Phenylpyridine Palladium Complex

Abstract

In general, heterocyclic amines such as pyridine react with palladium(II) dichloride to give a square-planar complex such as Pd(pyridine)2Cl2. However, the observation1) that azobenzenes and N,N-dimethylbenzylamine react with palladium(II) halides and platinum(II) halides in alcoholic solutions to give complexes (1) and (2) with carbon-metal a-bonds has led to an examination of a similar reaction between palladium(II) dichloride and heterocyclic amines. We have found that, in alcoholic media, 2-phenylpyridine undergoes a similar unusual reaction with sodium chloropalladate. 2-Phenylpyridine and sodium chloropalladate were dissolved in alcohol and allowed to stand at room temperature for two days. A pale yellow material believed to have the structure (3) was isolated in about a 70% yield. The compound (3) is insoluble in all common organic solvents and does not melt before decomposition, which occurs at about 270•Ž. The structure of the complex (3) was established by the results of the elementary analysis (Found: C, 44.38; H, 2.56; N, 4.57%. Calcd for C22H16N2-Pd2Cl2 : C, 44.82; H, 2.72; N, 4.14%) and the following data. In the infrared spectrum of the compound (3), the characteristic C-H out-of-plane deformation modes of a mono-substituted benzene at 770-730 and 690 cm-1 are absent and are replaced by one at 737cm-1, which can be assigned to a C-H deformation mode of an ortho-disubstituted benzene.2) The lithium aluminum hydride reduction of the compound (3) gave 2-phenylpyridine (4a), whose mass spectrum, picrate, and hydrochloride were identical with those of an authentic sample. On the other hand, the lithium aluminum deuteride reduction of the compound (3) gave 2-phenylpyridine-dl (4b). The position of the deuterium and, therefore, the site of the carbon-to-palladium ƒÐ-bond, were established by a comparison of the mass spectrum of (4b) with that of the undeuterated (4a). The compound (4a) gave peaks at m/e 155 (100%, parent ion), 128 (12%, loss of HCN), and 52 (21%, loss of PhCN). The mass spectrum of the compound (4b) showed peaks at m/e 156 (100%, parent ion), 129 (13%, loss of HCN), and 52 (21%, loss of PhCN-d1).