Palladium-Assisted Formation of Carbon−Carbon Bonds. Part 10.1 Insertion Reactions of Isocyanides into the Pd−C Bond of Orthopalladated Primary Amines. Synthesis of 2-R-Aminoisoindolinium Salts (R = tBu, 2,6-Xylyl)

Abstract

The palladated primary amines [Pd{C6H3CH2NH2-2-X-5}(μ-Br)]2 [X = H (1a), OMe (1b), NO2 (1c), F (1d)] react with isocyanides (Pd:RNC = 1:1) to give [Pd{C6H3CH2NH2-2-X-5}Br(RNC)] [R = Xy = C6H3Me2-2,6, X = H (2a), OMe (2b), NO2 (2c), F (2d), R = tBu, X = H (3a), OMe (3b), NO2 (3c), F (3d)]. When XyNC reacts with 1a (Pd:RNC = 1:2) or with 2a (Pd:RNC = 1:1), the complex [Pd{(CNXy)C6H4CH2NH2-2}(XyNC)Br] (4a) is obtained. The reactions of complexes 1 with isocyanides in the ratio Pd:RNC = 1:3 lead to Pd(I) complexes [Pd2Br2L4] [L = XyNC (5); L = tBu (6)]. On the basis of NMR data we propose the following reaction pathway for this reduction process: (1) formation of the corresponding monomer 2 or 3, (2) insertion of one molecule of the isocyanide into the Pd−C bond of 2 or 3 to give [Pd{(CNR)C6H3CH2NH2-2-X-5}(RNC)Br], (3) cleavage of the N−Pd bond and coordination of a new isocyanide molecule to give complexes [Pd{(CNR)C6H3CH2NH2-2-X-5}(RNC)2Br] [detected in solution for R = Xy, X = H (7a) and isolated as an ac...