N,N-Dialkyl-2-iodoanilines: A versatile source for the synthesis of Pd(ii) complexes. Synthesis of novel OCP- and CCN-pincer palladium complexes

Abstract

The reactivity of a series of N,N-dimethyl-2-iodoanilines bearing different chelating “arms” at the 3-position with Pd₂(dba)₃ has been explored. 3-[(Diphenylphosphino)methyl]-2-iodo-N,N-dimethylaniline (1) reacted with Pd₂(dba)₃ and PPh₃ under aerobic conditions to give the OCP-pincer complex 4, which was formed by sequential C(sp³)–H activation/oxidation at the α-position of the aniline N atom. On the other hand, under similar reaction conditions, 3-[2-(dimethylamino)ethyl]-2-iodo-N,N-dimethylaniline (2) afforded the CCN-pincer complex 5, after a second C–H activation process at the formyl group of the initially formed OCN-pincer complex. In contrast, 2-iodo-3-(1H-1,2,4-triazol-1-ylmethyl)-N,N-dimethylaniline (3a) and 2-iodo-3-(pyrazol-1-ylmethyl)-N,N-dimethylaniline (3b) reacted with Pd₂(dba)₃ and PPh₃, respectively, to give the 6-membered azapalladacycles 6a and 6b, in which the aniline nitrogen is merely a spectator substituent. Finally, treatment of iodide complex 6a with Tl(TfO) afforded the CN-bidentate cationic complex 8. Solid-state structures of palladium complexes 4, 5, and 8·CH₂Cl₂·3CH₃OH·5H₂O were determined by X-ray analysis.