Resorcinarenyl-phosphines in suzuki-miyaura cross-coupling reactions of aryl chlorides

Abstract

Two phosphines built on a bowl-shaped resorcin[4]arene skeleton, namely 5-diphenylphosphanyl- and 5-diisopropylphosphanyl-4(24),6(10),12(16),18(22)- tetramethylenedioxy-2,8,14,20-tetrapentylresorcin[4]arene, have been synthesised and tested in the Suzuki-Miyaura cross-coupling reaction of aryl halides. Combining these ligands with [Pd(OAc)2] resulted in highly active catalysts that allowed the formation of o,o′-biphenyls starting from aryl chlorides. The remarkable activities observed possibly arise from 1) the capacity of the phosphines to operate transiently as P,O chelators, thereby increasing the electron density of the metal, and 2) the ability of the ligands to embed metal-organic units, which, when occurring, makes the ligand considerably bulkier so as to disfavour the coordination of a second phosphine. Both features are known to facilitate the oxidative addition step. Palladium complexes containing cavitand-phosphines based on a resorcinarene skeleton display high reactivity in Suzuki-Miyaura cross-coupling reactions. The unusual performance of these ligands essentially relies on their bulkiness and ability to bind the metal centre in a hemilabile fashion. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.