The design and synthesis of bis(thiourea) ligands and their application in Pd-catalyzed heck and suzuki reactions under aerobic conditions

Abstract

New, bulky N,N-disubstituted acyclic and cyclic bis(thiourea) ligands have been designed and synthesized. Their palladium(0) complexes are very stable and are active catalysts for Heck and Suzuki coupling reactions of aryl iodides and bromides under aerobic conditions. Good TONs and TOFs were achieved in the coupling reactions [for PhI, TONs up to 1000000 and TOFs up to 200000 (h -1); for activated aryl bromide, TONs up to 89000]. In addition, further studies were conducted to know more about the nature of these catalysts. The active catalyst was found to be the chelate complex containing the bis(thiourea) and Pd in a 1:1 ratio. However, unlike a monothiourea, further coordination can occur to give a coordinatively saturated complex when bis(thiourea) and Pd are combined in a 2:1 ratio; this complex is catalytically inactive in coupling reactions. © Wiley-VCH Verlag GmbH & Co. KGaA, 2006.