A Simple Synthetic Route to Well-Defined [Pd(NHC)Cl(1-tBu-indenyl)] Pre-catalysts for Cross-Coupling Reactions

The development of robust, more efficient, general, easily accessible Pd(II)-NHC pre-catalysts remains a key issue in cross-coupling applications. A selection of well-defined, air and moisture stable [Pd(NHC)Cl(1-Bu-t-indenyl)] (NHC=IPr, IPrCl, IMes, SIMes, IPr*) pre-catalysts have been synthesized in good to excellent yields by reacting [Pd(1-Bu-t-indenyl)(mu-Cl)](2) and various NHC.HCl precursors in the presence of the weak base K2CO3 in green acetone. The synthesized Pd(II)-NHC derivatives displayed excellent catalytic activity in classical Suzuki-Miyaura and Buchwald-Hartwig reactions, especially when IPrCl is employed as ancillary ligand. Additionally, in the challenging Suzuki-Miyaura reaction between esters and arylboronic acids, the [Pd(IPr*)Cl(1-Bu-t-indenyl)] complex exhibited the optimum catalytic activity under very mild reaction conditions.

Automated summary

The synthesis of a series of stable Pd(II)-NHC pre-catalysts with excellent catalytic activity in Suzuki-Miyaura and Buchwald-Hartwig reactions has been successfully achieved in this study, especially when IPrCl is employed as an ancillary ligand. The [Pd(IPr*)Cl(1-Bu-t-indenyl)] complex also exhibited optimal catalytic activity in the challenging Suzuki-Miyaura reaction between esters and arylboronic acids under very mild reaction conditions.