A straightforward synthetic procedure to well-defined, air- and moisture- stable trans-[Pd(NHC)Cl-2(DMS/THT)] (NHC-IPr, SIPr, IMes, IPrCl,IPr*,IPr#) pre-catalysts is reported. These complexes were obtained by reacting NHC center dot HCl imidazolium salts with trans-[PdCl2(DMS/THT)(2)] precursors with the assistance of the weak base K2CO3 in green acetone at 40 degrees C. The scalability of this protocol was demonstrated. The catalytic activity of the synthesized complexes was studied in the Buchwald-Hartwig and Suzuki-Miyaura reactions. Remarkably, most of the synthesized complexes exhibit higher catalytic activity with respect to their PEPPSI congeners in the Buchwald-Hartwig amination 2-MeTHF. In particular, complex trans-[Pd(IPr#)Cl-2(DMS)] enabled the coupling of various (hetero)aryl chlorides and primary/secondary amines with a 0.2 mol% catalyst loading. In addition, trans-[Pd(IPOCI,(DMS)] showed excellent performance in the room-temperature Suzuki-Miyaura reaction involving various (hetero)aryl chlorides and aryl boronic acids. In summary, the synthesized complexes, especially trans-[Pd(NHC)Cl-2(DMS)], can be considered as greener alternatives to classical PEPPSI type catalysts based on the lower toxicity of the throw-away DMS ligand compared to 3-chloropyridine.
Versatile and Highly Efficient trans-[Pd(NHC)Cl2(DMS/THT)] Precatalysts for C-N and C-C Coupling Reactions in Green Solvents
Thomas Scattolin;
2022
Abstract
A straightforward synthetic procedure to well-defined, air- and moisture- stable trans-[Pd(NHC)Cl-2(DMS/THT)] (NHC-IPr, SIPr, IMes, IPrCl,IPr*,IPr#) pre-catalysts is reported. These complexes were obtained by reacting NHC center dot HCl imidazolium salts with trans-[PdCl2(DMS/THT)(2)] precursors with the assistance of the weak base K2CO3 in green acetone at 40 degrees C. The scalability of this protocol was demonstrated. The catalytic activity of the synthesized complexes was studied in the Buchwald-Hartwig and Suzuki-Miyaura reactions. Remarkably, most of the synthesized complexes exhibit higher catalytic activity with respect to their PEPPSI congeners in the Buchwald-Hartwig amination 2-MeTHF. In particular, complex trans-[Pd(IPr#)Cl-2(DMS)] enabled the coupling of various (hetero)aryl chlorides and primary/secondary amines with a 0.2 mol% catalyst loading. In addition, trans-[Pd(IPOCI,(DMS)] showed excellent performance in the room-temperature Suzuki-Miyaura reaction involving various (hetero)aryl chlorides and aryl boronic acids. In summary, the synthesized complexes, especially trans-[Pd(NHC)Cl-2(DMS)], can be considered as greener alternatives to classical PEPPSI type catalysts based on the lower toxicity of the throw-away DMS ligand compared to 3-chloropyridine.
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