Sterically enriched bulky 1,3-bis(N,N′-aralkyl)benzimidazolium based Pd-PEPPSI complexes for Buchwald–Hartwig amination reactions†
Pd-PEPPSI (palladium-pyridine enhanced pre-catalyst preparation stabilization and initiation) complexes are now emerging as well-defined catalysts for C–C and C–N bond formation. In connection with this, we prepared a family of six air and moisture stable, simple to bulky benzyl substituents bearing benzimidazolium core Pd-PEPPSI complexes, C1–C6. The structure of C6 was confirmed from X-ray diffraction (XRD) studies and the steric pressure of N-heterocyclic carbene was determined by % VBur calculation. Notably, these NHC–Pd–Py frameworks exhibit the good σ-donating and π-extended electronic properties of benzimidazolium NHCs, which is an essential requirement for catalysis. The prepared complexes are proved to achieve outstanding and overwhelming reactivity compared to other previously reported catalysts for the Buchwald–Hartwig cross-coupling reactions between 3-chloropyridine and various aryl/heteroaryl amines under mild reaction conditions. On the other hand, there is no need for external additives or ligands for the complete conversion of lead parent molecules to products. More remarkably, C6 accomplished significant catalytic activity compared to the other complexes, C1–C5 for C–N bond formation. Furthermore, the substrate scope could be extended to other heteroaryl chlorides, such as N-(5-chloro-4-methylpyridin-2-yl)acetamide, 2,4,6-trichloro-1,3,5-triazine, 3-chlorothiophene and 3-chloroquinoline.