Synthesis of N-heterocyclic carbene-palladium-PEPPSI complexes and their catalytic activity in the direct C-H bond activation

KALOGLU N., KALOĞLU M., TAHIR M. N., ARICI C., BRUNEAU C., DOUCET H., ...More

JOURNAL OF ORGANOMETALLIC CHEMISTRY, vol.867, pp.404-412, 2018 (SCI-Expanded, Scopus)

  • Publication Type: Article / Article
  • Volume: 867
  • Publication Date: 2018
  • Doi Number: 10.1016/j.jorganchem.2017.10.019
  • Journal Name: JOURNAL OF ORGANOMETALLIC CHEMISTRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.404-412
  • Keywords: N-heterocyclic carbene, Benzimidazolium salts, PEPPSI-Type palladium-NHC complexes, Pyrroles, Direct arylation, CROSS-COUPLING REACTIONS, PD-NHC PRECATALYST, DIRECT ARYLATION, ARYL CHLORIDES, HETEROAROMATIC-COMPOUNDS, SILVER(I) COMPLEXES, ORGANOMETALLIC CATALYSIS, NATURAL-PRODUCTS, METAL-COMPLEXES, LIGANDS
  • Inonu University Affiliated: Yes

Abstract

A series of benzimidazolium salts having their two nitrogen atoms substituted by bulky groups have been synthesized. The benzimidazolium salts were readily converted into the corresponding palladium-NHC-PEPPSI complexes with general formula [PdBr2(NHC) (Py)], (NHC = N-heterocyclic carbene; PEPPSI = pyridine-enhanced precatalyst preparation, stabilisation, and initiation). The structures of all new compounds were characterized by NMR, IR spectroscopy and microanalysis techniques, which support the proposed structures. The molecular structure of complex 2g was determined by singlecrystal X-ray diffraction study. Next, the palladium-NHC-PEPPSI complexes were used as catalysts in the direct C5-arylation of 1-methylpyrrole-2-carboxaldehyde by aryl halides. These complexes exhibited moderate to high catalytic activities and gave C-H activation selectively at the C5-position of 1methylpyrrole- 2-carboxaldehyde. Both electron-donating and electron-withdrawing substituents were well tolerated with catalytic systems based on these complexes, even non-activated aryl chlorides such as chlorobenzene or 4-chlorotoluene were coupled with pyrrole in moderate yields. (C) 2017 Elsevier B.V. All rights reserved.