Highly Active, Well‐Defined (Cyclopentadiene)(N‐heterocyclic carbene)palladium Chloride Complexes for Room‐Temperature Suzuki–Miyaura and Buchwald–Hartwig Cross‐Coupling Reactions of Aryl Chlorides and Deboronation Homocoupling of Arylboronic Acids

Abstract

A new class of well-defined N-heterocyclic carbene (NHC)-(cyclopentadiene)palladium chloride complexes such as CpPdA C H T U N G T R E N N U N G (NHC)Cl wasw synthesized from the readily available starting NHC-palladi-A C H T U N G T R E N N U N G um(II) chloride dimers. These air-stable, coordinatively saturated NHC-Pd complexes bearing the cyclopentadiene (Cp) unit exhibit high catalytic activity in the room temperature Suzuki-Miyaura and Buchwald-Hartwig cross-coupling reactions involving unactive aryl chlorides as the substrates. In addition, they are found to be extremely efficient catalysts in the deboronation homocoupling of arylboronic acids at room temperature.

Air-stable CpPd(NHC)Cl (NHC = N-heterocyclic carbene) complexes as highly active precatalysts for Kumada–Tamao–Corriu coupling of aryl and heteroaryl chlorides

“…In sharp contrast, for the larger sterically encumbered IPr and SIPr ligand, CpPd(NHC)Cl 1b and 1d under the same conditions exhibited obviously less effective which provided the yields of only 35 and 45%, respectively. The relationships between the sterically constrained Pd centre and catalytic activities we observed here are just opposite to the previous results in the PEPPSI catalysts [25] and SuzukieMiyaura coupling reactions [18], whereas the NHCePd catalysts with the larger sterically bulky substituents on the imidazole nitrogens showed higher efficacy. We ascribed the contrary to the existence of the Cp ring ligands.…”

“…Finally, the resulting mixture was directly subjected to flash column chromatography to give the desired CpPd(NHC)Cl complexes 1aed as a green crystal. Spectroscopic data for them are identical with literature [18]. …”

“…The new complexes CpPd(NHC)Cl 1 were initially prepared by treating the key intermediate NHCePdCl 2 dimers at room temperature with two equivalent, freshly prepared CpNa (CpNa ¼ sodium cyclopentadienylide) in a solution of tetrahydrofuran (THF), and the desired Cp-containing NHCePd complexes, CpPd(IMes)Cl 1a, CpPd(IPr)Cl 1b, CpPd(SIMes)Cl 1c, and CpPd(SIPr)Cl 1d, were conveniently obtained in almost quantitative yield [18]. The starting NHCePdCl 2 dimers could be readily prepared either from PdCl 2 (PhCN) 2 2 through the direct displacement of nitrile ligands with the free carbenes [19], or from [Pd (h 3 -allyl)Cl] 2 dimer via a two-step sequence with high overall yields [20].…”

“…Recently, we have synthesized a class of well-defined Cp-containing NHCePd complexes, i.e. CpPd(NHC)Cl 1, which exhibit highly catalytic activity in room temperature SuzukieMiyaura and BuchwaldeHartwig cross-coupling reactions involving unactive aryl chlorides as the substrates [18]. Additionally, they are found to be extremely efficient catalysts in the deboronation homocoupling of arylboronic acids at room temperature.…”

Facile synthesis of porous copper nanobelts and their catalytic performance

“…Palladium-based catalysts are frequently used for the coupling of arylboronic acids to obtain important intermediates for fuctional materials and natural products [49][50][51][52][53]. In view of the cost of palladium, the inexpensive catalysts to promote the coupling of arylboronic acids are desired.…”