Ruthenium(η⁶,η¹-arene-CH₂-NHC) Catalysts for Direct Arylation of 2-Phenylpyridine with (Hetero)Aryl Chlorides in Water.

Nazan Kaloğlu,Nevin Gürbüz,Hakan Arslan,Pierre Dixneuf,İsmail Özdemir

doi:10.3390/molecules23030647

Abstract

A series of new benzimidazolium halides were synthesized in good yields as unsymmetrical N-heterocyclic carbene (NHC) precursors containing the N–CH2–arene group. The benzimidazolium halides were readily converted into ruthenium(II)–NHC complexes with the general formula [RuCl2(η6,η1–arene–CH2–NHC)]. The structures of all new compounds were characterized by 1H NMR (Nuclear Magnetic Resonance), 13C NMR, FT-IR (Fourier Transform Infrared) spectroscopy and elemental analysis techniques. The single crystal structure of one benzimidazole ruthenium complex, 2b, was determined. The complex is best thought of as containing an octahedrally coordinated Ru center with the arene residue occupying three sites, the remaining sites being occupied by a (carbene)C–Ru bond and two Ru–Cl bonds. The catalytic activity of [RuCl2(η6,η1–arene–CH2–NHC)] complexes was evaluated in the direct (hetero)arylation of 2-phenylpyridine with (hetero)aryl chlorides in water as the nontoxic reaction medium. These results show that catalysts 2a and 2b were the best for monoarylation with simple phenyl and tolyl chlorides. For functional aryl chlorides, 2d, 2e, and 2c appeared to be the most efficient.

Highlights

The prevalence and importance of biaryl compounds in natural products, advanced materials, and pharmaceuticals have made the preparation of C(sp2 )–C(sp2 ) bond among the core interests of organic synthesis [1]
We described the synthesis and characterization of new unsymmetrical benzimidazolium connection, several ruthenium-catalyzed direct arylations in water or diethylcarbonate (DEC) as green halides (1a–e) and five new ruthenium(II) complexes of the general formula [RuCl2(η,6η1–1solvent using an additive were reported by Dixneuf’s group arylmethyl–3–butylbenzimidazol–2–ylidene)]
Results and Discussion complexes with KOAc partner were evaluated as catalyst precursors for the direct mono orthoarylation of 2-phenylpyridinearyl chlorides in water, without the need of surfactant

Summary

Introduction

The prevalence and importance of biaryl compounds in natural products, advanced materials, and pharmaceuticals have made the preparation of C(sp2 )–C(sp2 ) bond among the core interests of organic synthesis [1]. Traditional transition metal-catalyzed biaryl cross-coupling reactions, which generally employ aryl halides and organometallics as coupling partners, have served as the most common methods for constructing biaryl unions (Figure 1a) [8,9]. Despite the large scope of reactions and opportunities opened by these traditional methodologies, the starting organometallic reagents are often not commercially available. The amount of byproducts produced, whether in the synthesis of the organometallic reagent or during the coupling step itself, remains significant. There has been much interest in transition metal-catalyzed direct cross-coupling C–C bond formation of aromatic compounds with aryl halides as electrophilic

Methods

Results

Conclusion