Synthesis and Structural Characterization of Nickel(II) Complexes Supported by Pyridine-Functionalized N-Heterocyclic Carbene Ligands and Their Catalytic Acitivities for Suzuki Coupling

Abstract

The imidazolium salts bis(N-pyridylimidazoliumyl)methane hexafluorophosphate ([H2L1](PF6)2) and bis(N-picolyl)benzimidazoliumyl)methane hexafluorophosphate ([H2L2](PF6)2) as the precursors of potentially tetradentate NHC ligands were synthesized in 63–98% yields. Their reactions with Ag2O afforded silver−NHC complexes [Ag3(L1)2(CH3CN)2](PF6)3 (1) and [Ag4(L2)2(CH3CN)2](PF6)4 (2), respectively. Further reactions of these silver complexes as carbene transfer reagents yielded square-planar nickel(II) complexes [NiL1](PF6)2 (3) and [NiL2](PF6)2 (4), respectively. These silver and nickel complexes have been fully characterized by 1H and 13C NMR spectroscopy and X-ray diffraction analysis. Both 3 and 4 catalyzed Suzuki-type cross-coupling of aryl chlorides and bromides containing electron-withdrawing and electron-donating substituents. Complex 3 is a more active catalyst under mild conditions.

Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene–Isoquinoline Complex

“…The Ni-N and Ni-C bond lengths are within the typical range for these types of donors. 76,[102][103][104] Evaluation of Nickel N-Heterocyclic Carbene-Amine Complexes for Electrocatalytic CO 2 Reduction. The electrochemical behaviors of complexes 1c-4c were interrogated by cyclic voltammetry.…”

“…Literature methods were used to synthesize Ni(DME)Cl 2 , 111 2-benzimidazolylmethylpyridine (4a), 102 and [Ni( Me bbimpic)](PF 6 ) 2 (5c). 102 NMR spectra were recorded using Bruker spectrometers operating at 300, 400, or 500 MHz as noted. Chemical shifts are reported in ppm relative to residual protiated solvent; coupling constants are reported in Hz.…”

Formation of Homoleptic Tetracarbene versus cis‐Chelating Dicarbene Complexes of Nickel(II) and Applications in Kumada–Corriu Couplings

“…In particular, Pd-NHC complexes have been widely used in the making of C-C bonds often by employing the Mizoroki-Heck and Suzuki-Miyaura coupling reactions. Similarly, some Ni-NHC complexes have shown to be catalytically active for a wide range of reactions such as SuzukiMiyaura [21,22] and Kumada-Corriu [23][24][25][26][27][28] couplings, olefin dimerization [3] and polymerization, [29][30][31][32] C-C bond activation of biphenylene, [33] transfer hydrogenation of imines, [34] and amination [35] and dehalogenation [36] of aryl halides. Notably, most of these nickel complexes contain NHC ligands that are derived either from imidazole or imidazoline precursors, whereas the catalytic activity of Ni IIbenzimidazolin-2-ylidenes have rarely been studied.…”

Synthesis of Silver(I) and Gold(I) Complexes with Cyclic Tetra‐ and Hexacarbene Ligands

“…The AgÀC bond lengths are comparable (Ag À C1 2.077(11) , Ag À C15 2.057(11) ) and fall in the range previously observed for similar silver-dicarbene complexes. [9][10][11] The carbene ligand in [4] 3 + can be transferred to gold(I) to yield the complex [5]A C H T U N G T R E N N U N G (PF 6 ) 3 (Scheme 1). Similarly to the dinuclear silver and gold complexes [2] 2 + and [3] 2 + the monoA C H T U N G T R E N N U N G nuclear gold complex [5] 3 + leads to better resolved NMR spectra than observed for the silver complex [4] 3 + .…”