Search

Nucleophilic substitution of [(η5‐cyclopentadienyl)(η6‐chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η5‐1,2,3,4,5‐pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]+ substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X‐ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]+ unit at the NHC ligand. [ABSTRACT FROM AUTHOR]

Chiral magnetic materials are proposed for applications in second‐order non‐linear optics, magneto‐chiral dichroism, among others. Recently, we have reported a set of tetra‐nuclear Fe(II) grid complex conformers with general formula C/S‐[Fe4L4]8+ (L: 2,6‐bis(6‐(pyrazol‐1‐yl)pyridin‐2‐yl)‐1,5‐dihydrobenzo[1,2‐d : 4,5‐d′]diimidazole). In the grid complexes, isomerism emerges from tautomerism and conformational isomerism of the ligand L, and the S‐type grid complex is chiral, which originates from different non‐centrosymmetric spatial organization of the trans type ligand around the Fe(II) center. However, the selective preparation of an enantiomerically pure grid complex in a controlled manner is difficult due to spontaneous self‐assembly. To achieve the pre‐synthesis programmable resolution of Fe(II) grid complexes, we designed and synthesized two novel intrinsically chiral ligands by appending chiral moieties to the parent ligand. The complexation of these chiral ligands with Fe(II) salt resulted in the formation of enantiomerically pure Fe(II) grid complexes, as unambiguously elucidated by CD and XRD studies. The enantiomeric complexes exhibited similar gradual and half‐complete thermal and photo‐induced SCO characteristics. The good agreement between the experimentally obtained and calculated CD spectra further supports the enantiomeric purity of the complexes and even the magnetic studies. The chiral resolution of Fe(II)‐ [2×2] grid complexes reported in this study, for the first time, might enable the fabrication of magneto‐chiral molecular devices. [ABSTRACT FROM AUTHOR]

Organocatalytic asymmetric transformation of common aromatic heterocycles via in situ formation of highly reactive dearomatized ortho‐quinodimethane diene species and subsequent [4+2] cycloaddition with suitable dienophiles has become a powerful tool to enter cyclohexane‐fused heterocycles. Most of these reactions were previously applied to benzo‐fused heterocycles or poorly aromatic rings. Herein, we disclose how previously intractable aromatic imidazole rings, equipped with removable methylidene malononitrile activating handle, could be involved as competent cycloaddends with β‐aryl enals in efficient eliminative [4+2] cycloadditions under mild organocatalytic conditions. This method allowed the efficient and direct preparation of scantly represented 6,7‐dihydrobenzo[d]imidazoles with optimal enantio‐ and regioselectivities. Post‐cycloaddition chemical editing provided imidazole‐based ring systems with diverse oxidation state and functional groups. [ABSTRACT FROM AUTHOR]

Recently, the fields of organic light‐emitting diodes (OLEDs) and light‐emitting electrochemical cells (LECs) have improved tremendously with regard to tunable emission, efficiency, brightness, and thermal stability. Imidazole derivatives are excellent deep blue‐green light‐emitting layers in the OLED or LEC devices. This Review summarizes the major breakthroughs of various electroluminescence (EL) layers with imidazole‐containing organic or organometallic derivatives, the molecular design principles, and their light‐emitting performances as effective EL materials. The highly tunable chemical structures and flexible molecular design strategies of imidazole‐based compounds are advantages that provide great opportunities for researchers. They can provide a good basis for the design and development of new EL materials with narrower emission and higher efficiency. Moreover, imidazole compounds have demonstrated breakthrough performances in thermally activated delayed fluorescence (TADF) properties where triplet excitons are utilized to inhibit anti‐intersystem quenching, showing great promise in breaking the theoretical external quantum efficiencies (EQE) limits in traditional fluorescent devices. [ABSTRACT FROM AUTHOR]

Three donor‐acceptor compounds based on the imidazo‐pyrazine‐5,6‐dicarbonitrile (IPDC) acceptor were synthesized. The IPDC emitters exhibit blue to near‐infrared (NIR) emission with up to 54 % photoluminescent quantum yield. 9,9‐Dimethyl‐9,10‐dihydroacridine (ACR), phenoxazine (POX), and phenothiazine (PTZ) served as electron donors. IPDC‐POX displayed NIR emission in toluene solution, while showing room‐temperature phosphorescence in the solid state. IPDC‐ACR exhibited yellow thermally activated delayed fluorescence. Interestingly, dual‐emissive behavior as well as excitation‐dependent thermally activated delayed fluorescence (TADF) was found for IPDC‐PTZ, arising from the two conformers of phenothiazine derivatives. Overall, this work describes a novel strong electron acceptor from the fusion of imidazole, pyrazine, and nitrile functional groups into one conjugated heterocycle for materials exhibiting NIR emission, TADF, and/or room‐temperature phosphorescence (RTP). [ABSTRACT FROM AUTHOR]

Considering the difficulties associated with the conventional 'trial and error' method for a complete analysis of a giant molecular space, we took the aid of computational pathway (DFT) in screening a large space search of 780 (12×13×5) molecules to search for a host for the blue emitter. The selection process was completed in three Tiers with the conditions of highest theoretical triplet energy (>2.81 eV), aligned HOMO/LUMO levels w.r.t blue dopant (FIrpic), and position of substituents to meet the optimal requirements as host materials. Tier 1 screened twelve different imidazole heterocycle derivatives as base space groups which resulted in the selection of 4,5‐diphenyl‐1H‐imidazole. Tier 2 process converged the search to mCN‐CZ having the highest triplet energy and appropriate HOMO/LUMO level relative to FIrpic and ETL. Further, the carbazole of mCN‐CZ was replaced with different aromatic hydrocarbons to find the other best compound in terms of triplet energy and HOMO/LUMO. Tier 3 resulted in another promising candidate (mCN‐FL) as possible host materials. The band alignment with guest predicted mCN‐FL and mCN‐CZ to have optimal device performances compared to CZ‐CZ and the experimentally observed device performance was in accordance with virtual screening results when TAPC was utilized as the hole transporter. The device results of mCN‐CZ and mCN‐FL were better than the reference host TCTA. The obtained results thus proved that a virtual screening process will be a useful tool for synthetic chemists in designing task‐specific materials. [ABSTRACT FROM AUTHOR]

A new H‐bonded crystal [RuIII(Him)3(Im)3] with three imidazole (Him) and three imidazolate (Im−) groups was prepared to obtain a higher‐temperature proton conductor than a Nafion membrane with water driving. The crystal is constructed by complementary N−H⋅⋅⋅N H‐bonds between the RuIII complexes and has a rare Icy‐c* cubic network topology with a twofold interpenetration without crystal anisotropy. The crystals show a proton conductivity of 3.08×10−5 S cm−1 at 450 K and a faster conductivity than those formed by only HIms. The high proton conductivity is attributed to not only molecular rotations and hopping motions of HIm frameworks that are activated at ∼113 K, but also isotropic whole‐molecule rotation of [RuIII(Him)3(Im)3] at temperatures greater than 420 K. The latter rotation was confirmed by solid‐state 2H NMR spectroscopy; probable proton conduction routes were predicted and theoretically considered. [ABSTRACT FROM AUTHOR]

The 1‐methyl‐3‐(tricyanoborane)imidazolin‐2‐ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3‐methylimidazole adduct 1. Regarding charge and stereo‐electronic properties, anion 2 closes the gap between well‐known neutral NHCs and the ditopic dianionic NHC, the 1,3‐bis(tricyanoborane)imidazolin‐2‐ylidenate dianion (IIb). The influence of the number of N‐bonded tricyanoborane moieties on the σ‐donating and π‐accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3‐dimethylimidazolin‐2‐ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)4] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (%Vbur) and σ‐donor and π‐acceptor abilities of NHCs can be effectively fine‐tuned via the number of tricyanoborane substituents. [ABSTRACT FROM AUTHOR]

The first RhI‐catalyzed, directed decarbonylative C2−H alkenylation of imidazoles with readily available alkenyl carboxylic acids is reported. The reaction proceeds in a highly regio‐ and stereoselective manner, providing efficient access to C2‐alkenylated imidazoles that are generally inaccessible by known C−H alkenylation methods. This transformation accommodates a wide range of alkenyl carboxylic acids, including challenging conjugated polyene carboxylic acids, and diversely decorated imidazoles with high functional group compatibility. The presence of a removable pyrimidine directing group and the use of a bidentate phosphine ligand are pivotal to the success of the catalytic reaction. This process is also suitable for benzimidazoles. Importantly, the scalability and diversification of the products highlight the potential of this protocol in practical applications. Detailed experimental and computational studies provide important insights into the underlying reaction mechanism. [ABSTRACT FROM AUTHOR]

In this Concept article we provide a brief overview of the design and preparation of N‐heterocyclic carbenes carrying weakly coordinating anions (WCA‐NHCs). The anionic charge in these ligand systems is located on an exocyclic group, for example, B(C6F5)3, tethered to the backbone of the imidazole ring, thus resembling a weakly coordinating moiety. With the general guiding principle behind the application of WCA‐NHCs being the conversion of otherwise cationic NHC complexes into their overall neutral congeners, numerous transition metal as well as main group element complexes were isolated during the last decade, which are summarized herein. [ABSTRACT FROM AUTHOR]

Fused-imidazoles, Groebke-Blackburn-Bienaymé (GBB) reaction, Isocyanide Chemistry, Multicomponent reactions, [2.2]Paracyclophane Cover Feature: Diversity-Oriented Synthesis of [2.2]Paracyclophane-derived Fused Imidazo[1,2-a]heterocycles by Groebke-Blackburn-Bienaymé Reaction: Accessing Cyclophanyl Imidazole Ligands Library (Chem. Eur. J. 3/2022) Keywords: Fused-imidazoles; Groebke-Blackburn-Bienaymé (GBB) reaction; Isocyanide Chemistry; Multicomponent reactions; [2.2]Paracyclophane EN Fused-imidazoles Groebke-Blackburn-Bienaymé (GBB) reaction Isocyanide Chemistry Multicomponent reactions [2.2]Paracyclophane 1 1 1 01/18/22 20220113 NES 220113 B The Groebke-Blackburn-Bienaymé three-component reaction b (GBB-3CR) has contributed enormously to the progress of organic synthesis, medicinal chemistry, and materials science. [Extracted from the article]

This report describes the synthesis of a [2.2]paracyclophane‐derived annulated 3‐amino‐imidazole ligand library through a Groebke‐Blackburn‐Bienaymé three‐component reaction (GBB‐3CR) approach employing formyl‐cyclophanes in combination with diverse aliphatic and aromatic isocyanides and heteroaromatic amidines. The GBB‐3CR process gives access to skeletally‐diverse cyclophanyl imidazole ligands, namely 3‐amino‐imidazo[1,2‐a]pyridines and imidazo[1,2‐a]pyrazines. Additionally, a one‐pot protocol for the GBB‐3CR by an in situ generation of cyclophanyl isocyanide is demonstrated. The products were analyzed by detailed spectroscopic techniques, and the cyclophanyl imidazo[1,2‐a]pyridine was confirmed unambiguously by single‐crystal X‐Ray crystallography. The cyclophanyl imidazole ligands can be readily transformed to showcase their useful utility in preparing N,C‐palladacycles through regioselective ortho‐palladation. [ABSTRACT FROM AUTHOR]

In this work, we first designed and synthesized tetraphenylene‐fused aryl‐imidazole derivatives TM‐1–4 via regulation of molecular structure, which were consisted of 1H‐imidazo[4,5‐f][1,10]phenanthroline, 1H‐phenanthro[9,10‐d]imidazole, 4,5‐diphenyl‐1H‐imidazole, 3,3′‐(1H‐imidazole‐4,5‐diyl)dipyridine moieties and AIE‐active tetraphenylethene units, respectively. The results illustrated that TM‐1–4 exhibited clear AIE characteristics. Meanwhile, TM‐2 and TM‐3 show excellent solid emission properties (ΦTM‐2=13.73 % and ΦTM‐3=36.21 %), whereas TM‐1 and TM‐4 exhibit the opposite properties (ΦTM‐1=1.48 % and ΦTM‐4=4.83 %). The multiple rotors (pyridine and benzene ring) causes twisted conformations of the molecule that prevents π‐π stacking and enhances solid emission(ΦTM‐2<ΦTM‐3, ΦTM‐1<ΦTM‐4). Significantly, TM‐2 and TM‐3 also exhibited reversible mechanochromic behavior (Emission red shifts: ΔλTM‐2=43 nm and ΔλTM‐3=41 nm) with color changes between blue and green emissions. The powder X‐ray diffraction (PXRD) suggested the disordered state of ground sample could be readily returned to an ordered crystalline. Therefore, the mechanochromisms of TM‐2 and TM‐3 are ascribable to the phase transformation between crystal and amorphous structure. The single crystal X‐ray analysis of TM‐2 reveals a twisted conformation for TPE moiety and the absence of π‐π intermolecular stacking. These excellent optical properties of TM‐2 and TM‐3 make them potentially applications in mechanochromic materials and imaging agents. [ABSTRACT FROM AUTHOR]

A series of dicyano‐imidazole‐based molecules with thermally activated delayed fluorescence (TADF) properties were synthesized to obtain pure blue‐emitting organic light‐emitting diodes (OLEDs). The targeted molecules used dicyano‐imidazole with a short‐conjugated system as the electron acceptor to strong intermolecular π‐π interactions, and provide a relatively shallow energy level of the lowest unoccupied molecular orbital (LUMO). The cyano group was selected to improve imidazole as an electron acceptor due to its prominent electron‐transporting characteristics. Four different electron donors, that is, 9,9‐dimethyl‐9,10‐dihydroacridine (DMAC), 10H‐spiro(acridine‐9,9'‐fluoren) (SPAC), and 9,9‐diphenyl‐9,10‐dihydroacridine (DPAC), were used to alternate the highest occupied molecular orbital (HOMO) energy level to tune the emission color further. The crowded molecular structure in space makes the electron donor and acceptor almost orthogonal, reducing the energy gap (ΔEST) between the first excited singlet (S1) and the triplet (T1) states and introducing significant TADF property. The efficiencies of the blue‐emissive devices with imM‐SPAC and imM‐DMAC obtained in this work are the highest among the reported imidazole‐based TADF‐OLEDs, which are 13.8 % and 13.4 %, respectively. Both of Commission Internationale de l′Eclairage (CIE) coordinates are close to the saturated blue region at (0.17, 0.18) and (0.16, 0.19), respectively. Combining these tailor‐made TADF compounds with specific device architectures, electroluminescent (EL) emission from sky‐blue to deep‐blue could be achieved, proving their great potential in EL applications. [ABSTRACT FROM AUTHOR]