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Bis-imidazolium salts bearing N-2-fluorobenzyl substituents and methylene, ethylene, or propylene linkers ([H2-4]Br2–[H2-6]Br2) and the bis-imidazolium salt [H2-8]Br2 featuring an ethylene linker a...

Isolation of E-1,2-bis(4-bromophenyl)-1,2-diphenyl-ethylene from the E/Z isomer mixture obtained by a McMurry coupling reaction and reaction of this isomer with imidazole followed by N-alkylation with nBuBr and anion exchange yielded the bisimidazolium tetraphenylethylene (TPE) derivative H2-E-1(PF6)2. The reaction of H2-E-1(PF6)2 with Ag2O yielded the di-nuclear metallarectangle [Ag2(E-1)2](PF6)2 where the two bis-NHC donors E-1 bridge two silver atoms. Irradiation of [Ag2(E-1)2](PF6)2 leads to E/Z isomerization of the di-NHC ligand and formation of Z-1 in the mononuclear complex [Ag(Z-1)]PF6. Demetallation of the di-NHC ligand with NH4Cl/NH4PF6 yielded bisimidazolium salt H2-Z-1(PF6)2. The unique isomerization of the E-TPE derivative into its Z-isomer via metal complex formation/irradiation/demetallation cannot be achieved by irradiation of the individual imidazolium salt. The emissive properties of the TPE complexes [Ag2(E-1)2](PF6)2 and [Ag(Z-1)]PF6 have been investigated.

Reaction of 8-bromo-7-ethyl-3-methylxanthine 1 with zerovalent group 10 metal complexes gave via an oxidative addition of the C–Br bond the neutral complexes trans-[2] (M = Pd) and trans-[3] (M = Pt) bearing a theobromine-derived azolato ligand. While the oxidative addition to [Pd0(PPh3)4] gave exclusively trans-[2], the reaction with the more substitution-inert [Pt0(PPh3)4] yielded after 1 day the kinetic product cis-[3], which was converted under heating for a total of 3 days completely into the thermodynamically more stable complex trans-[3]. Treatment of trans-[2], trans-[3] or the mixture of cis-/trans-[3] with the proton source HBF4⋅Et2O led to complexes trans-[4]BF4, trans-[5]BF4 and a mixture of cis/trans-[5]BF4 with retention of the original ratio of cis to trans, respectively. The molecular structures of the azolato complexes trans-[2] and trans-[3] and of the theobromine derived pNHC complexes trans-[4]BF4 and trans-[5]BF4 have been determined by X-ray diffraction studies.

The diastereoselective synthesis of sulfonylated indolines is reported. A palladium-catalyzed dearomative sulfination of (aza)indole-tethered aryl iodides generates reactive benzylic sulfinates. These intermediates react with electrophiles in a one-pot, two-step process to generate sulfonylated products in good yields and excellent diastereoselectivity. This three-component sequence demonstrates good scalability and can be applied toward the synthesis of sulfonamides. Additionally, further derivatizations of aryl iodide containing products furnish spiro- and alkynylated indoline products.

CAAC precursors 2‐chloro‐3,3‐dimethylindole 1 and 2‐chloro‐1‐ethyl‐3,3‐dimethylindolium tetrafluoroborate 2BF4 have been prepared and oxidatively added to [M(PPh3)4] (M=Pd, Pt). Salt 2BF4 reacts with [Pd(PPh3)4] in toluene at 25 °C over 4 days to yield complex cis‐[3]BF4 featuring an N‐ethyl substituted CAAC, two cis‐arranged phosphines and a chloro ligand. Compound trans‐[3]BF4 was obtained from the same reaction at 80 °C over 1 day. Salt 2BF4 reacts with [Pt(PPh3)4] to give cis‐[4]BF4. The neutral indole derivative 1 adds oxidatively to [Pt(PPh3)4] to give trans‐[5] featuring a CAAC ligand with an unsubstituted ring‐nitrogen atom. This nitrogen atom has been protonated with py⋅HBF4 to give trans‐[6]BF4 bearing a protic CAAC ligand. The PdII complex trans‐[7]BF4 bearing a protic CAAC ligand was obtained in a one‐pot reaction from 1 and [Pd(PPh3)4] in the presence of py⋅HBF4., Cyclic (alkyl)(amino)carbene (CAAC) precursor salt 2BF4 reacts with [M(PPh3)4] (M=Pd, Pt) to give cis/trans‐[3]BF4 and cis‐[4]BF4, in which the CAAC ligand bears an unusual N‐alkyl substituent. trans‐[5] has a unique anionic CAAC ligand with an unsubstituted ring‐nitrogen atom which can be protonated to give trans‐[6]BF4 bearing a protic CAAC (pCAAC) ligand.

Various 8-halogenotheophyllines (halogen = Cl, Br, I) were selectively C8 metalated by an oxidative addition of the C8–halogen bond to [Pd(PPh3)4] to give the PdII azolato complexes [1]–[3]. The co...

The N9-imidazolium-substituted adenine derivative H-1Cl reacts with [MCl2(Cp*)]2 (M = Rh, Ir) in acetonitrile at 75 °C with formation of the CNHC^N3adenine chelate complexes [3]Cl and [4]Cl, respec...

Bis-NHC precursors composed of an azolium and a 2-halogenoazole group connected by different linkers have been site-selectively metallated to give heterobimetallic complexes from a single-frame bis-NHC ligand. The azolium group reacts with a base and oxidized metal centers to give NHC complexes with no participation of the halogenoazole, while the halogenoazole reacts in an oxidative addition with low-valent transition metals to give azolato complexes with no participation of the azolium group.

N-Heterocyclic carbenes (NHCs) are commonly prepared by deprotonation of azolium salts using strong anionic bases. This reaction is often unselective, yielding alkali metal NHC complexes or dimerized NHCs. Alternatively, free NHCs are obtained by the dechlorination of 2-chloroazolium salts using electron-rich phosphines. PPh

The reaction between an angular bis-imidazolidinium salt and [AuCl(SMe)2] allowed the preparation of a discrete digold complex, with a rigid angular bridging bis-imidazolindiylidene ligand. This complex reacts with a diethynylcarbazole to afford a tetragold cyclophane that contains two bis-imidazolindiylidenes and two carbazolyl-diethynyl ligands. Both the dimetallic and the tetrametallic complexes have been characterized by spectroscopic techniques and by singlecrystal X-ray diffraction. Due to the geometric constraints of the ligands, the cyclophane deviates from the expected planarity and shows a twisted structure. The work demonstrates that the rigid angular di-NHC ligand is a suitable scaffold for the reliable construction of organometallic-based metallosupramolecular assemblies.

Tuning the surface-embellishing ligands of metal nanoparticles (NPs) is a powerful strategy to modulate their morphology and surface electronic and functional features, impacting their catalytic activity and selectivity. In this work, we report the design and synthesis of a polytriazolium organic cage PIC-T, capable of stabilizing PdNPs within its discrete cavity. The obtained material (denoted Pd@PCC-T) is highly durable and monodispersed with narrow particle-size distribution of 2.06 ± 0.02 nm, exhibiting excellent catalytic performance and recyclability in the Sonogashira coupling and tandem reaction to synthesize benzofuran derivatives. Further investigation indicates that the modulation of N-heterocyclic carbene sites embedded in the organic cage has an impact on NPs’ catalytic efficiency, thus providing a novel methodology to design superior NP catalysts.

Metallosupramolecular poly-NHC-metal assemblies were prepared from trigonal hexakis (H6 -1 a(PF6 )6 and H6 -1 b(PF6 )6 ) or nonakis (H9 -3(BF4 )9 ) imidazolium salts and Ag2 O. Complexes [Ag6 (1 a)2 ](PF6 )6 and [Ag6 (1 b)2 ](PF6 )6 are built from six Ag+ ions sandwiched between two trigonal hexacarbene ligands with an inner and an outer NHC donor in each of the three ligand arms. The metal atoms are arranged in two triangles. The hexakis-NHC ligands bear cinnamic ester groups at the outlying NHC donors, used in postsynthetic [2+2] cycloaddition reactions linking two hexakis-NHC ligands by three cyclobutane units to give complexes [Ag6 (2 a)](PF6 )6 and [Ag6 (2 b)](PF6 )6 bearing a dodecacarbene ligand. From the related nonakisimidazolium salt H9 -3(BF4 )9 , complex [Ag9 (4)](BF4 )9 bearing an octadecacarbene ligand was obtained. Removal of the template metals yielded very large, stable, polyimidazolium cations with 12 or 18 internal imidazolium groups.

Neutral 2-chlorobenzimidazole (1) and its derivatives 8-chlorotheophylline (2) and 8-bromotheophylline (3) undergo at low temperature in THF an N–H polar oxidative addition reaction with Ni0 to giv...

The development of highly emissive dinuclear AgI or AuI complexes [M2 L](PF6 )2 (L=2 a, 2 b; M=Ag, Au) derived from tetraphenylethylene (TPE)-based tetrabenzimidazolin-2-ylidene ligands is reported. The new complexes exhibit a remarkable fluorescence enhancement compared to their parent benzimidazolium salts. The quantum yield (ΦF ) value for salt H4 -2 a(PF6 )4 in dilute solution (c=10-5 m) was found to be less than 1 %, whereas its metal complexes show ΦF values up to 55 % at similar solution concentration. This observation can be attributed to the rigidification of the TPE skeleton upon metalation resulting in a restriction of the intramolecular rotation of the phenyl groups. Functionalization of the complexes [M2 2 b](PF6 )2 (M=Ag, Au) with terminal coumarin groups and subsequent photoirradiation yielded the complexes [M2 3 b](PF6 )2 (M=Ag, Au) bearing a new type of ligand with an unaffected TPE moiety.

Preparation of iron(0) pNHC complexes by oxidative addition of N-phosphine-tethered azoles to [Fe3(CO)12] is described. Phosphine-tethered imidazoles 1 and 2 react with [Fe3(CO)12] to give mononucl...

The directed C–H activation at the C8 position of N-donor tethered theophylline with iridium(III) and rhodium(III) is presented. The donor strength of the N-tethered donor group has been varied. Proligands bearing a strongly donating imidazolin-2-ylidene or the weaker donating pyridine group were both metalated under similar conditions, suggesting that the electron density at the metal center does not play a significant role in the C–H activation step, which was concluded to proceed via a carboxylate-assisted route. The synthesis and characterization of iridium(III) and rhodium(III) complexes bearing chelating CNHC^Cazolato ligands (M = Ir: [4], M = Rh: [5]) and Npyridine^Cazolato ligands (M = Ir: [7], M = Rh: [8]) are reported. In addition, the NHC complexes which are the precursors to the CNHC^Cazolato complexes (M = Ir: [2], M = Rh: [3]) were isolated and characterized.

Reaction of in situ lithiated N-methylimidazole or 1,5,6-trimethylbenzimidazole with [M(cod)(μ-Cl)]2 (M = Rh, Ir) led to the exclusive formation of the homodinuclear head-to-head complexes [2]–[5], where the metal centers are bridged by two C,N-coordinated azolato ligands. The two metal centers are each coordinated by one cod ligand and either two carbon or two nitrogen donors of the azolato ligands. Access to a heterodinuclear Ir/Rh complex [6] was achieved via the lithiated iridium complex [7] and addition of an equimolar amount of [Rh(cod)(μ-Cl)]2. Deprotonation of caffeine with lithium diisopropylamide and addition of [M(cod)(μ-Cl)]2 (M = Rh, Ir) led to mixtures of the head-to-head (M = Ir: [8H–H]; M = Rh: [9H–H]) and head-to-tail isomers (M = Ir: [8H–T]; M = Rh: [9H–T]) of the homodinuclear complexes. The molecular structures of the homo- and heterodinuclear complexes [3], [5]·2C6H5F, [6]·2C6H5F, and [9H–T]·C4H8O have been determined by X-ray diffraction studies.

A bidentate triazolinylidene-pyrazole chelate ligand was metalated with [IrCp*Cl2]2 to give C,N-chelate complex [4]I. The N1-metalated pyrazole subsequently underwent a rollover metalation to give the complex with C5,C4-metalated pyrazolato ligand [5]. The reactivity of [5] toward insertion and protonation was investigated. Complex [5] was found to react with CO to give IrIII carbonyl complex [6]I, which subsequently reacted under migratory CO insertion into the Ir–C(pyrazolato) bond to give [7]. The reaction of [5] with the terminal alkyne methyl propiolate yielded 1,2 insertion product [8], featuring a 7-membered C,C-chelate ring.

EgeUn###, A series of monometallic complexes obtained by metalation of the phenanthrolin donor in 1,3-dibutyl-1H-imidazol[4,5-f][1,10]phenanthrolin}ium hexafluorophospate 1 (M = Pd 2, Ru 3, Ir 4) have been prepared. Subsequently, the imidazolium moiety of complexes 2-4 was metalated with M', leading to the heterobimetallic phenanthroline/NHC complexes (M/M' = Pd/Rh 5, Pd/Ir 6, Pd/Ru 7, Ru/Pd 8, Ir/Pd 9) and the homobimetallic complex (M/M' = Ir/Ir 10). The new complexes were characterized by elemental analysis, FTIR, UV-vis, and NMR spectroscopy. The molecular structures of the heterobimetallic complexes 5 and 6 were determined by X-ray diffraction studies. The catalytic activity of the heterobimetallic complexes 5-9 were tested in selected tandem reactions (dehalogenation/transfer hydrogenation and Suzuki-Miyaura coupling/transfer hydrogenation). It was found that the M/M' heterobimetallic complexes display higher catalytic activities when compared to equimolar mixtures of the mononuclear complexes M and M', thus indicating that an increase in the number of metal atoms in one complex leads to an increased activity in the tandem reactions. © 2019 American Chemical Society., Türkiye Bilimsel ve Teknolojik Araştirma Kurumu: 111T398 · 2013 FEN 062, 2012-BIL-042, Financial support from Ege University (Project 2012-BIL-042;· 2013 FEN 062) and TÜBITAK (111T398) is gratefully acknowledged. The authors acknowledge Dokuz Eylül University for the use of the Oxford Rigaku Xcalibur Eos Diffractometer (purchased under University Research Grant No 2010.KB.FEN.13). F.E.H. thanks the Deutsche For-schungsgemeinschaft (SFB 858 and IRTG 2027).

Part of the “RSEQ-GEQO Prize Winners” Special Collection Three metallosupramolecular assemblies composed of two bis-NHCs and two silver atoms, [4](PF6)2, two tetra-NHCs and foursilver atoms, [7](PF6)4, and two tri-NHCs and three silver atoms[8](BF4)3, have been prepared. Assemblies [4](PF6)2and [7](PF6)4feature NHC ligands decorated with terminal olefin groups.Irradiation of [4](PF6)2yielded complex [5](PF6)2with twoterminal cyclobutane rings linking the two bis-NHC ligands.Liberation of the macrocyclic tetrakisimidazolium salt H4-6(PF6)4was achieved by reaction of [5](PF6)2with NH4Cl/NH4PF6. No [2+2] cycloaddition was observed upon irradiation of [7](PF6)4,apparently due to an unfavorable orientation of the olefingroups. Irradiation of complex [8](BF4)3with three internal pairsof olefin groups leads to [9](BF4)3as a mixture of two isomersthat differ on the relative orientation of the internal cyclobutanerings. Reaction of [9](BF4)3with NH4Cl/NH4BF4yields an isomermixture of the novel cage-line hexakisimidazolium salt H6-10(BF4)6 Three poly-imidazolium salts with appended olefins were obtained. Subsequent reaction with Ag2O enabled the preparation of the related poly-NHC-derived silver assemblies, which, depending on the relative orientation of the pendant olefins, underwent [2+2] cyclization of the olefins upon irradiation. The macrocyclic poly-imidazolium salts can be achieved by de-metallation using NH4Cl. Funding for open access charge: CRUE-Universitat Jaume I

The tetrakisimidazolium salt H4‐2(Br)4, featuring a central benzene linker and 1,2,4,5‐(nBu‐imidazolium‐Ph‐CH=CH‐) substituents reacts with Ag2O in the presence of AgBF4 to yield the tetranuclear, oktakis‐NHC assembly [3](BF4)4. Cation [3]4+ features four pairs of olefins from the two tetrakis‐NHC ligands perfectly arranged for a subsequent [2+2] cycloaddition. Irradiation of [3](BF4)4 with a high pressure Hg lamp connects the two tetra‐NHC ligands through four cyclobutane linkers to give compound [4](BF4)4. Removal of the template metals yields the novel oktakisimidazolium salt H8‐5(BF4)8. The tetrakisimidazolium salt H4‐2(BF4)4 and the oktakisimidazolium salt H8‐5(BF4)8 have been used as multivalent anion receptors and their anion binding properties towards six different anions have been compared., Polyimidazolium cations: The octakisimidazolium salt H8‐5(BF4)8 has been obtained from two equivalents of tetrakisimidazolium salt H4‐2(BF4)4 in a template synthesis via the tetranuclear octakis‐NHC complex [Ag4(2)2] followed by postsynthetic irradiation and formation of four cyclobutane linkers between the two tetra‐NHC ligands and demetallation. The binding of selected anions by H8‐5(BF4)4 has been studied.

8-Bromo-2′-deoxy-3′,5′-di-O-acetylguanosine (1), 8-bromo-2′,3′,5′-tri-O-acetylguanosine (2), 8-bromo-2′-deoxy-3′,5′-di-O-acetyladenosine (3), and 8-bromo-2′,3′,5′-tri-O-acetyladenosine (4) react with [Pd(PPh3)4] via a C8–Br oxidative addition to give the C8-palladated azolato complexes [5]–[8] featuring an unprotonated N7 ring nitrogen atom. The complexes feature diastereotopic trans-disposed triphenylphosphine ligands, which allowed the determination of 2JPP for complexes of the type trans-[PdL2(PPh3)2] (2JPP = 442 Hz for [7]). In addition, two complex molecules of [7] form a trans-Watson–Crick/Hoogsteen AA base pair in the solid state. N7-protonation of the guanosine-derived complexes [5] and [6] with HBF4·Et2O and of adenosine-derived complexes [7] and [8] using lutidinium triflate yields complexes [9]BF4 and [10]BF4 and complexes [11]OTf and [12]OTf bearing protic NH,NR-NHC ligands derived from guanosine and adenosine, respectively.

Complexes bearing protic N-heterocyclic carbenes (protic NHCs, pNHCs), defined as cyclic carbenes stabilized by two heteroatoms including at least one NH group, have been less explored in comparison to the conventional N,N'-disubstituted NHCs. The small and reactive NH group of the pNHCs differentiates this class of compounds from the classical NR,NR-NHCs with regard to their properties and reactivity. While the free pNHCs have so far eluded isolation due to isomerization to the azole tautomer, a significant number of transition-metal pNHC complexes have by now been prepared by a variety of methods. This article reviews the coordination chemistry of the pNHCs. Synthetic approaches toward complexes of pNHCs are first described, followed by a discussion of the properties and reactivity of pNHC complexes with emphasis on the Brønsted-acidic nature of the NH wingtip. Involvement of the pNHC ligands in catalytically active intermediates and in cooperative catalysis is also discussed.

The imidazolium salt [(S,S)-tBuNC3H3NCHPhCHPhNH2]PF6, (S,S)-11·HPF6 is a precursor to the enantiopure “Kaibene” ligand, tBu-Kaibene, (S,S)-11 featuring a tert-butyl group on the N-heterocyclic carbene (NHC) ring-nitrogen atoms. It has been prepared in high yield and purity by refluxing a chiral cyclic sulfamidate with 1-tert-butylimidazole. Similarly (S,S)-12·HPF6 with a mesityl group at the imidazolium ring-nitrogen atom has been prepared in the same fashion and serves as a source of Mes-Kaibene, (S,S)-12. These bidentate Kaibene ligands feature an NHC and a primary amine separated by a chiral linker. Salts (S,S)-11·HPF6 or (S,S)-12·HPF6 react with base and AgI or CuI to give a total of four M(Kaibene)2I compounds (M = Ag or Cu). At 22 °C, the amine-functionalized imidazolium cations undergo oxidative addition to iridium(I) in [IrCl(cod)]2 (cod = 1,5-cyclooctadiene) to generate iridium(III) hydride R-Kaibene compounds [IrHCl(cod)((S,S)-11)](PF6) (17) and [IrHCl(cod)((S,S)-12)](PF6) (18), respectively, ea...

A series of bimetallic and trimetallic complexes has been prepared by N-alkylation of mononuclear half-sandwich rhodium and iridium di-NHC complexes featuring bidentate chelate ligands composed of a classical NHC and a C-azolato donor. The shape and the separation between metal centers in the obtained complexes are highly dependent on the alkylating agent used. While the polynuclear complexes were formed as diastereomeric mixtures according to NMR spectroscopy, X-ray diffraction analysis revealed their remarkable preference to crystallize as meso compounds. The reactivity of the bimetallic, olefin-bridged complexes in electrophilic addition reactions has been investigated.

ConspectusOver the past two decades, self-assembly of supramolecular architectures has become a field of intensive research due to the wide range of applications for the resulting assemblies in various fields such as molecular encapsulation, supramolecular catalysis, drug delivery, metallopharmaceuticals, chemical and photochemical sensing, and light-emitting materials. For these purposes, a large number of coordination-driven metallacycles and metallacages featuring different sizes and shapes have been prepared and investigated. Almost all of these are Werner-type coordination compounds where metal centers are coordinated by nitrogen and/or oxygen donors of polydentate ligands. With the evolving interest in the coordination chemistry of N-heterocyclic carbenes (NHCs), discrete supramolecular complexes held together by M–CNHC bonds have recently become of interest. The construction of such metallosupramolecular assemblies requires the synthesis of suitable poly-NHC ligands where the NHC donors form labile...

The oxidative addition of N-methyl-2-iodoimidazole 1 or N-benzyl-2-iodoimidazole 2 to complexes [Pd(PPh3)4] or [Pt(PPh3)4] followed by the protonation of the unsubstituted imidazolato ring-nitrogen atom yielded complexes trans-[M(NH,NMe-NHC)(PPh3)2I] (M = Pd: trans-[3]PF6; M = Pt: trans-[4]PF6) and trans-[M(NH,NBz-NHC)(PPh3)2I] (M = Pd: trans-[5]PF6); M = Pt: trans-[6]PF6) bearing imidazole derived protic NH,NR-NHC (pNHC) ligands. In the absence of a proton source, the reaction of 1 with [Pd(PPh3)4] yielded the dinuclear dipalladium complex [7] featuring bridging N,NMe-NHC imidazolato ligands metalated at the C2 ring-carbon atom and the N3 ring-nitrogen atom. Palladium complex trans-[3]PF6 undergoes halogen abstraction with AgPF6 to give acetonitrile complex trans-[Pd(NCCH3)(NH,NMe-NHC)(PPh3)2] trans-[8](PF6)2. This complex reacted further with 1,10-phenanthroline (phen), affording complex [Pd(NH,NMe-NHC)(PPh3)(phen)](PF6)2 [9](PF6)2.

Narzisstische Selbstsortierung wurde bei der Eintopfsynthese von drei metallorganischen molekularen Zylindern des Typs [M3{L-(NHC)3}2](PF6)3 (M=Ag+, Au+; L=Benzol, Triphenylamin oder 1,3,5-Triphenylbenzol) ausgehend von L-(NHC)3 und Silber(I)- oder Gold(I)-Ionen beobachtet. Die molekularen Zylinder enthalten stets nur einen Typ der Tris-NHC-Liganden, ohne dass Heteroligand-Verbindungen zu detektieren sind. Die Transmetallierung der Tris-NHC-Liganden von Ag+ auf Au+ in einer Eintopfreaktion verlauft unter Erhaltung der supramolekularen Strukturen. Selbstsortierung wurde auch bei der Eintopfreaktion von Benzol-verbruckten Tris- und Tetrakis-NHC-Liganden mit Ag2O beobachtet. Die vorliegende Studie ubertragt erstmals narzisstische Selbstsortierung von Metall-Ligand-Wechselwirkungen in Werner-Komplexen auf metallorganische Derivate.

The HOMO–LUMO energy gap of germylenes bearing CNHC∧Namido chelate ligands has been calculated in order to find suitable candidates for the activation of small molecules. Identified as promising structures, intramolecularly NHC-stabilized three-coordinate germylenes and stannylenes of type [E(CNHC∧Namido)Cl] (E = Ge and Sn) were synthesized and characterized by NMR spectroscopy and X-ray crystallography. Chlorido substitution at the EII center for tert-butoxido or hexamethyl disilazide ligands was also performed. Chlorido abstraction with NaBArF gave rise to cationic two-coordinate germylenes and stannylenes.