Synthesis,Characterization, and Properties of Organometallic Molecular Cylinders Bearing Bulky Imidazo[1,5-a]pyridine-Based N-Heterocyclic Carbene Ligands

The metal-controlled self-assembly of organometallic molecular cylinders from a series of imidazo[1,5-a]pyridine-based tris-NHC ligands is described in this report. The imidazo[1,5-a]pyridinium salts H₃- L (PF₆)₃ ( L = 4 a – 4 c ) were treated with 1.5 equivalents of Ag₂O to yield the trinuclear Ag^I hexacarbene cages [Ag₃( L )₂](PF₆)₃ ( L = 4 a – 4 c ), in which three Ag^I are sandwiched between the two tricarbene ligands. The silver(I) complexes [Ag₃( L )₂](PF₆)₃ underwent a facile transmetalation reaction in the presence of 3 equivalents of [AuCl(tht)] (tht=tetrahydrothiophene) to furnish the trinuclear Au^I cylinder-like cages [Au₃( L )₂](PF₆)₃ ( L = 4 a – 4 c ) without destruction of the metallosupramolecular structure. The new hexacarbene assemblies feature a large cavity that can easily accommodate a molecule of dimethyl sulfoxide as molecular guest. This is the first study of a unique “host–guest” system containing an organometallic cylinder-like cage derived exclusively from poly-NHC ligands.     

A trefoil-shaped macrocycle with [12]-imidazolium cations

A trefoil-like two-dimensional (2D) C_3v symmetric organic [12]-imidazolium cation H₁₂–2(PF₆)₁₂ featuring three [4]-imidazolium macrocycles was synthesized in three steps. The reaction of a dodecakis H₁₂–1(PF₆)₁₂ imidazolium salt with Ag₂O resulted in the formation of a hexanuclear Ag^I dodecacarbene assembly [Ag₆(1)](PF₆)₆. Upon UV irradiation, the photodimerization of the cinnamic ester pendants of [Ag₆(1)](PF₆)₆ led to the generation of a trefoil-like complex [Ag₆(2)](PF₆)₆ containing three closed metallacycles. Removal of metal ions allowed for the synthesis of the target molecule. All complexes were fully characterized by NMR spectroscopy (¹H, ¹³C{¹H} and 2D NMR) and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS).     

Strategy for the Construction of Diverse Poly-NHC-Derived Assemblies and Their Photoinduced Transformations

A series of supramolecular assemblies of types [Ag₈( L )₄](PF₆)₈ and [Ag₄( L )₂](PF₆)₄, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4-triazolium) salts H₄-L(PF₆)₄ and Ag^I ions, is described. The assembly type obtained dependends on the N-wingtip substituents of H₄-L(PF₆)₄. Changes in the lengths of the N4-wingtip substituents enables controlled formation of assemblies with either [Ag₄( L )₂](PF₆)₄ or [Ag₈( L )₄](PF₆)₈ stoichiometry. The molecular structures of selected [Ag₈( L )₄](PF₆)₈ and [Ag₄( L )₂](PF₆)₄ assemblies were determined by X-ray diffraction analyses. While H₄- L (PF₆)₄ does not exhibit fluorescence in solution, their tetra-NHC (NHC=N-heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light-induced, supramolecule-to-supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.     

Dinuclear Macrocyclic Quinoline Bridged Mercury and Silver Bis(N‐heterocyclic Carbene) Complexes: Synthesis,Structure, and Spectroscopic Studies

Quinoline bridged imidazolium precursors 5,8‐bis(N‐R‐imidazolylidenylmethylene)quinoline PF₆^– salts [H₂L](PF₆)₂ [R = Me ( 1a ), R = naphthylmethyl ( 1b )] were prepared by quaternization of N‐methylimidazole and N‐naphthylmethylimidazole with 5,8‐bis(bromomethyl)quinoline, respectively. Reaction of the imidazolium ligands 1a and 1b with Hg(OAc)₂ and Ag₂O in acetonitrile gave the macrocyclic transition metal carbene complexes [Hg₂L₂](PF₆)₄ ( 2a and 2b ) and [Ag₂L₂](PF₆)₂ ( 3a and 3b ), respectively. All the N‐heterocyclic carbene complexes were characterized in detail by NMR, ESI‐MS, and elemental analysis. Structures of complexes 2a and 3a were determined by X‐ray diffraction studies. Structural studies revealed that the coordination arrangement of the central mercury atom in complex 2a displays a tricoordinate mode and the molecular conformation results in a“closed” form with the bridging quinoline functionality in the macrocycle, whereas the silver complex 3a does not show an coordiantion between the bridging quinoline and the Ag^I ion, which results in an “open” conformation of the macrocycle. The Hg^II and Ag^I NHC complexes showed similar UV absorption and luminescence in acetonitrile solutions.     

Linear Pyrazole‐bridged Tetra(N‐heterocyclic carbene) Ligands and Their Hexanuclear Silver(I) Complexes

New hybrid ligands are reported that combine two types of popular donor groups within a single linear scaffold, viz., a central pyrazolate bridge and two appended bis(N‐heterocyclic carbene) units; the ligand strands thus provide two potentially tridentate {NCC} compartments. The pyrazole/tetraimidazolium proligands, [H₅L¹](PF₆)₄ and [H₅L²](PF₆)₄ , were synthesized via multi‐step protocols, and the NH prototropy of [H₅L¹](PF₆)₄ was examined by variable temperature (VT) NMR spectroscopy, giving solvent dependent activation parameters (ΔH^? = 27.6 kJ · mol^–1, ΔS^? = –125 J · mol^–1 · K^–1 in [D₃]MeCN; ΔH^? = 40.4 kJ · mol^–1, ΔS^? = –86.9 J · mol^–1 · K^–1 in [D₆]DMSO) that are in the range typical for pyrazoles. Reaction of the proligands with Ag₂O gave hexametallic complexes [Ag₆(L¹)₂](PF₆)₄ and [Ag₆(L²)₂](PF₆)₄ that involve all six potential donor atoms of the ligands, viz. the four C^NHC and two N^pz donors, in metal coordination. X‐ray crystallography revealed a chair‐like central {Ag₆} deck in both complexes but different arrangements of the ligand strands, which goes along with significantly different Ag^I ··· Ag^I distances that indicate more pronounced argentophilic interactions in case of [Ag₆(L¹)₂]^{4 +}.     

Strategy for the Construction of Diverse Poly‐NHC‐Derived Assemblies and Their Photoinduced Transformations

A series of supramolecular assemblies of types [Ag₈( L )₄](PF₆)₈ and [Ag₄( L )₂](PF₆)₄, obtained from the tetraphenylethylene (TPE) bridged tetrakis(1,2,4‐triazolium) salts H₄‐L(PF₆)₄ and Ag^I ions, is described. The assembly type obtained dependends on the N‐wingtip substituents of H₄‐L(PF₆)₄. Changes in the lengths of the N4‐wingtip substituents enables controlled formation of assemblies with either [Ag₄( L )₂](PF₆)₄ or [Ag₈( L )₄](PF₆)₈ stoichiometry. The molecular structures of selected [Ag₈( L )₄](PF₆)₈ and [Ag₄( L )₂](PF₆)₄ assemblies were determined by X‐ray diffraction analyses. While H₄‐ L (PF₆)₄ does not exhibit fluorescence in solution, their tetra‐NHC (NHC=N‐heterocyclic carbene) assemblies do upon NHC–metal coordination. Upon irradiation, all assemblies undergo a light‐induced, supramolecule‐to‐supramolecule structural transformation by an oxidative photocyclization involving phenyl groups of the TPE core, resulting in a significant change of the luminescence properties.     

Coinage Metal Complexes of Bis(quinoline-2-ylmethyl)phenylphosphine-Simple Reactions Can Lead to Unprecedented Results

The different coordination behavior of the flexible yet sterically demanding, hemilabile P,N ligand bis(quinoline-2-ylmethyl)phenylphosphine ( bqmpp ) towards selected Cu^I, Ag^I and Au^I species is described. The resulting X-ray crystal structures reveal interesting coordination geometries. With [Cu(MeCN)₄]BF₄, compound 1 [Cu₂(bqmpp)₂](BF₄)₂ is obtained, wherein the copper(I) atoms display a distorted square planar and square pyramidal geometry. The steric demand and π-stacking of the ligand allow for a short Cu⋅⋅⋅Cu distance (2.588(9) Å). Cu^I complex 2 [Cu₄Cl₃(bqmpp)₂]BF₄ contains a rarely observed Cu₄Cl₃ cluster, probably enabled by dichloromethane as the chloride source. In the cluster, even shorter Cu⋅⋅⋅Cu distances (2.447(1) Å) are present. The reaction of Ag[SbF₆] with the ligand leads to a dinuclear compound ( 3 ) in solution as confirmed by ³¹P{¹H} NMR spectroscopy. During crystallization, instead of the expected phosphine complex 3 , a tris(quinoline-2-ylmethyl)bisphenyl-phosphine ( tqmbp ) compound [Ag₂(tqmbp)₂](SbF₆)₂ 4 is formed by elimination of quinaldine. The Au(I) compound [Au₂(bqmpp)₂]PF₆ ( 5 ) is prepared as expected and shows a linear arrangement of two phosphine ligands around Au^I.     

C3‐Symmetric Assemblies from Trigonal Polycarbene Ligands and MI Ions for the Synthesis of Three‐Dimensional Polyimidazolium Cations

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 Ag₂O. 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.     

Triazole‐Functionalized N‐Heterocyclic Carbene Complexes of Palladium and Platinum and Efficient Aqueous Suzuki–Miyaura Coupling Reaction

Imidazolium salts bearing triazole groups are synthesized via a copper catalyzed click reaction, and the silver, palladium, and platinum complexes of their N‐heterocyclic carbenes are studied. [Ag₄(L1)₄](PF₆)₄, [Pd(L1)Cl](PF₆), [Pt(L1)Cl](PF₆) (L1=3‐((1‐benzyl‐1H‐1,2,3‐triazol‐4‐yl)methyl)‐1‐(pyrimidin‐2‐yl)‐1H‐imidazolylidene), [Pd₂(L2)₂Cl₂](PF₆)₂, and [Pd(L2)₂](PF₆)₂ (L2=1‐butyl‐3‐((1‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐4‐yl)methyl)imidazolylidene) have been synthesized and fully characterized by NMR, elemental analysis, and X‐ray crystallography. The silver complex [Ag₄(L1)₄](PF₆)₄ consists of a Ag₄ zigzag chain. The complexes [Pd(L1)Cl](PF₆) and [Pt(L1)Cl](PF₆), containing a nonsymmetrical NCN ′ pincer ligand, are square planar with a chloride trans to the carbene donor. [Pd₂(L2)₂Cl₂](PF₆)₂ consists of two palladium centers with CN₂Cl coordination mode, whereas the palladium in [Pd(L2)₂](PF₆)₂ is surrounded by two carbene and two triazole groups with two uncoordinated pyridines. The palladium compounds are highly active for Suzuki–Miyaura cross coupling reactions of aryl bromides and 1,1‐dibromo‐1‐alkenes in neat water under an air atmosphere.     

Metal‐Carbene‐Templated Photochemistry in Solution: A Universal Route towards Cyclobutane Derivatives

A series of dicarbene‐bridged metallacycles [Ag₂( 1 )₂](PF₆)₂, [Ag₂( 2 )₂](BF₄)₂, [Ag₂( 3 )₂](PF₆)₂, [Ag₂( 7 )₂](BF₄)₂, [Ag₂( 8 )₂](BF₄)₂ and [Ag₂( 11 )₂](PF₆)₂ were obtained in high yields via the reactions of 1,2,4‐triazole‐, 1,2,3‐triazole‐ and imidazo[1,5‐a]pyridine‐based ligands with Ag₂O in CH₃CN. The C=C double bonds in all of the newly synthesized metallacycles went through [2 + 2] photodimerization under UV irradiation condition (λ = 365 nm, T = 298 K) yielding the dinuclear rctt‐cyclobutane‐silver(I) complexes [Ag₂( 4 )](PF₆)₂, [Ag₂( 5 )](BF₄)₂, [Ag₂( 6 )](PF₆)₂, [Ag₂( 9 )](BF₄)₂, [Ag₂( 10 )](BF₄)₂ and [Ag₂( 12 )](PF₆)₂, respectively with quantitative yields. Treatment of the these cyclobutane‐bridged silver(I) complexes with NH₄Cl resulted in the exclusive formation of cyclobutane derivatives after removal of the silver(I) metal ions.     

Synthesis, structural characterization, and luminescence properties of multinuclear silver complexes of pyrazole-functionalized NHC ligands containing Ag-Ag and Ag-π interactions

A few pyrazole-functionalized imidazolium salts have been prepared via the reactions of N-alkylimidazole and 3,5-bis(chloromethyl)pyrazole or 2-(1-(2-chloroethyl)-5-methyl-1H-pyrazol-3-yl)-6-(5-methyl-1-vinyl-1H-pyrazol-3-yl) pyridine. Reactions of these imidazolium salts with Ag₂O led to the successful isolation of tetranuclear [Ag₄(L)₂](X)₂ (X = PF₆⁻ or BF₄⁻; H₃L1 = 3,5-bis(N-benzylimidazoliumyl)pyrazole, H₃L2 = 3,5-bis(N-(2,4,6-trimethylphenyl)imidazoliumyl)pyrazole, H₃L3 = imidazolium cyclophane from the condensation of 3,5-bis(chloromethyl)pyrazole and 1,4-bis(imidazolyl)butane) and trinuclear silver clusters supported by N-heterocyclic carbene ligands in high yields. The molecular structures of these silver complexes have been confirmed by ¹H, ¹³C NMR, ESI-MS spectroscopy, and X-ray diffraction analyses. The tetranuclear complexes [Ag₄(L1)₂](PF₆)₂ (1) and [Ag₄(L2)₂](BF₄)₂ (2) consist of a pair of Ag-Ag contacts (ca. 3.11 Å) showing weak silver-silver interaction. [Ag₄(L3)₂](PF₆)₂ (3) has a square planar Ag₄ core sandwiched by two NHC cyclophanes with Ag-Ag distances of 3.22 Å. All the silver atoms in 1-3 are located in the same linear C-Ag-N coordination environment. [Ag₃(L4)₂] (PF₆)₃ (HL4 = 2-(1-(2-methylimidazoliumylethyl)-5-methyl-1H-pyrazol-3-yl)-6-(5-methyl-1-vinyl-1H-pyrazol-3-yl) pyridine) (4) is a trinuclear complex in which the three silver are bridged by two L4 molecules, and the Ag₃ units form one-dimensional chain via Ag-π interaction. The luminescence properties of the imidazolium salts and their silver complexes were also studied.     

Encapsulation of tricopper cluster in a synthetic cryptand enables facile redox processes from CuICuICuI to CuIICuIICuII states

One-pot reaction of tris(2-aminoethyl)amine (TREN), [Cu^I(MeCN)₄]PF₆, and paraformaldehyde affords a mixed-valent [TREN₄Cu^IICu^ICu^I(μ₃-OH)](PF₆)₃ complex. The macrocyclic azacryptand TREN₄ contains four TREN motifs, three of which provide a bowl-shape binding pocket for the [Cu₃(μ₃-OH)]³⁺ core. The fourth TREN caps on top of the tricopper cluster to form a cryptand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of synthetic tricopper complexes reported so far, [TREN₄Cu^IICu^ICu^I(μ₃-OH)](PF₆)₃ exhibits several reversible single-electron redox events. The distinct electrochemical behaviors of [TREN₄Cu^IICu^ICu^I(μ₃-OH)](PF₆)₃ and its solvent-exposed analog [TREN₃Cu^IICu^IICu^II(μ₃-O)](PF₆)₄ suggest that isolation of tricopper core in a cryptand enables facile electron transfer, allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [TREN₄Cu^ICu^ICu^I(μ₃-OH)](PF₆)₂ can reduce O₂ under acidic conditions. The geometric constraints provided by the cryptand are reminiscent of Nature''s multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at Cu^ICu^ICu^I (4a), Cu^IICu^ICu^I (4b), and Cu^IICu^IICu^I (4c) states, providing structural and spectroscopic models for many intermediates in MCOs. Fast electron transfer rates (10⁵ to 10⁶ M⁻¹ s⁻¹) were observed for both Cu^ICu^ICu^I/Cu^IICu^ICu^I and Cu^IICu^ICu^I/Cu^IICu^IICu^I redox couples, approaching the rapid electron transfer rates of copper sites in MCO.

Geometric constraints and site isolation provided by the cryptand enable reversible redox of tricopper μ-oxo cluster.     

Coordination compounds and microorganisms,Part 12. Rhodium compounds of S-nicotine and their bacterial activity

Summary The activities of the nicotine complexes of rhodium(III)-[RhCl₃(nicH⁺)₃](PF₆)₃ andtrans-[RhCl₂(nic)₄](PF₆) (nicH⁺=monoprotonated S-nicotine, nic=unprotonated S-nicotine)—were studied onEscherichia coli B growing in a minimal glucose medium in both lag- and log-phases.[RhCl₃(nicH⁺)₃](PF₆)₃ at 50 ppm caused bacteriostasis, and at 100 ppm or more was bactericidal, whereastrans-[RhCl₂(nic)₄](PF₆) at 50 ppm or more was bactericidal in the lag-phase. However [RhCl₃(nicH⁺)₃](PF₆)₃ delayed cell division ofEscherichia coli B just entering the log phase by two generation times, whereby the bacteria transformed from the normal unicellular shape to filamentous forms. Cytotoxicities are reported.     

Insights into the Halogen Oxidative Addition Reaction to Dinuclear Gold(I) Di(NHC) Complexes

Gold(I) dicarbene complexes [Au₂(MeIm‐Y‐ImMe)₂](PF₆)₂ (Y=CH₂ ( 1 ), (CH₂)₂ ( 2 ), (CH₂)₄ ( 4 ), MeIm=1‐methylimidazol‐2‐ylidene) react with iodine to give the mixed‐valence complex [Au(MeIm‐CH₂‐ImMe)₂AuI₂](PF₆)₂ ( 1 a^I ) and the gold(III) complexes [Au₂I₄(MeIm‐Y‐ImMe)₂](PF₆)₂ ( 2 c^I and 4 c^I ). Reaction of complexes 1 and 2 with an excess of ICl allows the isolation of the tetrachloro gold(III) complexes [Au₂Cl₄(MeIm‐CH₂‐ImMe)₂](PF₆)₂ ( 1 c^Cl ) and [Au₂Cl₄(MeIm‐(CH₂)₂‐ImMe)₂](Cl)₂ ( 2 c^Cl‐Cl ) (as main product); remarkably in the case of complex 2 , the X‐ray molecular structure of the crystals also shows the presence of I‐Au‐Cl mixed‐sphere coordination. The same type of coordination has been observed in the main product of the reaction of complexes 3 or 4 with ICl. The study of the reactivity towards the oxidative addition of halogens to a large series of dinuclear bis(dicarbene) gold(I) complexes has been extended and reviewed. The complexes react with Cl₂, Br₂ and I₂ to give the successive formation of the mixed‐valence gold(I)/gold(III) n a^X and gold(III) n c^X (excluding compound 1 c^I ) complexes. However, complex 3 affords with Cl₂ and Br₂ the gold(II) complex 3 b^X [Au₂X₂(MeIm‐(CH₂)₃‐ImMe)₂](PF₆)₂ (X=Cl, Br), which is the predominant species over compound 3 c^X even in the presence of free halogen. The observed different relative stabilities of the oxidised complexes of compounds 1 and 3 have also been confirmed by DFT calculations.     

Synthesis,Structures, and Photophysics of Polynuclear Silver(I) Thiolate and Silver(I) Thiocarboxylate Complexes with Dppm Ligands

Trinuclear silver(I) thiolate and silver(I) thiocarboxylate complexes [Ag₃(μ‐dppm)₃(μ_n‐SR)₂](ClO₄) [n = 2, R = C₆H₄Cl‐4 ( 1 ) and C{O}Ph ( 2 ); n = 3, R = tBu ( 3 )], pentanuclear silver(I) thiolate complex [Ag₅(μ‐dppm)₄(μ₃‐SC₆H₄NO₂‐4)₄](PF₆) ( 4 ), and hexanuclear silver(I) thiolate complexes [Ag₆(μ‐dppm)₄(μ₃‐SR)₄]Y₂ [Y = ClO₄, R =C₆H₄CH₃‐4 ( 5 ) and C₁₀H₇ (2‐naphthyl) ( 7 ); Y = PF₆, R = C₆H₄OCH₃‐4( 6 )], were synthesized [dppm = bis(diphenylphosphanyl)methane] and their crystal structures as well as photophysical properties were studied. In the solid state at 77 K, trinuclear silver(I) thiolate and silver(I) thiocarboxylate complexes 1 and 2 exhibit luminescence at 470–523 nm, tentatively attributed to originate from the ³IL (intraligand) of thiolate or thiocarboxylate ligands, whereas hexanuclaer silver(I) thiolate complexes 5 and 7 produce dual emission, in which high‐energy emission is tentatively attributed to come from the ³IL of thiolate ligands and low‐energy emission is tentatively assigned to come from the admixture of metal ··· metal bond‐to‐ligand charge‐transfer (MMLCT) and metal‐centered (MC) excited states.     

Synthesis and characterization of dinuclear late transition-metal (copper(I), silver(I), rhenium(I)) complexes with a bis-pyridylimine ligand linked by S–S bonding

Two dinuclear complexes with novel coordination type, [Cu₂(DPDIDT)₂](PF₆)₂ (1) and [Ag₂(DPDIDT)₂](BF₄)₂ (2), plus a dinuclear complex of the usual coordination type, {Re(Cl)(CO)₃}₂(DPDIDT) (3) as a comparative complex were prepared from bis-(4-(2-pyridylmethyleneiminophenyl))disulfide (DPDIDT) and the relevant metal sources. Complexes (1) and (2) exist in solution as dimer structures of the square-pole type according to the interpretation of the ESI mass and ¹H NMR spectra. The density functional theory calculations for the monomer and dimer models of the Cu(I) complex cations, [Cu_n(DPDIDT)_n]ⁿ⁺ (n = 1, 2), demonstrated that the dimer form is structurally more stable than the monomer form. The UV–Vis absorption spectra of complexes (1) and (3) both exhibit a typical MLCT absorption band in the 400–700 nm region. The Re(I) complex (3) was revealed to possess a facial configuration with respect to the three carbonyl ligands by ¹H NMR and IR data.     

Turn‐On Fluorescence in Tetra‐NHC Ligands by Rigidification through Metal Complexation: An Alternative to Aggregation‐Induced Emission

Two tetraphenylethylene (TPE) bridged tetraimidazolium salts, [H₄ L ‐Et](PF₆)₄ and [H₄ L ‐Bu](PF₆)₄, were used as precursors for the synthesis of the dinuclear Ag^I and Au^I tetracarbene complexes [Ag₂( L ‐Et)](PF₆)₂, [Ag₂( L ‐Bu)](PF₆)₂, [Au₂( L ‐Et)](PF₆)₂, and [Au₂( L ‐Bu)](PF₆)₂. The tetraimidazolium salts show almost no fluorescence (Φ _F<1 %) in dilute solution while their NHC complexes display fluorescence “turn‐on” (Φ _F up to 47 %). This can be ascribed to rigidification mediated by the restriction of intramolecular rotation within the TPE moiety upon complexation. DFT calculations confirm that the metals are not involved in the lowest excited singlet and triplet states, thus explaining the lack of phosphorescence and fast intersystem crossing as a result of heavy atom effects. The rigidification upon complexation for fluorescence turn‐on constitutes an alternative to the known aggregation‐induced emission (AIE).     

Synthesis,Characterization, and Properties of Tetraphenylethylene-Based Tetrakis-NHC Ligands and Their Metal Complexes

The development of highly emissive dinuclear Ag^I or Au^I complexes [M₂L](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 (Φ_F) 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 Φ_F 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.     

Synthesis and characterization of iridium polypyridyl complexes with ester groups with potential applications in covalent attachment to metal oxide surfaces

We report the synthesis and characterization of two iridium polypyridyl complexes, [Ir(deeb)₂Cl₂](PF₆) and [Ir(deeb)₂(dpp)](PF₆)₃, where deeb?=?diethyl-2,2′-bipyridine-4,4′-dicarboxylate and dpp?=?2,3-bis(2-pyridyl)pyrazine. From ¹H NMR spectral data, the two deeb ligands are attached to Ir cis to each other. Mass spectra contain fragmentation patterns of the (M-PF₆)⁺ and (M-3PF₆)³⁺ molecular ions for [Ir(deeb)₂Cl₂](PF₆) and [Ir(deeb)₂(dpp)](PF₆)₃, respectively. The electronic absorption spectrum of [Ir(deeb)₂Cl₂](PF₆) shows maxima at 308?nm and 402?nm, which are assigned as ¹π?→?π* and metal-to-ligand charge transfer transitions, respectively. [Ir(deeb)₂(dpp)](PF₆)₃ exhibits peaks due to ¹π?→?π* transitions at 322?nm and 334?nm. [Ir(deeb)₂Cl₂](PF₆) has emission peaks at 538?nm in acetonitrile and 567?nm in the solid state, with lifetimes of 1.71?µs and 0.35?µs, respectively. [Ir(deeb)₂Cl₂](PF₆) has an unusually higher quantum yield than analogous compounds. [Ir(deeb)₂(dpp)](PF₆)₃ has emission peaks at 540?nm in acetonitrile and 599?nm in the solid state with lifetimes of 1.23?µs and 0.14?µs, respectively. Cyclic voltammetry of [Ir(deeb)₂Cl₂](PF₆) yields two reversible couples at ?0.72 and ?0.87?V versus Ag/AgCl, both corresponding to deeb ligand reductions, and a quasi-reversible couple at ?1.48?V corresponding to Ir^3+/+ reduction. Electrochemical reduction of [Ir(deeb)₂(dpp)](PF₆)₃ yields couples at ?0.38, ?0.54, ?0.71, and ?1.33?V, assigned as deeb^0/?, deeb^0/?, dpp^0/?, and Ir^3+/+ reductions, respectively.     

Self-assembly luminescent complexes with [Ag2 (μ-dppm)2 (MeCN)2](SbF6)2 and tptz as components

[Ag₂(μ-dppm)₂(tptz)(MeCN)](SbF₆)₂·2H₂O·2MeCN (1), [Ag₂(μ-dppm)₂(tptz)₂](SbF₆)₂·1.75H₂O (2) and [Ag₂(μ-dppm)(tptz)₂](SbF₆)₂· 2MeCN (3) were synthesized by self-assembly with metal diphosphine [Ag₂(μ-dppm)₂ (MeCN)₂](SbF₆) ₂ and tptz as components in different molar ratios [(dppm = bis(diphenylphosphino)methane and tptz = 2,4,6-tris(2′-pyridyl)-1,3,5-triazine)] and characterized by IR spectra, elemental analysis, ¹H NMR spectra, ³¹P NMR spectra and Visible–Ultraviolet spectra. Structures of all the complexes were determined by X-ray analysis. π − π interactions were found in complex (3). Further studies show that all the complexes were of well luminescent properties both in solution and solid state.