2.3.5. Multi-NHCs Linked by Spacers 3568 2.4. The Ag2O Route 3570 2.4.1. Feasibility 3570 2.4.2. Complications 3571 2.4.3. Theoretical Consideration 3572 2.5. Applications 3572 2.5.1. Ag(I)-NHCs in NHC Transfer 3572 2.5.2. Ag(I)-NHCs in Catalysis 3572 2.5.3. Ag(I)-NHCs in Medicine 3572 2.5.4. Ag(I)-NHCs in Nanomaterials 3573 3. Au(I)and Au(III)-NHCs 3573 3.1. Historical Background 3573 3.2. General Synthetic Methods 3573 3.3. Formation of Au(I)and Au(III)-NHCs 3574 3.3.1. Neutral [Au(NHC)L] 3574 3.3.2. Ionic [Au(NHC)L][Anion] 3576 3.3.3. Multinuclear Au(I)-NHCs 3578 3.3.4. Other Classes of Au(I)-NHCs 3578 3.3.5. Au(III)-NHC Complexes 3579 3.4. Applications 3579 3.4.1. Au(I)and Au(III)-NHCs in Catalysis 3579 3.4.2. Au(I)-NHCs in Medicine 3580 4. Cu(I)and Cu(II)-NHCs 3581 4.1. Historical Background 3581 4.2. General Synthetic Methods 3582 4.3. Formation of Cu(I)and Cu(II)-NHCs 3583 4.3.1. Complexes Containing the Cu(NHC)2 Core 3583 4.3.2. [Cu(NHC)(Halide)] 3583 4.3.3. [Cu(NHC)(Ligand)] 3584 4.3.4. Multinuclear Cu(I)and Cu(II)-NHCs 3589 4.4. Catalysis 3591 4.4.1. Past Events 3591 4.4.2. Recent Advancements 3591 5. Photoluminescence 3592 6. Conclusions 3594 7. Abbreviations 3594 8. Acknowledgments 3595 9. References 3595

Coinage Metal−N-Heterocyclic Carbene Complexes

ion of the chloride ligands, compound 2 was further reacted with MeMgCl, yielding the bimetallic compound 3 in which the biscarbene ligand is bridging two Cr(II) atoms, also bridged by two methyl ligands. Recent studies by Arnold and co-workers showed that the incorporation of an anionic functional group (alkoxide, amido, or amino) in an NHC unit allows the preparation of tridentate ligands capable of coordinating to d0 early transition metals such as yttrium, titanium, and zirconium.87 The lithium aminodicarbene chloride complex 5 reacts with Y[N(SiMe3)2]3 affording the yttrium(III) complex 6 (Scheme 10). Hexacoordinated titanium (7) and zirconium (8) complexes were synthesized by reaction of 4 with M(NEt2)4 (M ) Ti, Zr) (Scheme 10). Complexes 7 and 8 constituted the first examples of group 3 and 4 metal complexes with monoanionic biscarbene ligands. Another interesting example of early transition metal NHC-based complexes was described by Smith and coworkers.88 By the reaction shown in Scheme 11, the tris(NHC)borate 989,90 afforded a tricarbonyl complex of Mn(I) with a tripodal tris-NHC ligand, 10. The analysis of the ν(CO) bands on the IR spectrum of this complex showed that 9 is the most electron-donating tripodal ligand compared with all others that have been bound to the same Mntricarbonyl fragment. Compound 10 is air-sensitive and is easily oxidized to a homoleptic Mn(IV) complex (11, Scheme 11), which is the first example of a Mn(IV)-NHC complex reported to-date. 4.2. Catalytic Applications Although many catalytic applications of late transition metal complexes bearing poly-NHC ligands have been described, those of early transition metals are restricted to a few examples. In 2003, Gibson and co-workers reported Cr(III)-based ethylene oligomerization precatalysts that incorporate a CNC-pincer carbene ligand.91,92 More recently, McGuinness shed some light on the mechanism of the reaction with the mentioned pincer complexes in combination with MAO.93 The Cr(II) and Cr(III) complexes described by Theopold were tested for polymerization of ethylene with a MAO cocatalyst, showing low activities and a broad weight distribution of the polymers.85 In particular, Cr(II) compounds such as 2 (Scheme 9) were unreactive to ethylene when exposed to MAO, showing that the more Lewis acidic Cr(III) performs better in this reaction. The authors pointed out the ease with which the Cr(III) complexes are reduced to Cr(II), arguing that very strong σ-donating but soft NHC ligands may have a stronger affinity for the softer Cr(II) rather than the harder Cr(III). Thus, they concluded that this ligand system may be better suited for lower oxidation state chromium chemistry and that, due to the inactivity of the Cr(II) compounds tested, it would not lead to successful results in ethylene polymerization. 5. Poly-NHC Ligands in Complexes of Group 8 Metals

Complexes with poly(N-heterocyclic carbene) ligands: structural features and catalytic applications.

This review covers the advances made in the synthesis of luminescent transition metal complexes containing N-heterocyclic carbene (NHC) ligands. The presence of a high field strength ligand such as an NHC in the complexes gives rise to high energy emissions, and consequently, to the desired blue colour needed for OLED applications. Furthermore, the great versatility of NHC ligands for structural modifications, together with the use of other ancillary ligands in the complex, provides numerous possibilities for the synthesis of phosphorescent materials, with emission colours over the entire visible spectra and potential future applications in fields such as photochemical water-splitting, chemosensors, dye-sensitised solar cells, oxygen sensors, and medicine.

N-heterocyclic carbene metal complexes: photoluminescence and applications

Although the coordination chemistry of N-heterocyclic carbenes (NHCs) with transition metals has been explored for half a century, only in the past ten years has the chemistry of metallosupramolecular assemblies based on poly-NHC ligands been studied more extensively. Remarkable discrete assemblies featuring poly-NHC ligands including two-dimensional metallacycles and three-dimensional metallaprisms/cages have since emerged. These assemblies are mostly obtained starting from various imidazolium or benzimidazolium salts. Driven by the increasing interest in new supramolecular architectures from carbon donor ligands, design, and construction of poly-NHC metal assemblies has become a rapidly growing area of research. The metal–carbene bond length is fixed to approximately 2.0 A in linear NHC–M–NHC complexes. This allows the use of such complexes bearing olefin-substituted NHC ligands as templates for subsequent photochemical [2 + 2] cycloaddition reactions. The postassembly modification of such assemblies ha...

Preparation and Post-Assembly Modification of Metallosupramolecular Assemblies from Poly( N-Heterocyclic Carbene) Ligands.

To explore the influence of different aromatic polycarboxylates on the self-assembly and properties of d10 metal coordination frameworks, six coordination compounds containing a flexible bis(2-methylbenzimidazole) (pbmb) ligand, formulated as [Ag2(pbmb)(2,6-napdc)]n (1), {[Zn(pbmb)(tbta)]·H2O}n (2), {[Cd(pbmb)(tbta)]·H2O}n (3), [Zn2(pbmb)(btec)(H2O)]n (4), {[Zn2(OH)(pbmb)(bpdc)1.5]·H2O}n (5), and [Cd(pbmb)(3-npa)(H2O)]n (6), have been synthesized under hydrothermal conditions and characterized by physicochemical and spectroscopic methods as well as single-crystal X-ray diffraction analysis (2,6-H2napdc = 2,6-naphthalenedicarboxylic acid, H2tbta = tetrabromoterephthalic acid, H4btec = 1,2,4,5-benzenetetracarboxylic acid, H2bpdc = biphenyl-4,4′-dicarboxylic acid and H23-npa = 3-nitrophthalic acid). Complex 1 possesses an 8-connected 3D coordination framework with sqc3 topology based on rare tetranuclear Ag(I)-cluster secondary building units (SBUs). 2 and 3 possess 2D (4,4) grid structures. 4 shows a novel (3,4,5)-connected 2D network with the Schlafli symbol of {3·4·5}{3·42·52·6}{3·43·53·6·72}. 5 features a uninodal (4,4)-connected net containing binuclear {Zn2(OH)} SBUs and a 2-fold interpenetrating (3,6)-connected supramolecular framework with {42·6}{44·610·8}-3,6T24 topology that is formed via hydrogen bond interactions. Complex 6 is a 1D double-chain structure, which is finally extended to a 3D (4,5,5)-connected supramolecular network via hydrogen bonding interactions. Complexes 1–6 indicate high thermal stabilities and different photoluminescence behavior in the solid state. Moreover, all of these polymer materials manifest excellent photocatalytic activities for the degradation of methyl orange in the photo-Fenton-like process after 120 min (1: 99%, 2: 66%, 3: 91%, 4: 83%, 5: 91% and 6: 93%, respectively).

A series of d10 metal coordination polymers based on a flexible bis(2-methylbenzimidazole) ligand and different carboxylates: synthesis, structures, photoluminescence and catalytic properties

We report the synthesis of Au(I) and Au(III) complexes, involving alcohol functionalized bis(N-heterocyclic carbene) ligands. Two short reaction pathways lead to the diimidazolium precursors, namely 1,1′-(2,6-pyridinediyl)bis[3-(2-hydroxyethyl)-1H-imidazol-3-ium]diiodide (2), 3,3′(methanediyl)bis[1-(2-hydroxy-2-methylpropyl)-1H-imidazol-3-ium]dibromide (4) and 3,3′-(1,3-propanediyl)bis[1-(2-hydroxy-2-methylpropyl)-1H-imidazol-3-ium]bis(4-methylbenzenesulfonate) (6), in which the two azolium rings are bridged by a rigid pyridine unit or an aliphatic chain (C1 or C3). The Au(I) complexes [AuI(Lpy)]22+[PF6−]2 (11) and [AuI(LC1)]22+[PF6−]2 (13) were obtained by direct metallation of the salts 2 and 4, respectively, in the presence of sodium acetate with Au(SMe2)Cl, followed by an anionic metathesis in the presence of KPF6. The trimethylene compound [AuI(LC3)]22+[PF6−]2 (15) was prepared by transmetallation between the related precursor [AgI(LC3)]22+[PF6−]2 (10) and Au(SMe2)Cl. The Au(III) complexes, [AuIII(Lpy)Br2]22+[PF6−]2 (16), [AuIII(LC1)Br2]22+[PF6−]2 (17) and [AuIII(LC3)Br2]22+[PF6−]2 (18) were generated by oxidation of the corresponding Au(I) species with an excess of elemental bromine. Complexes 11, [AuI(LC1)]22+[Br−]2 (12) and 15 have been characterized by single-crystal X-ray diffraction analyses. The electrochemical and luminescence properties of the Au(I) and Au(III) compounds have been studied.

Dinuclear gold(I) and gold(III) complexes of bridging functionalized bis(N-heterocyclic carbene) ligands: synthesis, structural, spectroscopic and electrochemical characterizations

N-Functionalised heterocyclic dicarbene complexes of silver: Synthesis and structural studies

Block copolymers based on ethylene (E) and butadiene (B) were prepared using the ansa -bis(fluorenyl complex {Me 2 Si(C 13 H 8 ) 2 Nd(BH 4 ) 2 Li(THF)} 2 in combination with ( n- Bu)( n- Oct)Mg (BOMAG) as a chain transfer agent. The diblock copolymers incorporating a soft poly(ethylene- co -butadiene) segment, called EBR for Ethylene Butadiene Rubber, and a hard polyethylene (PE) one were obtained by simply adjusting the different feeds of monomers during the polymerization. The soluble EBR block was formed first by feeding the catalytic system dissolved in toluene at 70 °C with a mixture of ethylene and butadiene (E/B molar ratio = 80/20). Then the feeding was stopped leading to the consumption of a large part of the residual monomers. The reactor was finally fed with ethylene to form the PE block. By varying the molar mass of the latter, it is shown that the resulting soft- b -hard block copolymers can self-assemble simultaneously to the growth of the PE block in agreement with a polymerization-induced self-assembly (PISA) mechanism. The self-assembly is discussed considering the reaction conditions, the crystallization of the PE block and the polymerization mechanism involved.

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François Jean-Baptiste dit Dominique

Papers

Dinuclear gold(I) and gold(III) complexes of bridging functionalized bis(N-heterocyclic carbene) ligands: synthesis, structural, spectroscopic and electrochemical characterizations

N-Functionalised heterocyclic dicarbene complexes of silver: Synthesis and structural studies

Ethylene Coordinative Chain Transfer Polymerization-Induced Self-Assembly (CCTPISA).