{μ-5-[1,3-Bis(2,4,6-trimethyl­phen­yl)-3H-imidazolium-2-yl]-2-(2-oxoethenyl-1κC 1)furan-3-yl-2κC 3}-μ-hydrido-bis(tetra­carbonyl­rhenium) tetra­hydro­furan 0.67-solvate

The title complex, [Re2(C27H25N2O2)H(CO)8]·0.67C4H8O, was formed as a product in the reaction of a rhenium(I)–Fischer carbene complex with a free NHC carbene. The coordination environment about the two Re atoms is slightly distorted octahedral, including a bridging H atom. The imidazolium and furan groups are almost coplanar, whereas the mesityl substituents show an almost perpendicular arrangement with respect to both heterocyclic units. Mol­ecules of the complex pack in such a way as to form channels parallel with the bc unit-cell face diagonal running through the unit face diagonal. These channels are partially occupied by tetra­hydro­furan solvent mol­ecules

N-(2,4,6-Trimethyl­phen­yl)formamide

The title compound, C10H13NO, was obtained as the unexpected, almost exclusive, product in the attempted synthesis of a manganese(I)–N-heterocyclic carbene (NHC) complex. The dihedral angle between the planes of the formamide moiety and the aryl ring is 68.06 (10)°. In the crystal, mol­ecules are linked by N—H⋯O hydrogen bonds, forming infinite chains along the c axis

Cancer molecular biology and strategies for the design of cytotoxic gold(i) and gold(iii) complexes:a tutorial review

Abstract This tutorial review highlights key principles underpinning the design of selected metallodrugs to target specific biological macromolecules (DNA and proteins). The review commences with a descriptive overview of the eukaryotic cell cycle and the molecular biology of cancer, particularly apoptosis, which is provided as a necessary foundation for the discovery, design, and targeting of metal-based anticancer agents. Drugs which target DNA have been highlighted and clinically approved metallodrugs discussed. A brief history of the development of mainly gold-based metallodrugs is presented prior to addressing ligand systems for stabilizing and adding functionality to bio-active gold(I) and gold(III) complexes, particularly in the burgeoning field of anticancer metallodrugs. Concepts such as multi-modal and selective cytotoxic agents are covered where necessary for selected compounds. The emerging role of carbenes as the ligand system of choice to achieve these goals for gold-based metallodrug candidates is highlighted prior to closing the review with comments on some future directions that this research field might follow. The latter section ultimately emphasizes the importance of understanding the fate of metal complexes in cells to garner key mechanistic insights

Catalytic conversion of alkynes to α-vinyl sulfides mediated by carbene-linker-carbene (CXC) rhodium and iridium complexes

Abstract The catalytic activity of a set of mono- and bimetallic Rh(I) and Ir(I) complexes bearing carbene-linker-carbene (CXC) bis-triazolylidene ligands (with X = O, N) coordinated in a bridging or chelating fashion was evaluated in the hydrothiolation of alkynes. The hydrothiolation of 1-hexyne with thiophenol in the absence of an external base or other additives was selected as a model reaction. All rhodium complexes are highly selective catalysts towards Markovnikov product formation and display superior activity compared to the related iridium derivatives. DFT calculations were carried out to rationalize the reaction mechanism and selectivity of this process. Neutral dinuclear [Rh₂Cl₂(cod)₂(μ-COC)] was found to be the most effective catalyst for this transformation. Its applicability was further studied towards the hydrothiolation of different alkyl and aryl alkynes using predominantly aryl thiols and proved to be one of the most active and selective catalysts towards the α-vinyl sulfide product to date

Synthesis and structure of thienyl Fischer carbene complexes of PtII for application in alkyne hydrosilylation

Abstract Transmetallation of group 6 thienylene Fischer carbene complexes to PtII precursors yielded new examples of neutral platinum(II) bisethoxycarbene complexes with either 2-thienyl (T) or 5-thieno[2,3-b]thienylene (TT) carbene substituents. The use of analogous aminocarbene group 6 precursors proceeded to give isomeric platinum(II) product mixtures where the resultant bisaminocarbene ligands displayed different orientations due to restricted rotation around the Pt–aminocarbene bond caused by the sterically demanding TT substituents. The well-defined PtII ethoxycarbene complexes were screened as catalyst precursors in the benchmark hydrosilylation reaction employing phenylacetylene and triethylsilane substrates. Marked selectivity for the β-E isomer (E)-triethyl(styryl)silane was observed, and the (pre)catalysts proved recyclable, active in solvent-free reactions, and displaying a high alkyne functional group tolerance

Chelated Fischer carbene complexes of annulated thiophenes:synthesis, structure and electrochemistry

Abstract Two (thieno[3,2-b]thiophene) and three annulated thiophenes (dithieno[2,3-b;3′,2′-d]thiophene and dithieno[3,2-b;2′,3′-d]thiophene) were employed as building blocks to synthesize linear or semi-circular chelated mononuclear biscarbene and dinuclear tetracarbene complexes. The electronic properties of the annulated thienylene chelated carbene complexes were investigated by cyclic voltammetry experiments and compared to non-chelated Fischer-type monocarbene complexes. Density functional theory (DFT) calculations were used to assign the redox events and to probe the extent of electron delocalisation as well as the possibility of electronic (intramolecular metal–metal) communication as a result of intervalence. The differences of these electronic properties in the conjugated chelated carbene complexes are compared to chelated carbene compounds without a linear conjugated pathway

Fischer carbene complexes of cobalt(I):synthesis and structure

Abstract Three different aryl substrates thiophene (ThH), ferrocene (FcH) and p-bromodimethylaniline (p-DMABr) were lithiated and reacted with [Co(CO)₄SnPh₃], according to the Fischer carbene protocol. The products [CoSnPh₃(CO)₃{C(OEt)R}] (R =Th, 1, p-DMA, 2 and R = Fc, 3) were analysed to unravel the role of the aryl carbene substituent in stabilizing intermediates and final products. The ethoxy carbene complexes were aminolysed by in situ generated HNMe₂ to afford [CoSnPh₃(CO)₃{C(NMe₂)R}] (R =Th, 4, p-DMA, 5) and with N,N-dimethylethylenediamine [CoSnPh₃(CO)₃{C(NHCH₂CH₂NMe₂)R}] (R = p-DMA, 6) in high yields. The trigonal Co(CO)₃ in the equatorial plane is very stable and efforts to displace a carbonyl in 6 was unsuccessful, both by heating and irradiation. The role of the aryl carbene substituents in stabilizing the electrophilic carbene carbon was investigated and studied by NMR spectroscopy in solution and single crystal X-ray structure determinations

Synthesis, electronic structure and interaction of rhodium(I) and iridium(I) bisimine-acenaphthalene complexes with CO₂

Abstract The bis(arylimino)acenaphthalene (BIAN) group of α-diimine compounds has shown promising electron sink behaviour and redox non-innocent activity as ligands to main group and transition metals. Here we present a series of rhodium(I) and iridium(I) complexes of BIAN derivatives with 2,6-diisopropylphenyl (DippBIAN, DB) and 2,4,6-trimethylphenyl (MesBIAN, MB), featuring various electron withdrawing and donating ancillary ligands. The crystal structures of square planar complexes 1b [RhMB(cod)]PF₆, 1d [IrMB(cod)]PF₆, 2a [RhDB(CO)₂]PF₆, 2b [RhMB(CO)₂]PF₆, 2c [IrDB(CO)₂]PF₆ and 3a [RhDB(CO)(PEt₃)]PF₆ are reported, as well as the square pyramidal structure of 4c [IrDB(cod)Cl]. The C-N and C-C bond lengths within the bisimine moiety for the structures of 2a and 4c suggest that the DippBIAN ligands are present in a reduced state, however, all other data from our multi-technique analyses correspond to results for neutral BIAN ligands. These contrasting results are indicative of the DippBIAN’s non-innocent behaviour, accepting additional electron density from the metal centre due to push–pull mechanism between the ancillary and BIAN ligands. The electrochemical study in non-coordinating solvent CH₂Cl₂ revealed that all complexes featured at least one reversible, ligand-centred reduction event at less negative potentials (above –1.0 V vs Ag/Ag⁺). In addition, preliminary results from our electrocatalytic CO₂ reduction study has shown a promising interaction between CO₂ and complex 3a, paving the way for exploring heterogeneous catalysis on these class of compounds

Diverse Coordination Modes of Bidentate COC and Tridentate CNC Ligands Comprising 1,2,3-Triazol-5-ylidenes

Two readily available bis(1,2,3-triazol-5-ylidene) ligand precursors [H2(COC)](PF6)2 and [H2(CHNC)](PF6)2, bridged by an ether or amine functionality, respectively, were prepared. Their coordination versatility was evaluated predominantly by reacting Rh(I) and Ir(I) metal precursors with the in situ deprotonated salt precursors or in exceptional cases, via transmetallation from silver, to obtain those complexes not accessible via the preferred one-step route. A divergence in reactivity and coordination was observed for both ligand precursors depending on the base and metal employed. The carbon–ether–carbon (COC) ligand afforded mono- and bimetallic complexes of Rh(I) and Ir(I), chelates or bridges two metal centers. Conversely, the carbon–amine–carbon (CHNC) ligand displayed a greater predisposition for rhodium binding and poor coordination ability to iridium. As a result, two unusual bimetallic Rh(I) complexes bearing two metal centers bridged by the central (deprotonated) amido functionality, along with a monometallic Rh(I) containing the neutral amino-CNC pincer ligand were isolated. In contrast, only monometallic Ir(I) complexes bearing a pendant triazolium arm could be prepared