Facile synthesis of benzimidazolin-2-chalcogenones: Nature of the carbon–chalcogen bond

A bis-Phenolate Carbene-Supported bis-μ-Oxo Iron(IV/IV) Complex with a [FeIV(μ-O)2FeIV] Diamond Core Derived from Dioxygen Activation

The diiron(II) complex, [(OCO)Fe(MeCN)]2 (1, MeCN = acetonitrile), supported by the bis-phenolate carbene pincer ligand, 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)benzimidazolin-2-ylidene (OCO), was synthesized and characterized by single-crystal X-ray diffraction, 1H nuclear magnetic resonance, infrared (IR) vibrational, ultraviolet/visible/near-infrared (UV/vis/NIR) electronic absorption, 57Fe Mössbauer, X-band electron paramagnetic resonance (EPR) and SQUID magnetization measurements. Complex 1 activates dioxygen to yield the diferric, μ-oxo-bridged complex [(OCO)Fe(py)(μ-O)Fe(O(C═O)O)(py)] (2) that was isolated and fully characterized. In 2, one of the iron-carbene bonds was oxidized to give a urea motif, resulting in an O(CNHC═O)O binding site, while the other Fe(OCO) unit remained unchanged. When the reaction is performed at -80 °C, an intensively colored, purple intermediate is observed (INT, λmax = 570 nm; ε = 5600 mol L-1 cm-1). INT acts as a sluggish oxidant, reacting only with easily oxidizable substrates, such as PPh3 or 2-phenylpropionic aldehyde (2-PPA). The identity of INT can be best described as a dinuclear complex containing a closed diamond core motif [(OCO)FeIV(μ-O)2FeIV(OCO)]. This proposal is based on extensive spectroscopic [UV/vis/NIR electronic absorption, 57Fe Mössbauer, X-band EPR, resonance Raman (rRaman), X-ray absorption, and nuclear resonance vibrational (NRVS)] and computational studies. The conversion of the diiron(II) complex 1 to the oxo diiron(IV) intermediate INT is reminiscent of the O2 activation process in soluble methane monooxygenases (sMMO). Most importantly, the low reactivity of INT supports the consensus that the [FeIV(μ-O)2FeIV] diamond core in sMMO is kinetically inert and needs to open up to terminal FeIV═O cores to react with the strong C-H bonds of methane.

Electronic and ring size effects of N-heterocyclic carbenes on the kinetics of ligand substitution reactions and DNA/protein interactions of their palladium(II) complexes

The synthesis, substitution kinetics and DNA/BSA interactions of four cationic Pd(II) complexes [Pd(1)Cl]BF4 (Pd1), [Pd(2)Cl]BF4 (Pd2), [Pd(3)Cl]BF4 (Pd3) and [Pd(4)Cl]BF4 (Pd4), derived from the reaction of [PdCl2(NCCH3)2] with ligands 2,6-bis(3-methylimidazolium-1-yl)pyridine dibromide (1), 2,6-bis(3-ethylimidazolium-1-yl)pyridine dibromide (2), 2,6-bis(1-methylimidazole-2-thione)pyridine (3), and 2,6-bis(1-ethylimidazole-2-thione)pyridine (4), respectively are reported. The complexes were characterised by various spectroscopic techniques and single crystal X-ray diffraction for compound Pd2. Kinetic reactivity of the complexes with the biologically relevant nucleophiles thiourea (Tu), L-methionine (L-Met) and guanosine 5'-monophosphate sodium salt (5'-GMP) was in the order: Pd1 > Pd2 > Pd3 > Pd4, which was largely dependent on the electronic and ring size of the chelate ligands, consistent with Density functional theory (DFT) simulations. The interactions of the complexes with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) binding titrations showed strong binding. Both the experimental and in silico data reveal CT-DNA intercalative binding mode.

An Aluminum Telluride with a Terminal Al=Te Bond and its Conversion to an Aluminum Tellurocarbonate by CO2 Reduction

Facile access to dimeric heavier aluminum chalcogenides [(NHC)Al(Tipp)-μ-Ch]₂ (NHC=IiPr (1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, IMe₄ (1,3,4,5-tetramethylimidazol-2-ylidene); Tipp=2,4,6-iPr₃ C₆ H₂ ; Ch=Se, Te) by treatment of NHC-stabilized aluminum dihydrides with elemental Se and Te is reported. The higher affinity of IMe₄ in comparison with IiPr toward the Al center in [(NHC)Al(Tipp)-μ-Ch]₂ can be used for ligand exchange. Additionally, the presence of excess IMe₄ allows for cleavage of the dimers to form a rare example of a neutral multiply bonded heavier aluminum chalcogenide in the form of a tetracoordinate aluminum complex, (IMe₄ )₂ (Tipp)Al=Te. This species reacts with three equivalents of CO₂ across two Al-C^NHC and the Al=Te bond affording a pentacoordinate aluminum complex containing a dianionic tellurocarbonate ligand [CO₂ Te]^2- , which is the first example of tellurium analogue of a carbonate [CO₃ ]^2- .

Reactions of N-heterocyclic carbene-based chalcogenoureas with halogens: a diverse range of outcomes

We have investigated the reactions of chalcogenoureas derived from N-heterocyclic carbenes, referred to here as [E(NHC)], with halogens. Depending on the structure of the chalcogenourea and the identity of the halogen, a diverse range of reactivity was observed and a corresponding range of structures was obtained. Cyclic voltammetry was carried out to characterise the oxidation and reduction potentials of these [E(NHC)] species; selenoureas were found to be easier to oxidise than the corresponding thioureas. In some cases, a correlation was found between the oxidation potential of these compounds and the electronic properties of the corresponding NHC. The reactivity of these chalcogenoureas with different halogenating reagents (Br₂, SO₂Cl₂, I₂) was then investigated, and products were characterised using NMR spectroscopy and single-crystal X-ray diffraction. X-ray analyses elucidated the solid-state coordination types of the obtained products, showing that a variety of possible adducts can be obtained. In some cases, we were able to extrapolate a structure/activity correlation to explain the observed trends in reactivity and oxidation potentials.

Inorganic Synthesis Based on Reactions of Ionic Liquids and Deep Eutectic Solvents

Ionic liquids and deep eutectic solvents are of growing interest as solvents for the resource‐efficient synthesis of inorganic materials. This Review covers chemical reactions of various deep eutectic solvents and types of ionic liquids, including metal‐containing ionic liquids, [BF₄]⁻‐ or [PF₆]⁻‐based ionic liquids, basic ionic liquids, and chalcogen‐containing ionic liquids. Cases in which cations, anions, or both are incorporated into the final products are also included. The purpose of this Review is to raise caution about the chemical reactivity of ionic liquids and deep eutectic solvents and to establish a guide for their proper use.

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry

N-Heterocyclic carbenes (NHC) are nowadays ubiquitous and indispensable in many research fields, and it is not possible to imagine modern transition metal and main group element chemistry without the plethora of available NHCs with tailor-made electronic and steric properties. While their suitability to act as strong ligands toward transition metals has led to numerous applications of NHC complexes in homogeneous catalysis, their strong σ-donating and adaptable π-accepting abilities have also contributed to an impressive vitalization of main group chemistry with the isolation and characterization of NHC adducts of almost any element. Formally, NHC coordination to Lewis acids affords a transfer of nucleophilicity from the carbene carbon atom to the attached exocyclic moiety, and low-valent and low-coordinate adducts of the p-block elements with available lone pairs and/or polarized carbon-element π-bonds are able to act themselves as Lewis basic donor ligands toward transition metals. Accordingly, the availability of a large number of novel NHC adducts has not only produced new varieties of already existing ligand classes but has also allowed establishment of numerous complexes with unusual and often unprecedented element-metal bonds. This review aims at summarizing this development comprehensively and covers the usage of N-heterocyclic carbene adducts of the p-block elements as ligands in transition metal chemistry.

Synthesis and coordination chemistry of cyclic seleno- and telluroureas

Chalcogenated derivatives of N-heterocyclic carbene ligands have received increasing attention due to their diverse chemical reactivity and potential applications in fields such as medicine and materials chemistry. This chapter summarizes the synthetic methods for the preparation of cyclic heavy chalcogenoureas featuring heterocyclic cores and explores their diverse coordination chemistry with p- and d-block metals.

Transition metal mediated formation of dicationic diselenides stabilised by N-heterocyclic carbenes: designed synthesis

Designed syntheses of dicationic diselenides have been developed by (i) reduction of dihaloselones (routes A and B) and (ii) by oxidation of selone adducts of metal halides (route C).

Access to pure and highly volatile hydrochalcogenide ionic liquids

The reaction of H₂S with methylcarbonate salts allows access to pure hydrosulphide ILs, which show an astoundingly high volatility below 100 °C allowing high-end purification and ionic single crystal growth by sublimation.

Bis(chalcogenones) as pincer ligands: isolation and Heck activity of the selone-ligated unsymmetrical C,C,Se–Pd pincer complex

The reaction of meta-phenylene-bis(1-methyl-1H-imidazole-2(3H)-selone) with [Pd₂(μ-Cl)₂(2-C₆H₄CH₂NMe₂)₂] in dry benzene and glacial acetic acid resulted in the formation of an unsymmetrical 5,6-membered C,C,Se–Pd(ii) pincer complex.

Recent advances in the field of main-group mono- and diatomic "allotropes" stabilised by neutral ligands

The study of ligand stabilised mono- and diatomic zero oxidation state complexes is a young and fascinating topic. This area merges the fields of low-oxidation-state main-group chemistry, homoatomic multiple bonding and fundamental coordination chemistry. As with a great deal of recent coordination chemistry within the d-block, carbene ligands are clearly the star of the show, highlighting their importance within the p-block as well. This Minireview focuses on the significant developments of the past two years.