Synthesis, structural studies and computational evaluation of cyclophanes incorporating imidazole-2-selones

We report new cyclophanes containing imidazole-2-selone groups linked by xylylene rings. A set of imidazole-2-selone cyclophanes is synthesized by reaction corresponding to imidazolium cyclophanes with selenium in the presence of K₂CO₃. The structural behavior of the new imidazole-2-selone cyclophanes was determined by ¹H and ¹³C NMR spectra and X-ray diffraction studies. Cyclophanes incorporating o-xylylene or mesitylene-m-cyclophane linked by selone groups were mutually syn in both the solid state and solution, and the cyclophanes showed a conformation similar to the cone conformation of calix[4]arenes. Cyclophanes incorporating p-xylylene or m-xylylene linked by selone groups showed two conformations in the solution: one mutually syn and the other mutually anti. There was no interconversion for both conformations observed on the NMR timescale. In the solid state, three conformations were detected for the p-xylylene-linked cyclophane: one is mutually syn and the other two are mutually anti and partial cone conformations. In the m-xylylene-linked case, only anti-conformation was characterized in the solid state. A density functional analysis was conducted to interpret the stability of the studied compounds and shed light on their origin. The energy preference analysis is in consistent agreement with the observed geometries and their co-existence.

Proton reduction by a bimetallic zinc selenolate electrocatalyst

We report the synthesis and structural characterization of a bimetallic zinc selenolate complex consisting of a redox silent zinc metal ion and a trifunctional ligand that electrocatalyzes the reduction of protons into hydrogen gas.

Antimony(III) Halide-Assisted Stereospecific Coordination of Thione

The antimony halide-aided stereospecific coordination of a cyclic thiourea-type of ligand is observed for the first time. The antimony(III) imidazole thione complexes syn-[(L¹ )SbCl₃ ] (syn-1) and anti-[(L¹ )SbBr₃ ] (anti-2) have been synthesized in very good yield by the reaction between the spatially defined steric impact ligand [(IPaul)S] (L¹ ) ([(IPaul)S]=1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole thione) and corresponding antimony halide. The stereoselective formation of complexes syn-1 and anti-2 has been confirmed by both NMR and single-crystal X-ray diffraction studies. Interestingly the stereospecific nature of syn-1 and anti-2 remains intact in solution. Furthermore, the thermal stability of antimony(III) imidazole thione complexes were examined by TGA analysis.

Rare antimony(III) imidazole selone complexes: steric controlled structural and bonding aspects

Novel antimony(iii) imidazole selone complexes in a super crowded environment are reported for the first time. The super bulky selone antimony complexes, [{IPr*Se}(SbCl3)2] (1) and [{IPr*Se}(SbBr3)2] (2), were isolated from the reactions between IPr*Se (IPr*Se = [1,3-bis(2,6-diphenylmethylphenyl)imidazole selone]) and suitable antimony(iii) halides. 1 and 2 are dinuclear complexes with a Sb : Se ratio of 1 : 0.5 with an unusual coordination mode of selone. The molecules 1 and 2 consist of both Menshutkin-type Sbπaryl interactions and a Sb-Se coordination bond. However, the reaction between antimony(iii) halides and [(IPaul)Se] ([(IPaul)Se] = [1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole selone]) with a spatially defined steric impact gave the dinuclear complex [{(IPaul)Se}(SbCl3)]2 (3) and the mononuclear complex [{(IPaul)Se}(SbBr3)] (4) without Menshutkin-type interactions. The Sb : Se ratio in 3 and 4 is 1 : 1. Interestingly, the Menshutkin-type interaction was absent in 3 and 4 due to the efficient coordinating ability of the ligand [(IPaul)Se] with the Sb(iii) center compared to that of the super bulky ligand IPr*Se. The thermal property of these antimony selone complexes was also investigated. Density functional theory (DFT) calculations were carried out on the model systems [L(SbCl3)2] (1A), [L(SbCl3)] (1B), [L'(SbCl3)2] (1C), and [L'(SbCl3)] (1D), where L = [1,3-bis(2,6-diisopropyl-4-methyl phenyl)imidazole selone] and L' = [1,3-bis(phenyl)imidazole selone], to understand the nature of orbitals and bonding situations. The computed metrical parameters of 1A are in good agreement with the experimental values. Natural population analysis of the model system reveals that the natural charge and total population of antimony(iii) are comparable. The unequal interaction between selenium and antimony obtained using Wiberg bond indices (WBIs) is fully consistent with the findings of the single-crystal X-ray studies.

Catalytically active coordination polymer with a tiny Zn2Se2 ring bridged by bis-selone

The unprecedented architecture of a one-dimensional coordination polymer with a tiny Zn₂Se₂ ring system incorporated in the hydrogen-bonded array has been prepared, where the di-selone ligand functions as a unique neutral bridging ligand. The coordination polymer shows excellent catalytic activity in substituted 8-hydroxy-2-quinolinyl synthesis through Knoevenagel condensation reaction.

Highly active mesoionic chalcogenone zinc(ii) derivatives for C–S cross-coupling reactions

Mesoionic heavier chalcogenone complexes of zinc(ii) have been isolated and utilized as catalysts in C–S cross coupling reactions between thiophenols and aryl halides under convenient reaction conditions.

Homoleptic and heteroleptic Zn(ii) selone catalysts for thioetherification of aryl halides without scrubbing oxygen

Tetra-coordinated zinc imidazoline selone complexes were synthesized and utilized as potential catalysts in the thioetherification of aryl halides without scrubbing oxygen.

Coordination of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone to zinc and cadmium: Monotonic and non-monotonic bond length variations for [H(sebenzimMe)]2MCl2 complexes (M = Zn, Cd, Hg)

The reactions of 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzimMe), towards the zinc and cadmium halides, MX2 (M = Zn, Cd; X = Cl, Br, I), afford the adducts, [H(sebenzimMe)]2MX2, which have been structurally characterized by X-ray diffraction. The halide ligands of each of these complexes participate in hydrogen bonding interactions with the imidazole N-H moieties, although the nature of the interactions depends on the halide. Specifically, the chloride and bromide derivatives, [H(sebenzimMe)]2ZnX2 and [H(sebenzimMe)]2CdX2 (X = Cl, Br), exhibit two intramolecular N-H•••X interactions, whereas the iodide derivatives, [H(sebenzimMe)]2ZnI2 and [H(sebenzimMe)]2CdI2, exhibit only one intramolecular N-H•••I interaction. Comparison of the M-Se and M-Cl bond lengths of the chloride series, [H(sebenzimMe)]2MCl2 (M = Zn, Cd, Hg), indicates that while the average M-Cl bond lengths progressively increase as the metal becomes heavier, the variation in M-Se bond length exhibits a non-monotonic trend, with the Cd-Se bond being the longest. These different trends provide an interesting subtlety concerned with use of covalent radii in predicting bond length differences. In addition to tetrahedral [H(sebenzimMe)]2CdCl2, [H(sebenzimMe)]3,CdCl2•[H(sebenzim)Me]4CdCl2, which features both five-coordinate and six-coordinate coordinate centers, has also been structurally characterized. Finally, the reaction between CdI2 and H(sebenzimMe) at elevated temperatures affords the 1-methylbenzimidazole complex, [H(sebenzimMe)]-[H(benzimMe)]CdI2, a transformation that is associated with cleavage of the C-Se bond.

Luminescent zinc(ii) selone macrocyclic ring

The synthesis and photophysical properties of macrocyclic Zn(ii) selone molecule have been reported. The structural property of Zn(ii) selone was elucidated using single crystal X-ray diffraction study. The solid-state structure of zinc(ii) selone molecule exhibits a perfect zinc(ii) selone 28 membered ring system with tetra coordination geometry around zinc(ii) center. The zinc(ii) selone ring system can be considered as the largest zinc(ii) ring system known without any non-interacting centered guest moiety. Detailed trends in photophysical as well as thermal properties were probed. In photoluminescence study, the solid-state sample of zinc(ii) selone ring system emits the bluish-yellow color with considerable quantum yields, while the solution state sample of zinc(ii) selone ring system in DMSO emits bluish-yellow. The luminescence lifetime of zinc(ii) selone was measured using standard time-correlated single photon counting (TCSPC) technique.

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.

Five complexes based on a new racemic tetraoxaspiro ligand: correlation of potential coordination preferences with the structure, magnetic properties and luminescence properties

A new ligand, rac-(R,S)-3,9-bis(pyridin-3-yl)-2,4,8,10-tetraoxaspiro[5.5]undecane ((R,S)-bptu), is synthesized, and five novel complexes, namely, {[Cu[(R,S)-bptu]Cl2]·0.5NMP}n (1), {[Zn[(R,S)-bptu]Cl2]·CH3CN}n (2), {Cd2[(R,S)-bptu]2Cl4(NMP)2}n (3), {[Cd[(R,S)-bptu]2Cl2]·2CH3CN}n (4), and {Cd3[(R,S)-bptu]2Cl6(DMF)2}n (5), (NMP = N-methyl-2-pyrrolidone, DMF = N,N-dimethylformamide), are obtained via a layered diffusional reaction. (R,S)-bptu and complexes 1-5 are characterized by single-crystal X-ray diffraction, element analyses, powder X-ray diffraction (PXRD), and Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analyses (TGA). Complexes 1-3 show three different 1D structures: 1 is a mesomeric looped chain, 2 is a racemic helix compound, and 3 is a mesomeric zigzag chain, while 4 and 5 are two different mesomeric 2D structures, of which 4 is a 2D wave-like layer and 5 is a 2D cellular layer. Structural diversity indicates that the coordination preferences (cis- and trans-configurations) of (R,S)-bptu play a leading role in the self-assembly of complexes: cis-bptu tends to form one-dimensional structures 1-3, while trans-bptu is easier to construct higher dimensional structures 4-5. Secondly, the different transition metal atom M(ii) adopts diverse geometry in 1-5: Cu(ii) adopts square pyramidal geometry in 1, Zn(ii) employs a tetrahedron configuration in 2, and especially in 3-5, Cd(ii) displays a trigonal bipyramidal configuration, cis-cis-trans, cis and trans octahedral configuration. Finally, the different solvent system, the coordinated/free solvent, and the secondary building units (SBUs) affect the diversification of the structure. A variable temperature magnetic susceptibility investigation manifests that antiferromagnetic interactions exist between the neighbouring metal ions in 1. Furthermore, the luminescence properties of 2-5 are investigated in the solid state at room temperature, and 4 shows highly selective and sensitive sensing for Fe3+ ions.

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.

Role of C, S, Se and P donor ligands in copper(i) mediated C–N and C–Si bond formation reactions

The first comparative study of C, S, Se and P donor ligands-supported copper(i) complexes for C–N and C–Si bond formation reactions are described. The syntheses and characterization of eight mononuclear copper(i) chalcogenone complexes, two polynuclear copper(i) chalcogenone complexes and one tetranuclear copper(i) phosphine complex are reported. All these new complexes were characterized by CHN analysis, FT-IR, UV-vis, multinuclear NMR and single crystal X-ray diffraction techniques. The single crystal X-ray structures of these complexes depict the existence of a wide range of coordination environments for the copper(i) center. This is the first comparative study of metal–phosphine, metal–NHC and metal–imidazolin-2-chalcogenones in C–N and C–Si bond formation reactions. Among all the catalysts, mononuclear copper(i) thione, mononuclear copper(i) N-heterocyclic carbene and tetranuclear copper(i) phosphine are exceedingly active towards the synthesis of 1,2,3-triazoles as well as for the cross-dehydrogenative coupling of alkynes with silanes. The cross-dehydrogenative coupling of terminal alkynes with silanes represents the first report of a catalytic process mediated by metal–imidazolin-2-chalcogenones.

The first comparative study of C, S, Se and P donor ligands-supported copper(i) complexes for C–N and C–Si bond formation reactions.

Diverse silver(i) coordination chemistry with cyclic selenourea ligands

The reactions of cyclic selenoureas with silver(i) salts yield new coordination complexes with sterically-controlled solid state aggregation.

3,3′-[(2-Bromo-1,3-phenylene)bis(methylene)]bis(1-butyl-2,3-dihydro-1H-imidazole-2-selone)

In the title compound, C22H29BrN4Se2, the two Se atoms are directed in opposite directions with respect to the central benzene ring. The C=Se bond lengths at 1.848 (5) and 1.851 (5) Å are on the long side for a double bond but shorter than expected for a C—Se single bond. In the crystal, Br...Br intermolecular interactions [3.4685 (12) Å] link the molecules into a zigzag chain propagating along theb-axis direction. In addition, there are C—H...Se intermolecular interactions present, linking the chains to form slabs parallel to theabplane. One of the two butyl side chains is disordered over two conformations with occupancies of 0.777 (9) and 0.223 (9).

Natural product inspired design and synthesis of β-carboline and γ-lactone based molecular hybrids

β-Carboline and γ-lactone moieties have been selected by nature as privileged scaffolds and display a wide range of pharmacological properties. Following nature, we envisaged the preparation of new β-carboline and γ-lactone based molecular hybrids incorporating both the pharmacophores. In this regard, a water-assisted In-mediated environmentally benign and easy to execute single-step tandem Barbier type allylation-lactonisation process has been devised in order to afford the targeted molecular architectures. It is anticipated that aqueous medium plays the key role in allylation as well as in the subsequent lactonisation process for the diastereo-selective synthesis of these conjugates. It is believed that water drives the reaction pathway through dual activation, it increases the electrophilic character of formyl and ester functionalities and simultaneously enhances the nucleophilic potential of the hydroxyl group to facilitate the in situ intramolecular condensation. Importantly, during this synthetic strategy no column chromatographic purification was required at any stage.