Iridium Complexes Containing Bis(imidazoline thione) and Bis(imidazoline selone) Ligands for Visible-Light-Induced Oxidative Coupling of Benzylamines to Imines

Phenylbenzothiazole-Based Platinum(II) and Diplatinum(II) and (III) Complexes with Pyrazolate Groups: Optical Properties and Photocatalysis

Based on 2-phenylbenzothiazole (pbt) and 2-(4-dimethylaminophenyl)benzothiazole (Me2N-pbt), mononuclear [Pt(pbt)(R'2-pzH)2]PF6 (R'2-pzH = pzH 1a, 3,5-Me2pzH 1b, 3,5-iPr2pzH 1c) and diplatinum (PtII-PtII) [Pt(pbt)(μ-R'2pz)]2 (R'2-pz = pz 2a, 3,5-Me2pz 2b, 3,5-iPr2pz 2c) and [Pt(Me2N-pbt)(μ-pz)]2 (3a) complexes have been prepared. In the presence of sunlight, 2a and 3a evolve, in CHCl3 solution, to form the PtIII-PtIII complexes [Pt(R-pbt)(μ-pz)Cl]2 (R = H 4a, NMe2 5a). Experimental and computational studies reveal the negligible influence of the pyrazole or pyrazolate ligands on the optical properties of 1a-c and 2a,b, which exhibit a typical 3IL/3MLCT emission, whereas in 2c the emission has some 3MMLCT contribution. 3a displays unusual dual, fluorescence (1ILCT or 1MLCT/1LC), and phosphorescence (3ILCT) emissions depending on the excitation wavelength. The phosphorescence is lost in aerated solutions due to sensitization of 3O2 and formation of 1O2, whose determined quantum yield is also wavelength dependent. The phosphorescence can be reversibly photoinduced (365 nm, ∼ 15 min) in oxygenated THF and DMSO solutions. In 4a and 5a, the lowest electronic transitions (S1-S3) have mixed characters (LMMCT/LXCT/L'XCT 4a and LMMCT/LXCT/ILCT 5a) and they are weakly emissive in rigid media. The 1O2 generation property of complex 3a is successfully used for the photooxidation of p-bromothioanisol showing its potential application toward photocatalysis.

Selective aerobic coupling of amines to imines using solar spectrum-responsive flower-like Nen-graphene quantum dots (GQDs) decorated with 2, 4-dinitrophenylhydrazine (PH) as a photocatalyst

Indeed, the development of ecologically benign molecular fabrication methods for highly efficient graphene quantum dots-based photocatalysts is of great significant. Graphene quantum dots-based photocatalysts have promising applications in various field, including environmental remediation, energy conversion, and splitting of water. However, ensuring resource reusability and minimizing the environmental impact are crucial considerations in the development. From this perspective, attention has also been paid to the creation of easy to make solar light harvesting graphene quantum dots-based photocatalysts for synthesising pharmaceuticals and functional imines compounds. Imines are excellent significant building blocks in pharmaceutical chemistry and excellent examples of these valuable compounds' synthetic intermediates, and the environmentally friendly oxidative synthesis of imines from amines. Therefore, herein, we designed a facile and efficient condensation route to synthesize the Nen-GQDs@PH photocatalyst. This route involves coupling of 2,4-dinitrophenylhydrazine (PH) with nitrogen-enriched graphene quantum dots (Nen-GQDs). The Nen-GQDs@PH as photocatalyst functions in a highly selective and efficient manner, leading to high amines conversion efficiency to imines (95%). Our results highlight a novel and environmentally safe approach for generating highly selective imines from various types of amines, setting a new benchmark in the current research field.

Highly bioactive novel aryl-, benzyl-, and piperazine-selenoureas: synthesis, structural characterization and in vitro biological evaluation

Selenoureas are widespread as useful elements for constructing important species and biologically active molecules. Finding an efficient and straightforward method to prepare this motif and biologically screen derivatives thereof is crucial. Herein, we demonstrate the effectiveness of using ethanol as a solvent in the preparation of various substituted aryl-, benzyl-, and piperazine-selenoureas from isoselenocyanates and amines. The synthetic method includes mild reaction conditions, large substrate scope, and good isolated yields. Biological evaluation of the prepared products on MDA-MB-231 and MCF-7 cancer cell lines revealed several remarkably active compounds (IC₅₀ < 10 μΜ) with the best one exhibiting IC₅₀ values of 1.8 μΜ and 1.2 μΜ observed against the challenging former triple-negative breast cancer cell line and the latter one, respectively. The chemical structures of all new compounds were fully characterized by multinuclear nuclear magnetic resonance (NMR) spectroscopy and high accuracy mass measurements.

Extended phenothiazines: synthesis, photophysical and redox properties, and efficient photocatalytic oxidative coupling of amines

Herein, we successfully developed a ring-fusion approach to extend the conjugation length of phenothiazines that were demonstrated to be efficient photocatalysts for visible-light-driven oxidative coupling reactions of amines under an air atmosphere.

Singlet Oxygen Generation, Quenching, and Reactivity with Metal Thiolates

Metal thiolate complexes can act as photosensitizers for the generation of singlet oxygen, quenchers of singlet oxygen, and they may undergo chemical reactions with singlet oxygen leading to oxidized thiolate ligands. This review covers all of the chemical reactions of thiolate ligands with singlet oxygen (through early 2021). Since some of these reactions are self-sensitized photooxidations, singlet oxygen generation by metal complexes is also discussed. Mechanistic features such as the effects of protic vs. aprotic conditions are presented and compared with the comparatively well-understood photooxidation of organic sulfides. In general, the total rate of singlet oxygen removal correlates with the nucleophilicity of the thiolate ligand which in turn can be influenced by the metal. Some interesting patterns of reactivity have been noted as a result of this survey: Metal thiolate complexes bearing arylthiolate ligands appear to exclusively produce sulfinate (metal-bound sulfone) products upon reaction with singlet oxygen. In contrast, metal thiolate complexes bearing alkylthiolate ligands may produce sulfinate and/or sulfenate (metal-bound sulfoxide) products. Several mechanistic pathways have been proposed for these reactions, but the exact nature of any intermediates remains unknown at this time.

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.

Reframing primary alkyl amines as aliphatic building blocks

While primary aliphatic amines are ubiquitous in natural products, they are traditionally considered inert to substitution chemistry. This review highlights historical and recent advances in the field of aliphatic deamination chemistry which demonstrate these moieties can be harnessed as valuable C(sp3) synthons. Cross-coupling and photocatalyzed transformations proceeding through polar and radical mechanisms are compared with oxidative deamination and other transition metal catalyzed reactions.

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.

Bis-Anthracene Fused Porphyrin as an Efficient Photocatalyst: Facile Synthesis and Visible-Light-Driven Oxidative Coupling of Amines

Development of high-performance photocatalysts for the conversion of amines is of great importance, but has remained a challenging task. Here, a bis-anthracene fused porphyrin (AFP) was synthesized in a high yield by a facile synthetic protocol, which involves a Suzuki coupling for the conjugation of two anthracene groups with a porphyrin ring, followed by oxidative cyclodehydrogenation. When serving as a photocatalyst, AFP exhibits an outstanding photocatalytic performance for the visible-light-induced aerobic oxidation of amines to imines at ambient conditions. Density functional theory calculations revealed that the low energy band gap, caused by the large planar and π-extended porphyrin structure of AFP, contributed to its high photocatalytic performance.

Non-emissive RuII Polypyridyl Complexes as Efficient and Selective Photosensitizers for the Photooxidation of Benzylamines

Five new Ru^II polypyridyl complexes bearing N-(arylsulfonyl)-8-amidoquinolate ligands and three of their biscyclometalated Ir^III congeners have been prepared and employed as photocatalysts (PCs) in the photooxidation of benzylamines with O₂ . In particular, the new Ru^II complexes do not exhibit photoluminescence, rather they harvest visible light efficiently and are very stable in solution under irradiation with blue light. Their non-emissive behavior has been related to the low electrochemical energy gaps and rationalized on the basis of theoretical calculations (DFT analysis) that predict low S₀ ←T₁ energy values. Moreover, the Ru^II complexes, despite being non-emissive, display excellent activities in the selective photocatalytic transformation of benzylamines into the corresponding imines. The presence of an electron-withdrawing group (-CF3) on the arene ring of the N-(arylsulfonyl)-8-amidoquinolate ligand improves the photocatalytic activity of the corresponding photocatalyst. Furthermore, all the experimental evidence, including transient absorption spectroscopy measurements suggest that singlet oxygen is the actual oxidant. The Ir^III analogues are considerably more photosensitive and consequently less efficient photosensitizers (PSs).

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.

Cyclometalated rhodium and iridium complexes with imidazole containing Schiff bases: Synthesis, structure and cellular imaging

Cyclometalated rhodium(III) and iridium(III) complexes (1-4) of two Schiff base ligands L1 and L2 with the general formula [M(ppy)2(Ln)]Cl {M = Rh, Ir; ppy = 2-phenylpyridine; n = 1, 2; L = Schiff base ligand} have been synthesized. The new ligands and the complexes have been characterized with spectroscopic techniques. Electrochemistry of the complexes revealed anodic behavior, corresponding to an M(III) to M(IV) oxidation. The X-ray crystal structures of complexes 2 and 4 have also been determined to interpret the coordination behavior of the complexes. Photophysical study shows that all the complexes display fluorescence at room temperature with quantum yield of about 3 × 10-2 to 5 × 10-2. The electronic absorption spectra of all the complexes fit well with the computational studies. Cellular imaging studies were done with the newly synthesized complexes. To the best of our knowledge, this is the first report of organometallic complexes of rhodium(III) and iridium(III) with Schiff base ligands explored for cellular imaging. Emphasis of this work lies on the structural features, photophysical behavior, cellular uptake and imaging of the fluorescent transition metal complexes.

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.

Silver doped reduced graphene oxide as a promising plasmonic photocatalyst for oxidative coupling of benzylamines under visible light irradiation

Visible light assisted photocatalytic reduction of nitro-compounds has been found as an efficient and sustainable approach for the production of amines.

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.

Phosphorescent cationic iridium(iii) complexes bearing a nonconjugated six-membered chelating ancillary ligand: a strategy for tuning the emission towards the blue

Blue and blue-green-emitting cationic Ir(iii) complexes bearing a nonconjugated N^N ligand have been studied.

Synthesis, characterization and Pd(ii)-coordination chemistry of the ligand tris(quinolin-8-yl)phosphite. Application in the catalytic aerobic oxidation of amines

The ligand P(Oquin)₃ is reported and was coordinated to Pd(ii). This complex is a catalyst precursor for the homocoupling of amines.

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).

Stable luminescent iridium(iii) complexes with bis(N-heterocyclic carbene) ligands: photo-stability, excited state properties, visible-light-driven radical cyclization and CO2 reduction, and cellular imaging

Excited state properties, photo-catalysis and cellular imaging of photo-stable bis-NHC Ir(iii) complexes are described.

A new class of cyclometalated Ir(iii) complexes supported by various bidentate C-deprotonated (C^N) and cis-chelating bis(N-heterocyclic carbene) (bis-NHC) ligands has been synthesized. These complexes display strong emission in deaerated solutions at room temperature with photoluminescence quantum yields up to 89% and emission lifetimes up to 96 μs. A photo-stable complex containing C-deprotonated fluorenyl-substituted C^N shows no significant decomposition even upon irradiation for over 120 h by blue LEDs (12 W). These, together with the strong absorption in the visible region and rich photo-redox properties, allow the bis-NHC Ir(iii) complexes to act as good photo-catalysts for reductive C–C bond formation from C(sp³/sp²)–Br bonds cleavage using visible-light irradiation (λ > 440 nm). A water-soluble complex with a glucose-functionalized bis-NHC ligand catalysed a visible-light-driven radical cyclization for the synthesis of pyrrolidine in aqueous media. Also, the bis-NHC Ir(iii) complex in combination with a cobalt catalyst can catalyse the visible-light-driven CO₂ reduction with excellent turnover numbers (>2400) and selectivity (CO over H₂ in gas phase: >95%). Additionally, this series of bis-NHC Ir(iii) complexes are found to localize in and stain endoplasmic reticulum (ER) of various cell lines with high selectivity, and exhibit high cytotoxicity towards cancer cells, revealing their potential uses as bioimaging and/or anti-cancer agents.

Osmium(ii) complexes for light-driven aerobic oxidation of amines to imines

We have investigated new photocatalytic systems for imine formation under mild reaction conditions using three triazole-based Os(ii) complexes as potential photocatalysts.

Bismuth(iii)dichalcogenones as highly active catalysts in multiple C–C bond formation reactions

Thirteen new bismuth(iii) dichalcogenone derivatives with diversified structural motifs were successfully isolated and used as potential catalysts for the synthesis of triaryl- or triheteroarylmethanes.

Facile access to zinc and cadmium selones: highly active catalysts for Barbier reactions in aqueous media

Zinc and cadmium imidazoline selone complexes were synthesized and demonstrated to be potential catalysts for Barbier coupling in aqueous alcohol media.

Bioinspired organocatalytic aerobic C-H oxidation of amines with an ortho-quinone catalyst

A simple bioinspired ortho-quinone catalyst for the aerobic oxidative dehydrogenation of amines to imines is reported. Without any metal cocatalysts, the identified optimal ortho-quinone catalyst enables the oxidations of α-branched primary amines and cyclic secondary amines. Mechanistic studies have disclosed the origins of different performances of ortho-quinone vs para-quinone in biomimetic amine oxidations.

Factors influencing the regioselectivity of the oxidation of asymmetric secondary amines with singlet oxygen

Aerobic amine oxidation is an attractive and elegant process for the α functionalization of amines. However, there are still several mechanistic uncertainties, particularly the factors governing the regioselectivity of the oxidation of asymmetric secondary amines and the oxidation rates of mixed primary amines. Herein, it is reported that singlet-oxygen-mediated oxidation of 1° and 2° amines is sensitive to the strength of the α-C-H bond and steric factors. Estimation of the relative bond dissociation energy by natural bond order analysis or by means of one-bond C-H coupling constants allowed the regioselectivity of secondary amine oxidations to be explained and predicted. In addition, the findings were utilized to synthesize highly regioselective substrates and perform selective amine cross-couplings to produce imines.

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.

Singlet oxygen generation by cyclometalated complexes and applications

While cyclometalated complexes have been extensively studied for optoelectronic applications, these compounds also represent a relatively new class of photosensitizers for the production of singlet oxygen. Thus far, singlet oxygen generation from cyclometalated Ir and Pt complexes has been studied in detail. In this review, photophysical data for singlet oxygen generation from these complexes are presented, and the mechanism of (1) O2 generation is discussed, including evidence for singlet oxygen generation via an electron-transfer mechanism for some of cyclometalated Ir complexes. The period from the first report of singlet oxygen generation by a cyclometalated Ir complex in 2002 through August 2013 is covered in this review. This new class of singlet oxygen photosensitizers may prove to be rather versatile due to the ease of substitution of ancillary ligands without loss of activity. Several cyclometalated complexes have been tethered to zeolites, polystyrene, or quantum dots. Applications for photooxygenation of organic molecules, including "traditional" singlet oxygen reactions (ene reaction, [4 + 2] and [2 + 2] cycloadditions) as well as oxidative coupling of amines are presented. Potential biomedical applications are also reviewed.