Exploring Ligand Effects on Structure, Bonding, and Photolytic Hydride Transfer of Cationic Gold(I) Bridging Hydride Complexes of Molybdocene and Tungstenocene.

A diverse family of heterobimetallic bridging hydride adducts of the type [LAu(μ-H)MCp][X] (L = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, IPr; 1,3-bis(1-adamantyl)imidazole-2-ylidene, IAd; 1,3-bis(2,6-di--propylphenyl)-5,5-dimethyl-4,6-diketopyrimidinyl-2-ylidene, DAC; triphenylphosphine, PPh; 2-di--butylphosphino-2',4',6'-triisopropylbiphenyl, XPhos; X = SbF, BF or TfO) was synthesized by reacting group VI metallocene dihydrides CpMH (Cp = cyclopentadienyl anion; M = Mo, W) with cationic gold(I) complexes [LAu(NCMe)][X]. Trimetallic [L'Au(μ-H)WCp][X] and tetrametallic [L'Au{(μ-H)WCp}] [X] complexes (L' = -2,2'-bis(diphenylphosphino)-1,1'-binaphthalene or bis(diphenylphosphinomethane)) were obtained by reacting digold [L'{Au(NCMe)}][X] with CpWH in a 1:1 and a 1:2 stoichiometry. Accessing such a broad structural diversity allowed us to pinpoint roles played by the ancillary ligands and group VI metals on the bonding properties of this family of bridging hydrides.

Scramble-Free Synthesis of Unhindered -AB-Mesoaryl Porphyrins via Bromophenyl Dipyrromethanes.

-disubstituted porphyrins are highly valuable intermediates across diverse fields, but they pose a significant synthesis challenge in some cases due to scrambling and formation of complex mixtures. Conditions that minimize scrambling also lower yields, but steric hindrance around the meso-aryl substituent can effectively suppress scrambling altogether. Here we report a straightforward approach to valuable trans-AB porphyrin intermediates that are otherwise very difficult to obtain, through use of removable blocking bromide substituents.

Luminescent Au(III)-M(I) (M = Cu, Ag) Aggregates Based on Dicyclometalated Bis(alkynyl) Gold Anions†.

The syntheses and structures of a series of complexes based on the CC-chelated Au(III) unit (CC = 4,4'-bis(-butyl) 2,2'-biphenyl-1,1'-diyl) are reported, namely, [{(CC)Au(C≡CBu)}M], (CC)Au(C≡CR)(C≡NXyl), and [{(CC)Au(C≡CR)}{M(C≡NXyl)}] (M = Ag, Cu; R = Bu, CHBu-4, CHOMe-4; Xyl = 3,5-MeCH). The X-ray structures reveal a broad range of dispositions determined by the different coordination modes of Ag(I) or Cu(I). The complexes are bright photoemitters in the solid state and in poly(methyl methacrylate) (PMMA) films.

An expedient copper-catalysed asymmetric synthesis of γ-lactones and γ-lactams. Application to the synthesis of lucidulactone A.

The parent Josiphos ligand gave excellent ee values (95-99%) and good yields (60-97%) in the copper-catalysed asymmetric conjugate reduction of β-aryl α,β-unsaturated lactones and lactams with PMHS. The substrates were obtained from stereospecific copper-catalysed addition of arylboronic acids to alkynoates followed by deprotection and cyclisation. The acyclic lactam precursors also underwent reduction with good ee values (83-85%) and yields (79-95%).

The anticancer and EGFR-TK/CDK-9 dual inhibitory potentials of new synthetic pyranopyrazole and pyrazolone derivatives: X-ray crystallography, , and mechanistic investigations.

Treatment options for the management of breast cancer are still inadequate. This inadequacy is attributed to the lack of effective targeted medications, often resulting in the recurrence of metastatic disorders. Cumulative evidence suggests that epidermal growth factor receptor (EGFR-TK) and cyclin-dependent kinases-9 (CDK-9) overexpression correlates with worse overall survival in breast cancer patients.

Tweaking the bridge in metallocene Zr(IV)/W(IV) bimetallic hydrides.

Zirconocene cations react with CpWH affording the bimetallic [CpZr(μ-H)(μ-η:η-CH)WHCp] bridging hydride 1 (Cp = cyclopentadienyl anion, CH) σ-bond metathesis. Complex 1 features an atypical out of plane Zr(μ-H)W moiety, where no intermetallic interaction is involved, and a fluxional core. Coordination geometry and bond distances of the bridging hydride interaction can be modulated upon reaction with Lewis bases and unsaturated substrates.

Synthesis, Mechanism Elucidation and Biological Insights of Tellurium(IV)-Containing Heterocycles.

Inspired by the synthetic and biological potential of organotellurium substances, a series of five- and six-membered ring organotelluranes containing a Te-O bond were synthesized and characterized. Theoretical calculations elucidated the mechanism for the oxidation-cyclization processes involved in the formation of the heterocycles, consistent with chlorine transfer to hydroxy telluride, followed by a cyclization step with simultaneous formation of the new Te-O bond and deprotonation of the OH group. Moreover, theoretical calculations also indicated anti-diastereoisomers to be major products for two chirality center-containing compounds.

Coordination chemistry of [2 + 2] Schiff-base macrocycles derived from the dianilines [(2-NHCH)X] (X = CHCH, O): structural studies and ROP capability towards cyclic esters.

Reaction of the [2 + 2] Schiff-base macrocycles {[2-(OH)-5-(R)-C6H2-1,3-(CH)2][CH2CH2(2-C6H4N)2]}2 (R = Me, L1H2; tBu, L2H2) with FeBr2 afforded the complexes [FeBr(L1H2)]2[(FeBr3)2O]·2MeCN (1·2MeCN), [FeBr(L2H2)][X] (X = 0.5(FeBr3)2O, 2·0.5MeCN, X = Br, 3·5.

Quest for a Cure: Potential Small-Molecule Treatments for COVID-19, Part 2.

During the first year of the outbreak of the COVID-19 pandemic, many drugs and drug candidates have been evaluated as treatment options. None yet has proved to be an effective cure, but progress in controlling the disease has been made. In June 2020 we published an article that described the mechanistic rationale behind the repurposing of seven licensed drugs in clinical trials for the treatment of COVID-19 and reviewed synthetic routes to these drugs.

Stability in solution and chemoprotection by octadecavanadates(IV/V) in E. coli cultures.

Two mixed-valence octadecavanadates, (NH)(MeN)[VVOI]·MeNI·5HO (VI) and [{K(OH)VVO(PO)·4HO}] (VP), were synthesized and characterized by single-crystal X-ray diffraction analysis and FTIR, Raman, V NMR, EPR and UV/Vis/NIR spectroscopies. The chemoprotective activity of VI and VP towards the alkylating agent diethyl sulfate was assessed in E. coli cultures.

Complementary Syntheses Giving Access to a Full Suite of Differentially Substituted Phthalocyanine-Porphyrin Hybrids.

Phthalocyanines and porphyrins are often the scaffolds of choice for use in widespread applications. Synthetic advances allow bespoke derivatives to be made, tailoring their properties. The selective synthesis of unsymmetrical systems, particularly phthalocyanines, has remained a significant unmet challenge.

Seven-Coordinate Tb Complexes with 90% Quantum Yields: High-Performance Examples of Combined Singlet- and Triplet-to-Tb Energy-Transfer Pathways.

Seven-coordinate, pentagonal-bipyramidal (PBP) complexes [Ln(bbpen)Cl] and [Ln(bbppn)Cl], in which Ln = Tb (products and ), Eu ( and ), and Gd ( and ), with bbpen = ,'-bis(2-oxidobenzyl)-,'-bis(pyridin-2-ylmethyl)ethylenediamine and bbppn = ,'-bis(2-oxidobenzyl)-,'-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by single-crystal X-ray diffraction analysis, alternating-current magnetic susceptibility measurements, and photoluminescence (steady-state and time-resolved) spectroscopy. Under a static magnetic field of 0.1 T, the Tb complexes and revealed single-ion-magnet behavior.

First COVID-19 molecular docking with a chalcone-based compound: synthesis, single-crystal structure and Hirshfeld surface analysis study.

The first example of molecular docking of the SARS-CoV-2 main protease for COVID-19 [M, Protein Data Bank (PDB) code 7BQY] by a chalcone-based ligand, namely, (E)-1-(2,4-dichlorophenyl)-3-[4-(morpholin-4-yl)phenyl]prop-2-en-1-one, CHClNO, I, is presented. Two-dimensional (2D) LIGPLOT representations calculated for the inhibitor N3, viz. N-{[(5-methylisoxazol-3-yl)carbonyl]alanyl}-L-valyl-N-((1R,2Z)-4-(benzyloxy)-4-oxo-1-{[(3R)-2-oxopyrrolidin-3-yl]methyl}but-2-enyl)-L-leucinamide, and 7BQY are included for comparison with our chalcone-based complexes.

Planar chiral palladacycle precatalysts for asymmetric synthesis.

Chiral non-racemic palladacycles were employed as precatalysts for Pd(0) mediated asymmetric synthesis. Addition of HPAr2/base to a ferrocenyloxazoline planar chiral palladacycle resulted in ligand synthesis and palladium capture to give a bidentate Phosferrox/Pd(0) complex. A series of these complexes were generated in situ and applied successfully as catalysts for asymmetric allylic alkylation.

Quest for a COVID-19 Cure by Repurposing Small-Molecule Drugs: Mechanism of Action, Clinical Development, Synthesis at Scale, and Outlook for Supply.

The outbreak of the COVID-19 pandemic has spurred an intense global effort to repurpose existing approved drugs for its treatment. In this review, we highlight the development of seven small-molecule drugs that are currently being assessed in clinical trials for the treatment of COVID-19. Three sections are presented for each drug: (1) history, mechanism of action, and status of clinical trials; (2) scalable synthetic routes and final forms; and (3) outlook for supply should clinical trials show treatment efficacy.

Straightforward and Controlled Synthesis of Porphyrin-Phthalocyanine-Porphyrin Heteroleptic Triple-Decker Assemblies.

A versatile and straightforward protocol is disclosed for controlled synthesis of complex lanthanide-bridged heteroleptic porphyrin-phthalocyanine triple-decker assemblies. Two porphyrins, linked by a flexible spacer chain of intermediate length, sequentially capture lanthanide ions and a phthalocyanine to efficiently form the triple-decker complex. The bridge directs assembly, but also controls the mobility of the central macrocycle and further imparts a fully eclipsed arrangement of all three rings.

An Oxalate-Bridged Copper(II) Complex Combining Monodentate Benzoate, 2,2'-bipyridine and Aqua Ligands: Synthesis, Crystal Structure and Investigation of Magnetic Properties.

A dinuclear copper(II) complex of formula [{Cu()()(OH)}(μ-)] () (where = 2,2'-bipyridine, = benzoate and = oxalate) was synthesised and characterised by diffractometric (powder and single-crystal XRD) and thermogravimetric (TG/DTG) analyses, spectroscopic techniques (IR, Raman, electron paramagnetic resonance spectroscopy (EPR) and electronic spectroscopy), magnetic measurements and density functional theory (DFT) calculations. The analysis of the crystal structure revealed that the oxalate ligand is in bis(bidentate) coordination mode between two copper(II) centres. The other four positions of the coordination environment of the copper(II) ion are occupied by one water molecule, a bidentate and a monodentate ligand.

Allene-derived gold and platinum complexes: synthesis and first applications in catalysis.

We report here the synthesis, full characterisation and first application in catalysis of novel Au(i), Au(iii) and Pt(ii) carbene-type complexes formed from bis(pyridyl)allenes. The catalytic activity of the new Au(i)-complexes in the cyclisation of 1,6-enynes, a benchmark reaction for new Au and Pt complexes, was comparable to Au(i)-state-of-the-art catalysts used in these reactions. Reactions with the new Au(iii)- and Pt(ii)-complexes occurred under milder conditions than those reported with AuCl3 and PtCl2.

Stereoselective Synthesis of All Possible Phosferrox Ligand Diastereoisomers Displaying Three Elements of Chirality: Stereochemical Optimization for Asymmetric Catalysis.

All four possible diastereoisomers of phosphinoferrocenyloxazoline (Phosferrox type) ligands containing three elements of chirality were synthesized as single enantiomers. The configured oxazoline moiety (R = Me, -Pr) was used to control the generation of planar chirality by lithiation, with the alternative diastereoisomer formed by use of a deuterium blocking group. In each case subsequent addition of PhPCl followed by -TolMgBr resulted in a single -stereogenic diastereoisomer (,, and ,,, respectively).

Hydride Transfer to Gold: Yes or No? Exploring the Unexpected Versatility of Au⋅⋅⋅H-M Bonding in Heterobimetallic Dihydrides.

The potential for coordination and H-transfer from Cp MH (M=Zr, W) to gold(I) and gold(III) complexes was explored in a combined experimental and computational study. [(L)Au] cations react with Cp WH giving [(L)Au(κ -H WCp )] (L=IPr (1), cyclic (alkyl)(amino)carbene (2), PPh (3) and Dalphos-Me (4) [IPr=1,3-bis(diisopropylphenyl)imidazolylidene; Dalphos-Me=di(1-adamantyl)-2-(dimethylamino)phenyl-phosphine], while [Au(DMAP) ] (DMAP=p-dimethylaminopyridine) affords the C -symmetric [Au(κ-H WCp ) ] (5). The Dalphos complex 4 can be protonated to give the bicationic adduct 4 H, showing Au ⋅⋅⋅H -N hydrogen bonding.

H activation by zirconaziridinium ions: σ-bond metathesis versus frustrated Lewis pair reactivity.

Zirconaziridinium ions [CpZr(η-CHNR)] can potentially activate H by two routes: σ-bond metathesis or FLP reactivity. We show here that Zr-C hydrogenolysis by σ-bond metathesis precedes and enables subsequent heterolytic H cleavage through FLP pathways. DFT calculations show the involvement of transition states with approximately linear NHH and bent ZrHH arrangements without any direct Zr-amine interaction.

Do Gold(III) Complexes Form Hydrogen Bonds? An Exploration of Au Dicarboranyl Chemistry.

The reaction of 1,1'-Li [(2,2'-C B H ) ] with the cyclometallated gold(III) complex (C^N)AuCl afforded the first examples of gold(III) dicarboranyl complexes. The reactivity of these complexes is subject to the trans-influence exerted by the dicarboranyl ligand, which is substantially weaker than that of non-carboranyl anionic C-ligands. In line with this, displacement of coordinated pyridine by chloride is only possible under forcing conditions.

Unusual Nucleophilic Addition of Grignard Reagents in the Synthesis of 4-Amino-pyrimidines.

Pyrimidines have always received considerable attention because of their importance in synthesis and elucidation of biochemical roles, in particular that of vitamin B1. Herein, we describe a reaction pathway in a Grignard reagent-based synthesis of substituted pyrimidines. A general synthesis of α-keto-2-methyl-4-amino pyrimidines and their C6-substituted analogues from 4-amino-5-cyano-2-methylpyrimidine is reported.

Promoting a Significant Increase in the Photoluminescence Quantum Yield of Terbium(III) Complexes by Ligand Modification.

Two discrete mononuclear complexes, [Tb(bbpen)(NO)] () and [Tb(bbppn)(NO)] (), for which = -bis(2-hydroxybenzyl)--bis(pyridin-2-ylmethyl)ethylenediamine and = bis(2-hydroxylbenzyl)-bis(pyridin-2-ylmethyl)-1,2-propanediamine, were synthesized and characterized by FTIR, Raman, and photoluminescence (PL, steady-state and time-resolved modes) spectroscopy. The attachment of a methyl group to the ethylenediamine portion of the ligand backbone differentiates from and acts as a determining feature to both the structural and optical properties of the former. The single-crystal X-ray structure of is described here for the first time, while that of complex has been redetermined in the monoclinic 2 space group in light of new diffraction data.

Methyl Ester Functionalized Phenalenyl Arene- and Bipyridine-Ruthenium-Based Complexes for Electroactive Langmuir-Blodgett Films.

We report the synthesis of a new phenalenyl ligand, functionalized with a methyl ester electron withdrawing group, named 9-hydroxy-1-oxo-1 H-phenalen-5-methyl carboxylate (L), and the generated complexes [Ru(bpy)L]PF and [(η-CH)Ru(L)Cl]. Compounds were characterized by spectroscopic and X-ray diffraction methods, and their electrochemical behavior was investigated via cyclic voltammetry and UV-vis spectroelectrochemistry. The one-electron oxidized compounds have an unpaired electron located in the phenalenyl ring, as supported by theoretical calculations (DFT) and EPR results.