Organogold(III) metallacyclic chemistry. Part 4. Synthesis, characterisation, and biological activity of gold(III)-thiosalicylate and -salicylate complexes

The silver(I) oxide mediated reactions of the gold(III) dichloride complex [{C₆H₃(CH₂

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uCl₂] 2a with thiosalicylic or salicylic acid gives the respective complexes [{C₆H₃(CH₂

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)-2}] 3a (X=S) or 6b (X=O), containing chelating thiosalicylate or salicylate dianion ligands. X-ray studies show that for the thiosalicylate system, the thiosalicylate sulfur atom is trans to the N,N-dimethylamino group, whereas in the structure of the salicylate complex, it is the carboxylate group that is trans to NMe₂. Both complexes show puckered metallacycles in the solid state. Electrospray mass spectrometry (ESMS) shows strong [M+H]⁺ and [2M+H]⁺ ions for both the gold-thiosalicylate and -salicylate complexes, and these ions possess a high stability towards cone voltage-induced fragmentation. ESMS was also used to identify a minor impurity, the bis(cyclo-aurated) cationic complex [A

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Me₂)-2-(OMe)-5}2]⁺ in the starting dihalide complex 2a and in the product 3a. This complex can be formed by reaction of Me₄N[AuCl₄] with 2 equivalents of the organomercury precursor [Hg{C₆H₃(CH₂NMe₂)-2-(OMe)-5}Cl]. The biological (antitumour, antimicrobial and antiviral) activities are also reported, and these reveal the complexes have moderate to high anti-tumour, antibacterial and antifungal activity.     

Synthesis and crystallographic characterization of a ‘palladadehydrobenzo[19]annulene’

The trans-palladium bis(σ-acetylide) complex (Et₃P)₂Pd(C₃₀H₁₂) (2) was synthesized from hexane 4 in 77% yield via a simple three-step process. The X-ray crystal structure of 2 shows a strained and warped annulenic core upon insertion of the organometallic fragment. UV-vis data of the molecule suggest limited electronic delocalization throughout the metallacycle.     

Recent development of aminophosphine chalcogenides and boranes as ligands in s-block metal chemistry

The coordination chemistry of the aminophosphine chalcogenide ligands [Ph₂P(O)NHR], [Ph₂P(S)NHR], and [Ph₂P(Se)NHR] (R = 2,6-Me₂C₆H₃,^tBu, CHPh₂, CPh₃) or corresponding borane derivative [Ph₂P(BH₃)NHR] toward group 1 and 2 metals is reviewed. The structural characterization of a huge number of mono- and bis-aminophosphine chalcogenide/borane complexes with group 1 and 2 metals—in most cases lithium, sodium, potassium, magnesium, calcium, strontium, and barium complexes—reveals a poly-metallacyclic motif in each case. The coordination takes place from adjacent chalcogen/borane and nitrogen as donor atom or group of the ligand confirming the direct bond between metal and chalcogen/borane to develop homoleptic and heteroleptic complexes. The heteroleptic group 2 metal complexes were used as pre-catalysts in hydrophosphination and hydroamination reactions. Similarly, aminophosphine chalcogenide alkaline earth metal complexes were used in the catalytic ring-opening polymerization (ROP) study of ?-caprolactone.     

Conformational fluxionality in a palladium(II) complex of flexible click chelator 4-phenyl-1-(2-picolyl)-1,2,3-triazole: A dynamic NMR and DFT study

An experimental and theoretical DFT study was carried out on the solution behavior in [D₇]DMF for bis-chelate complex [Pd(L)₂](BF₄)₂·2CH₃CN (L = 4-phenyl-1-(2-picolyl)-1,2,3-triazole). In structure of [Pd(L)₂]²⁺, the central square-planar palladium(II) cation is trans-chelated by two L substrates, each through the pyridine and the triazole N2 nitrogen atoms, forming two six-membered metallacycles. These can adopt boat-like conformations anti-trans-[Pd(L)₂]²⁺ and syn-trans-[Pd(L)₂]²⁺ in which the picolyl methylene carbons are anti or syn, respectively, relative to the palladium coordination plane. In solution, the boat-to-boat inversion at both metallacycles takes place. The conformers are in a dynamic equilibrium, which was monitored by variable-temperature (VT) ¹H NMR spectroscopy in the temperature range of 223-353 K. The equilibrium lies on the side of the anti-trans-[Pd(L)₂]²⁺ conformer and the corresponding reaction enthalpy and entropy is estimated to be 0.6 ± 0.5 kcal mol⁻¹ and 0.8 ± 1 cal mol⁻¹ K⁻¹, respectively. From the full-line-shape analysis of resonances in the VT ¹H NMR spectra, the activation enthalpy and activation entropy was determined to be 13.0 ± 0.4 kcal mol⁻¹ and 2.7 ± 1.6 cal mol⁻¹ K⁻¹, respectively. The activation entropy close to zero suggests a nondissociative mechanism for the isomerisation. DFT investigation revealed that the isomerisation proceeds through a one step mechanism with a barrier of 11.40 kcal mol⁻¹. The structures of the syn and anti conformers as well as that of the transition state were characterized. Energy decomposition analysis was carried out in order to explore the origins of the stability difference between the syn and anti isomers.     

Oxidation reactions using water, hydrogen peroxide and halogens to give pallad(IV) cyclopentane complexes PdX(C4H8 {(pz)3BH} (X = OH, Cl, Br, I). The crystal structure of the hydroxoplatinum(IV) complex Pt(OH)Me2{(pz)3BH}, formed by use of water as an oxidant

The pallada(II)cyclopentane reagent [Pd(C₄H₈{(pz)₃BH}]⁻, generated by addition of potassium tris(pyrazol-1-yl)borate to the tetramethylethylenediamine analogue, reacts with water or hydrogen peroxide to give hydroxopalladium(IV) complex Pd(OH)(C₄H₈){(pz)₃BH}. Similar oxidation reactions occur with phenyliodonium dichloride, bromine and iodine to give PdX(C₄H₈){(pz)₃BH} (X = Cl, Br, I). The hydroxoplatinum(IV) complex Pt(OH)Me₂{(pz)₃BH} has been obtaine reaction of [PtMe₂(SEt₂)]₂ with K[(pz)₃BH], followed by addition of water, and its structure determined by an X-ray diffraction study.     

Platinum Metallacycle-Based Molecular Recognition: Establishment and Application in Spontaneous Formation of a [2]Rotaxane with Light-Harvesting Property

Macrocyclic molecule-based host–guest systems, which provide contributions for the design and construction of functional supramolecular structures, have gained increasing attention in recent years. In particular, platinum(II) metallacycle-based host–guest systems provide opportunities for chemical scientists to prepare novel materials with various functions and structures due to the well-defined shapes and cavity sizes of platinum(II) metallacycles. However, the research on platinum(II) metallacycle-based host–guest systems has been given little attention. In this article, we demonstrate the host–guest complexation between a platinum(II) metallacycle and a polycyclic aromatic hydrocarbon molecule, naphthalene. Taking advantage of metallacycle-based host–guest interactions and the dynamic property of reversible Pt coordination bonds, a [2]rotaxane is efficiently prepared by employing a template-directed clipping procedure. The [2]rotaxane is further applied to the fabrication of an efficient light-harvesting system with multi-step energy transfer process. This work comprises an important supplement to macrocycle-based host–guest systems and demonstrates a strategy for efficient production of well-defined mechanically interlocked molecules with practical values.     

Synthesis, structure and electrochemistry of CO incorporated diruthenium metallacyclic compounds [Ru2(CO)6{μ-η:η:η:η-1,4-Fc2C5H2O}] and [Ru2(CO)6{μ-η:η:η:η-1,5-Fc2C5H2O}]

Ferrocenyl substituted ruthenium metallacyclic compounds, [Ru₂(CO)₆{μ-η¹:η¹:η²:η²-1,4-Fc₂C₅H₂O}] (1) and [Ru₂(CO)₆{μ-η¹:η¹:η²:η²-1,5-Fc₂C₅H₂O}] (2) have been synthesized and structurally characterized. Electrochemical studies for 1 and 2 and the respective quinone derivatives 3 and 4 show weak to no electrochemical coupling at the mixed-valent intermediate state which is dependent on the complex frameworks.     

N- vs O-Coordination in cyclomanganation of 1,5-diaryl-3-(2-pyridyl)pentane-1,5-diones and 3-(2-pyridyl)chalcones; cyclomanganation at saturated carbon and the crystal structure of [1,5-diphenyl-κC-3-(2-pyridyl- κN)pentan-2-yl-κC-1,5-dione-κOκO]tetracarbonylmanganesetricarbonylmanganese

Reaction of 1,5-diphenyl-3-(2-pyridyl)pentane-1,5-dione (5a) with 2.5 moles of benzylpentacarbonylmanganese in petroleum spirit under reflux gives a small amount of the symmetric di-aryl-manganated product [1,5-diphenyl-κC²-3-(2-pyridyl)pentane-1,5-dione-κO¹κO⁵]bis-(tetracarbonylmanganese) (7a), but mostly [1,5-diphenyl-κC²-3-(2-pyridyl-κN)pentan-2-yl- κC²-1,5-dione-κO¹κO⁵]tetracarbonylmanganesetricarbonylmanganese (6a) which is manganated at only one aryl carbon [by Mn(CO)₄] but also [by Mn(CO)₃ with N and O coordination] at the methylene carbon adjacent to the Mn(CO)₄-coordinated ketone carbonyl. The latter is a rare example of direct cyclomanganation at a saturated carbon and the only known case adjacent to a carbonyl group; the X-ray crystal structure of 6a is reported. With 3 moles of benzylpentacarbonylmanganese the yield of 6a remains unchanged but some trimanganation product [1,5-diphenyl-κC^2′κC^2?-3-(2-pyridyl-κN)pentan-2-yl-κC²-1,5-dione-κO¹κO⁵]tris-(tetracarbonylmanganese) (8a) is formed, presumably from 7a. Routes to products are proposed and activating factors considered. 1,5-Di-(2-thienyl)-3-(2-pyridyl)pentane-1,5-dione (5b) and its 3-thienyl isomer (5c) similarly give 6a analogues [1,5-di-(2-thienyl-κC³)-3-(2-pyridyl-κN)pentan-2-yl-κC²-1,5-dione-κO¹κO⁵]tetracarbonylmanganesetricarbonylmanganese (6b) and [1,5-di-(3-thienyl-κC²)-3-(2-pyridyl-κN)pentan-2-yl-κC²-1,5-dione-κO¹κO⁵]tetracarbonylmanganesetricarbonylmanganese (6c).Also reported are the mono-cyclomanganation product [1-(2,6-dimethoxyphenyl)-3-(2-pyridyl-κN)prop-2-en-2-yl-κC²-1-one]tetracarbonylmanganese (16) and dicyclomanganation product [1-(2,5-dimethyl-3-thienyl-κC⁴)-3-(2-pyridyl-κN)prop-2-en-2-yl- κC²-1-one-κO ]bis-(tetracarbonylmanganese) (17) from reaction of the respective (E)-1-aryl-3-(2-pyridyl)prop-2-en-1-ones (3-(2-pyridyl)chalcones), the first reported examples of enone metallation at the α-carbon via N-coordination by a β-2-pyridyl group.     

Synthesis and characterization of pyridine- and thiophene-based platinacyclynes

Seven heterocyclic macrocycles, including the first platinacycles with pyridine and thiophene rings incorporated into the cyclyne system, are reported. Pt-acetylide cyclynes were assembled via tin transmetallation or amine-mediated oxidative addition with stoichiometric PtCl₂(PEt₃)₂ and CuI. The organometallic cyclynes exhibited enhanced electronic properties compared to previously described platinabenzocyclynes.     

Osmium-carbon multiple bonds: Reduction and C-C coupling reactions

This paper shows that the redox equilibria hydride-alkenylcarbyne/alkenylcarbene and alkenyl-alkenylcarbyne/dienylcarbene are readily governed by the electronic properties of the ligands of the complexes. Because we have learned to control the position of these equilibria, we are able to build, step by step, osmium derivatives with cyclic alkenylcarbene ligands and osmacyclopentapyrrole complexes. The dihydride OsH₂Cl₂(PⁱPr₃)₂ reacts with alkynols, allenes, enynes, and dienes to give hydride-alkenylcarbyne derivatives, OsHCl₂(CCR′CR₂)(PⁱPr₃)₂, which can be transformed into dicationic species by replacement of chloride ligands by acetonitrile molecules. The selective deprotonation of the alkenylcarbyne ligand of [OsH(CCHCPh₂)(CH₃CN)₂(PⁱPr₃)₂]²⁺ affords the hydride-allenylidene [OsH(CCCPh₂)(CH₃CN)₂(PⁱPr₃)₂]⁺, which undergoes the reduction of the C_α-C_β double bond of the cumulene in the presence of alcohols. The insertion of monosubstituted alkynes into the Os-H bond of the hydride-allenylidene complex leads to alkenyl-allenylidene derivatives, which are transformed into dienylcarbene compounds. The coordination of carbon monoxide to the osmium atom of the latter promotes the 4π-conrotation of the dienylcarbene ligand, to afford a cyclic alkenylcarbene complex via an η¹-cyclopentadienyl intermediate. Through a similar cyclization, in acetonitrile under reflux, the alkenyl-allenylidene complexes are converted into osmapyrrole derivatives by means of the formation of three C-C bonds involving the three carbon atoms of the cumulene, the alkenyl ligand, and an acetonitrile molecule.