Use of a porphyrin platform and 3,4-HPO chelating units to synthesize ligands with N4 and O4 coordination sites

Piperazine and 1,2-diaminobenzene have been previously used as anchoring molecules to synthesize 3-hydroxy-4-pyridinone (3,4-HPO) tetradentate ligands affording ligands with different flexibility and coordination properties. In order to have a relatively rigid and hindered structure, a porphyrin platform was selected to anchor one or two 3,4-HPO chelating units. This platform provides an additional N₄ coordination sphere and also very interesting optical properties to the synthesized conjugates. Depending on the metal ion present in the porphyrin core, conjugates with different spectroscopic properties are obtained. EPR spectroscopy has been used to characterize the copper(II) metalloporphyrins and to monitor and identify the species formed upon addition of copper(II) to solutions of two porphyrin conjugates with one and two 3,4-HPO arms. The porphyrin conjugates having two 3,4-HPO units are ligands that provide two separate binding sites with N₄ and O₄ coordination spheres, which allow accommodation of two metal ion centers that may be distinguished by spectroscopic methods.     

Metal Linkage Effects on Ultrafast Energy Transfer

We report the preparation of several new porphyrin homodimers bridged by a platinum(II) ion in which very intense electronic communication through the coordination link occurs. Moreover, the synthesis of a new porphyrin dyad and its photophysical properties are reported. This dyad exhibits the fastest singlet energy transfer ever reported for synthetic systems between a zinc(II) porphyrin and a porphyrin free base. This extremely fast transfer (～100 femtoseconds) is in the same range as the fastest one measured in natural systems. This feature is due to the platinum(II) linker, which allows for strong MO couplings between the two porphyrin units as experimentally supported by electrochemistry and corroborated by DFT computations.     

Structural parameters of close surroundings of Sr2+ and Ba2+ ions in aqueous solutions of their salts

Published data on various techniques of studying structural characteristics of close surroundings of strontium(II) and barium(II) ions in aqueous solutions of their salts under standard conditions (coordination numbers, interparticle distances, parameters of the second coordination sphere, and ionic association types) have been generalized. It has been concluded that the Sr²⁺ ion coordinates eight water molecules in the first coordination sphere, and the Ba²⁺ ion, nine water molecules, at average distances of 0.262 and 0.283 nm, respectively. Both ions form the second coordination sphere at average distances of 0.493 and 0.500 nm, respectively. There is a well-pronounced trend to the formation of ion pairs.     

Interactions of the ethanolamino groups of nanofilms with Co(II), Ni(II), Cu(II), Zn(II), and Cr(III) ammoniates at the surface of PVC plates

Interactions of nanofilms containing ethanolamino groups with cobalt(II), nickel(II), copper(II), and zinc(II) ammoniates at the surface of polyvinylchloride plates and with chromium(III) ammoniate in a solution of ammonium chloride were studied. It was found that the groups of the film, together with chloride ions, displace all ammonia molecules from the inner coordination sphere of the metal. The average number of the ethanolamino N atoms of the film participating in formation of the metal ion coordination sphere is 3.35, 3.47, 3.67, 3.42, and 3.37 for Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, and Cr³⁺ complexes, respectively. The average number of chloride ions is 2 for Co²⁺, Ni²⁺, Cu²⁺, and Zn²⁺ and 3 for Cr³⁺. The coordination number of the central atoms is 6. The Cr³⁺ ion forms a coordination sphere composed of three N atoms and three chloride ions and a coordination sphere (charged 1+) made up of four N atoms and two chloride ions, with the third chloride ion being in the outer sphere. The Co²⁺, Ni²⁺, and Cu²⁺ ions form uncharged coordination spheres of two types: (1) with four N atoms and two chloride ions and (2) with three N atoms, two chloride ions, and the O atom of the ethanol hydroxyl group.     

Calculations of microconstants and equilibrium formation constants for platinum(II) and palladium(II) halide complexes in solution

Distribution diagrams and formation functions for halide complexes [M(H₂O)_{4 ? n} Cl _n ]^{2 ? n} (M = Pt(II) or Pd(II)) and [PdCl_{4 ? n} Br _n ]^2? (n = 0?C4) in solution are analyzed in terms of the matrix model. Equilibrium constants for binding the first ligand $\left( {\bar K} \right)$ and corrections for the mutual influence between ligands (??) in the course of complex formation in solution are calculated. In examples analyzed, the substitution of chloride ion for water in the coordination sphere of platinum(II) and palladium(II) is an anti-cooperative process. The substitution of bromide ion for chloride ion in the coordination sphere of [PdCl₄]^2? is weakly cooperative. Quantum-chemical calculations show that platinum(II) and palladium(II) cis-bisaquadichloro complexes in the gas phase are thermodynamically less stable than trans-isomers. The cis-trans isomerization constants in the gas phase calculated by the DFT method and those found for solutions using the matrix model have the same order of magnitude.     

Highly Stable Water‐Soluble Platinum Nanoparticles Stabilized by Hydrophilic N‐Heterocyclic Carbenes

Controlling the synthesis of stable metal nanoparticles in water is a current challenge in nanochemistry. The strategy presented herein uses sulfonated N‐heterocyclic carbene (NHC) ligands to stabilize platinum nanoparticles (PtNPs) in water, under air, for an indefinite time period. The particles were prepared by thermal decomposition of a preformed molecular Pt complex containing the NHC ligand and were then purified by dialysis and characterized by TEM, high‐resolution TEM, and spectroscopic techniques. Solid‐state NMR studies showed coordination of the carbene ligands to the nanoparticle surface and allowed the determination of a ¹³C–¹⁹⁵Pt coupling constant for the first time in a nanosystem (940 Hz). Additionally, in one case a novel structure was formed in which platinum(II) NHC complexes form a second coordination sphere around the nanoparticle.     

Synthesis and properties of ms- and β-substituted Pt(II) and Pt(IV) tetraphenylporphyrinates

The interaction of 5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra-(4-chlorophenyl)porphyrin, 2-bromo-5,10,15,20-tetraphenylporphyrin, and 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin with platinum(II) chloride in boiling phenol has been studied. The corresponding platinum(II) porphyrinates have been synthesized; their subsequent treatment with bromine in chloroform resulted in platinum(IV) porphyrinates. The Pt(II) and Pt(IV)(Br)₂ porphyrinates have been identified by elemental analysis, electron absorption, IR, and ¹H NMR spectroscopy.     

Kinetic studies of a catalyzed metalloporphyrin formation

Kinetics of the incorporation of mercury(II) ion in tetra (p-trimethylammoniumphenyl)porphine have been investigated in aqueous solution at 30.0°C and 0.2 M (NaNO₃) ionic strength. The reaction was found to be first order each in mercury(II) and the porphyrin. The forward (formation) and the reverse (dissociation) rate constants were found to be 1.9 ± 0.2 × 10³ M^?1 s^?1 and 7 ± 2 × 10⁶ M^?1 s^?1, respectively. Kinetics of zinc(II) incorporation in tetra(p-trimethylammoniumphenyl)porphine catalyzed by mercury(II) were also investigated. This catalysis is explained in terms of steady-state formation of mono mercury(II) porphyrin followed by zinc(II) displacement of mercury(II) ion from the porphyrin. Such a mechanism also illustrates the importance of porphyrin core deformation to metal incorporation.     

A Tin(IV) Porphyrin with Two Axial Organometallic NCN‐Pincer Platinum Units

A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by ¹H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures.     

Facile synthesis of a tricyclohexylphosphine‐stabilized η3‐allyl‐carboxylato Ni(II) complex and its relevance in electrochemical butadiene carbon dioxide coupling

With the reaction of bis(1,5‐cyclooctadiene)nickel(0) and trans‐penta‐2,4‐dienoic acid in the presence of tricyclohexylphosphine, a new more general method was developed to synthesize cyclic π³‐allyl‐carboxylato Ni(II) complexes, which are known to be intermediates in the C? C coupling of butadiene and CO₂. The cyclic π³‐allyl‐carboxylato Ni(II) complex obtained is tested as a mediator in the electrochemical coupling reaction of butadiene and carbon dioxide. We also demonstrate the dependency on the coordination sphere by using platinum instead of nickel as the metal center. Copyright © 2005 John Wiley & Sons, Ltd.     

X-ray structure of a novel histidine-copper(II) complex

A new crystal structure of the dichloro(L-histidine)copper(II) half-hydrate is reported. In this complex, histidine acts as a bidentate ligand to the copper(II) cation. The coordination sphere of the copper cation is created by the carboxyl oxygen and the amine nitrogen from main chain group of histidine. Two additional chloride anions complete the square coordination of the central Cu⁺² cation. In the crystal, the copper cations are additionally surrounded by two chloride anions from neighboring complex molecules, which are located in the distant axial position and fill up the stretched octahedral coordination sphere Cu⁺². In the presented complex, the histidine molecule exists as a zwitter ion with an unprotonated negatively charged carboxyl group and with double protonated positively charged imidazole ring. Crystallographic study was supported by IR measurements confirming the presence of water in the crystal structure.     

Selective Endo and Exo Binding of Mono‐ and Ditopic Ligands to a Rhomboidal Diporphyrin Prism

Copper(I) can preferentially form heteroleptic complexes containing two phosphine and two nitrogen donors due to steric factors. This preference was employed to direct the self‐assembly of a porphyrin‐faced rhomboidal prism having two parallel tetrakis(4‐iminopyridyl)porphyrinatozinc(II) faces linked by eight 1,4‐bis(diphenylphosphino)benzene pillars. The coordination preferences of the Cu^I ions and geometries of the ligands come together to generate a slipped‐cofacial orientation of the porphyrinatozinc(II) faces. This orientation enables selective encapsulation of 3,3′‐bipyridine (bipy), which bridges the Zn^II ions of the parallel porphyrins, whereas 4,4′‐bipy exhibits weaker external coordination to the porphyrin faces. Reaction with 2,2′‐bipy, by contrast, results in the displacement of the tetratopic porphyrin ligand and formation of [{(2,2′‐bipy)Cu^I}₂(diphosphine)₂]. The differing strengths of interactions of bipyridine isomers with the system allows for a hierarchy to be deciphered, whereby 4,4′‐bipy may be displaced by 3,3′‐bipy, which in turn is displaced by 2,2′‐bipy.     

Electrochemistry as an Attractive and Effective Tool for the Synthesis and Immobilization of Porphyrins on an Electrode Surface

Magnesium(II) 10‐phenyl‐5,15‐p‐ditolylporphyrin is easily and cleanly transformed by electrolysis. A nitro group is first introduced at the free meso position by anodic substitution. Hydrogenation into the amine is then carried out electrocatalytically under ambient conditions with water as a hydrogen supplier. The synthesized porphyrin under the nickel(II) form can be covalently grafted onto a platinum electrode by electrochemical reduction of the diazonium cation, generated in situ by a reaction of the nickel(II) aminoporphyrin with sodium nitrite and trifluoroacetic acid. The electrosynthesized thin film gives an electrochemical response typical of a porphyrin material. Films grown under our conditions have a maximum surface coverage of approximately 5×10^?10 mol cm^?2. The modified electrode exhibits a reproducible electrochemical behavior and a good level of stability over potential cycling and exposition to air.     

Porphyrin–Fullerene Dyad Based on Indium(III) Complex. Donor–Acceptor Complex Formation Equilibrium

Formation kinetics and spectral properties of the donor–acceptor complexes of (5,10,15,20- tetra(2-methoxyphenyl)porphinato)chloroindium(III) with 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin- 2-yl)methylpyrrolidinyl[3′,4′:1,2][60]fullerene were studied. The formation of the donor–acceptor dyad [(Py₃F)InTPP(2-OCH₃)₄]⁺Cl^– occurs as a two-step reaction, including fast reversible coordination of the fullerene base molecule and slow irreversible displacement of the axial chloride ion to the second coordination sphere. Quantitative characteristics for the reaction rate and equilibrium were obtained. The reaction products were identified by IR and ¹H NMR spectroscopy. The most important electron optical and stability parameters of the porphyrin–fullerene dyads with inner- and outer-sphere chloride ions were determined. These results are important for studies of the photophysics of porphyrin–fullerene dyads and development of photoconverters based on them.     

THE CRYSTAL STRUCTURE OF DIBROMO (PHENYL-2-PYRIDYL DIMETHYLHYDRAZONE)PALLADIUM(II)

Abstract

Nitrogen-containing heterocyclic compounds play an important role in several biological processes. Furthermore, their biological activity seems often to depend upon interaction with a metal ion. Interest in the study of hydrazones and their metal complexes has been growing because of their physiological activity, coordination capability and application in analytical chemistry.^1,2 Many hydrazones and their metallic derivatives show very interesting biological activity, e.g., as antitumour or anticonvulsant agents, and behave as cytotoxic compounds toward tumour cells.³ During the past few years, in addition to platinum compounds, coordination compounds of palladium(II) and (IV) seem to be promising in cancer chemotherapy.⁴ Due to the biological activity of heterocyclic hydrazones and in continuing our systematic investigations of the platinum group metals with hydrazones and generally with heterocyclic nitrogen donor ligands,^5–10 we report here the crystal structure of dibromo(phenyl-2-pyridyldimethylhydrazone) palladium(II).     

Synthesis of the new ligand bis[3-(2-pyrazinyl-pyrazol-1-yl) dihydroborate,and the crystal structures of its complexes with thallium(I) and lead(II)

Reaction of 3-(2-pyrazinyl)pyrazole with KBH₄ in a 21:1 ratio afforded the new ligand bis3, 2, 1dihydroborate [L]⁻a bis(pyrazolyl)borate in which each pyrazolyl ring is functionalised with a pyrazin-2-yl group at the C³ position[L]⁻ is therefore a potentially chelating tetradentate ligand with two externally-directed N atoms (the pyrazinyl N⁴ atoms) which are available for additional metal–ion bindingleading to eg coordination polymers The crystal structure of [TlL] shows it to be a simple mononuclear complex with the Tl(I) ion coordinated in the N₄ binding pocket of the ligandand the externally-directed N atoms involved only in intermolecular N H–C hydrogen-bonding interactions The two Tl–N bonds to the pyrazolyl N² atoms (average length 270 Å) are much shorter than the bonds to the pyrazinyl N¹ atoms (average length 305 Å) also there is an obvious gap in the apical position of the metal–ion coordination sphere characteristic of a stereochemically active lone pair The crystal structure of [PbL₂] Et₂O shows that the Pb(II) centre is nine-coordinate with two tetradentate chelating ligands and the ninth donor being a pyrazinyl N⁴ atom from an adjacent complex unit The molecules therefore form infinite one-dimensional chains in the crystal via bridging pyrazinyl groups The coordination geometry about the Pb(II) ions is approximately capped square antiprismatic with no obvious gap in the coordination sphere suggesting that the lone pair is stereochemically inactive.     

Extraction of chlororuthenium(III) complexes from hydrochloric acid solutions by petroleum sulfoxides

The extraction of ruthenium(II) by petroleum sulfoxides (PSOs) from hydrochloric acid solutions has been studied. The extraction of ruthenium(III) by PSOs is implemented by the coordination mechanism with the incorporation of the sulfoxide oxygen atom of the extractant into the inner coordination sphere of the ruthenium(III) ion. The composition of the extraction compound is suggested using electronic, ¹H NMR, and IR spectroscopy, the slope method, and elemental analysis.     

Synthesis and Structural Elucidation of N,N ’-Ditosyl-1,11-diaza-4,8,14,18-tetraselena-cycloicosane and its Copper and Platinum Complexes

The reaction of 1,2-diselenacyclopentane with N,O,O-tri-(toluene-p-sulphonate)-diethanolamine afforded a new seleno-azacrown ether, i.e. N,N′-ditosyl-1,11-diaza-4,8,14,18-tetraselena cycloicosane (1), in 19% yield, which was comprehensively characterized by elemental analysis, UV–Vis, ¹H NMR and mass spectroscopy. The reaction of 1 with copper(II) perchlorate (Cu(ClO₄)₂) and platinum(IV) tetrachloride (PtCl₄) gave its corresponding copper (2) and platinum complexes (3), respectively. The crystallographic investigations showed that the disparity of metal ion led not only to the distinct crystal system and space group, i.e. monoclinic system (C2/c) for 2 and triclinic system (P-1) for 3, but also the different coordination modes of copper and platinum ions with 1, i.e. normal coordination mode for 2 and ring-contracted coordination mode for 3. Moreover, the metal ions in the crystals 2 and 3 were found in Cu(I) and Pt(II) forms, respectively, although Cu(II) and Pt(IV) were used at the initial stage of coordination reaction.     

Synthesis of non-covalent BODIPY–metalloporphyrin dyads and triads

Boron-dipyrromethenes (BODIPY) containing oxypyridine substituents at 3- and 3,5-positions and metalloporphyrins (Zn(II), Ru(II)) were used to synthesize four non-covalent BODIPY–metalloporphyrin dyads and four BODIPY–metalloporphyrin triads assembled using metal–pyridine ‘N’ interaction. The formation of BODIPY–metalloporphyrin assemblies was confirmed by 1D and 2D NMR methods and X-ray crystal structure obtained for one of the BODIPY–metalloporphyrin dyad. In ¹H NMR, the signals of oxypyridine group(s) of BODIPY unit showed significant upfield shifts supporting the coordination of oxypyridine group of BODIPY unit to metalloporphyrin unit. The NMR study also indicated that Zn(II) porphyrin forms relatively weak BODIPY–Zn(II) porphyrin conjugates, whereas Ru(II) porphyrin forms strong BODIPY–Ru(II) porphyrin conjugates. The X-ray structure solved for BODIPY–Zn(II)porphyrin dyad revealed that the Zn(II) porphyrin coordinated to the BODIPY unit obliquely and the angle between the Zn(II) porphyrin and the pyridyl ring is 70°. The absorption properties of stable BODIPY–Ru(II) porphyrin conjugates showed the overlapping absorption features of both the components and the fluorescence studies indicated that the BODIPY unit emission was significantly quenched on coordination with RuTPP(CO) unit. The electrochemical studies exhibited the features of both BODIPY and metalloporphyrin units in dyads and traids.     

Crystal structure of K[PtCl3(caffeine)] and its interactions with important nitrogen-donor ligands

The crystal structure of K[PtCl₃(caffeine)] was determined. The coordination geometry around platinum is square-planar formed by N9 of the caffeine ligand and three Cl^? ions. The bond lengths and angles of K[PtCl₃(caffeine)] were compared with those reported for [PtCl₃(caffeine)]^? and K[PtCl₃(theobromine)]. At the level of the statistical significance of the data we have compared, no differences in the bond distances and angles for any of these compounds were noticed. Weak interactions between K⁺ and Cl^? are responsible for the formation of 1-D polymeric chains in the crystal structure of the complex. The interactions of K[PtCl₃(caffeine)] with inosine (Ino) and guanosine-5′-monophosphate (5′-GMP) were studied by ¹H NMR spectroscopy at 295 K in D₂O in a molar ratio of 1 : 1. The results indicate formation of the reaction product [PtCl₃(Nu)] (Nu=Ino or 5′-GMP) with the release of caffeine from the coordination sphere of the starting complex. The higher stability of the bond between the Pt(II) ion and Ino or 5′-GMP compared to the stability of the platinum–caffeine bond is confirmed by density functional theory calculations (B3LYP/LANL2DZp) using as models 9-methylhypoxanthine and 9-methylguanine.