Computational design of magnetically active trinuclear heterometallic complexes on the basis of 1,3,5-triazapentadiene ligands

A series of trinuclear mixed-ligand complexes of iron(II) 2,6-di(pyrazol-1-yl)pyridine moieties with linkers on the basis of 1,3,5-triazapentadiene transition metal (M = Co, Ni, Cu, Zn) bischelates has computationally been designed using the density functional theory TPSSh/6-311++G(d,p) calculations. The systems possessing complete (M = Co, Ni) and partial (M = Cu, Zn) two-step spin-crossover phenomenon at ferrous ions have been revealed. Two spin-state switching mechanisms determining by spin-crossover at iron centers and configurational isomerism at cobalt ion may simultaneously occur in solution of corresponding heterometallic compound (M = Co). The nature of the exchange interactions between paramagnetic metal centers is controlled by variation of a metal in bischelate linker (M = Co, Ni, Cu, Zn). Energy and magnetic characteristics of electromeric forms of the complexes with nickel and copper central metal ions (M = Co, Ni) allow to consider them as promising candidates for the design of molecular switches.     

Novel pyridine-derived platinum complexes

Pyridine-derived platinum(II) complexes with the general formula [PtCl₂L₂] (L¹: 3,5-dimethylpyridine, L²: 2-amino-5-bromopyridine, L³: 4-(4-nitrobenzyl)pyridine) were synthesized. Characterization of the synthesized complexes was made via FT-IR, UV–Vis, ¹H-NMR and ¹³C-NMR techniques. While the thermal behavior of the complexes was investigated via DTA/TG combined system, their kinetic parameters were investigated by using Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods. The activation energy of the decomposition kinetics of the complexes was calculated to be 196.5–31.7 kJ mol^?1 for FWO and 203.4–29.2 kJ mol^?1 for KAS. The cytotoxic effect of the complexes against the colon cancer cell line (DLD-1), which is one of the most common types of cancer observed both in humans and animals, was investigated. The complexes showed high cytotoxicity on DLD-1. In particular, [PtCl₂L ¹₂ ] complex was found to be the most effective compounds against colon cancer cell line during the 24 h incubation period. According to these results, the pyridine-derived platinum(II) complexes would contribute to oncologic treatment as chemotherapeutic agents.

     

NiII-mediated coupling between iminoisoindolinones and nitriles leading to unsymmetrical 1,3,5-triazapentadienato complexes

Treatment of nickel acetate Ni(OAc)2.4H2O with 2 equiv of various 3-iminoisoindolin-1-ones in a suspension of RCN in the presence of triethanolamine leads to the formation of the nickel 1,3,5-triazapentadienato complexes [Ni{NHC(R)NC(C6R1R2R3R4CON)}2] (1-17) isolated in good 50-83% yields. The reaction proceeds under relatively mild conditions (from 5 to 7 h at 25-115 degrees C, depending on the boiling point of the nitrile) and has a general character insofar as it was successfully conducted with various nitriles RCN bearing donor (R = Me, Et, Prn, Pri, Bun), weak donor (R = CH2Ph, CH2C6H4OMe-p), acceptor (R = CH2Cl), and strong acceptor (R = CCl3) groups R of different steric hindrance and also with the nonsubstituted iminoisoindolinone (3-iminoisoindolin-1-one) or the iminoisoindolinones bearing donor methyl (3-imino-5-methylisoindolin-1-one) or acceptor fluoro (4,5,6,7-tetrafluoro-3-iminoisoindolin-1-one) groups in the benzene ring.     

Theoretical study of ammonia nucleophilic addition to nitriles in platinum complexes

The mechanism of the reaction of the ammonia nucleophilic addition to nitriles RC≡N, both free and activated in the platinum complex trans-[PtCl₂(N≡CCH₃)₂], was studied in detail by theoretical quantumchemical methods. The reaction resulting in the formation of free or coordinated amidines proceeds through consecutive formation of an orientation complex, a six-membered cyclic transition state, and a final reaction product, in which an amidine is in the E-configuration. Water containing in a solvent plays a role of a promoter of this process. The activation effect is interpreted from the viewpoint of both kinetic and thermodynamic factors. It was shown that the mechanism of the reaction product E-Z-isomerization includes the deprotonation of the amino-group nitrogen atom, the change of the coordinated ligand conformation, and the protonation of the nitrogen atom.     

Synthesis of amidine complexes by metal-mediated addition of amino acid esters to coordinated nitriles

The reaction of the nitrile platinum(IV) complex trans-[PtCl₄(EtCN)₂] with amino acid esters H₂NC(R¹)(R²)CO₂Me (R¹ = R² = H, H-Me, Me-Me, H-Ph) and H₂NCH₂CH₂CO₂Me in CH₂Cl₂ produces the amidine complexes trans-[PtCl₄{ Z-NH=C(Et)NHC(R¹)(R²)CO₂Me}₂] and trans-[PtCl₄{ Z-NH=C(Et)NHCH₂CH₂CO₂Me}₂], which were isolated in 70–80% yields and characterized by elemental analysis, mass spectrometry, IR spectroscopy, and ¹H and ¹³C{¹H} NMR spectroscopy. The structures of the complexes with R¹ = R² = H (1), R¹ = H, R² = Me (2), and R¹ = H, R² = Ph (4) were established by X-ray diffraction analysis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 601–605, March, 2005.     

Novel reaction of N,N'-bisarylmethanediamines with formaldehyde. Synthesis of some new 1,3,5-triaryl-1,3,5-hexahydrotriazines

The acid-catalyzed cyclocondensation of N,N'-bisaryl (aryl = 2-pyrimidinyl, 2-pyrazinyl and 4-nitrophenyl) methanediamines 5a-c with aqueous formaldehyde in refluxing acetonitrile leads to the formation of the corresponding 1,3,5-triaryl-1,3,5-hexa-hydrotriazines 6a-c. The stoichiometric reactions of 2-aminopyrimidine and 2-amino-pyrazine with aqueous formaldehyde in acetonitrile under reflux conditions also afforded 6a and 6b, respectively. Treatment of 2-aminopyrimidine with aqueous formaldehyde in a 3:2 ratio yielded N,N',N"-tris(2-pyrimidinyl)dimethylenetriamine (7a) as a sole product, which upon subsequent reaction with formaldehyde also afforded 6a. The reaction of N,N'-biphenylmethanediamine with formaldehyde was also investigated.     

Beta-diiminate platinum complexes for alkane dehydrogenation

New five-coordinate Pt(IV) complexes [{(o-R2-p-R'-C6H2)NC(R' ')}2CH]PtMe3 (R, R', R' ' = alkyl or H) are reported. The complex with R = Me, R' = tBu, R' ' = Me generates unsaturated Pt(II) species capable of alkane C-H bond activation and stoichiometric dehydrogenation.     

Iodo-methyl ligand exchange reaction in platinum complexes: A density functional study

A theoretical investigation at the gradient-corrected density functional (BP86) level of theory on the iodo-methyl ligand exchange reaction in platinum-diphosphine complexes is discussed. The reaction consists of two elementary steps: the oxidative addition of methyl-iodide, and reductive elimination of ethane from the intermediate Pt(bdpp)(CH₃)₃I complex which is the rate determining step with a free energy of activation of 19.5 kcal/mol in acetonitrile phase. The oxidative addition step takes place with S_N2 mechanism via a transition state with a collinear arrangement of the I-CH₃-Pt moiety.     

A modular strategy for tailoring fluorescent biosensors from ribonucleopeptide complexes

Fluorescent biosensors that facilitate reagentless sensitive detection of small molecules are crucial tools in the areas of therapeutics and diagnostics. However, construction of fluorescent biosensors with desired characteristics, that is, detection wavelengths and concentration ranges for ligand detection, from macromolecular receptors is not a straightforward task. An ATP-binding ribonucleopeptide (RNP) receptor was converted to a fluorescent ATP sensor without chemically modifying the nucleotide in the ATP-binding RNA. The RNA subunit of the ATP-binding RNP and a peptide modified with a pyrenyl group formed a stable fluorescent RNP complex that showed an increase in the fluorescence intensity upon binding to ATP. The strategy to convert the ATP-binding RNP receptor to a fluorescent ATP sensor was applied to generate fluorescent ATP-binding RNP libraries by using a pool of RNA subunits obtained from the in vitro selection of ATP-binding RNPs and a series of fluorophore-modified peptide subunits. Simple screening of the fluorescent RNP library based on the fluorescence emission intensity changes in the absence and presence of the ligand afforded fluorescent ATP or GTP sensors with emission wavelengths varying from 390 to 670 nm. Screening of the fluorescence emission intensity changes in the presence of increasing concentrations of ATP allowed titration analysis of the fluorescent RNP library, which provided ATP sensors responding at wide concentration ranges of ATP. The combinatorial strategy using the modular RNP receptor reported here enables tailoring of a fluorescent sensor for a specific ligand without knowledge of detailed structural information for the macromolecular receptor.     

Novel dinuclear platinum(II) complexes containing mixed nitrogen-sulfur donor ligands

A series of novel dinuclear platinum(II) complexes were synthesized containing a mixed nitrogen-sulfur donor bidentate chelate system in which the two platinum centers are connected by an aliphatic chain of variable length. The bidentate chelating ligands were selected to stabilize the complex toward decomposition. The pK(a) values and reactivity of the four synthesized complexes, namely, [Pt(2)(S(1),S(4)-bis(2-pyridylmethyl)-1,4-butanedithioether)(OH(2))(4)](4+) (4NSpy), [Pt(2)(S(1),S(6)-bis(2-pyridylmethyl)-1,6-hexanedithioether)(OH(2))(4)](4+) (6NSpy), [Pt(2)(S(1),S(8)-bis(2-pyridylmethyl)-1,8-octanedithioether)(OH(2))(4)](4+) (8NSpy), and [Pt(2)(S(1),S(10)-bis(2-pyridylmethyl)-1,10-decanedithioether)(OH(2))(4)](4+) (10NSpy), were investigated. This system is of special interest because only little is known about the substitution behavior of dinuclear platinum complexes that contain a bidentate chelate that forms part of the aliphatic bridging ligand. Moreover, the ligands as well as the dinuclear complexes were examined in terms of their cytotoxic activity, and the 10NSpy complex was found to be active. Spectrophotometric acid-base titrations were performed to determine the pK(a) values of all the coordinated water molecules. The substitution of coordinated water by thiourea was studied under pseudo-first-order conditions as a function of nucleophile concentration, temperature, and pressure, using stopped-flow techniques and UV-vis spectroscopy. The results for the dinuclear complexes were compared to those for the corresponding mononuclear reference complex [Pt(methylthiomethylpyridine)(OH(2))(2)](2+) (Pt(mtp)), by which the effect of the increasing aliphatic chain length of the bridged complexes could be investigated. The results indicate that there is a clear interaction between the two platinum centers, which becomes weaker as the chain length between the metal centers increases. Furthermore, differences and similarities of the N,S-system were compared to the corresponding dinuclear N,N-system studied previously in our group. In addition, quantum chemical calculations were performed to support the interpretation and discussion of the experimental data.     

Unsymmetrical Ni(II)-imidoylamidine complexes derived from a novel oxime-mediated single-pot reaction of nitriles

The neutral bisimidoylamidine (or 1,3,5-triazapentadiene) Ni(II) complexes [Ni{HN=C(R)N=C(C(6)H(4)CO)N}(2)] {R=Me, Et, nPr, iPr, (CH(2))(3)Cl}, bearing an iminoisoindolinone moiety, have been generated by a novel 2-propanone oxime-mediated single-pot reaction of phthalonitrile and nickel(II) acetate in solution of the corresponding alkylnitrile (RCN). Single-crystal X-ray diffraction analyses indicate a square-planar geometry of the imidoylamidine core. The synthesised compounds represent rare specimens of genuine unsymmetrical imidoylamidine complexes as well as their first examples generated from nitriles in a single-pot reaction.     

Effective biaryl compound synthesis using cross-coupling reaction with nickel complexes coordinated by diaminophosphine ligands

The cross-coupling reaction of aryl halides and aryl Grignard reagents was effectively catalyzed by the diaminophosphine complex catalysts and the reaction was much faster than that catalyzed by aminophosphine complexes and the nickel complexes were more active than palladium complexes. Various biaryl compounds were easily prepared by the reaction with nickel diaminophosphine catalysts.     

Ritter reaction of organic nitriles with 1-bromo- and 1-hydroxyadamantanes catalyzed by manganese compounds and complexes

Manganese compounds and complexes [MnCl₂, MnBr₂, Mn(OAc)₂, Mn(acac)₂, Mn(acac)₃, Mn₂(CO)₁₀] catalyze Ritter reaction of organic nitriles with 1-bromo- and 1-hydroxyadamantanes. The reaction proceeds in water environment in the absence of acids at 100–130°C over 3–5 h and affords N-(adamantan-1-yl)amides in 75–100% yields.     

Synthesis of CuII-RuII-CuII trinuclear complexes via redox reaction of copperI across thiosemicarbazones coordinated to rutheniumII

Pyridine-2-carbaldehyde thiosemicarbazones [C5H4N1-C(H)N2-N3H-C(S)-N4HR, R = H, L1H2; CH3, L2H2-Me; CH2CH3, L3H2-Et] with Ru(PPh3)3Cl2 have formed mononuclear RuII precursors for the generation of trinuclear complexes. The reaction of 2 mol each of L1H2, L2H2-Me, or L3H2-Et with Ru(PPh3)3Cl2 in the presence of Et3N has yielded mononuclear complexes [Ru(N3,S-L1H)2(PPh3)2] (1), [Ru(N3,S-L2H-Me)2(PPh3)2] (2), and [Ru(N3,S-L3H)2(PPh3)2] (3). The addition of 2 equiv of copperI chloride solution to complex 1 in acetonitrile has formed a novel trinuclear complex, (Ph3P)2RuII(L1)2CuII2Cl2 (4), in which the pendant amino group (-N4H2) loses one hydrogen along with the oxidation of CuI to CuII. In this complex, RuII is bonded to two P, two S, and two N3 atoms, while each CuII is coordinated to N1, N2, N4, and Cl atoms. Reaction with copper(I) bromide yielded a similar trinuclear complex, (Ph3P)2Ru(L1)2CuII2Br2 (5). From precursors 2 and 3, analogous complexes (Ph3P)2RuII(L2-Me)2CuII2Cl2 (6), (Ph3P)2RuII(L2-Me)2CuII2Br2 (7), (Ph3P)2RuII(L3-Et)2CuII2Cl2 (8), and (Ph3P)2RuII(L3-Et)2CuII2Br2 (9) have been synthesized. These complexes have been characterized using analytical, spectroscopic, and electrochemical techniques. Single-crystal X-ray crystallography has been carried out for precursor 2 and all of the trinuclear complexes, 4-9. X-band electron spin resonance and UV-vis spectra have confirmed the presence of CuII. The cyclic voltammetry studies support the RuII/RuIII redox behavior of this metal in trinuclear complexes.     

Transmetalation of arylpalladium and platinum complexes. Mechanism and factors to control the reaction

This article reviews recent studies on intra- and intermolecular transfer of the aryl ligand bonded to Pd(II) and Pt(II). Cationic arylpalladium complexes with bpy and THF ligands undergo intermolecular aryl group transfer to produce biaryl via a diarylpalladium intermediate. This reaction is applied to cyclization of cationic dinuclear arylpalladium complexes, affording the crown ether derivative with biphenylene units. Analogous arylplatinum complexes do not form diaryl complexes via transmetalation, while they react with CO and phenylallene to cause replacement of the coordinated solvent and insertion of the small molecules into the Pt–C bond, respectively. Conproportionation of PtCl₂(cod) and PtPh₂(cod) produces PtCl(Ph)(cod), which is induced by dissociation of a Cl ligand from the former complex. PtCl₂(cod) reacts also with diarylplatinum complexes with bpy and dppe. Disproportionation of PtPh(CH₂COMe)(cod) and conproportionation of PtPh₂(cod) and Pt(CH₂COMe)₂(cod) take place at 50 °C, but the rates of apparently reversible reactions differ from each other. Addition of OH⁻ to a solution of PtI(Ph)(cod) causes intermolecular phenyl ligand transfer to produce PtPh₂(cod). The dinuclear intermediate complex with bridging OH ligand is prepared from an independent route and fully characterized. The complex causes transmetalation of aryl group of aryl boronic acid.     

Novel platinum(II) and (IV) complexes of naphthaldimine schiff bases

Naphthaldimines containing N₂O₂ donor centers react with platinum(II) and (IV) chlorides to give two types of complexes depending on the valence of the platinum ion. For [Pt(II)], the ligand is neutral, [(H₂L¹)PtCl₂]·3H₂O (1) and [(H₂L³)₂Pt₂Cl₄]·5H₂O (3), or monobasic [(HL²)₂Pt₂Cl₂]·2H₂O (2) and [(HL⁴)₂Pt]·2H₂O (4). These complexes are all diamagnetic having square-planar geometry. For [Pt(IV)], the ligand is dibasic, [(L¹)Pt₂Cl₄(OH)₂]·2H₂O (5), [(L²)Pt₃Cl₁₀]·3H₂O (6), [(L³)Pt₂Cl₄(OH)₂]·C₂H₅OH (7) and [(L⁴)Pt₂Cl₆]·H₂O (8). The Pt(IV) complexes are diamagnetic and exhibit octahedral configuration around the platinum ion. The complexes were characterized by elemental analysis, UV-Vis and IR spectra, electrical conductivity and thermal analyses (DTA and TGA). The molar conductances in DMF solutions indicate that the complexes are non-ionic. The complexes were tested for their catalytic activities towards cathodic reduction of oxygen.     

1,3,5-三芳基吡唑类化合物合成的新方法

发现了一种以查耳酮(1a～1g)等不饱和酮(1h)和苯肼为主要原料,二氢铬酸四吡啶合钴(TPCD)为脱氢芳构化试剂,经“一锅法”合成1,3,5-三芳基吡唑(3a～3g)等吡唑类化合物的新方法.合成过程中首先生成的1,3,5-三取代吡唑啉不需要分离,直接在二氢铬酸四吡啶合钴氧化下脱氢芳构化成相应的吡唑类化合物,反应物分子中的碳-碳双键不受加入的二氢铬酸四吡啶合钴影响.该合成方法原料易得,反应条件温和,产率较高(65%～93%).     

Fluxional behavior of platinum(0) complexes: intra vs intermolecular reaction pathways

The fluxional behavior of two analogous platinum complexes has been studied in solution by NMR spectroscopy to elucidate the reaction mechanism and to determine the activation parameters. This includes variable temperature NMR spectroscopy, 2D (1)H- (1)H exchange spectroscopy, and spin saturation transfer measurements. A platinum moiety, Pt(PEt 3) 2, translocates between two carbon-carbon double bonds of two vinylpyridine moieties bridged by an arene (i.e., phenyl, anthracene) at elevated temperatures. Magnetization transfer NMR experiments in the presence of free ligands unambiguously revealed an intramolecular pathway for the "phenyl" system. An intermolecular pathway is proposed for the "anthracene" complex.     

Toward the design of novel polynuclear platinum antitumor complexes: a polydentate ligand system based on dipyridylamine and 1,3,5-trimethylenebenzene

A novel hexadentate ligand, N,N,N',N',N",N"-hexa(2-pyridyl)-1,3,5-tris(aminomethyl)benzene (L), was designed and synthesized. The X-ray structure analysis reveals that the three dipyridylamine (DPA) groups of L are almost perpendicular to the central trimethylenebenzene, and two of them are spacially close to each other while the third one is further apart. The trinuclear Pt(II) complexes [Pt(3)LCl(6)] (1) and [Pt(3)L(CBDCA)(3)] (2) (where CBDCA represents cyclobutane dicarboxylic acid) were prepared and fully characterized by IR, NMR, and ESMS spectroscopy. A mononuclear complex, [PtL(CBDCA)] (3), was also prepared and structurally characterized, which suggests that controlled formation of mono-, di-, and trinuclear complexes with L is possible. Spectroscopic data showed that complexes 2 and 3 are able to bind to calf thymus DNA and their CBDCA group can be readily replaced by thiourea.