Structure and characterization of platinum(II) and platinum(IV) complexes with protonated nucleobase ligands

The reaction of H₂[PtCl₆] · 6H₂O and (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O (18C6 = 18-crown-6) with 9-methylguanine (MeGua) proceeded with the protonation of MeGua forming 9-methylguaninium hexachloroplatinate(IV) dihydrate (MeGuaH)₂[PtCl₆] · 2H₂O (1).The same compound was obtained from the reaction of Na₂[PtCl₆] with (MeGuaH)Cl.On the other hand, the reaction of guanosine (Guo) with (H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O in methanol at 60 °C proceeded with the cleavage of the glycosidic linkage and with ligand substitution to give a guaninium complex of platinum(IV), [PtCl₅(GuaH)] · 1.5(18C6) · H₂O (2).Within several weeks in aqueous solution a slow reduction took place yielding the analogous guaninium platinum(II) complex, [PtCl₃(GuaH)] · (18C6) · 2Me₂CO (3).H₂[PtCl₆] · 6H₂O and guanosine was found to react in water, yielding (GuoH)₂[PtCl₆] (4) and in ethanol at 50 °C, yielding [PtCl₅(GuoH)] · 3H₂O (5).Dissolution of complexes 2 and 5 in DMSO resulted in the substitution of the guaninium and guanosinium ligands, respectively, by DMSO forming [PtCl₅(DMSO)]⁻.Reactions of 1-methylcytosine (MeCyt) and cytidine (Cyd) with H₂[PtCl₆] · 6H₂O and(H₃O)[PtCl₅(H₂O)] · 2(18C6) · 6H₂O resulted in the formation of hexachloroplatinates with N3 protonated pyrimidine bases as cation (MeCytH)₂[PtCl₆] · 2H₂O (6) and (CydH)₂[PtCl₆] (7), respectively. Identities of all complexes were confirmed by ¹H, ¹³C and ¹⁹⁵Pt NMR spectroscopic investigations, revealing coordination of GuoH⁺ in complex 5 through N7 whereas GuaH⁺ in complex 3 may be coordinated through N7 or through N9. Solid state structure of hexachloroplatinate 1 exhibited base pairing of the cations yielding (MeGuaH⁺)₂, whereas in complex 6 non-base-paired MeCytH⁺ cations were found. In both complexes, a network of hydrogen bonds including the water molecules was found. X-ray diffraction analysis of complex 3 exhibited a guaninium ligand that is coordinated through N9 to platinum and protonated at N1, N3 and N7. In the crystal, these NH groups form hydrogen bonds N–HO to oxygen atoms of crown ether molecules.     

Synthesis, X-ray crystal structure and NMR characterisation of mononuclear Pd(II) and Pt(II) complexes of didentate ligands with NN′-donor set

Two new 3,5-dimethylpyrazolic derived ligands that are N1-substituted by diamine chains, 1-[2-(diethylamino)ethyl]-3,5-dimethylpyrazole (L1) and 1-[2-(dioctylamino)ethyl]-3,5-dimethylpyrazole (L2) were synthesised. Reaction of the ligands, L1 and L2, with [MCl₂(CH₃CN)₂] yielded [MCl₂(L)] (M = Pd(II), Pt(II)) complexes. These complexes were characterised by elemental analyses, conductivity measurements, IR, ¹H, ¹³C{¹H} and ¹⁹⁵Pt{¹H} NMR spectroscopies. The crystal structure of [PdCl₂(L1)] was determined by single-crystal X-ray diffraction methods. The structure consists of mononuclear units. The Pd(II) atom is coordinated by a pyrazolic nitrogen, an amine nitrogen and two chlorine atoms in a cis disposition. In this structure, C-H?Cl, C-H?H-C and C-H?C-H intermolecular interactions have been identified.     

Synthesis and structural characterization of five-, six-, and seven-coordinate mononuclear manganese(II) complexes with N-tridentate ligands

A series of four mononuclear manganese (II) complexes with the N-tridentate neutral ligands 2,2^′:6,2^′′-terpyridine (terpy) and N,N-bis(2-pyridylmethyl)ethylamine (bpea) have been synthesized and crystallographically characterized. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligands used. The [Mn(bpea)(Br)₂] complex (1) has a five-coordinated manganese atom with a bipyramidal trigonal geometry, while [Mn(terpy)₂](I)₂ (2) is hexa-coordinated with a distorted octahedral geometry. Otherwise, the reactions of Mn(NO₃)₂ · 4H₂O with terpy or bpea afforded novel seven-coordinate complexes [Mn(terpy)(NO₃)₂(H₂O)] (3) and [Mn(bpea)(NO₃)₂] (4), respectively. 3 has a coordination polyhedron best described as a distorted pentagonal bipyramid geometry with one nitrate acting as a bidentate chelating ligand and the other nitrate as a monodentate one. 4 possesses a highly distorted polyhedron geometry with two bidentate chelating nitrate ligands. These complexes represent unusual examples of structurally characterized complexes with a coordination number seven for the Mn(II) ion and join a small family of nitrate complexes.     

Evaluation of in vitro cytotoxicity and hepatotoxicity of platinum(II) and palladium(II) oxalato complexes with adenine derivatives as carrier ligands

In vitro antitumour activity of the [Pt(ox)(L_n)₂] (1-7) and [Pd(ox)(L_n)₂] (8-14) oxalato (ox) complexes involving N6-benzyl-9-isopropyladenine-based N-donor carrier ligands (L_n) against ovarian carcinoma (A2780), cisplatin resistant ovarian carcinoma (A2780cis), malignant melanoma (G-361), lung carcinoma (A549), cervix epitheloid carcinoma (HeLa), breast adenocarcinoma (MCF7) and osteosarcoma (HOS) human cancer cell lines was studied. Some of the tested complexes were even several times more cytotoxic as compared with cisplatin employed as a positive control. The improved cytotoxic effect was demonstrated for the platinum(II) complexes 3 (IC₅₀ = 3.2 ± 1.0 μM and 3.2 ± 0.6 μM) and 5 (IC₅₀ = 4.0 ± 1.0 μM and 4.1 ± 1.4 μM) against A2780 and A2780cis, as compared with 11.5 ± 1.6 μM, and 30.3 ± 6.1 μM determined for cisplatin, respectively. The significant in vitro cytotoxicity against MCF7 (IC₅₀ = 8.2 ± 3.8 μM for 12) and A2780 (IC₅₀ = 5.4 ± 1.2 μM for 14) was evaluated for the palladium(II) oxalato complexes, which again exceeded cisplatin, whose IC₅₀ equalled 19.6 ± 4.3 μM against the MCF7 cells. Selected complexes were also screened for their in vitro cytotoxic effect in primary cultures of human hepatocytes and they were found to be non-hepatotoxic.     

Steric influence on platinum(II) ascorbate complexes

From the reaction between dihydroxoplatinum(II) and l-ascorbic acid, two types of platinum(II) ascorbate complexes were obtained and structurally characterized with ethylenediamine (en), N,N-dimethylethylenediamine (dmen) and N,N,N′-trimethylethylenediamine (trimen) as stabilizing ligands. In [Pt(en)(asc-C,O)] (1), [Pt(dmen)(asc-C,O)] (2) and [Pt(trimen)(asc-C,O)] (4), the ascorbate dianion forms a five-membered chelate ring, coordinating to the Pt(II) ion at the 2-carbon and the 5-oxygen atoms (C,O-chelate). From the same mother solution, crystals of [Pt(trimen)(asc-O,O′)] (3) were obtained during the precipitation of 4; in 3 the ascorbate is bound to the Pt at the 2- and 3-oxygen atoms (O,O′-chelate). Compounds 3 and 4 are the first well-characterized linkage isomers among the transition-metal ascorbate complexes. The O,O′-chelated 3 slowly changes to the C,O-chelated 4 in an aqueous solution. Bulkiness of the stabilizing ligand, i.e. en, dmen and trimen has an influence on the formation of the C,O-chelated species, 1, 2 and 4.     

Platinum(II) oxalato complexes with adenine-based carrier ligands showing significant in vitro antitumor activity

[Pt(L)₂(ox)] (1), [Pt(2-OMeL)₂(ox)] (2), [Pt(3-OMeL)₂(ox)] (3), [Pt(2,3-diOMeL)₂(ox)] (4), [Pt(2,4-diOMeL)₂(ox)] (5), [Pt(3,4-diOMeL)₂(ox)] (6) and [Pt(3,5-diOMeL)₂(ox)]·4H₂O (7) platinum(II) oxalato (ox) complexes were synthesized using the reaction of potassium bis(oxalato)platinate(II) dihydrate with 2-chloro-N6-(benzyl)-9-isopropyladenine or its benzyl-substituted analogues (nL). The complexes 1-7, which represent the first platinum(II) oxalato complexes involving adenine-based ligands, were fully characterized by various physical methods including multinuclear and two dimensional NMR spectroscopy. A single-crystal X-ray analysis of [Pt(2,4-diOMeL)₂(ox)]·2DMF (5·2DMF; DMF = N,N′-dimethylformamide), proved the slightly distorted square-planar geometry in the vicinity of the Pt(II) ion with one bidentate-coordinated oxalate dianion and two adenine derivatives (nL) coordinated to the Pt(II) centre through the N7 atom of an adenine moiety, thereby giving a PtN₂O₂ donor set. In vitro cytotoxicity of the prepared complexes was tested by an MTT assay against osteosarcoma (HOS) and breast adenocarcinoma (MCF7) human cancer cell lines. The best results were achieved for the complexes 2 and 5 in the case of both cell lines, whose IC₅₀ values equalled 3.6 ± 1.0, and 4.3 ± 2.1 μM (for 2), and 5.4 ± 3.8, and 3.6 ± 2.1 μM (for 5), respectively. The IC₅₀ equals 9.2 ± 1.5 μM against MCF7 cells in the case of 1. The in vitro cytotoxicity of the mentioned complexes significantly exceeded commercially used platinum-based anticancer drugs cisplatin (34.2 ± 6.4 μM and 19.6 ± 4.3 μM) and oxaliplatin (> 50.0 μM for both cancer cell lines).     

Synthesis, characterization and in vitro cytotoxicity studies of platinum(IV) complexes with thiouracil ligands

Reactions of [PtMe₃(bpy)(Me₂CO)][BF₄] (2) with the thionucleobases 2-thiouracil (s²Ura), 4-thiouracil (s⁴Ura) and 2,4-dithiouracil (s²s⁴Ura) resulted in the formation of complexes of the type [PtMe₃(bpy)(L-κS)][BF₄] (L = s²Ura, 3; s⁴Ura, 4; s²s⁴Ura, 5). The complexes were characterized by NMR spectroscopy (¹H, ¹³C, ¹⁹⁵Pt), IR spectroscopy as well as microanalyses. The coordination through the C4S groups (4, 5) was additionally confirmed by DFT calculations, where it was shown that these complexes [PtMe₃(bpy)(L-κS⁴)]⁺ (L = s⁴Ura, s²s⁴Ura) are about 5.8 (4b) and 3.3 kcal/mol (5b), respectively, more stable than the respective complexes, having thiouracil ligands bound through the C2X groups (X = O, 4a; S, 5a). For [PtMe₃(bpy)(s²Ura-κS²)][BF₄] (3) no preferred coordination mode could be assigned solely based on DFT calculations. Analysis of NMR spectra showed the κS² coordination. In vitro cytotoxic studies of complexes 3−5 on nine different cell lines (8505C, A253, FaDu, A431, A549, A2780, DLD-1, HCT-8, HT-29) revealed in most cases moderate activities. However, 3 and 5 showed significant activity towards A549 and A2780, respectively, possessing IC₅₀ values comparable to those of cisplatin. Cell cycle perturbations and trypan blue exclusion test on cancer cell line A431 using [PtMe₃(bpy)(s²s⁴Ura-κS⁴)][BF₄] (5) showed induction of apoptotic cell death. Furthermore, the reaction of [PtMe₃(OAc-κ²O,O′)(Me₂CO)] (6) with 4-thiouracil yielded the dinuclear complex [(PtMe₃)₂(μ-s⁴Ura_-H)₂] (7), which has been characterized by microanalysis, NMR (¹H, ¹³C, ¹⁹⁵Pt) and IR spectroscopy as well as ESI mass spectrometry. X-ray diffraction analysis of crystals yielded in an isolated case exhibited the presence of a hexanuclear thiouracilato platinum(IV) complex, possessing each three different kinds of methyl platinum(IV) moieties and 4-thiouracilato ligands. This exhibited the ability of 4-thiouracil platinum(IV) complexes to form multinuclear complexes.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

Synthesis and structural characterization of mercury(II) complexes with a novel ferrocenyliminophosphine

Synthesis of the novel ligand ferrocenyliminophosphine [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)CHN(C₆H₄-2-PPh₂)}] (1, L) and studies on its complexation properties with mercury (II) are reported. Halogen-bridged binuclear mercury (II) complexes [HgX(μ-X)L]₂ (X = Cl (2a), Br (2b)) and a mononuclear mercury (II) complex HgCl₂L₂ (4a) have been obtained under different reaction conditions. In both cases, the ferrocenyliminophosphine acts as a P-monodentate ligand and the imino nitrogen does not participate in coordination to mercury (II). All the new compounds 1, 2a, 2b and 4a were characterized by elemental analysis, ¹H NMR, ³¹P NMR and IR spectra. In addition, structures of 2a and 4a have been determined by X-ray single-crystal analysis.     

Synthesis and in vitro antitumoral activity of novel O,O'-di-2-alkyl-(S,S)-ethylenediamine-N,N'-di-2-propanoate ligands and corresponding platinum(II/IV) complexes

Syntheses of two novel ligand precursors O,O'-diisopropyl- (1a) and O,O'-diisobutyl-(S,S)-ethylenediamine-N,N'-di-2-propanoate dihydrochloride monohydrate (1b) and the corresponding dichloroplatinum(II) (2a and 2b) and tetrachloroplatinum(IV) complexes (3a and 3b) are described here. The substances were characterized by IR, (1)H and (13)C spectroscopy and elemental analysis. Crystal structures were determined for 1a and the corresponding platinum(IV) complex, 3a. In vitro antiproliferative activity was determined against tumor cell lines: human adenocarcinoma HeLa, human myelogenous leukemia K562, human malignant melanoma Fem-x, rested and stimulated normal immunocompetent cells (human peripheral blood mononuclear PBMC cells) using KBR test (Kenacid Blue Dye binding test). The IC(50)(microM) values for the most active compound 3a were: 30.48+/-2.54; 12.26+/-2.60; 13.68+/-3.22; 80.18+/-24.07 and 71.30+/-21.70, respectively.     

Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2-bipyridine: structural, electrochemical and spectral studies

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2^′-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄) · H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄) · H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case.     

Synthesis and structural studies of dimolybdenum(V), palladium(II) and dicopper(I) complexes that contain mixed pyridyl-iso-propylphosphine ligands

The reaction of Mo₂(μ-O₂CCH₃)₄ with 2-pyridyl(diisopropylphosphino)methane (NP) affords the dimolybdenum(V) complex Mo₂(μ-O)₂O₂Cl₂(η²-NP)₂ (1). Complexes of the related 2-pyridylbis(diisopropylphosphino)methane ligand (NP²) have been isolated, namely, a mixed bromo/chloro complex of composition PdBr_1.09Cl_0.91(η²-NP²) (2) and the dicopper(I) complex [Cu₂(μ-η³-NP²)₂](BF₄)₂ (3). The structures of 1, 2 and 3 have been established by X-ray crystallography.     

Dinuclear terephthalato-bridged copper(II) complexes: Syntheses, spectral and structural characterization, and magnetic properties

Herein, we report the syntheses, spectral and structural characterization, and magnetic behavior of four new dinuclear terephthalato-bridged copper(II) complexes with formulae [Cu₂(trpn)₂(μ-tp)](ClO₄)₂ · 2H₂O (1), [Cu₂(aepn)₂(μ-tp)(ClO₄)₂] (2), [Cu₂(Medpt)₂(μ-tp)(H₂O)₂](ClO₄)₂ (3) and [Cu₂(Et₂dien)₂(μ-tp)(H₂O)](ClO₄)₂ (4) where tp = terephthalate dianion, trpn = tris(3-aminopropyl)-amin, aepn = N-(2-aminoethyl)-1,3-propanediamine, Medpt = 3,3′-diamino-N-methyldipropylmine and Et₂dien = N,N-diethyldiethylenetriamine. The structures of these complexes consist of two μ-tp bridging Cu(II) centers in a bis(monodentate) bonding fashion. The coordination geometry of the Cu(II) ions in these compounds may be described as close to square-based pyramid (SP) with severe significant distortion towards trigonal bipyramid (TBP) stereochemistry in 1. The visible spectra of the complexes in aqueous solutions are in complete agreement with the assigned X-ray geometry around the Cu(II) centers. Also, the solid infrared spectral data for the stretching frequencies of the tp-carboxalato groups, the ν(COO⁻) reveals the existence of bis(monodentate) coordination mode for the bridged terephthalate ligand. The susceptibility measurements at variable temperature over the range 2-300 K are reported. Despite the same bonding mode of the tp bridging ligand, there has been observed slight antiferromagnetic coupling for the compounds 1 and 4 with J values of −0.5 and −2.9 cm³ K mol⁻¹, respectively, and very weak ferromagnetic coupling for 2 and 3 with J values of 0.8 and 10.1 cm³ K mol⁻¹, respectively. The magnetic results are discussed in relation to other related μ-terephthalato dinuclear Cu(II) published compounds.     

Synthesis, characterization, and structural studies of mercury(II) complexes of new bidentate phosphorus ylide

The reaction of Ph₂PCH₂CH₂PPh₂ (dppe) with BrCH₂C(O)C₆H₄NO₂ (1:1.05 molar ratio) in acetone produces a mixture of the new monophosphonium salt [Ph₂PCH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br (1) and the diphosphonium salt [NO₂C₆H₄C(O)CH₂PPh₂CH₂CH₂PPh₂CH₂C(O)C₆H₄NO₂]Br₂ (2). Compound 2 was insoluble in acetone and thus easily separated from the solution of 1. Further, by reacting both the mono- and diphosphonium salts with the appropriate bases the bidentate phosphorus ylides, [Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (3) and [NO₂C₆H₄C(O)CHPPh₂CH₂CH₂PPh₂CHC(O)C₆H₄NO₂] (4) were obtained. The reaction of ligand 3 with mercury(II) halides in dry methanol leads to the formation of the P,P-coordinated monomeric complexes {HgX₂(Ph₂PCH₂CH₂PPh₂CHC(O)C₆H₄NO₂)₂} [X = Cl (5), Br (6), I (7)]. The structure of complex 7 being unequivocally determined by single crystal X-ray diffraction techniques. Characterization of these species was also performed by elemental analysis, IR spectroscopy and ¹H, ³¹P, and ¹³C NMR techniques. These analyses being consistent with a 2:1 stoichiometry ylide/Hg(II) for compounds 5 through 7. Results obtained from theoretical studies are also consistent with a product in which two ylides are coordinated to the Hg(II) center through their phosphine groups, being this product the most stable among all the possible products.     

Metal-N-saccharide chemistry: synthesis and structure determination of two Cu(II) complexes containing glycosylamines

Two new complexes [Cu(N,N',N"-(D-Glc)3-tren)Cl]Cl (1) and [Cu(N,N',N"-(maltose)-tren)]Cl2.H2O (2), have been synthesized and characterized by elementary analysis, and the IR and UV spectra suggest that complex 1 and complex 2 are arranged in trigonal bipyramidal configuration and square-pyramidal configuration, respectively. The crystal structure of complex 1 has been determined by X-ray diffraction as: a = 9.3476(8), b = 17.4236(13), c = 9.7836(8) angstroms, beta = 91.197 degrees, and V = 1593.1(2) Angstroms3, Z = 2, and R = 0.0325, which shows that three secondary amine groups (N-1, N-2, N-3) of the glycosylamine ligand forms the equatorial plane, and the tertiary amine (N-4) and one Cl- are located at the apical positions.     

Neutral and cationic palladium(II) and platinum(II) complexes of 2,2′-dipyridylamine with saccharinate: Syntheses, spectroscopic, structural, fluorescent and thermal studies

Four palladium(II) and platinum(II) complexes of 2,2′-dipyridylamine (dpya) with saccharinate (sac), cis-[Pd(dpya)(sac)₂]·H₂O (1), cis-[Pt(dpya)(sac)₂]·H₂O (2), [Pd(dpya)₂](sac)₂·2H₂O (3) and [Pt(dpya)₂](sac)₂·2H₂O (4), have been synthesized and characterized by elemental analysis, IR, NMR, TG-DTA and X-ray diffraction. In 1 and 2, the metal ions are coordinated by two N-bonded sac ligands, and two nitrogen atoms of dpya, resulting in a neutral square-planar coordination sphere, while in 3 and 4, the metal ions are coordinated by two dpya ligands to generate square-planar cationic species, which are stabilized by two sac counter-ions. The mononuclear species of 1 and 2 interact each other through weak intermolecular N-H?O, C-H?O and π?π interactions to form a three-dimensional network, while the ions of 3 and 4 are connected by N-H?N and OW-H?O hydrogen bonds into one-dimensional chains. On heating at 250 °C, the solid cationic complexes of 3 and 4 convert to corresponding anhydrous neutral complexes of 1 and 2 after elimination of a dpya ligand. In addition, all complexes 1-4 are luminescent at room temperature and their emissions seem to be attributed to the MLCT fluorescence.     

Synthesis of new platinum(II) compounds with several bidentate and tridentate nitrogen-donor ligands. Structural analyses by H, C{H} and Pt{H} NMR spectroscopy and X-ray crystal structure

The reaction of the N-alkylaminopyrazole (NN′) ligands 1-[2-(ethylamino)ethyl]-3,5-dimethylpyrazole (deae), 1-[2-(tert-butylamino)ethyl]-3,5-dimethylpyrazole (deat), or (NN′N) ligands bis[(3,5-dimethylpyrazolyl)methyl]ethylamine (bdmae) and bis[(3,5-dimethylpyrazolyl)ethyl]ethylamine (ddae) with [PtCl₂(CH₃CN)₂] affords a series of square-planar Pt(II) complexes with formula [PtCl₂(NN′)] (NN′ = deae (1); deat (2)), [PtCl₂(bdmae)] (3), or [PtCl(ddae)]Cl (4). Treatment of complex 4 in the presence of AgBF₄ in CH₂Cl₂/methanol (3:1) gives [PtCl(ddae)](BF₄) (5). These Pt(II) complexes have been characterised by elemental analyses, conductivity measurements and IR, ¹H, ¹³C{¹H}, and ¹⁹⁵Pt{¹H} NMR spectroscopies. The ¹H NMR spectroscopic studies of the complexes prove the rigid conformation of the ligands when they are complexed. The solid-state structure of complex 1 was determined by single crystal X-ray diffraction methods. The deae ligand is coordinated through the N_pz and N_amino atoms to the metallic centre, which completes its coordination with two chlorine atoms in cis disposition.     

Crystal structures of Pt(II) and Pd(II) complexes with the free radical 4-aminoTEMPO

Pt(II) and Pd(II) compounds containing the free radical 4-aminoTEMPO (4amTEMPO) were synthesized and characterised by X-ray diffraction methods. The disubstituted complexes cis- and trans-Pt(4amTEMPO)₂I₂ were studied. The trans isomer was prepared from the isomerisation of the cis analogue. The two Pd(II) compounds trans-Pd(4amTEMPO)₂X₂ (X = Cl and I) were also characterised by crystallographic methods. A mixed-ligand complex cis-Pt(DMSO)(4amTEMPO)Cl₂ was synthesized from the isomerisation of the trans isomer in hot water. Its crystal structure was also determined. In all the complexes, the 4amTEMPO ligand is bonded to the metal through the -NH₂ group, since the nitroxide O atom is not a good donor atom for the soft Pt(II) and Pd(II) metals. The conformation of the 4-aminoTEMPO ligand was compared to those of the few reported structures in the literature.     

Lewis acidity of platinum(II)-based Baeyer-Villiger catalysts: An electrochemical approach

The electrochemical behavior of the Pt(II)-based Baeyer-Villiger catalysts of the general formulae [Pt(μ-OH)(P^∩P)]₂(BF₄)₂ (P^∩P = dppe (1a), 2Fdppe (1 b), 4Fdppe (1c), dfppe (1d), dmpe (1e), depe (1f), dippe (1g), dtbpe (1h)) and [Pt(OH₂)₂(P^∩P)](OTf)₂ (P^∩P = dppe (2a), 2Fdppe (2b), 4Fdppe (2c), dfppe (2d)) is reported. They exhibit irreversible reduction processes whose potentials reflect the Lewis acidity of the metal centres, showing (for the aromatic diphosphine complexes) overall relations with the number of fluorine atoms, with J_Pt-P, with the ν(CN) coordination shift of a ligand isocyanide probe and with the catalytic activity. Single-crystal X-ray diffraction analyses were carried out for [Pt(μ-OH)(4Fdppe)]₂(BF₄)₂ (1c) and [Pt(μ-OH) (dippe)]₂(BF₄)₂ (1g).     

Synthesis,characterization and DNA binding studies of platinum(II) complexes with benzimidazole derivative ligands

The aim of this study was to synthesize and evaluate plasmid DNA interaction of new platinum(II) complexes with some 2-substituted benzimidazole derivatives as carrier ligands which may have potent anticancer activity and low toxicity. Twelve benzimidazole derivatives carrying indole, 2-/or 3-/or 4-methoxyphenyl, 4-methylphenyl, 3,4-dimethoxyphenyl, 3,4,5-trimethoxyphenyl, 4-methoxybenzyl, 3,4,5-trimethoxybenzyl, 3,4,5-trimethoxystyryl, 3,4,5-trimethoxybenzylthio or dimethylamino ethyl groups in their position 2 and twelve platinum(II) complexes with these carrier ligands were synthesized. The chemical structure of the platinum complexes have been characterized by their elemental analysis and FIR, ¹H NMR and mass spectra and their ¹H NMR and FIR spectra were interpreted by comparison with those of the ligands. The interaction of all the ligands and their complexes with plasmid DNA and their restriction endonuclease reactions by BamHI and HindIII enzymes were studied by agarose gel electrophoresis. It was determined that complex 1 [dichloro-di(2-(1H-indole-3-yl)benzimidazole)platinum(II)·2H₂O] has stronger interaction than carboplatin and complex 10 [dichloro-di(2-(3,4,5-trimethoxystyryl)benzimidazole)platinum(II)·2H₂O] has stronger interaction than both carboplatin and cisplatin with plasmid DNA.