Role of the ancillary ligands on the stabilization of the imino-oxo tautomer of 1-methylcytosine in PtII complexes

The mixed nucleobases complexes cis-[L2Pt{1-MeTy(-H)}(1-MeCy,N3)]NO3 (L = PPh3, 1a; PMePh2, 1b), containing the N(3)-deprotonated 1-methylthymine (1-MeTy(-H)) and the neutral 1-methylcytosine (1-MeCy) have been prepared and characterised. The compounds were obtained by reacting the hydroxo complexes cis-[L2Pt(μ-OH)]2(NO3)2 with 1-methylthymine (1-MeTy), followed by the addition of 1 equivalent of 1-MeCy. In solution of DMSO, DMF or chlorinated solvents, 1a converts quantitatively into the isomer cis-[L2Pt{1-MeTy(-H)}(1-MeCy,N4)]NO3 (2a) containing the tautomeric form of the cytosine stabilized through the coordination at the N(4) atom, as shown by single-crystal X-ray analysis. The structural determination of 2a shows the presence in the unit cell of two crystallographic independent complexes having similar conformation, with a different orientation of the two nucleobases (head–head and head–tail) according to the presence of both isomers in solution. Complex 1b, having the less hindered PMePh2 ligands, in DMSO solution, contains the tautomeric forms of the cytosine in equilibrium and the migration of the metal from the N(3) to N(4) site occurs only to a minor extent

Mono- and Polynuclear Complexes of the Model Nucleobase 1-Methylcytosine. Synthesis and Characterization of cis-[(PMe2Ph)2Pt{(1-MeCy(−H)}]3(NO3)3 and cis-[(PPh3)2Pt{1-MeCy(−H)}(1-MeCy)]NO3

The hydroxo complex cis-[L2Pt(μ-OH)]2(NO3)2 (L = PMe2Ph), in various solvents, reacts with 1-methylcytosine (1-MeCy) to give as the final product the cyclic species cis-[L2Pt{1-MeCy(−H),N 3N 4}]3(NO3)3 (1) in high or quantitative yield. X-ray analysis of 1 evidences a trinuclear species with the NH2-deprotonated nucleobases bridging symmetrically the metal centers through the N3 and N4 donors. A multinuclear NMR study of the reaction in DMSO-d6 reveals the initial formation of the dinuclear species cis-[L2Pt{1-MeCy(−H),N 3N 4}]22+ (2), which quantitatively converts into 1 following a first-order kinetic law (at 50 °C, t1/2 = 5 h). In chlorinated solvents, the deprotonation of the nucleobase affords as the major product (60−70%) the linkage isomer of 1, cis-[L2Pt{1-MeCy(−H)}]33+ (3), in which three cytosinate ligands bridge unsymmetrically three cis-L2Pt2+ units. In solution, 3 slowly converts quantitatively into the thermodynamically more stable isomer 1. No polynuclear adducts were obtained with the hydroxo complex stabilized by PPh3. cis-[(PPh3)2Pt(μ-OH)]2(NO3)2 reacts with 1-MeCy, in DMSO or CH2Cl2, to give the mononuclear species cis-[(PPh3)2Pt{1-MeCy(−H)}(1-MeCy)](NO3) (4) containing one neutral and one NH2-deprotonated 1-MeCy molecule, coordinated to the same metal center at the N3 and N4 sites, respectively. X-ray analysis and NMR studies show an intramolecular H bond between the N4 amino group and the uncoordinated N3 atom of the two nucleobases

Structural Aspects of Palladium Systems Used as Catalyst Precursors in CO/olefins co- and ter-Polymerisation Reactions

The synthesis and characterisation of three palladium complexes, involved in the homogeneous catalysis towards the CO-olefins co-and ter-polymerisation reactions, are reported. The [Pd (dpk⋅CH3OH) (CF3CO2)2] (1), (dpk = di(2-pyridyl) ketone) and [Pd (dppp)(bipy)] [B(C6F5)4]2 (2), (bipy = 2,2’-bipyridine, dppp = 1,3-bis(diphenylphosphino)propane) compounds are examples of a neutral complex and of a dicationic mixed-ligands one, respectively. The catalytic activity of type 2 complexes was reported to be strongly dependent on the nature of the anion, and the tetra(perfluorophenyl) borate salt represents the best choice to date for the CO/aliphatic olefins copolymerisation. In both structures, the metal has a square planar coordination and the structural aspects of these complexes are discussed in comparison with their catalytic properties. The crystal structure of [Pd(bipy)(naphthoquinone)] (3), which is a putative intermediate of the catalytic cycle, is also reported

Irreversible Insertion of Benzonitrile into Platinum ( II ) - Nitrogen Bonds of Nucleobase Complexes. Synthesis and Structural Characterization of Stable Azametallacycle Compounds

Deprotonation of 1-methylcytosine (1-MeCy) and 9-methyladenine (9-MeAd) promoted by cis-[L2Pt(μ-OH)]2(NO3)2 (L = PPh3, PMePh2, 1/2dppe) in PhCN causes the irreversible insertion of a nitrile molecule into the Pt−N4 and Pt−N6 bonds of the cytosinate and adeninate ligands, respectively, to form the stable azametallacycle complexes cis-[L2PtNH═C(Ph){1-MeCy(−2H)}]NO3 (L = PPh3, 1; PMePh2, 2; 1/2dppe, 3) and cis-[L2PtNH═C(Ph){9-MeAd(−2H)}]NO3 (L = PPh3, 4; PMePh2, 5) containing the deprotonated form of the molecules (Z)-9-N-(1-methyl-2-oxo-2,3-dihydropyrimidin-4(1H)-ylidene)benzimidamide and (Z)-N-(9-methyl-1H-purin-6(9H)-ylidene)benzimidamide. Single-crystal X-ray analyses of 2 and 4 show the metal coordinated to the N3 cytosine site [Pt−N3 = 2.112(7) Å̊] and to the N1 site of adenine [Pt−N1 = 2.116(6) Å̊] and to the nitrogen atom of the inserted benzonitrile [Pt−N2 = 2.043(6) and 2.010(6) Å̊ in 2 and 4, respectively], with the exocyclic nucleobase amino nitrogen bound to the carbon atom of the CN group. Complex 2, in solution, undergoes a dynamic process related to a partially restricted rotation around Pt−P bonds, arising from a steric interaction of the oxygen atom of the cytosine with one ring of the phosphine ligands. The reaction of 4 with acetylacetone (Hacac) causes the quantitative protonation of the anionic ligand, affording the acetylacetonate complex cis-[(PPh3)2Pt(acac)]NO3 and the free benzimidamide NH═C(Ph){9-MeAd(−H)}. In the same experimental conditions, complex 3 reacts with Hacac only partially

Iron complexes with nitrogen bidentate ligands as green catalysts foralcohol oxidation

The iron(II) complexes [Fe(N-N)3](OTf)2(N-N = 2,2- bipyridine, 1,10-phenanthroline and substitutedderivatives) were employed as catalyst precursors for the oxidation of primary and secondary alcohols,including glycerol. The single-crystal structure of [Fe(bipy)3](OTf)2was determined by X-ray crystallog-raphy.The catalytic reactions were performed using either H2O2or tert-butilhydroperoxide (TBHP) asoxidating agent, in mild experimental conditions: with all catalysts employed, secondary alcohols wereoxidized to the corresponding ketones with up to 100% yields, whereas other substrates gave lowerconversions. Indications on the nature of the catalytically active species, which is probably formed viadissociation of a nitrogen ligand from the iron center, were obtained from NMR and ESI\u2013MS spectra

Epoxidation and catechol oxidation catalytic processes promoted by manganese(III) complexes of salen-type ligands

169-176Four new mononuclear manganese(III) complexes namely 1, 2, 3 and 4 of salen-type ligands H2L1-H2L4 (ligands were obtained in situ via Schiff-base condensation of 2-formyl-6-hydroxymethyl-4-methylphenol and amines cyclohexane-1,2-diamine, 2-methylpropane-1,2-diamine, propane-1,2-diamine and ethane-1,2-diamine, respectively) have been synthesised and characterised by routine physicochemical techniques. 1 is further characterised by X-ray single crystal structure analysis. Catalytic efficiencies of the complexes as epoxidation catalysts (substrates: styrene and (E)-stilbene; terminal oxidants: PhIO/NaOCl; solvent: MeCN /dicholorometane) and as catalysts for oxidation of catachol (substrates: 3,5-di-tert-butylcatechol (3,5-DTBC); solvent: methanol) have been evaluated. In both cases the catalytic efficiency increases on going from 4-1 although the actual mechanisms in those two catalytic reactions are completely different. However, the observations have been rationalized on the basis of steric and electronic factors exerted by the alkyl substituents present on the imine back-bone of the salen-type ligands. This study also verifies that there is at least another active epoxidizing species, [Cl–O–Mn(III)(salen)X] in addition to the discrete Mn(V)=O(salen) species in epoxidation of olefins depending upon the terminal oxidants employed

Synthesis and characterization of a hydrophilic conjugated 4+4 Re(I)-porphyrin metallacycle

The preparation and the full characterization, including the X-ray structure determination, of a polar trans-dipyridylporphyrin functionalized with two short polyoxyethylene chains is reported. Reaction of the porphyrin with a Re(I) complex yielded a 4+4 metallacycle showing an improved solubility and a lower tendency to aggregate with respect to analogous porphyrin cyclic derivatives. These properties allowed a full NMR characterization of the metallacycle including VT 1H DOSY-NMR experiments and, for the first time, the recording of a 13C-NMR spectrum giving further insight into the structural definition of these type of metallacycles. Spray deposition of the metallacycle on a heated mica substrate shows the formation of regular ring-like nano-structures which are not formed by the parent porphyrin

Ionic dioxidovanadium(V) complexes with Schiff-base ligands as potential insulin-mimetic agents : substituent effect on structure and stability

Four dioxidovanadium(V) complexes with Schiff-base ligands based on 2-hydroxybenzhydrazide with four different substituted salicylaldehydes (5-chlorosalicylaldehyde, 3,5-dichlorosalicylaldehyde, 5-nitrosalicylaldehyde, 3-bromo-5-chlorosalicylaldehyde) were synthesized and described, by using V(2)O(5) and triethylamine. The single crystal X-ray structure measurements as well as elemental analyses and IR spectra confirmed the formulas of the ionic complexes with a protonated triethylamine acting as counterion, HTEA[VO(2)(L)] (HL = Schiff-base ligand). The kinetic stability of the complexes at pH = 2 and 7 was discussed with respect to the neutral vanadium(V) complexes previously studied as potential insulin-mimetic agents. A correlation between the substituents in an aromatic ring of the Schiff-base ligands with crystal packing, and also with the stability of the compounds, was presented

Microstructural features of human bones and funerary practices in Mount Sirai (Sardinia)

In the attempt to set up a useful methodology for the investigation of burned human remains in archaeological, anthropological and forensic fields, we decided to compare the most common protocols for the study of bone bioapatites (Fourier Transform Infrared spectroscopy, FT-IR, and X-ray Diffraction, XRD) to those deriving from the application of X-ray scattering techniques using synchrotron light. In this way, we expect to take advantage of the wider and more dynamic qualities of such a valuable tool in order to examine a higher number of samples in a very short time compared to the “traditional” techniques, meanwhile assessing its applicability in the archaeological field