1,721,014 research outputs found
Nitrido technetium-99m core in radiopharmaceutical applications: Four decades of research
Full text linkThe knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing effcient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes
Crystral Structures of a Bis(cyclopentadienyl)(Z)-enyne Framed Manganese(I)-Rhenium(I) Complex and its [Co2(CO)8] Adduct
No full textSynthesis, characterization and catalytic activity in the carbonylation of ethene of cis-[Pd(H2O)2(PPh3)2]X2 · nH2O (X=p-CH3C6H4SO3, n=2; X=CH3SO3, n=0). X-ray structure of cis-[Pd(H2O)2(PPh3)2](p-CH3C6H4SO3)2 · 2H2O and of cis-[Pd(H2O)2(PPh3)2](CH3SO3)2 · 2CH2Cl2
Full text linkSynthesis, characterization and X-ray structural determination of palladium(0)–olefin complexes containing pyridin-thioethers as ancillary ligands. Equilibria and rates of olefin and ligand exchange
No full textInsertion of Isocyanides across the Pd-C Bond in Alkyl or Aryl Palladium(II) Complexes Bearing Mixed Nitrogen-Sulfur and Nitrogen-Phosphorus Ancillary Ligands. The Mechanism of Reaction
No full textAn exhaustive study dealing with the kinetic and mechanistic behavior of alkyl- and arylpalladium
complexes bearing pyridyl-thioethers (NS-R) and quinoline-phosphines (NP) as ancillary ligands when
reacting with 2,6-dimethyl isocyanide (DIC) and tosylmethyl isocyanide (TosMIC) was undertaken. In
these reactions some differently substituted isocyanides insert into the palladium-carbon bond of alkyl
and aryl complexes bearing mixed (NS or NP) ligands. The reactions were carried out under equimolecular
conditions since such a restrictive approach allows the determination of the rate constants related to the
isocyanide insertion attack. Reactions carried out under nonstoichiometric conditions were also taken
into account and the reaction products characterized. Usually the formation of an inserted bis-substituted
isocyanide halide derivative of palladium(II) was observed. In a particular case the formation of an imidoyl
dimer was detected. The structures of the monoinserted [Pd(NSt-Bu)(C(Tol)=NR2)I] (NSt-Bu ) 2-(tertbutylthiomethyl)
pyridine) and of the dimer [Pd(CNR2)(C(=NR2)Me)Cl]2 (R2 ) 2,6-Me2C6H3) were
reported
Catalytic properties of [Pd(COOMe)nX2-n(PPh3)2] (n = 0, 1, 2; X = Cl, NO2, ONO2, OAc and OTs) in the oxidative carbonylation of MeOH
No full textcis-[Pd(ONO2)2(PPh3)2] (1) reacts under mild conditions with CO in methanol (MeOH) in the presence of pyridine
(py), yielding trans-[Pd(COOMe)(ONO2)(PPh3)2] (1a). The use of NEt3 instead of py leads to a mixture of 1a,
trans-[Pd(COOMe)2(PPh3)2] (2), and [Pd(CO)(PPh3)3]. Pure 2 was prepared by reacting cis-[Pd(OTs)2(PPh3)2]
with CO in MeOH and subsequently adding NEt3. The nitro complex trans-[Pd(COOMe)(NO2)(PPh3)2] (3a) was
prepared by reacting trans-[Pd(COOMe)Cl(PPh3)2] with AgNO2 or with AgOTs and NaNO2. New syntheses for 1 and
trans-[Pd(NO2)2(PPh3)2] (3) are also reported. All complexes have been characterized by IR and 1H and 31P{1H}
NMR spectroscopies. Complexes 1 and 2 exchange irreversibly and quantitatively one nitrato with one carbomethoxy
ligand, yielding 1a. 2 in CD2Cl2 at 40 C decomposes with the formation of dimethyl carbonate (DMC), whereas under
4 atm of CO, DMC and dimethyl oxalate (DMO) are formed, ca. 12% each; in the presence of PPh3 and in the absence
of CO, decomposition occurs at 60 C with the formation of DMC only, suggesting that decarbonylation involves a fivecoordinate
intermediate or predissociation of a PPh3 ligand. The oxidative carbonylation of MeOH does not occur when
using NaNO2 or NaNO3 as the oxidant and 1, 1a, 3, or 3a as the catalyst precursor. On the contrary, when using
benzoquinone (BQ) as the oxidant, these complexes, 2, or [Pd(COOMe)2-nXn(PPh3)2] (X = Cl, OAc, OTs; n = 1, 2)
promote selective catalysis to DMO. After catalysis the precursors are transformed into [Pd(BQ)(PPh3)2]2 3 H2BQ,
[Pd(CO)(PPh3)]3 and [Pd(CO)(PPh3)3]. Also the last with BQ gives selective catalysis to DMO. The solid-state
structures of 1 3 CH2Cl2 and 1a have been determined by means of single-crystal X-ray diffraction
Assessment of spring waters from Lourdes (France) by contact angle method
Full text linkThe geochemical investigations on karst spring waters in the area of Lourdes showed differences between the waters for numerous components, including main solutes and trace elements. In this study, a multidisciplinary approach was proposed, based on the surface free energy of solids and the surface tension of liquids using the contact angle method, by raising the hypothesis that different spring waters diverge in surface tension characteristics, which allow to discriminate waters origin in a natural system. Surface energy characteristics of seven spring waters from Batsurguère Valley were investigated here using the contact angle measured over time and the tangent method in relation to the variations of the droplet volume. Wettability of various test solids was analyzed using static and kinetic contact angle methods which led to the individuation of the spring waters on the base of the different adhesion processes occurring at the interface between water and solid, particularly on the silica glass solid. The analyses demonstrated that the surface tensiometry technique can discriminate one of such spring waters (i.e. the Massabielle spring) from other studied spring waters, regardless of their natural hydrological conditions. Contact angle hysteresis in kinetic modality, based on several repeated and extemporary set of experiment determinations, suggested a link between the water chemistry and the wettability over time of the test solids, confirming that chemical composition has an influence on the surface tension of spring waters. This investigation demonstrates that the surface tensiometry approach may represent a useful tool for monitoring quality of natural waters
STRUCTURAL CHARACTERIZATION OF A TRINUCLEAR COMPLEX OF PLATINUM(II) CONTAINING BRIDGING 1-METHYLCYTOSINE LIGANDS - A COMBINED X-RAY AND MULTINUCLEAR NMR-STUDY
No full textThe dinuclear complexes cis-[(PMe3)2Pt(1-MeCy(-H))]2X2 (X = NO3- (1A), ClO4- (1B)), containing NH2-deprotonated 1-methylcytosine (1-MeCy(-H)) ligands, in aqueous or DMSO solution, at 80-degrees-C convert quantitatively into the corresponding trinuclear derivatives cis-[(PMe3)2Pt(1-MeCy(-H))]3X3(2A,B) which have been characterized in the solid state by single-crystal X-ray analysis and in solution by multinuclear (H-1, P-31, Pt-195, C-13, and N-15) NMR spectroscopy. The nitrate salt (2A) crystallizes from ethanol in the triclinic system, space group Pl. The crystals, stable only in the presence of the solvent, have the following cell dimensions: a = 13.542(5) angstrom, b = 17.352(5) angstrom, c = 20.721(6) angstrom, alpha = 113.13(2)degrees, beta = 104.30(3)degrees, gamma = 95.77(3)degrees, Z = 2. The structure, formulated as cis-[(PMe3)2Pt(1-MeCy(-H))]3(NO3)3.EtOH.H2O, was refined to R = 6.3 and R(w) = 6.3. Better structural data were obtained with the perchlorate derivative (2B), cis-[(PMe3)2Pt(1-MeCy(-H))]3(ClO4)3.2H2O, whose structure was refined to R = 4.4 and R(w) =4.9. The colorless prisms formed from aqueous solutions have the following crystallographic data: triclinic system, space group P1BAR, a = 14.634(7) angstrom, b = 14.791(9) angstrom, c = 14.980(9) angstrom, alpha = 101.93(5)degrees, beta = 103.46(5)degrees, gamma = 90.50(4)degrees, Z = 2. In both salts, the molecular structure of the cationic complex contains three cis-(PMe3)2Pt units linked to three 1-methylcytosine anions through the N(3) and N(4) atoms. The resulting 12-membered ring contains the pyrimidinic rings almost perpendicular to the plane defined by the metal atoms. Each platinum has a square-planar coordination with a Pt...Pt distance of 5.2A. The H-1, P-31, and C-13 NMR spectra indicate that the approximate S3 symmetry of the cation is maintained in solution. The compounds 1A and 2A were also characterized by N-15 NMR spectroscopy, at natural abundance. The spectroscopic data, obtained in DMSO-d6 solution, are compared with those of the derivative cis-[(PMe3)2Pt(1-MeCY)2](NO3)2 containing as ligands the neutral N(3)-bonded nucleobase. The dinuclear and trinuclear complexes exhibit very similar N-15 chemical shifts and 2J(PN) coupling constants but remarkably different from those of the mononuclear complex
Synthesis, Characterization and X-ray Structure of Pd(dppp)(SO4), a Catalyst for the CO-Ethene Copolymerization [dppp = 1,3-bis(diphenylphosphine)propane]
No full textThe role of ancillary ligands and of electron poor alkenes and alkynes in stabilizing Pd(0) derivatives: A comparative study
Full text linkThe peculiar characteristics of the ligand neocuproine (2,9-dimethylphenanthroline) allow a number of exchange equilibrium studies between the low valence complex [Pd(eta(2)-nq)(Neocup)] (nq = naphthoquinone; Neocup = neocuproine) and several alkenes and alkynes. A new order of stability which compares differently unsaturated molecules was established. An overview of the factors governing the stability of palladium(0) alkene and alkyne derivatives as a function of the steric and electronic characteristics of both the unsaturated molecule and the ligand becomes accessible and a comparison with the previously determined order was therefore feasible. Such a comparison enlightens the importance of the substituent methyl groups in ortho position of the hetero-aromatic ring which represents the molecular fragment common to all the ligands considered. Taking advantage of the steric requirements of the alkene tmetc (tmetc = tetramethylethylenetetracarboxylate) a kinetic investigation of the reaction between the olefin itself and the complexes [Pd(eta(2)-dmfu)(L-L')] (dmfu = dimethylfumarate; L-L' = 8-diphenylphosphanyl-2-methyl-quinoline, neocuproine, phenanthroline) was carried out. The structures of the complexes [Pd(eta(2)-dmfu)(DPPQ)] and [Pd(eta(2)-deta)(Neocup)] (deta = but-2-ynedioc acid diethyl ester) were also reported in the present paper. The structure of the latter represents the first example of a palladium(0) complex in which the N(2)C(2) donor set around the metal centre is supported by a chelating eta(2)-alkyne
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