Synthesis and characterization of Pd(II) Complexes with bis-pyridinium and isoquinolinium N-ylides: moderate C-H...O=C intramolecular hydrogen bonds as source of conformational preferences

The bis(N-ylide) Pd(II) complexes cis-[PdX2[eta2-[C(H)NCxHy]2CO]] (X=I, NCxHy=NC5H5, 2a; X=Br, NCxHy=NC5H5 and NC5H3-2,3-Me2, 2c, isoquinolinium NC9H7, 2d) have been prepared by reaction of the corresponding bis-pyridinium salts with Pd(OAc)2 (1:1 molar ratio). Compounds 2 react with AgClO4 and Tl(acac) (1:1:1 molar ratio) to give the acetylacetonato derivatives [Pd(acac-O,O'[eta2-[C(H)NCxHy]2CO]]ClO4 (3a, c, d). In compounds 2 and 3, the bis-ylide is bonded as a C,C-chelate ligand through the two ylidic Calpha atoms. The reaction is stereoselective, and only one diastereoisomer is observed (meso form, RS/SR). The origin of the observed stereoselectivity lies with the establishment of intramolecular C-H...O=C hydrogen bonds between the ortho protons of the pyridine or isoquinoline fragments and the carbonyl oxygen, as it has been shown by density functional theory (DFT) calculations (B3LYP level) and Bader analysis of the electron density on model pyridinium ylides. Despite the inherent weakness of the C-H...O=C bonds, the results show that in these N-ylides the hydrogen bonds are stronger than expected and should be classified as moderate H bonds.     

Synthese substituierter Cyclononatetraene

Synthesis of Substituted Cyclononatetraenes In the course of an exploration of possible synthetic pathways to nonafulvenes, a series of 1-substituted cyclononatetraenes (CNT) 4b–1 have been prepared in yields of about 60%. Their structures follow from spectroscopic data as well as from the quantitative valence isomerisation to 1-endo-substituted cis-3a, 7a-dihydroindenes 8 . Both all-cis-CNT⁻ 1 and cis,cis,cis,trans-CNT⁻ 2 have been used as nucleophiles. Whereas 2 is normally more nucleophilic than 1 , the yield of cyclononatetraenes 4 prepared with 2 may be reduced due to by-products such as 9 and 10 .     

Surfactant effects on electrokinetic processes in clay-rich soils remediation

The present work concerns the realisation of an equipment suitable for the choice of surfactants to be employed in the remediation of polluted soils by soil washing processes. The experimental activity has been focused to verify the surfactants efficiency in electrokinetic processes applied in low porosity soils, polluted with used vehicle oil. The equipment consents to estimate low electroosmotic permeabilities, electrical current and to analyse the electrolytic solutions. The concentration of the chemical species reached in both anodic and cathodic cells allows a more accurate evaluation of the ion mobility through the soil. The apparatus realised has been shown to be a useful instrument capable of providing directions for the choice of surfactants in electrokinetic soil remediation. The choice of an anionic surfactant for the oil removal has shown promising result.     

Preparation of dinitrogen complexes Mo(N2)2P4 stabilised by phosphonite PPh(OEt)2 and phosphinite PPh2(OEt) ligands

Dinitrogen complexes Mo(N₂)₂P₄1, 2 [P=PPh(OEt)₂ and PPh₂OEt] were prepared by allowing a MoCl₃(THF)₃ solution containing an excess of phosphine to react with magnesium under nitrogen. Substitution reactions with CO and p-tolylisocyanide were studied, and led to Mo(CO)₂P₄, Mo(CO)₃P₃, and Mo(p-tolylNC)₂P₄ derivatives. Treatment of dinitrogen compound Mo(N₂)₂[PPh(OEt)₂]₄ with an excess of HCl gave the hydrazido(2-) [MoCl(NNH₂){PPh(OEt)₂}₄]Cl derivative. Reduction reactions with zinc amalgam of complexes 1 and 2 in the presence of lutidine·HCl gave ammonia in about 8-10% yield.     

Versatile synthesis of (Z)-1-alkylidene-1,3-dihydroisobenzofurans and 1H-isochromenes by palladium-catalyzed cycloisomerization of 2-alkynylbenzyl alcohols

An easy synthesis of (Z)-1-alkylidene-1,3-dihydroisobenzofurans and 1H-isochromenes by palladium-catalyzed cycloisomerization of readily available 2-alkynylbenzyl alcohols under neutral conditions is reported. Reactions were carried out at 70-100°C in the presence of catalytic amounts (1-2%) of PdI₂ in conjunction with 2 equiv. of KI for 1.5-24 h. The preference towards the 5-exo-dig cyclization mode (leading to 1,3-dihydroisobenzofurans) or the 6-endo-dig cyclization mode (leading to isochromenes) turned out to be dependent on the substitution pattern of the substrate as well as reaction conditions. In several cases, by properly adjusting the reaction conditions, the same substrate could be selectively converted into either the dihydroisobenzofuran or the 1H-isochromene derivative.     

Zirconocene-mediated, high-yielding macrocyclizations of silyl-terminated diynes

A series of silyl-terminated diynes of varying lengths and substitution patterns have been prepared. These diynes undergo zirconocene coupling with selective formation of trimeric macrocycles from linear alkynes, while nonlinear diynes give cyclodimeric products. The length of the linear diynes can be increased for the preparation of macrocycles with large nanoscale cavities. Reaction of the zirconium-containing macrocycles with acid results in the synthesis of metal-free cyclophanes. All of these macrocycles were prepared in multigram quantities, in the absence of high-dilution conditions, to give products in > 75% yield that are easily purified as crystalline solids.     

Preparation and reactivity of penta- and tetracoordinate platinum(II) hydride complexes with P(OEt)3 and PPh(OEt)2 phosphite ligands

The pentacoordinate [PtH{P(OEt)3}4]BF4 (1) hydride complex was prepared by allowing the tetrakis(phosphite) Pt{P(OEt)3}4 to react with HBF4.Et2O at -80 degrees C. Depending on the nature of the acid used, however, the protonation of the related Pt{PPh(OEt)2}4 complex yielded the pentacoordinate [PtH{PPh(OEt)2}4]BF4 (3) or the tetracoordinate [PtH{PPh(OEt)2}3]Y (4) [Y = BF4- (a), CF3SO3- (b), Cl- (c)] derivatives. Neutral PtHClP2 (7,8) [P = P(OEt)3, PPh(OEt)2] hydride complexes were prepared by allowing PtCl2P2 to react with NaBH4 in CH3CN. The tetrakis(phosphite)[Pt{P(OEt)3}4](BF4)2 (2) derivative was also synthesised and then characterised spectroscopically and by an X-ray crystal structure determination. Reactivity with aryldiazonium cations of all the hydrides was investigated and found to proceed only with the PtHClP2 complex to yield the aryldiazene [PtCl(ArN=NH)P2]BF4[P = PPh(OEt)2] derivative. The hydrazine [PtCl(NH2NH2){PPh(OEt)2}2]BPh4 complex was also prepared by allowing PtHClP2 to react first with AgCF3SO3 and then with hydrazine.     

Capillary electrophoresis investigation of a partially unfolded conformation of beta(2)-microglobulin

Dialysis-related amyloidosis is a disease in which partial unfolding of beta(2)-microglobulin plays a key pathogenetic role in the formation of the amyloid fibrils. We have recently demonstrated that a partially unfolded conformer of beta(2)-microglobulin is involved in fibrillogenesis and that this species is significantly populated under physiological conditions. In this work capillary electrophoresis has been used to measure the equilibrium between the native protein and this conformer in samples known to have a higher or lower amyloidogenic potential, namely full-length beta(2)-microglobulin, two truncated species and a mutant, created by replacing histidine in position 31 with thyrosine. In addition, for all protein species folding stability experiments have been carried out by monitoring the secondary structure by circular dichroism at increasing concentrations of guanidinium chloride. The values of free energy of unfolding in the absence of denaturant, obtained by elaboration of these experiments, were found to be inversely correlated to the area percent of the partially unfolded conformer, as measured by capillary electrophoresis. Affinity capillary electrophoresis experiments have been also carried out under nondenaturing conditions to assess the affinity of copper and suramin to either the native form or the conformational intermediate of full-length beta(2)-microglobulin.     

2′-Methyl taxanes: synthesis and NMR configurational assignment

Capitalizing on an oxidation-alkylation approach, a non-diastereoselective entry into 2′-methyl taxanes was developed. The issue of configurational assignment at the newly formed side-chain quaternary stereocenter was solved and put into a more general context by integrating information from an alternative diastereoselective synthesis of model compounds and from spectroscopic measurements, critically comparing the J-Based and the Universal NMR Database approaches.     

Self-assembly of palladium(II) and platinum(II) complexes of 2-hydroxypyrimidine to novel metallacalix[4]arenes. Receptor properties through multiple H-bonding interactions

Reaction of [enM(H2O)2](NO3)2 (en = ethylenediamine, M = PdII, PtII) with 2-hydroxypyrimidine (Hpymo) in water results in self-assembly to cyclic complexes of type [enM(pymo-N1,N3)]4(NO3)4 (1, M = PdII; 2, M = PtII) which are structurally analogous to calix[4]arenes. The tetranuclear cations in compounds 1 and 2 adopt, in the solid state, a 1,3-alternate orientation of the pymo residues. Attempts to coordinate either soft (PdII, PtII), borderline (CuII, ZnII), or hard (LaIII, BeII, NaI) metal ions to the oxo surface of the metallacalix[4]arene lower rim were fruitless. In fact, X-ray studies performed on [[enPt(pymo-N1,N3)]4(ClO4)4]2.[Cu(H2O)6](ClO4)2.9H2O (4) showed that multiple H-bonding interactions between the water coordination sphere of the copper center and the oxo surface of two tetranuclear cations take place instead of a direct interaction between the heterometal and the oxo surface of the metallacalix[4]arene. Encapsulation of [Cu(H2O)6]2+ is also responsible for the stabilization of the pinched-cone conformation of the tetranuclear cations in 4. pH* dependent 1H NMR spectra of compounds 1 and 2 indicate a very low basicity of the O-donor group of the pymo residues, revealing no protonation of this position down to pH* 0. Moreover, recrystallization of 2 from strongly acidic aqueous solution (approximately 1 M HClO4) affords the adduct [[enPt(pymo-N1,N3)]4(ClO4)4]2.[H20O8](ClO4)4 (6). Analogously to 4, the cationic [H20O8]4+ species is sandwiched between two tetranuclear cations as a result of multiple H-bonding interactions with the oxo surface of two metallacalix[4]arenes. Again a pinched-cone orientation of the pymo residues is realized.