Preparation of some triethylammonium (organocyanoamino)chlorotriphenylstannates

Seven new anionic triphenytin complexes, triethylammonium (organocyanoamino)chlorotriphenylsannates, were prepared by the reaction of (triphenylstannyl) cyanamide with acid chlorides, alkyl chlorocarbonates, or benzenesulfonyl chloride in the presence of triethylamine. One of these complexes, triethylammonium (acethylcyanoamino)chlorotriphenylstannate, was also prepared by the reaction of triethylamine hydrochloride with N-(triphenylstannyl)-N-acetylcyanamide, which was obtained by following acetyl chloride to react with bis(triphenylstannyl)carbodiimide. The PMR and IR (4000-140 cm^?1) spectrum of each complex was measured. The Mössbauer parameters of two of the complexes were obtained, the quadrupole splittings being consistent with trigonal bipyramidal structures. p-Nitrobenzoyl chloride and terephthalyl chloride failed to give complexes on reaction with (triphenylstannyl)cyanamide and triethylamine, but instead gave the triethylammonium salt of the corresponding acylcyanamide. The new anionic complex, triethylammonium dichlorotriphenylstannate, was prepared by the reaction of triphenyltin chloride with triethylamine hydrochloride.     

Regioselective anti-addition of phenols to propargylic oxiranes by palladium(0) catalyst

(Z)-Phenol-substituted alkenes were produced by the palladium(0)-catalyzed reaction of propargylic oxiranes with phenols. The regio- and stereoselective addition of phenols to alkynes occurs via the formation of π-propargyl- and π-allylpalladium complexes. The phenoxy-substituted enones were produced simultaneously depending on the reaction conditions.     

Hydroformylation activity of multinuclear rhodium complexes coordinated to dendritic iminopyridyl and iminophosphine scaffolds

The synthesis of poly(propyleneimine)-iminopyridyl and iminophosphine rhodium(I) metallodendrimers, with rhodium coordinated to monodentate (N-donor) and chelating, heterobidentate (P,N) moieties respectively located on the periphery, has been accomplished in order to evaluate their potential as hydroformylation catalysts. Related mononuclear complexes were obtained in a similar manner to model the multinuclear complexes. The multinuclear rhodium(I) complexes were found to be effective catalyst precursors in the hydroformylation of 1-octene, achieving higher conversions, faster reaction rates and slightly enhanced catalytic activity when compared with analogous mononuclear rhodium complexes. Hydroformylation reactions using the tetra- and octanuclear rhodium complexes generally show a chemoselective formation of aldehydes, together with a small amount of isomerisation products.     

Molecular Complexes of μ-Carbidodimeric Iron(IV) Tetra-4-<Emphasis Type="Italic">tert</Emphasis>-butylphthalocyaninate with Nitrogenous Bases

The reaction of μ-carbidodimeric iron(IV) tetra-4-tert-butylphthalocyaninate with nitrogenous bases (imidazole and its derivatives, pyridine, diethylamine), which involves formation of donor?acceptor complexes with a preserved dimeric structure, was studied by spectral methods. The composition of such molecular complexes and their comparative stability were determined. The coordination power of μ- carbidodimeric iron(IV) tetra-4-tert-butylphthalocyaninate was found to depend on the nature of the nitrogenous base and macrocycle. Quantum-chemical modeling of the coordination reaction was performed. The energetic and geometric characteristics of the donor?acceptor complexes were obtained. The composition of the reaction products was shown to be affected of the degree of deformation of the macrocycle.     

Catalyzation of 1,4-additions of arylboronic acids to α,β-unsaturated substrates using nickel(I) complexes

Nickel(I) complexes were generated in situ from Ni (PPh₃)₂Cl₂ using activated iron and the complexes combined with N,N′-bis(4-fluorobenzylidene) ethane-1,2-diamine (BFBED) were then used as a catalyst for the 1,4-addition reaction of arylboronic acids to α,β-unsaturated substrates. The reaction proceeded to completion and did not require the addition of a base but the addition of potassium iodide is crucial to this cross-coupling reaction. Moreover, experimental observations suggested a possible Ni(I)–Ni(III) catalytic cycle mechanism.     

Rotamers of palladium complexes bearing IR active N-heterocyclic carbene ligands: Synthesis, structural characterization and catalytic activities

The preparation and properties of mono- versus bis(carbene) Pd(II) complexes bearing unsymmetrical cyano- and ester-functionalized NHC ligands as potential IR probes were studied in detail. Direct reaction of Pd(OAc)₂ with functionalized imidazolium salts afforded either bis(carbene) (3a, c) or monocarbene complexes (5, 6) with a N-coordinated imidazole co-ligand. The latter were exclusively obtained with N-ethylene substituted salts, which were found to undergo N-C cleavage reaction. The milder Ag-carbene transfer reaction on the other hand was tolerable to the length of the substituents and the nature of the functional groups. All bis(carbene) complexes (3a-c, 4a-c) were obtained as a inseparable mixture of square-planar trans-anti and trans-syn rotamers. The identity, ratio and dynamic equilibrium of these rotamers have been investigated and the relatively high rotational barrier for rotamers of 3a was estimated to be about 74 kJ mol⁻¹ at 380 K. All eight complexes were fully characterized by NMR and IR spectroscopies, ESI mass spectrometry and X-ray single crystal and powder diffraction. A preliminary catalytic study showed that ester-functionalized complexes 4a and 4b gave rise to highly active catalyst in the double Mizoroki-Heck coupling of aryl dibromides, while the in situ ester-hydrolyzed complexes were also active in the coupling of activated aryl chlorides.     

Synthesis and chemical stability of (5,15-bis(2-thienyl)- and 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-butyl-21H,23H-porphinato)copper(II)

(5,15-Bis(2-thienyl)-and 5,15-diphenyl-3,7,13,17-tetramethyl-2,8,12,18-tetra-n-butyl-21H,23H-porphinato)copper(II) complexes were synthesized and the basicity, absorption spectra (UV-Vis, IR, ¹H NMR) of the macrocyclic ligands and the stability of the complexes in AcOH-H₂SO₄ mixed solvents were studied with the aim to reveal the effect of 2-thienyl substituent on the properties of substituted porphyrins. Data on kinetics were obtained, reaction mechanism of complex dissociation was reasoned, and the effect of functional substitution on the properties of macrocyclic bases and their complexes with copper(II) were determined.     

Diversity oriented synthesis of conjugate dienes and alkenylcyclopropanes utilizing silyl group-substituted titanium carbene complexes as bimetallic synthetic reagents

Diversity oriented synthesis of conjugate dienes and alkenylcyclopropanes by the sequential reactions using silyl group-substituted titanium carbene complexes was studied. Dienylsilanes were obtained by the olefination of carbonyl compounds with γ-silylvinylcarbene complexes. Cyclopropanation of 1-alkenes with the vinylcarbene complexes produced (E)-(β-silylvinyl)cyclopropanes with high stereoselectivity. The reaction of β-(trialkylsilyl)carbene complexes with zinc alkoxides of homopropargyl alcohols produced 6-silyl-3,5-hexadien-1-ols with high regio- and stereoselectivity. The (E)-alkenylsilanes thus obtained were transformed into a range of unsaturated compounds by the palladium-catalyzed or copper(I)-promoted cross-coupling with organic halides with retention of configuration.     

Palladium catalyzed asymmetric allylic alkylation using chelating N-heterocyclic carbene–amino ligands

Several silver(I) complexes with chiral amino-N-heterocyclic carbene (NHC) ligands, which are not diastereomerically pure, were prepared and used to generate in situ chelating NHC–amino palladium(II) complexes. The potential of these palladium(II) complexes in asymmetric catalysis was evaluated in the allylic alkylation reaction. The influence of the structure and of the diastereomeric purity of the ligands on enantioselectivity, as well as the role of the silver salts, were studied. Enantiomeric excesses of up to 80% were obtained with the best ligand.     

Synthesis and characterization of asymmetric NHC complexes

New chiral and non-chiral rhodium(I)–NHC complexes were synthesized. The first attempt by deprotonation of an imidazolinium salt with KOtBu and reaction with [Rh(COD)Cl]₂ leads to the corresponding rhodium(I) complex. Due to the basic conditions during the reaction a loss of chirality occurs. An alternative transmetallation reaction with a silver(I)–NHC complex yields the desired rhodium(I)–NHC complex under retention of chirality. Both Rh complexes were fully characterized by analytical methods.     

Synthesis, X-ray structures, and catalytic applications of palladium(II) complexes bearing N-heterocyclic iminocarbene ligands

Two new Pd(II) N-heterocyclic iminocarbene complexes (C-N)PdCl₂ that contain 5-membered chelate rings have been prepared by carbene transfer from a silver iminocarbene precursor to (COD)PdCl₂. The new Pd imonocarbene complexes, as well as two that have been previously reported (altogether three 5-membered and one 6-membered chelate ring complexes) have been evaluated as catalysts for the Suzuki-Miyaura coupling reaction. The complexes were found to be active in the reaction, but without exceptional catalytic performances. The 5-membered chelate ring complexes appeared to be more robust and remained active for a longer time than the 6-membered ring congener. The catalytic performance of the 5-membered chelate ring complexes appeared to be rather insensitive to the steric demands of the imine-N-aryl group. The X-ray structure of one of the Ag iminocarbene complexes reveals the κ¹(C) bonding of the iminocarbene moiety in a nearly linear Ag(I) complex; two monomeric units are associated through a weak Ag-Ag interaction. The X-ray structures of two new Pd iminocarbene complexes (C-N)PdCl₂ confirm the chelating κ²(C,N) nature of the iminocarbene moiety; in both complexes, the Pd-Cl distances trans to carbene-C are slightly longer than those trans to imine-N.     

Investigation of the oxygen affinity of manganese(II), cobalt(II) and nickel(II) complexes with some tetradentate Schiff bases

Oxygen absorption–desorption processes for square planar Mn(II), Co(II) and Mn(II) complexes of tetradentate Schiff base ligands in DMF and chloroform solvents were investigated. The tetradentate Schiff base ligands were obtained by condensation reaction of ethylenediamine with salcyldehyde, o-hydroxyacetophenone or acetylacetone in the molar ratio 1:2. The square planar complexes were prepared by the reaction of the Schiff base ligands with Mn(II) acetate, Co(II) nitrate and Ni(II) nitrate in dry ethanol under nitrogen atmosphere. The sorption processes were undertaken in the presence and absence of (pyridine) axial-base in 1:1 M ratio of (pyridine:metal(II) complexes). Complexes in DMF indicate significant oxygen affinity than in chloroform solvent. Cobalt(II) complexes showed significant sorption processes compared to Mn(II) and Ni(II) complexes. The presence of pyridine axial base clearly increases oxygen affinity.     

Photophysical Properties and Kinetic Studies of 2-Vinylpyridine-Based Cycloplatinated(II) Complexes Containing Various Phosphine Ligands

A series of cycloplatinated(II) complexes with general formula of [PtMe(Vpy)(PR₃)], Vpy = 2-vinylpyridine and PR₃ = PPh₃ (1a); PPh₂Me (1b); PPhMe₂ (1c), were synthesized and characterized by means of spectroscopic methods. These cycloplatinated(II) complexes were luminescent at room temperature in the yellow–orange region’s structured bands. The PPhMe₂ derivative was the strongest emissive among the complexes, and the complex with PPh₃ was the weakest one. Similar to many luminescent cycloplatinated(II) complexes, the emission was mainly localized on the Vpy cyclometalated ligand as the main chromophoric moiety. The present cycloplatinated(II) complexes were oxidatively reacted with MeI to yield the corresponding cycloplatinated(IV) complexes. The kinetic studies of the reaction point out to an S_N2 mechanism. The complex with PPhMe₂ ligand exhibited the fastest oxidative addition reaction due to the most electron-rich Pt(II) center in its structure, whereas the PPh₃ derivative showed the slowest one. Interestingly, for the PPhMe₂ analog, the trans isomer was stable and could be isolated as both kinetic and thermodynamic product, while the other two underwent trans to cis isomerization.     

Effect of N1-substituted pyrazolic hybrid ligands on palladium catalysts for the Heck reaction

In this paper we have explored the influence of several linkers present on the [PdCl₂(L)] complexes, where L is 3,5-dimethylpyrazolic hybrid ligand N1-substituted by polyether chains and/or phenyl groups. These complexes have been used as pre-catalysts in the Heck reaction between phenyl halides and tert-butyl acrylate. The corresponding complexes efficiently catalyze the Heck olefination and provide good yields under phosphine-free conditions, even for aryl chlorides. Different reaction conditions were investigated and it was found that the nature of the ligand has an important influence on the effectiveness of the catalytic system. Ligand 1,8-bis(3,5-dimethyl-1H-pyrazol-1-yl)-3,6-dioxaoctane (L1), which has previously shown to be the most flexible and versatile, achieved high turnover numbers within very short reaction times and low catalyst loadings.     

Stereoselective aldol reactions of dihydroxyacetone derivatives catalyzed by chiral Zn2+ complexes

The direct aldol reaction between a protected dihydroxyacetone derivative and 4-nitrobenzaldehyde catalyzed by chiral Zn²⁺ complexes of 1-(n-carboxylalkyl)-7-aminoacyl-1,4,7,10-tetraazacyclododecane is reported. New Zn²⁺ complexes containing l-histidine and carboxylalkyl chains that mimic a class II aldolase, carboxypeptidase A and a serine protease were designed and synthesized. Syn-aldol products were mainly formed by an aldol reaction of acetonide-protected dihydroxyacetone with benzaldehydes and other benzaldehydes in N-methylpyrrolidone (NMP)/alcohol (MeOH, EtOH or 2-PrOH) in good yields with a high degree of diastereo- and enantioselectivity (56%～quant., 57～>99% ee). Mechanistic aspect based on ESI-HRMS, elemental analysis and pH titrations of model ligands is also discussed.     

Complexes of dibenzo-24-crown-8 with some sodium monoalkyl benzeneazophosphonates

Syntheses and properties of complexes of dibenzo-24-crown-8 with the sodium monoethyl ester and the sodium monobutyl ester of [α-(4-benzeneazoanilino)-N-benzyl]phosphonic acid, [α-(4-benzeneazoanilino)-N-4-hydroxybenzyl]phosphonic acid and [α-(4-benzeneazoanilino)-N-4-methoxybenzyl]phosphonic acid have been studied. The crystalline complexes formed were found to depend not only on the size of the cation and the crown ether cavity but also on the choice of anion and the reaction solvent. It was shown that the molecular structure and electronic configuration of the anion are important factors in a salt-ligand system which influence the case of solubilization and charge separation in solution. The complexes obtained were characterized on the basis of conductance measurements and UV, IR and ¹H NMR spectra.     

Synthesis and luminescent properties of neutral Eu(III) and Gd(III) complexes with 1-(1,5-dimethyl-1h-pyrazol-4-yl)-4,4,4-trifluoro-1,3-butanedione and 4,4,5,5,6,6,6-heptafluoro-1-(1-methyl-1H-pyrazol-4-yl)-1,3-hexanedione

Neutral [EuL₃Phen] complexes were synthesized by the reaction of EuCl₃ with heterocyclic diketones-1-(1,5-dimethyl-1H-pyrazol-4-yl)-4,4,4-trifluoro-1,3-butanedione and 4,4,5,5,6,6,6-heptafluoro-1-(1-methyl-1H-pyrazol-4-yl)-1,3-hexanedione—and 1,10-phenanthroline (Phen) in an aqueous alcohol solution in the presence of NaOH. The reaction of GdCl₃ with the same diketones under analogous conditions, but without adding 1,10-phenanthroline, yielded [GdL₃(H₂O)₂] complexes. The composition of the complexes was determined by elemental analysis, and their optical and luminescent properties were examined.     

Novel trinuclear palladium(0) complexes; tris(tribenzylideneacetylacetone) tripalladium(solvent) complexes and their reactions

In an extension of our studies on palladium(0)dibenzylideneacetone complexes, novel trinuclear palladium complexes with three molecules of tribenzylideneacetylacetone have been obtained and identified by elemental and spectroscopic analyses (IR, UV and NMR).Ligand exchange reactions, oxidative addition reactions and complex formation reaction with maleic anhydride, dimethyl acetylenedicarboxylate and para-quinones were investigated. These were found to be similar to those of palladium (0)dibenzylideneacetone complexes.     

Unsymmetric bimetal(II) complexes: Synthesis, structures and catalytic behaviors toward ethylene

A series of unsymmetric bimetal(II) (Fe, Co and Ni) complexes ligated by 2-methyl-2,4-bis(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines were synthesized and characterized by IR spectra and elemental analysis, while a representative nickel(II) complex (5a) was determined by single-crystal X-ray crystallography. These iron(II) complexes were found to exhibit good activities for ethylene oligomerization and polymerization in the presence of MMAO and afforded α-olefins in high selectivity, and the composition of oligomers followed the Schluz-Flory distribution. The nickel(II) complexes mainly dimerize ethylene with considerable activity. The influences of coordinative ligands and reaction parameters were fully investigated on the catalytic activity and properties of these complexes.     

Structure and catalytic activity of organopalladium(II) complexes based on 4,5-dihydro-1H-imidazol-5-one derivatives

The paper describes preparation of a chiral bidentate ligand - 2-(2-bromophenyl)-4,5-dihydro-1H-imidazol-5-one, and a tridentate ligand - 2-bromo-1,3-bis(4,5-dihydro-1H-imidazol-5-on-2-yl)benzene, whose oxidative addition reaction with Pd(0) giving neutral organopalladium(II) complexes has been studied. The structure of these complexes was studied by means of NMR spectroscopy and X-ray diffraction. After transformation of the neutral organopalladium(II) complexes into the corresponding ionic species the latter were studied as enantioselctive catalysts for asymmetric Friedel-Crafts alkylation and Michael addition.