Solvent effects in square planar complexes: Kinetics of substitution at [1-(2-hydroxyphenyl)-3,5-diphenylformazanato]palladium(II) complexes

Summary A kinetic study is reported on the substitutions: FoPdX+YFoPdY+X (H₂Fo=l-(2-hydroxyphenyl)-3,5-diphenylformazan) with X=NH₃ and py and Y = thiourea, tetramethylthiourea, triphenylphosphine and the thiocyanate ion, in seven nonaqueous pure solvents. Under pseudo first-order conditions a two-term rate-law is obeyed: k(obs)= k₁+k₂ [Y]. The results in terms of reactivity pattern and solvent effects on initial and transition states are very similar to the ones found for the analogous substitutions at platinum(II). The rate of solvolysis (k₁) is determined by the donor number of the solvent and is not related to the transfer free energy of solvation of the substrate. Nonspecific solvation effects dominate. The entropy of activation for the direct nucleophilic displacement, FoPdNH₃+Ph₃P, is found to lie between –110 and –20 JK^–1 mol^–1, indicating the associative character of the substitutions. The named reaction exhibits an isokinetic relationship in the various solvents. In spite of that, an initial state — transition state — final state comparison shows the position of the transition state on the reaction coordinate to be solvent dependent. The importance of charge transfer from the donor solvent to the metal ion in determining the Gibbs free energy of the transition state is emphasized.     

A new 6(5).8 topology and a distorted 6(5).8 CdSO4 topology: two new supramolecular isomers of [M2(bdc)2(L)2]n coordination polymers

We report the crystal structures of two new coordination polymers that have similar composition but, despite having the same circuit symbol and Schl?fli notation, different topologies: a novel 3D topology (USF-1) and a CdSO4-like topology.     

Shape of the optical absorption line in planar square complexes of [PtCl4]2- type

The theory of multiphonon processes is applied to the broad optical absorption bands of [PtCl₄]^2-. It is found that the width and the temperature dependence of the peak position are explained by interaction of the electron with intramolecular vibrations.We are indebted to Yu. E. Perlin, I. B. Bersuker, E. V. Vitiu, and B. S. Tsukerblat for valuable discussions.     

One-pot diastereoselective synthesis of tetrahydroepimino-benzo[b]azocines through sequential [3+2]-cycloaddition and Staudinger-aza-Wittig reactions

The one-pot synthesis of tetrahydro-epiminobenzo[b]azocines through a sequential 1,3-dipolar cycloaddition and intramolecular Staudinger-aza-Wittig reaction sequence is reported. This methodology provides a new and efficient approach for medium-sized and bridged nitrogen heterocyclic molecules.     

Facile synthesis of rotaxanes through condensation reactions of DCC-[2]rotaxanes

[reaction: see text] In this Letter, we present an easy method for the synthesis of rotaxanes using a novel DCC-[2]rotaxane. The DCC-[2]rotaxane is composed of dibenzo-24-crown-8 ether, an amino acid tether, and di-tert-butyl phenyl rings as blocking groups. It is relatively stable and can be purified by column chromatography. A series of model rotaxanes were obtained in good yields by condensing the DCC-[2]rotaxanes with N-(2-aminoethyl)-3,5-di-tert-butylbenzylamide in acetonitrile and chloroform.     

Synthesis of a green [60]fullerene derivative through cage-opening reactions

Open-cage derivative C(60)(O)(4)(OH)(2)(NC(6)H(4)(t)Bu)(2) reacts with ICl to form a Baeyer-Villiger type product, which yields an intense green product upon treatment with HI.     

Catalytic enantioselective [2 + 4] and [2 + 2] cycloaddition reactions with propiolamides

We report here the catalytic and highly enantioselective [2 + 4] and [2 + 2] cycloaddition reactions of electron-rich dienes or silyl enol ethers with electron-deficient propiolamide derivatives induced by copper(II).3-(2-naphthyl)-L-alanine amide complex.     

Rhodium N-heterocyclic carbene-catalyzed [4 + 2] and [5 + 2] cycloaddition reactions

[reactions: see text] A rhodium complex of N-heterocyclic carbene (NHC) has been developed for intra- and intermolecular [4 + 2] and intramolecular [5 + 2] cycloaddition reactions. This is the first use of a transition-metal NHC complex in a Diels-Alder-type reaction. For the intramolecular [4 + 2] cycloaddition reactions, all the dienynes studied were converted to their corresponding cycloadducts in 91-99% yields within 10 min. Moreover, up to 1900 turnovers have been obtained for the intramolecular [4 + 2] cycloaddition at 15-20 degrees C. For the intermolecular [4 + 2] cycloadditions, high yields (71-99%) of the corresponding cycloaddition products were obtained. The reaction time and yield were highly dependent upon the diene and the dienophile. For the intramolecular [5 + 2] cycloaddition reactions, all the alkyne vinylcyclopropanes studied were converted to their corresponding cycloadducts in 91-98% yields within 10 min. However, the catalytic system was not effective for an intermolecular [5 + 2] cycloaddition reaction.     

Polystyrene bis[N-(2-pyridyl) sulfonamide] palladium(II): Synthesis,characterization as a catalyst for coupling reactions

The [N-(2-pyridyl)] para-styrene sulfonamide (PSS) was prepared as a monomer, from the reaction of para-styrene sulfonyl chloride and 2-amino pyridine in the presence of potassium hydroxide solution 0.5 M as a base, and CH₃Cl. Polystyrene [N-(2-pyridyl) sulfonamide] (PPSS) was synthesized from the polymerization of [N-(2-pyridyl)] para-styrene sulfonamide (PSS). The Polystyrene bis [N-(2-pyridyl) sulfonamide] palladium (II) as a polymer- supporting palladium complex was also prepared from the reaction of PdCl₂ (CH₃CN)₂ with PPSS in the presence of KOH 0.5 M. Polystyrene bis [N-(2-pyridyl) sulfonamide] palladium (II) is produced as a novel heterogeneous catalyst for coupling reactions for C-C bond formation. This method includes higher yield and has an easier work-up procedure. The structures of the monomer, polymer and its Pd complex were confirmed by using FT-IR and ¹H-NMR spectroscopy. Elemental analysis of Pd by inductively coupled plasma (ICP) technique and hot filtration test showed loading of the metal into solution from the catalyst The heterogeneous catalyst was recycled without any loss in its properties.     

2-Phospha[3]ferrocenophanes with planar chirality: synthesis and use in enantioselective organocatalytic [3 + 2] cyclizations

Planar chiral phosphines displaying a new ferrocenophane scaffold have been prepared via a stereoselective approach. The P-cyclohexyl substituted phosphine affords high levels of asymmetric induction in the organocatalytic [3 + 2] annulation reaction between allenes and electron-poor olefins.     

Catalytic [2+2] and [3+2] cycloaddition reactions of allenoates with cyclic ketimines

Cyclic ketimines as electrophiles for [2+2] and [3+2] cycloaddition reactions of allenoates have been developed, affording functionalized sultam-fused azetidines and dihydropyrroles, respectively, in good yields with high regioselectivities.     

Formation of supramolecular isomers; poly[2]rotaxane and supramolecular assembly

Poly[2]rotaxane and supramolecular assembly have been prepared by modified cyclodextrins bearing an adamantyl group in an aqueous medium.     

Synthesis and ring opening reactions of a 2-silabicyclo[2.1.0]pentane

Methyl 2-silabicyclo[2.1.0]pentane-1-carboxylate, obtained by a photochemical intramolecular cyclopropanation reaction of an [small alpha]-allylsilyl-[small alpha]-diazoacetate, undergoes ring opening reactions under different conditions leading to methyl 2-[diisopropyl(methoxy)silylmethyl]cyclopropane-1-carboxylate, a 1-sila-4-cyclopentene-2-carboxylate or an allyl(methoxysilyl)ketene.     

Synthesis of [2]- and [3]rotaxanes through Sonogashira coupling

The synthesis of new [2]- and [3]rotaxanes through Sonogashira coupling has been accomplished in the aim to built oligo(phenyleneethynylene) (OPE) encircled by crown ethers. Optimization of the Sonogashira coupling for the formation of the [2]rotaxane (capping reaction) is presented and the best method has been applied for the synthesis of the longer [3]rotaxane.     

Synthesis of the monomethyl isomers of naphtho[1′,2′:4,5]thieno[2,3-c]quinoline

The synthesis of naphtho[1′,2′:4,5]thieno[2,3-c]quinoline ( 11 ) and four monomethyl isomers is described.     

Synthesis of a [2]rotaxane through first- and second-sphere coordination

In an effort to expand the application of a new template from interpenetrated to interlocked molecular species, we report the synthesis of a new [2]rotaxane by means of both first- and second-sphere coordination of a palladium(II) dichloride subunit.