Recent advances of achiral and chiral diene ligands in transition-metal catalyses

A series of achiral and chiral diene and the related ligands in transition-metal complexes is evaluated by percent buried volume (%V_bur) based on their molecular structures by X-ray analysis. Steric bulk of cyclic diene ligands in [Ru(acac)₂L] and [RhClL]₂ are sorted in the order of %V_bur. Recent developments on transition-metal catalyses using these ligands such as (i) conjugate arylations, alkenylation, and alkynylation, (ii) imine-arylations and alkenylations, (iii) kinetic resolutions, (iv) allylation, (v) cyclizations, (vi) defluorinations, (vii) CH bond activations, and (viii) cross-dimerizations are reviewed.     

Studies on dynamic mechanical and mechanical properties of vinyloxyaminosilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM-g-VOS/LLDPE) blends

The dynamic mechanical properties of vinyloxyaminosilane grafted ethylene propylene diene terpolymer/linear low density polyethylene (EPDM-g-VOS/LLDPE) blends have been evaluated with special reference to the effect of blend ratio. It has been found that increasing the proportion of LLDPE in the blends decreases the T_g values and increases the storage modulus (E^′) and loss modulus (E^′′) due to increase in crystallinity. A gradual increase in the values of tanδ_max is observed for the blends with increase in EPDM-g-VOS concentration, which indicates that no phase inversion occurs. But however the higher increase in tanδ_max after 50 wt.% of EPDM-g-VOS composition is due to small change in crystallinity and is ascertained by SEM micrographs. Mechanical properties such as tensile strength, Young’s modulus and hardness increase with increases in LLDPE concentration in the blends and with dicumyl peroxide (DCP) concentration whereas the values of elongation at break are decreased with increase in LLDPE and DCP concentration.     

Iridium and rhodium complexes with the planar chiral thioether ligands in asymmetric hydrogenation of ketones and imines

Rhodium complexes with the planar chiral phosphinoferrocenyl thioether ligands [Rh(P,SR)(diene)X] (R = Me, Bu^t, Ph, Bn, diene is cyclooctadiene (COD) or norbornadiene (NBD), X = Cl, BF₄) catalyze hydrogenation of ketones, imines, and heteroaromatic compounds; in the case of acetophenone, the enantioselectivity reached 60% ee. Similar iridium complexes demonstrate a good activity in the hydrogenation of imines, the maximal enantioselectivity in the case of N-phenyl-N-(1-phenylethylidene)amine was about 40% ee.     

Complexes olefiniques du ruthenium : IV. Etude des complexes [RuClH(diène)(amine)2], structure cristalline de [RuClH(cod)(pipéridine)2]

The polymer [RuCl₂(diene)]_n undergoes bridge cleavage reaction with amines giving, at temperatures dependant on the nature of the diene moiety, the monomer [RuClH(diene)(amine)₂]. The crystal structure of the compound [RuClH(cod)(pip)₂] has been determined from three dimensional X-ray data.The complex crystallizes in space group Pmcn of the orthorhombic system, a 16.808(4), b 11.520(2), c 9.744(2) Å D_m 1.44 D_c 1.46 g cm^?3; Z 4. The structure was solved by standard heavy atom methods and has been refined by least squares to a conventional R factor of 0.039 based on 3280 refections. The complex has a crystallographically C_s imposed symmetry. The coordination geometry around the ruthenium atom is octahedrally distorted with cis amine ligands, the chloro and the hydrido ligands being trans to each other and the cyclooctadiene moiety bound through the two double bonds. The CC distances of the olefinic bonds are longer (1.394(4) Å) than was to be expected according to the Dewar—Chatt—Duncanson model. Principal bond lengths are: RuH 1.57(4); RuCl 2.555(1) (demonstrating a high structural trans influence of the hydrido ligand); RuN, 2.240(2) Å. An order of increasing structural trans influence for RuCl distances is proposed. In the IR spectrum ν(RuH) was observed at 2040 cm^?1. Decomposition of the complexes in chlorinated solvents prevented NMR studies.     

Structure and redox behavior of Ru(II)-diene complexes

A series of Ru(acac)₂(η⁴-diene) complexes containing cis- and trans-diene coordination have been investigated by cyclic voltammetry to correlate structural bonding and conformation patterns of diene ligands with redox behaviors. The solid-state structure of Ru(acac)₂(2,3-dimethyl-1,3-butadiene) has been determined by single crystal X-ray diffraction methods. Ru(acac)₂(2,3-dimethyl-1,3-butadiene) crystallizes in the monoclinic space group C2/c with a = 12.368(2) Å, b = 17.0600(2) Å, c = 16.0110(2) Å, β = 98.4405(10)° and V = 3341.38(10) ų for Z = 8. A structural comparison between several Ru-trans-η⁴-diene complexes and Ru-η⁴-1,3-cyclohexadiene revealed no difference in the Ru-C(diene) bond distances. However, through cyclic voltammetry experiments these species demonstrated different redox behavior, as function of the coordinated diene ligand.     

Carbon-Carbon Bond Formation

The intramolecular exchange pathway in the complexes Fe(diene)L₃ (where L = P(OMe)3 and diene = butadiene, isoprene, and 2,3-dimethylbutadiene) has been delineated by analysis of their temperature dependent ³¹P{¹H} NMR spectra. The basic permutation which is required to produce simulated spectra in agreement with experiment can only be reconciled with a physical mechanism involving cyclical exchange of the three phosporus ligands. This mechanism is probably best described as a diene rotation.     

Cobalt-catalysed asymmetric hydrovinylation of 1,3-dienes

In the presence of bidentate 1,n-bis-diphenylphosphinoalkane-CoCl₂ complexes {Cl₂Co[P ∼ P]} and Me₃Al or methylaluminoxane, acyclic (E)-1,3-dienes react with ethylene (1 atmosphere) to give excellent yields of hydrovinylation products. The regioselectivity (1,4- or 1,2-addition) and the alkene configuration (E- or Z-) of the resulting product depend on the nature of the ligand and temperature at which the reaction is carried out. Cobalt(ii)-complexes of 1,1-diphenylphosphinomethane and similar ligands with narrow bite angles give mostly 1,2-addition, retaining the E-geometry of the original diene. Complexes of most other ligands at low temperature (–40 °C) give almost exclusively a single branched product, (Z)-3-alkylhexa-1,4-diene, which arises from a 1,4-hydrovinylation reaction. A minor product is the linear adduct, a 6-alkyl-hexa-1,4-diene, also arising from a 1,4-addition of ethylene. As the temperature is increased, a higher proportion of the major branched-1,4-adduct appears as the (E)-isomer. The unexpectedly high selectivity seen in the Co-catalysed reaction as compared to the corresponding Ni-catalysed reaction can be rationalized by invoking the intermediacy of an η⁴-[(diene)[P ∼ P]CoH]⁺-complex and its subsequent reactions. The enhanced reactivity of terminal E-1,3-dienes over the corresponding Z-dienes can also be explained on the basis of the ease of formation of this η⁴-complex in the former case. The lack of reactivity of the X₂Co(dppb) (X = Cl, Br) complexes in the presence of Zn/ZnI₂ makes the Me₃Al-mediated reaction different from the previously reported hydroalkenylation of dienes. Electron-rich phospholanes, bis-oxazolines and N-heterocyclic carbenes appear to be poor ligands for the Co(ii)-catalysed hydrovinylation of 1,3-dienes. An extensive survey of chiral ligands reveals that complexes of DIOP, BDPP and Josiphos ligands are quite effective for these reactions even at –45 °C and enantioselectivities in the range of 90–99% ee can be realized for a variety of 1,3-dienes. Cobalt(ii)-complex of an electron-deficient Josiphos ligand is especially active, requiring only <1 mol% catalyst to effect the reactions.     

Combined effect of pH level and surface treatment of Sm2O3, SmBO3 and ATO particles on cure,mechanical and electric properties of EPDM composites

The aim of this study is to investigate the effect of pH level and surface treatment of samarium oxide (Sm₂O₃), samarium borate (SmBO₃) and Sb-doped SnO₂ (ATO) particles on properties of peroxide-cured ethylene–propylene–diene rubber (EPDM) composites. The bis-(-3-(triethoxysilyl)propyl)tetra-sulfide (KH845-4) treated particles were added to EPDM at various filler contents. The pH values of particles, and cure, mechanical and electric properties of the EPDM composites were evaluated. It was found that alkaline SmBO₃ particles would accelerate cure by producing more radicals from dicumyl peroxide (DCP), but acidic ATO particles would retard vulcanization because of making DCP generate less radicals, and neutral Sm₂O₃ particles did not affect the cure process. Moreover, sulfuric linkages from KH845-4 on the filler surface would provide sulfuric radicals to form S–C linkages. Therefore, composites with SmBO₃ exhibited excellent mechanical properties. Additionally, polar fillers could reduce electrical properties of composites due to increased composite polarity.     

Stereospecific synthesis of dienone iron tricarbonyl complexes by friedelcrafts acylation

Acylation of diene Fe(CO)₃ complexes using the Perrier complexes RCOCl/AlCl₃ in methylene chloride at 0°C gives dienone complexes in high yield. Substitution occurs only at unsubstituted terminal carbons of the diene unit. Quenching the reaction mixtures in cold aqueous ammonia gives cis dienone complexes only. Trans dienone complexes are prepared by subsequent isomerization in methanolic sodium methoxide. Formylation of diene Fe(CO)₃ complexes proceeds in modest yield using dichloromethylmethyleter/AlCl₃ in methylene chloride to give trans-dienal complexes. Reduction of the dienone and dienal complexes as well as those of dienols and dienoic esters with 4 : 1 AlCl₃/LiAlH₄ results in complete removal of the oxygen function to give trans-diene complexes in good yield.     

Reactions of dodecacarbonyltriosmium with dienic ligands

Dodecacabonyltriosmium reacts with diene ligands (D) such as 2,4-trans, trans- and 2,4-cis, trans-hexadiene and 1,6- and 1,5-heptadiene to give H₂Os₃D(CO)₉, H₄Os₄(CO)₁₂ and two isomers of molecular formula HOs₃-(D  H)(CO)₉ in addition to Os₂(D  2H)(CO)₆ and OsD(CO)₃. The structures of the trimetal complexes show that dehydrogenation, isomerization and rearrangement of the organic substrates occur before the coordination to the metal cluster. 2,3-Dimethyl-1,3-butadiene and dodecacabonyltriosmium give only the well known bi- and mono-metal complexes. The results are compared with those obtained in the reactions of the some organic molecules with dodecacabonyltriruthenium.     

Asymmetric Catalysis in Liquid Confinement: Probing the Performance of Novel Chiral Rhodium–Diene Complexes in Microemulsions and Conventional Solvents

The role of liquid confinement on the asymmetric Rh catalysis was studied using the 1,2-addition of phenylboroxine ( 2 ) to N-tosylimine 1 in the presence of [RhCl(C₂H₄)₂]₂ and chiral diene ligands as benchmark reaction. To get access to Rh complexes of different polarity, enantiomerically pure C₂-symmetric p-substituted 3,6-diphenylbicyclo[3.3.0]octadienes 4 and diastereomerically enriched unsymmetric norbornadienes 5 and 6 carrying either the Evans or the SuperQuat auxiliary were synthesized. A microemulsion containing the equal amounts of H₂O/KOH and toluene/reactants was formulated using the hydrophilic sugar surfactant n-octyl β-d -glucopyranoside (C₈G₁) to mediate the miscibility between the nonpolar reactants and KOH, needed to activate the Rh–diene complex. Prominent features of this organized reaction medium are its temperature insensitivity as well as the presence of water and toluene-rich compartments with a domain size of 55 Å confirmed by small-angle X-ray scattering (SAXS). Although bicyclooctadiene ligands 4 a , b , e performed equally well under homogeneous and microemulsion conditions, ligands 4 c , d gave a different chemoselectivity. For norbornadienes 5 , 6 , however, microemulsions markedly improved conversion and enantioselectivity as well as reaction rate, as was confirmed by kinetic studies using ligand 5 b .     

C2-Symmetric bicyclo[3.3.1]nona-2,6-diene and bicyclo[3.3.2]deca-2,6-diene: new chiral diene ligands based on the 1,5-cyclooctadiene framework

As a new type of C₂-symmetric chiral diene ligands, which coordinate to a metal by their 1,5-cyclooctadiene framework, we prepared 2,6-disubstituted bicyclo[3.3.1]nona-2,6-diene (bnd*) and bicyclo[3.3.2]deca-2,6-diene (bdd*), and examined their catalytic activity and enantioselectivity for rhodium-catalyzed asymmetric 1,4-addition to α,β-unsaturated ketones and 1,2-addition to N-sulfonylimines. High enantioselectivity of the Ph-bnd* ligand was observed in the addition of phenylboroxine to N-tosylimine and N-4-nitrobenzenesulfonylimine of 4-chlorobenzaldehyde to give phenyl(4-chlorophenyl)methylamines in high enantiomeric excess (98–99% ee).     

Diencarbonsäuren aus 1,3-dienen und CO2 durch C-C-verknüpfung an nickel(0)

(Lig)Ni⁰ systems react with 1,3-dienes in the presence of CO₂ to give nickela carboxylates. The influence of ligands and temperature on the regioselectivity of the CC bond formation is elucidated. In some cases the nickela carboxylates undergo reductive elimination under the influence of maleic anhydride, and the coupled diene/CO₂ moiety rearranges to give the diene carboxylic acid. A possible reaction sequence is discussed.     

Challenges in modelling and optimisation of stability constants in the study of metal complexes with monoprotonated ligands: Part I. A glass electrode potentiometric and polarographic study of a Cu-TAPSO-OH system

The behaviour of solutions containing 3-(N-tris[hydroxymethyl]methylamine)-2-hydroxypropanesulfonic acid (TAPSO) and copper(II) was studied by two analytical techniques, direct current polarography (DCP) and glass electrode potentiometry (GEP), at fixed total TAPSO to total copper(II) concentration ratios and various pH values, at 25 °C and ionic strength 0.1 M KNO₃. DCP and GEP, when used independently, were not able to provide a final metal-ligand model. Combined interpretation of data from DCP and GEP indicated the formation of six main species, CuL⁺, CuL(OH), CuL(OH)₂⁻, CuL₂, CuL₂(OH)⁻ and CuL₂(OH)₂²⁻ for which stability constants (as log β) were found to be 4.41, 11.43, 17.55, 8.08, 14.3 and 20.3, respectively. Five of these complexes, CuL(OH), CuL(OH)₂⁻, CuL₂, CuL₂(OH)⁻ and CuL₂ (OH)₂²⁻ are reported for the first time.     

Simple fast preparation of neutral palladium(II) complexes with SnCl− 3 and Cl− ligands

A new method for preparing neutral trichlorostannate complexes of Pd^II, based on the interaction between solid [PdCl₂(MeCN)₂] and SnCl₂ suspension and a solution of an appropriate ligand in CH₂Cl₂, has been developed. The analogous method can be used to prepare complexes without tin, as well as compounds containing mixed anionic ligands. A number of complexes (including several new compounds) with amines, phosphines and diene ligands have been obtained by these methods. The procedures are simple and fast – the total preparation time (without recrystallisation) is ca. 30 min.     

Influences of molecular weight and crystalline structure on fracture behavior of controlled-rheology-polypropylene prepared by reactive extrusion

The molecular weight of ethylene-block-co-polypropylene (co-PP) was adjusted by reactive extrusion with the incorporation of dicumyl peroxide (DCP), and the effect of molecular weight on the crystallization behavior, crystal morphology, and fracture behavior was investigated. It was found that, with increasing DCP content, the molecular weight (MW) decreased and the polydispersity (M_w/M_n) slightly decreased. After modification, the number of spherulites with obscure boundaries increased, and the size of the spherulites was more even due to increasing amount of grafting and micro-cross-linking structures, generated in co-PP degradation, which were acting as nucleating agents. Evaluated by essential work of fracture method, the specific essential work of fracture, w_e, was found to be strongly dependent on the molecular weight, especially, on the number average molecular weight (M_n) linearly, while the specific non-essential work of fracture, βw_p, was enhanced with decreasing z-average molecular weight (M_z), probably owing to the reduction of ultra-high molecular weight component in degraded co-PP.     

Spectroscopic Studies on the Interaction of 2,4-Dichlorophenol with Bovine Serum Albumin

The interaction between 2,4-dichlorophenol (DCP) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy combined with UV-vis absorption and circular dichroism (CD) spectroscopy under simulative physiological conditions. The experiment results show that the fluorescence intensity of BSA is dramatically decreased owing to the formation of a DCP–BSA complex. The corresponding effective quenching constants (K _a) between DCP and BSA at four different temperatures (292, 298, 304 and 310 K) were determined to be 10.08×10⁴, 9.082×10⁴, 8.177×10⁴, and 7.260×10⁴ L?mol^?1, respectively. The thermodynamics parameters enthalpy change (ΔH) and entropy change (ΔS) were calculated to be ?13.64 kJ?mol^?1 and 49.08 J?mol^?1?K^?1, which suggested that hydrophobic interaction was the predominant intermolecular force. Site marker competitive experiments indicated that the binding of DCP to BSA primarily takes place in subdomain IIA. The binding distance (r) between DCP and the tryptophan residue of BSA ias 4.09 nm according to Förster’s theory of non-radioactive energy transfer. The conformational investigation demonstrated that the presence of DCP decreased the α-helical content of BSA and induced a slight unfolding of the polypeptides of protein, which confirmed the occurrence some micro environmental and conformational changes of BSA molecules.     

Spectral and electrochemical investigation of 1,8-diaminonaphthalene upon encapsulation of p-sulfonatocalix[4]arene

The ligand salt, Me₆[14]diene·2HClO₄ (L·2HClO₄) was prepared by condensation of acetone and ethylene diamine in the presence of perchloric acid. On reduction of this diene ligand salt, L·2HClO₄ with sodium borohydride, the two isomeric ligands, ‘tet-a’ and ‘tet-b’ were produced. The ligands, on reaction with ZnX₂ (X=Cl, ClO₄, NO₃ or CH₃COO) and ZnSO₄ produced the corresponding complexes. These complexes have been characterized on the basis of elemental analyses; IR, UV–Vis and ¹H-NMR spectroscopies; magnetic and conductance data. Based on these data, all of the complexes of the diene ligand L, as well as the perchlorate complexes of all of the ligands attained a square-pyramidal arrangement, whereas the complexes of ‘tet-a’ and ‘tet-b’, with X=NO₃, Cl or CH₃COO and with ZnSO₄ salt, were octahedral. Moreover, all complexes were monometallic except the nitrato complex, [(ZnL)₂(µ-NO₃)](ClO₄)₃ which is bimetallic. The structure of [(ZnL)₂(µ-NO₃)](ClO₄)₃ has been confirmed by X-ray crystallography. In this complex the zinc centres lie within a N₄O donor set, with the four nitrogen donors from L and one of the oxygen atom stemming from the bridging NO₃. The complexes show different electrolytic behavior in different solvents. The antibacterial activities of the ligands and complexes towards different phytopathogenic bacteria have been investigated.     

The synthesis of diene and of vinyl copolymers containing predetermined quantities of polynuclear hydrocarbons or heterocyclic adducts

Copolymers have been prepared by reacting a suitable vinyl or diene monomer (M) with alkali metal in tetrahydrofuran in the presence of a polynuclear hydrocarbon (A), followed by linking the dianions thus generated with a difunctional species (RX₂). With a diene as monomer, anthracene as polynuclear hydrocarbon and an alkyl dihalide as linking agent, the copolymer has the average repeat unit —[A—M_n—A—R]— where n represents the molar ratio of diene to anthracene present initially. Other linking agents include epichlorhydrin, diepoxyoctane and dimethyldichlorosilane. Acenaphthylene has been shown to behave in a manner analogous to anthracene. When the vinyl monomers styrene or α-methylstyrene are used, the copolymers are more random, for reasons which are discussed, but again the reagents are quantitatively converted into polymer. Similar reactions have been carried out with heterocyclic molecules such as acridine, quinoline or pyridine replacing the polynuclear hydrocarbon, and poly (tertiary amides) have been prepared by titration with diacylchlorides.Si sono preparati dei copolimeri facendo reagire un adatto monomero di vinile oppure diene (M) son un metallo alcalino, in tetraidrofurano, in presenza di un idrocarburo polinucleare (A), e facendo seguire a ciò il legamento dei dianioni così generati con una specie bifunzionale (RX₂). Con un diene come monomero. un'antracene come idrocarburo polinucleare e un dialide alchilico come agente legante, il copolimero presenta il gruppo ripetitivo medio —(A—M_n—A—R)— in cui n rappresenta il rapporto molare diene antracene presenti inizialmente. Altri agenti leganti sono: epiclorindrin, diepossiottano e dimetilclorosdilano. Si mostra che l'acenaftilene si comporta in maniera analoga all'antracene. Quando si impiegano i monomeri di vinile stirene oppure α-metilstirene, i copolimeri sono più a caso, per le ragioni discusse, però, anche qui, i reagenti sono trasformati quantitativamente in polimero. Si sono eseguite reazioni simili con molecole eterocicliche, del tipo dell'acridina, quinolina oppure piridina, sostituendo l'idrocarburo polinucleare, e si sono preparate delle poli(amide terziarie) mediante titrazione con diacilcloruri.     

Modelling of Pb-(TAPS)x-(OH)y system and refinement of stability constants in the region of lead hydrolysis and lead hydroxide precipitation

The influence of [(2-hydroxy-1,1-bis(hydroxymethyl)ethyl)amino]-1-propanesulfonic acid (TAPS) on solutions containing lead(II) was studied by direct current polarography (DCP) and glass electrode potentiometry (GEP). The readings were taken at fixed total TAPS to total lead(II) concentration ratios and various pH values, at 25.0 ± 0.1 °C and ionic strength 0.1 M KNO₃.Due to the basic pK_a of the ligand, which occurs in the pH range where large amount of lead polynuclear species are formed, and the occurrence of ligand adsorption, that disabled the use of high concentrations of TAPS on DCP experiments, GEP and DCP experimental conditions were put to the limit in order to provide the correct Pb-TAPS-OH model and reliable stability constants.The proposed final model is: PbL, PbL₂, PbL₂(OH) and PbL₂(OH)₂ with overall stability constants values, as log β, 3.27 ± 0.06, 6.5 ± 0.1, 12.7 ± 0.1 and 17.27 ± 0.06, respectively.A comparative analysis of the strength of complexation of TAPS and a structural related buffer, 2-hydroxy-3-[tris(hydroxymethyl)methylamino]-1-propanesulfonic acid (TAPSO), with lead is also discussed.