Copper-free monomeric and dendritic palladium catalysts for the Sonogashira reaction: substituent effects, synthetic applications, and the recovery and re-use of the catalysts

A series of bis(tert-butylphosphine)- and bis(cyclohexylphosphine)-functionalized Pd(II) monomers and polyamino (DAB) dendritic catalysts were synthesized and investigated for Sonogashira carbon-carbon coupling reactions in a copper-free procedure. The influence of phosphine substituents (tBu versus Cy) on the reaction kinetics was investigated by a GPC technique to monitor the reactions. The dendritic catalysts containing the cyclohexylphosphine ligands could be recovered and reused without loss of efficiency until the fifth cycle. The dendritic Pd(II) catalysts show a negative dendritic effect, that is, the catalyst efficiency decreases as the dendrimer generation increases.     

Ionomers for proton exchange membrane fuel cells by sulfonation of novel dendritic multiblock copoly(ether‐sulfone)s

The synthesis and properties of the first examples of dendritic multiblock co PES s, bearing sulfonated dendritic clusters, that form strong membranes are described. End‐capped dendritic multiblock co PES s with various average block lengths (n = 50–80) were synthesized by two‐step reactions. The synthesis of dendritic blocks consisting of difunctional dendritic block and monofunctional dendritic end‐group was accomplished by an aromatic nucleophilic substitution reaction of hexakis(4‐(4‐fluorophenylsulfonyl)phenyl)benzene with varying amounts of 1‐(4‐hydroxyphenyl)‐2,3,4,5,6‐pentaphenylbenzene, which provides a number of pendant phenyl rings as postsulfonation sites. Polycondensation of a controlled molar ratio between 4,4′‐dihydroxybenzophenone and bis(4‐fluorophenyl)sulfone monomers was carried out in the presence of the difunctional and monofunctional dendritic blocks in sulfolane at 215 °C for 3.5 h. Essentially six sulfonic acid groups were introduced into each hexaphenylbenzene moiety on the dendritic blocks by reaction with a large excess of chlorosulfonic acid, followed by hydrolysis with KOH aqueous solution. The introduction of longer average blocks (n = 60–80) into the dendritic PES s improved the mechanical properties of the resulting sulfonated dendritic PES membranes. At a level of IEC (0.92–1.26 meq/g) similar to Nafion (0.91 meq/g), PES membranes showed proton conductivities (58–67 mS/cm) comparable with that of Nafion (99 mS/cm). © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5461–5473, 2009     

两亲性树状聚合物*

树状聚合物及其功能化是近年来高分子科学界的研究热点之一。本文综述了不同类型的树状聚合物,分别有聚酯、聚丙三醇、聚乙烯亚胺等超支化聚合物,聚酰胺-胺、聚丙烯亚胺等树枝状聚合物。通过对树状聚合物末端大量官能团的亲水（亲油）改性可以制备两亲性树状聚合物,改性方法主要有酰胺化反应、酯化反应、麦克尔加成反应等。与通过缩聚反应所得到的上述树状聚合物不同,近年来配位聚合领域出现的通过“链行走”机理形成的树状聚乙烯,引起了高度关注,这方面着重介绍了乙烯与极性单体直接共聚合或者采用链行走与原子转移自由基聚合联用制备两亲性树状乙烯聚合物。最后对两亲性树状聚合物领域的发展前景进行了展望。     

Synthesis of novel dendritic 2,2'-bipyridine ligands and their application to Lewis acid-catalyzed diels-alder and three-component condensation reactions

A series of dendritic ligands with a 2,2'-bipyridine core was synthesized through the coupling of 4,4'-dihydroxy-2,2'-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf)2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.     

新型树枝状PNP铬催化剂的合成及催化性能

以1.0代聚酰胺-胺(PAMAM)为配体骨架,氯代二苯基膦为原料,通过取代反应合成了1种含有较大空间位阻的新型树枝状PNP配体,再以Cr Cl3(THF)3为络合试剂,通过络合反应合成树枝状PNP铬催化剂.采用傅里叶变换红外光谱(FTIR)、紫外-可见分光光度计(UV-Vis)、核磁共振波谱(NMR)、电喷雾电离质谱(ESI-MS)和元素分析等手段证实合成的新型树枝状PNP配体及其铬催化剂的结构与理论设计的结构一致.以甲基铝氧烷(MAO)为助催化剂,对乙烯齐聚反应进行了研究,考察了溶剂种类、反应温度、反应压力及Al/Cr摩尔比对该催化剂活性和选择性的影响.结果表明,以甲苯为溶剂,MAO为助催化剂,当反应温度为25℃,反应压力为0.9 MPa,Al/Cr摩尔比为500时,该催化剂的活性高达2.15×105g/(mol Cr·h),催化剂对乙烯三聚、四聚反应的选择性共达到36.76%.     

多重环境刺激响应性聚苄醚型树状分子凝胶制备及性能研究

环境刺激响应性超分子凝胶材料在传感器、光开关、人工触角、药物缓释等领域表现出潜在的应用前景。本文设计合成了一种新型的核心含偶氮苯官能团聚苄醚型树枝状分子凝胶因子CA-G2。成胶性能测试表明,该凝胶因子在23种有机溶剂和混合溶剂中均可以形成稳定的淡黄色凝胶,其中在苯中表现出最优的成凝胶性能,临界成胶浓度(CGC)可达2.0mg/mL(0.23(wt)%),相当于一个树枝状分子可以固定1.5×10⁴个溶剂分子,表明该凝胶因子具有非常优异的成凝胶性能。并且,该类凝胶材料能够同时对热、超声和触变等外界环境刺激产生响应,并伴随着宏观上凝胶-溶胶的相互转变。此外,该类凝胶对罗丹明B染料分子具有优异的吸附性能,吸附效率高达96.7%。     

Self-assembly of two-component peptidic dendrimers: dendritic effects on gel-phase materials

The self-assembly of diaminododecane solubilised by different dendritic peptides, possessing increasing levels of dendritic branching, was investigated. The dendritic peptides were based on l-lysine building blocks and were of first, second and third generation, containing one, three and seven amino acid repeat units respectively. By applying these structures as potential gelator units, the dendritic effect on gelation was investigated. The degree of structuring was modulated, with the dendritic peptide controlling the aggregate morphology and the ability of the self-assembled state to manifest itself macroscopically as gelation. First generation gelator units (G1) did not induce macroscopic gelation with diaminododecane under any conditions, whilst those self-assemblies based on second (G2) and third (G3) generation branches did form gel-phase materials. Furthermore, gel-phase materials based on G2 exhibited optimum gelation behaviour compared to those based on G3(in terms of the thermal strength of the materials). Circular dichroism showed that the dendritic effect, programmed in at the molecular level, is directly related to the degree of chiral organisation within the self-assembled state. The dendritic generation of the peptide controls the pattern of amide-amide hydrogen bonding in terms of binding strength and alignment as determined using NMR methods. The mode of self-assembly can be qualitatively rationalised in terms of an attractive enthalpic interaction (i.e., amide-amide hydrogen bonding), a repulsive interaction (i.e., steric interactions between dendritic peptides) and an entropic term related to the hierarchical organisation of the gelator building blocks. It is argued that the balance between these factors determines the nature of the dendritic effect.     

Synthesis of a PEG-PNIPAm thermosensitive dendritic copolymer and investigation of its self-association

A Novel thermosensitive dendritic copolymer based on polyethylene glycol(PEG) and poly(Nisopropylacrylamide)(PNIPAm) with a cloud point(CP) around 36 ?C was successfully synthesized by preparation of a dendritic polyol and followed by atom transfer radical polymerization(ATRP) of N-isopropylacrylamide. The dendritic copolymer was characterized using gel-permeation chromatography(GPC), FTIR and 1H-NMR spectroscopy. The selfassociation behavior of the copolymer in aqueous medium was investigated by dynamic light scattering(DLS) and transmission electron microscopy(TEM). These investigations confirmed that the dendritic copolymer showed different association behaviors at various temperatures.     

A recyclable nanosize aminoarenethiolato copper(I) catalyst for C-C coupling reactions

An aminoarenethiolato copper(I) catalyst was attached to a carbosilane dendritic wedge, which had been prepared via a novel convergent synthetic method. Compared with the unsupported complex, this novel dendritic copper(I) catalyst is more robust towards hydrolysis and oxidation and has increased solubility in common organic solvents. The catalytic activity of the dendritic copper catalyst was tested in the 1,4-addition of Et₂Zn to 2-cyclohexenone. In both polar (Et₂O) and apolar (hexane) solvents excellent activity was observed. The fact that the catalytic copper site remains attached to the nanosize dendritic aminoarenethiolate ligand allows separation of this catalyst by means of nanofiltration.     

Synthesis and structural characterization of dendritic‐linear PMA‐APM‐r‐PS copolymers for a self‐assembled microporous matrix

A set of dendritic‐linear copolymers, poly(maleic anhydride‐grafted‐3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate))‐random‐polystyrene (PMA‐APM‐r‐PS), was successfully prepared by copolymerization of the novel dendritic macromonomer, 4‐(4‐(bis(3‐(4‐(bis(3‐methoxy‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐2‐methyl‐3‐oxopropyl)amino)phenylamino)‐4‐oxobut‐2‐enoic acid (MA‐APM), with styrene monomer. The dendritic MA‐APM macromonomer dendron 3,3′‐dimethyl‐(4‐aminophenylazanediyl)bis(2‐methylpropanoate) (APM) was then grafted by using the divergent growth method. FTIR, ¹H NMR, and ¹³C NMR spectra were used to identify the structures of the dendron, the dendritic macromonomer, and the dendritic‐linear PMA‐APM‐r‐PS copolymer. Furthermore, microporous dendritic‐linear PMA‐APM‐r‐PS copolymer films were prepared by using solvent‐induced phase separation at room temperature. We investigated the phase separation behavior and morphological structures of the dendritic‐linear copolymer film as functions of dendritic GMA‐HPAM segments in the content using SEM. Self‐assembly of the dendritic‐linear PMA‐APM‐r‐PS copolymer in the MG2‐X system, which represented the second generation dendron containing X wt % of the dendritic MA‐APM segment, resulted in submicron phase segregation. Interestingly, the submicron phase segregation morphology of the MG2–43 sample presented a uniform size distribution of ordered‐array structures. The results of this study demonstrate that controlling the appropriate macromonomer content via the grafting of a three‐dimensional structure results in a self‐assembly process that is capable of providing an ordered‐array microporous morphology in a polymer film. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3290–3301, 2010     

Dendrimer-based hydrogen-bonded liquid crystalline complexes: Synthesis and characterization

Three generations of dendritic polyester macromolecules based on 5-hydroxyisophthalic acid were synthesized by the divergent growth approach. The characterization of dendritic fragments was performed using a combination of ¹H NMR, ¹³C NMR spectroscopy and elemental analysis. The dendritic hydrogen-bonded supramolecular liquid crystalline complexes were prepared from different generation of dendritic acids and stilbazole derivative containing pyridyl units. The polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) were used for investigation of the liquid crystalline properties of the hydrogen-bonded dendritic supramolecular complexes.     

Site-isolation effects in a dendritic nickel catalyst for the oligomerization of ethylene

Dendrimers, specifically suited to construct site-isolated groups due to their well-defined hyperbranched structure, have been used as a ligand design element for the construction of nickel catalysts for ethylene oligomerization. The dendritic P,O ligand indeed suppresses the formation of inactive bis(P,O)Ni complexes in toluene, as is evident from NMR studies, and, as a consequence, outperforms the parent ligand in catalysis in this solvent. The dendritic effect observed in methanol is more subtle because both the dendritic ligand 1 and the parent 2 form bis(P,O)nickel complexes in solution according to NMR spectroscopy. Unlike the parent complex 8, the dendritic bis(P,O)Ni complex 7 derived from dendrimer ligand 1 is able to dissociate to a mono-ligated species under catalytic conditions, that is, 40 bar ethylene and 80 degrees C, which can enter the catalytic cycle. Indeed, dendritic ligand 1 gives much more active nickel catalysts for the oligomerization in methanol than does 2.     

Nonconjugated dendritic iridium(III) complexes with tunable pyridine-based ligands: synthesis, photophysical, electrochemical, and electroluminescent properties

A simple synthetic route was developed for nonconjugated dendritic iridium(III) complex based on tunable pyridine-based ligands. From an intermediate 2-bromopyridyl-4-methanol, three series of polybenzyloxy dendritic pyridine-based ligands with 2-phenyl, 2-benzothienyl, and 2,4-difluorophenyl subsitituents were easily synthesized via two-step reactions (Suzuki reaction and etherifying reaction). Using these pyridine derivatives as the CwedgeN ligands, these dendritic iridium(III) complexes exhibiting tunable photoluminescence from blue to red were obtained. The photoluminescence quantum yields of these dendritic complexes in neat films increased with the increasing generation number of dendritic CwedgeN ligands. Importantly, these iridium complexes were used as dopants for successfully fabricating polymer-based electrophosphorescent light-emitting diodes (PLEDs) with the highest external quantum efficiency of 12.8%.     

基于树形链转移剂的可逆加成断裂链转移聚合

可逆加成断裂链转移(RAFT)聚合是最近十多年来发展起来的一种活性/可控技术,链转移剂(CTA)为该技术的核心.本文介绍了采用R路径合成法、Z路径合成法合成R核与Z核树形链转移剂以及它们调控不同单体的RAFT聚合,合成树形-线性二嵌段共聚物、树形-线性-树形三嵌段共聚物和树形-星形聚合物等树枝状聚合物的研究进展.     

Concomitant synthesis of polyaniline and highly branched gold nanoparticles in the presence of DNA

The reduction of chloroauric acid using aniline adsorbed on DNA produces highly branched dendritic gold nanoparticles with concomitant formation of polyaniline (PANI) in contrast to the formation of spherical Au nanoparticles in the absence of DNA. The conformation of DNA remains intact in the process as evident from circular dichroism (CD) spectra. The UV-Vis spectrum exhibits a broad absorption peak at 520-900 nm, for a combined effect of the gold surface plasmon and π band to localized polaron band transition of DNA-doped PANI. Both the dendritic Au-PANI-DNA and the spherical Au-PANI systems emit two peaks for excitation with radiation of 300 nm and the intensity ratio of the emission and FRET peak is higher in the dendritic Au-PANI than that in the spherical Au-PANI system. The dc-conductivity values of spherical Au-PANI and dendritic Au-PANI-DNA systems are 1.2×10(-10) and 1.7×10(-8) S/cm at 30°C, respectively.     

Electrochemical synthesis of dendritic zinc films composed of systematically varying motif crystals

Polycrystalline zinc films with new dendritic frameworks were electrodeposited from nonaqueous formamide media containing 0.01-0.3 M Zn(ClO4)2.6H2O as the Zn2+ source and 0.1 M LiClO4.3H2O as the supporting electrolyte. Formamide media offer a wider range of deposition temperatures and deposition potentials than aqueous solutions, which provides a higher degree of freedom in creating new polycrystalline architectures. The growth patterns of zinc crystals could be precisely controlled (e.g., faceted growth and dendritic growth) by changing the interplay between the growth rate and the mass transport rate. The effect of deposition potential, temperature, and Zn2+ concentration on the onset potential of dendritic growth and the detailed dendritic features were studied systematically. The zinc dendrites obtained in this study were composed of submicron-sized crystals of a uniform shape (motif crystals) that grow repetitively fused together to form three-dimensionally dispersed dendritic backbones. This unique organization achieves a remarkable physical and electrical continuity between crystals while generating high surface areas, which is difficult to accomplish simultaneously in polycrystalline films. The shape of motif crystals can be finely tuned from hexagons to fern-shaped leaves by the deposition potential applied, which in turn alters the overall degree of branching of dendritic backbones. Cyclic voltammetry of the resulting zinc electrodes with various growth patterns was carried out and discussed in conjunction with the films' morphological variation.     

Temperature dependent dendritic domain shapes in Langmuir monolayers of tetradecanoyl N-ethanolamide at the air-water interface

The effect of temperature on the surface phase behavior of tetradecanoyl N-ethanolamide (NHEA-14) in Langmuir monolayers at the air-water interface has been investigated by film balance and Brewster angle microscopy (BAM). It has been observed that dendritic domains are formed in the coexistence region between liquid-expanded (LE) and liquid-condensed (LC) phases at different temperatures. At 10 and 15°C, the domains are four-armed dendrites having wide arms which have a tendency to be fractal while growing in size. At 20°C, five-armed dendritic domains are formed. At a temperature higher than 20°C, the domains are mainly six-armed dendrites having very narrow and sharp arms. The formation of dendritic domains should be due to the presence of interfacial hydrogen bonding among the head groups of the amphiphile. Increased dehydration of the head groups with an increase in the temperature should be responsible for the temperature dependency of the dendritic domain shapes in the monolayers of NHEA-14.     

NMR and ESR investigations of the interaction between a carboxylic acid and an amine at the focal point of L-lysine based dendritic branches

This paper reports the characterisation of supramolecular complexes formed between the carboxylic acid group at the focal point of host dendritic branches based on l-lysine building blocks and an amine group on an appropriate guest molecule. (1)H NMR titration investigations indicate that the interaction is relatively weak. Interestingly the dendritic generation appears to have no effect on the thermodynamics of benzylamine recognition - in contrast to previous studies in which charged guests have been bound to dendritic hosts. Control experiments using dendritic branches in which the carboxylic acid is protected as a methyl ester indicate that there is only a small amount of non-specific binding of the amine functionalised guest molecule within the dendritic framework itself. ESR investigations clearly show the binding between the dendritic branch and amine functionalised TEMPO radicals. Most interestingly, rotational correlation times can be determined from the ESR studies and they indicate that the mobility of the TEMPO radical is diminished on binding to the dendritic branch. Notably this effect is generation dependent, with larger dendritic branches having a more dramatic effect on the tumbling of the radical. Control experiments clearly prove the importance of the acid-base interaction and also demonstrate that effective binding only occurs in non-polar solvents. These results therefore illustrate that using host-guest chemistry at the focal point of a dendritic structure is an effective way to control and modify the solution phase properties and mobility of active species such as radicals.     

Experimental and quantum chemical studies of cooperative enhancement of three-photon absorption, optical limiting, and stabilization behaviors in multibranched and dendritic structures

This paper reports on cooperative enhancement of three-photon absorption (3PA) cross section, studied by nonlinear transmission method, in going from a one-branched to a three-branched and then to a dendritic structure. Experimentally, we observe a 72% enhanced 3PA cross-section value in going from the one-branched chromophore to the dendritic chromophore, and a 49% enhanced 3PA cross-section value in going from the one-branched chromophore to the three-branched chromophore, when the 3PA cross-section values are normalized per structure unit. Quantum chemical calculation for the one- and three-branched structures, using the cubic response (CR) theory applied to a single determinant self-consistent field (SCF) reference state, also predicts such an enhancement. Two-dimensional pi-delocalization, resulting in extended charge-transfer network in the case of the multibranched structures, is the main cause of the cooperative enhancement. Owing to the increased 3PA cross-section value for the dendritic chromophore, improved optical limiting performance at an optical communication wavelength of 1310 nm was observed, compared with the one-branched (or three-branched) chromophore, using comparable structure-unit-based concentrations. Optical stabilization capability of the dendritic chromophore was also observed at this wavelength.     

新型树状结构手性联二萘酚衍生物的合成及催化性能研究

报道了树状结构的手性联二萘酚(BINOL)配体的合成及其在二乙基锌对醛的不对称加成反应中的应用.(R)-2,2′-二羟基-1,1′-联萘-3,3′-二羧酸与末端为氨基的Frechet聚芳醚型树状分子经缩合反应,以中等产率得到0～3代的树状分子配体,用¹HNMR,IR和MALDI-TOF质谱进行了结构表征.这些树状手性配体与Ti(OPrⁱ)₄在无水甲苯溶液中形成的配合物是二乙基锌对醛不对称加成反应的高效催化剂,树状分子载体的体积对催化剂的对映选择性没有明显的影响.以邻氯苯甲醛为底物时,反应的对映选择性随树状分子代数的增加而有所提高.