大位阻烯烃不对称环氧化合成手性环氧化合物

采用大位阻的有机锂试剂或格氏试剂与卤代烯烃偶联合成了7种大位阻取代烯烃. 以Oxone(KHSO₅)作为氧化剂, 分别在D-果糖衍生酮和(2S,5R)-2-异丙基-5-甲基环己酮为催化剂的催化下, 将合成的7种大位阻取代烯烃转变成了7个大位阻的手性环氧化合物. 其中以D-果糖衍生酮的对映选择性最好, 当双键碳上含有3个取代基时, 对映选择性最高, e.e.值为96.8%~99.5%. (2S, 5R)-2-异丙基-5-甲基环己酮的对映选择性较差, 无论是一取代的烯烃还是三取代的烯烃, 其e.e.值均介于25.6%~34.1%之间.     

Control of pi-stacking for highly emissive poly(p-phenylenevinylene)s: synthesis and photoluminescence of new tricyclodecane substituted bulky poly(p-phenylenevinylene)s and its copolymers

In the present work, we have demonstrated a facile approach to increase the luminescence of the poly (p-phenylenevinylene)s via controlling the molecular aggregates induced by pi-stacking. We have synthesized new bulky tricyclodecane (TCD) substituted PPVs: poly(2-methoxy-5-tricyclodecanemethyleneoxy-1,4-phenylenevinylene) (MTCD-PPV), poly(bis-2,5-tricyclodecanemethyleneoxy-1,4-phenylenevinylene) (BTCD-PPV), and a series of symmetrically substituted bulky PPV copolymers (P-1-P-7) covering the entire composition range from 0 to 100 mol %. The structures of the monomers and polymers were confirmed by 1H NMR and FTIR, and the molecular weights were determined by gel permeation chromatography. The composition analysis by NMR revealed that the bulky monomer was highly reactive and the incorporation of bulky units in MEH-PPV increased irrespective of the feed ratio. The polymers possess good solubility, high molecular weights, good thermal stability, and so forth. The molecular weights of the PPV copolymers were also significantly affected by the bulky substitution: the higher the incorporation of bulky units, the lower the molecular weight. The absorption and emission studies revealed that there was no influence on the MEH-PPV by TCD substitution in solution whereas in the solid state the photoluminescence intensity of PPV increased more than 10 times. The luminescence increase in PPV was observed throughout the entire bulk and was not confined to any particular domain in the polymer. The bulky PPV copolymers showed that both the luminescence intensity (in film) and quantum yields (in solution) increased with an increase in the extent of BTCD incorporation in the MEH-PPV and attained a maximum for 50% BTCD. The TCD unit has thus proved to be an efficient bulky susbstituent for PPV as it controls the pi-stack-induced molecular aggregates in the polymer chains by increasing the interchain distances. The new bulky PPV copolymers are highly soluble, thermally stable, and highly luminescent besides being economically cheap compared to the other materials reported so far for the bulkier approach in pi-conjugated materials.     

Self-organization-induced three-dimensional honeycomb pattern in structure-controlled bulky methacrylate polymers: Synthesis, morphology, and mechanism of pore formation

Here we report, for the first time, a novel molecular design for three-dimensional honeycomb structures through a self-organization of hydrogen-bonded bulky anchoring group in a methacrylic polymer backbone. The polymerizable monomer design includes a methacrylic double bond linked to various hydrophobic anchoring units such as ethane, n-decane, tricyclodecane (TCD), and adamantane via a hydrogen-bonded cycloaliphatic urethane linkage. The structures of the polymers were confirmed by nuclear magnetic resonance (NMR) and the molecular weights of the polymer were determined by gel permeation chromatography (GPC). The methacrylate polymers having tricyclodecane and adamantane bulky anchoring groups self-organized to produce three-dimensional honeycomb patterns in tetrahydrofuran-water solvent mixture at ambient conditions, whereas its linear analogues (ethane, n-decane) failed to produce any micropattern. The scanning electron microscopy (SEM) analysis of the above-prepared polymer films revealed that the structure of the polymer played a major role in the formation of the honeycomb patterns. The solution Fourier transform infrared (FTIR) measurements confirmed that the bulky tricyclodecane and adamantane polymers have strong hydrogen-bonding interaction compared to that of their linear analogues, which is the driving force for the micropatterns. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the bulky polymers revealed that the polymers exist as vesicles or micelles in the solution, which leads to the formation of the honeycomb pattern. The honeycomb pattern formation in the bulky polymer systems suggests that two cooperative factors such as hydrogen-bonding interaction and hydrophobicity of bulky anchoring units are necessary to induce three-dimensional honeycomb structures. To investigate the effect of molecular weights and its distribution on the self-organization process, both benzoyl peroxide (BPO) initiated free radical and atom transfer radical polymerization (ATRP) techniques were employed for the polymerization. Micropores formed irrespective of differences in molecular weight and polydispersity index (PDI); however, the pore size distribution was influenced by both molecular weights and PDI. Low molecular weight samples afforded polydisperse pores with the ATRP samples with more narrow PDI producing pores with large dimensions. The approach has also been investigated for polystyrene-bulky methacrylic copolymer, and the results revealed that uniform honeycomb patterns were produced for copolymers having more than 50 mol % incorporation of bulky units.     

Transformation of Type III to Type II Porous Liquids by Tuning Surface Rigidity of Rhodium(II)-Based Metal-Organic Polyhedra for CO2 Cycloaddition

Porous liquids (PLs), a summation of porous hosts and bulky solvents bestowing permanent cavities, are the prominent emerging materials. Despite great efforts, exploration of porous hosts and bulky solvents is still needed to develop new PL systems. Metal-organic polyhedra (MOPs) with discrete molecular architectures can be considered as porous hosts; however, many of them are insoluble entities. Here we report the transformation of type III PL to type II PLs by tuning the surface rigidity of insoluble MOP, Rh₂₄L₂₄, in a bulky ionic liquid (IL). Functionalization of N-donor molecules on Rh−Rh axial sites ensue their solubilization in bulky IL which confer type II PLs. Experimental and theoretical studies reveal the bulkiness of IL as per the cage apertures, and the cause of their dissolution as well. The obtained PLs, capturing more CO₂ than neat solvent, have depicted higher catalytic activity for CO₂ cycloaddition compared to individual MOPs and IL.     

Organic radicals based on phenalenyl and verdazyl units

Stable phenalenyl (PLY) radicals without sterically bulky substituents need to be synthesized for application as neutral organic molecular conductors. Verdazyl radicals, which have high stability even without sterically bulky substituents, were combined with PLY radicals to produce two novel radicals. The stability of the dimethylthiourea substituted PLY radical is supported by the experimental results and quantum chemical calculations.     

Bulky guanidinates for the stabilization of low oxidation state metallacycles

This article summarizes the development of a new class of very bulky guanidinate ligands. These have been used to prepare unprecedented examples of heterocycles containing groups 2, 13, 14 or 15 elements in the +1 oxidation state. The ligands have also been harnessed in the preparation of the only examples of guanidinato, and/or closely related amidinato, complexes of iron(I), cobalt(I) and planar four-coordinate lanthanide(II) metals. Preliminary studies of the further chemistry of these very reactive complexes are also reviewed. Throughout, the tendency of the bulky guanidinate ligands to exhibit ligating and stabilizing properties more akin to those of bulky β-diketiminate ligands than less bulky amidinates or guanidinates, will be discussed.     

A Bulky Pyridinyl?uorene/Triphenylamine Hybrid Used as Host Material for Heavily‐Doped Blue Electrophosphorescent Devices

In this work, a novel molecule pyridinyl?uorene/triphenylamine hybrid ( TPyFTPA ) with bulky steric hindrance effects has been synthesized successfully by substituting 9‐(pyridine‐2‐yl)‐fluoren‐9‐yl with triphenylamine (TPA) via Friedel‐Crafts reaction, which possesses good thermal stability and triplet energy (E_T) of 420°C with 5% weight loss and 2.86 eV, respectively. Moreover, the bulky steric hindrance material shows high stable morphology by heating to 200°C without finding melting phenomena and crystallization that is demonstrated by differential scanning calorimetry (DSC) curve. The bulky pyridinyl?uorene end‐capped TPA has been used as host material for blue phosphorescent organic light‐emitting diodes (PhOLEDs) with maximum external quantum efficiencies (EQEs) of 2.7%, 3.7%, and 3.5%, at the doping ratios of 10%, 30%, and 40%, respectively. The performances of TPyFTPA ‐based blue PhOLEDs own wide concentration ranging from 10% to 40%, which indicates the bulky TPyFTPA might be a potential candidate for inexpensive products with simplifying process for the applications in full‐color display and solid state lighting.     

A Theoretical and Experimental Study of the Effects of Silyl Substituents in Enantioselective Reactions Catalyzed by Diphenylprolinol Silyl Ether

The effect of silyl substituents in diphenylprolinol silyl ether catalysts was investigated. Mechanistically, reactions catalyzed by diphenylprolinol silyl ether can be categorized into three types: two that involve an iminium ion intermediate, such as for the Michael‐type reaction (type A) and the cycloaddition reaction (type B), and one that proceeds via an enamine intermediate (type C). In the Michael‐type reaction via iminium ions (type A), excellent enantioselectivity is realized when the catalyst with a bulky silyl moiety is employed, in which efficient shielding of a diastereotopic face of the iminium ion is directed by the bulky silyl moiety. In the cycloaddition reaction of iminium ions (type B) and reactions via enamines (type C), excellent enantioselectivity is obtained even when the silyl group is less bulky and, in this case, too much bulk reduces the reaction rate. In other cases, the yield increases when diphenylprolinol silyl ethers with bulky substituents are employed, presumably by suppressing side reactions between the nucleophilic catalyst and the reagent. The conformational behaviors of the iminium and enamine species have been determined by theoretical calculations. These data explain the effect of the bulkiness of the silyl substituent on the enantioselectivity and reactivity of the catalysts.     

Selected Reaction of (Z)-Dimethyl α-(Bromomethyl) Fumarate with Secondary Amines

Regioselective reaction of (Z)-dimethyl α-(bromomethyl) fumarate 2 with bulky secondary amines in ether as solvent at room temperature, leads exclusively to the rearranged substitution α-(functional alkyl amino) acrylic esters 4a-i in high yields. The less and more bulky amine gives rise respectively to the two successive (S_N2′) and (S_N2) substitution derivatives 5j,k and 51.     

Kinetic study of radical polymerization of dialkyl fumarates using electron spin resonance spectroscopy

The radical polymerization of dialkyl fumarates (DRF) bearing various ester alkyl groups was kinetically studied. The propagation and termination rate constants were determined using electron spin resonance (ESR) spectroscopy. The introduction of the bulky ester alkyl groups such as a tert-butyl group decreased the termination rate constant as expected. However, it has also been revealed that the bulky groups promote propagation despite the steric repulsion. The propagation rate and mechanism are discussed in relation to the propagation manner, i.e., tacticity of the polymer. © 1996 John Wiley & Sons, Inc.     

Sodium Dithionite-Mediated Decarboxylative Sulfonylation: Facile Access to Tertiary Sulfones

A straightforward multicomponent decarboxylative cross coupling of redox-active esters (N-hydroxyphthalimide ester), sodium dithionite, and electrophiles was established to construct sterically bulky sulfones. The inorganic salt sodium dithionite not only served as the sulfur dioxide source, but also acted as an efficient radical initiator for the decarboxylation. Notably, diverse naturally abundant carboxylic acids and artificially prepared carboxyl-containing drugs with multiple heteroatoms and sensitive functional groups successfully underwent this decarboxylative sulfonylation to provide sterically bulky tertiary sulfones. Mechanistic studies further demonstrated that decarboxylation was the rate-determining step and occurred via a single-electron transfer (SET) process with the assistance of sodium dithionite.     

A Strategy for Synthesizing Axially Chiral Naphthyl‐Indoles: Catalytic Asymmetric Addition Reactions of Racemic Substrates

A new strategy for enantioselective synthesis of axially chiral naphthyl‐indoles has been established through catalytic asymmetric addition reactions of racemic naphthyl‐indoles with bulky electrophiles. Under chiral phosphoric acid catalysis, azodicarboxylates and o‐hydroxybenzyl alcohols served as bulky but reactive electrophiles that were attacked by C2‐unsubstituted naphthyl‐indoles, which underwent a dynamic kinetic resolution to afford two series of axially chiral naphthyl‐indoles in good yields (up to 98 %) and high enantioselectivities (up to 98:2 er).     

The influence of peripheral ligand bulk on nitrogen activation by three‐coordinate molybdenum complexes—A theoretical study using the ONIOM method

Electronic structure methods have been combined with the ONIOM approach to carry out a comprehensive study of the effect of ligand bulk on the activation of dinitrogen with three‐coordinate molybdenum complexes. Calculations were performed with both density functional and CCSD(T) methods. Our results show that not only is there expected destabilization of the intermediate on the pathway due to direct steric interactions of the bulky groups, but also there is significant electronic destabilization as the size of the ligand increases. This latter destabilization is due to the inability of the molecule to accommodate a rotated amide group bound to the molybdenum once the amide reaches a certain size. This destabilization also leads to a clear preference for the triplet intermediate (rather than the singlet intermediate) for bulky substituents which is in agreement with experiment. Overall, the calculated reaction profile for the bulky substituents shows a good correlation with the available experimental data. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Probing the pi-stacking induced molecular aggregation in pi-conjugated polymers, oligomers, and their blends of p-phenylenevinylenes

The role of pi-stack induced molecular aggregation on solution and solid-state luminescent properties was investigated for the tricyclodecane substituted bulky (p-phenylenevinylene)s (BTCD-60, with 60% bulky group), oligophenylenevinylenes (MEH-OPV and BTCD-OPV)s, and their polymer-oligomer binary blends. The natures of the solvent, concentration, solvent combinations (good or bad), and temperature were employed as stimuli to probe the origin of the molecular aggregates in bulky conducting polymers. Absorption, photoluminescence (PL), and time-resolved fluorescence spectroscopic techniques were employed as tools to trace aggregation in solvents such as toluene, tetrahydrofuran (THF), THF and methanol, or THF and water as well as in the solid state. The absorbance spectra of poly(2-methoxy-5-(2-ethylhexyloxy))-1,4-phenylenevinylene (MEH-PPV) and BTCD-60 indicated that the films obtained from polymers that were dissolved in aromatic solvents such as toluene were found to possess more pi-stacking as compared to that of films obtained from a good solvent such as THF. The solid-state emission spectrum of BTCD-60 was found to show almost a 5-6 times enhancement in PL intensity as compared to that of MEH-PPV. Concentration dependent excitation spectra of the polymers confirmed the presence of aggregated polymer chains in MEH-PPV, which is the main reason for the quenching of luminescence intensity in the polymer. Solvent induced aggregation studies of polymers in THF and methanol mixture further supports the existence of strong aggregation in MEH-PPV as compared to that of bulky BTCD-60. Variable temperature absorption studies confirmed the reversibility of molecular aggregation on heating/cooling cycles, and the extent of aggregation was found more in MEH-PPV chains as compared to that of BTCD-60. MEH-PPV/OPV binary blends were prepared in the entire composition range from 0 to 100% via solution blending techniques. Through selective PL excitation techniques, the effect of oligomer-to-polymer energy transfer and also luminescent enhancement in MEH-PPV via interchain separation were investigated. Both the energy transfer and the interchain separation were found to be more effective on the enhancement of luminescence properties in the BTCD blends as compared to that of MEH blends. Time-resolved fluorescence studies confirmed the existence of two types of species corresponding to the free and aggregated chains in the polymer matrix with lifetimes in the range of 0.5-2.0 ns. In the present investigation, we have successfully shown that the molecular aggregation of the pi-conjugated polymers, oligomers, and their binary blends can be controlled via suitable bulky substitution to tune their emission properties in solution as well as in the solid state.     

Structure–property correlations of sulfonated polyimides. I. Effect of bridging groups on membrane properties

A series of six‐membered sulfonated polyimides were synthesized using 1,4,5,8‐naphthalenetetracarboxylic dianhydride, 4,4′‐diaminobiphenyl 2,2′‐disulfonic acid as the sulfonated diamine, and various nonsulfonated diamine monomers having different bridging groups. These bulky bridging groups have the capacity to increase hydrolytic stability and proton conductivity. Polyimides with bulky bridging groups showed increased solubility but exhibited lower thermal stability. The ion exchange capacity and water uptake reduced with increase in the bulkiness of the bridging group. This was attributed to the increase in the molecular weight of the repeating unit and hence effectively reduced the sulfonic acid content. In low temperatures, the conductivity was lower than Nafion®115 and, with increase in temperature, the conductivity rapidly increased and exhibited better conductivity than Nafion®115. Polyimides with bulky bridging groups 4‐amino phenyl sulfone, and 2‐bis[4‐(4‐aminophenoxy)phenyl]hexafluoropropane showed higher conductivity than other polyimides and Nafion®115 despite low ion exchange capacity. The hydrolytic stability of the polyimides with bulky bridging groups was higher than the polyimides with less bulky atoms because of the imparted flexibility. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3612–3620, 2004     

Progress in fluorene-based wide-bandgap steric semiconductors

Molecular bulks are favorable for the thermal and morphological stability in organic wide-bandgap semiconducting polymers with potential applications in both information and energy electronics. In this review, we present our progress in the design of fluorene-based bulky semiconductors with a fractal four-element pattern. Firstly, we established one-pot methods to spirofluorenes, especially spiro[fluorene-9,9′-xanthene](SFX) serving as the next-generation spiro-based semiconductors. Secondly, we observed the supramolecular forces at the bulky groups and discovered the supramolecular steric hindrance(SSH) effect on polymorphisms, nanocrystals as well as device performance. Thus, a synergistically molecular attractor-repulsor theory(SMART) was proposed for the control of nanocrystal morphology, thin film phase and morphology. Thirdly, the third possible type of defects has been identified to generate green band(g-band) emission in widebandgap semiconductors by the introduction of molecular strain design of cyclofluorene. Finally, the first bulky polydiarylfluorene with highly crystalline and β conformation was achieved by an attractor-repulsor design of tadpole-shape monomer, which offered an effective platform to fabricate stable wide-bandgap semiconducting devices. All the discoveries offer the solid basis to break through bottlenecks of organic/polymer wide-bandgap semiconductors by the improvements of overall performances.     

Highly emissive organic solids containing 2,5-diboryl-1,4-phenylene unit

We disclosed a series of pi-conjugated systems containing 2,5-bis(dimesitylboryl)-1,4-phenylene as the core unit and electron-donating amino groups at the terminal positions. The extension of the ppi-pi* conjugation in the diborylphenylene moiety along the short axis of the pi-conjugated framework as well as the incorporation of two bulky dimesitylboryl groups at the para-positions makes this moiety act as a unique bulky pi-electron-accepting unit. As a consequence, these systems behave like donor-acceptor-donor quadrupolar pi-electron systems and show a large solvatochromism in the fluorescence spectra. Moreover, these organoboron pi systems exhibit intense fluorescence even in the solid state with the quantum yields of 0.73-0.90.     

Development of highly chemoselective bulky zincate complex, tBu4ZnLi2: design, structure, and practical applications in small-/macromolecular synthesis

We present full details of the unique reactivities of the newly developed dianion-type bulky zincate, dilithium tetra-tert-butylzincate (tBu(4)ZnLi(2)). With this reagent, halogen-zinc exchange reaction of variously functionalized haloaromatics and anionic polymerization of N-isopropylacrylamide (NIPAm)/styrene with excellent chemoselectivity were realized. Halogen-zinc exchange reaction followed by electrophilic trapping with propargyl bromide provided a convenient route to functionalized phenylallenes, particularly those with electrophilic functional groups (such as cyano, amide and halogens). Spectral and computational studies of the structure in the gas and liquid phases indicated extraordinary stabilization of this dianion-type zincate by its bulky ligands.     

Asymmetric Michael addition of substituted rhodanines to α,β-unsaturated ketones catalyzed by bulky primary amines

A bulky group was introduced by design into a diamine catalyst, and a series of robust and tunable bulky chiral primary amine catalysts were developed and successfully applied in the direct conjugate addition of substituted rhodanines to α,β-unsaturated ketones. High yields (up to 99%) and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to 98% ee) were observed.     

Suzuki-Miyaura coupling reaction of aryl chlorides using di(2,6-dimethylmorpholino)phenylphosphine as ligand

Suzuki-Miyaura coupling was achieved on a variety of aryl chlorides by using di(2,6-dimethylmorpholino)phenylphosphine (L1) as a bulky electron-rich monoaryl phosphine ligand. We report the couplings of various chlorobenzenes and heteroaryl chlorides.