Showing papers by "Virgil Percec published in 2012"
TL;DR: The kinetic and structural analyses of the polymer resulting from the Cu(0)/Me6-TREN-mediated polymerization of methyl acrylate (MA) initiated with methyl 2-bromopropionate (MBP) in solvents mediating different degrees of disproportionation are reported in this paper.
Abstract: The kinetic and structural analyses of the polymer resulting from the Cu(0)/Me6-TREN-mediated polymerization of methyl acrylate (MA) initiated with methyl 2-bromopropionate (MBP) in solvents mediating different degrees of disproportionation are reported. Accurate analyses of the polymerization and of the resulting polymer demand a minimum combination of techniques that includes kinetics, GPC, 1H NMR, and MALDI-TOF both performed before and after chain-end functionalization via thio–bromo “click” chemistry and reinitiation experiments. At [MA]0/[MBP]0 = 222 the use of the disproportionating solvent DMSO generated first-order kinetics and 97% active chain ends of the polymer at 89% conversion. The less disproportionating solvent MeCN produced two linear first-order kinetics and a decrease of bromine chain-end functionality of the polymer with conversion, yielding 77% active chain ends at 89% conversion. The nondisproportionating solvent toluene, in the presence of TEMPO, produced two linear first-order kine...
138 citations
123 citations
TL;DR: This new class of dendronized polymers acts as thermal actuator that decrease the length of the supramolecular column when the temperature is increased and therefore, are called reverse thermal actuators.
Abstract: The synthesis and structural analysis of polymers dendronized with self-assembling Janus dendrimers containing one fluorinated and one hydrogenated dendrons are reported. Janus dendrimers were attached to the polymer backbone both from the hydrogenated and from the fluorinated parts of the Janus dendrimer. Structural analysis of these dendronized polymers and of their precursors by a combination of differential scanning calorimetry, X-ray diffraction experiments on powder and oriented fibers, and electron density maps have demonstrated that in both cases the dendronized polymer consists of a vesicular columnar structure containing fluorinated alkyl groups on its periphery. This vesicular columnar structure is generated by a mechanism that involves the intramolecular assembly of the Janus dendrimers into tapered dendrons followed by the intramolecular self-assembly of the resulting dendronized polymer in a vesicular column. By contrast with conventional polymers dendronized with self-assembling tapered den...
118 citations
TL;DR: The efficiency of mesylates and sulfamates as C-O-based electrophiles attached to the 1- or 2-position of naphthalene and to activated and nonactivated phenyl substrates was compared for the first time in Ni-catalyzed cross-coupling with phenyl neopentylglycolboronates containing electron-rich and electron-deficient substituents in their para-position.
Abstract: The efficiency of mesylates, sulfamates, esters, carbonates, carbamates, and methyl ethers as C–O-based electrophiles attached to the 1- or 2-position of naphthalene and to activated and nonactivated phenyl substrates was compared for the first time in Ni-catalyzed cross-coupling with phenyl neopentylglycolboronates containing electron-rich and electron-deficient substituents in their para-position. These experiments were performed in the presence of four different Ni(II)- and Ni(0)-based catalysts. Ni(II)-based catalysts mediate the cross-coupling of most 2-naphthyl C–O electrophiles with both arylboronic acids and with neopentylglycolboronates when K3PO4 is used as base. The same catalysts are not efficient when CsF is used as base. However, Ni(0)-based catalysts exhibit selective efficiency, and when reactive, their efficiency is higher than that of Ni(II)-based catalysts in the presence of both K3PO4 and CsF. These results provide both reaction conditions for the cross-coupling, and for the elaboratio...
79 citations
TL;DR: Arylboron-based nucleophiles, boronic acid, potassium trifluoroborate, neopentylglycolboronate, and pinacol boronate in nickel-catalyzed Suzuki-Miyaura cross-coupling reactions with the two C-O electrophiles, mesylates, and sulfamates was compared.
Abstract: The efficiency of arylboron-based nucleophiles, boronic acid, potassium trifluoroborate, neopentylglycolboronate, and pinacol boronate in nickel-catalyzed Suzuki–Miyaura cross-coupling reactions with the two C–O electrophiles, mesylates, and sulfamates was compared. Arylboronic acid is the most reactive and most atom-economic of the four boron species studied. Arylpotassium trifluoroborate cross-couples efficiently only in the presence of water. In the absence of water, aryl neopentylglycolboronate is more efficient, less expensive, and more atom-economic than aryl pinacolboronate.
72 citations
TL;DR: In this paper, the Cu(0)/Me6-TREN-catalyzed polymerization of methyl acrylate (MA) initiated by methyl 2-bromopropionate (MBP) in DMSO at 25 °C was performed in a UV cuvette, and the absorbance of CuBr2 was monitored online in aUV-vis spectrophotometer as a function of the monomer conversion.
Abstract: The Cu(0)/Me6-TREN-catalyzed polymerization of methyl acrylate (MA) initiated by methyl 2-bromopropionate (MBP) in DMSO at 25 °C was performed in a UV cuvette, and the absorbance of CuBr2 was monitored online in a UV–vis spectrophotometer as a function of the monomer conversion. A continuous increase of CuBr2 absorbance throughout the reaction demonstrated no reduction of CuBr2 concentration during the entire polymerization process. In addition, the 100% chain-end functionality of the polymer observed from 10% to 95% monomer conversion indicated that in this polymerization the bimolecular termination required to provide the persistent radical effect in ATRP was not responsible for the production of CuBr2.
65 citations
TL;DR: Together with the nickel-catalyzed, one-pot, two-step neopentylglycolborylation, this bench stable and inexpensive Ni(II)-based catalyst can be utilized as an alternative to Ni(COD)(2)/PCy(3) to provide an inexpensive, robust, and convenient synthesis of biaryl and heterobiaryl compounds.
Abstract: trans-Chloro(1-naphthyl)bis(triphenylphosphine)nickel(II) complex/PCy3 system has been successfully applied as catalyst for the Suzuki–Miyaura cross-coupling of aryl and heteroaryl neopentylglycolboronates with aryl and heteroaryl mesylates and sulfamates in THF at room temperature. This cross-coupling reaction tolerates various functional groups, including keto, imino, ester, ether, and cyano. Together with the nickel-catalyzed, one-pot, two-step neopentylglycolborylation, this bench stable and inexpensive Ni(II)-based catalyst can be utilized as an alternative to Ni(COD)2/PCy3 to provide an inexpensive, robust, and convenient synthesis of biaryl and heterobiaryl compounds.
63 citations
TL;DR: The commercially available tris(2-aminoethyl)amine (TREN) was used as ligand to mediate the singleelectron transfer-living radical polymerization (SET-LRP) of methyl acrylate in dimethyl sulfoxide initiated with the bifunctional initiator bis(2bromopropionyl)ethane and catalyzed by both nonactivated and activated Cu(0) wire.
Abstract: The commercially available tris(2-aminoethyl)amine (TREN) was used as ligand to mediate the single-electron transfer-living radical polymerization (SET-LRP) of methyl acrylate in dimethyl sulfoxide initiated with the bifunctional initiator bis(2-bromopropionyl)ethane and catalyzed by both nonactivated and activated Cu(0) wire. A comparative study between TREN and tris(2-dimethylaminoethyl)amine (Me6-TREN) ligand, that is more commonly used in SET-LRP, demonstrated that TREN provided a slower polymerization but the chain-ends functionality of the resulting bifunctional poly(methyl acrylate) was near quantitative and comparable to that obtained when Me6-TREN was used as a ligand. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.
53 citations
TL;DR: This approach elucidates a mechanism of selecting a homochiral relationship between dissimilar but neighboring α-amino acids through thermodynamic preference for homochirality in solution-phase and bulk supramolecular helical polymerization.
Abstract: Biological macromolecules are homochiral, composed of sequences of stereocenters possessing the same repeated absolute configuration. This chapter addresses the mechanism of homochiral selection in polypeptides. In particular, the relationship between the stereochemistry (l or d) of structurally distinct α-amino acids is explored. Through functionalization of Tyr–Xaa dipeptides with self-assembling dendrons, the effect of stereochemical sequence of the dipeptide on the thermodynamics of self-assembly and the resulting structural features can be quantified. The dendritic dipeptide approach effectively isolates the stereochemical information of the shortest sequence of stereochemical information possible in polypeptide, while simultaneously allowing for dendron driven tertiary and quaternary structure formation and subsequent transfer of chiral information from the dipeptide to the dendritic sheath. This approach elucidates a mechanism of selecting a homochiral relationship between dissimilar but neighboring α-amino acids through thermodynamic preference for homochirality in solution-phase and bulk supramolecular helical polymerization.
30 citations
TL;DR: In this paper, the main stages of the self-assembling of supramolecular ensembles have been revealed by studying different functional wedged macromolecules: polymethacrylates with tapered side chains based on gallic acid, their macromonomers, and salts of 2,3,4 and 3,4,5-tris(dodecyloxy)benzenesulphonic acid.
Abstract: The main stages of the self-assembling of supramolecular ensembles have been revealed by studying different functional wedged macromolecules: polymethacrylates with tapered side chains based on gallic acid, their macromonomers, and salts of 2,3,4- and 3,4,5-tris(dodecyloxy)benzenesulphonic acid. The first stage is the formation of individual supramolecular aggregates (long cylinders or spherical micelles) due to the weak noncovalent interactions of mesogenic groups and the subsequent ordering in these aggregates, which is accompanied by a decrease in the free energy of the system. Supramolecular aggregates, in turn, form 2D or 3D lattices. The shape of supramolecular aggregates and its change with temperature are delicate functions of the mesogen chemical structure; this circumstance makes it possible to rationally design complex self-assembling systems with the ability to respond smartly to external stimuli. X-ray diffraction analysis allows one to study the structure of supramolecular systems with different degrees of order, determine the type of mesophases formed by these systems, and reveal the phase behavior of the material. Particular attention has been paid to the method for reconstruction of electron density distribution from the relative reflection intensity. The application of a suite of experimental methods, including wide- and small-angle X-ray diffraction, molecular modeling, differential scanning calorimetry, and polarization optical microscopy, allows one to establish the relationship between the shape of the structural unit (molecule or molecular aggregate), the nature of the interaction, and the phase behavior of the material.
13 citations
Patent•
26 Apr 2012TL;DR: In this article, the design of an environmentally friendly and efficient fluorous phase based on dendritic architectures containing short semifluorinated groups on their periphery is discussed, and the authors present an efficient fluorescence phase with a short semi-fluorinated group on the periphery.
Abstract: The present invention concerns the design of an environmentally friendly and efficient fluorous phase based on dendritic architectures containing short semifluorinated groups on their periphery.
TL;DR: In this article, the efficiency of coupling aryl mesylates, sulfamates, carbamates and carboates with boronates was investigated, and it was shown that the efficiency depends on the conditions.
Abstract: The efficiency concerning coupling of aryl mesylates, sulfamates, carbamates, pivalates, carboates, and methyl ethers with boronates (II) is found to depend on the conditions.
TL;DR: The reaction allows a convenient and inexpensive access to a wide range of biaryls and heterobiaryls as discussed by the authors, and it is used in a variety of applications, such as bioinformatics.
Abstract: The reaction allows a convenient and inexpensive access to a wide range of biaryls and heterobiaryls.