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Arborescent polymers: Designed macromolecules with a dendritic structure
Published in Y. Yagci, M.K. Mishra, O. Nuyken, K. Ito, G. Wnek, Tailored Polymers & Applications, 2020
The method developed for isoprene copolymers is also applicable to the synthesis of copolymers carrying poly(2-vinylpyridine) side chains [15]. These molecules are particularly interesting because of their basic character, leading to arborescent cationic polyelectrolytes by simple quaternization of the pendent pyridine units (e.g., with HCl). These systems are synthesized by polymerization of 2-vinylpyridine in THF at −78°C in the presence of Ν,Ν,Ν′,Ν′-tetramethy-ethylenediamine (TMEDA), and titration of the “living” anions with a solution of a chloromethylated polystyrene grafting substrate at −40°C. Due to the relatively low reactivity of the poly(2-vinylpyridine) anions, no capping is necessary prior to grafting to avoid metal-halogen exchange. The red coloration of the anions also facilitates monitoring of the titration process. The addition of TMEDA to the reaction is beneficial in achieving “clean” polymerization and grafting conditions, by minimizing nucleophilic attack of the pyridine rings by the macroanions. This is confirmed by the residual yellow coloration, characteristic of ring addition, observed for reactions carried out in the absence of TMEDA. The products obtained with TMEDA, in contrast, are completely colorless.
CVD of nanocomposite coatings
Published in Kwang Leong Choy, Chemical Vapour Deposition (CVD), 2019
ZnO-TiO2 nanocomposites were synthesised by sequential CVD deposition. ZnO nanoplatelets (host) were initially grown on Si(100) and Al2O3 substrates, followed by the dispersion of TiO2 nanoparticles (guest) leading to the formation of ZnO-TiO2 nanocomposite deposits with an average thickness of 140 nm, whose characteristics were directly affected by the host matrix porosity and the guest amount and dispersion, tailored by varying the TiO2 deposition time. The chemical precursors for Ti and Zn sources were Ti(O/Pr)2 (dpm)2 and Zn(hfa)2•TMEDA (O/Pr: iso-propoxy; dpm: 2,2,6,6-tetramethyl-3,5-heptanedionate; hfa:1, 1,1,5,5,5-hexafluoro-2,4-pentanedionate; and TMEDA: N, N,N´,N´ tetramethyl ethylenediamine). CVD was performed at relatively low temperatures (350°C–400°C) in nitrogen plus wet-oxygen atmospheres, without further heat treatment [30].
Direct (Hetero)Arylation Polymerization for the Preparation of Conjugated Polymers
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
J. Terence Blaskovits, Mario Leclerc
The most widely-used catalysts in this regard are PCy3 and P(t-Bu)2Me.HBF4. Substantial steric hindrance is therefore necessary, and yet there are examples in which phosphines that are too sterically demanding inhibited the reaction. For example, the copolymerization of tetrafluorobenzene or octafluorobiphenyl with other phenyl derivatives required the presence of a sterically demanding phosphine (P(t-Bu)2Me.HBF4), whereas in the presence of other, even more bulky phosphines (P(t-Bu)3.HBF4 or SPhos), the reaction did not occur (Figure 5.19).91,125 The significance of the ligand in suppressing β-defects in polar conditions was also shown in a study which promoted various degrees of branching in P3HT through the choice of ligand used. Of the reaction conditions tested, the ligand-free system led to the highest degree of branching, while the bidentate ligands 2,2ʹ-bipyridine and tetramethylethylenediamine (TMEDA) suppressed β-branching entirely.
Assembly of nucleobases into rings and cages via metal ions
Published in Journal of Coordination Chemistry, 2022
Bernhard Lippert, Pablo J. Sanz Miguel
As mentioned above, cis-(PMe3)2PtII forms a dinuclear head-tail complex with 1MeC [31], but likewise a C3 symmetrical cyclic trimer [56]. With the closely related cis-(PMe2Ph)2PtII the initially formed head-tail dimer converts quantitatively into an analogous cyclic trimer when heated in DMSO, yet to an unsymmetrical cyclic trimer (second linkage isomer) in CDCl3, as established by NMR spectroscopy [57]. Self-condensation reactions of [Pd(tmeda)(C-N3)(OH)]+ (tmeda = N,N,N',N'-tetramethylethylenediamine) with C = 1MeC [58] or cytidine [59] likewise lead to the symmetrical cyclic trimer. In it, a twelve-membered ring [-M-N3-C4-N4-]3, formally to be considered also a [12]metallaazacrown-3, functions as a belt in a double-cone structure, with three cytosine rings on one side, and three (tmeda)PdII entities on the other. As compared to the head-tail dimers of 1MeC–H, the major structural difference in the C3 symmetrical cycle refers, apart from ring size, to the different spatial orientations of the metals: They are anti in the trimer as opposed to syn in the dimer (Scheme 6 and Figure 1). It is likely that it is the steric bulk of the tmeda ligand in the Pd trimers which prevents head-tail dimer formation and drives the equilibrium toward the larger cycle.
Mesophase behaviour of 1,2,3-triazole-based nematic liquid crystals influenced by varying alkyl chains and halogen atom substitution
Published in Liquid Crystals, 2022
Dan Xiong, Xiaoping Xiong, Ziran Chen, Wenhao Yu, Chun Feng, Hongmei Chen, Hailiang Ni, Biqin Wang, Keqing Zhao, Ping Hu
The intermediate alkyl azide compounds were synthesised by a nucleophilic substitution reaction between the corresponding alkyl bromides and sodium azide [39]. As depicted in Figure 1, the Steglich esterification reaction of 4-ethynylbenzoic acid with 4-(4'-propyl)-cyclohexylphenol afforded the key intermediate 2. The 4-(4-propylcyclohexyl)phenyl 4-(1-alkyl-5-hydro/halo-1,2,3 -triazol-4-yl)benzoate series 1 was synthesised by the classical copper(I)-catalysed azide alkyne cycloaddition (CuAAC) reaction between 2 and alkyl azide with different alkyl chain lengths in a CuI catalytic system (0.3 eq) under nitrogen atmosphere [33]. The 1,4-substituted-5-halo-1,2,3-triazole products 1c-X (× = Cl, Br, and I) were successfully prepared by the one-step in situ tandem reaction of CuAAC, aerobic oxidation, and halogenation reaction in a CuX catalytic system (1.3 eq) under air atmosphere [40]. Note that the reaction medium with products 1c-Cl and 1c-I must be added to NCS and TBDMsCl as additives, respectively, to effectively obtain the product in high yield. The 1,4-substituted-5-fluoro-1,2,3-triazole compound 1c-F was prepared by halogen exchange between 1,4-substituted 5-iodo-1,2,3-triazole compounds 1c-I and 5 eq of AgF using tetramethylethylenediamine (TMEDA) as a ligand, in a heated system [41]. Furthermore, the 1,4-substituted-5-thiophene-1,2,3-triazole-based compound 1c-Th was synthesised by the Suzuki coupling reaction of 1c-I with 2-thiopheneboronic acid.
Inverse coordination metal complexes with oxalate and sulfur, selenium and nitrogen analogues as coordination centers. Topology and systematization
Published in Journal of Coordination Chemistry, 2020
Nickel forms numerous oxalate centered inverse coordination complexes with ammonia [(µ-C2O4){Ni(en)2}2]2+(73) [118], pyridine [(µ-C2O4){Ni(py)3(NO2)}2]0(74) [119], ethylenediamine [(µ-C2O4){Ni(en)2}2]2+(75) [120(a-d)], propanediamine [(µ-C2O4){Ni(pn)2}2]2+ [120e], terpyridine-methanol [(µ-C2O4){Ni(terpy)(MeOH)}2]2+(76) [121], tetramethylethylenediamine/acetylacetone [(µ-C2O4){Ni(tmeda)(acac)}2]0(77) [122], methyl/trimethylphosphine [(µ-C2O4){NiMe(PMe3)}2]0(78) [123] (Scheme 20), substituted diethylentriamines (79-82) [124–127], bis(aminopropyl)ethylenediamine [(µ-C2O4){Ni(H2NC3H6NHC2H4NHC3H6NH2)}2]2+(83) [128], bis(aminoethyl)propanediamine [(µ-C2O4){Ni(H2NC2H4NHC3H6NHC2H4NH2)}2]2+(84) [129] (Scheme 21), 2,2′-bipyridine [(µ-C2O4){Ni(bipy)2}2]2+(85) [130] and di(2-pyridyl)amine [(µ-C2O4){Ni(dipyam)2}2]0(86) [131] (Scheme 22).