RESUMEN
High concentrations of active carriers on the surface of a semiconductor through energy/electron transfer are the core process in the photocatalytic hydrogen production from water. However, it remains a challenge to significantly improve photocatalytic performance by modifying simple molecular modulation. Herein, a new strategy is proposed to enhance the photocatalytic hydrogen evolution performance using boron and nitrogen elements to construct BâN coordination bonds. Experimental results show that polynaphthopyridine borane (PNBN) possessing BâN coordination bonds shows a hydrogen evolution rate of 217.4 µmol h-1 , which is significantly higher than that of the comparison materials 0 µmol h-1 for polyphenylnaphthalene (PNCC) and 0.66 µmol h-1 for polypyridylnaphthalene (PNNC), mainly attributed to the formation of a strong built-in electric field that promotes the separation of photo-generated electrons/holes. This work opens up new prospects for the design of highly efficient polymeric photocatalysts at the molecular level.
RESUMEN
Three potassium crown ether complexes supported with bulky amidinate ligands were synthesized for the ring-opening polymerization (ROP) of rac-lactide. The side polymerization reaction initiated directly by ligand anion was suppressed well in the presence of alcohol as our design, and the synthesis of linear polylactide with a molecular weight as high as 117.7 kg/mol was successful together with an isoselectivity value of Pm = 0.88 at -70 °C. In this system, lactide can be deprotonated by amidinate anion to give lactide enolate, which can initiate the ROP of lactide as a side reaction in the absence of alcohol; however, this side reaction can also be suppressed well in the presence of alcohol by a decrease in temperature. An interesting anti-Arrhenius-like behavior in the polymerization was discovered, which can be attributed to the fact that the active catalyst can be converted to a less active lactide enolate potassium complex at a high temperature.
RESUMEN
Polyesters, especially poly(lactide) (PLA), are used widely as biodegradable and biocompatible materials, yet their controllable synthesis, especially the stereoselective synthesis of polyesters, is still a challenge. Recently some excellent Lewis pair catalysts for ring-opening polymerization (ROP) of lactide and related cyclic esters have emerged. This review article will highlight the key advances in the ROP catalyzed by Lewis pair compounds with the aim of encouraging the wider application of Lewis pair catalysts in the polymerization of lactide and related cyclic esters.
Asunto(s)
Dioxanos/química , Ésteres , Polimerizacion , Aluminio/química , Boro/química , Catálisis , Lactonas/química , Magnesio/química , Conformación Molecular , Estructura Molecular , PoliésteresRESUMEN
The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) can give diverse poly(α-hydroxy acid)s (PAHAs) with different functional groups because of easy modification of the side group of OCAs, which can extend applications of PAHAs widely. The stereoselective polymerization of O-carboxyanhydrides and further sequence controlled alternating copolymerization of OCAs were still big challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr value up to 0.95. Furthermore, these initiators were successfully applied in the precisely alternating sequence controlled copolymerization of PheOCA and Tyr(Bn)OCA, and alternating copolymerization of LacOCA and PheOCA was also achieved.
RESUMEN
Correction for 'Photoswitchable ring-opening polymerization of lactide catalyzed by azobenzene-based thiourea' by Zhongran Dai et al., Chem. Commun., 2016, 52, 8826-8829.
RESUMEN
The reactivity of a catalytic polymerization system using photoresponsive azobenzene-based thiourea/PMDETA as a catalyst could be switched between slow and fast states by alternating exposure to UV and ambient light, because the active site of azobenzene thiourea is blocked via intramolecular hydrogen bonding when the azobenzene thiourea transfers from the E isomer to the Z isomer under UV irradiation.
Asunto(s)
Compuestos Azo/química , Dioxanos/síntesis química , Tiourea/química , Catálisis , Dioxanos/química , Enlace de Hidrógeno , Luz , Estructura Molecular , Procesos Fotoquímicos , PolimerizacionRESUMEN
In the binuclear title complex, [Ag(2)(C(31)H(22)N(4)O)(2)](ClO(4))(2)·2C(3)H(7)NO, the Ag(I) atom is penta-coordinated by three N atoms from the tridentate chelating terpyridyl group and by one N atom and one O atom from the quinolin-8-yl-oxy group in a distorted square-pyramidal geometry with the O atom at the apical position. The centrosymmetric complex cation involves intra-molecular π-π stacking inter-actions [centroid-centroid distance = 3.862â (4)â Å] between the central pyridine and benzene rings. In the crystal structure, inter-molecular C-Hâ¯O hydrogen bonds result in the formation of a supra-molecular network.