Stannylated Vinylic Addition Polynorbornene: Probing a Reagent for Friendly Tin-Mediated Radical Processes

Producción CientíficaVinylic addition polynorbornenes (VA-PNB) with stannyl functional groups have been prepared and used in tin- mediated radical dehalogenation reactions. The aliphatic and robust scaffold of VA-PNB is well suited for a support in radical processes. VA-PNB-(CH2)nSnHBu2 can be used as a stoichiomet- ric reagent and VA-PNB-(CH2)nSnBu2Cl as a catalyst in the pres- ence of a hydride donor for the reduction of RBr. The mixture KF (aq.)/polymethylhydrosiloxane (PMHS) is the most convenient hydride source to generate VA-PNB-(CH2)nSnHBu2 in situ. Although quite popular in this context, boron hydrides, being a source of radicals themselves, are not adequate to correctly evaluate the performance of the anchored organotin group. VA- PNB-(CH2)4SnBu2Cl can be recycled and, even if it loses activity upon reuse, it is still useful after ten cycles. The stannylated VA- PNB can be separated from the products by simple filtration, and it leads to very low tin contamination (at least 250 times lower than that with use of conventional separation methods).MINECO-SGPI CTQ2013-48406-PMINECO-SGPI CTQ2016-80913-

α-Diimine–Palladium Complexes Incorporated in Vinylic- Addition Polynorbornenes: Synthesis and Catalytic Activity

Producción Científicaα-Diimine polymeric ligands have been synthesized using the bicyclic norbornane structure, present in vinylic-addi- tion polynorbornene ( VA-PNB). The VA-PNB–diimine ligands have been prepared by functionalization of the copolymer ob- tained by Ni-catalyzed polymerization of norbornene and nor- bornenylcarbonate. Immobilized palladium complexes of the type VA-PNB–diimine–PdX2 have been prepared, and their cata- lytic activity has been tested. The trifluoroacetato complex (X =CF3COO) can be used as a recyclable precatalyst in the Suzuki reaction. It is the source of minute amounts of homogeneous palladium active species, which carry out the catalysis with high turnover numbers. The recovered polymeric complex can be reused several times with no significant loss of activity. The polymeric analogue to Brookhart's catalyst, VA-PNB–diimine– PdMeCl, can also polymerize ethylene, although it is less active than its monomeric counterparts.MINECO-SGPI, grant CTQ2013-48406-PMINECO-SGPI, grant CTQ2016-80913-PJunta de Castilla y León, grant VA302U1

Template Route to Chemically Engineering Cavities at Nanoscale: A Case Study of Zn(OH)2 Template

A size-controlled Zn(OH)2 template is used as a case study to explain the chemical strategy that can be executed to chemically engineering various nanoscale cavities. Zn(OH)2 octahedron with 8 vertices and 14 edges is fabricated via a low temperature solution route. The size can be tuned from 1 to 30 μm by changing the reaction conditions. Two methods can be selected for the hollow process without loss of the original shape of Zn(OH)2 template. Ion-replacement reaction is suitable for fabrication of hollow sulfides based on the solubility difference between Zn(OH)2 and products. Controlled chemical deposition is utilized to coat an oxide layer on the surface of Zn(OH)2 template. The abundant hydroxyl groups on Zn(OH)2 afford strong coordination ability with cations and help to the coating of a shell layer. The rudimental Zn(OH)2 core is eliminated with ammonia solution. In addition, ZnO-based heterostructures possessing better chemical or physical properties can also be prepared via this unique templating process. Room-temperature photoluminescence spectra of the heterostructures and hollow structures are also shown to study their optical properties

Thermoreversible (Ionic-Liquid-Based) Aqueous Biphasic Systems

The ability to induce reversible phase transitions between homogeneous solutions and biphasic liquid-liquid systems, at pre-defined and suitable operating temperatures, is of crucial relevance in the design of separation processes. Ionic-liquid-based aqueous biphasic systems (IL-based ABS) have demonstrated superior performance as alternative extraction platforms, and their thermoreversible behaviour is here disclosed by the use of protic ILs. The applicability of the temperature-induced phase switching is further demonstrated with the complete extraction of two value-added proteins, achieved in a single-step. It is shown that these temperature-induced mono(bi)phasic systems are significantly more versatile than classical liquid-liquid systems which are constrained by their critical temperatures. IL-based ABS allow to work in a wide range of temperatures and compositions which can be tailored to fit the requirements of a given separation process