RESUMO
Electrophilic fluorophosphonium triflates bearing pyridyl (3[OTf]) or imidazolyl (4[OTf])-substituents act as intramolecular frustrated Lewis pairs (FLPs) and reversibly form 1 : 1 adducts with CO2 (5+ and 6+ ). An unusual and labile spirocyclic tetrahedral intermediate (72+ ) is observed in CO2 -pressurized (0.5-2.0â bar) solutions of cation 4+ at low temperatures, as demonstrated by variable-temperature NMR studies, which were confirmed crystallographically. In addition, cations 3+ and 4+ actively bind carbonyls, nitriles and acetylenes by 1,3-dipolar cycloaddition, as shown by selected examples.
RESUMO
The preparation of polymer brushes (PBs) bearing α-hydroxyalkylphenylketone (2-hydroxy-2-methyl-1-phenylpropan-1-one) moieties as photoreactive polymer backbone substituents is presented. Photoreactive polymer brushes with defined thicknesses (up to 60 nm) and high grafting densities are readily prepared by surface initiated nitroxide mediated radical polymerization (SINMP). The photoactive moieties can be transformed via Norrish-type I photoreaction to surface-bound acyl radicals. Photolysis in the presence of a persistent nitroxide leads to chemically modified PBs bearing acylalkoxyamine moieties as side chains resulting from trapping of the photogenerated acyl radicals with nitroxides. Application of functionalized nitroxides to the photochemical PB postmodification provides functionalized PBs bearing cyano, polyethylene glycol (PEG), perfluoroalkyl, and biotin moieties. As shown for one case, photochemical postfunctionalization of the PB through a mask using a biotin-conjugated nitroxide as the trapping reagent leads to the corresponding site-selective chemically modified PB, which is successfully used for site-specific streptavidin immobilization. Surface analysis of PBs was performed by contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR), fourier transform infrared (FTIR) spectroscopy, and fluorescence microscopy.
Assuntos
Óxidos de Nitrogênio/química , Polímeros/síntese química , Química Click , Estrutura Molecular , Processos Fotoquímicos , Polimerização , Polímeros/química , Propriedades de SuperfícieRESUMO
The synthesis of bifunctional mesoporous silica nanoparticles is described. Two chemically orthogonal functionalities are incorporated into mesoporous silica by co-condensation of tetraethoxysilane with two orthogonally functionalized triethoxyalkylsilanes. Post-functionalization is achieved by orthogonal surface chemistry. A thiol-ene reaction, Cu-catalyzed 1,3-dipolar alkyne/azide cycloaddition, and a radical nitroxide exchange reaction are used as orthogonal processes to install two functionalities at the surface that differ in reactivity. Preparation of mesoporous silica nanoparticles bearing acidic and basic sites by this approach is discussed. Particles are analyzed by solid state NMR spectroscopy, elemental analysis, infrared-spectroscopy, and scanning electron microscopy. As a first application, these particles are successfully used as cooperative catalysts in the Henry reaction.
RESUMO
Bifunctional mesoporous silica nanoparticles (MSNs) bearing Pd-complexes and additional basic sites were prepared and tested as cooperative active catalysts in the Tsuji-Trost allylation of ethyl acetoacetate. Functionalization of the MSNs was realized by postmodification using click-chemistry. The selectivity of mono versus double allylation was achieved by control of reaction temperature and the nature of the catalyst.
Assuntos
Nanopartículas/química , Dióxido de Silício/química , Acetoacetatos/química , Alquilação , Aminas/química , Azidas/química , Catálise , Química Click , Compostos Organometálicos/química , Porosidade , Dióxido de Silício/síntese química , Propriedades de SuperfícieRESUMO
Arylboronic acids are shown to be valuable precursors for aryl radicals upon treatment with manganese triacetate. Under these oxidative conditions the intermediately generated aryl radicals undergo addition to olefins to give the arylhydroxylation products A in the presence of dioxygen. In the absence of dioxygen, for some olefins double olefin addition and subsequent homolytic aromatic substitution provide tetrahydronaphthaline derivatives B in moderate to good yields.