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.
The
structure of mixed-network former glasses in the system (M2O)0.33[(Ge2O4)
x
(P2O5)1–x
]0.67.(M = Na, K) has been studied by 31P and 23Na high-resolution and dipolar solid state nuclear
magnetic resonance (NMR) techniques, O-1s X-ray photoelectron spectroscopy,
and Raman spectroscopy. Using an iterative fitting procedure, a quantitative
structural model has been developed that is consistent with all of
the experimental data and which provides a detailed description of
network connectivities, network modification processes, and spatial
cation distributions. Formation of heteroatomic P–O–Ge
linkages is generally preferred over homoatomic P–O–P
and Ge–O–Ge linkages, as shown by a detailed comparison
with a random linkage model. An exception occurs in glasses with low
germanium contents (x = 0.2) where a pronounced nonlinear
dependence of the glass transition temperature on x can be related to a cross-linking of the sodium ultraphosphate network
by fully polymerized germanium species, possibly including also 5-
and 6-fold coordination states. At higher x values,
the Ge component is modified as well, however, the fraction of anionic
nonbridging oxygen atoms bound to germanium is always lower than expected
for proportional modifier sharing between both network formers. Rather,
the phosphate component is preferentially modified by the cations,
leading to the formation of P(1) units at high x values. Consequently, the local coordination of the cations
is dominated by phosphorus, as is clearly evident from the 23Na{31P} rotational echo double resonance (REDOR) results.
This preferred association, combined with the formation of P(1) units, results in partially clustered cation distributions, which
can be detected by 23Na spin echo decay spectroscopy. Finally,
the joint interpretation of all of the data from NMR, Raman, XPS,
and thermal analysis measurements offers indirect evidence for the
formation of higher germanium coordination states in this glass system.
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.
A novel synthetic route toward poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl) (PTMA) is described. The polymerization of alkoxyamine-based
monomers by atom transfer radical polymerization (ATRP) was investigated,
as the polyalkoxyamine serves as the precursor for PTMA. The polydispersity
indices (PDIs) and the kinetic data of the polymerization indicate
a controlled reaction. The oxidative C–O bond cleavages of
the polyalkoxyamine lead to PTMA. This transformation occurs with
excellent yields, and it is possible to transfer the narrow PDIs of
the prepolymer to PTMA. The material is characterized in detail using
cyclic voltammetry in solution and magnetic susceptibility measurements
as well as multinuclear solid state NMR and EPR spectroscopies. The
conversion of the precursor polymer to the polynitroxide can be conveniently
monitored by 1H and 19F magic-angle spinning
(MAS) as well as 13C{1H} cross-polarization
(CP)-MAS NMR. In addition, the intermolecular interaction of the nitroxide
side chain units in the polymer at high conversion can be detected
and monitored by the observation of pronounced low-frequency shifts.
2014Charge compensation in RE3+ (RE = Eu, Gd) and M+ (M = Li, Na, K) co-doped alkaline earth nanofluorides obtained by microwave reaction with reactive ionic liquids leading to improved optical properties Journal of Materials Chemistry C,Cambridge : Royal Society of Chemistry -RSC,v. 2, n. 44, p. 9439-9450, 2014 http://www.producao.usp.br/handle/BDPI/50592 (REDOR) studies, reveal distinct local fluoride environments, the populations of which are discussed in relation to spatial distribution and clustering models. In the co-doped samples, fluoride species having both Na + and La 3+ ions within their coordination sphere can be identified and quantified. This interplay of mono-and trivalent ions in the CaF 2 lattice appears to be an efficient charge compensation mechanism that allows for improved performance characteristics of such co-doped phosphor materials.
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