Vanadium-containing silicate MCM-41 (V-MCM-41) zeolite and
aluminophosphate AFI (VAPO-5) zeolite
were synthesized and characterized by spectroscopic techniques. In
as-synthesized form, the vanadyl ions
(VIVO)2+ were found to be the major
vanadium species in the form of atomic dispersion on AFI by
EPR
and to exist simultaneously with tetrahedral
(T
d) V5+ in MCM-41 by UV−vis.
29Si MAS NMR investigations
suggested that the vanadium ions might attach to MCM-41 through
interaction with the silanol groups on the
internal wall of hexagonal tubes. The V5+ (in
T
d) ions are incorporated into the lattice of
MCM-41 during
synthesis, while the VO2+ (in T
d)
is the loosely bound V species. The results of Raman spectroscopy
indicated
that the rodlike aggregation of cationic surfactant
(cetyltrimethylammonium bromide, CTAB) was encapsulated
in the intrachannel space of synthetic MCM-41 as in an aqueous
solution. After calcination and hydration,
the V4+ species in as-synthesized V-MCM-41 was totally
oxidized to +5 as shown by UV−vis and EPR
spectroscopies, and they further aggregated as two-dimensional vanadate
chain species that were nonuniformly
deposited on the wall of MCM-41 channels as verified by Raman and HREM
with EDS spectroscopies,
while the V5+ species of synthetic V-MCM-41 remains
stable in a tetrahedral coordination. Comparatively,
two types of VO2+ ions were observed in as-synthesized
VAPO-5 by EPR and they could be oxidized by
calcination treatment. The presence of water vapor facilitates the
oxidation of (VIVO)2+ and the
formation
of V2O5 cluster instead of isolated
(VVO)3+ species.
TpRuPPh 3 (CH 3 CN) 2 PF 6 (3 mol %) was very active in catalytic benzannulation of 1-phenyl-2-ethynylbenzenes in dichloroethane (60 °C, 36 h) to afford phenanthrene in 95% yield. This method is applicable to the synthesis of various polycyclic aromatic hydrocarbons via two-and four-fold benzannulations, including various substituted coronene derivatives (53-86% yields) using this catalyst at a moderate loading (10 mol %).
Triple rounds: A regioselective hydrative cyclization of triynes has been developed to give bicyclic β‐hydroxy spiro ketones, which undergo subsequent dehydration to give the β,γ‐unsaturated ketones (see scheme). Model reactions suggest that this platinum catalysis includes two selective hydrations, an alkyne insertion, and an aldol condensation.
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