Assembly of a Metalloporphyrin–Polyoxometalate Hybrid Material for Highly Efficient Activation of Molecular Oxygen

Organic metalloporphyrins
and inorganic polyoxometalates (POMs) are two kinds of efficient molecular
catalysts to prompt a variety of chemical reactions. They have been
used as active moieties for the synthesis of porous materials to realize
highly efficient heterogeneous catalysis. Both of them are regarded
as the organic/inorganic equivalent counterparts to complement the
individual features. Therefore, the combination of metalloporphyrins
and POMs in the same hybrid materials might generate interesting catalytic
properties by emerging their unique individual functions. To avoid
the random connections between metalloporphyrins, POMs, and lanthanide
connecting nodes, we have developed a “step-by-step”
aggregation strategy, including the reaction of POMs with metal ions
to bind metal nodes on the surfaces of POMs at the first step and
the reaction of the resulting POM derivatives with metalloporphyrin
linkers to result in hybrid materials at the second step. Catalytic
experiments demonstrate that the resulting hybrid material exhibits
interesting catalytic properties in the heterogeneous epoxidation
of olefins, in which the conversion, epoxide selectivity, turnover
number, and turnover frequency for the epoxidation of styrene to (1,2-epoxyethyl)­benzene
are >99%, 94%, 220000, and 22000 h–1, respectively.
These results demonstrate that the collaborative work of multiple
active sites in hybrid materials can achieve superior high efficiency
in heterogeneous catalysis.