Novel Coordination Polymers with (Pyrazolato)-Based Tectons: Catalytic Activity in the Peroxidative Oxidation of Alcohols and Cyclohexane

Coupling five rigid or flexible bis­(pyrazolato)-based
tectons with
late transition metal ions allowed us to isolate 18 coordination polymers
(CPs). As assessed by thermal analysis, all of them possess a remarkable
thermal stability, their decomposition temperatures lying in the range
of 340–500 °C. As demonstrated by N2 adsorption
measurements at 77 K, their Langmuir specific surface areas span the
rather vast range of 135–1758 m2/g, in agreement
with the porous or dense polymeric architectures retrieved by powder
X-ray diffraction structure solution methods. Two representative families
of CPs, built up with either rigid or flexible spacers, were tested
as catalysts in (i) the microwave-assisted solvent-free peroxidative
oxidation of alcohols by t-BuOOH, and (ii) the peroxidative
oxidation of cyclohexane to cyclohexanol and cyclohexanone by H2O2 in acetonitrile. Those CPs bearing the rigid
spacer, concurrently possessing higher specific surface areas, are
more active than the corresponding ones with the flexible spacer.
Moreover, the two copper­(I)-containing CPs investigated exhibit the
highest efficiency in both reactions, leading selectively to a maximum
product yield of 92% (and TON up to 1.5 × 103) in
the oxidation of 1-phenylethanol and of 11% in the oxidation of cyclohexane,
the latter value being higher than that granted by the current industrial
process.