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

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posted on 06.05.2015, 00:00 by Ivan Timokhin, Claudio Pettinari, Fabio Marchetti, Riccardo Pettinari, Francesca Condello, Simona Galli, Elisabete C. B. A. Alegria, Luísa M. D. R. S. Martins, Armando J. L. Pombeiro
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.