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.

将五种刚性或柔性的双(吡唑酸根)基构筑单元与后过渡金属离子进行偶联组装，我们成功分离得到18种配位聚合物(Coordination Polymers, CPs)。通过热分析表征发现，所有产物均具有优异的热稳定性，其分解温度区间为340~500 ℃。77 K下的氮气吸附测试结果表明，这些配位聚合物的朗缪尔比表面积分布范围极广，达135~1758 m²/g，这与通过粉末X射线衍射结构解析法得到的多孔或致密聚合物骨架结构相符。我们选取两类分别由刚性间隔基与柔性间隔基构筑的代表性配位聚合物家族作为催化剂，开展了两项催化测试：其一为以叔丁基过氧化氢(t-BuOOH)为氧化剂的微波辅助无溶剂醇类过氧化氧化反应；其二为以过氧化氢(H₂O₂)为氧化剂、乙腈为溶剂的环己烷过氧化氧化制备环己醇与环己酮的反应。带有刚性间隔基且比表面积更高的配位聚合物，其催化活性优于对应柔性间隔基的配位聚合物。此外，所研究的两种含铜(I)的配位聚合物在两项反应中均展现出最优的催化效率：在1-苯乙醇的氧化反应中，目标产物的最大选择性收率可达92%，转化数(Turnover Number, TON)最高达1.5×10³；在环己烷氧化反应中，产物收率可达11%，该数值优于当前工业工艺的对应指标。