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.

将五种刚性或柔性双(吡唑酸根)基构筑单元与后过渡金属离子进行配位组装，成功得到18种配位聚合物(coordination polymers, CPs)。通过热分析表征可知，所有产物均具备优异的热稳定性，分解温度区间为340~500 ℃。经77 K下氮气吸附测试表征，其朗缪尔比表面积分布范围宽达135~1758 m²/g，与通过粉末X射线衍射结构解析方法得到的多孔或致密聚合物骨架一致。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作为催化剂，分别开展两项催化测试：(i) 以叔丁基过氧化氢(t-BuOOH)为氧化剂，实现无溶剂微波辅助醇类过氧化氧化反应；(ii) 以过氧化氢(H₂O₂)为氧化剂，在乙腈溶剂中实现环己烷过氧化氧化为环己醇与环己酮的反应。带有刚性间隔基且具备更高比表面积的配位聚合物，其催化活性优于对应柔性间隔基配位聚合物。此外，本次研究中的两款含铜(I)配位聚合物在两项测试反应中均展现出最优催化性能：在1-苯乙醇氧化反应中，目标产物选择性收率最高可达92%（转化数(TON)最高达1.5×10³）；在环己烷氧化反应中收率为11%，该数值高于当前工业工艺的对应水平。