A mixed-valence oxotrimer metal–organic framework (MOF), Ni-MIL-127, with a fully coordinated nickel atom and two iron atoms in the inorganic node, generates a missing linker defect upon thermal treatment in helium (>473 K) to engender an open coordination site on nickel which catalyzes propylene oligomerization devoid of any cocatalysts or initiators. This catalyst is stable for ∼20 h on stream at 500 kPa and 473 K, unprecedented for this chemistry. The number of missing linkers on synthesized and activated Ni-MIL-127 MOFs is quantified using temperature-programmed oxidation, ¹H nuclear magnetic resonance spectroscopy, and X-ray absorption spectroscopy to be ∼0.7 missing linkers per nickel; thus, a majority of Ni species in the MOF framework catalyze propylene oligomerization. In situ NO titrations under reaction conditions enumerate ∼62% of the nickel atoms as catalytically relevant to validate the defect density upon thermal treatment. Propylene oligomerization rates on Ni-MIL-127 measured at steady state have activation energies of 55–67 kJ mol^–1 from 448 to 493 K and are first-order in propylene pressures from 5 to 550 kPa. Density functional theory calculations on cluster models of Ni-MIL-127 are employed to validate the plausibility of the missing linker defect and the Cossee–Arlman mechanism for propylene oligomerization through comparisons between apparent activation energies from steady-state kinetics and computation. This study illustrates how MOF precatalysts engender defective Ni species which exhibit reactivity and stability characteristics that are distinct and can be engineered to improve catalytic activity for olefin oligomerization.

中文翻译：

---

用于丙烯低聚催化的 MIL-127 MOF 中骨架镍物种的结构和位点演化

混合价氧代三聚体金属有机骨架 (MOF) Ni-MIL-127 在无机节点中具有完全配位的镍原子和两个铁原子，在氦气 (>473 K) 中进行热处理时会产生缺失的接头缺陷在镍上产生一个开放的配位点，在没有任何助催化剂或引发剂的情况下催化丙烯齐聚。这种催化剂在 500 kPa 和 473 K 下可稳定运行约 20 小时，这对于这种化学来说是前所未有的。使用程序升温氧化对合成和活化的 Ni-MIL-127 MOF 上缺失的接头数量进行量化，¹H 核磁共振光谱和 X 射线吸收光谱为每镍约 0.7 个缺失接头；因此，MOF 框架中的大多数 Ni 物种催化丙烯齐聚。反应条件下的原位 NO 滴定枚举了约 62% 的镍原子与催化相关，以验证热处理时的缺陷密度。^{在稳态下测得的 Ni-MIL-127 上的丙烯低聚速率具有 55–67 kJ mol –1}的活化能从 448 到 493 K，在 5 到 550 kPa 的丙烯压力中是一级的。通过对 Ni-MIL-127 簇模型的密度泛函理论计算，通过比较稳态动力学和计算的表观活化能，验证缺失接头缺陷和丙烯齐聚的 Cossee-Arlman 机制的合理性。这项研究说明了 MOF 预催化剂如何产生有缺陷的 Ni 物质，这些物质表现出独特的反应性和稳定性特征，并且可以通过设计来提高烯烃低聚反应的催化活性。