Pincer-ligated iridium complexes of the form [Ir(^R4PCP)L] (^R4PCP = κ³-C₆H₃-2,6-(XPR₂)₂; X = CH₂, O; R = tBu, iPr) are efficient homogeneous alkane dehydrogenation catalysts that have been reported to be highly active at temperatures of 240 °C or below. In this work, silica-supported [Ir(C₂H₄)(p-^tBu₂PO-^tBu4POCOP)] (1/SiO₂) was used to study a model continuous-flow gas-phase acceptorless alkane dehydrogenation system. This particular supported framework is thermally stable at temperatures up to 340 °C, 100 °C above the highest temperature at which analogous homogeneous complexes have been reported to show stable activity, with observed butane dehydrogenation rates of ca. 80 mol_butenes mol_cat.^–1 h^–1. Solid-state ³¹P MAS NMR and ATR IR are used to demonstrate that the backbone pincer ligand remains intact and coordinated at 340 °C. The complex is fully converted to [Ir(CO)(p-^tBu₂PO-^tBu4POCOP)] (3/SiO₂) above 300 °C. 3/SiO₂ is observed to be catalytically active at the higher temperatures tested, and reaction rates are comparable to those of 1/SiO₂. 3/SiO₂ and 1/SiO₂ act as resting states for the active 14-electron fragment, through dissociation of the CO or olefin ligand, respectively. Given that 3/SiO₂ is air resistant at ambient temperature and is structurally stable and catalytically active at elevated temperatures, it is a suitable candidate as a catalyst for the highly endothermic acceptorless dehydrogenation of alkanes.

中文翻译：

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负载钳式铱催化剂在高温下连续流烷烃脱氢

形式的[Ir（的钳连接的铱络合物^R4 PCP）L]（^R4 PCP =κ ³ -C ₆ ħ ₃ -2,6-（XPR ₂）₂ ; X = CH ₂，O; R =吨卜，i Pr）是有效的均相烷烃脱氢催化剂，据报道在240°C或更低的温度下具有很高的活性。在这项工作中，二氧化硅负载的[Ir（C ₂ H ^ ₄）（p -^吨卜₂ PO-^吨BU4 POCOP）]（1 /的SiO ₂）用于研究模型连续流气相无受体烷烃脱氢系统。该特定的支撑构架在高达340°C的温度下是热稳定的，比据报道类似的均相配合物显示出稳定的活性的最高温度高100°C，观察到的丁烷脱氢速率约为。80 mol_丁烯mol _cat。^–1小时^–1。固态³¹ P MAS NMR和ATR IR用于证明主链钳配体在340°C下保持完整并配位。该复合物完全转化成物[Ir（CO）（p -^吨卜₂ PO-^吨BU4 POCOP）]（3 /二氧化硅₂）高于300°C。观察到3 / SiO ₂在所测试的较高温度下具有催化活性，并且反应速率与1 / SiO ₂相当。3 / SiO ₂和1 / SiO ₂分别通过CO或烯烃配体的解离作用作为活性14电子片段的静止状态。考虑到3 / SiO ₂在环境温度下是耐空气的，并且在高温下结构稳定并且具有催化活性，因此它是烷烃高度吸热的无受体脱氢的催化剂的合适候选者。