Electrophilic Organoiridium(III) Pincer Complexes on Sulfated Zirconia for Hydrocarbon Activation and Functionalization

Single-site supported organometallic catalysts bring together the favorable aspects of homogeneous and heterogeneous catalysis while offering opportunities to investigate the impact of metal–support interactions on reactivity. We report a (dmPhebox)­Ir­(III) (dmPhebox = 2,6-bis­(4,4-dimethyloxazolinyl)-3,5-dimethylphenyl) complex chemisorbed on sulfated zirconia, the molecular precursor for which was previously applied to hydrocarbon functionalization. Spectroscopic methods such as diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS), dynamic nuclear polarization (DNP)-enhanced solid-state nuclear magnetic resonance (SSNMR) spectroscopy, and X-ray absorption spectroscopy (XAS) were used to characterize the supported species. Tetrabutylammonium acetate was found to remove the organometallic species from the surface, enabling solution-phase analytical techniques in conjunction with traditional surface methods. Cationic character was imparted to the iridium center by its grafting onto sulfated zirconia, imbuing high levels of activity in electrophilic C–H bond functionalization reactions such as the stoichiometric dehydrogenation of alkanes, with density functional theory (DFT) calculations showing a lower barrier for β-H elimination. Catalytic hydrogenation of olefins was also facilitated by the sulfated zirconia-supported (dmPhebox)­Ir­(III) complex, while the homologous complex on silica was inactive under comparable conditions.单一位点负载型有机金属催化剂兼具均相催化与多相催化的双重优势，同时为研究金属-载体相互作用对反应活性的影响提供了理想平台。本研究报道了一种负载于硫酸化氧化锆（sulfated zirconia）上的(dmPhebox)Ir(III)配合物，其中dmPhebox为2,6-双(4,4-二甲基恶唑啉基)-3,5-二甲基苯基；该配合物的分子前驱体此前已被应用于烃类官能化反应。研究采用漫反射红外傅里叶变换光谱（DRIFTS）、动态核极化（DNP）增强固态核磁共振（SSNMR）光谱以及X射线吸收光谱（XAS）等多种光谱手段对该负载型物种进行了表征。实验发现，四丁基醋酸铵可将该有机金属物种从载体表面脱附，从而可结合传统表面表征方法，使用溶液相分析技术开展后续分析。铱中心通过接枝到硫酸化氧化锆表面而被赋予阳离子特性，使其在亲电C-H键官能化反应（如烷烃的化学计量脱氢反应）中表现出极高的催化活性；密度泛函理论（DFT）计算表明，该反应的β-H消除能垒显著降低。硫酸化氧化锆负载的(dmPhebox)Ir(III)配合物同样可高效催化烯烃加氢反应，而在相同反应条件下，二氧化硅负载的同系配合物则无催化活性。