A Site-Isolated Iridium Diethylene Complex Supported on Highly Dealuminated Y Zeolite:  Synthesis and Characterization

Highly dealuminated Y zeolite-supported mononuclear iridium complexes with reactive ethylene ligands were synthesized by chemisorption of Ir(C₂H₄)₂(C₅H₇O₂). The resultant structure and its treatment in He, CO, ethylene, and H₂ were investigated with infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopies. The IR spectra show that Ir(C₂H₄)₂(C₅H₇O₂) reacted readily with surface OH groups of the zeolite, leading to the removal of C₅H₇O₂ ligands and the formation of supported mononuclear iridium complexes, confirmed by the lack of Ir−Ir contributions in the EXAFS spectra. The EXAFS data show that each Ir atom was bonded to four carbon atoms at an average distance of 2.10 Å, consistent with the presence of two ethylene ligands per Ir atom and in agreement with the IR spectra indicating π-bonded ethylene ligands. The EXAFS data also indicate that each Ir atom was bonded to two oxygen atoms of the zeolite at a distance of 2.15 Å. The supported iridium−ethylene complex reacted with H₂ to give ethane, and it also catalyzed ethylene hydrogenation at atmospheric pressure and 294 K. Treatment of the sample in CO led to the formation of Ir(CO)₂ complexes bonded to the zeolite. The sharpness of the υ_CO bands indicates a high degree of uniformity of these complexes on the support. The iridium−ethylene complex on the crystalline zeolite support is inferred to be one of the most nearly uniform supported metal complex catalysts. The results indicate that it is isostructural with a previously reported rhodium complex on the same zeolite; thus, the results are a start to a family of analogous, structurally well-defined supported metal complex catalysts.