Synthesis, Modeling, and Catalytic Properties of HY Zeolite-Supported Rhodium Dinitrosyl Complexes

HY zeolite-supported Rh(CO) 2 complexes were used as precursors for the surface-mediated synthesis of Rh(NO) 2 species. The results of FTIR, EXAFS, and mass spectrometry measurements, as well as DFT calculations, show that the replacement of the CO ligands in the Rh(CO) 2 complexes by NO is a facile substitution process which is not affected by the Si/Al ratio of the zeolite support used. The Rh(NO) 2 complexes thus formed are site-isolated 14-electron species with a Rh–N bond distance of 1.77 Å, a N–Rh–N angle of ∼104°, and NO ligands significantly deviating from a linear configuration (Rh–N–O angle ∼148°). These species exhibit a characteristic set of well-defined ν NO bands at 1855 and 1779 cm –1 in their FTIR spectra and have an additional empty d orbital at the rhodium center allowing for coordination of a third electron-donating ligand. Therefore, the Rh(NO) 2 species react with C 2 H 4 to form 16-electron Rh(NO) 2 (C 2 H 4 ) species which are stable in the presence of gas-phase C 2 H 4 and can be further converted into Rh(NO) 2 (C 2 H 5 ) complexes by addition of H 2 . The Rh(NO) 2 /HY30 material catalyzed both C 2 H 4 hydrogenation and dimerization reactions at room temperature with TOFs of 0.01 and 6.7 × 10 –3 s –1 at steady state, respectively. During these processes, the Rh sites remain monodispersed. An inverse kinetic isotope effect was observed for both reactions, thus underlining the similarities of the catalytic properties of the supported Rh(NO) 2 species examined and molecular organometallic Rh complexes in solution. This is a notable example demonstrating that Rh dinitrosyl complexes anchored on a solid support can catalyze hydrocarbon reactions.