Photochemical Activation of C-H Bonds on a Rhodium Catalyst. Observation of a Competitive Effect on the Surface

Quaternary phosphonium polymer-supported dual-ionically bound [Rh(CO)I3]2– catalyst for heterogeneous ethanol carbonylation

“…8 shows two peaks at 2051 and 1986 cm -1 , assigned to the symmetric and asymmetric stretching vibration of the carbonyls as a decisive verification of the two Rh-CO bonds in [PPh3Et] + [Rh(CO)2I2] -. However, only one peak was observed at 2044 cm -1 in the IR spectra of Rh-TPISP, suggesting that the structure of the active Rh center contains only one Rh-CO bond [60][61][62][63], which is consistent with the proposed active site model of [Rh(CO)I3] 2-. As is commonly recognized, the carbonyl group acts as not only an σ-donor, but also as a strong π-acceptor, whereas the iodide anion (I -) can only act as a σ-donor, which suggests higher electron-donating ability of Ithan carbonyl.…”

Chemical Bond Activation on Surface Sites Generated Photochemically from RhI(CO)2Species

“…It was recently discovered that interesting chemical processes can occur by exposing the Rh I (CO) 2 /Al 2 O 3 species to ultraviolet light at low temperatures (<300 K). − 9a When irradiated, one of the CO ligands is ejected, creating a coordinatively unsaturated Rh site. This site is then capable of activating strong chemical bonds such as the C−H bond in alkanes, − which would not be activated thermally at these temperatures on the unphotolyzed Rh I (CO) 2 species.…”

“…It was recently discovered that interesting chemical processes can occur by exposing the Rh I (CO) 2 /Al 2 O 3 species to ultraviolet light at low temperatures (<300 K). − 9a When irradiated, one of the CO ligands is ejected, creating a coordinatively unsaturated Rh site. This site is then capable of activating strong chemical bonds such as the C−H bond in alkanes, − which would not be activated thermally at these temperatures on the unphotolyzed Rh I (CO) 2 species. This photochemically generated site has been used extensively to cause a variety of molecular bond-breaking processes to occur, including the activation of the H−H bond in hydrogen, the OO bond in O 2 , and the CO bond in CO 2 .…”

Nitrogen Chemisorption on the Coordinatively Unsaturated Rh Site on Al2O3

“…The ultraviolet photolysis of Rh I (CO) 2 species, supported on Al 2 O 3 (designated Rh I (CO) 2 /Al 2 O 3 ), produces an unstable and coordinatively unsaturated Rh(CO) intermediate which can activate the C−H bond in alkanes − and the H−H bond in hydrogen . The atomically-dispersed Rh I (CO) 2 supported on Al 2 O 3 is produced from disruption and oxidation of alumina-supported metallic Rh particles in a reaction with CO gas and surface hydroxyl groups. − A critical step for successful bond activation in alkanes and in H 2 is the temporary adsorption of the molecule on the photochemically-generated Rh(CO) centers.…”