Oxidative Alkenylation of Arenes Using Supported Rh Materials: Evidence that Active Catalysts are Formed by Rh Leaching

摘要

This work focuses on the synthesis of supported Rh materials and study of their efficacy as pre-catalysts for the oxidative alkenylation of arenes. Rhodium particles supported on silica (Rh/SiO2; similar to 3.6 wt% Rh) and on nitrogen-doped carbon (Rh/NC; similar to 1.0 wt% Rh) are synthesized and tested. Heating mixtures of Rh/SiO2 or Rh/NC with benzene and ethylene or alpha-olefins and CuX2 {X=OPiv (trimethylacetate) or OHex (2-ethyl hexanoate)} to 150 degrees C results in the production of alkenyl arenes. When using Rh/SiO2 or Rh/NC as catalyst precursor, the conversion of benzene and propylene or toluene and 1-pentene yields a ratio of anti-Markovnikov to Markovnikov products that is nearly identical to the same ratios as the molecular catalyst precursor [Rh(mu-OAc)(eta(2)-C2H4)(2)](2). These results and other observations are consistent with the formation of active catalysts by leaching of soluble Rh from the supported Rh materials.