Rhodium catalysts bound to functionalized mesoporous silica

Phosphine and amine functionalized mesoporous silica materials were metallated with Rh(CO)₂(i-Pr₂NH)Cl or Rh₂(CO)₄Cl₂, respectively, to yield catalysts containing the Rh(PPh₂R)₂(CO)Cl or Rh(CO)₂(NH₂R)Cl, where R is a propyl chain bonded to the silica surface, reactive centers. In order to ascertain the effect of pore size on rates of hydroformylation catalysis both 35 and 45 Å pore size materials were used. Using the hydroformylation of octene as a reference reaction, the phosphine based, 45 Å catalysts were 1.5-1.3 times faster than the amine based, 45 Å catalysts, and the 45 Å materials were 2.6-2.1 times faster than the 35 Å materials. The orientation of the catalyst relative to the functionalized surface, and the steric environment around the catalyst active site appear to be significant in determining rate of reaction. The ability of the surface bound phosphine catalysts to affect hydroformylation was strongly influenced by the steric constraints of the substrate. Terminal alkenes were readily hydroformylated and norbornene was slowly hydroformylated, but pinene, trans-cyclododecene, cyclohexene and cholesterol were nonreactive to the catalytic center.