Polymer-Bound Rhodium Hydroformylation Catalysts

摘要

A survey of the applicability of bulky phosphite modified rhodiumhydroformylation catalysts in polymer bound catalyst systems is presented. To get more insight into the catalytic cycle of this class of catalysts, a mechanistic study was carried out on the low molecular weight homogeneous tri (2-t-butylphenyl) phosphite rhodium hydroformylation catalyst. Using the information gained by this study a bulky phosphite was designed and attached to a polymer chain. The copolymer chain used to bind the ligands of the catalyst appeared to be formed by an ideally azeotropic copolymerization. This means that the ligands are perfectly randomly distributed along and among the polymer chains. This facilitates the study of the polymer bound catalyst, for the mean inter ligand distance can directly be related to the polymer chain loading. The bulky phosphite ligand used yielded active catalysts and no decrease of activity was observed when the catalyst was attached to the polymer chain, but the coordination constant of the ligand for rhodium was too low for application of this system in continuous flow reactors. A slightly smaller phosphite, which forms bis-phosphite rhodium complexes, was used in the proceeding studies. A closer examination of the influence of the polymer chain in the complex formation and activity of the copolymer bound catalyst was performed. Especially the dependency of the complex formation on the chain loading alpha (phosphite comonomer fraction) is studied. An X-ray study of the low molecular weight bis-phosphite rhodium complex was performed and proved to be of great help in understanding the sterical conformation of low molecular weight as well as polymer bound rhodium phosphite complexes. The polymer bound catalyst was grafted on an inert silica sphere. The so formed silica grafted polymer bound catalyst system was successfully used in a continuous flow reactor for the hydroformylation of styrene.