The catalytic properties of poly(4-vinylpyridine) bound Rh(I) complex for carbonylation of methanol to acetic acid

Polymer-immobilized Rh(I) complexes were prepared by the reaction of poly(4-vinylpyridine) (PVPy), poly(1-methyl-4-vinylpyridium iodide) (PVPyMe+ I-) and copoly (4-vinylpyridine/1-methyl-4-vinylpyridium iodide) [P(VPy-VPyMe+ I-)] with Rh-2(CO)(4)Cl-2, and their catalytic behaviors for the carbonylation of methanal to acetic acid with CH3I as unique promotor was investigated. The IR studies of the catalysts indicated that the different active species produced by means of different bonding states between Rh(I) complex ions and functional groups in the above polymeric chains demonstrated a remarkable influence on the catalytic reactivities. The chelate-type catalyst with the double coordinations of two free base pyridine ligand groups to cis-dicarbonyl rhodium, Rh(I)/PVPy, exhibited apparently a lower catalytic reactivity, while the ionically hound catalyst Rh(I)/PVPyMe+ I- and the hetero-bound catalyst Rh(I)/P(VPy-VPyMe+ I-) were revealed to be of higher catalytic activities and selectivities under the same reaction conditions. in particular, the catalyst Rh(I)/P(VPy-VPyMe+ I-) had the best rate enhancement for the catalytic carbonylation because of the formation of a five-coordinate intermediate which had a better nucleophilicity towards methyl iodide, and was found to be more active and favorable to the oxidative addition of the later.