Polymer-induced catalyst activity modification

Abstract

Insoluble polymers were shown to be capable of modifying catalyst activity when used as a support either for a transition metal catalyst or a ligand absorbing reagent. Polymer-bound Cp(,2)TiCl(,2) reduced by Grignard reagents catalyzed isomerization of terminal alkenes to E- and Z-2-alkenes. Both Grignard and organolithium reagents generated alkene hydrogenation catalysts from PS-Cp(,2)TiCl(,2) although the activity of these catalysts was less than homogeneous systems employing Cp(,2)TiCl(,2) and the reducing agent. Polymer-bound Cp(,2)ZrCl(,2) treated wit organolithium, Grignard, or hydride reducing reagents did not hydrometallate alkenes. The complex also displayed no hydrogenation activity. Silver(I) polystyrene sulfonate, PS-SO(,3)Ag, increased the hydrogenation rate of some alkenes in reactions catalyzed by RhCl(PPh(,3))(,3), RuCl(,2)(PPh(,3))(,3), and RuHCl(PPh(,3))(,3). Its ability to absorb dissociated PPh(,3) or HCl is the source of the activity enhancement. Addition of PS-SO(,3)Ag to hydroformylation reactions of 1-hexene catalyzed by RhHCO(PPh(,3))(,3) was detrimental in terms of rate and product yield. In this case it was suggested that PS-SO(,3)Ag absorbed a second mole of PPh(,3) which was necessary in the catalytic cycle. Hydrosilation of 1-hexene catalyzed by RhCl(PPh(,3))(,3) was not accelerated by addition of PS-SO(,3)Ag, even when ethylene pretreatment was used successfully in hydrogenations also catalyzed by RhCl(PPh(,3))(,3) was employed. PS-SO(,3)Ag did cause a change in product distribution causing the formation of more 12 than 11 (pg 134). In reactions run without PS-SO(,3)Ag more 11 is produced than 12. Triphenylphosphine added to hydrosilation reactions did not inhibit the reaction as in the hydrogenations. The lack of rate retardation caused by added PPh(,3) explains why removal of this ligand by PS-SO(,3)Ag did not accelerate hydrosilation reactions.