42961-B1
Catalyses Involving Immobilized 1,10-Phenanthroline Complexes: A Study of Internal Resin Effects
Research efforts during this year focused on two major problems: 1) continuing study of the bimolecular Heck reactions using polystyrene/divinylbenzene immobilized phenazine-palladium catalyst, and 2) development of a recyclable epoxidation catalyst. As noted in previous reports, immobilized phenazine-palladium acetate complexes are conveniently prepared on solid-phase supports and these materials accommodate a wide suite of polar and nonpolar spacer groups. Yield and selectivity data from the Heck coupling of naphthyl triflate and butylvinyl ether demonstrate that the catalytic properties of the palladium complex changes between Cycle 1 of the activated resin and all other cycles as compared to the homogenous catalytic system. For instance, the immobilized palladium complex built from 1,3-propanediol gives a 72%:28% ratio (internal standard method) of 1,1-alkene product to 1,2-alkene products (20%:8% geometric mixture). However, all subsequent cycles using the solid-phase catalyst gave mixtures nearly identical to the homogenous variant (91%:9%, 1,1-isomer:1,2-isomer). The undergraduate conducting these experiments designed an interesting set of thermal conditioning experiments and showed that a heating-cooling cycle for the immobilizing phenazine-palladium resin, followed by the standard catalytic recipe, gave selectivity data similar to the second cycle of all catalytic resins. Currently, we believe that the spatial or conformational environment of the catalyst changes during the heating of our resins, and as a result the catalytic performance changes. The research associate doing this work has expressed interest in chemical engineering as a career option, and this experience is relevant that exploration.
Based on our hypothesis that the spatial environment within the resin impacts catalytic performance more than polarity, we started a new area of investigation in which a Salophen-MnIII complex is immobilized in the presence of a chiral spacer. We developed a efficient resin preparation utilizing myrtenol as the spacer. After activation with Mn(OAc)2 and air oxidation, we found that the polystyrene/ divinylbenzene-Salophen ensemble catalyzes the epoxidation of mono-substituted alkenes, and that the resins maintain excellent catalytic activity through four cycles. This area of investigation will be the basis for future grant requests and publications.
