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Activation of Carbon Chlorine Bonds Using Palladium (II) Catalysts Briana Goddard and Derk A. Wierda Saint Anselm College, Department of Chemistry Abstract Chlorophenylbis(tricyclohexylphosphine)palladium(II) showed catalytic activity capable of activating carbon chlorine bonds in chlorobenzene, metadichlorobenzene, 2,4-dichlorotoluene and possibly chloropentane. Chloro(pchlorophenyl)bis(tricyclohexylphosphine)palladium(II) showed catalytic activity with chlorobenzene, but not with para-dichlorobezene or with metadichlorobenzene. Results and Discussion GC/MS Chromatogram for Catalyst (2) in Chlorobenzene The catalytic activity of both (1) and (2) were tested in the presence of various monochlorinated and dichlorinated species. The base triethylamine was used to trap the hydrochloric acid generated and precipitated out of solution. The resulting solutions were analyzed using gas chromatography and mass spectroscopy. As expected, (1) was active with chlorobenzene, and yielded benzene. Before the Reaction Chlorophenylbis(tricyclohexyl phosphine)palladium(II) (1) Chloro(p-chlorophenyl)bis (tricyclohexylphosphine)palladium(II) (2) When in the presence of para-dichlorobenzene and ortho-dichlorobenzene, the catalyst was inactive. However, when in solution with meta-dichlorobenzene the reaction produced both benzene and chlorobenzene. Toluene Chlorobenzene Triethylamine Introduction Polychlorinated Biphenyls (PCBs) are stable molecules with high boiling points and electrical insulating properties. Due to these characteristics, they were used in various industrial equipment, including transformers, capacitors, and hydraulic systems. However, PCBs also have many adverse health affects, including carcinogenic properties. In order to safely dispose of these chemicals, the inert carbon chlorine bond must be activated. (1) was also tested with 2,4-dichlorotoluene, generating chlorotoluene and probably toluene, but the results were obscured by the solvent peak. In order to test whether (1) could activate chlorinated molecules that are not aromatic, chloropentane was used. The results showed evidence of a reaction, but were inconclusive. After the Reaction (2) was active in chlorobenzene, producing benzene. In the presence of paradichlorobenzene and meta-dichlorobenzene, no benzene was produced. In both reactions hydrogen gas was consumed, and a solid was produced, but no benzene was detected. It is possible that the para-dichlorobenzene and metadichlorobenzene were causing the polymerization of the phenyl groups. Toluene Benzene In the past there has been success activating carbon chlorine bonds with transition metals complexes. Nickel and platinum have been used, but palladium seems to be the most reactive. The reaction of Pd(DBA)3 and 2PR3 creates phosphine complexes containing Pd(0). PR3 can be PCy3, PCy2Ph, PBz3, or Pmtolyl3. Chlorobenzene and dichloromethane been activated using some of these phosphine complexes in an oxidative addition reaction. When pressurized under hydrogen the catalyst chlorophenylbis(tricyclohexylphosphine)palladium(II) undergoes a reductive elimination reaction, yielding the active complex bis(tricyclohexylphosphine)palladium(0), as well as benzene and hydrochloric acid. The active species can then react again with chlorobenzene in an oxidative addition reaction, regenerating the catalyst. A base must be present in the reaction to trap the hydrochloric acid and prevent it from reacting with the active catalyst. References Huser, M.; Youinou, M.; Osborn, J. A. Chlorocarbon Activaton: Catalytic Carbonylation of Dichloromethane and Chlorobenzene. Angew. Chem. Int. Ed. Engl. 1989, 28.1386-1388 Results using Catalyst (1) Chlorobenzene Results using Catalyst (2) Acetone Conclusion Standard Conditions Solvent Toluene Base Pressure Triethylamine Began at 57 psi, and dropped as the reaction proceeded Time At least 8 hours Temperature Room temperature Concentration The reactant was in a 50:1 mole ratio with the catalyst Chlorophenylbis(tricyclohexylphosphine)palladium(II) underwent a reductive elimination reaction to yield the fourteen valence electron reactive species bis(tricyclohexylphosine)palladium(0), which readily participated in oxidative addition reactions to activate carbon chlorine bonds. Catalyst (1) can activate both monochlorinated and dichlorinated species. Chloro(pchlorophenyl)bis(tricyclohexylphosphine)palladium(II) also exhibited catalytic activity, but was far less reactive than catalyst (1). Catalyst (2) has not yet activated a dichlorinated molecule, but was successful in yielding benzene from chlorobenzene.