Electropholic Transition Metal Complexes: Catalysis of Isotope Exchange. April 1, 1992 - December 3, 1996. Final Report.

摘要

The central aim of this project is to exploit transition metal dihydrogen complexes to develop catalysts for isotope exchange reactions between hydrogen and substrates such as water. The authors have partially met this goal by the synthesis of novel cationic rhenium complexes of the form [Re(CO){sub 3}(PR{sub 3}){sub 2}(H{sub 2})]{sup +}. These complexes bind hydrogen somehwat more strongly than the neutral tungsten analogs but also activate the bound H{sub 2} to heterolytic cleavage. Thus rapid proton (deuteron) exchange between hydrogen and water can be achieved. An example of this reaction is the rapid formation of bound HD from the complex [Re(CO){sub 3}(PR{sub 3}){sub 2}(H{sub 2})]{sup +} and deuterium gas. Rapid incorporation of deuterium from D{sub 2}O has also been observed. In these systems, the competitive binding of water to the metal center is a drawback. The affinity of the Re center for water depends upon the nature of the phosphine ligands, with the presumably more electrophilic PPh{sub 3} complex binding water strongly and irreversibly, while the PCy{sub 3} complex binds water reversibly. These results have been published in J.Am.Chem.Soc 1994, 116, 4515 and J.Am.Chem.Soc 1997, 119, 4172.