Metal Complexes Catalyzed Cyclization with CO2

This chapter describes in general terms the catalytic methodology that has been made available for the use of carbon dioxide (CO2) in cyclization reactions that incorporate an intact CO2 fragment without changing the formal oxidation state of the carbon center. The major focus of this chapter will be on the most successful organometallic/inorganic complexes that have been used as catalyst systems throughout the last decade and the preferred ligand frameworks leading to elevated reactivity and/or selectivity behavior in CO2 coupling reactions. Attention will be especially given to homogeneous catalyst systems as they have proven to be more versatile in CO2 conversion catalysis and often have modular characteristics that allow for optimization of structure-activity relationships. The most important reactions that have been studied in the current context are designated CO2 "addition" reactions to small molecule heterocycles such as epoxides and aziridines, though more recently other coupling partners such as diamines, dialcohols, and amino nitriles have further advanced the use of CO2 in organic synthesis providing access to a wider range of structures. This chapter will serve to demonstrate the utility of CO2 as a carbon reagent in the catalytic formation of the most prominent organic structures using cyclization strategies specifically.