Stereoselective epoxide polymerization

The vast majority of papers reporting stereoselective epoxide polymerization focus on isospecific propylene oxide polymerization. For clarity, this chapter is organized by the type of metal of the catalyst active center. The three most commonly used metals for discrete stereoselective epoxide polymerization catalysts are aluminum, zinc, and cobalt, and research using these metals forms the foundation of this chapter. 

Well-defined [A(,A( -bis(2-hydroxybenzylidene)-(lR,2/ )-l,2-cyclohexane diamine] (R-salcy) aluminum complexes (e.g.. Figure 24.1, 4) have been used as stereoselective epoxide polymerization catalysts. Polymerization of racemic propylene oxide in the presence of 5 mol% 4 yields 70% conversion to poly(propylene oxide) after 62 h. The remaining unreacted monomer exhibits an optical rotation of 4-1.85°, which corresponds to an ee of 15% (Scheme 24.7). The modest r-factor... 

Although significant advances in stereoselective epoxide polymerization have been achieved over the last half-century, few known catalysts are capable of excellent levels of stereocontrol. Historically, most catalysts for epoxide polymerization have been of the heterogeneous variety and have exhibited poor selectivity. It is our opinion that the most fertile area for future catalyst exploration involves homogeneous, discrete catalysts that are capable of involving multiple metal centers in the polymerization mechanism. If the spatial environment of the active catalyst is precisely controlled, new generations of stereoselective epoxide polymerization catalysts will become available. Our current research focuses on the search for such catalysts. 

A comprehensive review on the field of stereoselective epoxide polymerization is currently being prepared (Ajiro, H Allen, S. D. Coates, G. W., manuscript in preparation). 

Chapter 24 Discrete Catalysts for Stereoselective Epoxide Polymerization. 627... 

Many of the important contributors to the field of stereoselective epoxide polymerization have written accounts of their research " we have recently written a comprehensive review which forms the basis for this review. This chapter focuses on discrete catalysts for the stereoselective polymerization of racemic (chiral) and meso (prochiral) epoxides. Due to space limitations, catalysts bearing at least one ancillary ligand that... 

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