Investigations on the use of main group metal complexes of salen ligands as catalysts for the copolymerization of CO2 and epoxides

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Title: Investigations on the use of main group metal complexes of salen ligands as catalysts for the copolymerization of CO2 and epoxides
Author: Billodeaux, Damon Ray
Abstract: Current industrial processes for the production of polycarbonates , a thermoplastic valued for commercial applications , leave much to be desired from an environmental viewpoint . Research into alternative methods for production of polycarbonates has focused on the copolymerization of carbon dioxide and epoxides for the benefits of eliminating phosgene as a reagent , and for the economic impact of incorporating CO2 as a low cost C1 feedstock . Early work in this field focused on the use of zinc -derived catalysts , but recent studies indicate that chromium complexes of the salen (N ,N -bis - (salicylidene ) -1 ,2 -ethylene diimine ) family of ligands are far superior to the zinc complexes in terms of reactivity and diminishing the formation of unwanted byproducts . Concomitant to the studies of chromium salen complexes , investigations of main -group salen metal complexes were carried out . Aluminum complexes were able to produce polycarbonate in the presence of tetrabutyl ammonium salts and neutral Lewis bases . Gallium complexes were essentially inactive for generating any product . Tin (IV ) complexes were active for the production of polyether , the result of homopolymerization of epoxide without CO2 insertion . Tin (II ) complexes generated the monomeric cyclic carbonate product but no copolymer . An additional aspect of research relative to this field of study is the development of polymeric materials from several different epoxide monomers . The complex [hydrotris (3 -phenyl -pyrazol -1 -yl )borate]Cd (II ) acetate was used to study the thermodynamics of the binding of a series of potential epoxide monomers to a metal center via 113Cd NMR . Activation of the epoxide by a metal center was found to not play a significant role in the ability of the complex to be subsequently ring -opened for polymerization . A final relevant area of study involved the synthesis of cadmium analogues of Fe /Zn double metal cyanide (DMC ) complexes . Heterogeneous DMCs are well known in patent literature as excellent catalysts for the production of polycarbonates and cyclic carbonates from CO2 and epoxides . Previous studies on homogeneous Fe /Zn DMCs have only provided cyclic carbonate . Cd analogues of these species provide a convenient NMR handle for studies on the activity of the metal centers in presence of an epoxide and by changes to the DMC structure .
URI: http : / /hdl .handle .net /1969 .1 /2425
Date: 2005-08-29

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Investigations on the use of main group metal complexes of salen ligands as catalysts for the copolymerization of CO2 and epoxides. Available electronically from http : / /hdl .handle .net /1969 .1 /2425 .

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