Zirconium as catalysts

In a subsequent investigation, the products of the current invention were used with zirconium as catalyst co-components in the preparation of elastomeric copolymers of ethylene (4). 

In 1981 Bayer patented a process for the production of N.O-disubstituted carbamates (urethanes) by reacting primary aromatic amines with dialkylcarbonates in the presence of neutral or basic inorganic or organic compounds of lead, titanium, zinc or zirconium as catalysts. Table 5 summarises some of the most interesting examples reported. 

Schmid, M. A. Alt, H. G Mihus, W. Unbridged cyclopentadienyl-fluorenyl complexes of zirconium as catalysts for homogeneous olefin polymerization. J. Organomet. Chem. 1995, 501,101-106. 

The ROP of lactide in the presence of metal compounds of tin, aluminum, zinc, titanium or zirconium as catalysts proceeds via the coordination-insertion mechanism. The initiators in this type of reaction are usually metal alkoxides. In the first step, temporary coordination of lactide through the carbonyl group with the metal in the initiator leads to increased nucleophilicity of the alkoxide and electrophilicity of the carbonyl group, thereby facilitating the insertion of the monomer into the metal O bond. This is the most investigated and applied method for the synthesis of PLA due to the mild reaction conditions, since the reaction proceeds via covalent species. High molecular weights of 200000 g mol are easily achievable with minimum side reactions and racemization. 

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