Trispyrazolylborate ligands as ancillary ligands in the development of single-site metal alkoxide catalysts for ring-opening polymerization of cyclic esters

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• 作者：Malcolm H. Chisholm
• 关键词：Pyrazolylborate ; Calcium ; Magnesium ; Zinc alkoxide
• 刊名：Inorganica Chimica Acta
• 出版年：2009
• 出版时间：15 September 2009
• 年：2009
• 卷：362
• 期：12
• 页码：4284-4290
• 全文大小：940 K

文摘

The development of a new class of single-site metal alkoxide catalysts employing trispyrazolyl ligands is described where the metal ions are Mg(2+), Zn(2+) and Ca(2+). A particularly promising ligand for the kinetically labile Ca(2+) ion is tris[3(-2-methoxy-1,1-dimethylpyrazolyl)] hydroborate, Tp^C*. This ligand is capable of being extremely flexible in its coordination modes and its coordination with various group 1 and 2 metal ions is described. The complexes Tp^C*MI exist as salts [Tp^C*M]⁺I⁻, where M = Mg and Ca, but Tp^C*ZnI contains a four coordinate Zn(2+) center. The complexes Tp^C*CaN(SiMe₃)₂ and Tp^C*CaOC₆H₄-p-Me contain 5 and 7 coordinate Ca(2+) ions and serve as initiators for the ring-opening polymerization of lactide and ε-caprolactone. The compounds [Tp^C*M]⁺[Tp^C*]⁻, where M = Mg and Ca, exist as salts in the solid-state and in solution show exchange between coordinated and free Tp^C* ligands as determined by NMR spectroscopy.