Mechanism of the alternating copolymerization of epoxides and CO2 using β-diiminate zinc catalysts:: Evidence for a bimetallic epoxide enchainment

被引:441
作者
Moore, DR [1 ]
Cheng, M [1 ]
Lobkovsky, EB [1 ]
Coates, GW [1 ]
机构
[1] Cornell Univ, Baker Lab, Dept Chem & Biol Chem, Ithaca, NY 14853 USA
关键词
D O I
10.1021/ja030085e
中图分类号
O6 [化学];
学科分类号
0703 ;
摘要
A series of zinc beta-diiminate (BDI) complexes and their solid-state structures, solution dynamics, and copolymerization behavior with CO2 and cyclohexene oxide (CHO) are reported. Stoichiometric reactions of the copolymerization initiation steps show that zinc alkoxide and bis(trimethylsilyl)amido complexes insert CO2, whereas zinc acetates react with CHO. [(BDl-2)ZnOMe](2) [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] and (BDI-1)(ZnOPr)-Pr-i [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] react with CO2 to form [(BDI-2)Zn(mu-OMe) (mu,eta(2)-O2COMe)Zn(BDI-2)] and [(BDI-1)Zn(mu-eta(2)-(O2COPr)-Pr-i)](2), respectively. (BDI-2)ZnN(SiMe3)(2) inserts CO2 and eliminates trimethylsilyl isocyanate to give [(BDI-2)Zn(mu-OSiMe3)](2). [(BDI-7)Zn(mu-OAc)](2) [(BDI-7) = 3-cyano-2-((2,6-diethylphenyl) amido)-4-((2,6-diethylphenyl)imino)-2-pentene) reacts with 1.0 equiv of CHO to yield [(BDI-7)Zn(mu,eta(2)-OAc)-(mu,eta(1)-OCyOAc)Zn(BDI-7)]. Under typical polymerization conditions, rate studies on the copolymerization exhibit no dependence in [CO2], a first-order dependence in [CHO], and orders in [Zn]tot ranging from 1.0 to 1.8 for [(BDI)ZnOAc] complexes. The copolymerizations of CHO (1.98 M in toluene) and 300 Psi CO2 at 50 degreesC using [(BDI-1)ZnOAc] and [(BDI-2)ZnOAc] show orders in [Zn](tot) of 1.73 +/- 0.06 and 1.02 +/- 0.03, respectively. We propose that two zinc complexes are involved in the transition state of the epoxide ring-opening event.
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收藏
页码:11911 / 11924
页数:14
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