Dual-Chain Polymerization at an Early Transition-Metal Single-Site Catalyst
Dual-Chain Polymerization at an Early Transition-Metal Single-Site Catalyst
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DOI：
10.1021/acscatal.2c01240
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发表时间：
2022-08
期刊：
影响因子：
12.9
通讯作者：
T. McDaniel;N. E. Smith;Eric S. Cueny;C. Landis
中科院分区：
文献类型：
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作者：
T. McDaniel;N. E. Smith;Eric S. Cueny;C. Landis
铪配合物（NoctNdipp）Hf（Me）3（1，NoctNdipp= N-辛基-N′-（2，6-二异丙基苯基）-1，4-二氮杂-2，3，3-三甲基-1-丁烯）含有一个双齿的亚氨基苯胺配体。该络合物通过铵布朗斯台德酸[HN（Me）（C18 H37）2][B（C6 F5）4]进行质子分解，以产生胜任的烯烃聚合预催化剂[（NoctNdipp）Hf（Me）2（N（Me）（C18 H37）2）][B（C6 F5）4]（2）。与大多数烯烃聚合预催化剂不同，2含有两个Hf-Me基团，其具有同时引发和增长两个聚合物链的潜力。在这里，我们证明，2确实增长两个聚合物链在每个铪中心。早期过渡金属催化剂的其他不寻常的特征包括：（1）数均聚合物摩尔质量（Mn）与单体浓度无关;（2）聚合过程中单体浓度与时间的线性关系曲线表明速率对单体浓度的明显零级依赖性;（3）稳态聚合速率与单体初始浓度的表观一级关系。虽然相对于单体浓度的饱和行为是常见的后过渡金属衍生的催化剂，增长率的法律，前过渡金属络合物压倒性地是一阶的单体浓度。基于操作核磁共振动力学、端基分析、发色团猝灭标记的活性位点计数、碘猝灭研究和凝胶渗透色谱，我们提出了1-辛烯与2聚合的统一动力学和机理模型。
The hafnium complex (NoctNdipp)Hf(Me)3(1, NoctNdipp=N-octyl-N′-(2,6-diisopropylphenyl)-1,4-diaza-2,3,3-trimethyl-1-butene) contains a bidentate imino-anilido ligand. This complex undergoes protonolysis by the ammonium Brønsted acid [HN(Me)(C18H37)2][B(C6F5)4] to produce a competent alkene polymerization precatalyst, [(NoctNdipp)Hf(Me)2(N(Me)(C18H37)2)][B(C6F5)4] (2). Unlike most alkene polymerization precatalysts,2contains two Hf–Me groups, which have the potential to initiate and propagate two polymer chains simultaneously. Herein, we demonstrate that2does indeed grow two polymer chains at each hafnium center. Additional unusual characteristics for an early transition-metal catalyst include: (1) the number-average polymer molar mass (Mn) is independent of the concentration of monomer; (2) linear plots of monomer concentration as a function of time during polymerization indicate apparent zeroth-order dependence of rate on the monomer concentration; and (3) apparent first-order dependence of steady-state rate of polymerization on theinitialconcentration of monomer. While saturation behavior with respect to monomer concentration is common with late transition-metal-derived catalysts, propagation rate laws for early transition-metal complexes overwhelmingly are first-order in monomer concentration. Based onoperandoNMR kinetics, end group analysis, active site counting with chromophore quench labels, iodine quenching studies, and gel permeation chromatography, we propose a unified kinetic and mechanistic model for the polymerization of 1-octene with2.