The complex (μ-Me₂C-3,3′){(η⁵-cyclopentadienyl)[1-Me₂Si-(^tBuN)](TiMe₂)}₂ (3) was prepared as a new binuclear catalyst motif for homogeneous olefin polymerization. Complex 3 exists as rac-3 and meso-3 diastereomers, which can be separated and characterized by solution NMR spectroscopy and single-crystal X-ray diffraction. While meso-3 has high thermal stability, rac-3 undergoes thermolysis in solution to quantitatively form the dimeric methylidene complex (μ-Me₂C-3,3′){(η⁵-cyclopentadienyl)[1-Me₂Si(^tBuN)][(μ-CH₂)Ti]}₂ (rac-4). Activation of rac-3 and meso-3 with 1 equiv of Ph₃C⁺B(C₆F₅)₄^– yields [(μ-CMe₂-3,3′){(η⁵-cyclopentadienyl)[1-Me₂Si(^tBuN)]}₂(μ-CH₂)(μ-CH₃)Ti₂]⁺B(C₆F₅)₄^– (5; rac-5 and meso-5, respectively). Interestingly, meso-5 is stable in the presence of an additional 1 equiv of Ph₃C⁺B(C₆F₅)₄^–, while rac-5 reacts to yield rac-[(μ-CMe₂-3,3′){(η⁵-cyclopentadienyl)[1-Me₂Si(^tBuN)]}₂(μ-CH₂)[(TiCH₃)(Ti-η¹-Ph₃C)]²⁺[B(C₆F₅)₄^–]₂ (rac-6) as indicated by multinuclear NMR spectroscopy and DFT computation. meso-3 reacts with 2 equiv of B(C₆F₅)₃ to yield meso-[(μ-CMe₂-3,3′){(η⁵-cyclopentadienyl)[1-Me₂Si(^tBuN)]}₂(μ-CH₂)(μ-CH₃)Ti₂]⁺MeB(C₆F₅)₃^– (meso-7) containing the same meso-5 cation but with a MeB(C₆F₅)₃^–counteranion. These findings, along with catalytic results, indicate that rac-3 and meso-3 remain structurally intact during polymerization, consistent with the observed diastereoselectivity effects. Under identical ethylene/1-octene copolymerization conditions, only activated bimetallic rac-3 produces appreciable polymer, with meso-3 exhibiting low activity, but both yield polymer with a branch density >2× that of the monometallic control [(3-^tBu-C₅H₃)SiMe₂N^tBu]TiMe₂ (Ti₁). In ethylene/styrene copolymerizations, rac-3 produces polymers with 3.1× higher M_n and 2.1× greater styrene incorporation versus Ti₁, while meso-3 catalyzes only ethylene-free styrene homopolymerization. In 1-octene homopolymerizations, meso-3 + B(C₆F₅)₃ (i.e., meso-7) produces highly isotactic poly-1-octene (mmmm 91.7%), while rac-3 + Ph₃C⁺B(C₆F₅)₄^– (i.e., rac-5), rac-3 + B(C₆F₅)₃ (i.e., rac-7), and meso-3 + Ph₃C⁺B(C₆F₅)₄^– (i.e., meso-5) produce only atactic poly-1-octene. These bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product M_n, tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.

中文翻译：

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双金属钛烯烃聚合催化剂中独特的立体化学联系的协同作用

配合物（μ-ME ₂ C-3,3'）{（η ⁵ -环戊二烯基）[1-ME ₂ SI-（^吨BUN）]（时间₂）} ₂（3）作为一种新的双核催化剂基序用于均相烯烃聚合。配合物3以rac -3和meso -3非对映异构体的形式存在，可以通过溶液NMR光谱和单晶X射线衍射进行分离和表征。而内消旋-3具有高的热稳定性，外消旋-3经历热解溶液定量地形成二聚亚甲基络合物（μ-ME ₂C-3,3'）{（η ⁵ -环戊二烯基）[1-ME ₂的Si（^吨BUN）] [（μ-CH ₂）的Ti]} ₂（外消旋-4）。的活化外消旋-3和内消旋-3与1个当量的Ph ₃ Ç ⁺ B（C ₆ ˚F ₅）₄ ^-的产率[（μ-CME ₂ -3,3'）{（η ⁵ -环戊二烯基）[1-ME ₂的Si（^吨BUN）]} ₂（μ-CH ₂）（μ-CH ₃）的Ti ₂ ] ⁺ B（C₆ F ₅）₄ ^–（5；rac -5和meso -5）。有趣的是，内消旋-5是在额外的1个当量的Ph的存在下是稳定₃ Ç ⁺ B（C ₆ ˚F ₅）₄ ^- ，而外消旋-5反应以产生外消旋- [（μ-CME ₂ -3,3' ）{（η ⁵ -环戊二烯基）[1-ME ₂的Si（^吨BUN）]} ₂（μ-CH ₂）[（TICH ₃）（TI-η ¹ -Ph ₃ C）] ²⁺ [B（C ₆ ˚F ₅）₄ ^- ] ₂（外消旋-6）通过多核NMR谱和DFT运算所指示的。内消旋-3发生反应与2当量B（C的₆ ˚F ₅）₃，得到的内消旋- [（μ-CME ₂ -3,3'）{（η ⁵ -环戊二烯基）[1-ME ₂的Si（^吨BUN）] } ₂（μ-CH ₂）（μ-CH ₃）的Ti ₂ ] ⁺ MEB（C₆ F ₅）₃ ^–（meso -7）含有相同的meso -5阳离子，但带有MeB（C ₆ F ₅）₃ ^–抗衡阴离子。这些发现以及催化结果表明，rac -3和meso -3在聚合过程中保持结构完整，与观察到的非对映选择性作用一致。在相同的乙烯/ 1-辛烯共聚条件下，只有活化的双金属rac -3产生明显的聚合物，而meso-3表现出低的活性，但具有分支密度> 2×两者收率聚合物，所述单金属的控制[（3-^吨卜-C ₅ H ^ ₃）森达₂ Ñ^吨卜]时间₂（钛₁）。在乙烯/苯乙烯共聚中，rac -3生成的聚合物的M _n值比Ti ₁高3.1倍，苯乙烯的掺入量比Ti ₁高2.1倍，而内消旋-3仅催化无乙烯的苯乙烯均聚。在1-辛烯均聚中，内消旋-3 + B（C ₆ F ₅）₃（即，内消旋-7）产生高度全同立构聚-1-辛烯（MMMM 91.7％），而外消旋-3 +博士₃ Ç ⁺ B（C ₆ ˚F ₅）₄ ^- （即，外消旋-5），外消旋- 3 + B（C ₆ ˚F ₅）₃（即，外消旋-7），和内消旋-3 +博士₃ ç ⁺ B（C ₆ ˚F ₅）₄ ^- （即，内消旋-5）仅产生无规立构的聚1-辛烯。这些双金属聚合催化剂表现出独特的协同作用，影响产物M _n，立构规整​​度和共聚单体的选择，表明双核催化剂的立体化学因素是重要的。