Birajdar Rajkumar S, Gupta Poonam, Gonnade Rajesh G, Chikkali Samir H
Polymer Science and Engineering Division, CSIR-National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411008, India.
Academy of Scientific and Innovative Research (AcSIR), Sector 19, Kamla Nehru Nagar, Ghaziabad 201002, Uttar Pradesh, India.
Inorg Chem. 2025 Jan 13;64(1):25-36. doi: 10.1021/acs.inorgchem.4c04117. Epub 2024 Dec 26.
Metal complexes with tunable ligands play a crucial role in olefin polymerization and impart control over molecular weight, crystallinity, and stereoregularity. We report the single-step synthesis of imine-phenoxy ligands in excellent yields (81-93%). The identity of electronically tuned imine-phenoxy ligands was unambiguously ascertained by using a combination of spectroscopic and analytical methods. These ligands were treated with [Pd(COD)MeCl] in the presence of 2,6-lutidine, resulting in the formation of discrete mononuclear palladium complexes Pd1-Pd4 in excellent yields. 1-2D NMR spectroscopy, mass spectrometry analysis, and single-crystal X-ray diffraction confirmed the identity of the palladium complexes. X-ray analysis revealed a distorted square planar geometry around the palladium center. Proton NMR analysis suggested that the Pd1 catalyst was deshielded, indicating electronically deficient palladium metal compared to the other complexes. Moreover, the Pd1 catalyst showed the highest buried volume percentage (%V = 44.9). When exposed to norbornene, Pd1-Pd4 were found to be active and produced poly(norbornene) (PNB). High-temperature SEC analysis revealed that the electronically deficient and sterically hindered Pd1 catalyst produced the highest molecular weight polymer (PNB 37.4 kDa). Boron and aluminum-based cocatalysts were screened, and MMAO was found to outperform others with high catalytic activity (up to 63.2 × 10 g of PNB (mol Pd) h).
具有可调节配体的金属配合物在烯烃聚合中起着关键作用，并能控制分子量、结晶度和立构规整性。我们报道了以优异产率（81 - 93%）单步合成亚胺 - 苯氧基配体。通过光谱和分析方法相结合，明确确定了电子调节的亚胺 - 苯氧基配体的结构。在2,6 - 二甲基吡啶存在下，这些配体与[Pd(COD)MeCl]反应，以优异产率生成离散的单核钯配合物Pd1 - Pd4。一维和二维核磁共振光谱、质谱分析以及单晶X射线衍射确定了钯配合物的结构。X射线分析表明钯中心周围为扭曲的平面正方形几何结构。质子核磁共振分析表明，与其他配合物相比，Pd1催化剂的屏蔽作用减弱，表明钯金属电子缺乏。此外，Pd1催化剂的埋藏体积百分比最高（%V = 44.9）。当暴露于降冰片烯时，发现Pd1 - Pd4具有活性并生成聚降冰片烯（PNB）。高温尺寸排阻色谱分析表明，电子缺乏且空间位阻较大的Pd1催化剂生成的聚合物分子量最高（PNB 37.4 kDa）。筛选了硼基和铝基助催化剂，发现甲基铝氧烷（MMAO）的催化活性最高（高达63.2 × 10 g PNB /（mol Pd·h）），优于其他助催化剂。
