Polymetallic Zr catalysts for the ROP of lactide

“这是一个化学博士研究项目，单中心的刘易斯酸性金属中心通常用于丙交酯的开环聚合（ROP）。这些是明确定义的引发剂，其目的是提供高水平的活性沿着控制聚合过程。虽然这些引发剂对丙交酯的ROP显示出高活性，但一些引发剂在手套箱外可能缺乏稳定性。多核或聚集的引发剂通常具有改善的稳定性，但由于在solution.In最近的两个publications 1，2中定义其核相关的并发症，建立这些物种的结构-活性关系更具挑战性，我们已经表明，多核钛络合物，胺双（酚盐）配体（图1）桥接，在丙交酯的ROP中是活跃的。复合物有几个优势，传统的，单点引发剂，因为它们是稳定的空气和水分，并表现为真正的catalysts.We现在建议进一步发展这种化学结合到复杂的锆（无论是单独或串联与钛）。Zr被公认为对于丙交酯的ROP比Ti更有活性，并且表现出更大的立体选择性。Zr络合物通常在空气/水分存在下更容易降解，因此这些超分子络合物被理想地放置以开发用于丙交酯ROP的实验室稳定但高活性的催化剂。我们目前的重点是将氨基酸纳入配体框架。这些新化合物将通过容易获得的起始材料为我们提供一系列手性配体。一旦准备好，我们将尝试与Zr络合物配位，一旦我们有了可靠的程序，我们将尝试通过形成氧桥（使用文献先例）或羧酸根桥（来自本组内的既定先例）来形成多金属络合物。学生将使用光谱方法（NMR，IR，UV-vis），质谱，元素分析和单晶X射线衍射来表征复合物。一旦复合物已经制成，我们将在丙交酯的ROP中试验这些以确定它们的活性。聚合物将通过NMR和凝胶渗透色谱法（GPC）进行表征。

"This is a PhD research project in Chemistry.Single-site, Lewis acidic metal centers are often applied to the ring-opening polymerisation (ROP) of lactide. These are well defined initiators that aim to provide high levels of activity along with control over the polymerisation process. While these initiators show high activity towards the ROP of lactide, some can lack stability outside of the glovebox. Polynuclear or aggregated initiators generally have improved stability but structure-activity relationships are more challenging to establish for these species due to complications associated with defining their nuclearity in solution.In two recent publications1,2 we have shown that polynuclear Ti complexes, bridged by amine bis(phenolate) ligands (Fig 1), are active in the ROP of lactide. The complexes have several advantages over traditional, single site initiators as they are stable to air and moisture, and behave as true catalysts.We now propose to further develop this chemistry by incorporation of Zr into the complex (either exclusively or in tandem with Ti). Zr is well established to be a more active than Ti for the ROP of lactide and exhibits greater stereoselectivity. Zr complexes are generally more susceptible to degrading in the presence of air/moisture so these supramolecular complexes are ideally placed to develop a bench stable but highly active catalyst for the ROP of lactideInitially the student will create several amine bis(phenol) pro-ligands using literature procedures (or minor modifications thereof). We are currently focussing on incorporating amino acids into the ligand framework. These new compounds will provide us with a range of chiral ligands via readily accessible starting materials. Once prepared we will attempt coordination to Zr complexes, once we have a reliable procedure we will attempt to form polymetallic complexes via the formation of oxo bridges (using literature precedent) or carboxylate bridges (from established precedent within the group). The complexes will be characterised by the student using spectroscopic methods (NMR, IR, UV-vis), mass spectrometry, elemental analysis and single crystal x-ray diffraction. Once the complexes have been made we will trial these in the ROP of lactide to ascertain their activity. Polymers will be characterised via NMR and gel permeation chromatography (GPC).