From Low to High Oxidation States - New Oxidative Routes to Lanthanide Multiple Bonds

镧系元素是14种化学性质相关的元素，它们表现出不同的光学和磁性，这有助于它们在各种技术应用中的应用。它们的定义是它们的高度极化的键，这是由静电吸引主导的，以及它们在绝大多数络合物中呈现+3氧化态的显著倾向。作为这些体系中以静电键为主的直接结果，多键稀土化学与相应的d-嵌段化学相比不发达，到目前为止仅限于碳的双键。考虑到d-过渡金属双键配合物的催化应用，发展稀土元素-多键化学是一个长期的合成目标，并提出通过合理选择支持配体和合成路线，最终的稀土元素-元素双键与各种p-嵌段元素是可以实现的。这些配合物的性质将与众所周知的d-嵌段化学的例子形成对比和补充。在这项提议中，目标是与氮、磷和硫族(O、S、Se、Te)具有末端多键的Ce(IV)配合物。Ce在稀土元素中是独一无二的，因为它具有易于访问的+4氧化态。Ce(IV)的络合物是强氧化剂，这一性质已被用于合成无处不在的试剂，如硝酸铈铵(CAN)。鉴于CaN具有一定的选择性和溶解性问题，本文中开发的Ce(IV)配合物将作为合成化学中CaN的替代品进行可行性研究。二价稀土化学，金属处于正式+2氧化态，以前仅限于少数几种稀土元素，但该领域最近的重大进展现在允许分离和研究所有稀土元素的二价化学，但放射性钚除外。这项建议中的Ce(II)合成子本身就是有趣的络合物，具有独特的氧化潜力。因此，它们将被研究作为合成中广泛使用的单电子还原剂二碘化钐的替代品。为了实现新的合成方法学，扩大这一领域是很重要的。这里制备的所有络合物都将通过先进的分析和计算技术进行分析。这将从根本上洞察末端的Ce3+多键，虽然这些配合物的性质无法准确预测，但它们有望具有高度的活性和趣味性。与早期的d-过渡金属配合物相比，目标Ce(IV)配合物将显示出更高的反应活性，因为它们还将是强氧化剂。详细的分析将确定这些配合物是否像原型Ce(IV)配合物那样在材料化学和催化方面有希望。预计这些研究产生的结果将值得发表在领先的国际期刊上，如《科学》、《自然出版集团》、《美国化学学会杂志》和《Angewandte Chemie》。这些基础研究将不仅仅局限于教科书上的例子，因为这项研究的结果将对物理、工程和材料科学产生影响。这项拨款的授予将使首席研究人员能够培训具有处理高度空气敏感的f元素络合物的罕见能力的研究生和博士生工作人员。最近，政府以及核工业和精细化工行业强调，高度敏感的f元素络合物是一个主要的技能短缺。这项研究将通过外展活动向公众宣传，因为它对社会和环境的好处有利于公众对科学的看法。

The lanthanides are fourteen chemically related elements which exhibit diverse optical and magnetic properties that have facilitated their employment in a myriad of technological applications. They are defined by their highly polarised bonding, which is dominated by electrostatic attractions, and their marked tendency to exhibit the +3 oxidation state in the vast majority of their complexes.As a direct consequence of the predominantly electrostatic bonding in these systems, multiply-bonded lanthanide chemistry is underdeveloped in comparison to corresponding d-block chemistry and is limited to double bonds to carbon to date. Given the catalytic applications of d-transition metal complexes exhibiting double bonds, the development of lanthanide-multiple bond chemistry is a long-term synthetic target and it is proposed that with judiciously selected supporting ligands and synthetic routes terminal lanthanide-element double bonds with a variety of p-block elements are accessible. These complexes will exhibit properties that contrast with and complement examples from well-understood d-block chemistry.In this proposal, cerium(IV) complexes exhibiting terminal multiple bonds to nitrogen, phosphorus and chalcogens (O, S, Se, Te) are targeted. Cerium is unique amongst the lanthanides in having a readily accessible +4 oxidation state. Complexes of Ce(IV) are strong oxidising agents and this property has been utilised in synthesis with ubiquitous reagents such as ceric ammonium nitrate (CAN). Given that CAN has some selectivity and solubility issues, the Ce(IV) complexes developed herein will be investigated for their viability as alternatives to CAN in synthetic chemistry.The Ce(IV) complexes targeted in this proposal will be prepared from Ce(II) synthon precursors. Divalent lanthanide chemistry, with metals in a formal + 2 oxidation state, was previously limited to only a handful of lanthanides but recent major advances in this field have now allowed the isolation and study of divalent chemistry for all lanthanides with the exception of radioactive promethium. The Ce(II) synthons in this proposal will be interesting complexes in their own right with distinctive and unique oxidation potentials. Therefore they will be investigated as alternatives to the widely-used one electron reducing agent samarium(II) diiodide in synthesis. It is important to expand this area in order to realise new synthetic methodologies.All complexes prepared herein will be analysed by advanced analytical and computational techniques. This will give fundamental insight into terminal cerium multiple bonds and although the properties of these complexes cannot be accurately predicted, they promise to be highly reactive and interesting. The target Ce(IV) complexes will exhibit enhanced reactivity in comparison to their early d-transition metal counterparts as they will additionally be strong oxidising agents. Detailed analysis will determine if these complexes hold promise in materials chemistry and catalysis, as archetypal Ce(IV) complexes have previously shown.It is expected that results generated from these studies will be worthy of publication in leading international journals such as Science, Nature Publishing Group, Journal of the American Chemical Society and Angewandte Chemie. These fundamental studies will not just be confined to textbook examples because results from this research will have implications for physics, engineering and materials science.The award of this grant will give the principal investigator the means to train post-graduate and -doctoral workers with the rare ability to handle highly air sensitive f-element complexes, recently highlighted as a major skills shortage by government and the nuclear and fine chemical industries. This research will be communicated to the public by outreach activities as its benefit to society and the environment are favourable for the public perception of science.