Oxidocobalt(IV) Cores Based on Oxidation Resistant Guanidine Donors

甲烷选择性转化制甲醇被认为是未来替代矿物油的工业碳原料，引起了工业界和学术界的极大兴趣。甲烷的工业化功能化显然需要一种廉价和高度丰富的试剂，即氧气，O2。根据以往的实验研究和密度泛函理论计算，可以预见，一类末端为M=O单元的稀有单体后过渡金属络合物LNM=O，其中M是后过渡金属，如钴、镍或铜，非常适合作为催化剂。对LnCoIV=O核心的综合访问涉及到该项目的主要主题。值得注意的是，只有在极少数情况下，才能在非四方配位场中分离到第8族右侧的末端后过渡金属-氧代物种(也称为C4v对称性的“氧代壁”)。这里采用的稳定这类难以捉摸的中间体的主要策略是：a)在四角场中衰减赤道配体捐赠，以实现独特的1：3：1 d轨道分裂模式，以支持具有高d电子计数的金属氧核；b)加入稳定的氢键相互作用，以减少富电子氧中心和后过渡金属中心之间预期的强烈斥力；以及c)利用氧化能力强的鸟嘌呤配体和供体。详细的反应性研究，包括C-H键活化和氧原子转移反应，结合这些长期受到追捧的LnCoIV=O中间体的光谱和理论，可能有助于我们理解金属中心的空间和电子性质如何调节它们的反应性。这将为丰富的金属催化领域提供重要的见解。

The selective transformation of methane to methanol has generated great interest in industry and academia, since it has been deemed as the future industrial carbon feedstock substituting mineral oil. The industrial scale functionalization of methane will obviously require an inexpensive and highly abundant reagent, i.e. dioxygen, O2. Based on previous experimental investigations and DFT calculations, it is anticipated that the rare class of monomeric, late transition metal complexes with a terminal M=O unit, LnM=O, where M is a late transition metal like cobalt, nickel or copper are perfectly suited as catalysts. The synthetic access to the LnCoIV=O core involves the main theme of this project. Notably, isolation of terminal late transition metal-oxo species to the right of group 8 (also known as “the oxo wall” for C4v symmetry) has only been achieved in extremely rare cases in ligand fields that are not tetragonal. The main strategies that have been employed here for the stabilization of such elusive intermediates are : a) attenuation of equatorial ligand donation in a tetragonal field so as to achieve a unique 1:3:1 d-orbital splitting pattern that can support metal-oxo cores with high d-electron count; b) incorporation of stabilizing Hydrogen bonding interaction in order to reduce the anticipated strong repulsion between the electron-rich oxo and late transition metal centers; and c) utilization of oxidatively robust guandine ligand donors. Detailed reactivity studies, including C-H bond activation and oxygen atom transfer reactions, in conjunction with spectroscopy and theory on these long sought-after LnCoIV=O intermediates may help us to understand how the steric and electronic properties of the metal centers modulate their reactivities. This will provide vital insights into the field of abundant metal catalysis.