Low-valent Alkaline Earth Metal Complexes: Synthesis, Structure and Reactivity

第一个Zn（I）配合物Cp*ZnZnCp* 的偶然发现刺激了低价s区金属化学的研究活动。这导致在2007年发现了第一个以（BDI）MgMg（BDI）形式的Mg（I）络合物，这是一种受到极大关注的化合物类别，并且被发现是化学中的通用还原剂（BDI = β-二酮亚胺配体）。除了稀有的Be（0）或Be（I）物质和Ca（I）络合物之外，迄今还没有重碱土（Ae）金属Ca、Sr和Ba的（BDI）AeAe（BDI）络合物的实例。我们尝试分离（BDI）CaCa（BDI）复合物，导致芳香族溶剂或N2的2 e-还原和（BDI）Ca（芳烃）Ca（BDI）或（BDI）Ca（N2）Ca（BDI）复合物的形成。与Frenking（马尔堡）合作的理论分析表明，Ca上的d轨道在N2活化中起着至关重要的作用。分离Ca-N2络合物的关键是由于3-戊基取代基而使得能够使用烷烃溶剂的超大体积的α-二酮亚胺配体。使用更大体积的BDI配体来试图裂解（BDI）MgMg（BDI）中的Mg-Mg键，这将导致迄今未知的高反应性（BDI）Mg●自由基。这一尝试导致分离出独特的（BDI）Mg + Na+络合物，其中零价Mg中心携带-1的形式电荷。这类新的镁基钠配合物具有富电子的Mg中心，并显示出与带正电荷的Mg 2+中心的普通Mg配合物完全相反的反应性。项目目标：1）通过光谱方法（NMR，EPR和钙价核X射线发射光谱研究）和理论（部分合作），加深我们对（BDI）Ca（芳烃）Ca（BDI）和（BDI）Ca（N2）Ca（BDI）系列化合物中成键的认识。我们的主要兴趣是d-轨道在成键中的重要性。2）通过设计更大的配体（L）将这种化学扩展到更重的Ae金属Sr和Ba，并试图分离LAeAeL，我们研究的原始目标。 3)研究了LAe（arene）AeL、LAe（N2）AeL和LAeAeL复合物的芳烃或N2官能化和极端氧化还原反应性。4）使用超体积配体分离LMg●自由基。 5)研究新化合物类（BDI）Mg-Na+与亲核Mg中心的反应性，这是目前的无人区。6)开发了一个通用的路线，LAe M+配合物的较重的Ae金属钙，锶和钡。7)使用（BDI）Mg + Na+试剂在与MXn（X =卤化物，M = s-、p-或d-区金属）的盐复分解路线之后产生Mg-金属键。8)用DFT，NBO和AIM方法对新络合物进行理论分析。我们的目标是与两名博士生一起运行该项目，并预测将在高影响力期刊上发表8-10篇完整论文。

The serendipitous discovery of the first Zn(I) complex, Cp*ZnZnCp*, has stimulated research activities in low-valent s-block metals chemistry. This led in 2007 to discovery of the first Mg(I) complexes in the form of (BDI)MgMg(BDI), a compound class that received enormous attention and was found to be a versatile reducing agent in chemistry (BDI = -diketiminate ligand). Apart from rare Be(0) or Be(I) species and a Ca(I) complex, there are hitherto no examples for (BDI)AeAe(BDI) complexes of the heavier alkaline earth (Ae) metals Ca, Sr and Ba. Our attempts to isolate a (BDI)CaCa(BDI) complex resulted in 2e-reduction of either the aromatic solvent or N2 and formation of (BDI)Ca(arene)Ca(BDI) or (BDI)Ca(N2)Ca(BDI) complexes. Theoretical analyses in cooperation with Frenking (Marburg) showed that d-orbitals on Ca play an essential role in N2 activation. The key to isolation of the Ca-N2 complex is a superbulky -diketiminate ligand that, due to 3-pentyl substituents, enables use of alkane solvents. An even bulkier BDI ligand was used in an effort to cleave the Mg-Mg bond in (BDI)MgMg(BDI) which would result in a highly reactive, hitherto unknown, (BDI)Mg● radical. This attempt led to isolation of a unique (BDI)MgˉNa+ complex in which the zerovalent Mg center carries a formal charge of -1. This new class of magnesyl sodium complexes features an electron-rich Mg center and displays reactivity that is a complete opposite of that of common Mg complexes with positively charged Mg2+ centers.Project aims:1) Deepening our knowledge on bonding in an extended series of (BDI)Ca(arene)Ca(BDI) and (BDI)Ca(N2)Ca(BDI) complexes using spectroscopic methods (NMR, EPR and Calcium Valence-to-Core X‑ray Emission Spectroscopy studies) and theory (partially in collaboration). Our main interest is the importance of d-orbitals in bonding.2) Extending this chemistry to the heavier Ae metals Sr and Ba by design of bulkier ligands (L) and attempts to isolate LAeAeL, the original target of our studies. 3) Studying arene or N2 functionalization and the extreme redox-reactivity of LAe(arene)AeL, LAe(N2)AeL and LAeAeL complexes.4) Isolation of LMg● radicals using superbulky ligands. 5) Investigating the reactivity of the new compound class (BDI)MgˉNa+ with nucleophilic Mg centers that is currently a no-man’s land. 6) Developing a general route to LAeˉM+ complexes for the heavier Ae metals Ca, Sr and Ba. 7) Use the (BDI)MgˉNa+ reagent to create Mg-metal bonds following a salt metathesis route with MXn (X = halide, M = s-, p- or d-block metal). 8) Theoretical analysis of new complexes with DFT, NBO and AIM methods.We aim to run the project with two PhD students and forecast an output of 8-10 full papers which will likely be published in high-impact journals.