Structure Determination of Organolithium Compounds by 7Li Residual Quadrupolar Couplings

核磁共振（NMR）光谱是表征溶液中有机锂和其他有机金属试剂的最重要的分析方法，即在合成化学中通常采用的条件下。虽然经典的溶液NMR光谱提供了丰富的信息（各向同性1H，13 C和6/7 Li化学位移，标量耦合，核Overhauser效应），它是盲目的各向异性相互作用，如屏蔽各向异性，偶极和四极耦合。拟议的项目旨在使这些各向异性NMR参数在弱对齐（定向）下可见，但类似溶液的条件下，并可用于有机锂和其他有机金属/有机硼化合物的结构测定。作为取向介质，将使用在惰性条件下制备并溶胀至约80%溶剂含量的交联聚苯乙烯并进一步优化。在结构确定的第一步中，将在刚性和对称的锂化合物中测量7 Li残余四极耦合（RQC），其中从残余偶极耦合（RDC）获得对准张量，并且使用密度泛函理论（DFT）计算电场梯度（EFG）。在进一步的步骤中，我们的目标是在一个更好的理解的锂配位球，使用的组合实验7 Li RQC，固态NMR，电荷密度从X射线衍射数据和DFT计算在气相和固态中进行。最后，还将对含有其他碱金属（23 Na，87 Rb，133 Cs）和第13族元素（11 B，27 Al，71 Ga）的化合物进行RQC测量。这种新颖而有前途的方法大大受益于项目组及其合作者在各向异性和固态NMR，X射线衍射，锂，有机金属和量子化学领域的综合专业知识，并将有助于理解固态和溶液结构之间的相互作用。

Nuclear magnetic resonance (NMR) spectroscopy is the most important analytical method for the characterization of organolithium and other organometallic reagents in solution, i.e. under conditions where these are typically employed in synthetic chemistry. Although classical solution NMR spectroscopy provides a wealth of information (isotropic 1H, 13C and 6/7Li chemical shifts, scalar couplings, nuclear Overhauser effects), it is blind to anisotropic interactions such as shielding anisotropies, dipolar and quadrupolar couplings. The proposed project aims at making these anisotropic NMR parameters visible under weakly aligned (oriented), nevertheless solution-like, conditions and accessible to the structure determination of organolithium and other organometallic/organoboron compounds. As alignment medium, crosslinked polystyrene, prepared under inert conditions and swollen to ~80% solvent content will be used and further optimized. In a first step towards structure determination, 7Li residual quadrupolar couplings (RQCs) will be measured in rigid and symmetric lithium compounds, where the alignment tensor is obtained from residual dipolar couplings (RDCs), and the electric field gradient (EFG) is calculated using density functional theory (DFT). In a further step, we aim at an improved understanding of the Li coordination sphere, using a combination of the experimental 7Li RQCs, solid-state NMR, charge densities from X-ray diffraction data and DFT calculations performed both in the gas phase and in the solid-state. Finally, RQC measurements will also be done on compounds containing other alkali metals (23Na, 87Rb, 133Cs) and Group 13 elements (11B, 27Al, 71Ga). This novel and promising approach strongly benefits from the combined expertise of the project group and its collaborators in the fields of anisotropic and solid-state NMR, X-ray diffraction, lithium, organometallic and quantum chemistry and will help to understand the interplay between solid-state and solution structures.