Structure Determination of Organolithium Compounds by 7Li Residual Quadrupolar Couplings

核磁共振波谱是表征有机锂和其他有机金属试剂在溶液中的最重要的分析方法，也就是在通常用于合成化学的条件下。虽然经典溶液核磁共振谱提供了丰富的信息(各向同性1H、13C和6/7Li化学位移、标量耦合、核Overhauser效应)，但它对屏蔽各向异性、偶极和四极耦合等各向异性相互作用是视而不见的。该项目的目的是使这些各向异性核磁共振参数在弱排列(定向)但类似溶液的条件下可见，并可用于确定有机锂和其他有机金属/有机硼化合物的结构。采用惰性条件下制备的溶胀至80%左右的交联型聚苯乙烯作为对准介质，并对其进行进一步优化。在结构确定的第一步，将测量刚性和对称锂化合物中的7Li剩余四极耦合(RQCs)，其中排列张量由剩余偶极耦合(RDC)获得，电场梯度(EFG)由密度泛函理论(DFT)计算。在进一步的步骤中，我们的目标是通过结合实验的7Li RQC，固态核磁共振，来自X射线衍射数据的电荷密度和在气相和固态中进行的密度泛函计算，来更好地理解Li配位球。最后，还将对含有其他碱金属(23Na、87Rb、133Cs)和第13族元素(11B、27Al、71Ga)的化合物进行RQC测量。这一新的和有希望的方法强烈受益于项目组及其合作者在各向异性和固态核磁共振、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.