New insights into frustrated Lewis pairs: structural investigations of intramolecular phosphane-borane adducts by using modern solid-state NMR techniques and DFT calculations.
New insights into frustrated Lewis pairs: structural investigations of intramolecular phosphane-borane adducts by using modern solid-state NMR techniques and DFT calculations.
复制标题
DOI：
10.1021/ja210160k
复制
发表时间：
2012-02
影响因子：
15
通讯作者：
Thomas Wiegand;H. Eckert;Olga Ekkert;R. Fröhlich;G. Kehr;G. Erker;S. Grimme
中科院分区：
文献类型：
--
作者：
Thomas Wiegand;H. Eckert;Olga Ekkert;R. Fröhlich;G. Kehr;G. Erker;S. Grimme
利用固态核磁共振技术和伴随的DFT计算，研究了一系列“受挫刘易斯对”（FLPs）（主要是取代乙烯连接的分子内磷硼烷加合物）中刘易斯酸和刘易斯碱官能团之间的共价键相互作用。（11）B核磁共振各向同性化学位移和核电四极耦合参数都是这种相互作用的极其敏感的实验探针，揭示了硼磷核间距离的线性相关性。（11）B电场梯度张量的主成分V（zz）与硼-磷核间矢量略微倾斜（~20°），从而提高了对FLPs显著反应性的理解。互补的（31）P{(1)H}- cpmas实验揭示了显著的（31）P-(11)B标量自旋-自旋相互作用（(1)J≈50 Hz），证明了反应中心之间的共价键相互作用。最后，（11）B{(31)P}旋转回声双共振（REDOR）实验与基于x射线晶体学计算的核间距离曲线存在系统偏差。这些偏差表明各向异性间接自旋-自旋（J各向异性）相互作用的贡献非零，从而为共价键的存在提供了额外的证据。
Covalent bonding interactions between the Lewis acid and Lewis base functionalities have been probed in a series of "frustrated Lewis pairs" (FLPs) (mainly substituted vinylene linked intramolecular phosphane-borane adducts), using solid-state nuclear magnetic resonance techniques and accompanying DFT calculations. Both the (11)B NMR isotropic chemical shifts and nuclear electric quadrupolar coupling parameters turn out to be extremely sensitive experimental probes for such interactions, revealing linear correlations with boron-phosphorus internuclear distances. The principal component V(zz) of the (11)B electric field gradient tensor is tilted slightly away (~20°) from the boron-phosphorus internuclear vector, leading to an improved understanding of the remarkable reactivity of the FLPs. Complementary (31)P{(1)H}-CPMAS experiments reveal significant (31)P-(11)B scalar spin-spin interactions ((1)J ≈ 50 Hz), evidencing covalent bonding interactions between the reaction centers. Finally, (11)B{(31)P} rotational echo double resonance (REDOR) experiments show systematic deviations from calculated curves based on the internuclear distances from X-ray crystallography. These deviations suggest non-zero contributions from anisotropic indirect spin-spin (J anisotropy) interactions, thereby offering additional evidence for covalent bonding.