Synthesis and characterization of stable hypervalent carbon compounds (10-C-5) bearing a 2,6-bis(p-substituted phenyloxymethyl)benzene ligand
Synthesis and characterization of stable hypervalent carbon compounds (10-C-5) bearing a 2,6-bis(p-substituted phenyloxymethyl)benzene ligand
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DOI：
10.1021/ja043802t
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发表时间：
2005-04-27
影响因子：
15
通讯作者：
Nagase, S
中科院分区：
文献类型：
--
作者：
Akiba, KY;Moriyama, Y;Nagase, S
铋的X射线分析（对氟苯基）甲基阳离子，带有2，6-双（对甲苯氧基甲基）苯配体显示出对称结构（10-C-5），其中两个C-O距离相同，尽管距离（2.690（4）埃）比我们最近报道的1，8-二甲氧基-9-二甲氧基甲基蒽一价阳离子的（2.43（1）和2.45（1）埃）长。然而，X-射线分析的更稳定的芳香族黄嘌呤阳离子与相同的苯配体显示四配位的碳结构，其中只有一个的两个氧配体与中心碳原子配位。这些结果清楚地表明，带有空间柔性苯配体的碳正离子（10-C-5）对中心碳原子上的电子效应相当敏感。通过精确的X射线测量进行的电子分布分析和对最初提到的双（对氟苯基）甲基阳离子的密度泛函计算清楚地表明，中心碳原子和两个氧原子是键合的，即使键是弱的并且基于键临界点处的小的电子密度值（p（r））和小的正拉普拉斯值（Delta（2）rho（r））的离子键。
X-ray analysis of bis(p-fluorophenyl)methyl cation bearing a 2,6-bis(p-tolyloxymethyl)benzene ligand showed a symmetrical structure (10-C-5) where the two C-O distances are identical, although the distance (2.690(4) angstrom) is longer than those (2.43(1) and 2.45(1) angstrom) of 1,8-dimethoxy-9-dimethoxymethyl-anthracene monocation, which was recently reported by us. However, X-ray analysis of the more stable aromatic xanthylium cation with the same benzene ligand showed the tetracoordinate carbon structure where only one of the two oxygen ligands is coordinated with the central carbon atom. These results clearly indicate that the carbocations (10-C-5) bearing the sterically flexible benzene ligand were quite sensitive to the electronic effect on the central carbon atom. The electron distribution analysis by accurate X-ray measurements and the density functional calculation on the initially mentioned bis(p-fluorophenyl)methyl cation clearly show that the central carbon atom and the two oxygen atoms are bonded even if the bond is weak and ionic based on the small value of the electron density (p(r)) and the small positive Laplacian value (Delta(2)rho(r)) at the bond critical points.