The viability of small endohedral hydrocarbon cage complexes:: X@C4H4, X@C8H8, X@C8H14, X@C10H16, X@C12H12, and X@C16H16
The viability of small endohedral hydrocarbon cage complexes:: X@C4H4, X@C8H8, X@C8H14, X@C10H16, X@C12H12, and X@C16H16
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DOI：
10.1021/ja0345470
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发表时间：
2003-09-17
影响因子：
15
通讯作者：
Schleyer, PV
中科院分区：
文献类型：
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作者：
Moran, D;Woodcock, HL;Schleyer, PV
在B3 LYP/6- 31 G（d）杂化HF/DFT水平上研究了笼心内原子和离子（X = H+，H，He，Ne，Ar，Li-0，Li-+，Be-0，Be-+，Be-2+，Na-0，Na-+，Mg-0，Mg-+，Mg-2+）的小分子碳氢化合物（X@cage）.没有四面体（C_4H_4，T-d）的配合物是最小的，即使是非常小的氢原子或铍二价阳离子。Cubane（C8 H8，O-h）和bicyclo[2.2.2]octane（C8 H14，D-3 h）最小值仅限于小于Ne和Na+的包封物质。尽管金刚烷（C10 H16，T-d）具有中等大小，但它可以包含各种各样的内配体原子和离子，包括H、He、Ne、Li-0、Li-+、Be-0、Be-+、Be-2+、Na-0、Na-+和Mg 2+。相比之下，截短的四面体（C12 H12，T-d）包裹了较少的物种，而D-4d对称的C16 H16烃笼（见目录图）包裹了除了较大的Be，Mg和Mg+物种之外的所有物种。当金属原子而不是阳离子在内部时，宿主笼具有更紧凑的几何形状。这是由于内配体金属向C-C键和C-H反键笼形分子轨道提供电子。通过比较它们的能量（E-endo）与它们的孤立组分之和（E-inc = E-endo - E-cage - E-x）和它们的外消旋体能量（E-isom = E-endo - E-exo）来评估内消旋体极小值的相对稳定性。尽管外侧面结合毫无例外地优选于内侧面封装（即，电子异构体总是放热的），Be 2 +@C10H16（T-d; -235.5 kcal/mol），Li+@C12H12（T-d; 50.2 kcal/mol），Be 2 +@C12H12（T-d; -181.2 kcal/mol），Mg2+@C12H12（T-d; -45.0 kcal/mol），Li+@C16H16（D-4d; 13.3 kcal/mol），Be+@C16H16（C-4v; 31.8 kcal/mol），Be2+ @C16H16（D-4d，-239.2 kcal/mol）和Mg2+@C16H16（D-4d，-37.7kcal/mol）与实验已知的He@C20H2O（I-h）相比相对稳定，其具有E-inc = 37.9kcal/mol和E-isom =-35.4kcal/mol。总体而言，具有低母体笼应变能、大笼内腔体积和小的高电荷客体物种的内笼络合物是最可行的合成目标。
Small hydrocarbon complexes (X@cage) incorporating cage-centered endohedral atoms and ions (X = H+, H, He, Ne, Ar, Li-0,Li-+, Be-0,Be-+,Be-2+, Na-0,Na-+, Mg-0,Mg-+,Mg-2+) have been studied at the B3LYP/6-31G(d) hybrid HF/DFT level of theory. No tetrahedrane (C4H4, T-d) endohedral complexes are minima, not even with the very small hydrogen atom or beryllium dication. Cubane (C8H8, O-h) and bicyclo[2.2.2]octane (C8H14, D-3h) minima are limited to encapsulating species smaller than Ne and Na+. Despite its intermediate size, adamantane (C10H16, T-d) can enclose a wide variety of endohedral atoms and ions including H, He, Ne, Li-0,Li-+, Be-0,Be-+,Be-2+, Na-0,Na-+, and Mg2+. In contrast, the truncated tetrahedrane (C12H12, T-d) encapsulates fewer species, while the D-4d symmetric C16H16 hydrocarbon cage (see Table of Contents graphic) encapsulates all but the larger Be, Mg, and Mg+ species. The host cages have more compact geometries when metal atoms, rather than cations, are inside. This is due to electron donation from the endohedral metals into C-C bonding and C-H antibonding cage molecular orbitals. The relative stabilities of endohedral minima are evaluated by comparing their energies (E-endo) to the sum of their isolated components (E-inc = E-endo - E-cage - E-x) and to their exohedral isomer energies (E-isom = E-endo - E-exo). Although exohedral binding is preferred to endohedral encapsulation without exception (i.e., E-isom is always exothermic), Be2+@C10H16 (T-d; -235.5 kcal/mol), Li+@C12H12 (T-d; 50.2 kcal/mol), Be2+@ C12H12 (T-d; -181.2 kcal/mol), Mg2+@C12H12 (T-d; -45.0 kcal/mol), Li+@C16H16 (D-4d; 13.3 kcal/mol), Be+@C16H16 (C-4v; 31.8 kcal/mol), Be2+ @C16H16 (D-4d, -239.2 kcal/mol), and Mg2+@C16H16 (D-4d, -37.7 kcal/mol) are relatively stable as compared to experimentally known He@C20H20 (I-h), which has an E-inc = 37.9 kcal/mol and E-isom = -35.4 kcal/mol. Overall, endohedral cage complexes with low parent cage strain energies, large cage internal cavity volumes, and a small, highly charged guest species are the most viable synthetic targets.