Lithium-cation/π complexes of aromatic systems.: The effect of increasing the number of fused rings
Lithium-cation/π complexes of aromatic systems.: The effect of increasing the number of fused rings
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DOI：
10.1021/ja029843b
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发表时间：
2003-08-27
影响因子：
15
通讯作者：
Abboud, JLM
中科院分区：
文献类型：
--
作者：
Gal, JF;Maria, PC;Abboud, JLM
用傅里叶变换离子回旋共振(FT-ICR)质谱仪测定了萘、天青烯、菲、菲的气相锂离子碱性(LCB)。在B3LYP/6-311+G(3df，2p)//B3LYP/6-31G(D)水平上研究了相应配合物的结构和相对稳定性。在理论研究中，还包括了芘、冠烯、[3]亚苯、角[3]亚苯和环冠烯。与给定芳香环的结合强度随着直接与其融合的环数的增加而降低。因此，Li+连接到外环上的外层pi-络合物的稳定性系统地大于金属连接到内环上的络合物的稳定性。这些局部极小值之间的能量差随着系统中熔环数量的增加而减小。这一结果似乎表明，随着系统大小的增加，环往往会失去它们的特性，在石墨薄片的限制下，所有环都将表现出相同的特性和反应性。计算的LCB与实验值之间的良好一致性支持了外部络合物的稳定性增强。连接这些局部极小值的激活势垒随着融合循环数量的增加而减少，但似乎趋于极限。[3]亚苯基和角[3]亚苯基表现出增强的LCB，反映了不可忽略的Mills-Nixon效应，从而增加了这些芳基苯环的电子给体性质。
The gas-phase lithium cation basicities (LCBs) of naphthalene, azulene, anthracene, and phenanthrene were measured by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The structures of the corresponding complexes and their relative stabilities were investigated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) level of theory. In the theoretical survey, pyrene, coronene, [3]phenylene, angular [3]phenylene, and circumcoronene were also included. The strength of the binding to a given aromatic cycle decreases as the number of cycles directly fused to it increases. Hence, the stability of the outer pi-complexes, in which Li+ is attached to the peripheral rings, is systematically greater than that of the complexes in which the metal is attached to the inner rings. The energy gap between these local minima decreases as the number of fused rings in the system increases. This result seems to indicate that, as the size of the system increases, the rings tend to lose their peculiarities, in such a way that in the limit of a graphite sheet all rings would exhibit identical characteristics and reactivity. The good agreement between calculated LCBs and experimental values lends support to the enhanced stability of the outer complexes. The activation barriers connecting these local minima decrease as the number of fused cycles increases, but seems to tend toward a limit. [3]Phenylene and angular [3]phenylene exhibit enhanced LCBs reflecting nonnegligible Mills-Nixon effects that increase the electron-donor properties of these annelated benzenes.