Kang Hong Seok
College of Natural Science, Jeonju University, Hyoja-dong, Wansan-ku, Chonju, Chonbuk 560-759, Republic of Korea.
J Phys Chem A. 2005 May 19;109(19):4342-51. doi: 10.1021/jp044293k.
Using density functional theory, we have theoretically studied various kinds of complexes of cyclopentadienyl and dicyclopentadienyl ligands with zinc and cadmium atoms of oxidation state +1. We first find that a sandwich complex Cp-Zn-Zn-Cp that was recently identified by Resta et al, (Science 2004, 305, 1136) has a large overall binding energy (=-3.19 eV), where Cp denotes the pentamethyl cyclopentadienyl group. In addition, Cp-Zn-Zn-Cp is found to have a binding energy even larger by 0.93 eV, where Cp is a cyclopentadienyl ligand without methyl groups attached. Electronic structure analysis shows accumulation of electron density between Zn atoms, confirming the existence of Zn-Zn bond that is as strong as typical transition metal-halide bonds. In addition, our calculation suggests the possible existence of similar complexes Cp-Zn-Cd-Cp and Cp-Zn-Cd-Cp with a Zn-Cd bond not known thus far. Furthermore, study on the dimetallic complexes of dicyclopentadienyl ligands also predicts results which hold potential application to organometallic chemistry and organic synthesis: (a) Complexes involving a stiff ligand Dp can presumably exist in the form of dimerized sandwich complexes Dp-2M(1)-2M(2)-Dp (M(1), M(2) = Zn, Cd) with two metal-metal bonds. Their overall binding energies amount to -1.84 to -3.48 eV depending upon the kinds of metallic atoms, the strongest binding corresponding to dizinc complex. (b) Complexes involving more flexible ligand Ep can also form similar sandwich complexes Ep-2M(1)-2M(2)-Ep, but with much larger overall binding energies (=-4.97 to -7.09 eV). In addition, they can also exist in the form of nonsandwich complexes M(1)-Ep-M(2) involving only one ligand. Unlike most of dimetallic complexes of other transition metals, syn conformations are found to be exceptionally stable due to the formation of M(1)-M(2) bonds. Careful electronic structure analysis gives deep insight into the nature of observed phenomena.
利用密度泛函理论，我们从理论上研究了环戊二烯基和二环戊二烯基配体与氧化态为 +1 的锌和镉原子形成的各种配合物。我们首先发现，Resta 等人（《科学》，2004 年，305 卷，1136 页）最近鉴定出的夹心配合物 Cp-Zn-Zn-Cp 具有很大的总结合能（=-3.19 eV），其中 Cp 表示五甲基环戊二烯基。此外，发现 Cp-Zn-Zn-Cp（其中 Cp 是未连接甲基的环戊二烯基配体）的结合能还要大 0.93 eV。电子结构分析表明锌原子之间存在电子密度积累，证实了 Zn-Zn 键的存在，其强度与典型的过渡金属 - 卤化物键相当。此外，我们的计算表明可能存在类似的配合物 Cp-Zn-Cd-Cp 和 Cp-Cd-Zn-Cp，其中 Zn-Cd 键迄今尚不为人所知。此外，对二环戊二烯基配体的双金属配合物的研究还预测了一些对有机金属化学和有机合成具有潜在应用价值的结果：(a) 涉及刚性配体 Dp 的配合物可能以具有两个金属 - 金属键的二聚夹心配合物 Dp-2M(1)-2M(2)-Dp（M(1), M(2) = Zn, Cd）的形式存在。它们的总结合能根据金属原子的种类在 -1.84 至 -3.48 eV 之间，最强的结合对应于二锌配合物。(b) 涉及更灵活配体 Ep 的配合物也可以形成类似的夹心配合物 Ep-2M(1)-2M(2)-Ep，但总结合能要大得多（=-4.97 至 -7.09 eV）。此外，它们还可以以仅涉及一个配体的非夹心配合物 M(1)-Ep-M(2) 的形式存在。与大多数其他过渡金属的双金属配合物不同，由于形成了 M(1)-M(2) 键，顺式构象被发现异常稳定。仔细的电子结构分析深入洞察了所观察到的现象的本质。
