Cissell Julie A, Vaid Thomas P, Yap Glenn P A
Department of Chemistry and Center for Materials Innovation, Washington University, St. Louis, Missouri 63130, USA.
J Am Chem Soc. 2007 Jun 27;129(25):7841-7. doi: 10.1021/ja070794i. Epub 2007 Jun 6.
Treatment of GeCl2(dioxane) with Li2(TPP)(OEt2)2 (TPP = tetraphenylporphyrin) in THF yields Ge(TPP), the first free Ge(II) porphyrin complex. In pyridine Ge(TPP) is converted to Ge(TPP)(py)2, an antiaromatic Ge(IV) complex, whereas in benzene the reaction is reversed, and pyridine dissociates from Ge(TPP)(py)2 to form Ge(TPP). That reversible reaction represents an unusual, if not unique, example of an oxidation-state change in a metal induced by coordination of a dative ligand. UV-vis and 1H NMR spectroscopy show that Ge(TPP) is an aromatic Ge(II) porphyrin complex, while the 1H NMR spectrum of Ge(TPP)(py)2 clearly indicates the presence of a strong paratropic ring current, characteristic of an antiaromatic compound. Both Ge(TPP) and Ge(TPP)(py)2 have been crystallographically characterized, and the antiaromaticity of Ge(TPP)(py)2 leads to alternating short and long C-C bonds along the 20-carbon periphery of its porphine ring system. Coordination of pyridine to Ge(TPP) greatly increases its reducing ability: the Ge(TPP)0/2+ redox potential is about +0.2 V, while the Ge(TPP)(py)2(0/+) redox potential is -1.24 V (both vs. ferrocene). The equilibrium constant of the reaction Ge(TPP) + 2 py = Ge(TPP)(py)2 in C6D6 is 22 M-2. The germanium complex of the more electron-withdrawing tetrakis[3,5-bis(trifluoromethyl)phenyl]porphyrin, Ge(TArFP), and its pyridine adduct Ge(TArFP)(py)2 were synthesized. The equilibrium constant of the reaction Ge(TArFP) + 2 py = Ge(TArFP)(py)2 in C6F6/C6D6 is 2.3 x 10(4) M-2. Density functional theory calculations are consistent with the experimental observation that M(TPP)(py)2 formation from M(TPP) and pyridine is most favorable for M=Si, borderline for Ge, and unfavorable for Sn.
在四氢呋喃（THF）中，用二乙氧基二锂（TPP）（Li2(TPP)(OEt2)2，TPP = 四苯基卟啉）处理二氯锗（GeCl2(dioxane)）可得到Ge(TPP)，即首个游离的二价锗卟啉配合物。在吡啶中，Ge(TPP)会转化为反芳香性的四价锗配合物Ge(TPP)(py)2，而在苯中反应则相反，吡啶会从Ge(TPP)(py)2上解离，形成Ge(TPP)。该可逆反应代表了一个由给体配体配位引发金属氧化态变化的不同寻常（即便不是独一无二）的例子。紫外可见光谱和核磁共振氢谱（1H NMR）表明，Ge(TPP)是一种芳香性的二价锗卟啉配合物，而Ge(TPP)(py)2的核磁共振氢谱清楚地显示出存在强的抗磁环电流，这是反芳香性化合物的特征。Ge(TPP)和Ge(TPP)(py)2均已通过晶体学表征，Ge(TPP)(py)2的反芳香性导致其卟吩环体系20个碳原子的外围出现交替的短碳 - 碳键和长碳 - 碳键。吡啶与Ge(TPP)配位极大地增强了其还原能力：Ge(TPP)的0/2 + 氧化还原电位约为 +0.2 V，而Ge(TPP)(py)2的0/+氧化还原电位为 -1.24 V（两者均相对于二茂铁）。在C6D6中，反应Ge(TPP) + 2 py = Ge(TPP)(py)2的平衡常数为22 M-2。合成了吸电子能力更强的四[3,5 - 双（三氟甲基）苯基]卟啉的锗配合物Ge(TArFP)及其吡啶加合物Ge(TArFP)(py)2。在C6F6/C6D6中，反应Ge(TArFP) + 2 py = Ge(TArFP)(py)2的平衡常数为2.3×10(4) M-2。密度泛函理论计算与实验观察结果一致，即由M(TPP)和吡啶形成M(TPP)(py)2对于M = Si最为有利，对于Ge处于临界状态，而对于Sn则不利。
