Shubina Tatyana E, Marbach Hubertus, Flechtner Ken, Kretschmann Andreas, Jux Norbert, Buchner Florian, Steinrück Hans-Peter, Clark Timothy, Gottfried J Michael
Computer-Chemie-Centrum, Universität Erlangen-Nürnberg, Nägelsbachstrasse 25, Erlangen, Germany.
J Am Chem Soc. 2007 Aug 1;129(30):9476-83. doi: 10.1021/ja072360t. Epub 2007 Jul 11.
The direct metalation of tetraphenylporphyrin with bare metal atoms (Co and Zn) was studied with X-ray photoelectron spectroscopy, scanning tunneling microscopy, and temperature-programmed reaction measurements on ordered monolayer films of the molecules adsorbed on a Ag(111) surface. The mechanism of this novel type of surface reaction was investigated using density functional theory (DFT) calculations for the related gas-phase reactions of the unsubstituted porphyrin with the metals Fe, Co, Ni, Cu, and Zn. The reaction starts with the formation of an initial complex, in which the metal atom is coordinated by the intact unreduced porphyrin. This complex resembles the sitting-atop complex proposed for porphyrin metalation with metal ions in solution. In two subsequent steps, the pyrrolic hydrogen atoms are transferred to the metal atom, forming H2, which is eventually released. The activation barriers of the H-transfer steps vary for the different metal atoms. DFT calculations suggest that metalations with Fe, Co, and Ni show two-state reactivity, while those with Cu and Zn proceed on a single potential energy surface. For metalation with Zn, we calculated a barrier of the first hydrogen transfer step of 32.6 kcal mol(-1), in good agreement with the overall experimental activation energy of 31 kcal mol(-1).
利用X射线光电子能谱、扫描隧道显微镜以及对吸附在Ag(111)表面的分子有序单层膜进行程序升温反应测量，研究了四苯基卟啉与裸金属原子（钴和锌）的直接金属化反应。使用密度泛函理论(DFT)计算未取代卟啉与金属铁、钴、镍、铜和锌的相关气相反应，研究了这种新型表面反应的机理。反应始于初始络合物的形成，其中金属原子由完整未还原的卟啉配位。该络合物类似于溶液中卟啉与金属离子金属化所提出的顶位络合物。在随后的两个步骤中，吡咯氢原子转移到金属原子上，形成H₂，最终释放出来。不同金属原子的氢转移步骤的活化能垒各不相同。DFT计算表明，铁、钴和镍的金属化表现出双态反应性，而铜和锌的金属化则在单一势能面上进行。对于锌的金属化，我们计算出第一个氢转移步骤的能垒为32.6 kcal mol⁻¹，与31 kcal mol⁻¹的整体实验活化能吻合良好。
