On the Photochemistry of the Low-Lying Excited State of Fe2(CO)6S2. A DFT and QTAIM Investigation
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- 作者：Luca Bertini ; Piercarlo Fantucci ; Luca De Gioia
- 刊名：Organometallics
- 出版年：2011
- 出版时间：February 14, 2011
- 年：2011
- 卷：30
- 期：3
- 页码：487-498
- 全文大小：997K
- 年卷期：v.30,no.3(February 14, 2011)
- ISSN：1520-6041
文摘
The photochemistry originated by the Fe2(CO)6S2 low-lying excited states is investigated using density functional theory (DFT), time-dependent density functional theory (TDDFT), and the quantum theory of atoms in molecules (QTAIM) methods.
The 11A1 excitation is the most intense among the low-lying excited states computed at the TDDFT level, which is assigned to the 449 nm metal-to-ligand charge transfer (MLCT) band observed experimentally. We then investigated the nine excited states in a range of 卤35 nm centered on the 11A1 excitation energy, which reproduces the range of wavelengths covered by a recent 450 卤 35 nm low-energy laser photolysis experiment. The results presented in this paper suggest that the 450 nm photochemistry recently investigated proceeds mainly through the 11B2 lowest energy singlet excited state. The comparison between tetrahedrane ground state and 11B2 vertical excited state QTAIM atomic net charges evidenced the Fe鈫扴 MLCT character but also a significant CO鈫扴 ligand-to-ligand charge transfer (LLCT). Geometry relaxation of the nine excited state structures shows a S鈭扴 bond distance elongation that reaches the highest value for the 11B2 state. Moreover, during geometry optimization of the 11B2 state, the HOMO/LUMO crossing occurs, favoring the formation of the Fe鈭扚e butterfly isomer upon decay to the ground state, in agreement with experimental findings. Delocalization indexes allow us to describe the shift of the bonding electron density along the 11B2 photochemical reaction path that connects the tetrahedrane ground state to the Fe鈭扚e butterfly intermediate. Along this path, the S鈭扴 bond is progressively weakened until its breaking in the Fe鈭扚e butterfly isomer, while the Fe鈭扚e bond is only partially weakened. The S atom is progressively reduced with a total increasing of its negative charge by 0.211 electron, leading to the Fe鈭扚e butterfly intermediate suitable for oxidative addition. In light of the results obtained, a mechanism of the photochemical ethylene oxidative addition to Fe2(CO)6S2 is proposed.
The 11A1 excitation is the most intense among the low-lying excited states computed at the TDDFT level, which is assigned to the 449 nm metal-to-ligand charge transfer (MLCT) band observed experimentally. We then investigated the nine excited states in a range of 卤35 nm centered on the 11A1 excitation energy, which reproduces the range of wavelengths covered by a recent 450 卤 35 nm low-energy laser photolysis experiment. The results presented in this paper suggest that the 450 nm photochemistry recently investigated proceeds mainly through the 11B2 lowest energy singlet excited state. The comparison between tetrahedrane ground state and 11B2 vertical excited state QTAIM atomic net charges evidenced the Fe鈫扴 MLCT character but also a significant CO鈫扴 ligand-to-ligand charge transfer (LLCT). Geometry relaxation of the nine excited state structures shows a S鈭扴 bond distance elongation that reaches the highest value for the 11B2 state. Moreover, during geometry optimization of the 11B2 state, the HOMO/LUMO crossing occurs, favoring the formation of the Fe鈭扚e butterfly isomer upon decay to the ground state, in agreement with experimental findings. Delocalization indexes allow us to describe the shift of the bonding electron density along the 11B2 photochemical reaction path that connects the tetrahedrane ground state to the Fe鈭扚e butterfly intermediate. Along this path, the S鈭扴 bond is progressively weakened until its breaking in the Fe鈭扚e butterfly isomer, while the Fe鈭扚e bond is only partially weakened. The S atom is progressively reduced with a total increasing of its negative charge by 0.211 electron, leading to the Fe鈭扚e butterfly intermediate suitable for oxidative addition. In light of the results obtained, a mechanism of the photochemical ethylene oxidative addition to Fe2(CO)6S2 is proposed.