Coordination of N,N-Chelated Re(CO)3Cl Units Across a Mo2 Quadruple Bond: Synthesis, Characterization, and Photophysical Properties of a Re鈥揗o2鈥揜e Triad and Its Compon

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• 作者：Samantha E. Brown-Xu ; Malcolm H. Chisholm ; Christopher B. Durr ; Terry L. Gustafson ; Thomas F. Spilker
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：July 25, 2013
• 年：2013
• 卷：117
• 期：29
• 页码：5997-6006
• 全文大小：489K
• 年卷期：v.117,no.29(July 25, 2013)
• ISSN：1520-5215

文摘

2-(2-Pyridyl)-4-methylthiazole carboxylic acid (PMT-H) and rhenium tricarbonyl chloride react to form the red crystalline compound fac-Re(PMT-H)(CO)₃Cl, I, which is an analog of the well-known Re(bpy)(CO)₃Cl molecule, where bpy is 2,2鈥?bipyridine. The acids PMT-H (2 equiv) and Re(PMT-H)(CO)₃Cl (2 equiv) also react with Mo₂(TⁱPB)₄ (TⁱPB = 2,4,6-triisopropylbenzoate) in toluene to give the red compound trans-Mo₂(TⁱPB)₂(PMT)₂, II, and the royal blue compound trans-Mo₂(TⁱPB)₂[(PMT)Re(CO)₃Cl]₂, III, respectively. The X-ray and spectroscopic characterization of I confirms its close relationship with Re(bpy)(CO)₃Cl, as does the spectroscopic characterization of compounds II and III as analogs of other compounds of the form trans-M₂(TiPB)₂L₂, where L is a 蟺-acceptor ligand. Electronic structure calculations on model compounds II鈥?and III鈥? where formate ligands substitute for TⁱPB, show that the highest occupied molecular orbital (HOMO) in II is Mo₂未. When the Re(CO)₃Cl unit is attached to the PMT ligand to form III, this orbital is stabilized significantly and now becomes associated with a close in energy band of Re d⁶, t_2g type orbitals. Oxidation of III is shown to be Mo₂-based, as evident by EPR spectroscopy, and the lowest-energy electronic absorption corresponds to a Mo₂未-to-PMT 蟺* transition. The S₁ states in both II and III are metal-to-ligand charge-transfer (MLCT), and the lowest-energy triplet sate, T₁ is ³MoMo未未*, as evidenced by its steady state emission spectral features. The excited states of compounds I (T₁) and III (S₁ and T₁) have been investigated by time-resolved infrared spectroscopy (TRIR). The spectral features of I parallel those for Re(bpy)(CO)₃Cl, with the lowest-energy T₁ state corresponding to Re d蟺 to PMT-H 蟺* charge transfer, producing higher-energy CO stretching vibrations relative to the ground state. For III, the CO vibrations are shifted to lower energy, consistent with charge being located on the PMT ligand, which enhances Re-to-CO backbonding. In the MoMo未未* T₁ state, however, the backbonding is reduced to the PMT ligand, and the CO stretches are at slightly higher energy relative to the ground state.