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)b>3b>Cl, <b>Ib>, which is an analog of the well-known Re(bpy)(CO)b>3b>Cl molecule, where bpy is 2,2鈥?bipyridine. The acids PMT-H (2 equiv) and Re(PMT-H)(CO)b>3b>Cl (2 equiv) also react with Mob>2b>(TⁱPB)b>4b> (TⁱPB = 2,4,6-triisopropylbenzoate) in toluene to give the red compound trans-Mob>2b>(TⁱPB)b>2b>(PMT)b>2b>, <b>IIb>, and the royal blue compound trans-Mob>2b>(TⁱPB)b>2b>[(PMT)Re(CO)b>3b>Cl]b>2b>, <b>IIIb>, respectively. The X-ray and spectroscopic characterization of <b>Ib> confirms its close relationship with Re(bpy)(CO)b>3b>Cl, as does the spectroscopic characterization of compounds <b>IIb> and <b>IIIb> as analogs of other compounds of the form trans-Mb>2b>(TiPB)b>2b>Lb>2b>, where L is a 蟺-acceptor ligand. Electronic structure calculations on model compounds <b>IIb>鈥?and <b>IIIb>鈥? where formate ligands substitute for TⁱPB, show that the highest occupied molecular orbital (HOMO) in <b>IIb> is Mob>2b>未. When the Re(CO)b>3b>Cl unit is attached to the PMT ligand to form <b>IIIb>, this orbital is stabilized significantly and now becomes associated with a close in energy band of Re d⁶, tb>2gb> type orbitals. Oxidation of <b>IIIb> is shown to be Mob>2b>-based, as evident by EPR spectroscopy, and the lowest-energy electronic absorption corresponds to a Mob>2b>未-to-PMT 蟺* transition. The Sb>1b> states in both <b>IIb> and <b>IIIb> are metal-to-ligand charge-transfer (MLCT), and the lowest-energy triplet sate, Tb>1b> is ³MoMo未未*, as evidenced by its steady state emission spectral features. The excited states of compounds <b>Ib> (Tb>1b>) and <b>IIIb> (Sb>1b> and Tb>1b>) have been investigated by time-resolved infrared spectroscopy (TRIR). The spectral features of <b>Ib> parallel those for Re(bpy)(CO)b>3b>Cl, with the lowest-energy Tb>1b> state corresponding to Re d蟺 to PMT-H 蟺* charge transfer, producing higher-energy CO stretching vibrations relative to the ground state. For <b>IIIb>, 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* Tb>1b> state, however, the backbonding is reduced to the PMT ligand, and the CO stretches are at slightly higher energy relative to the ground state.