Perturbation of the Charge Density between Two Bridged Mo2 Centers: The Remote Substituent Effects
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- 作者：Tao Cheng ; Miao Meng ; Hao Lei ; Chun Y. Liu
- 刊名：Inorganic Chemistry
- 出版年：2014
- 出版时间：September 2, 2014
- 年：2014
- 卷：53
- 期：17
- 页码：9213-9221
- 全文大小：415K
- ISSN：1520-510X
文摘
A series of terephthalate-bridged dimolybdenum dimers with various formamidinate ancillary ligands, denoted as [Mo2(ArNCHNAr)3]2(渭-O2CC6H4CO2) (Ar = p-XC6H4, with X = OCH3 (1), CH3 (2), F (3), Cl (4), OCF3 (5), and CF3 (6)), has been synthesized and studied in terms of substituent effects on electron delocalization between the two dimetal sites. X-ray structural analyses show that these complexes share the same molecular scaffold with the para-substituents (X) being about 8 脜 away from the Mo2 center. It is found that the remote substituents have the capability to tune the electronic properties of the complexes. For the series 1 to 6, the metal鈥搈etal bond distances (dMo鈥揗o) decrease slightly and continuously; the potential separations (螖E1/2) for the two successive one-electron oxidations decrease constantly, and the metal to ligand transition energies (位max) increase in order. More interestingly, the two types of methine protons, H鈭?/sub> on the horizontal and H鈯?/sub> on the vertical ligands with respect to the plane defined by the Mo鈥揗o bond vectors and bridging ligand, display separate resonant signals 未鈭?/sub> and 未鈯?/sub> in the NMR spectra. The displacements of the chemical shifts, 螖未鈭モ€撯姤 = 未鈭?/sub> 鈥?未鈯?/sub>, are getting smaller as the substituents vary from electron-donating to -withdrawing. These results show that the peripheral groups on the [Mo2] units function to fine-tune the metal鈥搈etal interactions crossing the bridging ligand. The experimental parameters, 螖E1/2, 位max, and 螖未鈭モ€撯姤, which are linearly related with the Hammett constants (蟽X) of the X groups, can be used to probe the charge density on the two [Mo2] units and the electronic delocalization between them.