Electronic Excited States of Tungsten(0) Arylisocyanides

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• 作者：Hana Kvapilov谩 ; Wesley Sattler ; Aaron Sattler ; Igor V. Sazanovich ; Ian P. Clark ; Michael Towrie ; Harry B. Gray ; Stanislav Z谩li拧 ; Anton铆n Vl膷ek
• 刊名：Inorganic Chemistry
• 出版年：2015
• 出版时间：September 8, 2015
• 年：2015
• 卷：54
• 期：17
• 页码：8518-8528
• 全文大小：680K
• ISSN：1520-510X

文摘

W(CNAryl)₆ complexes containing 2,6-diisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited states. These properties are enhanced upon appending another aryl ring, e.g., W(CNdippPh^OMe₂)₆; CNdippPh^OMe₂ = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide (Sattler et al. J. Am. Chem. Soc. 2015, 137, 1198鈭?205). Electronic transitions and low-lying excited states of these complexes were investigated by time-dependent density functional theory (TDDFT); the lowest triplet state was characterized by time-resolved infrared spectroscopy (TRIR) supported by density functional theory (DFT). The intense absorption band of W(CNdipp)₆ at 460 nm and that of W(CNdippPh^OMe₂)₆ at 500 nm originate from transitions of mixed 蟺蟺*(C鈮鈥揅)/MLCT(W 鈫?Aryl) character, whereby W is depopulated by ca. 0.4 e^{鈥?/sup> and the electron-density changes are predominantly localized along two equatorial molecular axes. The red shift and intensity rise on going from W(CNdipp)₆ to W(CNdippPhOMe₂)₆ are attributable to more extensive delocalization of the MLCT component. The complexes also exhibit absorptions in the 300鈥?20 nm region, owing to W 鈫?C鈮 MLCT transitions. Electronic absorptions in the spectrum of W(CNXy)₆ (Xy = 2,6-dimethylphenyl), a complex with orthogonal aryl orientation, have similar characteristics, although shifted to higher energies. The relaxed lowest W(CNAryl)₆ triplet state combines 蟺蟺* excitation of a trans pair of C鈮鈥揅 moieties with MLCT (0.21 e鈥?/sup>) and ligand-to-ligand charge transfer (LLCT, 0.24鈥?.27 e鈥?/sup>) from the other four CNAryl ligands to the axial aryl and, less, to C鈮 groups; the spin density is localized along a single Aryl鈥揘鈮鈥揥鈥揅鈮鈥揂ryl axis. Delocalization of excited electron density on outer aryl rings in W(CNdippPhOMe₂)₆ likely promotes photoinduced electron-transfer reactions to acceptor molecules. TRIR spectra show an intense broad bleach due to 谓(C鈮), a prominent transient upshifted by 60鈥?5 cm鈥?, and a weak down-shifted feature due to antisymmetric C鈮 stretch along the axis of high spin density. The TRIR spectral pattern remains unchanged on the femtosecond-nanosecond time scale, indicating that intersystem crossing and electron-density localization are ultrafast (<100 fs).}