Photochemistry and Photophysics of a Pd(II) Metalloporphyrin: Re(I) Tricarbonyl Bipyridine Molecular Dyad and its Activity Toward the Photoreduction of CO2 to CO
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- 作者：Jacob Schneider ; Khuong Q. Vuong ; James A. Calladine ; Xue-Zhong Sun ; Adrian C. Whitwood ; Michael W. George ; Robin N. Perutz
- 刊名：Inorganic Chemistry
- 出版年：2011
- 出版时间：December 5, 2011
- 年：2011
- 卷：50
- 期：23
- 页码：11877-11889
- 全文大小：542K
- 年卷期：v.50,no.23(December 5, 2011)
- ISSN：1520-510X
文摘
The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2鈥?bipyridine-4鈥?carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO)3(Pic)Bpy-PdTPP][PF6]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO)3(NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)掳, 178.1(7)掳, and 156.8(9)掳 between porphyrin plane, porphyrin-linked C6H4 group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (位ex = 520 nm) of [Re(CO)3(Pic)Bpy-PdTPP][PF6] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO)3(Pic)Bpy-PdTPP][PF6] is employed as a photocatalyst for the reduction of CO2 to CO in DMF/NEt3 solution with 位ex > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO)3(Pic)Bpy][PF6] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms after a slight induction period and during the concurrent photoreduction of the sensitizer to a Pd(II) chlorin species. Palladium(II) meso-tetraphenylchlorin, the hydrogenated porphyrin analogue of PdTPP, has been synthesized independently and can be substituted for PdTPP in the two-component system with [Re(CO)3(Pic)Bpy][PF6], forming 9 TNs CO. An intramolecular electron transfer process for the dyad is supported by cyclic voltammetry and steady-state emission studies, from which the free energy change was calculated to be 螖Gox* = 鈭?.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO)3(Pic)Bpy-PdTPP][PF6] was monitored using time-resolved infrared (TRIR) spectroscopy in the 谓(CO) region on several time scales with excitation at 532 nm. Spectra were recorded in CH2Cl2 with and without NEt3. Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the 蟺鈥撓€* excited state (2029 cm鈥?) and to the charge-separated state (2008, 1908 cm鈥?); these bands decay and the parent recovers with lifetimes of 20鈥?0 ps. Spectra recorded on longer time scales (ns, 渭s, and seconds) show the growth and decay of further species with 谓(CO) bands indicative of electron transfer to Re(Bpy).