Photochemical H₂ Evolution Catalyzed by Porphyrin-based Cubic Cages Singly and Doubly Encapsulating PtCl₂(4,4′-dimethyl-2,2′-bipyridine)

Abstract

A porphyrin-based cubic cage (Cube) was reacted with a Pt(II)-based molecular H 2 -evolving catalyst, PtCl 2 (dmbpy) (PtDmb; dmbpy: 4,4¤-dimethyl-2,2¤-bipyridine), to give Cubes incorporated with one or two equivalents of PtDmb, i.e., Cube(PtDmb) and Cube(PtDmb) 2 , which was confirmed by ESI-TOF MS spectroscopy. A photochemical H 2 -evolving system consisting of EDTA (sacrificial electron donor), [Ru(bpy) 3 ] 2+ (photosensitizer), and methylviologen (electron relay) was used to demonstrate that the catalyst encapsulated can also serve as an effective H 2 -evolving catalyst. In spite of continued increase in global energy consumption, we face a critical problem arising from a shortage of fossil fuels as well as global warming due to continued CO 2 emission. One belief has been to solve these problems based on the application of hydrogen energy, which may be effectively produced in a large scale by splitting water using solar energy. Among various efforts towards this target, photodriven electron transfer processes combined with catalysis of water oxidation and reduction, all based on molecular processes, have attracted great attention in view of mimicking natural photosynthesis.

A Diprotonated Porphyrin as an Electron Mediator in Photoinduced Electron Transfer in Hydrogen-Bonded Supramolecular Assemblies

“…Note that the one-electron-reduced species ( BV •+ ) is relatively stable, enabling to form a long-lived ET state in supramolecules. In addition, viologen derivatives have been often used as electron mediators in photocatalytic reduction reactions. − Thus, we have employed a BV 2+ derivative having a carboxyl group ( BV 2+ COOH ) as an electron acceptor in a hydrogen-bonded supramolecular assembly with H 2 DPP , H 4 DPP 2+ (BV 2+ COO – ) 2 . We have examined the photodynamics of H 4 DPP 2+ (BV 2+ COO – ) 2 to confirm that H 4 DPP •+ acts as an electron mediator in the hydrogen-bonded supramolecule.…”

Supramolecular Coordination Cages for Artificial Photosynthesis and Synthetic Photocatalysis

“…127 Following the same principle, Sakai and co-workers introduced molecular Pt(II) PRCs such as Pt II (dmb)Cl 2 (9) bearing π-conjugated ligands as guest into the cavity of C7 (Figure 11). 128 In addition to 3a as PS and ethylenediaminetetra acetic acid (EDTA) as sacrificial reductant, methyl viologen (10) was used as electron relay in the photochemical system with [9⊂C7] as catalyst in aqueous acetate buffer at pH 5. The role of the redox mediator is to act as shuttle between PS and catalyst.…”

Enhanced photoreduction of water catalyzed by a cucurbit[8]uril-secured platinum dimer

“…The design of artificial photosynthetic systems that split water into molecular hydrogen and oxygen remains a major challenge of our times. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Explored extensively by Sakai and coworkers, [17][18][19][20][21][22][23][24][25][26][27][28] the photoreduction of water requires a photosensitizer, an electron relay and a hydrogen-evolving catalyst, either as a three-component system, 1,2 or with one [3][4][5][6][7][8][9][10] or two 11,12 multifunctional components. Sakai showed that Platinum(II) terpyridyl (tpy) chloride 1a can be used both as a photosensitizer and H 2 -evolving catalyst in the presence of ethylenediaminetetraacetic acid (EDTA) as the sacrificial electron donor.…”