The Active Site Model for Iron-Only Hydrogenases Coordinatively Bonded to a Metalloporphyrin Photosensitizer

Abstract

Treatment of the parent model [(μ-SCH2)2NH]Fe2(CO)6 (1) with 4-pyridinecarboxylic acid chloride or benzoyl chloride in the presence of Et3N afforded the simple model compounds [(μ-SCH2)2NC(O)C5H4N]Fe2(CO)6 (2) and [(μ-SCH2)2NC(O)Ph]Fe2(CO)6 (4). Further treatment of 2 with the photosensitizer zinc tetraphenylporphyrin (ZnTPP) produced the target model compound [(μ-SCH2)2NC(O)C5H4N]Fe2(CO)6(ZnTPP) (3), which is the first metalloporphyrin-containing active site model for the Fe-only hydrogenases.

Synthesis and characterization of a supramolecular assembly based on a pyridyl-functionalized [FeFe]-hydrogenase mimic and zinc tetraphenylporphyrin

“…Due to the coordination effect of ZnTPP, the Fe1\ \Fe2 bond of 2 is shorter by about 0.1 Å compared to that of 1. The coordination geometry around the Zn-centre in 2 is strongly similar to those in other reported ZnTPP-associated assemblies with a normal Zn1\ \N1 bond length (2.185(7) Å) [10,14]. The dihedral angle between the pyridine ring and the ZnTPP plane is about 74°.…”

“…Since the functional mimic, [(μ-SCH 2 ) 2 NC(O)C 5 H 4 N]Fe 2 (CO) 6 ·ZnTPP, was synthesized by Song and co-workers, a handful of similar assemblies combining [FeFe]-hydrogenase mimics with zinc tetraphenylporphyrin (ZnTPP) have been reported in succession by other researchers [9][10][11][12]. However, the catalytic activities of reported assemblies still lag far behind those observed in the hydrogenases [13].…”

Hydrogen Production by Noble‐Metal‐Free Molecular Catalysts and Related Nanomaterials

“…A coordinately linked ZnPorÀFeFe complex (1, Figure 1), where a pyridyl group, tethered to the azadithiolate bridge of the diiron catalytic unit, is axially coordinated to the Zn II ion of porphyrin, was constructed and structurally characterized by Song and co-workers. [19] Although the proposed intramolecular electron transfer was not experimentally verified by time-resolved spectroscopy and H 2 evolution was not reported for this complex, the ZnPorÀ FeFe system is attractive because both catalyst and photosensitizer are based on bioinspired complexes. A similar ZnPorÀ FeFe complex 2 (Figure 1), self-assembled in solution, was used as photocatalyst for H 2 generation.…”

“…So far, completely noble-metal-free molecular devices effective for photoinduced H 2 generation have been limited to pho- [19][20][21][22] The good photophysical properties of zinc porphyrins (ZnPor) make them applicable, inexpensive photosensitizers for H 2 production. A coordinately linked ZnPorÀFeFe complex (1, Figure 1), where a pyridyl group, tethered to the azadithiolate bridge of the diiron catalytic unit, is axially coordinated to the Zn II ion of porphyrin, was constructed and structurally characterized by Song and co-workers.…”

“…Almost all reported molecular catalyst systems for photoinduced H 2 production suffer from limited lifetimes of photosensitizers (PSs), regardless of whether noble-metal-containing PSs, [2][3][4][5][6][7][8][9][10][11][12][13][14] porphyrin-derived PSs, [19][20][21][22] or organic dyes are used. [18] Finding robust and efficient PSs is one of the most crucial problems for constructing practically useful H 2 -evolving systems.…”