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The first model of the iron hydrogenase active site has been prepared which concomitantly carries a proton and a hydride; the title species was characterized by IR and NMR spectroscopy and is reduced at more positive potential than any other mimic of this kind.

Herein we report the first high turnover photocatalytic hydrogen formation reaction based on an earth-abundant FeIII-NHC photosensitiser. The reaction occurs via reductive quenching of the 2LMCT excited state that can be directly excited with green light and employs either Pt-colloids or [Co(dmgH)2pyCl] as proton reduction catalysts and [HNEt3][BF4] and triethanolamine/triethylamine as proton and electron donors. The outstanding photostability of the FeIII-NHC complex enables turnover numbers >1000 without degradation. [ABSTRACT FROM AUTHOR]

Early intermediates of catalytic water reduction by a Co(ii)–polypyridyl species have been characterized. Electrochemical detection of the Co(iii)-hydride and time-resolved spectroscopic detection of the Co(i)-ligand intermediates provide an understanding of their reactivity in electrolytic or light-driven reduction of protons to hydrogen. [ABSTRACT FROM AUTHOR]

Mononuclear pentacoordinate iron complexes with a free coordination site were prepared as mimics of the distal Fe (Fed) in the active site of [FeFe] hydrogenases. The complexes catalyze the electrochemical reduction of protons at mild overpotential. [ABSTRACT FROM AUTHOR]

A model of the iron hydrogenase active site with the structure [µ-ADT)Fe2(CO)6] (ADT= azadithiolate (S-CH2NR-CH2-S), (2: R = 4-bromophenyl, 3: R = 4-iodophenyl)) has been assembled and covalently linked to a [Ru(terpy)2]2+ photosensitizer. This trinuclear complex 1 represents one synthetic step toward the realization of our concept of light-driven proton reduction. A rigid phenylacetylene tether has been incorporated as the linking unit in 1 in order to prolong the lifetime of the otherwise short-lived [Ru(terpy)2]2+ excited state. The success of this strategy is demonstrated by comparison of the photophysical properties of 1 and of two related ruthenium complexes bearing acetylenic terpyridine ligands, with those of [Ru(terpy)2]2+. IR and electrochemical studies reveal that the nitrogen heteroatom of the ADT bridge has a marked influence on the electronic properties of the [Fe2(CO)6] core. Using the Rehm-Weller equation, the driving force for an electron transfer from the photoexcited *[Ru(terpy)2]2+ to the diiron site in 1 was calculated to be uphill by 0.59 eV. During the construction of the trinuclear complex 1, n-propylamine has been identified as a decarbonylation agent on the [µ-ADT)Fe2(CO)6] portion of the supermolecule. Following this procedure, the first azadithiolate-bridged dinuclear iron complex coordinated by a phosphine ligand [(µ-ADT)Fe2(CO)5PPh3] (4, R = 4-bromophenyl) was synthesized. [ABSTRACT FROM AUTHOR]