This study provides detailed mechanistic insights into light-driven hydrogen production using an abundant copper−iron system. It focuses on the role of the heteroleptic copper photosensitizer [Cu(P ∧ P)(N ∧ N)] + , which can be oxidized or reduced after photoexcitation. By means of IR, EPR, and UV/vis spectroscopy as well as computational studies and spectroelectrochemistry, the possibility of both mechanisms was confirmed. UV/ vis spectroscopy revealed the reorganization of the original heteroleptic photosensitizer during catalysis toward a homoleptic [Cu(N ∧ N) 2 ] + species. Operando FTIR spectroscopy showed the formation of a catalytic diiron intermediate, which resembles well-known hydrogenase active site models.

An extended study of a novel visible-light-driven water reduction system containing an iridium photosensitizer, an in situ iron(0) phosphine water reduction catalyst (WRC), and triethylamine as sacrificial reductant is described. The influences of solvent composition, ligand, ligand-to-metal ratio, and pH were studied. The use of monodentate phosphine ligands led to improved activity of the WRC. By applying a WRC generated in situ from Fe(3) (CO)(12) and tris[3,5-bis(trifluoromethyl)phenyl]phosphine (P[C(6)H(3)(CF(3))(2)](3), Fe(3)(CO)(12)/PR(3)=1:1.5), a catalyst turnover number of more than 1500 was obtained, which constitutes the highest activity reported for any Fe WRC. The maximum incident photon to hydrogen efficiency obtained was 13.4% (440 nm). It is demonstrated that the evolved H(2) flow (0.23 mmol H(2) h(-1) mg(-1) Fe(3)(CO)(12)) is sufficient to be used in polymer electrolyte membrane fuel cells, which generate electricity directly from water with visible light. Mechanistic studies by NMR spectroscopy, in situ IR spectroscopy, and DFT calculations allow for an improved understanding of the mechanism. With respect to the Fe WRC, the complex [HNEt(3)](+)[HFe(3)(CO)(11)](-) was identified as the key intermediate during the catalytic cycle, which led to light-driven hydrogen generation from water.

A bi-catalytic system, in which Ru-MACHO-BH and Ru(H)2(dppe)2 interact in a synergistic manner, was developed for the base-free dehydrogenation of methanol. A total TON > 4200 was obtained with only trace amounts of CO contamination (<8 ppm) in the produced gas.

The iron-catalyzed dehydrogenation of formic acid has been studied both experimentally and mechanistically. The most active catalysts were generated in situ from cationic Fe(II) /Fe(III) precursors and tris[2-(diphenylphosphino)ethyl]phosphine (1, PP3 ). In contrast to most known noble-metal catalysts used for this transformation, no additional base was necessary. The activity of the iron catalyst depended highly on the solvent used, the presence of halide ions, the water content, and the ligand-to-metal ratio. The optimal catalytic performance was achieved by using [FeH(PP3 )]BF4 /PP3 in propylene carbonate in the presence of traces of water. With the exception of fluoride, the presence of halide ions in solution inhibited the catalytic activity. IR, Raman, UV/Vis, and EXAFS/XANES analyses gave detailed insights into the mechanism of hydrogen generation from formic acid at low temperature, supported by DFT calculations. In situ transmission FTIR measurements revealed the formation of an active iron formate species by the band observed at 1543 cm(-1) , which could be correlated with the evolution of gas. This active species was deactivated in the presence of chloride ions due to the formation of a chloro species (UV/Vis, Raman, IR, and XAS). In addition, XAS measurements demonstrated the importance of the solvent for the coordination of the PP3 ligand.

Light on the water: The coupling of Raman and EPR spectroscopy was crucial in the study of the activation, operation, and deactivation steps in the light‐driven splitting of water catalyzed by iridium and iron. The results may provide the foundation for improved water‐reduction catalysts. IrPS=iridium photosensitizer, TEA=triethylamine.

Photocatalytic processes to convert CO2 to useful products including CO and HCOOH are of particular interest as a means to harvest the power of the sun for sustainable energy applications. Herein, we report the photocatalytic reduction of CO2 using iron-based catalysts and visible light generating varying ratios of synthesis gas.

Herein, we report highly active (cyclopentadienone)iron-tricarbonyl complexes for CO2 photoreduction using visible light with an Ir complex as photosensitizer and TEOA as electron/proton donor. Turnover numbers (TON) of ca. 600 (1 h) with initial turnover frequencies (TOF) up to 22.2 min(-1) were observed. Operando FTIR measurements allowed for the proposal of a plausible mechanism for catalyst activation.

A detailed quantitative study of phosphine-modified hydrido iridium complexes relevant for the hydroformylation reaction has been performed using HP-FTIR and HP-NMR spectroscopy. The equilibrium composition under typical reaction conditions has been characterized. Investigation of the temperature dependency allowed even for a distinction between both configurational isomers of [HIr(CO)2(PPh3)2]. The trihydride complex [H3Ir(CO)(PPh3)2] is part of the investigated equilibrium depending on the ratio of p(H2)/p(CO). Single rate constants for the sequence of corresponding equilibrium reactions have been estimated from stopped-flow experiments and conventional measurements, monitoring the concentrations after changing reactant concentrations.