Organometallic Rhodium(III) Complexes as Catalysts for the Photoreduction of Protons to Hydrogen on Colloidal TiO₂

Abstract

The photoreduction of H+ to H2 by sunlight and colloidal TiO2 in the presence of the rhodium(III) complexes 1 (ppy = oligopyridine ligand, e.g., bipyridyl; L=H2O, Cl⊖, Br⊖, I⊖; n = 1, 2) is possible without the participation of colloidal platinum and is not restricted to alkaline solution. The complexes are thereby reduced, via the RhII stage, to RhI complexes, which then undergo transformation to the RhIII complexes with evolution of hydrogen. The course of the reaction was investigated by cyclic voltammetry and pulse radiolysis as well as by transient absorption spectroscopy.

Water‐Soluble Phenanthroline Complexes of Rhodium, Iridium and Ruthenium for the Regeneration of NADH in the Enzymatic Reduction of Ketones

“…Transfer hydrogenation of NAD + to NADH in aqueous solution catalysed by cationic chlorido complexes 1 to 5 by using the formate anion as the hydrogen source. [36] the new 5-nitro-and 5-amino-1,10-phenanthroline cations 2, 3 and 4 are chiral, and compounds [2]Cl, [3]Cl and [4]Cl are produced as racemic mixtures.…”

Product Selectivity in Homogeneous Artificial Photosynthesis Using [(bpy)Rh(Cp*)X]n+-Based Catalysts

“…The molecular structure of the actual active rhodium catalyst has been under debate during the last years. Since the late 1980s, the catalytically active species has been described as a Rh III -H (structure A in Figure 4) [33,45]. The experimental proof of the existence of this species has been performed by Steckhan et al [51], as well as Fukuzumi et al [60], using a 6,6 -dimethylated bipyridine as the N,N-chelating ligand.…”

“…Since the late 1980s, the catalytically active species has been described as a Rh III -H (structure A in Figure 4) [33,45]. The experimental proof of the existence of this species has been performed by Steckhan et al [51], as well as Fukuzumi et al [60], using a 6,6′-dimethylated bipyridine [33][34][35][36][37][38], reaction (b) [39,40], reaction (c) [26,29,[41][42][43][44], reaction (d) [45][46][47][48][49][50][51][52][53][54][55], and reaction (e) [48,[56][57][58][59].…”

“…Access to the reactive [(NN)Rh I (Cp*)] intermediate is accomplished via a two electron reduction at a rather low cathodic voltage (ranging from −700 to −900 mV against Ag/AgCl depending on the N,N-chelating ligand) [51]. After the addition of one electron, the primarily obtained coordinatively unstable Rh II species disproportionates extremely rapidly, leading to the desired Rh I compound (for the majority of the applied complexes [64]), as this process is merely connected with the easy loss of a weakly bound monodentate ligand [33,37,65]. In addition, a crystal structure of the reduced d 8 intermediate [(bpy)Rh I (Cp*)] revealed that the bpy and the Cp* plane are lying perpendicular to each other, as depicted in Figure 4, different to the piano-stool like structure of the d 6 species [(bpy)Rh III (Cp*)X] n+ [66].…”

“…In order to use molecular hydrogen as a green fuel, efficient catalytic liberation from the storage materials is an important prerequisite for this technology. It has been shown that [(bpy)Rh(Cp*)(H2O)] 2+ is able to selectively decompose formic acid into H2 and CO2 via a rhodium formato and a rhodium hydride intermediate without the production of CO [60] [33,58,70].…”