A Supramolecular Photocatalyst for the Production of Hydrogen and the Selective Hydrogenation of Tolane

Abstract

Light‐driven metallo‐organic catalysis: Intramolecular photoelectron transfer in the heterodinuclear complex 1 facilitates the photocatalytic production of hydrogen and the selective hydrogenation of tolane to give cis‐stilbene. All three well‐coordinated parts of the supramolecular system are essential: the (tbbpy)2Ru fragment as a photoactive unit, the redox‐active bridging ligand as an electron relay and storage site, and the palladium as a catalytically active center.

Tuning of photocatalytic activity by creating a tridentate coordination sphere for palladium

“…In comparison, the complexation of the unsubstituted tpphz with [(tbbpy) 2 RuCl 2 ] has to be performed at 200°C in refluxing ethylene glycol with a three-fold excess of the ligand to guarantee a sufficient solvation of tpphz and to avoid a complexation of the ruthenium moiety on both coordination sites. 30 In the case of the methoxyphenyl-substituted tpphz ligand much milder conditions, i.e. a 1 : 1 ratio of the reactants and a lower reaction temperature, are sufficient, since the likelihood of a double complexation is strongly reduced due to steric hindrance of the bulky substituents in ortho-position to the nitrogens.…”

“…30 Furthermore, we have investigated the impact of the addition of the second metal centre on the photophysics. Regarding the absorption features of Ru(bmptpphz)PdCl in comparison with the mononuclear Ru(bmptpphz), the absorption maximum in the visible range is shifted to a higher wavelength (447 nm) (see Table 1 and ESI Fig.…”

“…47 In general, the photochemical reduction of the Pd(II) centre to Pd(0) is a prerequisite for both, metal colloid formation and catalytic turnover of protons to hydrogen. 30 The cyclometallation in Ru(bmptpphz)PdCl will influence both, the redox properties of the Pd centre and the stability and reactivity of the metal centre in all oxidation states since Pd(0) forms stable bonds to organometallic ligands. 48 (3) Moreover, also the steric shielding by the anisyl-substituents might have an impact on the catalytic performance of the Pd centre.…”

Supramolecular activation of a molecular photocatalyst

“…Recent examples of intramolecular photocatalysts include water oxidation catalysts, water reduction catalysts and carbon dioxide reducing catalysts. [2][3][4][5][6][7][8][9][10][11] In direct comparison with intermolecular [12][13][14][15][16] and heterogeneous photocatalysts, [17][18][19][20] intramolecular photocatalysis, however, often suffer from lower catalytic activity. It is therefore of paramount importance to learn more about the factors determining the catalytic activity of intramolecular photocatalysts.…”

Electron Transfer and Solvent-Mediated Electronic Localization in Molecular Photocatalysis

“…These systems contain, within one molecule, three principle components: A photoabsorber, a catalytic center and bridging unit that enables electron transfer between absorber and catalyst. 31 In recent years, many reports have been made on such model systems, and similar complexes. [31][32][33][34][35][36][37][38][39][40] The system under investigation [(bpy) 2 Ru II (tpphz)Co III (bpy) 2 ] 5+ -3 (where bpy = 2,2-bipyridine, tpphz = tetrapyrido (3,2 -a:2'3'-c:3",2" -h::2"',3"' -j) phenazine (abbreviated as "[Ru=Co]") is shown in figure 1.…”