Stabilisation effects of phosphane ligands in the homogeneous approach of sunlight induced hydrogen production

Abstract

Most of the systems for photochemical hydrogen production are not stable and suffer from decomposition. With bis(bidentate) tetraphosphane ligands the stability increases enormously, up to more than 1000 h. This stability was achieved with a system containing osmium(ii) as a light harvesting antenna and palladium(ii) as a water reduction catalyst connected with a bis(bidentate) phosphane ligand in one molecule with the chemical formula [Os(bpy)(dppcb)Pd(dppm)](PF). With the help of electrochemical measurements as well as photophysical data and its single crystal X-ray structure, the electron transfer between the two active metal centres (light harvesting antenna, water reduction catalyst) was analysed. The distance between the two active metal centres was determined to be 7.396(1) Å. In a noble metal free combination of a copper based photosensitiser and a cobalt diimine-dioxime complex as water reduction catalyst a further stabilisation effect by the phosphane ligands is observed. With the help of triethylamine as a sacrificial donor in the presence of different monophosphane ligands it was possible to produce hydrogen with a turnover number of 1176. This completely novel combination is also able to produce hydrogen in a wide pH-range from pH = 7.0 to 12.5 with the maximum production at pH = 11.0. The influence of monophosphane ligands with different Tolman cone angles was investigated. Monophosphane ligands with a large Tolman cone angle (>160°) could not stabilise the intermediate of the cobalt based water reduction catalyst and so the turnover number is lower than for systems with an addition of monophosphane ligands with a Tolman cone angle smaller than 160°. The role of the monophosphane ligand during sunlight-induced hydrogen production was analysed and these results were confirmed with DFT calculations. Furthermore the crystal structures of two important Co(i) intermediates, which are the catalytic active species during the catalytic pathway, were obtained. The exchange of PPh with other tertiary phosphane ligands can have a major impact on the activity, depending on the coordination properties. By an exchange of monophosphane ligands with functionalised phosphane ligands (hybrid ligands) the hydrogen production was raised 2.17 times.

Application of a Water‐Soluble Matrix‐Stabilized Palladium Nanoparticle Catalyst for Photocatalytic Hydrogen Generation with High Activity and Stability

“…The molecular structure of 8 gave rational suggestions for its observed photocatalytic stability.T he combination of 1 and 8 (long-lived photosensitizer) made it possible to test 1 under exceptionally long experimental conditions (45 days) and to prove that the PEGylated Pd nanoparticles increased only slightly in size under real photocatalyticc onditions, making them ideal candidates to conduct the catalytic reaction homogeneously.T his stabilityo utperforms colloidal platinum catalysts as well as comparable molecular Os-Pd dyads. [26,28,29] Further investigation is necessary to optimize the Pd catalyst and further increasei ts high hydrogen yield. In addition, the longevity of the osmium dyei su nprecedented for homogeneous catalysis and am ethodn eeds to be found to optimize this photocatalytic system for hydrogen production from water.…”

Biocompatible Osmium Telluride-Polypyrrole Nanocomposite Material: Application in Prostate Specific Antigen Immunosensing

“…On the other hand, the absorbance band at 320 nm is due to d valence band of Os 8+ [22]. Lastly, the formation of TGA-OsTe 2 QD was determined by the absorbance band appearing at 400 nm [23]. The incorporation of polypyrrole with TGA-OsTe 2 QD (Figure 2A, line (c)) produced a more pronounced absorbance band at 262 nm.…”

The influence of trinuclear complexes on light-induced hydrogen production

“…1,2 Artificial systems, inspired by natural photosynthesis, were designed to convert light energy into chemical energy and were studied for their hydrogen production ability. [3][4][5][6] Light-induced water splitting based on the concept of molecular artificial photosynthesis (AP), consisting of a photosensitiser (PS), a water reducing catalyst (WRC) and a sacrificial donor, which first reduces the PS as a consequence of its excess, is applied with the designed systems.…”

“…A special phosphine ligand was invented to stabilise WRCs 5,[7][8][9][10] during catalysis and to increase the rigidity of the ligand backbone for chromophores. [11][12][13] The electronic and steric effects of the substituents on the phosphine ligand have an influence on the auxiliary ligands and their transition metal complexes: electronegative substituents lower the energy gap of the anti-binding s*-orbitals, benefitting p-acceptor properties.…”

“…Moreover, anisyl phosphines exhibit enhanced catalytic stability compared to phenyl phosphine analogues. 5,6,15,16 Another beneficial preparative side effect is that the educt di-ortho anisyl phosphine is a powder and easy to handle in comparison to its easily inflammable diphenyl phosphine relative, which makes it attractive for larger scale reactions. Similar systems of the monoand bis-ligand with phenyl instead of anisyl groups already exist.…”