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

Abstract

Pd@(BiPy‐PEG‐OMe) is a catalyst comprised of palladium nanoparticles (Pd‐NPs) stabilized and made water soluble by 2,2′‐bipyridine‐end‐functionalized polyethylene glycol monomethyl ether (BiPy‐PEG‐OMe). The catalyst has been used in the past for nitrile hydrogenation. In this work, we prove that it is also very active for photocatalytic hydrogen generation, which might be true for more catalysts of its kind and therefore worthy of further investigation. Using the inexpensive photosensitizer Eosin Y, high turnover numbers (TONs) of over 4 500 were achieved for the evolution of molecular hydrogen from pure water under visible‐light irradiation. Replacing Eosin Y, which showed only a short lifetime under experimental conditions (i.e. a few hours), by a novel osmium‐based metal complex, which is also characterized by its crystal structure, the longevity of the system can be boosted to over one and a half months with a maximum TON of 1 500. Combining excellent yield and stability is a clear goal for further research.

Photochemical Synthesis of cis,trans,cis‐1,2,3,4‐Tetrakis(diphenylphosphanyl)buta‐1,3‐diene and Its Metal Coordination

“…The reaction between [Os(bpy) 2 Cl 2 ] and dppbd conducted in a 2:1 molar ratio (Scheme ) gave a 1:1 mixture of the dimer Os complexes, meso ‐ΔΛ,ΛΔ‐[Os 2 (bpy) 4 (dppbd)](PF 6 ) 4 ( 10 ) and rac ‐ΔΔ,ΛΛ‐[Os 2 (bpy) 4 (dppbd)](PF 6 ) 4 ( 11 ). The corresponding single‐crystal X‐ray structures have been reported recently . The UV/Vis spectrum of a 1:1 mixture of these two diastereoisomers is shown in Figure .…”

“…The use of the new tetraphosphane ligand dppbd in 10 and 11 has produced a chromophore with extraordinary stability . This is certainly a consequence of the bis(bidentate) coordination behavior of dppbd and the resulting five‐membered chelate rings.…”

“…The corresponding single-crystal X-ray structures have been reported recently. [16] The UV/Vis spectrum of a 1:1 mixture of these two diastereoisomers is shown in Figure 7. As shown above for 7 and 8 the ligand centered (LC) π→π* transitions at 230 nm and 275 nm are assigned to the phenyl groups and butadiene, respectively.…”

“…They are typical for a planar conformation of dppbd in agreement with both single-crystal X-ray structures of 10 and 11. [16] Figure 7. UV/Vis spectrum of a 1.0 × 10 -5 M MeCN solution of a 1:1 mixture of 10 and 11 at 25 °C.…”

“…The use of the new tetraphosphane ligand dppbd in 10 and 11 has produced a chromophore with extraordinary stability. [16] This is certainly a consequence of the bis(bidentate) coordination behavior of dppbd and the resulting five-membered chelate rings. Furthermore, planar conformations of dppbd as shown in the single crystal structures of 10 and 11 lead to a further stabilization due to an excessive delocalization of electron density throughout the butadiene backbone and the adjacent phosphorus atoms.…”