The role of bridging ligand in hydrogen generation by photocatalytic Ru/Pd assemblies

Abstract

The synthesis and characterisation of two terpyridine based ruthenium/palladium heteronuclear compounds are presented. The photocatalytic behaviour of the Ru/Pd complex containing the linear 2,2′:5′,2′′-terpyridine bridge (1a) and its analogue the non-linear 2,2′:6′,2′′-terpyridine bridge (2a) are compared together with the respective mononuclear complexes 1 and 2. Irradiation of 1a with visible light (e.g., 470 nm) results in the photocatalytic generation of dihydrogen gas. Photocatalysis was not observed with complex 2a by contrast. A comparison with the photocatalytic behaviour of the precursors 1 and 2 indicates, that while for 1a the photocatalysis is an intramolecular process, for the mononuclear precursors it is intermolecular. The photophysical and electrochemical properties of the mono-and heterobinuclear compounds are compared. Raman spectroscopy and DFT calculations indicate that there are substantial differences in the nature of the lowest energy 3 MLCT states of 1a and 2a, from which the contrasting photocatalytic activities of the complexes can be understood.

Enhancing Photocatalytic Hydrogen Generation: the Impact of the Peripheral Ligands in Ru/Pd and Ru/Pt Complexes

“… Bridging ligands discussed in the text: 2,2’‐bipyridine (bpy), diethyl 2,2’‐bipyridine‐4,4’‐dicarboxylate (dceb), 2,3‐ di(pyridin‐2‐yl)pyrazine (2,3‐dpp), [3b] 2,5‐di(pyridin‐2‐yl)pyrazine (2,5‐dpp), 2,2’:5’,2’’‐terpyridine, (2,5‐bpp) and 2,2’:5’,3’’:6’’,2’’’‐quaterpyridine (bisbpy; this work).…”

Optimization of Hydrogen‐Evolving Photochemical Molecular Devices

“…[12,13] These so called photochemical molecular devices (PMDs) combine the photocenter,the electron relay,and the catalytic center in one single molecule and offer the potential for as pecific modification of the single modules to optimize the PMDs efficiencya nd stability during catalysis.Aparticular example of this approach, which has been investigated in great detail, [14] is shown in Figure 1. It has become clear, however,t hat the design and optimization of such aPMD is by no means straight forward and it is surprising that, while extensive effort has been taken in the variation of the bridging [15] or peripheral ligands, [16,17] the structural features of the attached catalytic center have …”

Deliberate boxes and accidental wheels

“…[9][10][11][12][13][14] Terpyridines are excellent ligands, providing tridentate metal binding domains with high affinity for many metal ions and limited possibilities for formation of different stereoisomers. [15][16][17][18][19][20] Thus a terpyridine ligand will bind in a meridional fashion to an octahedral metal ion and, depending on the relative amounts of metal and ligand that are present, a second ligand may bind as well.…”