We
report a series of ferrocene-based derivatives and their corresponding
oxidized forms in which the introduction of simple electron donating
groups like methyl or tert-butyl units on cyclopentadienyl-rings
afford great tunability of Fe+III/Fe+II redox
potentials from +0.403 V down to −0.096 V versus saturated
calomel electrode. The spin forbidden d–d transitions of ferrocene
derivatives shift slightly toward the blue region with an increasing
number of electron-donating groups on the cyclopentadienyl-rings with
very little change in absorptivity values, whereas the ligand-to-metal
transitions of the corresponding ferricinium salts move significantly
to the near-IR region. The electron-donating groups also contribute
in the strengthening of electron density of Fe+III d-orbitals,
which therefore improves the chemical stability against the oxygen
reaction. Further, density functional theory calculations show a reducing
trend in outer shell reorganization energy with an increasing number
of the electron donating units.
Here, we describe a photoredox-assisted catalytic system for the direct reductive coupling of two carbon electrophiles. Recent advances have shown that nickel catalysts are active toward the coupling of sp-carbon electrophiles and that well-controlled, light-driven coupling systems are possible. Our system, composed of a nickel catalyst, an iridium photosensitizer, and an amine electron donor, is capable of coupling halocarbons with high yields. Spectroscopic studies support a mechanism where under visible light irradiation the Ir photosensitizer in conjunction with triethanolamine are capable of reducing a nickel catalyst and activating the catalyst toward cross-coupling of carbon electrophiles. The synthetic methodology developed here operates at low 1 mol % catalyst and photosensitizer loadings. The catalytic system also operates without reaction additives such as inorganic salts or bases. A general and effective sp-sp cross-coupling scheme has been achieved that exhibits tolerance to a wide array of functional groups.
The effect of the water concentration on the quantitation of formate from dimethylformamide in the presence of electron-donating bases using ion chromatography is reported. This observation has important implications in the area of the photocatalytic reduction of CO(2), where formate levels are often used to calculate catalyst turnover numbers.
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.
Interfacing proteins with electrode surfaces is important for the field of bioelectronics. Here, a general concept based on phage display is presented to evolve small peptide binders for immobilizing and orienting large protein complexes on semiconducting substrates. Employing this method, photosystem I is incorporated into solid‐state biophotovoltaic cells.
The bridging ligand 2,2',5',3'',6'',2'''-quaterpyridine was utilised to tether [(bpy) 2 Ru] 2 + and [Re(CO) 3 Cl] subunits for the purpose of photocatalytic CO 2 reduction. The photophysics and electrochemistry of the complex and associated mononuclear species are reported herein, in addition to photocatalytic, picosecond time-resolved infrared and computational studies. Photophysical, time-resolved IR, and electrochemical data together with quantum chemical calculations indicate weak communication between the two metal centres. As a result of the electronwithdrawing effect of the ligand on both the Ru and Re subunits, the reducing power of the photosensitiser and catalytic unit were significantly attenuated relative to the intermolecular approach utilising [(bpy) 3 Ru] 2 + and (bpy)Re(CO) 3 Cl.
A pyrazine bridged ruthenium/palladium bimetallic photocatalyst with peripheral 4,4'-dicarboxyethyl-2,2'-bipyridine ligands, EtOOC-RuPd, is reported, together with its 2,2'-bipyridine analogue. Upon irradiation with visible light, EtOOC-RuPd catalyses the production of hydrogen gas whereas the complex RuPd does not.
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