Photochemical Dihydrogen Production Using an Analogue of the Active Site of [NiFe] Hydrogenase

Abstract

Photoproduction of dihydrogen (H2) by a low molecular weight analogue of the active site of [NiFe] hydrogenase has been investigated by reduction of the [NiFe2] cluster, 1, by a photosensitier PS (PS = [ReCl(CO)3(bpy)] or [Ru(bpy)3][PF6]2). Reductive quenching of the (3)MLCT excited state of the photosensitizer by NEt3 or N(CH2CH2OH)3 (TEOA) generates PS(•-), and subsequent intermolecular electron transfer to 1 produces the reduced anionic form of 1. Time-resolved infrared spectroscopy (TRIR) has been used to probe the intermediates throughout the reduction of 1 and subsequent photocatalytic H2 production from [HTEOA][BF4], which was monitored by gas chromatography. Two structural isomers of the reduced form of 1 (1a(•-) and 1b(•-)) were detected by Fourier transform infrared spectroscopy (FTIR) in both CH3CN and DMF (dimethylformamide), while only 1a(•-) was detected in CH2Cl2. Structures for these intermediates are proposed from the results of density functional theory calculations and FTIR spectroscopy. 1a(•-) is assigned to a similar structure to 1 with six terminal carbonyl ligands, while calculations suggest that in 1b(•-) two of the carbonyl groups bridge the Fe centers, consistent with the peak observed at 1714 cm(-1) in the FTIR spectrum for 1b(•-) in CH3CN, assigned to a ν(CO) stretching vibration. Formation of 1a(•-) and 1b(•-) and production of H2 was studied in CH3CN, DMF, and CH2Cl2. Although the more catalytically active species (1a(•-) or 1b(•-)) could not be determined, photocatalysis was observed only in CH3CN and DMF.

Electron Accumulation on Naphthalene Diimide Photosensitized by [Ru(2,2′-Bipyridine)3]2+

“…Prolonged irradiation will eventually bring even this small residual amount of NDI 0 to reaction with Et 3 N to afford NDI -, and with NDI 0 being continuously consumed, more and more NDI 2is formed (grey shaded area in Scheme 2c), also by the reaction of newly produced Et 2 NC⋅=CH 3 radicals (process (vii) in Scheme 2c). [44][45][46][47] It seems plausible that this thermal overall process (which, however, clearly relies on further light input) is in fact the main electron-accumulating step, particularly in view of the fact that excitation of [Ru(bpy) 3 ] 2+…”

Neutral Lipophilic Palladium(II) Complexes and their Applications in Electrocatalytic Hydrogen Production and C‐C Coupling Reactions

“…A continuous flow‐rig with in‐line GC analysis was used to detect the molecular hydrogen produced during electrocatalytic proton reduction using PdL 3 in DMF in the presence of TFA Applying a potential of –0.36 V vs. NHE to a boron‐doped diamond working electrode resulted in detection of molecular hydrogen (Figure ). The rate of H 2 produced was determined by calibration with a known flow rate of a H 2 /Ar mixture, by checking the proportionality between the peak area and the volume of injected hydrogen per minute.…”

Uncontracted core Pople basis sets in vibrational frequency calculations

“…Consequently, several electronic structure methods have successfully been developed that exploit the unimportance of core electrons to reduce the computational cost. Frozen core approximations are used to remove excitations involving core electrons from wavefunction expansions when calculating correlation energies, electron core potentials (ECPs) are used to replace core basis functions when calculating properties including vibrational frequencies for transition metal atoms, and atom‐centered basis sets often have a reduced number of contracted basis functions optimized to fit the core region . These approximations are generally well founded and can be highly accurate for calculating many properties.…”