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 3MLCT 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 H 2 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 CH 2Cl2. 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 CH 3CN, assigned to a v(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.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry