Photoinduced Terminal Hydride of [FeFe]-Hydrogenase Biomimetic Complexes

Area of Science:

• Bioinorganic Chemistry
• Organometallic Chemistry
• Catalysis

Background:

• The active site of [FeFe]-hydrogenase ([FeFe]-H2ase) features a unique H-cluster with a terminal hydride in the Hhyd intermediate.
• Synthetic mimics of [FeFe]-H2ase often form bridging hydrides, with terminal hydrides being challenging to achieve.
• Previous studies on [Fe2(μ-pdt)(μ-H)(CO)4(PMe3)2]+ (1H+) observed only bridging hydrides during protonation or hydrogen exchange.

Purpose of the Study:

• To investigate the photoinduced species of the [FeFe]-H2ase mimic, [Fe2(μ-pdt)(μ-H)(CO)4(PMe3)2]+ (1H+).
• To determine if terminal hydride intermediates can be formed and observed in synthetic [FeFe]-H2ase mimics.
• To gain insights into the reaction mechanisms of [FeFe]-H2ase and its synthetic analogs.

Main Methods:

• Fourier-transform infrared (FTIR) spectroscopy was used to study the photoinduced species of 1H+ under CO.
• Longer irradiation times were employed to reveal new photoinduced species.
• Density functional theory (DFT) calculations were used to analyze CO vibrational frequencies and assign species.

Main Results:

• FTIR spectroscopy revealed several new photoinduced species upon prolonged CO irradiation of 1H+.
• In addition to CO loss species, many photoinduced products were assigned to 1H+ with a terminal hydride.
• Comparison of experimental CO vibrational frequencies with DFT calculations supported the assignment of terminal hydride species.

Conclusions:

• The study successfully generated and identified photoinduced species with a terminal hydride in a synthetic [FeFe]-H2ase mimic.
• This provides experimental evidence for the existence of terminal hydride intermediates, previously only proposed.
• The findings contribute to a better understanding of the mechanistic pathways in [FeFe]-hydrogenase and the design of advanced biomimetic catalysts.