A photocycle for hydrogen production from two-electron mixed-valence complexes

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Catalysis

Background:

• Dirhodium complexes with phosphine ligands are investigated for their reactivity.
• Understanding the photochemistry of metal-hydride complexes is crucial for catalytic applications.

Purpose of the Study:

• To synthesize and characterize dihydride dirhodium complexes.
• To investigate the photolysis of these complexes and elucidate the mechanism of hydrogen photogeneration.
• To construct a complete photocycle for H2 photogeneration.

Main Methods:

• Synthesis of dirhodium dihydride complexes with tfepma ligands.
• X-ray diffraction for structural characterization of isomers.
• Photolysis experiments with isotopic labeling and gas analysis (Toepler pump).
• Spectroscopic analysis of photoproducts.
• Isolation and characterization of related metal complexes (Rh and Ir) with tfepm and dfpma ligands.

Main Results:

• Three isomeric forms (syn, anti, cis) of Rh2(II,II)(tfepma)3H2Cl2 were characterized.
• Photolysis of the syn isomer resulted in prompt H2 formation and a blue Rh2(I,I) photoproduct.
• The mechanism involves reductive elimination of H2, confirmed by isotopic labeling.
• Related Rh and Ir complexes with tfepm ligands were synthesized, including bridged and non-bridged halide species.
• A complete photocycle for H2 photogeneration by dirhodium dfpma complexes in hydrohalic acids was proposed.

Conclusions:

• Dirhodium dihydride complexes can photochemically generate H2.
• The photocycle involves reductive elimination of H2 from the dihydride species.
• Structural and electronic properties of related complexes provide insights into the photocycle mechanism.