Impact of Ligand Exchange in Hydrogen Production from Cobaloxime-Containing Photocatalytic Systems

Ligand exchange on the Co(dmgH)2(py)Cl water reduction catalyst was explored under photocatalytic conditions. The photosensitizer fluorescein was connected to the catalyst through the axially coordinated pyridine. While this two-component complex produces H2 from water under visible light irradiation in the presence of triethanolamine (TEOA), it is less active than a system containing separate fluorescein and [CoIII(dmgH)2(py)Cl] components. NMR and photolysis experiments show that the Co catalyst undergoes pyridine exchange. Interestingly, glyoximate ligand exchange was also observed photocatalytically and by NMR spectroscopy, thereby showing that integrated systems in which the photosensitizer is linked directly to the Co(dmgH)2(py)Cl catalyst may not remain intact during H2 photogeneration. These studies have also given rise to insights into the catalyst decomposition mechanism.