Hydrogen production through photocatalytic acceptorless alcohol dehydrogenation with a homogeneous nickel complex

Abstract

The need for sustainable hydrogen production has driven the search for efficient, earth-abundant catalysts. We report a breakthrough in photocatalytic acceptorless alcohol dehydrogenation (AAD) using a well-defined, air-stable nickel(II) complex, [Ni(2,6-{Ph₂PNH}₂(NC₅H₃))Br]⁺ (1⁺) which represents the first fully characterized nickel complex to catalyze photocatalytic AAD. This catalyst operates at room temperature under visible light irradiation to selectively produce hydrogen from various aliphatic alcohols. Catalyst performance is significantly enhanced by introducing dimethylethanolamine (DMEA) as an efficient electron donor, an electron donor previously unexplored in photoredox reactions. Mechanistic studies, supported by computational analysis, reveal the crucial role of the flexible pincer ligand in facilitating the catalytic cycle. The proposed transformation of the “PN³P” ligand to a bidentate PN configuration, supported by DFT optimization, creates an open coordination environment at the nickel centre, key for β-hydrogen elimination. This work addresses challenges in hydrogen production and bridges the gap between traditional catalysis and photoredox chemistry and represents a significant step towards more economical and environmentally friendly hydrogen generation.