H2 evolution from H2O via O–H oxidative addition across a 9,10-diboraanthracene

Abstract

The water reactivity of the boroauride complex ([Au(B₂P₂)][K(18-c-6)]; (B₂P₂, 9,10-bis(2-(diisopropylphosphino)-phenyl)-9,10-dihydroboranthrene) and its corresponding two-electron oxidized complex, Au(B₂P₂)Cl, are presented. Au(B₂P₂)Cl is tolerant to H₂O and forms the hydroxide complex Au(B₂P₂)OH in the presence of H₂O and triethylamine. [Au(B₂P₂)]Cl and [Au(B₂P₂)]OH are poor Lewis acids as judged by the Gutmann–Becket method, with [Au(B₂P₂)]OH displaying facile hydroxide exchange between B atoms of the DBA ring as evidenced by variable temperature NMR spectroscopy. The reduced boroauride complex [Au(B₂P₂)]⁻ reacts with 1 equivalent of H₂O to produce a hydride/hydroxide product, [Au(B₂P₂)(H)(OH)]⁻, that rapidly evolves H₂ upon further H₂O reaction to yield the dihydroxide compound, [Au(B₂P₂)(OH)₂]⁻. [Au(B₂P₂)]Cl can be regenerated from [Au(B₂P₂)(OH)₂]⁻via HCl·Et₂O, providing a synthetic cycle for H₂ evolution from H₂O enabled by O–H oxidative addition at a diboraanthracene unit.