H2 Evolution from H2O via O–H Oxidative Addition Across a 9,10-Diboraanthracene

The boron-centered 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 twoelectron oxidized complex, Au(B2P2)Cl, are presented. The tolerance of Au(B2P2)Cl towards H2O was demonstrated and subsequent hydroxide/chloride exchange was acheived in the presence of H2O and triethylamine to afford Au(B2P2)OH. 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 31P NMR and low temperature 1H and 11B NMR. The reaction of the reduced boroauride complex [Au(B2P2)]– with 1 equivalent of H2O produces a hydride/hydroxide product, [Au(B2P2)(H)(OH)]–, that, upon addition of a second equivalent of H2O, rapidly evolves H2 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.