Photocatalytic Hydrogen Evolution Driven by [FeFe] Hydrogenase Models Tethered to Fluorene and Silafluorene Sensitizers

Abstract

It is successfully shown that photocatalytic proton reduction to dihydrogen in the presence of a sacrificial electron donor, such as trimethylamine (TEA) and ascorbate, can be driven by compact sensitizer-catalyst dyads, that is, dithiolate-bridged [FeFe] hydrogenase models tethered to organic sensitizers, such as fluorenes and silafluorenes (1 a-4 a). The sensitizer-catalyst dyads 1 a-4 a show remarkable and promising catalytic activities as well as enhanced stabilities during photocatalysis performed under UV-light irradiation. The photocatalysis was carried out both in non-aqueous and aqueous media. The latter experiments were performed by solubilizing the photocatalysts within micelles formed by either sodium dodecyl sulfate (SDS) or cetyltrimethylammonium bromide (CTAB). In this study a turnover number of 539 (7 h) is achieved under optimized conditions, which corresponds to an exceptionally high turnover frequency of 77 h^-1 . Theoretical investigations as well as emission decay experiments were performed to understand the observed phenomena together with the mechanisms of photocatalytic H₂ generation.