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 . Theoretical investigations as well as emission decay experiments were performed to understand the observed phenomena together with the mechanisms of photocatalytic H generation.

Experimental and Theoretical Investigation of the Light‐Driven Hydrogen Evolution by Polyoxometalate–Photosensitizer Dyads

“…Lower maximum turnover numbers are observed for Ir‐POM Co ( TON =34) and Ir‐POM Fe ( TON =20). In comparison, other non‐POM based covalent dyads (many of them noble‐metal‐based) feature typical TONs in the ten to several hundred region . Notably, electrochemical, UV/Vis, and emission spectroscopic stability studies show that no cluster degradation (e.g., by cleavage of the imine bond) is observed during catalysis, so that a similar chemical stability can be suggested for the three Ir‐POM dyads (see the Supporting Information).…”

Comprehensive review and future perspectives on the photocatalytic hydrogen production

“…EDTA is the tertiary amine that can act as electron donor at a lower pH, ranging between 5 and 7 . Under relatively acidic conditions, ascorbic acid is used widely as electron donor (p K a s 4 and 11.3), it has the ability to act also as proton donor, providing H + to be reduced to H 2 . Carboxylic acids, such as lactic acid (p K a 3.9) and oxalic acid (p K a 1.2 and 4.2), also have been used in aqueous solutions over a wide pH range from slightly acid to slightly basic .…”

Catalytic Metallopolymers from [2Fe‐2S] Clusters: Artificial Metalloenzymes for Hydrogen Production

“…Aqueous micellar solutions prepared from surfactants, which help disperse hydrophobic [2Fe‐2S] clusters in water, have been studied by different research groups during the past decade. The surfactants used in these systems to encapsulate [FeFe]‐hydrogenase active‐site mimetics were sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and dodecyltrimethylammonium bromide (DTAB) . In addition to the micellar systems, other biomimetic self‐assembling supporting systems such as phospholipid vesicle membranes were used for either embedding the components, for H 2 evolution catalysis, into the membranes or adsorbing the cluster to the membrane interface …”

“…Kurzaufsätze encapsulate [FeFe]-hydrogenase active-site mimetics were sodium dodecyl sulfate (SDS), [33][34][35][36] cetyltrimethylammonium bromide (CTAB), [36] and dodecyltrimethylammonium bromide (DTAB). [37] In addition to the micellar systems,o ther biomimetic self-assembling supporting systems such as phospholipid vesicle membranes were used for either embedding the components,f or H 2 evolution catalysis,i nto the membranes or adsorbing the cluster to the membrane interface.…”