Photodriven Oxidation of Water by Plastoquinone Analogs with a Nonheme Iron Catalyst

Abstract

Photoirradiation of an acetonitrile solution containing p-benzoquinone derivatives (X-Q) as plastoquinone analogs, a nonheme iron(II) complex, [(N4Py)Fe II ] 2+ (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine), and H 2 O afforded the evolution of O 2 and the formation of the corresponding hydroquinone derivatives (X-QH 2 ) quantitatively. During the photodriven oxidation of water by X-Q, [(N4Py)Fe II ] 2+ was oxidized by the excited state of X-Q to produce the iron(IV)-oxo complex ([(N4Py)-Fe IV (O)] 2+ ) quantitatively. The concentration of [(N4Py)-Fe IV (O)] 2+ remained virtually the same during the repeated cycles of photodriven oxidation of water by X-Q. [(N4Py)Fe IV (O)] 2+ was further oxidized by the excited state of X-Q to [(N4Py)Fe V (O)] 3+ ; this Fe V -oxo species is proposed as an active oxidant that affects the water oxidation. The photocatalytic mechanism of the water oxidation by X-Q with [(N4Py)Fe II ] 2+ was clarified by detecting intermediates using various spectroscopic techniques, such as transient absorption and electron paramagnetic resonance measurements. To the best of our knowledge, the present study reports the first example of a functional model of Photosystem II (PSII) using X-Q as plastoquinone analogs in the photocatalytic oxidation of water.

An Iron(III) Complex with Pincer Ligand—Catalytic Water Oxidation through Controllable Ligand Exchange

“…The first evidence about iron complexes catalyzing the oxidation of water in the early 1980s [28] was followed only by a few other examples until 2010 [10,29]. More recently, different types of homogeneous Fe-based WOCs have been described [20,[30][31][32][33][34][35][36][37]. According to the light-driven (LD) [38], chemical (by ceric ammonium nitrate, CAN) [39], or electrochemical (EC) activation mode [8,9,11] of the Fe-WOCs, some typical representatives have been summarized in Figure 1.…”

Photoinduced Generation of Superoxidants for the Oxidation of Substrates with High C−H Bond Dissociation Energies

“…Extensive efforts have been devoted to realize artificial photosynthesis by mimicking charge‐separation and redox processes in PSII and PSI . However, neither the intermediate nor the stoichiometry of photo‐driven H 2 O oxidation by plastoquinone (PQ) or its analogues had been established, until photocatalytic driven H 2 O oxidation was reported using p ‐benzoquinone derivatives (X−Q) as PQ analogues and a non‐heme Fe II species ([(L’)Fe II ] 2+ ; L’=N4Py= N , N ‐bis(2‐pyridylmethyl)‐ N ‐bis(2‐pyridyl)methylamine) as a redox catalyst in presence of H 2 O . Scheme shows the photocatalytic mechanism of the H 2 O oxidation by DDQ with a non‐heme Fe II complex .…”

“…However, neither the intermediate nor the stoichiometry of photo‐driven H 2 O oxidation by plastoquinone (PQ) or its analogues had been established, until photocatalytic driven H 2 O oxidation was reported using p ‐benzoquinone derivatives (X−Q) as PQ analogues and a non‐heme Fe II species ([(L’)Fe II ] 2+ ; L’=N4Py= N , N ‐bis(2‐pyridylmethyl)‐ N ‐bis(2‐pyridyl)methylamine) as a redox catalyst in presence of H 2 O . Scheme shows the photocatalytic mechanism of the H 2 O oxidation by DDQ with a non‐heme Fe II complex . Photoexcitation of DDQ results in the generation of 3 DDQ*, followed by ET from [(L’)Fe II ] 2+ to 3 DDQ* to form [(L’)Fe III ] 3+ and DDQ .− .…”

“…The further oxidation of [(L’)Fe III (OOH)] 2+ by DDQ via HAT produces [(L’)Fe III (O 2 .− )] 2+ . Finally, O 2 is rapidly released from [(L’)Fe III (O 2 .− )] 2+ to reproduce [(L’)Fe II ] 2+ to complete the photocatalytic cycle in Scheme …”

The most reactive iron and manganese complexes with N-pentadentate ligands for dioxygen activation—synthesis, characteristics, applications

“…These intermediates were identified with different spectroscopic techniques, on the basis of which it was founded that, they have a high-spin [spin ( S ) = 2] iron(IV)-oxo centre and the bond between the oxygen atom and iron ion shows double bond feature [ 24 ]. Furthermore, high-valent iron and manganese oxo complexes, produced in the reaction of water oxidation, were determining species in the "oxygen-evolving complex" (OEC) in photosystem II [ 4 , 7 , 26 ]. Manganese also plays an important role in many biological processes in which, similarly to iron, is present in different oxidation states.…”