Homogeneous Photochemical Water Oxidation by Biuret-Modified Fe-TAML: Evidence of Fe^V(O) Intermediate

Abstract

Water splitting, leading to hydrogen and oxygen in a process that mimics natural photosynthesis, is extremely important for devising a sustainable solar energy conversion system. Development of earth-abundant, transition metal-based catalysts that mimic the oxygen-evolving complex of photosystem II, which is involved in oxidation of water to O2 during natural photosynthesis, represents a major challenge. Further, understanding the exact mechanism, including elucidation of the role of active metal-oxo intermediates during water oxidation (WO), is critical to the development of more efficient catalysts. Herein, we report Fe(III) complexes of biuret-modified tetra-amidomacrocyclic ligands (Fe-TAML; 1a and 1b) that catalyze fast, homogeneous, photochemical WO to give O2, with moderate efficiency (maximum TON = 220, TOF = 0.76 s(-1)). Previous studies on photochemical WO using iron complexes resulted in demetalation of the iron complexes with concomitant formation of iron oxide nanoparticles (NPs) that were responsible for WO. Herein, we show for the first time that a high valent Fe(V)(O) intermediate species is photochemically generated as the active intermediate for the oxidation of water to O2. To the best of our knowledge, this represents the first example of a molecular iron complex catalyzing photochemical WO through a Fe(V)(O) intermediate.

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

“…[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] While these catalysts are of interest because of their high abundance and low toxicity, their performance is much poorer than their Ru or Ir analogues, and in addition their mechanistic pathways are in most cases basically unknown. [28][29][30][41][42][43] We have very recently reported a new complex based on Cu, containing the amidate ligand OPBAN that can carry out the water oxidation reaction in a very efficient manner. Surprisingly from a mechanistic perspective it does not follow the WNA or I2M schemes just described but rather a step by step one electron process that we have termed SET-WNA.…”

Reinvestigation of Water Oxidation Catalyzed by a Dinuclear Cobalt Polypyridine Complex: Identification of CoOx as a Real Heterogeneous Catalyst

“…3 Since OER is associated with the transfer of multiple electrons/protons and O-O bond formation in a high energy barrier process, it becomes kinetically slow and leads to significant consumption of overpotential in the water-splitting process. 4 Thus the design and synthesis of efficient water oxidation catalysts (WOCs) based on earth-abundant elements [5][6][7][8][9][10][11][12][13][14][15][16][17][18] remain great challenge. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 3 Recently, cobalt-based WOCs have been extensively investigated for their remarkable performance, [19][20][21][22][23][24] in which soluble cobalt complexes as homogeneous WOCs 11,[25]…”

Kagóme Cobalt(II)‐Organic Layers as Robust Scaffolds for Highly Efficient Photocatalytic Oxygen Evolution

“…[60] H 2 18 O( 2mL, 97 %e nriched) and borate buffer solution (0.2 m,p H8.0) that contained 2 (2 mg), [Ru(bpy) 3 ] 2+ + (1.0 mm), and K 2 S 2 O 8 (9.0 mm)w as irradiated using a4 50 nm LED lamp in as mall tube sealed with ar ubber plug after bubbling Ar.A fter 60 min, ap ortion (100 mL) of the gas in the headspace was injected into am ass spectrometer (MID, model;O mnistar/quadrupole mass analyzer;P feiffer Vacuum) with He (flow 30 mL min À1 )a st he carrier gas for analysis. As ac ontrol experiment, H 2…”