Bio-Inspired Molecular Catalysts for Water Oxidation

Abstract

The catalytic tetranuclear manganese-calcium-oxo cluster in the photosynthetic reaction center, photosystem II, provides an excellent blueprint for light-driven water oxidation in nature. The water oxidation reaction has attracted intense interest due to its potential as a renewable, clean, and environmentally benign source of energy production. Inspired by the oxygen-evolving complex of photosystem II, a large of number of highly innovative synthetic bio-inspired molecular catalysts are being developed that incorporate relatively cheap and abundant metals such as Mn, Fe, Co, Ni, and Cu, as well as Ru and Ir, in their design. In this review, we briefly discuss the historic milestones that have been achieved in the development of transition metal catalysts and focus on a detailed description of recent progress in the field.

Preparation and Characterization of a Formally NiIV–Oxo Complex with a Triplet Ground State and Application in Oxidation Reactions

“…Generation of 3 is accompanied by the rise of a new absorption feature at 728 nm in the UV−vis spectrum. The presence of an oxo-type ligand in 3 is supported by CSI-MS spectrometry in conjecture with 18 O isotope labeling. In agreement with the formal Ni(IV) state, the complex is EPR silent.…”

“…For all reactivity studies, 3 was generated by reacting 1 with 1.5 equiv PhIO (in TFE) followed by addition of 1 equiv of HOTf in MeCN at −40 °C or at 0 °C. 3-18 O was prepared using PhI 18 O instead of PhI 16 O. 3 can be generated in more than 95% yield using other solvents such as acetone, TFE, and also a mixture of solvents such as acetonitrile/acetone (v/v 1:9) and acetonitrile/ butyronitrile (v/v 1:2).…”

“…CSI-MS of 3 shows poor intensity in both positive 1b). The observation of the two-mass unit shift upon 18 O introduction indicates that 3 contains one isotopesensitive oxygen atom. The X-band EPR spectrum of 3, measured at 5 K, is silent (Figure S7a).…”

“…Product analysis of the thioanisole oxidation reactions revealed the formation of methyl phenyl sulfoxide as an organic product. In addition, the thioanisole oxidation reaction carried out with 3-18 O revealed the 85% 18 O incorporation into the methyl phenyl sulfoxide (Figure S28). The main inorganic product, characterized by CSI-MS and EPR spectroscopy, was [Ni III (TAML)] − (Figure S29).…”

“…19 Additionally, though more recently developed, there are several molecular Ni-based OER catalysts that also likely operate through high-valent Ni−O intermediates. 18 Well-studied, mononuclear, terminal Ni−oxo complexes are much more rare than their lower atomic number counterparts. 1,20 This is related to the concept of the "oxo wall".…”