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Metal-coordinated water-soluble cavitands act as C-H oxidation catalysts.

ABSTRACT: Cavitands can be smoothly derivatized by CuAAC chemistry to incorporate ligand species at the upper rim. These species can coordinate metal species in a number of different conformations, leading to self-assembly. The metal-coordination confers water solubility on the cavitands, and the iron-bound species are capable of catalytic C-H oxidations of fluorene under mild conditions.

SUBMITTER: Djernes KE

PROVIDER: S-EPMC4014350 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Metal-coordinated water-soluble cavitands act as C-H oxidation catalysts.

Djernes Katherine E KE Moshe Orly O Mettry Magi M Richards Donald D DD Hooley Richard J RJ

Organic letters 20120124 3

Cavitands can be smoothly derivatized by CuAAC chemistry to incorporate ligand species at the upper rim. These species can coordinate metal species in a number of different conformations, leading to self-assembly. The metal-coordination confers water solubility on the cavitands, and the iron-bound species are capable of catalytic C-H oxidations of fluorene under mild conditions. ...[more]

PMID: 22273494

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Project description:A central question in biological water splitting concerns the oxidation states of the manganese ions that comprise the oxygen-evolving complex of photosystem II. Understanding the nature and order of oxidation events that occur during the catalytic cycle of five S i states (i = 0-4) is of fundamental importance both for the natural system and for artificial water oxidation catalysts. Despite the widespread adoption of the so-called "high-valent scheme"-where, for example, the Mn oxidation states in the S2 state are assigned as III, IV, IV, IV-the competing "low-valent scheme" that differs by a total of two metal unpaired electrons (i.e. III, III, III, IV in the S2 state) is favored by several recent studies for the biological catalyst. The question of the correct oxidation state assignment is addressed here by a detailed computational comparison of the two schemes using a common structural platform and theoretical approach. Models based on crystallographic constraints were constructed for all conceivable oxidation state assignments in the four (semi)stable S states of the oxygen evolving complex, sampling various protonation levels and patterns to ensure comprehensive coverage. The models are evaluated with respect to their geometric, energetic, electronic, and spectroscopic properties against available experimental EXAFS, XFEL-XRD, EPR, ENDOR and Mn K pre-edge XANES data. New 2.5 K 55Mn ENDOR data of the S2 state are also reported. Our results conclusively show that the entire S state phenomenology can only be accommodated within the high-valent scheme by adopting a single motif and protonation pattern that progresses smoothly from S0 (III, III, III, IV) to S3 (IV, IV, IV, IV), satisfying all experimental constraints and reproducing all observables. By contrast, it was impossible to construct a consistent cycle based on the low-valent scheme for all S states. Instead, the low-valent models developed here may provide new insight into the over-reduced S states and the states involved in the assembly of the catalytically active water oxidizing cluster.

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Metal-coordinated water-soluble cavitands act as C-H oxidation catalysts.

Publications

Metal-coordinated water-soluble cavitands act as C-H oxidation catalysts.

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