Issue 33, 2024

Mechanistic elucidation of O2 production from tBuOOH in water using the Mn(ii) catalyst [Mn2(mcbpen)2(H2O)2]2+: a DFT study

Abstract

This study employs density functional theory at the SMD/B3LYP-D3/6-311+G(2d,p),def2-TZVPP//SMD/B3LYP-D3/6-31G(d),SDD level of theory to explore the mechanistic details of O2 generation from tBuOOH, using H218O as the solvent, in the presence of the Mn(II) catalyst [Mn2(mcbpen)2(H2O)2]2+. Since this chemistry was reported to occur through the reaction of Mn(III)(μ-O)Mn(IV)–O˙ with water, we first revaluated this proposal and found that it occurs with an activation barrier greater than 36 kcal mol−1, ruling out the functioning of such a dimer as the active catalyst. Experimental evidence has shown that the oxidation of [Mn2(mcbpen)2(H2O)2]2+ by tBuOOH in H218O produces the Mn(IV) species [Mn(18O)(mcbpen)]+. Our investigations revealed a plausible mechanism for this observation in which [Mn (18O)(mcbpen)]+ acts as the active catalyst, generating the tert-butyl peroxyl radical (tBuOO˙) through its reaction with tBuOOH. In this proposed mechanism, the O–O bond is formed through the interaction of tBuOO˙ with another [Mn(18O)(mcbpen)]+, finally leading to the formation of the 16O[double bond, length as m-dash]18O product. Our findings underscore the pivotal role of [Mn(18O)(mcbpen)]+ in both generating the active species tBuOO˙ and consuming it to produce 16O[double bond, length as m-dash]18O. With activation barriers as low as about 9 kcal mol−1, these elementary steps highlight the feasibility of our proposed mechanism. Moreover, this mechanism elucidates why, experimentally, one of the oxygen atoms in the released O2 comes from water, while the other originates from tBuOOH. This research broadens our understanding of high oxidation state manganese chemistry, setting the stage for the development of more efficient Mn-based catalysts, aimed at improving processes in both renewable energy and synthetic chemistry.

Graphical abstract: Mechanistic elucidation of O2 production from tBuOOH in water using the Mn(ii) catalyst [Mn2(mcbpen)2(H2O)2]2+: a DFT study

Supplementary files

Article information

Article type
Paper
Submitted
11 Jun 2024
Accepted
29 Jul 2024
First published
02 Aug 2024

Dalton Trans., 2024,53, 14089-14097

Mechanistic elucidation of O2 production from tBuOOH in water using the Mn(II) catalyst [Mn2(mcbpen)2(H2O)2]2+: a DFT study

A. Ariafard, M. Longhurst, G. F. Swiegers and R. Stranger, Dalton Trans., 2024, 53, 14089 DOI: 10.1039/D4DT01700E

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