Engineering Mechanisms of Proton-Coupled Electron Transfer to a Titanium-substituted Polyoxovanadate-alkoxide

Shannon E Cooney; S. Genevieve Duggan; M. Rebecca A Walls; Noah J Gibson; James M Mayer; Pere Miro; Ellen Matson

doi:10.1039/D4SC06468B

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Engineering Mechanisms of Proton-Coupled Electron Transfer to a Titanium-substituted Polyoxovanadate-alkoxide

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Engineering Mechanisms of Proton-Coupled Electron Transfer to a Titanium-substituted Polyoxovanadate-alkoxide

Shannon E Cooney, S. Genevieve Duggan, M. Rebecca A Walls, Noah J Gibson, James M Mayer, Pere Miro and Ellen Matson

Chemical science (Cambridge), Vol.16(6), pp.2886-2897

02/14/2025

DOI: 10.1039/D4SC06468B

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Abstract

Metal oxides are promising catalysts for small molecule hydrogen chemistries, mediated by interfacial proton-coupled electron transfer (PCET) processes. Engineering the mechanism of PCET has been shown to control the selectivity of reduced products, providing an additional route for improving reductive catalysis with metal oxides. In this work, we present kinetic resolution of the rate determining proton-transfer step of PCET to a titanium-doped POV, TiV5O6(OCH3)13 with 9,10-dihydrophenazine by monitoring the loss of the cationic radical intermediate using stopped-flow analysis. For this reductant, a 5-fold enhanced rate (kPT = 1.2 x 104 M-1 s-1) is accredited to a halved activation barrier in comparison to the homometallic analogue, [V6O7(OCH3)12]1-. By switching to hydrazobenzene as a reductant, a substrate where the electron transfer component of the PCET is thermodynamically unfavorable (ΔGET = +11 kcal mol-1), the mechanism is found to be altered to a concerted PCET mechanism. Despite the similar mechanisms and driving forces for TiV5O6(OCH3)13 and [V6O7(OCH3)12]1-, the rate of PCET is accellerated by 3-orders of magnitude (kPCET = 0.3 M-1 s-1) by the presence of the Ti(IV) ion. Possible origins of the acceleration are considered, including the possibility of strong electronic coupling interactions between TiV5O6(OCH3)13 with hydrazobenzene. Overall, these results offer insight into the governing factors that control the mechanism of PCET in metal oxide systems.

Details

Title: Subtitle: Engineering Mechanisms of Proton-Coupled Electron Transfer to a Titanium-substituted Polyoxovanadate-alkoxide
Creators: Shannon E Cooney - University of Rochester
S. Genevieve Duggan
M. Rebecca A Walls - University of Rochester
Noah J Gibson - Yale University
James M Mayer - Yale University
Pere Miro - University of Iowa
Ellen Matson - University of Rochester
Resource Type: Journal article
Publication Details: Chemical science (Cambridge), Vol.16(6), pp.2886-2897
Publisher: Royal Society of Chemistry
DOI: 10.1039/D4SC06468B
ISSN: 2041-6520
eISSN: 2041-6539
Language: English
Electronic publication date: 01/07/2025
Date published: 02/14/2025
Academic Unit: Chemistry
Record Identifier: 9984772249202771

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