When Can an Off-Cycle Reservoir Raise a Catalyst’s Turnover Number?
- 1Department of Chemistry, KU Leuven, Celestijnenlaan 200F, Leuven, Belgium, 3001
Abstract
Off-cycle species are typically considered detrimental to catalytic activity; however, a dormant form can also extend catalyst lifetime. This study shows under which conditions a reversible off-cycle reservoir can increase the turnover number (TON) of a homogeneous catalyst. When both turnover and all deactivation steps are first order in catalyst, branching remains constant over time and the reservoir only holds the catalyst in a dormant state, the distribution of turnovers per catalyst does not change, regardless of the number of reservoirs. The reaction is slowed, and under an external clock, such as a poison that forms independently of the catalyst, the TON decreases. When deactivation is of higher order in catalyst than turnover, a fast reservoir of depth acts as a -fold dilution. This increases the TON up to a ceiling set by the first-order deactivation pathways, and for a given batch time there is an optimal depth. In the published model of (DTBM-SEGPHOS)CuH, the HBpin adduct protects the catalyst from aggregation but is 2.9–5.9 times deeper than optimal. In Hoveyda–Grubbs metathesis, a styrenyl-ether reservoir slows the reaction threefold without reducing the TON. A reservoir can be beneficial only if the catalyst-limited TON decreases as catalyst loading increases, that is, if the slope of log TON against log loading is negative. Dilution experiments and a series with graded amounts of additive then show whether it will be.
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BibTeX
@misc{sims2026when,
title = {{When Can an Off-Cycle Reservoir Raise a Catalyst’s Turnover Number?}},
author = {Joshua M. Sims},
howpublished = {ChemRxiv},
year = {2026},
month = oct,
doi = {10.26434/chemrxiv.15010890/v1},
url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010890/v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - When Can an Off-Cycle Reservoir Raise a Catalyst’s Turnover Number?
AU - Joshua M. Sims
PY - 2026
DA - 2026/10/22
PB - ChemRxiv
DO - 10.26434/chemrxiv.15010890/v1
UR - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010890/v1
AB - Off-cycle species are typically considered detrimental to catalytic activity; however, a dormant form can also extend catalyst lifetime. This study shows under which conditions a reversible off-cycle reservoir can increase the turnover number (TON) of a homogeneous catalyst. When both turnover and all deactivation steps are first order in catalyst, branching remains constant over time and the reservoir only holds the catalyst in a dormant state, the distribution of turnovers per catalyst does not change, regardless of the number of reservoirs. The reaction is slowed, and under an external clock, such as a poison that forms independently of the catalyst, the TON decreases. When deactivation is of higher order in catalyst than turnover, a fast reservoir of depth acts as a -fold dilution. This increases the TON up to a ceiling set by the first-order deactivation pathways, and for a given batch time there is an optimal depth. In the published model of (DTBM-SEGPHOS)CuH, the HBpin adduct protects the catalyst from aggregation but is 2.9–5.9 times deeper than optimal. In Hoveyda–Grubbs metathesis, a styrenyl-ether reservoir slows the reaction threefold without reducing the TON. A reservoir can be beneficial only if the catalyst-limited TON decreases as catalyst loading increases, that is, if the slope of log TON against log loading is negative. Dilution experiments and a series with graded amounts of additive then show whether it will be.
ER -