Year: 2026
Type: preprint
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.
Source: ChemRxiv
Author: Joshua M. Sims
Institution: KU Leuven
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
Funder: KU Leuven
OpenAlex ID: W7223177190