Hydrostibination of Alkynes: A Radical Mechanism

19 June 2020, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

The addition of Sb-H bonds to alkynes was reported recently as a new hydroelementation reaction that exclusively yields anti-Markovnikov Z-olefins from terminal acetylenes. We examine four possible mechanisms that are consistent with the observed stereochemical and regiochemical outcomes. A comprehensive analysis of solvent, substituent, isotope, additive, and temperature effects on hydrostibination reaction rates definitively refutes three ionic mechanisms involving closed-shell charged intermediates. Instead the data support a fourth pathway featuring neutral radical SbII and SbIII intermediates. Density Functional Theory (DFT) calculations are consistent this model, predicting an activation barrier that is within 1 kcal mol-1 of the experimental value (Eyring analysis) and a rate limiting step that is congruent with experimental kinetic isotope effect. We therefore conclude that hydrostibination of arylacetylenes is initiated by the generation of stibinyl radicals, which then participate in a cycle featuring SbII and SbIII intermediates to yield the observed Z-olefins as products. This mechanistic understanding will enable rational evolution of hydrostibination as a methodology for accessing challenging products such as E-olefins.

Keywords

mechanism
main group hydrides
hydrostibination
antimony
radicals
catalysis
density functional theory

Supplementary materials

Title
Description
Actions
Title
ESI-chemrxiv
Description
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.