Structural Investigation of Photochemical Intermediates in Solution by Cold UV Spectroscopy in the Gas Phase: Photosubstitution of Dicyanobenzenes by Allylsilanes

Abstract

Electrospray ion sources with an in-line quartz cell were constructed to produce photochemical intermediates in solution. These ion sources can detect photochemical intermediates having lifetimes longer than a few seconds. Intermediates formed by photosubstitution of 1,4-dicyanobenzene (DCB) by allyltrimethylsilane (AMS) in acetonitrile using a Xe lamp were injected into the mass spectrometer. The cationic intermediate (C 11 H 10 N 2 •H + ) was observed at m/z = 171, but no anionic intermediate was found, although C 11 H 9 N 2 − was expected based on prior studies. Theoretical studies suggested that C 11 H 9 N 2 − was simultaneously converted to neutral C 11 H 10 N 2 and cationic C 11 H 10 N 2 •H + species, which can be stable intermediates in the photosubstitution reaction. The UV photodissociation (UVPD) spectrum of C 11 H 10 N 2 •H + under cold (∼10 K) gas-phase conditions determined the conformation of the C 11 H 10 N 2 unit of the C 11 H 10 N 2 •H + cation. This report demonstrates that cold gas-phase UV spectroscopy is a prospectively powerful tool for investigation of the electronic and geometric structures of photochemical intermediates produced in solution.

A Photoreactor-Interfaced Mass Spectrometer: An Online Platform to Monitor Photochemical Reactions

“…In previous studies, online reactors coupled with ESI have successfully detected short-lived transient intermediates formed in organometallic photochemical reactions, but they typically utilize high-powered broad-spectrum irradiation regimes without detailed kinetics analysis. − In contrast, this relatively simple and widely applicable apparatus rapidly acquires both kinetic and mechanistic information without altering the experimental conditions, as demonstrated by two examples: (i) the photoinitiated polymerization of methyl methacrylate and (ii) the photocatalyzed alkyne insertion into a 1,2,3-benzotriazinone.…”

Gas-Phase Characterization of Redox-Active Manganese Complexes

“…ESI-MS has proven to be an efficient tool to track such intermediates by sampling the reaction mixture. ,, The “in situ” preparation of reactive intermediates falls into two categories depending on the activation step. Photochemical activation is either achieved by illumination immediately prior to transferring the ions into the vacuum, i.e., within a capillary in front of the needle or the spray region, or by illumination within the ion trap tracking the dissociation pathways. ,− The alternative is to react the precursor of choice within the ion trap with a neutral reactant and monitor the charged reaction products. ,− …”