Direct Observation of the Dynamics of Ylide Solvation by Hydrogen-bond Donors Using Time-Resolved Infrared Spectroscopy

Abstract

The photoexcitation of α-diazocarbonyl compounds produces singlet carbene intermediates that react with nucleophilic solvent molecules to form ylides. The zwitterionic nature of these newly formed ylides induces rapid changes in their interactions with the surrounding solvent. Here, ultrafast time-resolved infrared absorption spectroscopy is used to study the ylide-forming reactions of singlet carbene intermediates from the 270 nm photoexcitation of ethyl diazoacetate in various solvents and the changes in the subsequent ylide–solvent interactions. The results provide direct spectroscopic observation of the competition between ylide formation and C–H insertion in reactions of the singlet carbene with nucleophilic solvent molecules. We further report the specific solvation dynamics of the tetrahydrofuran (THF)-derived ylide (with a characteristic IR absorption band at 1636 cm –1 ) by various hydrogen-bond donors and the coordination by lithium cations. Hydrogen-bonded ylide bands shift to a lower wavenumber by −19 cm –1 for interactions with ethanol, −14 cm –1 for chloroform, −10 cm –1 for dichloromethane, −9 cm –1 for acetonitrile or cyclohexane, and −16 cm –1 for Li + coordination, allowing the time evolution of the ylide–solvent interactions to be tracked. The hydrogen-bonded ylide bands grow with rate coefficients that are close to the diffusional limit. We further characterize the specific interactions of ethanol with the THF-derived ylide using quantum chemical (MP2) calculations and DFT-based atom-centered density matrix propagation trajectories, which show preferential coordination to the α-carbonyl group. This coordination alters the hybridization character of the ylidic carbon atom, with the greatest change toward sp 2 character found for lithium-ion coordination.

Photoredox-HAT Catalysis for Primary Amine α-C–H Alkylation: Mechanistic Insight with Transient Absorption Spectroscopy

“…The TEAS data were collected using an ultrafast laser system at the University of Bristol, whereas TVAS data over extended time ranges from sub-picosecond to microsecond were obtained using the LIFEtime facility at the STFC Rutherford-Appleton Laboratory (RAL). , The experimental methods used for TEAS and TVAS have been reported previously, ,,,,,,− and are described in Section S1 in the Supporting Information, together with the methods used for steady-state spectroscopic characterization of samples.…”

A new candidate for smart drug synthesis via silver (I)-NHC complexes

“…2) Among these compounds, compound 3a showed the best performance against both gram-positive and gram-negative bacteria [34]. The structures of whole synthesized NHC complexes were examined with spectroscopic techniques such as 1 H-NMR, 13 C-NMR [35] conductivity analysis [36], FT-IR spectra [37],…”

A new candidate of smart drug synthesis via silver (I)-NHC complexes

“…Among these compounds, compound 3a showed the best performance against both gram-positive and gram-negative bacteria [34]. The structures of all synthesized NHC complexes were examined with spectroscopic techniques such as 1 H-NMR, 13 C-NMR [35], conductivity analysis [36], FT-IR spectra [37], elemental analysis [38], LC-Mass spectra [39], UV-vis spectra [40], TGA-DTA analysis [41] and XRD spectra [42]. Activity tests for Ag(I)-NHC complexes against grampositive and gram-negative bacteria and fungi were performed.…”