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Photochemistry of furyl- and thienyldiazomethanes: spectroscopic characterization of triplet 3-thienylcarbene. J Am Chem Soc 2012 Apr 11;134(14):6443-54

Date

04/03/2012

Pubmed ID

22463599

Pubmed Central ID

PMC3994982

DOI

10.1021/ja300927d

Scopus ID

2-s2.0-84859564605 (requires institutional sign-in at Scopus site)   17 Citations

Abstract

Photolysis (λ > 543 nm) of 3-thienyldiazomethane (1), matrix isolated in Ar or N(2) at 10 K, yields triplet 3-thienylcarbene (13) and α-thial-methylenecyclopropene (9). Carbene 13 was characterized by IR, UV/vis, and EPR spectroscopy. The conformational isomers of 3-thienylcarbene (s-E and s-Z) exhibit an unusually large difference in zero-field splitting parameters in the triplet EPR spectrum (|D/hc| = 0.508 cm(-1), |E/hc| = 0.0554 cm(-1); |D/hc| = 0.579 cm(-1), |E/hc| = 0.0315 cm(-1)). Natural Bond Orbital (NBO) calculations reveal substantially differing spin densities in the 3-thienyl ring at the positions adjacent to the carbene center, which is one factor contributing to the large difference in D values. NBO calculations also reveal a stabilizing interaction between the sp orbital of the carbene carbon in the s-Z rotamer of 13 and the antibonding σ orbital between sulfur and the neighboring carbon-an interaction that is not observed in the s-E rotamer of 13. In contrast to the EPR spectra, the electronic absorption spectra of the rotamers of triplet 3-thienylcarbene (13) are indistinguishable under our experimental conditions. The carbene exhibits a weak electronic absorption in the visible spectrum (λ(max) = 467 nm) that is characteristic of triplet arylcarbenes. Although studies of 2-thienyldiazomethane (2), 3-furyldiazomethane (3), or 2-furyldiazomethane (4) provided further insight into the photochemical interconversions among C(5)H(4)S or C(5)H(4)O isomers, these studies did not lead to the spectroscopic detection of the corresponding triplet carbenes (2-thienylcarbene (11), 3-furylcarbene (23), or 2-furylcarbene (22), respectively).

Author List

Pharr CR, Kopff LA, Bennett B, Reid SA, McMahon RJ

Author

Brian Bennett D.Phil. Professor and Chair in the Physics department at Marquette University




MESH terms used to index this publication - Major topics in bold

Carbon
Computer Simulation
Diazomethane
Electrochemistry
Electron Spin Resonance Spectroscopy
Magnetic Resonance Spectroscopy
Methane
Models, Chemical
Models, Molecular
Molecular Conformation
Photochemistry
Software
Spectrophotometry