Quest for diatomic selenium

Abstract

Metallocene pentaselenides and elemental selenium were employed in an effort to generate diatomic selenium (Se₂) under thermal conditions. Trapping experiments were carried out with six dienes. A successful formation of a diselenium adduct was observed in the case of 5,6-dimethylene-cyclohexa-1,3-diene (1a). The other dienes produced the corresponding dihydroselenophenes. The in-depth study of the limitations of our method to generate Se₂ is described; a plausible mechanism rationalizing the observed results is proposed.

Keywords:

• dihydrodiselenin
• diatomic selenium
• selenium transfer
• selenophene
• trapping

Acknowledgements

We thank the Natural Sciences and Engineering Research Council of Canada for support. We thank Professor D. Scott Bohle and Dr Lijuan Zhang for solving X-ray structure of compound 2d, as well as Francine Belanger-Gariepy for solving structure 20.

Notes

For a more complete list see (2k).

The spin states of Se₂ have been theoretically established with the singlet state lower than the triplet by a range of 11.5–16 kcal/mol: see National Institute of Standards and Technology (NSIT), Gaithersburg, MD, 20899–1070. URL: http://cccbdb.nist.gov/stgap2.asp?casno=12185170&charge=0 (accessed July 20, 2010).

For other selenophene-related references see (8c).

We have used a microwave oven applying conditions described by Illescas et al. 14.