Studies on Stable 1,3-Diphosphacyclobutane-2,4-diyls

Abstract

Various kinds of stable 1,3-diphosphacyclobutane-2,4-diyls, sterically protected by bulky Mes* (2,4,6-tri-t-butylphenyl) groups, were prepared from Mes*-phosphaethyne. The structures and physical and chemical characters were studied. They are discussed in terms of ground-state singlet biradicals and have been confirmed by spectroscopic analyses, X-ray crystallography and theoretical calculations. EPR studies were also carried out to validate the paramagnetic species related to the 1,3-diphosphacyclobutane-2,4-diyls. The reactions of the biradical species are described including oxidation and sulfurization.

Keywords:

• Biradical
• radicals
• phosphorus heterocycles
• steric protection

Acknowledgments

This work was supported in part by Grants-in-Aid for Scientific Research (No. 13304049 and 14044012) from the Ministry of Education, Culture, Sports, Science and Technology, Japan; the National Science Foundation (CHE-0413521, CHE-0342921 and CHE-0079498), U.S.A.; U.S. Department of Energy Grant (DE-FG02-86ER13465); and the Department of Energy, Office of Energy Efficiency and Renewable Energy under the Hydrogen Storage Grand Challenge (DE-PS36-03GO93013).

The authors thank Dr. Hiroki Sugiyama and Mr. Manabu Kikuchi at Tohoku University for the synthetic and analytical studies, as well as Prof. Lowell D. Kispert and Dr. Tatyana Konovalova at the University of Alabama for EPR studies.