Can. J. Chem., 83, 1324-1338 (2005).

National Research Council of Canada, 2005

Time-Resolved Spectroscopic Studies of the Photochemistry of Some Diphenylgermylene (Ph2Ge:) Precursors.

Cameron R. Harrington, William J. Leigh,* Bryan K. Chan, Peter P. Gaspar, and Dong Zhou

Contribution from the Department of Chemistry, McMaster University, Hamilton, ON  Canada  L8S 4M1 and the Department of Chemistry, Washington University, St. Louis, MO 63130

The photochemistry of diphenylbis(trimethylsilyl)germane (2a) and 1,4-dihydro-5-methyl-1,2,3,4,9,9-hexaphenyl-1,4-germanonaphthalene (11) has been studied in solution by steady state and laser flash photolysis methods with a view to detecting the transient germylene derivative diphenylgermylene (Ph2Ge), which has been shown previously to be the major product of photolysis of 2a and a closely related derivative of 11. Steady state trapping experiments confirm the formation of Ph2Ge as the major germanium-containing primary product in both cases; with 2a, the results indicate that other transient species are also formed in minor yields, including phenyl(trimethylsilyl)germylene (Ph(TMS)Ge; ca. 6%) and diphenyl(trimethylsilyl)germyl radicals (Ph2(TMS)Ge; ca 15%). Laser flash photolysis of 2a in deoxygenated hexane solution yields a complex mixture of overlapping transient absorptions, which is shown to be comprised of Ph2Ge, tetraphenyldigermene (15) and its oligomerization products, and another species with spectral characteristics similar to the Ph2(TMS)Ge radical. The latter has been independently generated by hydrogen abstraction from diphenyl(trimethylsilyl)germane by tert-butoxyl radicals. Compound 11 extrudes Ph2Ge more cleanly and efficiently upon photolysis in solution, yet laser flash photolysis affords excited triplet and triplet-derived species as the only detectable transient products; interpretation of the results for this compound is made difficult by its slow thermal decomposition to 5-methyl-1,2,3,4-tetraphenylnaphthalene. It is concluded that in spite of the fact that both 2a and 11 afford Ph2Ge in high yield upon photolysis, they are poor precursors for study of the species in solution by time-resolved uv-vis methods, owing to the formation of other, more strongly absorbing transient products than Ph2Ge, whose lowest energy absorption is characteristically weak.


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