Can. J. Chem., 84, 934-948 (2006).

National Research Council of Canada

Direct Detection of Methylphenylgermylene and 1,2-Dimethyl-1,2-diphenyldigermene. Kinetic Studies of their Reactivities in Solution.

William J. Leigh,* Ileana Dumbrava, and Farahnaz Lollmahomed

Contribution from the Department of Chemistry, McMaster University, 1280 Main Street West, Hamilton, ON Canada L8S 4M1.

Photolysis of 1,3,4-trimethyl-1-phenylgermacyclopent-3-ene (5) in hydrocarbon solvents containing isoprene, methanol, or acetic acid affords 2,3-dimethyl-1,3-butadiene (DMB) and the expected trapping products of methylphenylgermylene (GeMePh) in chemical yields exceeding 90%. The germylene has been detected in hexane solution by laser flash photolysis, as a short-lived species (t ~ 2 ms) exhibiting a UV/vis absorption spectrum centered at lmax = 490 nm. It decays with second-order kinetics and a rate constant close to the diffusion-controlled limit, with the concomitant growth of a second, longer-lived transient (lmax = 415 nm) that is assigned to a mixture of E- and Z-1,2-dimethyl-1,2-diphenyldigermene (4). Absolute rate constants have been determined for reaction of the germylene with primary and tertiary amines (n-BuNH2 and Et3N, respectively), acetic acid (AcOH), a terminal alkyne and alkene, isoprene, DMB, CCl4, the Group 14 hydrides Et3SiH and Bu3SnH. GeMePh is slightly more reactive than GePh2 towards all the reagents studied in this work; both are significantly less reactive than GeMe2 toward the same substrates. Absolute rate constants for reaction of 4 have also been measured or assigned upper limits in every case, and are compared to previously reported values for tetraphenyl- and tetramethyldigermene with the same reagents.


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