- On the synthesis, structure, and reactivity of tetramesityldigermene
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Tetramesityldigermene (1) can be synthesized cleanly and quantitatively by photolysis of hexamesitylcyclotrigermane (2) in THF at low temperature. A solution of tetramesityldigermene (1) in THF is stable for several weeks at room temperature; the digermene does not dissociate or rearrange. The molecular structure of tetramesityldigermene (1) has been determined using X-ray crystallography. The effectiveness of the new protocol for the synthesis of tetramesityldigermene (1) and its derivatives has been demonstrated in the study of the addition of carboxylic acids to tetramesityldigermene (1).
- Hurni, Krysten L.,Rupar, Paul A.,Payne, Nicholas C.,Baines, Kim M.
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p. 5569 - 5575
(2008/10/09)
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- Substituent effects on the reactions of diarylgermylenes and tetraaryldigermenes with acetic acid and other lewis bases in hydrocarbon solution
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A series of three 1,1-diaryl-3,4-dimethylgermacyclopent-3-ene derivatives bearing polar substituents in the para-positions of the 1,1-diphenyl rings have been synthesized, and their photochemistry has been studied by steady state and laser flash photolysis methods. Photolysis in hydrocarbon solvents affords the corresponding diarylgermylenes in chemical and quantum yields similar to those of the parent (1,1-diphenyl) compound, as shown by the results of trapping experiments with methanol (MeOH) and acetic acid (HOAc). The germylenes exhibit UV/vis absorption spectra (λmax -480-500 nm) and kinetic behavior (τ ≈ 2 μs) similar to that of the parent, diphenylgermylene (GePh2), in hexane solution. Their decay results in the formation of new transient products assigned to the corresponding tetraaryldigermenes (Ge2Ar4), whose absorption spectra (λmax = 440 nm) and lifetimes are also similar to those exhibited by the parent, Ge2Ph4. Both the germylenes and the corresponding digermenes are quenched rapidly by added HOAc and Et2NH, with rate constants that increase with increasing electron-withdrawing power of the aryl substituents, consistent with reaction mechanisms that involve initial nucleophilic attack at germanium in all cases. The Lewis acid-base complexation of the three germylenes with THF and ethyl acetate (EtOAc) has also been studied and supports a two-step mechanism for the reaction with HOAc that involves initial, rate-determining nucleophilic attack at germanium followed by rapid proton transfer. A similar mechanism is proposed for reaction of this substrate with Ge2Ph4 on the basis of the measured Hammett ρ-value. Tetramesityldigermene reacts with HOAc in toluene or THF solution to afford the 1,2-addition product, 1-acetoxy-1,1,2,2-tetramesityldigermane, while no reaction could be detected with Et2NH.
- Huck, Lawrence A.,Leigh, William J.
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p. 1339 - 1348
(2008/10/09)
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- Thermolysis of hexamesitylsiladigermirane or hexamesitylcyclotrigermane in the presence of 2,3-dimethylbutadiene or water
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The thermolysis of hexamesitylsiladigermirane and hexamesitylcyclotrigermane in the presence of 2,3-dimethylbutadiene (DMB) or water has been investigated. Thermolysis of hexamesitylsiladigermirane (1) in the presence of DMB results in the formation of two major compounds: 1,1-dimesityl-3,4-dimethyl-1-germacyclopent-3-ene (3) and 1-mesityl-1-(trimesitylsilyl)-3,4-dimethyl-1-germacyclopent-3-ene (4). Compounds 3 and 4 are most probably formed by initial thermal regioselective cleavage of the siladigermirane to give tetramesitylgermasilene and dimesitylgermylene, which is immediately trapped by the diene. The germasilene does not appear to react with DMB but rather, under the reaction conditions, undergoes a 1,2-mesityl shift at a faster rate to give a silylgermylene, which is subsequently trapped by the diene. Similarly, thermolysis of hexamesitylcyclotrigermane (5) in the presence of DMB yields compounds 3 and 1-mesityl-1-(trimesitylgermyl)-3,4-dimethyl-1-germacyclopent-3-ene (6), in contrast to an earlier report. Again, the intermediate digermene rearranges to a germylgermylene, which is the species trapped, at a faster rate than reaction with DMB. Thermolysis of 1 or 5, in the presence of water, results in the formation of products clearly derived from the addition of water across the double bond of the intermediate germasilene or digermene. Unlike the addition of methanol, the addition of water across the germasilene is not completely regioselective. The synthetic utility and mechanistic implications of this reaction are discussed.
- Baines, Kim M.,Cooke, Jeffrey A.,Dixon, Craig E.,Liu, Hui Wen,Netherton, Matthew R.
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p. 631 - 634
(2008/10/08)
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