New photochemical routes to germylenes and germenes and kinetic evidence concerning the germylene-diene addition mechanism

Bobbitt, Kevin L.; Maloney, Vincent M.; Gaspar, Peter P.

doi:10.1021/om00054a046

Cited by 44 publications

(54 citation statements)

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“…The UV/vis absorption spectrum of the species, which was assigned to vinylgermirane 11b, is nearly identical to that of 9, as might be expected. It exhibits a lifetime τ ∼ 500 μs in the presence of 50 mM added diene, which was proposed to reflect the rate of (thermal) isomerization to the isomeric germacyclopent-3-ene derivative [24], the ultimate product of the reaction of GePh 2 with isoprene [23,36,37]. A species assignable to vinylgermirane 11a can be detected as a product of photolysis of 1, provided that the photolysis is carried out under conditions where the compound is rendered incapable of dissociation to free germylene and diene, such as in a rigid matrix at low temperatures.…”

Section: Resultsmentioning

confidence: 99%

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

et al. 2006

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The photochemistry of 3,4-dimethyl-1,1-diphenylsilacyclopent-3-ene (2), a potential precursor to diphenylsilylene (SiPh 2 ), has been studied in hydrocarbon and methanol solution by steady state and laser flash photolysis techniques. The results are consistent with the formation of three major photoproducts: SiPh 2 (ca. 20%), 2,3-dimethyl-1,3-butadiene (DMB; ca. 20%), and 2-methyl-2-(1-methylethenyl)-1,1-diphenylsilirane (9; ca. 75%), the product of formal photochemical (1,3)-sigmatropic rearrangement of 2. Attempts to detect the silylene by laser flash photolysis were unsuccessful, but the vinylsilirane could be easily detected as a long-lived transient exhibiting λ max = 285 nm and lifetime τ = 1.3 s in hexane at 25 • C. The same spectrum is observed in neat methanol solution, where the lifetime of the species is shortened to τ = 36 ms and it is quenched by sodium methoxide and methanesulfonic acid with absolute rate constants of k MeO -= 2.0 × 10 6 M −1 s −1 and k H+ = 2.6 × 10 3 M −1 s −1 , respectively. The photochemistry of 2 is compared to that of the corresponding germanium homologue (1), whose photolysis in solution has been previously shown to afford diphenylgermylene and DMB cleanly and in high yields. The corresponding vinylgermirane (11a), though not detectable as a primary photoproduct from 1 in solution, is the exclusive product of photolysis of 1 in a 3-methylpentane glass at 78 K, where it exhibits an essentially identical UV/vis spectrum to that of 9. The rate constant for its unimolecular thermal isomerization to regenerate 1 is three orders of magnitude larger than that of the corresponding process in the homologous vinylsilirane (9) in hydrocarbon solution at 25 • C.

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Section: Resultsmentioning

confidence: 99%

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

et al. 2006

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“…, (16) gave the high pressure limiting rate constants, k ∞ . The Arrhenius parameters calculated from the tem perature dependence of k ∞ are presented in Table 8.…”

Section: Methodsmentioning

confidence: 99%

“…This product then rearranges to the germacyclopentene, 5,28,29 the formal 1,4 adduct, or adds a second molecule of the diene to give 3,4 divinyl germacyclopent 3 ene. 4, 16 Both reactions proceed simul taneously. Under the gas phase conditions, the diene con centration is too low, thus rendering trapping of the initial 1,2 adduct highly unlikely.…”

Section: R = H Bu Tmentioning

confidence: 99%

Gas phase kinetic and theoretical studies of reactions of germylenes and dimethylstannylene

et al. 2005

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The results of time resolved gas phase studies of labile germylenes (GeH 2 and GeMe 2 ) and dimethylstannylene (SnMe 2 ) reactions reported to date are considered together with data of quantum chemical investigations of the potential energy surfaces of these systems. Reaction mechanisms are discussed. A comparison of reactivity in the series of carbene analogs, ER 2 (E = Si, Ge, Sn, R = H, Me), is made.

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“…Since the report nearly 20 years ago by Ando et al (1) of the UV spectra of several simple, photochemically generated germylene derivatives in hydrocarbon matrixes at low temperature, there have been a number of studies published on the direct detection and study of reactive diarylgermylenes (2-10) and dialkylgermylenes (6,(11)(12)(13)(14)(15) in solution by laser flash photolysis techniques. Most of these studies employed Group 14 catenates as photochemical precursors to these "heavy carbene" analogues, such as 1-3 in the case of diphenylgermylene (Ph 2 Ge).…”

Section: Introductionmentioning

confidence: 99%

Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph₂Ge:) precursors

Harrington¹,

Leigh²,

Chan³

et al. 2005

Can. J. Chem.

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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 previously been shown 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, ≥15%). Laser flash photolysis of 2a in deoxy genated 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 UVvis methods, owing to the formation of other, more strongly absorbing transient products than Ph2Ge, whose lowest energy absorption is characteristically weak.Key words: germylene, germyl radical, flash photolysis, disilylgermane, photochemistry.

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New photochemical routes to germylenes and germenes and kinetic evidence concerning the germylene-diene addition mechanism

Cited by 44 publications

References 0 publications

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

Gas phase kinetic and theoretical studies of reactions of germylenes and dimethylstannylene

Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph₂Ge:) precursors

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New photochemical routes to germylenes and germenes and kinetic evidence concerning the germylene-diene addition mechanism

Cited by 44 publications

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The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

The photochemistry of a potential diphenylsilylene precursor. Time-resolved spectroscopic studies of the reactivity of a transient vinylsilirane

Gas phase kinetic and theoretical studies of reactions of germylenes and dimethylstannylene

Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph2Ge:) precursors

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Time-resolved spectroscopic studies of the photochemistry of some diphenylgermylene (Ph₂Ge:) precursors