Absolute rate constants for the gas-phase silicon-hydrogen insertion reactions of dimethylsilylene with silane and the methylsilanes in the temperature range 300-600 K

Baggott, J. E.; Blitz, Mark A.; Frey, H. M.; Walsh, Robin

doi:10.1021/ja00179a018

Cited by 44 publications

(54 citation statements)

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“…For SiMez + MeOH agreement is less good, the rate constants covering a range of a factor of 40. However, as has been pointed out before [5,21] The rate data here offers strong support both for the involvement of intermediate donor-acceptor complexes and for the initial electron pair donation into the emptyp-orbital of %Mez. Figure 10 shows a plot of the correlation between rate constants and ionization energies [27,28] for the 0-donors for which data are available.…”

Section: Discussionsupporting

confidence: 84%

“…For SiMez + MeOH agreement is less good, the rate constants covering a range of a factor of 40. However, as has been pointed out before [5,21], there are reasons to doubt the validity of the values of Gaspar et al…”

Section: Discussionmentioning

confidence: 86%

“…The equipment and method have been described previously as have the production and characterization of SiMez [13,16,17,21]. Briefly, transient concentrations of SiMez were produced via 193 nm photolysis of either pentamethyldisilane (PMDS) or octamethyltrisilane (OMTS) using an ArF exciplex laser (Oxford Lasers KX2).…”

Section: Methods and Equipmentmentioning

confidence: 99%

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Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

Baggott

Blitz

Frey

et al. 1992

Int J of Chemical Kinetics

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The reactions of dimethylsilylene, SiMez, generated by laser flash photolysis from pentamethyldisilane and octamethyltrisilane, and detected via its 457.9 nm absorption, have been investigated with a number of oxygen containing molecules, including oxygen itself, carbon monoxide, water, alcohols, and ethers at 295 K. Some substrate molecules were deuterated. Apart from GO, all molecules reacted with SiMez with second order rate constants (in cm3 molecule-' s-l) in the range 7.7 x to 4.7 x lo-". While most of the reactions of SiMez studied went to completion those with dimethylether and tetrahydrofuran were partially reversible. The reaction of SiMep with oxirane was pressure dependent.The data are generally consistent with a mechanism involving initial formation of a donoracceptor, zwitterionic complex. In the case of reaction with alcohols, there is a small overall isotope effect, suggesting formation of a complex followed by rapid H-transfer, which only marginally affects the rate. In the case of ethers, complexes are formed which (i) may react further (MezSi . . . oxetane), (ii) may react further but also reversibly decompose (MezSi . . . oxirane), or (iii) do not seem to react further (MezSi . . .OMez, MezSi . . .THF) but partially redissociate.The donor-acceptor bond strength has been estimated in these last cases to be ca. 40 k J mol-I. Supporting arguments and mechanistic details of all reactions investigated are presented.

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Section: Discussionsupporting

confidence: 84%

Section: Discussionmentioning

confidence: 86%

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Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

Baggott

Blitz

Frey

et al. 1992

Int J of Chemical Kinetics

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“…The monitoring lasers were a CW argon ion laser (Coherent Innova 90-5) for SiMe 2 and a single mode dye laser (Coherent 699-21) pumped by the Ar ion laser for SiH 2 . Both silylenes were detected via absorption in their strong Ã ( 1 B 1 ) r X ( 1 A 1 ) absorption bands, SiMe 2 at 457.9 nm 21,22 and SiH 2 at 579.39 nm (17259.50 cm -1 ), a strong vibration-rotation transition. [23][24][25] Gas mixtures for photolysis were made up containing a small pressure of precursor (PhSiH 3 between 2 and 15 mTorr; OMTS between 30 and 200 mTorr), varying pressures of substrate (C 3 H 6 up to 250 mTorr; i-C 4 H 8 up to 300 mTorr; C 2 H 4 up to 9.8 Torr) together with inert diluent (sulfur hexafluoride, SF 6 ) at total pressures between 1 and 100 Torr.…”

Section: Methodsmentioning

confidence: 99%

Direct Gas-Phase Kinetic Studies of Silylene Addition Reactions: SiH₂ + C₃H₆, SiH₂ + i-C₄H₈, and SiMe₂ + C₂H₄. The Effects of Methyl Substitution on Strain Energies in Siliranes

et al. 1998

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Time-resolved studies of the title reactions have been carried out over the pressure range 1−100 Torr (in SF6 bath gas) and at temperatures in the range 293−600 K, using laser flash photolysis techniques to generate and monitor the silylenes, SiH2 and SiMe2. All three reactions showed evidence of pressure dependence, consistent with third-body assisted association reactions to form silirane products. Extrapolation of the pressure-dependent rate constants gave the following Arrhenius parameters: SiH2 + C3H6, log(A/cm3 molecule-1 s-1) = −9.79 ± 0.03, Ea (kJ mol-1) = −1.9 ± 0.3; SiH2 + C4H8, log(A/cm3 molecule-1 s-1) = −9.91 ± 0.04, Ea (kJ mol-1) = −2.5 ± 0.3; SiMe2 + C4H8, log(A/cm3 molecule-1 s-1) = −12.12 ± 0.02, Ea(kJ mol-1) = −8.5 ± 0.2. These parameters are consistent with fast, nearly collision-controlled processes for SiH2 but a tighter transition state for SiMe2. Rice, Ramsperger, Kassel, Marcus theory (RRKM) modeling, based on consistent transition states for silirane decomposition, and employing a weak collisional deactivation model, gave good fits to the pressure-dependent curves for each system, provided an appropriate value of Eo (fitting parameter) was used for each reaction. The kinetic results are consistent with an electrophilically led addition mechanism, although methyl substitution in the alkene hardly affects the rate constants. The RRKMderived Eo values have been used to derive reaction enthalpies which are in reasonable agreement with values obtained by ab initio calculations at the G2 (MP2,SVP) level. The experimental ΔH° values yield strain energies of 190, 196, and 216 kJ mol-1 for 2-methyl-, 2,2-dimethyl-, and 1,1-dimethylsilirane, respectively. Compared to the strain enthalpy of 167 kJ mol-1 for silirane itself, this shows that methyl substituents in the silirane products substantially increase the strain energies. Theory supports this. Disciplines Chemistry CommentsReprinted (adapted) M. S. Gordon Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011-3111ReceiVed: April 22, 1998; In Final Form: June 16, 1998 Time-resolved studies of the title reactions have been carried out over the pressure range 1-100 Torr (in SF 6 bath gas) and at temperatures in the range 293-600 K, using laser flash photolysis techniques to generate and monitor the silylenes, SiH 2 and SiMe 2 . All three reactions showed evidence of pressure dependence, consistent with third-body assisted association reactions to form silirane products. Extrapolation of the pressuredependent rate constants gave the following Arrhenius parameters: SiH 2 + C 3 H 6 , log(A/cm 3 molecule -1 s -1 ) ) -9.79 ( 0.03, E a (kJ mol -1 ) ) -1.9 ( 0.3; SiH 2 + C 4 H 8 , log(A/cm 3 molecule -1 s -1 ) ) -9.91 ( 0.04, E a (kJ mol -1 ) ) -2.5 ( 0.3; SiMe 2 + C 4 H 8 , log(A/cm 3 molecule -1 s -1 ) ) -12.12 ( 0.02, E a (kJ mol -1 ) ) -8.5 ( 0.2. These parameters are consistent with fast, nearly collision-controlled processes for SiH 2 but a tighter transition state for SiMe 2 . Rice, Ramsperger, Kassel, Marcus theory (RRKM) m...

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“…In spite of this, relatively few quantitative data exist on the reactivity of simple transient derivatives in solution. The chemistry of the parent molecule, SiH 2 , has been extensively characterized in the gas phase, chiefly by Walsh and his group [5], who have also carried out similar studies of SiMe 2 [6][7][8]. The latter silylene has been studied in detail in solution by Das and Shizuka and their coworkers, who measured absolute rate constants for reaction of the species in cyclohexane solution with alcohols, ethers, alkenes, alkynes, O 2 , trialkylsilanes, and tri-n-butylstannane and examined its complexation with ethers, amines, and acetonitrile [9][10][11][12].…”

Section: Introductionmentioning

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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Absolute rate constants for the gas-phase silicon-hydrogen insertion reactions of dimethylsilylene with silane and the methylsilanes in the temperature range 300-600 K

Cited by 44 publications

References 1 publication

Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

Direct Gas-Phase Kinetic Studies of Silylene Addition Reactions: SiH₂ + C₃H₆, SiH₂ + i-C₄H₈, and SiMe₂ + C₂H₄. The Effects of Methyl Substitution on Strain Energies in Siliranes

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

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Absolute rate constants for the gas-phase silicon-hydrogen insertion reactions of dimethylsilylene with silane and the methylsilanes in the temperature range 300-600 K

Cited by 44 publications

References 1 publication

Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

Time resolved kinetic studies of the gas‐phase reactions of dimethylsilylene with some O‐Donor molecules: Part I. Room temperature studies

Direct Gas-Phase Kinetic Studies of Silylene Addition Reactions: SiH2 + C3H6, SiH2 + i-C4H8, and SiMe2 + C2H4. The Effects of Methyl Substitution on Strain Energies in Siliranes

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

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Direct Gas-Phase Kinetic Studies of Silylene Addition Reactions: SiH₂ + C₃H₆, SiH₂ + i-C₄H₈, and SiMe₂ + C₂H₄. The Effects of Methyl Substitution on Strain Energies in Siliranes