Temperature dependence of a reaction of silylene with deuterium

Baggott, J. E.; Frey, H. M.; King, Keith D.; Lightfoot, Philip; Walsh, Robin; Watts, Ivy M.

doi:10.1021/j100325a006

Cited by 62 publications

(51 citation statements)

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“…Prior to this study we have found no pressure dependencies in kinetic systems [13,16,17] involving SiMez (unlike those for SiHz [18,19]). Total pressures are listed in Table I.…”

Section: Resultsmentioning

confidence: 75%

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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“…Prior to this study we have found no pressure dependencies in kinetic systems [13,16,17] involving SiMez (unlike those for SiHz [18,19]). Total pressures are listed in Table I.…”

Section: Resultsmentioning

confidence: 75%

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 apparatus and equipment for these studies have been described in detail previously [24,25]. Only essential and brief details are therefore included here.…”

Section: Equipment Chemicals and Methodsmentioning

confidence: 99%

The reaction between silylene and ammonia: Some gas-phase kinetic and quantum chemical studies

2006

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Time-resolved kinetic studies of the reaction of silylene, SiH 2 , generated by 193 nm laser flash photolysis of silacyclopent-3-ene, have been carried out in the presence of ammonia, NH 3 . Second order kinetics were observed. The reaction was studied in the gas phase at 10 Torr total pressure in SF 6 bath gas at each of the three temperatures, 299, 340 and 400 K. The second order rate constants (laser pulse energy of 60 mJ/pulse) fitted the Arrhenius equation:Experiments at other pressures showed that these rate constants were unaffected by pressure in the range 10-100 Torr, but showed small decreases in value at 3 and 1 Torr. There was also a weak intensity dependence, with rate constants decreasing at laser pulse energies of 30 mJ/pulse. Ab initio calculations at the G3 level of theory, show that SiH 2 +NH 3 should form an initial adduct (donor-acceptor complex), but that energy barriers are too great for further reaction of the adduct. This implies that SiH 2 +NH 3 should be a pressure dependent association reaction. The experimental data are inconsistent with this and we conclude that SiH 2 decays are better explained by reaction of SiH 2 with the amino radical, NH 2 , formed by photodissociation of NH 3 at 193 nm. The mechanism of this previously unstudied reaction is discussed.

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“…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. Pressures were measured by capacitance manometers (MKS, Baratron).…”

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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Temperature dependence of a reaction of silylene with deuterium

Cited by 62 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

The reaction between silylene and ammonia: Some gas-phase kinetic and quantum chemical 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

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Temperature dependence of a reaction of silylene with deuterium

Cited by 62 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

The reaction between silylene and ammonia: Some gas-phase kinetic and quantum chemical 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

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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