- Gas-Phase Kinetic Study of the Prototype Silylene Addition Reaction SiH2 + C2H4 over the Temperature Range 298 - 595 K. An Example of a Third-Body Mediated Association
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Time-resolved studies of silylene, SiH2, generated by laser flash photolysis of phenylsilane, have been carried out to obtain rate constants for its bimolecular reaction with ethene.The reaction was studied in the gas phase, over the pressure range 1 - 100 Torr (in SF6 bath gas) at five temperatures in the range 298 - 595 K.The reaction of SiH2 with C2H4 is pressure dependent, consistemt with a third-body assisted association reaction to form silirane.While silirane was too labile to be detected, vinylsilane, another possible product, was ruled out by GC analysis.Extrapolation of the pressure dependent rate constants gave the Arrhenius equation: log(k/cm3 molecule-1 s-1) = (-9.97 +/- 0.03) + (2.9 +/- 0.2) kJ mol-1/RT ln 10.These parameters are consistent with a fast, nearly collision-controlled, association process.RRKM modeling, based on a consistent transition state for silirane decomposition, gave a good fit to the pressure dependent curves.The calculations employed a weak collisional deactivation model and confirmed (within +/- 12 kJ mol-1) the most recent theoretical value for ΔH0f(silirane) of 124 kJ mol-1.An enthalpy surface for the reaction highlights the importance of entropy, rather than enthalpy (or energy), in determining the breakdown pathway of silirane.
- Al-Rubaiey, N.,Walsh, R.
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p. 5303 - 5309
(2007/10/02)
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- Hetero-?-Systems, 8. Silaethene
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By means of a combination of vacuum flash pyrolysis and matrix isolation silaethene (1a) and its simply substituted derivatives 1b-f can be prepared starting with precursors 9a-f of the silabicyclooctadiene type.Silaolefins 1a-f are stable in argon at 10 K and can be identified by their characteristic IR and UV spectra.
- Maier, Guenther,Mihm, Gerhard,Reisenauer, Hans Peter
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p. 2351 - 2368
(2007/10/02)
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- Hetero-?-Systems, 9. About the Relationships between Silaethenes and Methylsilylenes
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Silaethenes 1 and the isomeric methylsilylenes 2 are separately existing species, but can readily be interconverted in an argon matrix via a photochemically induced 1,2-H shift.In case of the thermal excitation in the gas phase examples for both directions have been dedected spectroscopically: the isomerisation of a silaolefin into the corresponding silylene (1d -> 2d) and the formation of a silene from a silylene (2f -> 1f).
- Maier, Guenther,Mihm, Gerhard,Reisenauer, Hans Peter,Littmann, Dieter
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p. 2369 - 2381
(2007/10/02)
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