Some mechanistic suggestions for silylene to silylene interconversions

Mechanistic Study of Thermal Decomposition of Hexamethyldisilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory

Thermal decomposition of hexamethyldisilane (HMDS) was studied from room temperature to 1310 K using flash pyrolysis vacuum ultraviolet single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS). Decomposition pathways of HMDS and initial reaction intermediates were also investigated using density functional theory (DFT) at the B3LYP/6-311++G(d,p) level. Unimolecular decomposition reactions of HMDS involving Si-Si and Si-C bond cleavage, as well as decomposition producing Me₄Si and :SiMe₂ via a three-centered elimination, were determined as the initiation reactions. Me₃SiSi(Me)₂^•, Me₄Si, Me₃Si^•, and :SiMe₂ were major products of the initiation reactions. These initial products were apt to decompose by homolytic reactions. Me₂Si═CH₂, :SiMe₂, and other silene/silylene intermediates preferred decomposing through molecular eliminations. Both homolytic and molecular elimination reactions are important in the pyrolysis of HMDS.

Mechanism of the thermal decomposition of tetramethylsilane: a flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry and density functional theory study

The thermal decomposition of tetramethylsilane (TMS) was studied over the temperature range of 298-1450 K by combining flash pyrolysis vacuum ultraviolet photoionization time-of-flight mass spectrometry (VUV-PI-TOFMS) and density functional theory (DFT). The initial step in TMS pyrolysis produced a methyl radical (Me˙) and Me3Si˙. Me3Si˙ underwent subsequent loss of a hydrogen atom to form Me2Si[double bond, length as m-dash]CH2 and loss of a methyl radical to form Me2Si:. Isomerizations via 1,2-shift and H2 eliminations were major secondary decomposition reactions of Me2Si[double bond, length as m-dash]CH2 and Me2Si:. Among the various isomers, silylene species containing Si-H bonds, such as :Si(H)CH2CH2CH3, :Si(H)CH2CH[double bond, length as m-dash]CH2, :Si(H)CH2CH3, and :Si(H)CH[double bond, length as m-dash]CH2, played an important role in H2 elimination reactions. On the other hand, silene species were insignificant in H2 eliminations. Unlike the silylene species, H2 elimination of :Si[double bond, length as m-dash]CH2 was energetically unfavorable.