Untangling the reaction dynamics of the silylidyne radical (SiH; X2Π) with acetylene (C2H2; X1Σg+)

Abstract

Chemical reaction dynamics of silylidyne (SiH; X 2 Π) with acetylene (C 2 H 2 ; X 1 Σ g +) were studied exploiting the crossed molecular beam approach, and compared with previous studies on D1silylidyne with acetylene. The reaction is initiated by a barrierless addition of silylidyne to one or both carbons of acetylene leading to 1-sila-1-propene-1,3-diylidene and/or the cyclic 1silacyclopropenyl with the former isomerizing to the latter. 1-Silacyclopropenyl eventually loses atomic hydrogen yielding silacyclopropenylidene (c-SiC 2 H 2) in an overall exoergic reaction (experiment:-14.7 ± 8.5 kJ mol-1 ; theory:-13 ± 3 kJ mol-1). The enthalpy of formation for silacyclopropenylidene is determined to be 421.4 ± 9.3 kJ mol-1 .

Formation of the 2,3-Dimethyl-1-silacycloprop-2-enylidene Molecule via the Crossed Beam Reaction of the Silylidyne Radical (SiH; X2Π) with Dimethylacetylene (CH3CCCH3; X1A1g)

“…The reaction dynamics of the silylidyne–dimethylacetylene system mirror the chemical dynamics elucidated for the silylidyne–acetylene , and silylidyne–methylacetylene reactions studied earlier. In all reactions, the silylidyne radical adds without entrance barrier to the carbon–carbon triple bond either to one or simultaneously to both carbon atoms, yielding acyclic and cyclic intermediates, which are bound between 34–74 and 152–174 kJ mol –1 .…”

“…This yields an enthalpy of formation of the previously elusive 2,3-dimethyl-1-silacycloprop-2-enylidene isomer to be 275 ± 21 kJ mol −1 (experimentally) and 294 ± 8 kJ mol −1 (computationally). The reaction dynamics of the silylidyne−dimethylacetylene system mirror the chemical dynamics elucidated for the silylidyne−acetylene 10,39 and silylidyne−methylacetylene 11 reactions studied earlier. In all reactions, the silylidyne radical adds without entrance barrier to the carbon−carbon triple bond either to one or simultaneously to both carbon atoms, yielding acyclic and cyclic intermediates, which are bound between 34− 74 and 152−174 kJ mol −1 .…”