A combined crossed molecular beams and ab initio investigation on the formation of vinylsulfidoboron (C₂H₃¹¹B³²S)

We exploited crossed molecular beams techniques and electronic structure calculations to provide compelling evidence that the vinylsulfidoboron molecule (C₂H₃¹¹B³²S) - the simplest member of hitherto elusive olefinic organo-sulfidoboron molecules (RBS) - can be formed via the gas phase reaction of boron monosulfide (¹¹B³²S) with ethylene (C₂H₄) under single collision conditions. The reaction mechanism follows indirect scattering dynamics via a barrierless addition of the boron monosulfide radical to the carbon-carbon double bond of ethylene. The initial reaction complex can either decompose to vinylsulfidoboron (C₂H₃¹¹B³²S) via the emission of a hydrogen atom from the sp³ hybridized carbon atom, or isomerize via a 1,2-hydrogen shift prior to a hydrogen loss from the terminal carbon atom to form vinylsulfidoboron. Statistical (RRKM) calculations predict branching ratios of 8% and 92% for both pathways leading to vinylsulfidoboron, respectively. A comparison between the boron monosulfide (¹¹B³²S) plus ethylene and the boron monoxide (¹¹BO) plus ethylene systems indicates that both reactions follow similar reaction mechanisms involving addition - elimination and addition - hydrogen migration - elimination pathways. Our experimental findings open up a novel pathway to access the previously poorly-characterized class of organo-sulfidoboron molecules via bimolecular gas phase reactions, which are difficult to form through ' classical’ organic synthesis.