Reversible Formation of Organyl(oxo)boranes (RBO) (R = C₆H₅or CH₃) from Boroxins ((RBO)₃):  A Matrix Isolation Study

Flash vacuum pyrolysis of triphenyl- and trimethylboroxin and subsequent trapping of the gas phase products in a large excess of argon at T < 20 K allows matrix isolation and characterization by IR spectroscopy of phenyl(oxo)borane and methyl(oxo)borane. The nature of the matrix isolated species, monomeric CH 3 BO, 1:1 dimer complex of CH 3 BO, (CH 3 BO) 2, and (CH 3 BO) 3, depends strongly on the trapping temperature and matrix host gas (Ar vs Xe) with the boroxin dominating at 30 K (Ar) or 55 K (Xe). An ab initio investigation (second-order Møller−Plesset perturbation theory) of the potential energy surface for trimerization of CH 3 BO is in agreement with the experimental observations.