Laser pyrolysis studies of β-diketonate chemical vapour deposition precursors. Part 1: β-diketones

Abstract

The thermal decomposition of the β-diketones pentane-2,4-dione, 1,1,1,5,5,5-hexafluoropentane-2,4-dione, and 2,2,6,6-tetramethylheptane-3,5-dione has been studied using the technique of IR laser-powered homogeneous pyrolysis combined with the ab initio calculation of activation energies of possible reaction pathways. Pentane-2,4-dione decomposes by two parallel molecular elimination pathways, the keto tautomer affording acetone and ketene via a 6-electron retroene reaction and the enol tautomer 2-methylfuran via H₂O elimination, followed by cyclisation. 1,1,1,5,5,5-Hexafluoropentane-2,4-dione eliminates HF with ring closure to yield 2,2-difluoro-5-(trifluoromethyl)furan-3(2H)-one. There is also a minor route of loss of one or two CF₃ radicals, followed by H-abstraction to yield 3,3-difluoroacryloylfluoride and carbon suboxide, respectively. 2,2,6,6-Tetramethylheptane-3,5-dione decomposes via central C–CO bond homolysis, followed by CO or ketene loss from the resultant radicals and subsequent disproportionation of t-Bu radicals to produce 2-methylpropene and 2-methylpropane.