An IR matrix isolation and DFT theoretical study of the first steps of the Ti(0) ethylene reaction: Vinyl titanium hydride and titanacyclopropene

Two new species have been formed by codeposition of ground-state Ti atoms and ethylene molecules in excess argon at low temperature, followed by selective electronic excitation of the Ti atoms. The two products are identified as H2Ti(C2H2) (titanacyclopropene) and HTi(C2H3) (vinyltitanium monohydride) based on IR spectroscopy with various isotopic precursors ((C2H4)-C-12, (C2H4)-C-13, C2D4, CH2CD2, and the natural Ti isotopes), vibrational analysis, and density functional theory (DFT) calculations. Theoretical results are also presented for a Ti(C2H4) pi-complex structure, nor observed in this study. Although DFT predicts a strongly bound Ti(C2H4) system having a stability similar to H2Ti(C2H2) and HTi(C2H3), this molecule is not observed in our experiments. It is found that Ti atoms react with ethylene when in the first excited states (F-3, D-3, or (3)G) to form first an insertion product and next, after a 1,2-hydrogen shift, the dihydrotitanacyclopropene.