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Activity of Peroxo and Hydroperoxo Complexes of Ti IV in Olefin Epoxidation: A Density Functional Model Study of Energetics and Mechanism
Author(s) -
Yudanov Ilya V.,
Gisdakis Philip,
Di Valentin Cristiana,
Rösch Notker
Publication year - 1999
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(199912)1999:12<2135::aid-ejic2135>3.0.co;2-x
Subject(s) - chemistry , olefin fiber , ethylene , density functional theory , coordination sphere , oxygen atom , reaction mechanism , stereochemistry , catalysis , computational chemistry , photochemistry , medicinal chemistry , molecule , organic chemistry
Epoxidation of olefins by Ti IV peroxo and hydroperoxo (alkylperoxo) complexes was investigated using a hybrid DFT method (B3LYP). Reaction energies and activation barriers for direct oxygen transfer to ethylene as a model olefin were computed for various model complexes to compare the epoxidation activity of Ti(η 2 ‐O 2 ) and TiOOR (R = H, CH 3 ) moieties. The activity of complexes with a Ti(O 2 ) peroxo group is shown to be essentially quenched when the coordination sphere of the complex is saturated by strongly basic (σ‐donor) ligands. In contrast, the activity of a TiOOH functional group depends only weakly on the saturation of the coordination sphere of the Ti center. Substitution of methyl for hydrogen in a TiOOH group is found to slightly increase the activation barrier of epoxidation. The computational results give preference to reaction paths that involve TiOOR species. The factors governing the activity of Ti(O 2 ) and TiOOR groups, in particular the effects of donor ligands, are discussed on the basis of a molecular orbital analysis.