Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides

Abstract

The reactivity of the "tuck-over" species [Ti2(η5-C5Me5)(CH2Ph)3(μ-η5-C5Me4CH2-κC)(μ-O)] (1) and [Ti2(η5-C5Me5)(CH2CMe3)(μ-η5-C5Me4CH2-κC)(μ-CH2CMe2CH2)(μ-O)] (2) toward isocyanides has been examined both synthetically and theoretically. Treatment of 1with the isocyanides RNC, R = Me3SiCH2, 2,6-Me2C6H3, tBu,iPr, leads to a series of η2-iminoacyl species (3−6) where the molecule of isocyanide inserts into one of the terminal metal−alkyl bonds. The analogous reaction of the "tuck-over" metallacycle species 2 with 2,6-Me2C6H3NC andtBuNC results inthe initial insertion of one isocyanide into the terminal Ti−alkyl bondto form the iminoacyl complexes 7 and 8, followed by a secondinsertion into the metallacycle moiety to generate 9, in the case of tertbutylisocyanide. DFT calculations support the selective reactivity observed experimentally with a kinetic and thermodynamicpreference for RNC insertion on the terminal alkyl groups bound to both metallic centers over the alternative insertion on the "tuck-over"ligand.