Reactivity of Tuck-over Titanium Oxo Complexes with Isocyanides

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 1 with 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 and tBuNC results in the initial insertion of one isocyanide into the terminal Ti–alkyl bond to form the iminoacyl complexes 7 and 8, followed by a second insertion into the metallacycle moiety to generate 9, in the case of tert-butylisocyanide. DFT calculations support the selective reactivity observed experimentally with a kinetic and thermodynamic preference for RNC insertion on the terminal alkyl groups bound to both metallic centers over the alternative insertion on the “tuck-over” ligand.