sp3 versus sp2 C–H bond activation chemistry of 2-picoline by Th(IV) and U(IV) metallocene complexes

The thorium alkyl complex (C5Me5)2Th(CH3)2 and 2-picoline react to give preferential sp3 C–H bond activation in the presence of a more reactive sp2 C–H bond, while the analogous uranium complex, (C5Me5)2U(CH3)2, reacts with only the ortho 2-picoline sp2 C–H bond, as originally expected. Herein, we describe this competitive sp3 versus sp2 C–H bond activation chemistry with 2-picoline and (C5Me5)2An(CH3)2 (An = Th, U) and provide experimental observations that suggest different mechanistic reaction pathways are operative for the uranium and thorium complexes. We also report the X-ray crystal structures for the thorium picolyl complex, (C5Me5)2Th(CH3)[η2-(N,C)-2-CH2-NC5H3], and the η2-pyridyl complexes (C5Me5)2Th(CH3)[η2-(N,C)-6-CH3-NC5H3] and (C5Me5)2U(CH3)[η2-(N,C)-6-CH3-NC5H3].