sp~3 versus sp~2 C-H bond activation chemistry of 2-picoline by Th(IV) and U(IV) metallocene complexes

摘要

The thoriumalkyl complex (C_5Me_5 )_2Th(CH_3)_2 and 2-picoline react to give preferential sp~3 C-H bond activation in the presence of a more reactive sp~2 C-Hbond, while the analogous uranium complex, (C_5Me_5)_2U(CH_3)_2, reacts with only the ortho 2-picoline sp~2 C-H bond, as originally expected. Herein, we describe this competitive sp~3 versus sp~2 C-H bond activation chemistry with 2-picoline and (C_5Me_5)_2An(CH_3)_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, (C_5Me_5)_2Th(CH_3)[eta~2-(Af,C)-2-CH_2-NC_5H_3], and the eta~2-pyridyl complexes (C_5Me_5)_2(CH_3)[eta~2-(N,C)-6-CH_3-NC_5H_3] and (C_5Me_5)_2U(CH_3)[eta~2-(N,C)-6-CH_3-NC_5H_3].