Synthesis of actinide η2-pyridyl and η2-α-picolyl complexes by carbon–hydrogen bond activation

Studies in our laboratory have shown that the thorium(IV) complexes (C5Me5)2ThPh2 and (C5Me5)2Th(CH2Ph2)2 mediate carbon–nitrogen bond cleavage and dearomatization of the pyridine ring in pyridine N-oxide. Based upon these results, we examined the analogous chemistry with a variety of pyridine compounds to determine if the electron-withdrawing oxygen present in pyridine N-oxide was required for reactivity of this type. Interestingly, reaction of (C5Me5)2An(CH3)2 (An = Th, U) with pyridine and substituted analogues produces CH4 and the corresponding η2-(N,C)-pyridyl complexes by activation of the sp2-hybridized ortho C–H bond. Isotopic labeling studies indicate that the C–H activation reactions are consistent with a σ-bond metathesis mechanism. Additionally, the η2-(N,C)-pyridyl complexes undergo ligand-exchange reactions with both pyridine-d5 and α-picoline.