Multiple N−H Bond Activation: Synthesis and Reactivity of Functionalized Primary Amido Ytterbium Complexes

A series of new functionalized amido complexes of ytterbium, [Cp2YbNHR]2 (R = 8-quinolyl(Qu) (1a), 2-pyridyl(Py) (1b), 2-aminophenyl (1c), 3-amino-2-pyridyl (1d), and Cp2Yb[NHC6H4(CH2NH2-2)] (1e), have been synthesized by metathesis of Cp2YbCl and the corresponding amido lithium salts. Their reactivity toward carbodiimides has been investigated, in which multiple N−H activation behavior for metal-bound neutral NH2 and anionic nitrogen-containing fragments, a property that is expressed without dissociation from the lanthanide center, is observed. These results provide an alternative mechanistic insight for the metal-mediated mono- and diguanylation of primary amines and elucidate factors that affect the chemo- and regioselectivities of the addition and protonation steps. Reaction of 1a with 2 equiv of RNCNR [R = cyclohexyl (Cy), isopropyl (iPr)] leads to the formal insertion of carbodiimide into the N−H bond of the Yb-bonded amido group to yield Cp2Yb[η1:η2-RNC(NHR)NQu]2 [R = Cy (2a), iPr (2b)]. Interestin...