Synthesis and Studies on the Reactivities of Dicyclopentadienylytterbium Derivatives Containing Carbazolate and Pyrazolate Ligands

Two ytterbocene derivatives containing aromatic nitrogen ligands, (C5H5)2YbCbz(THF) (1)
and (C5H5)2YbPzMe2(THF) (4), were synthesized, and their reactivities toward N,N‘-diisopropylcarbodiimide, phenyl isothiocyanate, and phenyl isocyanate were studied. Abstraction of cyclopentadienyl from (C5H5)3Yb with 1 equiv of carbazole (HCbz) in THF at room
temperature gives 1. Reaction of 1 with N,N‘-diisopropylcarbodiimide (iPrNCNiPr) results
in monoinsertion of iPrNCNiPr into the Yb−N(Carbazolate) bond, yielding the ytterbocene
guanidinate (C5H5)2Yb[iPrNC(Cbz)NiPr] (2), while treatment of 1 with 1 equiv of phenyl
isothiocyanate (PhNCS) gives the unexpected monocyclopentadienylytterbium complex
(C5H5)Yb[SC(Cbz)NPh]2(THF) (3) and (C5H5)3Yb(THF), which may be rationalized by
the ligand rearrangement of the monoinsertion product (C5H5)2Yb[SC(Cbz)NPh]. (C5H5)3Yb reacts with 3,5-dimethylpyrazole (HPzMe2) in a 1:1 ratio at ambient temperature to form
complex 4. Reaction of 4 with PhNCO gives the insertion product (C5H5)2Yb[OC(NPh)PzMe2](THF) (5). In contrast to 1, however, complex 4 does not react with iPrNCNiPr under
the same conditions. All these complexes were characterized by elemental analysis and
spectroscopic properties. The structures of complexes 2−5 were also determined by X-ray
single-crystal diffraction analyses. These reactions present the first example of 1,3-heterocumulene insertions into the Ln−N(aromatic ring) bond and provide a new strategy
for introducing a substituent at the nitrogen atom of organic heterocycle compounds.