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

Abstract

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 (iPrNCNiPr) results in monoinsertion of iPrNCNiPr 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.