Synthesis and Dimethylsilicone Insertion into the Ln−N Bond of Cyclopentadienyl Lanthanide Pyrazolate Complexes

Abstract

Reactions of Cp3Ln (Cp = C5H5; Ln = Ho, Dy, Yb, Sm) with 2 equiv of HPzMe2 (HPzMe2 = 3,5-dimethylpyrazole) in THF at room temperature yield complexes CpLn(PzMe2)2 [Ln = Ho (1), Dy (2)], Cp2Yb(PzMe2)(HPzMe2) (3), and Sm(PzMe2)3 (5), respectively, indicating that the number of cyclopentadienyl groups liberated from a Cp3Ln moiety is largely influenced by the size of the lanthanide ion. Reaction of Cp3Er and 1 equiv of HPzMe2 under the same conditions gave Cp2Er(PzMe2)(THF) (4). The structures of 3 and 4 were determined by X-ray diffraction. In both complexes the central metal ions are coordinated to four ligands in a typical "bent metallocene" geometry. Complexes 1 and 2 react with dimethylsilicone grease to give the corresponding Me2SiO insertion products [CpLn(PzMe2)(OSiMe2PzMe2)]2 [Ln = Ho (6), Dy (7)]. The results of the investigation show that the insertion of dimethylsilicone into the Ln−N bond is only possible for the monocyclopentadienyl-type organolanthanide pyrazolates. X-ray diffraction reveals complex 6 to be a centrosymmetric dimer in which each holmium atom is coordinated to one cyclopentadienyl group, two bridging oxygen atoms, and three nitrogen atoms, two from the chelating PzMe2 ligand and one from the bridging 3,5-dimethylpyrazolyl siloxide ligand to form a distorted octahedron.