Synthesis and dimethylsilicone insertion into the Ln-N bond of cyclopentadienyl lanthanide pyrazolate complexes

Reactions of Cp(3)Ln (Cp = C5H5; Ln = Ho, Dy, Yb, Sm) with 2 equiv of HPzMe (2) (HPzMe(2) = 3,5-dimethylpyrazole) in THF at room temperature yield comp lexes CpLn(PzMe(2))(2) [Ln = Ho (1) Dy (2)], Cp2Yb(PzMe(2))(HPzMe(2)) (3), and Sm(PzMe(2))(3) (5), respectively, indicating that the number of cyclope ntadienyl groups liberated from a Cp(3)Ln moiety is largely influenced by t he size of the lanthanide ion. Reaction of Cp3Er and 1 equiv of HPzMe(2) un der the same conditions gave Cp2Er(PzMe(2))(THF) (4). The structures of 3 a nd 4 were determined by X-ray diffraction. In both complexes the central me tal ions are coordinated to four ligands in a typical "bent metallocene" ge ometry. Complexes 1 and 2 react with dimethylsilicone grease to give the co rresponding Me2SiO insertion products [CpLn(PzMe(2))(OSiMe(2)PzMe(2))](2) [ Ln = Ho (6), Dy (7)]. The results of the investigation show that the insert ion of dimethylsilicone into the Ln-N bond is only possible for the monocyc lopentadienyl-type organolanthanide pyrazolates. X-ray diffraction reveals complex 6 to be a centrosymmetric dimer in which each holmium atom is coord inated to one cyclopentadienyl group, two bridging oxygen atoms, and three nitrogen atoms, two from the chelating PzMe(2) ligand and one from the brid ging 3,5-dimethylpyrazolyl siloxide ligand to form a distorted octahedron.