Yttrium and lanthanide complexes with various P,N ligands in the coordination sphere: Synthesis, structure, and polymerization studies

摘要

Yttrium and lanthanide complexes with different P,N ligands in the coordination sphere have been synthesized. First the chloride complexes [{CH(PPh2NSiMe3)(2)}Ln{(Ph(2)p)(2)N}Cl] (Ln=Y (1a), La (1b), Nd (1c), Yb (1d)) having the bulky [CH(PPh2NSiMe3)(2)](-) and the flexible [(Ph2P)(2)N](-) ligands in the same molecule were prepared by three different synthetic pathways. Compounds 1a-d can be obtained by reaction of [{[CH(PPh2NSiMe3)(2)]LnCl(2)}(2)] with [K(thf)(n)N(PPh2)(2)] (n=1.25 1.5) or by treatment of [{(Ph2P)(2)N}LnCl(2)(thf)(3)] with K[CH(PPh2NSiMe3)(2)]. Further-more, a one-pot reaction of K[CH(PPh2NSiMe3)(2)] with LnCl(3) and [K(thf)(n)N(PPh2)(2)] leads to the same products. Single-crystal X-ray structures of 1a-d show that the conformation of the six-membered metallacycle (N1-P1-C1-P2-N2-Ln) which is formed by chelation of the [CH(PPh2NSiMe3)(2)](-) ligand to the lanthanide atom is influenced by the ionic radius of the central metal atom. In solution dynamic behavior of the [(Ph2P)2N]- ligand is observed, which is caused by rapid exchange of the two different phosphorus atoms. Further reaction of 1b with KNPh2 resulted in [{(Me3SiNPPh2)(2)CH}La{N(PPh2)(2)}(NPh2)] (2). Compounds 1a-d and 2 are active in the ring-opening polymerization of F-caprolactone and the polymerization of methyl methacrylate. In some cases high molecular weight polymers with good conversions and narrow polydispersities were obtained. In both polymerizations the catalytic activity depends on the ionic radius of the metal center.