The invention relates to η5:η1-cyclopentadienylidene-
phosphorane constrained geometry complexes of
rare earth metals, abbreviated to η5:η1-CpPC-CGC, method for production and use of same. The η5:η1-CpPC-CGCs correspond to the general formula (1), wherein SE=Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu; X=independently of one another, a mono-anionic diorganoamido-, bistrimethylsilylamido-, halogenido-,
alkyl-,
aryl-, alkoxo-, aryloxo- or alkylaluminate (AlR4−)
substituent; L=neutral ligand (PR3, NR3,
pyridine),
solvent molecule (THF,
ether, DMF, DMSO, HMPT,
tetrahydropyran THP, tetrahydrothiofuran THT); R=
alkyl with up to 1-10 C atoms or mono- or polycyclical
aryl with 6 to 20 C atoms; R1, R4=independently of one another H or methyl; R2, R3=independently of one another, H or methyl or
tertiary butyl or together a substituted cycloalkyl group; R5, R6=methyl, n-butyl,
tertiary butyl or phenyl; R7, R8=independently of one another H,
trimethylsilyl,
alkyl with 1-10 C atoms or mono- or polycyclical
aryl with 6 to 20 C atoms, and m=0, 1, 2 or 3.