Homoleptic lanthanide complexes of chelating bis(phosphanyl)amides: Synthesis, structure, and ring-opening polymerization of lactones

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Roesky, Peter W. ; Gamer, Michael T. ; Puchner, Mario ; Greiner, Andreas:
Homoleptic lanthanide complexes of chelating bis(phosphanyl)amides: Synthesis, structure, and ring-opening polymerization of lactones.
In: Chemistry : a European Journal. Bd. 8 (2002) Heft 22 . - S. 5265-5271.
ISSN 1521-3765
DOI: https://doi.org/10.1002/1521-3765(20021115)8:22<5265::AID-CHEM5265>3.0.CO;2-V

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Abstract

Treatment of the bis(phosphanyl)amide (Ph2P)(2)NH with KH in boiling THF followed by crystallization from THF/n-pentane leads to K(thf)n]N(PPh2)(2)] (n=1.25, 1.5). Reaction of K(thf)(n)]N(PPh2)(2)] with anhydrous yttrium or lanthanide trichlorides in a 3:1 molar ratio afforded homoleptic bis(phosphanyl)amide complexes Ln{N(PPh2)(2)}(3)] (Ln=Y, Er) as large crystals in good yields. Ln{N(PPh2)(2)}(3)] can also be obtained by reaction of the homoleptic bis(trimethylsilyl)amides of Group 3 metals and lanthanides Ln{N(SiMe3)(2)}(3)] (Ln = Y, La, Nd) with three equivalents of (Ph2P)(2)NH in boiling toluene. The single-crystal X-ray structures of these complexes always show eta(2) coordination of the ligand. Dynamic behavior of the ligand is observed in solution and is caused by rapid exchange of the two different phosphorus atoms. Ln{N(PPh2)(2)}(3)] was used as catalyst for the polymerization of epsilon-caprolactone. Significant differences in terms of correlation of theoretical and experimental molecular weights as well as polydispersities were observed depending on the nature of Ln. On the basis of the crystal structure of the heteroleptic complex Lu{N(PPh2)(2)}(3)- (thf)], we suggest that in the initiation step of e-caprolactone polymerization the lactone adds to the lanthanide atom to form a sevenfold coordination sphere around the central atom.