2,5-Bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl borohydride complexes of the divalent lanthanides - Synthesis, structures and ring-opening polymerization of ε-caprolactone

The borohydride complexes [(DIP(2)pyr)Ln(BH4)(THF)(3)] (Ln = Eu (1), Yb (2); (DIP(2)pyr)(-) = 2,5-bis{N-(2,6-diisopropylphenyl)iminomethyl}pyrrolyl) were synthesized by reaction of [Ln(BH4)(2)(THF)(2)] (Ln = Eu, Yb) with [(DIP(2)pyr)K] in THF. The X-ray solid-state structures of 1 and 2 show that the (DIP(2)pyr)(-) ligand coordinates in a kappa(3)-fashion to the europium atom, while the smaller ytterbium atom is only kappa(2)-coordinated by the (DIP(2)pyr)(-) ligand with one Schiff base nitrogen atom pointing away from the metal center. Whereas compound 1 can be stored under nitrogen at room temperature for several months, compound 2 is less stable, decomposing under these same conditions. The corresponding two-fold ligated compound [(DIP(2)pyr)(2)Yb(THF)] was isolated from the reaction of [(DIP(2)pyr)K] with anhydrous ytterbium diiodide in THF. The X-ray solid state structure suggests one kappa(3)-coordinated (DIP(2)pyr)(-) ligand while the second ligand is kappa(2)-coordinated to the metal center. Compound 1 was found active in promoting the ring-opening polymerization (ROP) of epsilon-caprolactone under mild conditions. (C) 2013 Elsevier B.V. All rights reserved.