Heteroleptic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands: synthesis, structure and their application in the polymerization of ε-caprolactone

Abstract

A convenient method for the synthesis of anionic lanthanide amide complexes bearing carbon-bridged bis(phenolate) ligands is described and the catalytic activity of the complexes in the ring-opening polymerization of ε-caprolactone was studied.

Carbon bridged biphenolate ligands in rare earth chemistry

“…Treatment of [Ln{N(SiMe 3 ) 2 } 2 ] with one equivalent of biphenol (bpoH 2 ) at 60 °C led to formation of [Ln(bpo){N(SiMe 3 ) 2 }], which could undergo further protolysis with 3,5-dimethylpyrazole (MePzH), yielding [Ln(bpo)(Me 2 Pz)(thf) 3 ] (Scheme 16). 35…”

“…3 -IV). Simple heteroleptic complexes have also been reported containing a trivalent Ln centre with one fully deprotonated mbmp 2À ligand, and an ancillary monoanionic ligand [Ln(mbmp)L] 16,[34][35][36] (L = Cp, N(SiMe 3 ) 2 or 3,5-dimethylpyrazolate) (Fig. 3 -VI).…”

“…Analogous complexes [Ln(mbmp)Cp(thf) 2 ] (Ln = Sm and Nd) were also synthesised by the same route, but, were not treated further with mbmpH 2 (Scheme 14). 34 The partially deprotonated complexes of Y, Yb and Sm are of particular interest, as the protonated phenol allows for further 35 Furthermore, a range of phenols and alcohols of varying steric bulk were applied in the same fashion using the [Ln(mbmp)Cp(thf) 2 ] (Ln = La, Sm, Nd and Yb) starting materials, yielding a variety of mono-and di-nuclear complexes (Scheme 17). 16,43 Similar to the metathesis reactions previously described with heteroleptic lanthanoid amide halide starting materials (Scheme 13), these reagents can also be utilised directly for Scheme 16 Stepwise protolysis of lanthanoid silylamide starting materials with bulky biphenols (mbmpaH 2 and mbbpaH 2 ) and subsequent protolysis with 3,5-dimethylpyrazole.…”

“…16,43 Similar to the metathesis reactions previously described with heteroleptic lanthanoid amide halide starting materials (Scheme 13), these reagents can also be utilised directly for Scheme 16 Stepwise protolysis of lanthanoid silylamide starting materials with bulky biphenols (mbmpaH 2 and mbbpaH 2 ) and subsequent protolysis with 3,5-dimethylpyrazole. 35 Scheme 17 Reactions of alcohols and phenols with [Ln(mbmp)Cp(thf) 2 ] yielding both mono-and di-nuclear complexes. 16,43 protolysis reactions owing to the basic nature of the amide ligand.…”