Anca Dumitrescu

Zinc(II), Samarium(III) and Tin(II) Complexes Featuring a Tridentate Nitrogen Donor for the Ring-Opening Copolymerization of (D,L)-Lactide and Glycolide

The design of discrete metal complexes that could be highly active and selective catalysts for the polymerization of a variety of monomer classes is of considerable current interest.[1] A significant aim is to construct less expensive catalysts while retaining the benefits of discrete metal complexes. These goals are especially important with respect to the copolymerization of lactide (L) and glycolide (G), to give poly(lactide-co-glycolide) (PLGA), biodegradable and biocompatible polyesters that are garnering great interest due to their biomedical, pharmaceutical, and agricultural applications.[2] To this end complexes of various metals (aluminum,[3 5] tin,[6] zinc,[7 9] iron,[10] magnesium,[7d] zirconium[11]) and lanthanides (yttrium,[12,13] lanthanum,[12,13] samarium,[13] ytterbium[13]) have been studied. Chelating nitrogen ligands are often used for stabilizing low-valent species.[14] We have recently shown that diamidoamino ligands [(RNCH2CH2)2NR ]2 , initially developed by Cloke,[15] are particularly well adapted for the stabilization of neutral as well as cationic group 13 Lewis acids.[3] Due to the formation of a rather rigid bicyclic core, these tridentate nitrogen donors enforce an approximately trigonal-monopyramidal coordination geometry around the metal, and the ensuing empty axial coordination site has been used for promoting the ring-opening polymerization of heterocycles such as propylene oxide and (,)-lactide.[3] We have also shown that stannylenes featuring diamidoam-

A Crystalline Phosphenium Salt Featuring the Electron‐Withdrawing 2,6‐Bis(trifluoromethyl)phenyl Group

The presence of a sigma-withdrawing group such as the 2,6-bis-(trifluoromethyl)phenyl substituent does not prevent the isolation of a highly electrophilic phosphenium salt, ((C) Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002).