Bridging β-lactam coordination at dinuclear zinc sites

Two highly preorganized dizinc scaffolds based on compartmental pyrazolate ligands are found to incorporate 2-azetidinone in its deprotonated beta-lactamide form as an N,O-bridging ligand within the dimetallic pocket. Both dizinc beta-lactamide complexes 3(.)(ClO4)(2) and 4(.)(ClO4)(2) have been characterized structurally and spectroscopically, revealing a strengthening of the beta-lactamide C-N bond and a weakening of the C=O bond relative to free 2-azetidinone. These findings contrast the reverse geometrical changes observed recently by Brombacher and Vahrenkamp for beta-lactamide N-bound to only a single zinc ion, thus underlining the particular dimetallic effect that is achieved by the cooperativity of two adjacent metal ions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).