title: Dinuclear barium(II) complexes based on a calix[4]arene scaffold as catalysts of acyl transfer.
abstract: Two novel regioisomeric calix[4]arene derivatives (2 and 3), decorated with two aza[18]crown-6 units at vicinal (1,2) or diagonal (1,3) positions of the upper rim, were synthesized. The catalytic activities of their dinuclear Ba2+ complexes were investigated in the ethanolysis of esters 8-11, endowed with a carboxylate anchoring group. Major results are as follows: 1) the two metal ions in the dinuclear catalysts work together in a cooperative fashion; 2) the vicinal calix[4]arene catalyst 2 is far superior to its diagonal regioisomer 3 in the reactions of all of the investigated esters; and 3) the distance between the carboxylate and ester carbonyl, which increases regularly from 8 to 11, influences reactivity of catalytic ester cleavage in a way that is decidedly suggestive of the importance of a good match between ester size and metal-to-metal distance. However, the superiority of the vicinal catalyst 2 relative to 3 cannot be explained on the basis of the putative match of ester size to intermetal distance, thus providing an indication that additional, still poorly understood effects may contribute significantly to catalytic efficiency.
authors.affiliation: IMC CNR Sezione Meccanismi di Reazione and Dipartimento di Chimica, Università La Sapienza, P.le A. Moro 5, Box 34-Roma 62, 00185 Roma, Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Cacciapaglia
authors.forename: Alessandro
authors.initials: A
authors.lastname: Casnati
authors.forename: Stefano
authors.initials: S
authors.lastname: Di Stefano
authors.forename: Luigi
authors.initials: L
authors.lastname: Mandolini
authors.forename: Daniele
authors.initials: D
authors.lastname: Paolemili
authors.forename: David N
authors.initials: DN
authors.lastname: Reinhoudt
authors.forename: Andrea
authors.initials: A
authors.lastname: Sartori
authors.forename: Rocco
authors.initials: R
authors.lastname: Ungaro
mesh_terms: D001464:Barium / Q000737:chemistry*; D047250:Calixarenes / Q000737:chemistry*; D002384:Catalysis; D018360:Crystallography, X-Ray; D004952:Esters / Q000138:chemical synthesis*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*
chemical_list: D004952:Esters; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; C121325:calix(4)arene; D047250:Calixarenes; D001464:Barium