PALLADIUM(II) COMPLEXES OF 1,4-BENZODIAZEPINES - CRYSTAL-STRUCTURE AND REACTIVITY IN DIMETHYLSULFOXIDE OF [PD(BROMAZEPAM)CL2]

The crystal structure of the title complex has been determined from single crystal X-ray data. The palladium atom is in the usual square planar arrangement with 7-bromo-1,3-dihydro-5-(2-pyridyl)-2H-1,4-benzodiazepine-2-one (bromazepam) coordinated with the two alpha-diimine nitrogen atoms of bromazepam and two cis-chlorine atoms. The geometry of the molecule and its crystal packing are similar to the corresponding platinum(II) complex, where the usual boat conformation of bromazepam is retained. The kinetics of displacement of coordinated bromazepam, by 1,10-phenanthroline and 2,2'-bipyridine, in [Pd(bromazepam)Cl2] have been studied by stopped-flow spectrophotometry in dimethylsulphoxide at 25-degrees-C. The data have been interpreted in terms of a mechanism implying two reacting forms, the complex and a solvo-species with mono-coordinated bromazepam. In the case of the less reactive bipyridine, ring closure of bromazepam and entry of the nucelophile compete for the reaction centre.