Deuteration Reaction of Malonate Hydrogens in Some Monomalonatocobalt(III) Compounds

Abstract

Abstract The rate of deuteration at malonate hydrogens has been measured for [Co(mal)(N)4]+ and [Co(malH)(NH3)5]2+ ions in aqueous solution over the pD range of 2 to 8, where mal=malonate dianion, malH=malonate monoanion, and (N)4=(NH3)4, (ethylenediamine)2, (1,3-propanediamine)2, (1,10-phenanthroline)2, or (2,2′-bipyridine)2. For the tetraamine type complexes with a chelated malonate ligand, the deuteration process is acid-catalysed up to pD=about 4 and base-catalysed at higher pD values. This contrasts with the behavior of the unidentate malonate ligand, for which the deuteration is base-catalysed up to pD=3.5, whereupon the deprotonation of the carboxylate group takes place and the deuteration rate steps down to a constant, pH-independent value. The deuteration mechanisms are discussed.