Collect. Czech. Chem. Commun. 1995, 60, 983-989

Synthesis and Kinetics of Isomerization of mer and fac[CoCO3(en)(Amino Acidato)] Isomers

Pavel Tyle and František Jursík

Department of Inorganic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6, Czech Republic


Reaction of [CoXY(en)(AB)]n+ (AB = glycinato or (S)-α-alaninato anion, X = H2O, Y = Cl; AB = (S)-valinato anion, X = Y = Cl) with HCO-3) or Ag(2CO)3 gives mixture of mer- and fac-[CoCO(3(en)(AB)] isomers, ratio of which is temperature dependent. Both isomers undergo in aqueous solution to spontaneous isomerization which does not occur when carbonato group is replaced by oxalato or malonato one. This suggests that the source of stereolability in these complexes is a strain imposed by the four-membered carbonato chelate ring. The equilibrium constants (K = fac/mer) increase in the order KGly < KVal < KAla. The total rate constants obtained at 45 °C and 55 °C increase in the order kAla < kVal < kGly. λ-mer-[CoCO3(en)(S)-Val)] isomer undergoes at 22 °C racemization at the octahedral centre yielding the mixture of 59% δ and 41% λ isomers.