Equilibria in complexes of N-heterocyclic molecules. Part 25. Kinetics of pseudo-base formation in metal complexes and quaternized organic molecules derived from 5-nitro-1,10-phenanthroline

Abstract

The kinetics of pseudo-base formation with [OH]– in various doubly charged quaternary cations and co-ordination compounds formed from 5-nitro-1,10-phenanthroline have been studied in detail. The groups bridging the 1,10-nitrogen atoms are FeII, RuII, (CH2)2, and (CH2)3. For the reaction [Fe(5NO2-phen)3]2++[OH]–⇌[Fe(5NO2-phen)2(5NO2-phen.OH)]+, values of the forward and reverse rate constants are respectively 2.24 dm3 mol–1 s–1 and 0.014 s–1 at 291 K. The corresponding values for the ruthenium(II) analogue are 0.58 dm3 mol–1 s–1 and 0.024 s–1 at 290 K. For the bridging group (CH2)3, the kinetics of the same reaction have been followed and the forward and reverse rate constants are respectively 5.35 × 103 dm3 mol –1 s–1 and 0.34 s–1 at 273 K. For the ethylene-bridged compound, a second [OH]– group can be added to the molecule, viz., [5NO2-phen(CH2)2·OH]++[OH]–⇌[5NO2-phen(CH2)2·2OH]°. The equilibrium constant for this reaction is 95.4 dm3 mol–1 at 273 K. The results obtained are compared with those for a wide variety of quaternized N-heterocyclic molecules and co-ordination complexes.