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 Fe^II, Ru^II, (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.