1.10- Phenanthroline, reaction with complexes

F. E. Lyttle and D. M. Hercules 161) investigated the energetic relations in the chemiluminescent reaction of ruthenium chelate complexes (Ru-III-2.2 -bipyridyI-, — 5-methyl-1.10-phenanthrolin — and other complexes) with hydroxyl ion or hydrazide. The general reaction is... 

Activation volumes for aquation of Schiff base complexes [Fe(C5H4NCH=NHR)3]2+ (R = Me, Et, nPr, nBu) are between +11 and +14 cm3 mol-1 (107), and thus within the range established earlier (108) for (substituted) tris-l,10-phenanthroline-iron(II) complexes, viz. +11 to +22 cm3 mol-1. These positive values are consistent with dissociative activation. Kinetic studies of the reaction of a CH2S(CH2)3SCH2 -linked bis(terpy) ligand (L6) with [Fe(terpy)2]2+ showed a very slow two-step process. The suggested mechanism consisted of slow loss of one terpy, rapid formation of [Fe(terpy)(L6)], and finally slow displacement of the second terpy as the partially-bonded L6 becomes hexadentate (109). 

Noticeably, the reaction of Ni2+ with dithizone is quite slow and sluggish. Nevertheless, this slow reaction is significantly accelerated by the addition of nitrogen-containing bases like 1, 10-phenanthroline. The resulting complex may be represented by the following equation ... 

The reactions of alcohols related to phenolphthalein and fluorescein with Ag1 ions have been investigated for their application as colorimetric reagents in determining trace amounts of silver. A simple, rapid and sensitive method was found which used 2,4,5,7-tetra-bromofluorescein and 1,10-phenanthroline. A ternary complex was formed with a deep pink colour (Ama 550 nm) in the presence of silver(I) ions and the two reagents. No significant colour change was observed in the absence of the diimine.227... 

This order of base activity corresponds almost exactly to that observed in the formation of pyrroles from ketoximes and acetylene, evidently for the same causes. The failure of trimethylbenzylammonium hydroxide to catalyze the reaction of vinylation is believed (59MI1 66MI1) to be caused by its lack of coordination. Along with inhibition of the reaction with water, pyridine, o-phenanthroline, and diketones, this indicates the reaction occurs by complex ionic mechanisms in which the participation of the complex ion as an intermediate is possible. 

Rate equations of this type are normally associated with the formation of associative intermediates or the involvement of deprotonated ligand forms in reactions with two (or more) competitive pathways. However, in the case of octahedral metal complexes of ligands such as 2,2 -bipyridine or 1,10-phenanthroline, such mechanisms do not appear to be likely. Associative mechanisms would involve seven-co-ordinate intermediates, which are likely to be sterically strained and electronically disfavoured on ligand field grounds. Furthermore, this type of ligand does not appear to contain any strongly acidic protons which are likely to be involved in reactions with aqueous hydroxide ion (but see later). 

Many of the studies purporting to show nucleophilic attack upon co-ordinated heterocyclic ligands have been performed with complexes of 5-nitro-l,10-phenanthro-line, 8.20. Unfortunately, this ligand proves to be a less than optimal choice, as nitroalke-nes undergo facile reactions with nucleophiles and, in contrast to simple pyridines, the free ligand reacts with hydroxide ion. Hydroxide ion and other nucleophiles react with 8.20 at the 6-position to give the stabilised anion 8.21 (Fig. 8-20). It is almost certain that the majority of the reactions of 5-nitro-l,10-phenanthroline complexes with hydroxide... 

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