Extraction properties for alkali metal picrates of macrocyclic trinuclear (p-cymene)ruthenium(II) and (pentamethylcyclopentadienyl)rhodium(III) complexes

The solvent extraction properties of macrocyclic trinuclear organometallic complexes, [(p-cymene)Ru(pyO2)]3 and [Cp∗Rh(pyO2)]3 ( pyO 2 2 - = 2 , 3 -dioxopyridine, Cp ∗ = pentamethylcyclopentadienyl ) , for Li+, Na+, and K+ picrates have been investigated in a dichloromethane–water system at 25 °C. The extraction rates of the alkali metal picrates with these macrocyclic complex ligands are unusually slow; the shaking times required to attain equilibrium are at least 1 h for [(p-cymene)Ru(pyO2)]3 and 20–40 h for [Cp∗Rh(pyO2)]3. From analysis of the equilibrium data, the extraction constants (Kex = [ML+A−]o/[M+][L]o[A−]; M+ = alkali metal ion, L = macrocyclic ligand, A− = picrate ion, o = organic phase) have been determined. The log Kex value varies in the sequences, Li+ (5.72) > Na+ (4.50) > K+ (2.88) for [(p-cymene)Ru(pyO2)]3 and Li+ (4.79) > Na+ (2.70) ≈ K+ (2.69) for [Cp∗Rh(pyO2)]3. The Kex values of 6,6-dibenzyl-14-crown-4 (DBz14C4), which is one of the best Li+-selective crown ethers, have also been determined for comparison. It is revealed that [Cp∗Rh(pyO2)]3 is much superior to DBz14C4 both in the extractability for Li+ and the selectivity for Li+ over Na+.