Extraction Ability and Selectivity for Lithium Ion of Macrocyclic Trinuclear (Alkylbenzene)ruthenium(II) Complexes Bridged by 2,3-Pyridinediolato Ligands

• Published in: Bulletin of the Chemical Society of Japan 2011-01, Vol.84 (3), p.259-265
• Main Authors: Katsuta, Shoichi, Nomura, Hajime, Egashira, Takuya, Imoto, Takahiro, Kudo, Yoshihiro, Takeda, Yasuyuki
• Format: Article
• Language: English
• ISSN: 0009-2673; 1348-0634; 1348-0634
• DOI: 10.1246/bcsj.20100282

A series of macrocyclic trinuclear complexes of (η6-alkylbenzene)ruthenium(II) bridged by 2,3-pyridinediolato ligands were synthesized and their liquid–liquid extraction properties for Li+ and Na+ were investigated at 25 °C. The alkylbenzenes used were p-cymene, 1,2,3-trimethylbenzene, 1,3,5-trimethylbenzene, 1,3,5-triethylbenzene, 1,2,4,5-tetramethylbenzene, and hexamethylbenzene. Most of the trinuclear complexes were stable for 48 h or more in a dichloromethane–water system. The extraction constants (Kex = [ML+A−]o/([M+][A−][L]o); M+: alkali metal ion, L: trinuclear complex, A−: counter anion (picrate), and o: organic phase (dichloromethane)) were determined from analysis of the extraction equilibria. Each trinuclear complex exhibited a larger Kex value for Li+ than for Na+; particularly large separation factor, SF = Kex(Li+)/Kex(Na+), was observed for the complexes of Ru(1,3,5-trimethylbenzene) (SF = 1.7 × 103) and Ru(1,2,4,5-tetramethylbenzene) (SF = 1.6 × 103). The extraction separation of Li+ from seawater could be achieved by using the trinuclear complex of Ru(1,3,5-trimethylbenzene) with the aid of washing the organic phase with water to remove co-extracted Na+.