(Mesitylene)ruthenium π-complexes with benzo-15-crown-5 and dibenzo-18-crown-6

The reactions of benzo-15-crown-5 and dibenzo-18-crown-6 with 1 equiv. of [(mes)Ru(MeNO2)3]2+ (mes = 1,3,5-C6H3Me3) give the mononuclear complexes [(mes)Ru(η6-benzo-15-crown-5)]2+ (1) and [(mes)Ru(η6-dibenzo-18-crown-6)]2+ (2) in 50% yield. Similar reaction with 2 equiv. of [(mes)Ru(MeNO2)3]2+ produces the dinuclear complex [(μ-η6:η6-dibenzo-18-crown-6)Ru2(mes)2]4+ (3) in 96% yield as a 2:3 mixture of cis- and trans-isomers. Structures of 2(OTf)2 and trans-3(OTf)4 were confirmed by X-ray diffraction. The NMR titration showed that mononuclear dications 1 and 2 bind Na+ ion less effective (Ka = 600 and 250 M–1) than free benzo-15-crown-5 and dibenzo-18-crown-6 (Ka = 2 × 105 and 5 × 106 M−1). The dinuclear tetracation 3 does not bind Na+ within measurable limits of NMR titration method. The electrochemical behaviour of complexes 1–3 was studied in propylene carbonate solution. They exhibit a partially chemically reversible Ru(II)/Ru(I) reduction, which in the case of the dinuclear complex 3 proceeds through two slightly separated steps. The redox activity of the complexes is substantially unaffected by the presence of sodium ion.

Reactions of benzocrown ethers with the cationic [(mes)Ru]2+ fragment afford mono and binuclear π-complexes. Ruthenium complexation strongly decreases Na+ binding ability of the crown ether cavity.Figure optionsDownload as PowerPoint slide