Synthesis, structures, and properties of ruthenium(ii) complexes of N-(1,10-phenanthrolin-2-yl)imidazolylidenes

Abstract

Mononuclear ruthenium complexes [RuCl(L1)(CH₃CN)₂](PF₆) (2a), [RuCl(L2)(CH₃CN)₂](PF₆) (2b), [Ru(L1)(CH₃CN)₃](PF₆)₂ (4a), [Ru(L2)(CH₃CN)₃](PF₆)₂ (4b), [Ru(L2)₂](PF₆)₂ (5), [RuCl(L1)(CH₃CN)(PPh₃)](PF₆) (6), [RuCl(L1)(CO)₂](PF₆) (7), and [RuCl(L1)(CO)(PPh₃)](PF₆) (8), and a tetranuclear complex [Ru₂Ag₂Cl₂(L1)₂(CH₃CN)₆](PF₆)₄ (3) containing 3-(1,10-phenanthrolin-2-yl)-1-(pyridin-2-ylmethyl)imidazolylidene (L1) and 3-butyl-1-(1,10-phenanthrolin-2-yl)imidazolylidene (L2) have been prepared and fully characterized by NMR, ESI-MS, UV-vis spectroscopy, and X-ray crystallography. Both L1 and L2 act as pincer NNC donors coordinated to ruthenium (II) ion. In 3, the Ru(II) and Ag(I) ions are linked by two bridging Cl⁻ through a rhomboid Ag₂Cl₂ ring with two Ru(II) extending to above and down the plane. Complexes 2–8 show absorption maximum over the 354–428 nm blueshifted compared to Ru(bpy)₃²⁺ due to strong σ-donating and weak π-acceptor properties of NHC ligands. Electrochemical studies show Ru(II)/Ru(III) couples over 0.578–1.274 V.