Ruthenium-mediated selective cleavage of nitrogen–carbon bond of the diimine function. Synthesis, spectroscopic and redox properties of the complexes [Ru(L) 2{ −OC 6H 4C(CH 3)NH}][ClO 4] (L=2,2′-bipyridine and 1,10-phenanthroline) and the crystal structure of the bipyridine derivative

Abstract

The reactions of Ru(bpy) 2(CO 3) (bpy=2,2′-bipyridine) and Ru(phen) 2(CO 3) (phen=1,10-phenanthroline) with the binucleating phenolato diimine function, OHC 6H 4C(CH 3)NCH 2C 6H 4CH 2N(CH 3)CC 6H 4OH, H 2L in ethanol solvent under dinitrogen atmosphere result in ruthenium bipyridine/phenanthroline heterochelates [Ru(bpy) 2/(phen) 2L′](ClO 4) 1 where L′ corresponds to the ketonic imine function −OC 6H 4C(CH 3)NH incorporating the rare CNH fragment. In the course of the reaction the NC bond of the diimine function in H 2L has been selectively cleaved. The formation of 1 has been authenticated by single-crystal X-ray structure of the bipyridine derivative ( 1a). The RuN 5O coordination sphere is distorted octahedral. The diamagnetic complexes 1 exhibit 1:1 conductivity in acetonitrile solution. The complexes show strong Ru II→π*(bpy)/(phen) MLCT transitions in the visible region and intra-ligand transitions in the UV region. The complexes exhibit moderately strong emissions near 700 nm from the lowest energy MLCT bands ( Φ=1.7–2.2×10 −2). The complexes ( 1a and 1b) display reversible ruthenium(III)–ruthenium(II) couple near 0.5 V, irreversible ruthenium(III)→ruthenium(IV) oxidation near 1.7 V and one ligand-based (L′) oxidation near 2.0 V versus SCE. The reductions of the bpy and phen ligands have been observed at the negative side of SCE. The electrochemically oxidized ruthenium(III) complexes ( 1a + and 1b + ) are found to be unstable at 298 K and exhibit rhombic EPR spectra having three distinct g values corresponding to the trivalent ruthenium(III) under distorted octahedral arrangement. The oxidized complexes ( 1a + and 1b + ) exhibit LMCT transitions near 750 nm.