A hemiacetalate complex of Ru(II)

Reaction of cis-Ru(bisox)2Cl2, where bisox is 4,4,4′,4′-tetramethyl-2,2′-bisoxazoline, with excess of pyridine-2-carboxaldehyde (py-2-al) in 1:1 (v/v) methanol–water mixture under nitrogen atmosphere and subsequent addition of excess of NH4PF6 give [Ru(bisox)2(py-2-al)](PF6)2 · H2O (1). Refluxing of 1 in dehydrated methanol in presence of triethylamine yields the corresponding hemiacetalate complex: [Ru(bisox)2 (pyridine-2-(α-methoxymethanolato))]PF6 · 1.5H2O (2). Both the complexes have been characterised by single crystal X-ray crystallography, FTIR and NMR. In cyclic voltammetry in acetonitrile at a glassy carbon electrode, 2 displays a quasireversible Ru(II/III) couple at 1.08 V versus NHE which is not observed in 1. A tentative mechanism is proposed for the conversion of 1 to 2. DFT calculations with the LanL2DZ basis set have been performed to investigate these observations theoretically.

Graphical abstractThe first example of a hemiacetalate complex of Ru(II) is synthesised by carrying out the shown reaction with methanol in presence of a base with L = 4,4,4′,4′-tetramethyl-2,2′-bisoxazoline. The 2,2′-bipyridine or 1,10-phenanthroline analogues could not be prepared.Figure optionsDownload full-size imageDownload as PowerPoint slide