1-Nitroso-2-naphtholate complexes of ruthenium(II) : Synthesis, isomerization and, spectral and electrochemical properties

Department of Chemistry, Inorganic Chemistry Section, Jadavpur University, Kolkata-700 032, India

E-mail : samaresh_b@hotmail.com

Manuscript received online 09 December 2013, accepted 06 January 2014

Reaction of 1-nitroso-2-naphthol (Hnn) with [Ru(PPh₃ )₃Cl₂ ] in 2 : 1 mole ratio in refluxing ethanol affords two geometrical isomers of a complex of type [Ru(PPh₃ )₂ (nn)₂ ], in which the 1-nitroso-2-naphtholate ligand is coordinated to ruthenium as a mono-anionic bidentate N,O-donor. The two isomers are labeled as ttt and cct, indicating respectively trans-trans-trans and cis-cis-trans disposition of the N, O and P donor atoms around the metal center. Structures of both the ttt and cct isomers of the [Ru(PPh₃ )₂ (nn)₂ ] complex have been determined by X-ray crystallography. This cct isomer is found to be energetically less stable, and is quantitatively convertible into the thermodynamically more stable ttt isomer simply by refluxing in ortho-xylene. Both the ttt- and cct-[Ru(PPh₃ )₂ (nn)₂ ] complexes are diamagnetic, and show characteristic ¹H NMR spectra. They also show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on the ttt- and cct-[Ru(PPh₃ )₂ (nn)₂ ] complexes shows an oxidative response near 0.8 V vs SCE and a reductive response within –0.3 to –0.5 V vs SCE. DFT calculations have been carried out to explain the electronic spectral, as well as electrochemical, observations.