An electron-rich {RuNO}6 complex: trans-[Ru(DMAP)4(NO)(OH)]2+ (DMAP = 4-N,N’ dimethylaminopyridine). Structure and reactivity

OSA CODESIDO, N.; DE CANDIA, A. G.; WEYHERMULLER, T.; OLABE, J. A.; SLEP, L. D.

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2012 p. 4301 - 4309

1434-1948

The pseudooctahedral nitrosyl species trans-[Ru(DMAP)4(NO)(OH)]2+ (DMAP = 4-dimethylaminopyridine) (12+) has been prepared by reaction between [Ru(DMAP)5H2O]2+ and NaNO2 under mild conditions (room temperature, pH 6-8), and precipitated with NaBF4 or NaPF6. Single-crystal X-ray diffraction data of 1(BF4)22H2O support a {RuNO}6 electronic configuration for the cation, though with a significant deviation from the expected linear arrangement of the RuNO moiety (169.3 deg). The remarkable low value of the stretching mode νNO at 1832 cm–1 in the solid salt corresponds to an electron rich ligand environment, with strong back-bonding interactions between d metal orbitals and π*NO orbitals of the (formally) NO+ (nitrosonium) ligand. Consistently, the complex behaves as a poor electrophile: it is extremely unreactive toward OH–, and the stronger nucleophile cysteine. Cyclic voltammetric (CV) experiments show three reduction processes in acetonitrile. The first one at –0.50 V (vs Ag/AgCl, KCl ss) is reversible in the CV timescale. Spectroelectrochemical experiments (IR and UV-vis) suggest that the reduced complex has a {RuNO}7 configuration. The value of νNO at 1603 cm–1 agrees with a reduction mostly centered at the nitrosyl ligand. This species appears to be inert toward substitution in the coordination sphere, and the original {RuNO}6 ion can be quantitatively recovered upon oxidation. On the contrary, further reduction of this species is completely irreversible, even in the CV timescale, probably due to the lability of the seemingly produced nitroxyl (NO–) ligand.