Ruthenium complexes containing 2-(2-nitrosoaryl)pyridine : structural, spectroscopic and theoretical studies
Date of Issue2011
School of Physical and Mathematical Sciences
Ruthenium complexes containing 2-(2-nitrosoaryl)pyridine (ON∧N) and tetradentate thioether 1,4,8,11-tetrathiacyclotetradecane (aneS4), [Ru(ON∧N)(aneS4)]2+ [ON∧N = 2-(2-nitrosophenyl)pyridine (2a), 10-nitrosobenzo[h]quinoline (2b), 2-(2-nitroso-4-methylphenyl)pyridine, (2c), 2-(2-nitrosophenyl)-5-(trifluoromethyl)pyridine (2d)] and analogues with the 1,4,7-trithiacyclononane (aneS3)/tert-butylisocyanide ligand set, [Ru(ON∧N)(aneS3)(C≡NtBu)]2+ (4a and 4b), have been prepared by insertion of a nitrosonium ion (NO+) into the Ru–aryl bond of cyclometalated ruthenium(II) complexes. The molecular structures of the ON∧N-ligated complexes 2a and 2b reveal that (i) the ON∧N ligands behave as bidentate chelates via the two N atoms and the bite angles are 86.84(18)–87.83(16)° and (ii) the Ru–NNO and N–O distances are 1.942(5)–1.948(4) and 1.235(6)–1.244(5) Å, respectively. The Ru–NNO and N–O distances, together with νN═O, suggest that the coordinated ON∧N ligands in this work are neutral moiety (ArNO)0 rather than monoanionic radical (ArNO)•– or dianion (ArNO)2– species. The nitrosated complexes 2a–2d show moderately intense absorptions centered at 463–484 nm [εmax = (5–6) × 103 dm3 mol–1 cm–1] and a clearly discriminable absorption shoulder around 620 nm (εmax = (6−9) × 102 dm3 mol–1 cm–1), which tails up to 800 nm. These visible absorptions are assigned as a mixing of d(Ru) → ON∧N metal-to-ligand charge-transfer and ON∧N intraligand transitions on the basis of time-dependent density functional theory (TD-DFT) calculations. The first reduction couples of the nitrosated complexes range from −0.53 to −0.62 V vs Cp2Fe+/0, which are 1.1–1.2 V less negative than that for [Ru(bpy)(aneS4)]2+ (bpy = 2,2′-bipyridine). Both electrochemical data and DFT calculations suggest that the lowest unoccupied molecular orbitals of the nitrosated complexes are ON∧N-centered. Natural population analysis shows that the amount of positive charge on the Ru centers and the [Ru(aneS4)] moieties in 2a and 2b is larger than that in [Ru(bpy)(aneS4)]2+. According to the results of the structural, spectroscopic, electrochemical, and theoretical investigations, the ON∧N ligands in this work have considerable π-acidic character and behave as better electron acceptors than bpy.
© 2011 American Chemical Society. This is the author created version of a work that has been peer reviewed and accepted for publication by Inorganic Chemistry, American Chemical Society. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [http://dx.doi.org/10.1021/ic201570d].