Ruthenium complexes containing 2-(2-nitrosoaryl)pyridine : Structural, spectroscopic, and theoretical studies

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Original languageEnglish
Pages (from-to)11636-11643
Journal / PublicationInorganic Chemistry
Volume50
Issue number22
Publication statusPublished - 21 Nov 2011

Abstract

Ruthenium complexes containing 2-(2-nitrosoaryl)pyridine (ON^N) and tetradentate thioether 1,4,8,11-tetrathiacyclotetradecane ([14]aneS4), [Ru(ON^N)([14]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 ([9]aneS3)/tert-butylisocyanide ligand set, [Ru(ON^N)([9]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-N NO 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)([14]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([14]aneS4)] moieties in 2a and 2b is larger than that in [Ru(bpy)([14]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.