Issue 46, 2011

Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2′-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects

Abstract

The present article describes ruthenium nitrosyl complexes with the {RuNO}6 and {RuNO}7 notations in the selective molecular frameworks of [RuII([9]aneS3)(bpy)(NO+)]3+ (43+), [RuII([9]aneS3)(pap) (NO+)]3+ (83+) and [RuII([9]aneS3)(bpy)(NO˙)]2+ (42+), [RuII([9]aneS3)(pap)(NO˙)]2+ (82+) ([9]aneS3 = 1,4,7-trithiacyclononane, bpy = 2,2′-bipyridine, pap = 2-phenylazopyridine), respectively. The nitrosyl complexes have been synthesized by following a stepwise synthetic procedure: {RuII–Cl} → {RuII–CH3CN} → {RuII–NO2} → {RuII–NO+} → {RuII–NO˙}. The single-crystal X-ray structure of 43+ and DFT optimised structures of 43+, 83+ and 42+, 82+ establish the localised linear and bent geometries for {Ru–NO+} and {Ru–NO˙} complexes, respectively. The crystal structures and 1H/13C NMR suggest the [333] conformation of the coordinated macrocyclic ligand ([9]aneS3) in the complexes. The difference in π-accepting strength of the co-ligands, bpy in 43+ and pap in 83+ (bpy < pap) has been reflected in the ν(NO) frequencies of 1945 cm−1 (DFT: 1943 cm−1) and 1964 cm−1 (DFT: 1966 cm−1) and E°({RuII–NO+}/{RuII–NO˙}) of 0.49 and 0.67 V versusSCE, respectively. The ν(NO) frequency of the reduced {Ru–NO˙} state in 42+ or 82+ however decreases to 1632 cm−1 (DFT: 1637 cm−1) or 1634 cm−1 (DFT: 1632 cm−1), respectively, with the change of the linear {RuII–NO+} geometry in 43+, 83+ to bent {RuII–NO˙} geometry in 42+, 82+. The preferential stabilisation of the eclipsed conformation of the bent NO in 42+ and 82+ has been supported by the DFT calculations. The reduced {RuII–NO˙} exhibits free-radical EPR with partial metal contribution revealing the resonance formulation of {RuII–NO˙}(major)↔{RuI–NO+}(minor). The electronic transitions of the complexes have been assigned based on the TD-DFT calculations on their DFT optimised structures. The estimated second-order rate constant (k, M−1s−1) of the reaction of the nucleophile, OH with the electrophilic {RuII–NO+} for the bpy derivative (43+) of 1.39 × 10−1 is half of that determined for the pap derivative (83+), 2.84 × 10−1 in CH3CN at 298 K. The Ru–NO bond in 43+ or 83+ undergoes facile photolytic cleavage to form the corresponding solvent species {RuII–CH3CN}, 22+ or 62+ with widely varying rate constant values, (kNO, s−1) of 1.12 × 10−1 (t1/2 = 6.2 s) and 7.67 × 10−3 (t1/2 = 90.3 s), respectively. The photo-released NO can bind to the reduced myoglobin to yield the Mb-NO adduct.

Graphical abstract: Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2′-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects

Supplementary files

Article information

Article type
Paper
Submitted
26 Apr 2011
Accepted
31 Aug 2011
First published
11 Oct 2011

Dalton Trans., 2011,40, 12527-12539

Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2′-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects

P. De, S. Maji, A. Dutta Chowdhury, S. M. Mobin, T. Kumar Mondal, A. Paretzki and G. K. Lahiri, Dalton Trans., 2011, 40, 12527 DOI: 10.1039/C1DT10761E

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