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

De, Prinaka ; Maji, Somnath ; Chowdhury, Abhishek Dutta ; Mobin, Shaikh M. ; Mondal, Tapan Kumar ; Paretzki, Alexa ; Lahiri, Goutam Kumar (2011) Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects Dalton Transactions (46). pp. 12527-12539. ISSN 0300-9246

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Official URL: http://pubs.rsc.org/en/Content/ArticleLanding/2011...

Related URL: http://dx.doi.org/10.1039/C1DT10761E

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 versus SCE, 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-1 s-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 κ. 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 (t½ = 6.2 s) and 7.67 × 10-3 (t½ = 90.3 s), respectively. The photo-released NO can bind to the reduced myoglobin to yield the Mb-NO adduct.

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