title: Factors That Control the Reactivity of Cobalt(III)-Nitrosyl Complexes in Nitric Oxide Transfer and Dioxygenation Reactions: A Combined Experimental and Theoretical Investigation.
abstract: Metal-nitrosyl complexes are key intermediates involved in many biological and physiological processes of nitric oxide (NO) activation by metalloproteins. In this study, we report the reactivities of mononuclear cobalt(III)-nitrosyl complexes bearing N-tetramethylated cyclam (TMC) ligands, [(14-TMC)Co(III)(NO)](2+) and [(12-TMC)Co(III)(NO)](2+), in NO-transfer and dioxygenation reactions. The Co(III)-nitrosyl complex bearing 14-TMC ligand, [(14-TMC)Co(III)(NO)](2+), transfers the bound nitrosyl ligand to [(12-TMC)Co(II)](2+) via a dissociative pathway, {[(14-TMC)Co(III)(NO)](2+) → {(14-TMC)Co···NO}(2+)}, thus affording [(12-TMC)Co(III)(NO)](2+) and [(14-TMC)Co(II)](2+) as products. The dissociation of NO from the [(14-TMC)Co(III)(NO)](2+) complex prior to NO-transfer is supported experimentally and theoretically. In contrast, the reverse reaction, which is the NO-transfer from [(12-TMC)Co(III)(NO)](2+) to [(14-TMC)Co(II)](2+), does not occur. In addition to the NO-transfer reaction, dioxygenation of [(14-TMC)Co(III)(NO)](2+) by O2 produces [(14-TMC)Co(II)(NO3)](+), which possesses an O,O-chelated nitrato ligand and where, based on an experiment using (18)O-labeled O2, two of the three O-atoms in the [(14-TMC)Co(II)(NO3)](+) product derive from O2. The dioxygenation reaction is proposed to occur via a dissociative pathway, as proposed in the NO-transfer reaction, and via the formation of a Co(II)-peroxynitrite intermediate, based on the observation of phenol ring nitration. In contrast, [(12-TMC)Co(III)(NO)](2+) does not react with O2. Thus, the present results demonstrate unambiguously that the NO-transfer/dioxygenation reactivity of the cobalt(III)-nitrosyl complexes bearing TMC ligands is significantly influenced by the ring size of the TMC ligands and/or the spin state of the cobalt ion.
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Pankaj
authors.initials: P
authors.lastname: Kumar
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Yong-Min
authors.initials: YM
authors.lastname: Lee
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Lianrui
authors.initials: L
authors.lastname: Hu
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Park
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Jiannian
authors.initials: J
authors.lastname: Yao
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.affiliation: Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, United States.
authors.forename: Kenneth D
authors.initials: KD
authors.lastname: Karlin
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
authors.forename: Wonwoo
authors.initials: W
authors.lastname: Nam