摘要
Nitrosylation of [PPN] 2 [(ONO) 2 Fe(Î 2 - ONO) 2 ] [1; PPN = bis(triphenylphosphoranylidene)ammonium] yields the nitrite-containing {Fe(NO)} 7 mononitrosyliron complex (MNIC) [PPN] 2 [(NO)Fe(ONO) 3 (Î 2 -ONO)] (2). At 4 K, complex 2 exhibits an S = 3 / 2 axial EPR spectrum with principal g values of g ⊥ = 3.971 and g ∥ = 2.000, suggestive of the {Fe III (NO - )} 7 electronic structure. Addition of 1 equiv of PPh 3 to complex 2 triggers O-atom transfer of the chelating nitrito ligand under mild conditions to yield the {Fe(NO) 2 } 9 dinitrosyliron complex (DNIC) [PPN][(ONO) 2 Fe(NO) 2 ] (3). These results demonstrate that both electronic structure [{Fe III (NO - )} 7 , S = 3 / 2 ] and redox-active ligands ([RS] - for [(RS) 3 Fe(NO)] - and [NO - ] for complex 2) are required for the transformation of {Fe(NO)} 7 MNICs into {Fe(NO) 2 } 9 DNICs. In comparison with the PPh 3 - triggered O-atom abstraction of the chelating nitrito ligand of the {Fe(NO) 2 } 9 DNIC [(1-MeIm) 2 (Î 2 -ONO) Fe(NO) 2 ] (5; 1-MeIm = 1-methylimidazole) to generate the {Fe(NO) 2 } 10 DNIC [(1-MeIm)(PPh 3 )Fe(NO) 2 ] (6), glacial acetic acid protonation of the N-bound nitro ligand in the {Fe(NO) 2 } 10 DNIC [PPN][(Î 1 -NO 2 )(PPh 3 )Fe(NO) 2 ] (7) produced the {Fe(NO) 2 } 9 DNIC [PPN][(OAc) 2 Fe(NO) 2 ] (8), nitric oxide, and H 2 O. These results demonstrate that the distinct electronic structures of {Fe(NO) 2 } 9/10 motifs [{Fe(NO) 2 } 9 vs {Fe(NO) 2 } 10 ] play crucial roles in modulating nitrite binding modes (O-bound chelating/monodentate nitrito for {Fe(NO) 2 } 9 DNICs vs N-bound nitro as a Ïε acceptor for {Fe(NO) 2 } 10 DNICs) and regulating nitrite activation pathways (O-atom abstraction by PPh 3 leading to the intermediate with a nitroxyl-coordinated ligand vs protonation accompanied by dehydration leading to the intermediate with a nitrosonium-coordinated ligand). That is, the redox shuttling between the {Fe(NO) 2 } 9 and {Fe(NO) 2 } 10 DNICs modulates the nitrite binding modes and then triggers nitrite activation to generate nitric oxide. © 2010 American Chemical Society.