Stoichiometric and catalytic secondary O-atom transfer by Fe(III)-NO2 complexes derived from a planar tetradentate non-heme ligand: reminiscence of heme chemistry.
An Fe(III) nitro complex [(bpb)Fe(NO2)(py)] (2) of the tetradentate ligand 1,2-bis(pyridine-2-carboxamido)benzene (H2bpb, H is the dissociable amide proton) has been synthesized via addition of NaNO2 to [(bpb)Fe(py)2](ClO4) (1) in MeCN or DMF. This structurally characterized Fe(III) nitro complex exhibits its nuNO2 at 1384 cm(-1). The reaction of 1 with 2 equiv of Et4NX (X = Cl-, Br-) affords the high-spin complexes (Et4N)[(bpb)Fe(Cl2)] (3) and (Et4N)[(bpb)Fe(Br)2] (4), respectively. The structure of 4 has been determined. The addition of an equimolar amount of Et4NCl, Et4NBr, or Et4NCN to a solution of 2 affords the mixed-ligand complexes (Et4N)[(bpb)Fe(NO2)(Cl)] (5), (Et4N)[(bpb)Fe(NO2)(Br)] (6), and (Et4N)[(bpb)Fe(NO2)(CN)] (7), respectively. These complexes are all low spin with isotropic g values of 2.15. Under anaerobic conditions, the reactions of 5-7 with Ph3P in MeCN afford the five-coordinate {Fe-NO}7 nitrosyl [(bpb)Fe(NO)] (and Ph3PO) via secondary oxygen-atom (O-atom) transfer. The O-atom transfer to Ph3P by 5-7 becomes catalytic in the presence of dioxygen with transfer rates in the range of 1.70-13.59 x 10-3 min(-1). The O-atom transfer rates and turnover numbers (5 > 6 > 7) are reflective of the strength of the axial donors (Cl- > Br- > CN-). The catalytic efficiencies of complexes 5-7 are limited due to formation of the thermodynamic end products [(bpb)Fe(X)2]- (where X = Cl- for 5, Br- for 6, and CN- for 7).
Afshar
Raman K
RK
Department of Chemistry and Biochemistry, University of California, Santa Cruz, California 95064, USA.
Eroy-Reveles
Aura A
AA
Olmstead
Marilyn M
MM
Mascharak
Pradip K
PK
D001554:Benzene / Q000737:chemistry; D001665:Binding Sites; D002384:Catalysis; D004579:Electron Transport; D005290:Ferric Compounds / Q000737:chemistry*; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D008024:Ligands; D009569:Nitric Oxide / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D011725:Pyridines / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013057:Spectrum Analysis; D013816:Thermodynamics; D013854:Thioamides / Q000737:chemistry
D005290:Ferric Compounds; D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D012997:Solvents; D013854:Thioamides; C494246:pyridine-2-carbothioamide; D009569:Nitric Oxide; D006418:Heme; D001554:Benzene; D010100:Oxygen