Reactivity studies on Fe(III)-(O2(2-))-Cu(II) compounds: influence of the ligand architecture and copper ligand denticity.
Heme-Cu/O2 adducts are of interest in the elucidation of the fundamental metal-O2 chemistry occurring in heme-Cu enzymes which effect reductive O-O cleavage of dioxygen to water. In this report, the chemistry of four heme-peroxo-copper [FeIII-(O22-)-CuII]+ complexes (1-4), varying in their ligand architecture, copper-ligand denticity, or both and thus their structures and physical properties are compared in their reactivity toward CO, PPh3, acids, cobaltocene, and phenols. In 1 and 2, the copper(II) ligand is N4-tetradentate, and the peroxo unit is bound side-on to iron(III) and end-on to the copper(II). In contrast, 3 and 4 contain a N3-tridentate copper(II) ligand, and the peroxo unit is bound side-on to both metal ions. CO "displaces" the peroxo ligand from 2-4 to form reduced CO-FeII and CO-CuI species. PPh3 reacts with 3 and 4 displacing the peroxide ligand from copper, forming (porphyrinate)FeIII-superoxide plus CuI-PPh3 species. Complex 2 does not react with PPh3, and surprisingly, 1 reacts neither with PPh3 nor CO, exhibiting remarkable stability toward these reagents. The behavior of 1 and 2 compared to that of 3 and 4 correlates with the different denticity of the copper ligand (tetra vs tridentate). Complexes 1-4 react with HCl releasing H2O2, demonstrating the basic character of the peroxide ligand. Cobaltocene causes the two-electron reduction of 1-4 giving the corresponding micro-oxo [FeIII-(O2-)-CuII]+ complexes, in contrast to the findings for other heme-peroxo-copper species of different design. With t-butyl-substituted phenols, no reaction occurs with 1-4. The results described here emphasize how ligand design and variations influence and control not only the structure and physical properties but also the reactivity patterns for heme-Cu/O2 adducts. Implications for future investigations of protonated heme/Cu-peroxo complexes, low-spin analogues, and ultimately O-O cleavage chemistry are discussed.
Chufán
Eduardo E
EE
Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218, USA.
Mondal
Biplab
B
Gandhi
Thirumanavelan
T
Kim
Eunsuk
E
Rubie
Nick D
ND
Moënne-Loccoz
Pierre
P
Karlin
Kenneth D
KD
D000143:Acids / Q000737:chemistry; D002248:Carbon Monoxide / Q000737:chemistry; D015392:Chemistry, Inorganic / Q000379:methods*; D003300:Copper / Q000737:chemistry*; D006418:Heme / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D008024:Ligands; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013059:Spectrum Analysis, Raman / Q000379:methods
D000143:Acids; D008024:Ligands; D006418:Heme; D003300:Copper; D002248:Carbon Monoxide; D007501:Iron; D010100:Oxygen