Macrocyclic complexes neutral adducts

These systems exhibit considerable affinity for halide anions. X-ray analysis ascertained the formation of an anionic 2 1 chloride adduct of (1) where the chloride is simultaneously bound by four mercury atoms. In the crystal structures of (2) Cl and (2) l2, the anions are located within the macrocycle and complexed cooperatively by the four mercury(II) centers. Several anionic complexes of (3), including bromide, iodide, and thiocyanide salts, have been isolated. The compounds adopt multidecker stmctures with the hexacoordinated anions effectively sandwiched between two successive molecules of (3). The Lewis acidity of perfluoro-ortAo-phenylenemercury (3) has also been substantiated by its ability to form stable adducts with neutral substrates (HMPA, DMSO, ethyl acetate, and acetonitrile) and arenes. The (3) -CeHe adduct exists as extended stacks of nearly parallel, staggered molecules of (3), which sandwich benzene molecules. Similar structures have been reported for the corresponding adducts with biphenyl, naphthalene, pyrene, and triphenylene. 

Fig. 3. Catalytic cycle of cytochrome P-450 and the postulated partial structures of the intermediates. The dianionic porphyrin macrocycle is abbreviated as a parallelogram with nitrogens at the comers, in this and subsequent figures. Oxy-P-450 (4) is shown as a complex of ferric porphyrin and superoxide anion, but could also be describe as an adduct of neutral dioxygen and ferrous porphyrin. States 6 and 7 are hypothetical intermediates whose structures have not been established. Structures /, 2, and 7 are neutral (the dot and the positive charge on 7 indicate the radical state and electron deficiency of the n electron system of the porphyrin ring), while the overall charge on structures 3, 4, and 5 is minus one and on structure 6 is minus two. Adapted from Ref. [22]...

---