Mechanistic Insight into the Nitric Oxide Dioxygenation Reaction of Nonheme Iron(III)–Superoxo and Manganese(IV)–Peroxo Complexes

Reactions of nonheme Fe^III–superoxo and Mn^IV–peroxo complexes bearing a common tetraamido macrocyclic ligand (TAML), namely [(TAML)Fe^III(O₂)]^2? and [(TAML)Mn^IV(O₂)]^2?, with nitric oxide (NO) afford the Fe^III–NO₃ complex [(TAML)Fe^III(NO₃)]^2? and the Mn^V–oxo complex [(TAML)Mn^V(O)]^? plus NO₂^?, respectively. Mechanistic studies, including density functional theory (DFT) calculations, reveal that M^III–peroxynitrite (M=Fe and Mn) species, generated in the reactions of [(TAML)Fe^III(O₂)]^2? and [(TAML)Mn^IV(O₂)]^2? with NO, are converted into M^IV(O) and ^.NO₂ species through O?O bond homolysis of the peroxynitrite ligand. Then, a rebound of Fe^IV(O) with ^.NO₂ affords [(TAML)Fe^III(NO₃)]^2?, whereas electron transfer from Mn^IV(O) to ^.NO₂ yields [(TAML)Mn^V(O)]^? plus NO₂^?.     

Synthesis and characterization of reduced heme and heme/copper carbonmonoxy species

Carbon monoxide readily binds to heme and copper proteins, acting as a competitive inhibitor of dioxygen. As such, CO serves as a probe of protein metal active sites. In our ongoing efforts to mimic the active site of cytochrome c oxidase, reactivity toward carbon monoxide offers a unique opportunity to gain insight into the binding and spectroscopic characteristics of synthetic model compounds. In this paper, we report the synthesis and characterization of CO-adducts of ((5/6)L)Fe(II), [((5/6)L)Fe(II)...Cu(I)](B(C(6)F(5))(4)), and [(TMPA)Cu(I)(CH(3)CN)](B(C(6)F(5))(4)), where TMPA = tris(2-pyridylmethyl)amine and (5/6)L = a tetraarylporphyrinate tethered in either the 5-position ((5)L) or 6-position ((6)L) to a TMPA copper binding moiety. Reaction of ((5/6)L)Fe(II) [in THF (293 K): UV-vis 424 (Soret), 543-544 nm; (1)H NMR delta(pyrrole) 52-59 ppm (4 peaks); (2)H NMR (from ((5)L-d(8))Fe(II)) delta(pyrrole) 53.3, 54.5, 55.8, 56.4 ppm] with CO in solution at RT yielded ((5/6)L)Fe(II)-CO [in THF (293 K): UV-vis 413-414 (Soret), 532-533 nm; IR nu(CO)(Fe) 1976-1978 cm(-1); (1)H NMR delta(pyrrole) 8.8 ppm; (2)H NMR (from ((5)L-d(8))Fe(II)-CO) delta(pyrrole) 8.9 ppm; (13)C NMR delta((CO)Fe) 206.8-207.1 ppm (2 peaks)]. Experiments repeated in acetonitrile, acetone, toluene, and dichloromethane showed similar spectroscopic data. Binding of CO resulted in a change from five-coordinate, high-spin Fe(II) to six-coordinate, low-spin Fe(II), as evidenced by the upfield shift of the pyrrole resonances to the diamagnetic region ((1)H and (2)H NMR spectra). Addition of CO to [((5/6)L)Fe(II)...Cu(I)](B(C(6)F(5))(4)) [in THF (293 K): UV-vis ((6)L only) 424 (Soret), 546 nm; (1)H NMR delta(pyrrole) 54-59 ppm (multiple peaks); (2)H NMR (from [((5)L-d(8))Fe(II).Cu(I)](B(C(6)F(5))(4))) delta(pyrrole) 53.4 ppm (br)] gave the bis-carbonyl adduct [((5/6)L)Fe(II)-CO...Cu(I)-CO](B(C(6)F(5))(4)) [in THF (293 K): UV-vis ((6)L only) 413 (Soret), 532 nm; IR nu(CO)(Fe) 1971-1973 cm(-1), nu(CO)(Cu) 2091-2093 cm(-1), approximately 2070(sh) cm(-1); (1)H NMR delta(pyrrole) 8.7-8.9 ppm; (2)H NMR (from [((5)L-d(8))Fe(II)-CO...Cu(I)-CO](B(C(6)F(5))(4))) delta(pyrrole) 8.9 ppm; (13)C NMR delta((CO)Fe) 206.8-208.1 ppm (2 peaks), delta((CO)Cu) 172.4 ((5)L), 178.2 ((6)L) ppm]. Experiments in acetonitrile, acetone, and toluene exhibited spectral features similar to those reported. The [((5/6)L)Fe(II)-CO.Cu(I)-CO](B(C(6)F(5))(4)) compounds yielded (CO)(Fe) spectra analogous to those seen for ((5/6)L)Fe(II)-CO and (CO)(Cu) spectra similar to those seen for [(TMPA)Cu(I)-CO](B(C(6)F(5))(4)) [in THF (293 K): IR nu(CO)(Cu) 2091 cm(-1), approximately 2070(sh) cm(-1); (13)C NMR delta((CO)Cu) 180.3 ppm]. Additional IR studies were performed in which the [((5)L)Fe(II)-CO...Cu(I)-CO](B(C(6)F(5))(4)) in solution was bubbled with argon in an attempt to generate the iron-only mono-carbonyl [((5)L)Fe(II)-CO.Cu(I)](B(C(6)F(5))(4)) species; in coordinating solvent or with axial base present, decreases in characteristic IR-band intensities revealed complete loss of CO from copper and variable loss of CO from the heme.     

The behaviour of some ferrocene derivatives under electron impact

The behaviour of some mono- and di-substituted ferrocene compounds under electron impact has been investigated by means of low-resolution mass spectrometry. Some characteristic rearrangement processes have been observed and discussed.