Reaction of a Nitrosyl Complex of Cobalt Porphyrin with Hydrogen Peroxide: Putative Formation of Peroxynitrite Intermediate

Abstract

The cobalt porphyrin complex [(ClTPP)Co], 1, {ClTPP = 5,10,15,20-tetrakis(4'-chlorophenyl)porphyrinate dianion} in dichloromethane solution was subjected to react with nitric oxide (NO) gas and resulted in the formation of the corresponding nitrosyl complex [(ClTPP)Co(NO)], 2, having {CoNO} description. It was characterized by spectroscopic studies and single-crystal X-ray structure determination. It did not react with dioxygen. However, in CHCl/CHCN solution, it reacted with HO to result in the Co-nitrito complex [(ClTPP)Co(NO)], 3, with the simultaneous release of O. It induced ring nitration to the added phenol in an appreciable yield. The reaction presumably proceeds through the formation of corresponding Co-peroxynitrite intermediate.

Bent and Linear {CoNO}8 Entities: Structure and Bonding in a Prototypic Class of Nitrosyls

“…If we thus restrict ourselves to well-solved structures, about 20 {CoNO} 8 cases have been published with a clear focus on bent CoNO bonding with an overall pentacoordination of the cobalt center. For various donor sets of the coligands (N 4 , N 3 P, HNP 2 , N 3 Cl, N 2 S 2 , and O 4 ), the Co–N–O angle was found in the range of 118–129°. − Two hexacoordinate structures with trans -chlorido ligands were reported with the same degree of CoNO bending (122 and 124°). , Outside this region, we find pentacoordinate centers with a carbon atom in the donor set (CClP 2 , 140°; CHP 2 , 164°) and a linear CoNO function (177°) in a tetracoordinate species with a CP 2 donor set. , When the quality criteria mentioned below are applied, a disappointing result is obtained in that no unambiguously solved crystal structure of a pentacoordinate CoNO center of the linear subclass is available to date, including early reports such as the structure analyses on [Co­(das) 2 (NO)]­(ClO 4 ) 2 [das = 1,2-bis­(dimethylarsino)­benzene], which shows an unreliable ellipsoid of the N NO atom stretched along the CoNO axis and [CoI 2 (NO)­(PMe 3 ) 2 ] with a large O NO ellipsoid through a crystallographic mirror plane and an unreliably short N–O distance. − …”

“…Prior to an inclusion of triplets in the discussion, the small size of the [Co(NH 3 ) 4 (NO)] 2+ species was used to check the dependence of charges and OS assignments from the applied method. In particular, because the small active (8, 7) space of the larger systems had kept us from deriving more quantitative results, except the antibond population, the larger (12,14) active space was included. This configuration space contains 14 orbitals: five Co(3d) orbitals, five Co(4d) second-shell orbitals, two N−O π* orbitals, the nitrosyl donor orbital (3σ in NO's MO scheme), and the major cobalt−ammine bonding orbital.…”

“…Complete-active-space self-consistent-field CASSCF(8,7) calculations were used for illustrative purposes because of the more localized nature of molecular orbitals (MOs) by this wavefunction approach and, essentially, to show the nitrosyl−metal typical amount of static correlation in terms of antibonding population. A larger active space was included in a CASSCF (12,14) approach on two isomers of the small species [Co(NH 3 ) 4 (NO)] 2+ , as well as CCSD single-point calculations. There, also various density functionals were employed to evaluate the dependence of the charges and OSs from the level of theory.…”

Nitric Oxide Dioxygenase Activity of a Nitrosyl Complex of Cobalt(II) Porphyrinate in the Presence of Hydrogen Peroxide via Putative Peroxynitrite Intermediate

“…This is attributed to the facile loss of the axial NO group, which has been observed earlier in other nitrosyl complexes of Co(II)-porphyrinates. 23,24 Complex 2 in CH 2 Cl 2 or CH 3 CN solution did not react with dioxygen; however, it reacts with H 2 O 2 . Upon addition of 2.2 equiv of H 2 O 2 , complex 2 in CH 3 CN solution at −40 °C resulted in the formation of corresponding nitrate complex, 3 (Scheme 1).…”

“…Spiro and co-workers reported the ν NO stretching to appear at 1699 cm −1 in CH 2 Cl 2 . 21 23 In the ESI mass spectrum, complex 2 displayed a peak at m/z 815.27 assignable to the [Co(F 8 TPP)] (calcd m/z = 815.08). This is attributed to the facile loss of the axial NO group, which has been observed earlier in other nitrosyl complexes of Co(II)-porphyrinates.…”