Cobalt complexes porphyrins

Very recently, a series of trihalomethyl cobalt porphyrin complexes Co(OEP)CX was prepared either by the reaction of Co(OEP) with CBrCl, CBr4 or CI4, or by the reaction of fCo(OEP)] with CCI4 or CB14. The dihalomethyl complexes, formed in small amounts in these reactions, were prepared in larger amounts from lCo(OEP)P with In a similar fashion, R SnH reacted with Co(OEP)CH ,... 

Only a small number of structurally characterized organometallic cobalt porphyrin complexes have been reported, and selected data for these are collected... 

Cobalt porphyrin complexes are involved in the chain transfer catalysis of the free-radical polymerization of acrylates. Chain transfer catalysis occurs by abstraction of a hydrogen atom from a grow ing polymer radical, in this case by Co(Por) to form Co(Por)H. The hydrogen atom is then transferred to a new monomer, which then initiates a new propagating polymer chain. The reaction steps are shown in Eqs. 12 (where R is the polymer chain. X is CN), (13), and (14)." ... 

Experiments have been carried out to compare nanoscale catalysts composed of Fe-, Ni-, and Co-complexes of several porphyrins or cyanocobalamin (Dror et al. 2005). A cobalt-porphyrin complex and cyanocobalamin in the presence of Ti(III)citrate reduced the initial concentrations of tetrachloromethane and tetrachloroethene by —99.5%, and the porphyrin was equally effective with trichloroethene. The advantage of using heterogeneous catalysts was shown by experiments in repetitive cycling of tetrachloromethane. Zero-valent metals degrade vicinal dichlorides such as tetrachloroethene by a-elimination to produce dichloroacetylene and hnally acetylene (Roberts et al. 1996). 

While the control resins were deep red in color due to the presence of soluble porphyrin complexes, the methacrylate resins obtained after removal of the polyethylene-supported catalysts varied from light yellow to nearly water-white (APHA < 25). UV-Vis spectrophotometric analysis of the yellow resins indicated an absorption signal for the cobalt porphyrin complex Soret band (wavelength of cobalt(ll) porphyrin species appears at -415 nm free porphyrin ligand is formd at -423 tun). Resin samples that visttally appear as water-white show little or no porphyrin species present in the spectrum. Measured catalyst activity and PDl of the polyethylene-supported porphyrin complexes are in the expected range for soluble porphyrin CCT catalysts (PDl = M /Mn - 1.2- 2.0)." The screening resrrlts clearly... 

Recent work by Nagata et al. ]75] has demonstrated the photoactivation of a cobalt porphyrin complex. Covalently... 

The separation of dioxygen from air has been carried out using a cobalt porphyrin complex tethered to the surface of a Vycor glass mem-... 

Diffuse reflectance UV-vis spectroscopy was applied in electrocatalysis by El Mouahid et al. (1998), who followed the electropolymerization of a cobalt porphyrin complex on a vitreous carbon electrode. The thin polymer... 

The epoxidation of alkenes by 02 is catalyzed by polydentate iron and by cobalt porphyrin complexes the latter also operate in a perfluoroalkane/MeCN biphasic system.166 Ruthenium complexes, such as (22-XL), catalyze alkene epoxidations with bis(acetoxy)iodobenzene.167... 

Other uses of cobalt(I) catalysts include the reductive intramolecular cyclization of bromocyclohexenones to form bicyclic ketones [391] and the radical cyclization of bro-moacetals [392,393]. Krautler and coworkers [394] found that 1,4-dibromobutane interacts with electrogenerated cob(I)alamin to afford a tetramethylene-l,4-di = Co -cobalamin species. In a recent study of the reactions of cobalt(I) tetraphenyl porphyrin with benzyl chloride or 1-chlorobutane, Zheng and coworkers [395] reported that alkyl radicals are transferred from the cobalt center to a nitrogen of a pyrrole ring, leading to formation of an A-alkyl cobalt porphyrin complex. 

Comparison with analogous investigations on [(TPP)Co] reveals that for the cobalt porphyrin complex [(T BuP)Co] the first electrochemical oxidation occurs metal-centred, leading to a Co(III) species [(T BuP)Co(III)]. The second... 

The kinetics of the OERR on carbon [27] and graphite [27] in alkahne solution has been explained in terms of the dominant contribution of the peroxide reaction pathway. On the other hand, the direct four-electron pathway predominates on graphite electrodes modified by adsorbed tetrasul-fonated phtalocyanine [57] and attached face-to-face di-cobalt-porphyrin complexes [58]. In principle, when both pathways operate simultaneously on a given surface, the kinetics is referred to as involving a parallel mechanism [59]. 

H. Nishide, M. Ohyanagi, O. Okada, E. Tsuchida, Dual mode transport of molecular oxygen in a membrane containing a cobalt porphyrin complex, Polym. J. 19 (7) (1987) 839-844. 

Summing up, we may conclude that insufficient evidence exists in the literature on the real participation of N-bound peroxynitrite intermediates, although with the recognition that a recent proposal provides experimental and theoretical support for the intermediacy of such a species in the oxidation of triphenylphosphine and cyclohexene by 02, catalyzed by Naflon-bound six-coordinate (nitro) cobalt porphyrin complexes.99 In this context, the results and mechanistic interpretations on the autoxidation of Fe(CN)5NO]3 (Equation 7.23)58 may be highlighted (Section 7.4.4). In fact, the above commented ambiguity on the possible rate-limiting NO dissociation is absent for this reaction, because k NO is 10-fold slower, and the measured oxidation rate is comparatively very fast. The stoichiometry and the DFT-calculated results on the structure of the N-bound peroxynitrite intermediate are valuable points in the proposed mechanism. It should be remarked that the NO+ -bound product is equivalent to N02 that is, no isomerization to N03 has been possible because of the higher competitive reactivity of [Feln(CN)5N(0)00]3 with the initial reactant, [Fe(CN)5NO]3 (Equation 7.25). 

Oxygen transport has received considerable attention. "Picket fence" cobalt porphyrin complexes are selectively blocked at the hindered face so that imidazole bases may only coordinate from the open side. As seen in Scheme 11, the imidazole-coordinated picket fence complex has a vacant coordination site at the top. The small linear oxygen molecule can traverse the "fence" to coordinate reversibly with cobalt from the top side. By dispersing such complexes in films one can build membranes which facilitate oxygen transport. This type of chemistry is one approach to making artificial blood. 

Cobalt porphyrin complexes are often employed as synthetic models for vitamin Bj2 because of their ease of synthesis and the ability to obtain unambiguous structural and spectroscopic data. Some of the (por)Co complexes themselves are known to play important roles in the activation and reduction of NO. For example, [(2-TMPPyP)Co] (1 9j and (TPP)Co supported on TiO2(190,191) have been used as catalyst for the reduction of NO. 

Miscellaneous. Trisyl azide itself underwent an intramolecular C-EI amination in the presence of a catalytic amount of cobalt porphyrin complex to give the corresponding benzosultam (eq41). ... 

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