Porphyrins 5, 15-dioxo

Dioxo-ruthenium porphyrin (19) undergoes epoxidation.69 Alternatively, the complex (19) serves as the catalyst for epoxidation in the presence of pyridine A-oxide derivatives.61 It has been proposed that, under these conditions, a nms-A-oxide-coordinated (TMP)Ru(O) intermediate (20) is generated, and it rapidly epoxidizes olefins prior to its conversion to (19) (Scheme 8).61 In accordance with this proposal, the enantioselectivity of chiral dioxo ruthenium-catalyzed epoxidation is dependent on the oxidant used.55,61 In the iron porphyrin-catalyzed oxidation, an iron porphyrin-iodosylbenzene adduct has also been suggested as the active species.70... 

Oxidizing enzymes use molecular oxygen as the oxidant, but epoxidation with synthetic metalloporphyrins needs a chemical oxidant, except for one example Groves and Quinn have reported that dioxo-ruthenium porphyrin (19) catalyzes epoxidation using molecular oxygen.69 An asymmetric version of this aerobic epoxidation has been achieved by using complex (7) as the catalyst, albeit with moderate enantioselectivity (Scheme 9).53... 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

Although the chiral ketoiminatomanganese(lll) complexes were reported to catalyze the asymmetric aerobic alkene epoxidations, an aldehyde such as pivalaldehyde is required as a sacrihcial reducing agent. Groves reported that the dioxo(porphyrinato)ruthenium complexes 31, prepared with m-chloroperoxyben-zoic acid, catalyzed the aerobic epoxidation without any reductant. " On the basis of these reports, Che synthesized the optically active D4-porphyrin 35 and applied it to the truly aerobic enantioselective epoxidation of alkenes catalyzed by the chiral frani-dioxo (D4-porphyrinato)ruthenium(Vl) complex. The dioxoruthenium complex catalyzed the enantioselective aerobic epoxidation of alkenes with moderate to good enantiomeric excess without any reductant. In the toluene solvent, the turnovers for the epoxidation of T-(3-methylstyrene reached 20 and the ee of the epoxide was increased to 73% ee. 

Metal(V) species derived from the complexes in Table I are rare. In fact, only one such species, L1Cr(V) (presumably a dioxo or hydro-oxo species), has been observed and characterized by ESR and UV-visible spectroscopies (45,69), Figs. 5 and 6. This Cr(V) species, which has a lifetime of several seconds at room temperature, was generated from a hydroperoxo precursor by an intramolecular transformation that closely resembles the proposed, but so far unobserved step in the chemistry of cytochrome P450, whereby the hydroperoxoiron(III) is transformed to the FeIV(P + ) form also known as oxene (P += porphyrin radical cation). All the steps in Scheme 1 for the L1Cr(H20)2+/02 reaction have been observed directly (45,69). 

In the presence of neutral donor ligands L (e.g. L = Py, 1-Meim, THT), and an excess of a reductant, e.g. dithionite or hydrazine, dioxo complexes are transformed into bisligandmetal(II) species (ruthenochromes or osmochromes paths j,k). The logic intermediate in such a four-electron reduction, an oxometal(IV) porphyrin, was only observed for M = Ru (path j, P = OEP, TMP R = EtOH) when norbornene served as a mild oxygen acceptor. 

Results to 3 One method giving polyphenylalanines (19) starts from the diazide (15 o) and others reacting with 4-benzyl-24 dioxo-oxozolidinc in pyridine (Eq. 9). Polypeptides containing the porphyrins in various ratxK are obtained. Now from stereoisomeric N-carbonic acid anhydrides of phenylalanines the D-, L- and DJL-fonns of fte polyphenylalanines were prepared. 

The constitution of f/v-NCC-1 (2, 31,32,82-trihydroxy-l,4,5,10,15,20-(22//,24//)-octahydro-132-(methoxycarbonyl)-4,5-dioxo-4,5-seco-phyto-porphyrinate (see Scheme 2) gave first clues on the basic transformations involving the Chl-chromophore (1, 2, 4, 10). When, in addition, the structure of the fluorescent chlorophyll catabolite pFCC (10) was revealed, an isomerization of the chromophore of the FCCs into that of... 

Cyclopenten-l-ol, l,3-dimethyl-2-(7-methyl-3,7-tridecadien-ll-ynyl), , )-, 91-92, 279-280 2-Cyclopenten-1 -one, 3-methyl-2-(2-pentenyl)-, (Z)- (fasmone) synthesis, 29 2-Cyclopenten-l-ones syntheses by cyclizations from 1,4-dioxo compounds, 69, 79 from 5-nitro-l,3-diones, 81 Cyclophanes of porphyrins, 253 meta-Cyclophanes, 38, 338 pora-Cyciophanes = tricyclo[8.2.2.24,7]hexadeca-4,6,10,12,13,15-hexaenes synth., 38-39 Cyclopropane derivs. See Carbocycles, 3-membered... 

Ru(0EP)X]20 (X = Cl , Br , OH) shows three, two electron redox couples in CHjClj assigned to Ru" Ru /Ru Ru and Ru" Ru /Rti Ru processes and oxidation of the porphyrin rings More recently, oxidation of [Ru(porph)CO] (porph = 429) with MCPBA or iodosyl benzene has yielded the trans-dioxo ruthenium(VI) species [Ru(porph)02] which reacts with P(OMe)j to give two equivalents of MejPO and [Ru(porph)(P(OMe)3)2]. Interestingly, oxidation of the tolyl complex (419) yielded the Ru fx-oxo dimer, suggesting that steric hindrance of (429) is important for the generation of the mononuclear Ru oxo derivative. " ... 

Our idea is once more described as follows. First, a hydrophobic environment to retard the proton-driven oxidation [Eq. (4)] is constructed around porphinatoiron in aqueous media by embedding porphinatoiron in a phospholipid bilayer. Secondly, the porphinatoiron is molecularly dispersed in the phospholipid bilayer and the porphyrin plane of the porphinatoiron is oriented parallel to the bilayer, which prevents the oxidation via a p-dioxo dimer [Eq. (3)] (see Fig. 4). We further synthesized novel, sterically modified and amphiphilic porphinatoiron derivatives, in order to improve the compatibility of the porphinatoiron with the phospholipid bilayer of the liposome. 

Oxygen ligands form very stable complexes with hard Lewis-acid met-alloporphyrins such as Sn(IV), Zr(IV), Mn(III), Mo(V), but also with P(V)-porphyrins. Mixed-metal dimers were synthesized from Al(Me)OEP and phosphorus, arsenic or antimony porphyrins in the form of fi-oxo dimers [73]. hi most cases, polymeric structures are obtained because Sn(IV)-, Mn(III)- and Fe(III)-porphyrins can bind two axial ligands on either side of the porphyrin referred to as trans-binding. This is schematically represented in Fig. 25a. An example includes the linear trinuclear or polymers /r-frans-dioxo-MoTPP [74,75]. 

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