Metalloporphyrin alkylated

The synthesis of metalloporphyrins which contain a metal-carbon a-bond can be accomplished by a number of different methods(l,2). One common synthetic method involves reaction of a Grignardreagent or alkyl(aryl) lithium with (P)MX or (PMX)2 where P is the dianion of a porphyrin macrocycle and X is a halide or pseudohalide. Another common synthetic technique involves reaction of a chemically or electrochemically generated low valent metalloporphyrin with an alkyl or aryl halide. This latter technique is similar to methods described in this paper for electrosynthesis of cobalt and rhodium a-bonded complexes. However, the prevailing mechanisms and the chemical reactions... 

In summary, the four chemical systems described in this paper demonstrate the versatility and selectivity of electrochemical methods for synthesis and characterization of metal-carbon a-bonded metalloporphyrins. The described rhodium and cobalt systems demonstrate significant differences with respect to their formation, stability and to some extend, reactivity of the low valent species. On the other hand, properties of the electroche-mically generated mono-alkyl or mono-aryl germanium and silicon systems are similar to each other. 

The most widely studied class of metalloporphyrins contains six to eight alkyl side chains in the positions 1-8 (see [4]). 

The trans influence of a ligand arises principally from its inductive a-donor ability, transmitted to the trans-ligand by the appropriate metal pa-orbital. How far can this statement, made by Mason (18) and cited by Shustorovich (9), be applied to metalloporphyrins There are only a few examples of alkylmetalloporphyrins M(P)R with M = Fe, Co (69), or Rh (70) in the d6 configuration. In metal alkyl systems the strongest tram effects are to be expected hydridorhodium porphyrins are also known (71). Ogoshi (70) has prepared a variety of complexes Rh(OEP)LX ([22] ... 

Epoxidation Catalyzed by Metalloporphyrins. Metalloporphyrins, which have thoroughly studied as catalysts in alkane oxygenations, have also been tested as epoxidation catalysts.119,122,244,245,307 Iodosylbenzene (PhIO), sodium hypochlorite, alkyl hydroperoxides, potassium hydrogen persulfate, and molecular oxygen are the oxygen sources used most frequently in these oxidations.119... 

Porphyrins have four inner nitrogens and show four stepwise add-base reactions (equation l).14 The pX, and pK2 values are estimated to be 16, pX3 is 5, and pX4 is 2 for /J-alkylated porphyrins. Because of N protonation, electrophilic meso deuteration of metal-free porphyrins is slower in strong acids (H2OEP in TFA-d, T,/2 = 275h at 90 °C) than in weak acids (t1/2 = 140 + 14 min in refluxing AcOD).2 Metalloporphyrins are more easily deuterated in strongly acidic media, e.g. M(OEP) (M = Fe, Cu, Pt) are completely meso-deuterated in TFA- CDC (1 1) at room temperature within 20 min. Meso deuteration of M(OEP) is possible under basic conditions (Mgl2-D20 or MeOD-hot pyridine).2... 

The ligand field of the macrocycle is also modified by ring distortion.154 The metal to alkylated nitrogen distance is 2.33 A (Fe) to 2.53 A (Zn) which is considerably longer than the normal value of 2.0-2.1 A for the first row transition metalloporphyrins in a high spin state, while the extension is small for the other three M—Npor bonds. The reduced and distorted ligand field of the macrocycle makes it possible for even the Co complexes as well as other metals to take a high spin state. 

Only a few compounds containing Ru, Os, Rh or Ir do not possess type C. Notable are the metalloporphyrin dimers with Ru = Ru (entry 3) or Rh-In bonds (entry 34), the alkyl or acyl rhodium(III) (entries 31, 36, 38), alkyl-iridium(III) (entry 39) or arylruthenium(III) compounds (entry 12). All these species contain pentacoordinate noble metal ions, Type B. A reason for this unusual behavior of the metal ions is seen in the strong trans effect of the axial ligand L in these systems which is a strong o-donor (metalloporphyrinyl, alkyl, aryl, acyl) which precludes further coordination in the trans position of L. The reluctance of RhMe(OEP) to accept an axial ligand is shown by its crystallization as a re-dimer from n-hexane in presence of the base 1-Meim. 

Alkyl and aryl systems - As already mentioned in Sect. 3.2, dialkyl ruthenium and osmium porphyrins have been synthesized according to Eq. (22) by the reaction of metalloporphyrin dianions [M(P)]2 with alkyl iodides [223, 260, 261,307]. These dianions have been obtained by reduction of porphyrin dimers [M(P)]2. 

The metal-centered reduction of iron and cobalt porphyrins [(por)Afn] yields metalloporphyrin anions [Eq. (13.13)]. The reduction potential for this reaction is 13, and is equivalent to the N- value for the oxidation of the metal-centered nucleophile [(por)uM-]. The one-electron reduction of alkyl halides yields the... 

The data seem to support an alternative mechanism compared with the so-called Lyons mechanism in which O2 is activated forming a metal-oxo (M=0) species.1831 Via reaction of a second metalloporphyrin with a primarily formed superoxo (Me-OO0) or peroxo species, a metal-oxo is formed, reacting eventually with an alkane according to the oxygen rebound mechanism. Alternatively, radicals present in solution, upon reaction with dioxygen, may form alkyl hydroperoxides that are decomposed by metalloporphyrins.[83]... 

Speciation studies have been focused on relatively few elements, mainly aluminum, antimony, arsenic, chromium, lead, mercury, selenium, and tin. The primary species of these elements studied with ICP-MS detection are presented in Table 3 and they include different oxidation states, alkylated metal and/or metalloid compounds, selenoaminoacids, and selenopeptides. In addition, applications in studies of the pharmacokinetics of metal-based drugs (Pt, V, Au), metalloporphyrins (Ni, V, Fe, etc.), heavy metals in phytochelatins (Cd, Cu, Zn, Hg, etc.) and in humic substances should be mentioned. 

Octaalkylporphyrins Metalloporphyrins H2TPP X in alkyl X in beta X in meso Xin phenyl ortho 5x 10 2x10 10 2x 10 2x10 10 5x10 10 2x10 ... 

Relative stabilities and reactivities of the two metalloporphyrins can be observed by comparison of the parameters. The alkylation index shows that vanadyl chelation promotes transalkylation relative to nickel. On the other hand, nickel porphyrins are degraded more rapidly through the loss of metiiylene groups and/or etio series generation than vanadyl porphyrins. These differences between the two chelates are best observed by comparison of the series mode and weighted average mass shown in Table IV. 

D. Mansuy, J. F. Bartoli, J. C. Chottard, M. Lange, Metalloporphyrin-catalyzed hydroxylation of cyclohexane by alkyl hydroperoxides pronounced efficiency of iron-porphyrins, Angew. Chem. Int. Ed. Engl. 19 (1980) 909. 

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