Molybdenum complexes porphyrins

Of other related systems, molybdenum(V) porphyrin exhibits very high stereoselectivity with tert-BuOOH as the oxygen source (97% m-2-hexene oxide and 99% trans-2-hexene oxide from cis- and trans-2-hexene, respectively).329 Nonporphyrin complexes of iron were found to be stereoselective in the epoxidation of stil-bene isomers. Iron cyclam, a nonporphyrin iron complex, gives the corresponding cis and trans epoxides in epoxidation with H202.330 Fe(acac)3, in contrast, yields the trans epoxide from both stilbene isomers.331... 

Titanium(IV)-porphyrin [TiO(TPP)] as well as molybdenum(V)-porphyrin [MoO(OMe)(TPP)] complexes were found to be active for the catalytic epoxidation of alkenes by alkyl hydroperoxides, whereas their peroxo derivatives are inactive.632 Iron(III)-porphyrin-peroxo complexes such as Fe(TPP)02NMe4 did not react with hydrocarbons, but form sulfato complexes upon reaction with S02.632 Manganese(III)-porphyrin-peroxo complexes Mn(02)(TPP) K+ were recently characterized by X-ray crystallography.634... 

Various metal-metal single o-bonded complexes have been obtained by the reaction of metal carbonyls with metal-carbon o-bonded porphyrins or by the reaction of metal carbonyl anions and chlorometalloporphyrins (Scheme 14). For example, the reaction of dimanganese carbonyl and methyl indium(III) porphyrin gives manganese pen-tacarbonyl indium porphyrin In(Por)Mn(CO)5. The same compound is isolated when chloroindium porphyrin is allowed to react with the manganese pentacarbonyl monoanion. Various iron, cobalt, tungsten, and molybdenum complexes have been prepared by these two methods. 

Spectroscopic and chemical studies of vanadyl OEP have been reported, including m 50-substitution to form nitro-, chloro-, and benzoyloxy-derivatives trans-alkylation occurs when the vanadyl porphyrin is heated on clay and other supports, thus providing a model for the generation of homologous polyalkyl-porphyrins in crude oil and bitumen. m sa-Tetraferrocenyl-porphyrin and its copper complex have been prepared, and spectroscopic and other studies carried out on mixed-valence oxidation products, as models for the study of thermal electron-transfer processes in cytochrome-c. X-Ray crystal structures have been reported for diaquo and perchlorate complexes of Fe" TPP, " dichloro-molybdenum complexes of OEP and TPP, and for the bis-[(R5)-l-phenyl-ethylamine] complex " of Co TPP. Oxomolybdenum complexes TPP-... 

Pulse radiolysis has been used to investigate the reactions of radicals with molybdenum(V) porphyrins such as [MoO(TPP)Cl] and with oxy hemoproteins. The CHj radical reacts with [Cu(gly)2] to give an adduct with decomposes to the copper(III) species, [Cu(gly)2], and CH4. The former species decomposes rapidly by ligand oxidation. Pulse radiolysis studies of the oxidation of the 2-hydroxycyclohexyl radical indicate that the key intermediate is a transient complex formed with [Cu q]. The bound... 

Porphyrin, octaethyl-, molybdenum hydroxide oxide complex... 

The last decade has seen the development of a rich and varied chemistry for or-ganometallic porphyrin complexes of the early transition metals (groups 3 and 4). However, there have been many fewer developments in the organometallic chemistry of the middle transition elements. Despite the paucity of its organometallic porphyrin compounds, molybdenum has played a very important role in... 

Some of the metallic constituents were somewhat soluble in the propane-oil portion, but all tended to be concentrated in the asphaltic portion. Although vanadium (0.02% by weight in the original crude petroleum) was present in all fractions, the greater part was found in the cyclohexane and benzene fractions. From the similarity of the absorption spectra of the vanadium concentrates from petroleum and those of synthetic vanadium porphyrin complexes, Skinner arrived at the conclusion that vanadium compounds from the petroleum of the Santa Maria Valley Field in California exist as porphyrin complexes. Additional metallic constituents were detected by Skinner as these became concentrated in the various solvent fractions, including aluminum, titanium, calcium, and molybdenum. 

Complexes with tetradentate ligands L (L = (salen)2-, (acacen)2-), of the form [MoCl2L], have been prepared by reaction of [MoCl4(NCMe)2] or [MoCl3(py)3] with H2L.159 The reaction of HC1 with [MoO(TPP)] (TPP = dianion of 5,10,15,20-tetra-4-tolylporphyrin) forms [MoCl2(TPP)] the structure of the latter involves a planar porphyrin ring with the tram chlorides at distances from the molybdenum of 2.347(4) and 2.276(4) A, although they appear to be chemically equivalent.113... 

The lack of adequate experimental data on chelates of germanium, boron, titanium, and vanadium prevents a similar comparison for these elements however, their high ionic potentials do indicate that they should form stable chelates. Vanadium does occur naturally in the very stable vanadium porphyrin complex. For similar reasons, molybdenum and tin are not discussed further. 

This type of complex is derived from the mononuclear superoxo species via a further one-electron reduction of the dioxygen moiety. Cobalt is the only metal to form these complexes by reaction with dioxygen in the absence of a ligating porphyrin ring. Molybdenum and zirconium form peroxo-bridged complexes on reaction with hydrogen peroxide. In most cases the mononuclear dioxygen adducts of cobalt will react further to form the binuclear species unless specific steps are taken to prevent this. 

A number of unusual structural features have been noted. The ruthenium porphyrin formed by reaction of triruthenium dodecacarbonyl with an N, AT-vinyl-bridged tetraphenylporphyrin involves disruption of a pyrrole C-N bond to give a product in which the ruthenium is bound to two pyrrole N atoms, the C and N atoms of the ruptured pyrrole ring, and two mutually cis carbonyl ligands. The remaining pyrrole N is uncoordinated.613 Mutually cis configurations have also been found for the dicarbonyl complex of molybdenum tetraphenylporphyrin and for some dinitrosyl porphyrins. 

Cyclic voltammetry and controlled-potential electrolysis are the techniques that have been used to investigate the electrochemistry of oxo-chromium and oxo-molybdenum corrolates. The data have been related to those obtained for similar porphyrin complexes. Redox potentials are reported in Table 17. 

True porphyrin complexes also exist for molybdenum, and their chemistry has been explored by Collman and coworkers (equation 39). Oxidation of these complexes has been shown to increase the bond order ft om 2.0 to 3.0 for these redox-active systems. ... 

In summary, a 6-substituted pterin was first identified as a structural component of the molybdenum cofactor from sulfite oxidase, xanthine oxidase and nitrate reductase in 1980 (24). Subsequent studies provided good evidence that these enzymes possessed the same unstable molyb-dopterin (1), and it seemed likely that 1 was a constituent of all of the enzymes of Table I. It now appears that there is a family of closely related 6-substituted pterins that may differ in the oxidation state of the pterin ring, the stereochemistry of the dihydropterin ring, the tautomeric form of the side chain, and the presence and nature of a dinucleotide in the side chain. In some ways the variations that are being discovered for the pterin units of molybdenum enzymes are beginning to parallel the known complexity of naturally occurring porphyrins, which may have several possible side chains, various isomers of such side chains, and a partially reduced porphyrin skeleton (46). 

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