Molybdenum complexes porphyrin, oxidation

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... 

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... 

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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