Iron group alkoxides

Fig. 4. The structure of the cation of 4B, [Fe402(BICOH)2(BICO)2 (02CPh)4]showing the 40% probability thermal ellipsoids. Only the first atom of the phenyl rings is shown. BICOH stands for bis(N-methylimldazol-2-yl)carbinol. BICO is the alkoxide anion, (a) The Fe402 core iron coordination spheres and bridging benzoate groups. Continued on next page.

Some reactions of 2,2 -bipyridine /V-oxides have been reported. The l,T-dioxide is nitrated readily to 4,4 -dinitro-2,2 -bipyridine 1,T-dioxide. ° ° °" 2,2 -Bipyridine 1-oxide is also nitrated in the 4 position. The nitro groups in 4,4 -dinitro-2,2 -bipyridine l,T-dioxide are reactive, being replaced by chlorine with concentrated hydrochloric acid," by bromine with acetyl bromide, by hydroxyl with dilute sulfuric acid, and by alkoxy groups with sodium alkoxides. Some of the dialkoxy derivatives are useful catalysts for the oxidation of aromatic compounds. The dinitro dioxide is deoxygenated to 4,4 -dinitro-2,2 -bipyridine with phosphorus trichloride in chloroform, and other substituted l,T-dioxides behave similarly, but with phosphorus trichloride alone, 4,4 -dichloro-2,2 -bipyridine results. The dinitro dioxide is reduced by iron powder in acetic acid to 4,4 -diamino-2,2 -bipyridine, whereas 4,4 -dichloro-2,2 -bipyridine l,T-dioxide is converted to its 4,4 -diamino analogs with amines. Related reactions have been described. ... 

In contrast to the carbometallation with aryl-Grignard reagents to unfunctionalized alkynes, this reaction does not require a co-catalyst such as copper. Only in one example, applying PhMgBr, was CuBr added in accord with the protocol reported by Hayashi s group. Although the nature of the catalytically active species remains unclear, an alkoxide-directed carbometallation which yields a (vinyl)iron intermediate is proposed. 

Iron porphyrins, the prosthetic group of the heme proteins are of course of great interest. Tetraphenylporphine, (TPPH2) (Fig. 2) is not a naturally occurring porphyrin. But because of its ease of preparation and close similarity to other porphyrins, tetraphenylporphinatoiron (TFPFe) derivatives have been extensively studied. Hemes are Fe(II) compounds such as TPPFe(II), and hemins are rive coordinate Fe(III) derivatives such as TFPFe(III) X (X = halide, pseudohalide, carboxylate, alkoxide, etc.)16). Six coordinate Fe(III) prophyrins are known as hemichromes, such as [TPPFe(III) L2] X (L = pyridine, piperidine, imidazole, etc.)16). Hemichromes are usually low spin, S = 1/2, systems 0 eff 1-9 B.M.) and hemins are of the high spin,... 

It seems reasonable to propose that the primary interaction inducing the proposed C-H activation mechanism consists in the interaction of the C-H bond with ferric ions, which are the oxidizing agents, as already proposed for the oxidation of different hydrocarbons at the surface chromate species of oxidized MgCr204 [8]. This mechanism implies that the two electrons of the C-H bond are assumed by the catalyst surface, where two ferric ions can become reduced to ferrous ions. But-3-en-2-oxide decomposes easily by elimination (as most alkoxides do) to the corresponding olefin, 1,3-butadiene in this case, and a surface OH group. Two OH s condense to allow water to desorb and oxygen reoxidizes the reduced iron cations. This is a very reasonable catalytic cycle for 1,3-butadiene production. 

A stepwise reaction is discussed in which the second carbonyl group is attacked externally from the irons side (transition slate II), at higher alkoxide concentrations, yielding the civ-diol. At low alkoxide concentrations (transition state I) the reaction proceeds intramolecularly to afford the tram- diol56. 

Another synthetically useful carbon bond-forming reaction involves reaction of diiron nonacarbonyl with halo-carbonyl compounds. Noyori found that a,a -dibromoketones (498) react with diiron nonacarbonyl [Fe2(CO)9] to give an iron stabilized alkoxy zwitterion (499). The intermediate Jt-allyl iron species reacts with alkenes in a stepwise manner (initially producing 500) to give cyclic ketones such as 501, 23 and the product is equivalent to the product of a [3-t2]-cycloaddition with an alkene (sec. 11.11). This cyclization method is now known as Noyori annulation. This reaction is related to the Nazarov cyclization previously discussed in Section 12.3.C. Enamines can react with 498, but the initially formed enamino ketone product eliminates the amino group to form cyclopentanone derivatives. Intermediates such as 499 may actually exist as cations hound to a metal rather than as the alkoxide-iron structures shown.323b-d noted that Zn/B(OEt)3 is... 

Stoichiometric experiments were conducted with the functionalized alkenes to further explore iron-substrate interactions and gauge relative coordination affinities. Several bis(imino)pyridine iron amine and ketone compounds were isolated and studied using a combination of X-ray diffraction, NMR and Mossbauer spectroscopy and established electronic structures similar to that for ( PDI)Fe(N2)2-In the absence of H2, diallyl ether and allyl ethyl ether underwent facile C-0 bond cleavage and yielded a near equimolar mixture of the corresponding iron allyl and alkoxide complexes [89]. Our group has recently published a comprehensive study on these types of reachons and discovered rare examples of C-0 bond cleavage in saturated esters [89]. 

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