Molybdenum substitution

A certain iron-base alloy contains 5% Cr and 10% W by weight. It is desired to make a new alloy with molybdenum substituting for tungsten on an atom for atom basis. That is, one atom of Mo replaces one atom of W. What wt.% Mo should the alloy contain The following data are available ... 

By means of 183W and 95Mo NMR, it has been established that all possible mixtures of [(Mo,W)7024]6 are formed, but that molybdenum substitution into paratungstate-B, [H2Wi2O42]10, and metatungstate, single site in both cases 63... 

Pra4] Prakash, U., Buekley, R.A., Jones, H., Effect of Molybdenum Substitution on B2 Antiphase Domain Formation in Rapidly Solidified Fe-Al-Mo Alloys , Mater. Sci. Eng., A133, 588-591 (1991) (Experimental, Morphology, 18)... 

Nis] Nishino, Y, Inkson, B.J., Ogawa, T., Humphreys, C.J., Effect of Molybdenum Substitution on Phase Stability and High-Temperature Strength of Fe3Al Alloys , Phil. Mag. Lett, 78(2), 97-103 (1998) (Experimental, Phase Relations, 20)... 

Vacuum Radiation Furnaces. Vacuum furnaces are used where the work can be satisfactorily processed only in a vacuum or in a protective atmosphere. Most vacuum furnaces use molybdenum heating elements. Because all heat transfer is by radiation, metal radiation shields ate used to reduce heat transfer to the furnace casing. The casing is water-cooled and a sufficient number of radiation shields between the inner cavity and the casing reduce the heat flow to the casing to a reasonable level. These shields are substitutes for the insulating refractories used in other furnaces. 

Divalent molybdenum compounds occur in mononuclear, dinuclear, and hexanuclear forms. Selected examples are shown in Figure 6. The mononuclear compounds are mostiy in the realm of organometaUic chemistry (30—32). Seven-coordinate complexes are common and include MoX2(CO)2(PR3)2, where X = Cl, Br, and I, and R = alkyl MoCl2(P(CH3)3)4, heptakis(isonitrile) complexes of the form Mo(CNR) 2 (Fig. 6d), and their chloro-substituted derivatives, eg, Mo(CNR)3CR. The latter undergo reductive coupling to form C—C bonds in the molybdenum coordination sphere (33). 

As electrophilic substitutes for peracids, the use of borate ester induced decomposition of alkyl hydroperoxides and molybdenum VI peroxy-complexes have been reported in the recent literature. Although these reagents have led to the epoxidation of olefins in greater than 90% yield there are no reports yet of their application to steroid olefins. 

All three structures have 0(, symmetry and are very similar. The bond length from the central atom to the carbonyl group is slightly different in each compound, and it is longest for the molybdenum substituent. The internal structure of the carbonyl groups is essentially unchanged by substitution. ... 

When methylene chloride was used as a solvent, it was found that 28 are obtained in minor amounts, while the dominating product is the -coordinated chloro-carbyne species [(> -Tp )Mo(CO)2(=CCl)], whose yield increases abruptly with substitution in the pyrazol-l-yl fragments (3-methyl-, 3,4,5-trimethyl-, and 3,5-dimethyl-4-chloro derivatives) [90AX(C)59,95JCS(D) 1709]. The tungsten analog can be prepared similarly. The chlorocarbyne molybdenum complex follows also from the reaction of the parent anion with triphenylsulfonium cation but conducted in dichloromethane. The bromo- and iodocarbyne derivatives are made similarly. 

Wlien tlie diiral molybdenum -K-allyl-substituted enone 147 was treated witli litliium dimetliylciiptate, formation of adduct 148 witli fait selectivity was observed tSdieme 6.29) [69], Interestingly, bigber selectivities were obtained in tlie presetice of boron ttlbuotlde etlierate. It is assumed tliat Lewis acid coordination induces tlie s-trans reactive conformation 149 [64], Consequently, nudeopb de attack anti to tlie molybdetiLim ftagmetit sbould afford tlie major diastereomer 148. 

Stable enolates such as diethyl malonate anions react with allyl sulfones (or acetates) in the presence of nickel complexes to give a mixture of the a- and /-product83. The regioselectivity is generally poor in the nickel-catalyzed reaction, but the molybdenum-catalyzed reaction is selective for alkylation at the more substituted allylic site, thereby creating a quaternary carbon center84. 

Substitution of known values in Equation 6-6 gives a lower value of a (3520 as against 4410) than that corresponding to the experimental points in Figure 6-4, which indicates that the counting rates measured for chromium Ka are higher than expected on the basis of the treatment given above. Such an increase in the intensity of this characteristic line could be due to its excitation by the characteristic lines of the substrate, notably molybdenum Ka experimental evidence for this excitation process was obtained.10... 

Steric effects in substituted halocarbonyls of molybdenum and tungsten. R. Colton, Coord. Chem. Rev., 1971, 6,269-284 (29). 

Diene 265, substituted by a bulky silyl ether to prevent cycloaddition before the metathesis process, produced in the presence of catalyst C the undesired furanophane 266 with a (Z) double bond as the sole reaction product in high yield. The same compound was obtained with Schrock s molybdenum catalyst B, while first-generation catalyst A led even under very high dilution only to an isomeric mixture of dimerized products. The (Z)-configured furanophane 266 after desilylation did not, in accordance with earlier observations, produce any TADA product. On the other hand, dienone 267 furnished the desired macrocycle (E)-268, though as minor component in a 2 1 isomeric mixture with (Z)-268. Alcohol 269 derived from E-268 then underwent the projected TADA reaction selectively to produce cycloadduct 270 (70% conversion) in a reversible process after 3 days. The final Lewis acid-mediated conversion to 272 however did not occur, delivering anhydrochatancin 271 instead. 

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