Magnesium species

The initially formed tetra-alkylferrate(II) represents the reactive intermediate in both reactions that undergoes a carboferration of the triple bond in eq. 2, Scheme 29. Transmetallation from Fe to Mg yields a vinyl-magnesium species, which liberates the desired olefin upon hydrolysis within the acidic work-up procedure. In the above two reactions, a competing p-hydride elimination from the ferrate yields the unreactive Fe-H species and hence is considered to be the deactivation step in the catalytic cycle. 

The addition of carbonyl compounds towards lithiated 1-siloxy-substituted allenes does not proceed in the manner described above for alkoxyallenes. Tius and co-work-ers found that treatment of 1-siloxy-substituted allene 67 with tert-butyllithium and subsequent addition of aldehydes or ketones led to the formation of ,/i-unsaturated acyl silanes 70 (Scheme 8.19) [66]. This simple and convenient method starts with the usual lithiation of allene 67 at C-l but is followed by a migration of the silyl group from oxygen to C-l, thus forming the lithium enolate 69, which finally adds to the carbonyl species. Transmetalation of the lithiated intermediate 69 to the corresponding zinc enolate provided better access to acylsilanes derived from enolizable aldehydes. For reactions of 69 with ketones, transmetalation to a magnesium species seems to afford optimal results. 

An alternative formation of titanated alkoxyallenes could be achieved by reaction of 3-alkoxy-2-propyn-l-yl carbonates 78 with (r/2-propene)titanium diisopropoxylate (79). Successive addition of 80 to benzaldehyde afforded the corresponding addition products 81 in high yield (Scheme 8.22) [70]. The results demonstrate that titanium species 75 and 80 can serve as easily available ester homoenolate equivalents. Notably, conversion of lithiated alkoxyallenes to the magnesium species by treatment with MgBr2 followed by addition to chiral carbonyl compounds resulted in a mixture of a- and y-products [71]. 

Realizing the importance and effectiveness of the magnesium species in the sorption of SO, in the late 1980s, Akzo Nobel patented the use of hydrotalcite and related compounds for nse in an FCC to reduce SO emissions [8,9,10]. Hydrotalcite contains more active Mg species than spinel. Hydrotalcite-based compounds typically contain 3-4 moles of Mg per mole of Al, while spinels contain only 1 mole of Mg per 2 moles of Al (Figure 16.4). 

In those cases where the initially added electrophile is chemically nonreactive toward the magnesium reagent, further reaction can be achieved to give a 6-magnesium species 334, and this can be performed either separately, or in a one-pot procedure <2006OL3737>. 

A variety of other olefins were studied 1,6-diphenylhexatriene, anthracene and cyclooc-tatetraene also displace butadiene from its polymeric magnesium complex. Now should these olefin-magnesium species be viewed as magnesacycles Or as contact ion pairs with olefin dianions In any case, no enthalpies of hydrolysis are available, nor quantitation of stabilities by even equilibrium constants. We welcome this information. 

Thioamides of secondary amines are deprotonated with isopropyhnagnesium to give (Z)-enolates. Thioamides of primary amines react with two equivalents of /-PrMgBr to afford dianions that have been shown to have the (Z)-configuration. These magnesium species are versatile intermediates in stereoselective aldol reaction (equation 50, Table 5 ... 

Step 3 Mass balance. This is a little tricky. From Reaction 8-30, we could say that the concentrations of all species containing OH equal two times the concentrations of all magnesium species. However, Reaction 8-32 also creates 1 OH for each H+. The mass balance accounts for both sources of OH- ... 

Seitz, L. M., and Brown, T. L., Organometallic exchange reactions. VII. Distribution of phenyl and alkyl groups on lithium and lithium-magnesium species in ether, J. Am. Chem. Soc., 89, 1607 (1967). 

Second, 25 is converted into the alkynyl magnesium species 8 by treatment with nBuMgCl, because the alkyl Grignard reagent is more basic than the alkynyl, so deprotonation of the alkyne 25 under loss of nbutane takes place. 

Benzyne generated from 2-iodophenyl 4-chlorobenzenesulfonate by treatment with tropropyl magnesium chloride at low temperature adds to the magnesium thiolate derived from thiosalicylic acid 530 to form thioxanthone. The carboxyl function behaves as an electrophile towards the intermediate aryl magnesium species and an intramolecular cyclization ensues (Scheme 212) <2005AGE4258>. 

Treatment of (dibromomethyl)methyldiphenylsilane with Bu3MgLi at — 78 °C leads to a smooth exchange reaction. Addition of CuCN-LiCl causes migration of the butyl group affording a-silyl substituted magnesium species. They react with allyl bromide, acyl chlorides, or a/i-cnoncs in the presence of a copper catalyst.79,7911... 

To calculate the soda ash requirement for the calcium noncarbonate hardness by-product, let M gca represent the mass of the magnesium species that precipitates and results in the production of the additional calcium hardness cation, where the Ca, again, is written as a reminder. Refer to Eqs. (10.17), (10.18), and (10.19) to see how the calcium hardness is produced from the precipitation of noncarbonate magnesium. The number of equivalents of the calcium hardness produced is equal to the number of equivalents of the noncarbonate hardness of magnesium precipitated [which is equal to MMgCa/(Mg/2), where Mg/2 is the equivalent mass of Mg as obtained from Eqs. (10.17), (10.18), and (10.19)]. Because this is calcium hardness, we aheady have the method of determining the amount of soda ash needed to remove it as shown in Equation (10.25). Letting this amount be is... 

Aminosilyl)magnesium species are obtained by reaction of the silyllithiums with /-PrMgBr (Scheme 8). The silylmagnesium reagents are milder... 

Biscyclopentadienyl magnesium species have an unusually narrow v i, 2 of 100-500 Hz. This is rationalized by penta-hapto bonding, y-Cp-Mg [42,43]. In these systems, Mg-NMR spectroscopy provides a direct contribution to the discussion of whether the bonding is ionic or covalent [45]. 

---