Alkaline earth metal alkoxides

Alkaline earth metal alkoxides decompose to carbonates, olefins, hydrogen, and methane calcium alkoxides give ketones (65). For aluminum alkoxides, thermal stability decreases as follows primary > secondary > tertiary the respective decomposition temperatures are ca 320°C, 250°C, and 140°C. Decomposition products are ethers, alcohols, and olefins. 

Double Alkoxides. Complex double alkoxides are formed when a solution of an alkaU or alkaline earth metal alkoxide is added to a solution of an alkoxide of aluminum, titanium, or tirconium and a series of such compounds have been prepared (44). 

Table 12.2. Magnesium and alkaline earth metal alkoxides... 

For the quantitative deprotonation of nitroalkanes and active-methylene compounds, there is no need to employ the heavy artillery of lithium amides. Rather, it suffices to employ alkaline earth metal alkoxides or alkaline earth metal hydroxides. In addition, equilibrium reactions between these C,H acids and amines form enough enolate to initiate enolate reactions. 

Remember what we discussed in the context of Figure 13.44 ketones usually do not undergo aldol additions if they are deprotonated to only a small extent by an alkaline earth metal alkox-ide or hydroxide. The driving force behind that reaction simply is too weak. In fact, only a very few ketones can react with themselves in the presence of alkaline earth metal alkoxides or alkaline earth metal hydroxides. And if they do, they engage in an aldol condensation. Cyclopentanone and acetophenone, for example, show this reactivity. 

Remember what we discussed in the context of Figure 10.39 ketones usually do not undergo aldol additions if they are deprotonated to only a small extent by an alkaline earth metal alkoxide or hydroxide. The driving force behind that reaction simply is... 

The exact role of the organolithium reagent remains unclear, but it seems plausible that the components function as alkaline earth metal-containing superbase analogs, with a alkali-alkaline earth metal alkoxide/organometallic aggregate as the metallating species. ... 

SBN is a solid solution system containing strontium, barium, and niobium oxides. The sol-gel solution preparation requires special precautions. This is because the alkaline-earth metal alkoxides dissolve in alcohols slowly and they are extremely moisture sensitive. Although alkoxides of both barium and stron-... 

Interest in the synthesis and chemistry of soluble and volatile alkaline earth metal alkoxides experienced a sudden upsurge in the 1990s, owing to the discovery of superconducting ceramics" " containing Ba and Ca. 

Similar behaviour has also been observed in the case of magnesium and other alkaline earth metal alkoxides. The normal dialkoxides of magnesium, calcium, strontium, and barium are insoluble and nonvolatile "" whereas the alkylmagnesium alkoxides are soluble in common organic solvents and some of these (especially methyl and ethyl derivatives) can be volatilized in usually accompanied by... 

The properties "" of alkaline earth metal alkoxides appear to be dominated by their ionic character and preference for attaining metal coordination numbers >6, leading to rather large associated species. 

The H NMR spectra of only a few heavier alkaline earth metal alkoxide derivatives that are soluble in suitable organic solvents have been studied so far. The complex Ba2(OCPh3)4(THF)3 shows only a single line for aryl ring protons down to —43°C, and the NMR spectrum also shows only one aryl environment. ... 

The most widely used cross-coupling arylation reaction is the Suzuki-Miyaura reaction (Scheme 1.10), which was first reported in 1979 [12, 26, 27]. The reaction involves transmetallation with an organoboron reagent that is usually a boronic acid or ester. No transmetallation occurs under neutral conditions only in the presence of a base, which is usually an alkaline earth metal alkoxide, although weak bases such as K COj can be used [12] (Scheme 1.10b). Pd(OAc)2 or Pdj(dba)3 are the common sources of Pd(0). In some circumstances, arenediazonium tetrafluoroborates have been used [12e]. Nickel complexes can be used under some circumstance instead of Pd. 

Complex Formation Between Two Alkoxides (Method 2.1). The pronounced Lewis basicity of the alkoxide ligands of the alkaU and alkaline earth metal alkoxides explains their capacity to form heterometalhc conplexes in solution with the vast majority of high-valent transition or main group metal alkoxides, for example ... 

Addition of Sulfonylimidates to Imines. Alkaline earth metal alkoxides are attractive catalysts in organic chemistry as they display both Lewis acidic and basic properties. They are perfectly suited for the addition of enolates to electrophiles due to their chelating properties. In particular, catalytic Mg(OtBu)2 can be used in the addition of sulfonylimidate nucleophiles 1 to Boc-protected imines 2 (eq 1). Both yields and anti/syn ratios are... 

The choice of commercially available simple metal alkoxides is actually a bit larger, incorporating diluted solutions of alkali and some alkaline earth metal alkoxides in parent alcohols as welL The latter are very sensitive to moisture and oxygen on storage. In feet, they can be produced by customary synthesis in situ. 

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