Acid-base reactions organometallics

The acetylide anions discussed in Chapter 11 are another example of organometallic compounds. These reagents are prepared by an acid-base reaction of an alkyne with a base such as NaNH2 or NaH. We can think of these compounds as organosodium reagents. Because sodium is even more electropositive (less electronegative) than lithium, the C-Na bond of these organosodium compounds is best described as ionic, rather than polar covalent. 

Rapid acid-base reactions occur between organometallic reagents and all of the following functional groups ROH, RCOOH, RNH2, RzNH, RCONH2, RCONHR, and RSH. 

Carbonyl compounds that also contain N - H or O - H bonds undergo an acid-base reaction with organometallic reagents, not nucleophilic addition. 

Dendrimers having phosphines as branching points (Figure 39 Rh = [Rh(cod)Cl]) were synthesized by acid-base hydrolysis of aminosilanes with alcohols. This organometallic compound could be considered as a periphery- and core-functionalized dendrimer. Interestingly, the complexes can be formed before or after the acid-base reaction that forms the dendrimer. The Rh(l) metallodendrimer of Figure 39 was catalytically active in the hydrogenation of... 

For example, treating a hydroxyaldehyde with a Grignard reagent leads to an acid-base reaction that destroys the organometallic reagent, and not to carbon-carbon bond formation. 

In many of the examples we have considered and wiU consider later in this chapter, a catalyst is present to promote the reaction. If this is a homogeneous catalyst in one of the reactant phases such as an acid, base, or a dissolved organometallic complex, there are no mass transfer resistances to reaction, and the process behaves as a true homogeneous reaction. 

Reactions other than Lewis acid-base associations/dissociations are frequently observed wit donor molecules, leading notably to solvolysis, oxygen or sulfur abstraction, insertion reaction and carbon-carbon coupling reactions. The tendency to form metal-element multiple bonds i remarkable in this respect the activation of dinitrogen by tantalum or niobium is unique. Th formation and chemistry of constrained reactive metallacycles open another promisin fast-developing area, on the frontier with organometallic chemistry. 

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