Lewis adds organometallics

Lewis add-base interactions are very common in chemistry and are often rather subtle. You are about to meet, in the next chapter, an important way of making C-C bonds by adding organometallics to carbonyl compounds, and in many of these reactions there is an interaction at some point between a Lewis acidic metal cation and a Lewis basic carbonyl group. 

A comprehensive survey on organometallic Lewis adds is given in Ref. 12. 

Alkyllithium compounds interact with organometallic compounds of different metals (MtR ), most notably those of Groups I, II, and III, which behave like Lewis adds, to form mixed organometallic compounds, referred to as ate complexes, schematically represented in the following equation ... 

The synthesis of functionalized zinc organometallics can be accomplished with a variety of methods that have been developed in recent years. The intrinsic moderate reactivity of organozinc reagents can be dramatically increased by the use of the appropriate transition-metal catalyst or Lewis add. Furthermore, the low ionic character of the carbon-zinc bond allows the preparation of a variety of chiral zinc organometallics with synthetically useful configurational stability. These properties make organozinc compounds ideal intermediates for the synthesis of complex and polyfunctionalized organic molecules. 

This is useful for the synthesis of alkynyl ketones, which are difficult to make directly with conventional organometallic reagents such as alkynyl-Li or -MgBr because they add to the ketone product. Alkynyl silanes react with acid chlorides in die presence of Lewis acids, such as aluminium chloride, to give the ketones. 

Chiral Lewis acids combined with less reactive organometallics like organotins (organostannanes) can add to carbonyls to give one enantiomer selectively. The chiral Lewis acid complex with the carbonyl makes one face of the carbonyl more accessible to the organometallie nucleophile. The product chirality is set by the chiral catalyst. 

Since many organometallics behave as Lewis bases due to electron-rich metals, protonation is a common reaction. For example, the tungsten hydride 3 undergoes reversible protonation at the metal, forming the water-soluble cationic hydride 4 (Eq. 5). In nickelocene 5, a 20e complex, protonation occurs at the jr-bonded cyclo-pentadienyl ligand the intermediate 6 has a stable, isolable counterpart in the fully methylated derivative. Consecutive loss of cyclopentadiene forms the cation 7, which adds to unchanged nickelocene forming the tripledecker sandwich 8 (Scheme 3). 

In terms of what I was doing, his most important paper was published in 1958, with Sten Ahrland and Norman Davies. This paper was entitled The Relative Affinities of Ligand Atoms for Acceptor Molecules and Ions. The authors drew on a large basis set of data available to them. This included equilibrium data in aqueous solution and in the gas phase, but also data on the general stability and ease of preparation of the transition metal organometallics. This enabled them to add carbon donor ligands to the more common examples. Their acceptors included the metal atoms in various oxidation states and Lewis acids of the type GaMe3 and BF3. 

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