Donor-acceptor adducts

First donor-acceptor adduct (coordination compound) NH3.BF1 prepared by J. L. Gay Lussac (A. Werner s theory, I89I-5). 

In analogy to its complexes with nitrosyl cation (as described above), benzene can form donor-acceptor adducts with a variety of metallic and non-metallic Lewis acids. These lead to materials with novel optical and electrical properties that can be tuned through substituents on the aromatic ring. 

The enthalpy change during donor-acceptor adduct formation has been related by Drago to the sum of two terms (1) the product of the electrostatic properties of the acid and the base, Ef. and E and (2) the product of their tendency toward covalent bonding, Ca and Cb [10]. For the particular case, where the acceptor is specified to be SbCb (and the inert solvent is 1,2-dichloroethane), the negative of this enthalpy change (in kcal mol", 1 cal = 4.184 J) is the Gutmann donor number, DN [2,11]. These concepts are further discussed in Chapter 3. 

In boron trifluoride adducts, fluorine displacement is relatively difficult and, thus, the widest range of adducts has been prepared for the trifluoride (66,120). As fluorine is replaced by successively heavier halogens the displacement of halogen occurs more readily and secondary reactions of the initially formed donor-acceptor adducts... 

The pathways to compounds 2-12 probably require that in the first step the silylene 1 behaves towards MX as a nucleophile yielding an intermolecular donor-acceptor adduct B, followed by subsequent intramolecular insertion of either 1 into the M-X bond or X into the Si-M bond (Scheme 7), resulting in C. 

Pairs of Lewis acids and bases normally form stable donor-acceptor adducts. When steric effects prevent this adduct formation. Frustrated Lewis Pairs (FLPs) are obtained instead. Such FLPs are promising reagents for the... 

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