Beryllium compounds Lewis acid complexes

To investigate complexes of the Lewis acid BeO may seem strange from the experimental point of view. BeO is a polymeric solid with a high melting point and it is very difficult to obtain monomeric BeO. Moreover, beryllium is very poisonous and its compounds are difficult... 

The fact that NHCs form stable compounds with beryllium, one of the hardest Lewis acids known and without p-electrons to back donate, shows the nu-cleophilicity of these ligands. Reaction of l,3-dimethylimidazolin-2-ylidene with polymeric BeCl2 results in the formation of the neutral 2 1 adduct 23 or the cationic 3 1 adduct 24. The first NHC-alkaline earth metal complex to be isolated was the 1 1 adduct 25 with MgEt2- Whereas l,3-dimesitylimidazolin-2-ylidene results in the formation of a dimeric compound, the application of sterically more demanding l,3-(l-adamantyl)imidazolin-2-ylidene gives a monomeric adduct. ... 

By functioning as Lewis acids, many beryllium compounds attain maximum coordination of the metal atom. Thus the chloride forms etherates, Cl2Be(OR2)2, and complex ions such as BeF and [Be(H20)4]2+ exist. In chelate compounds such as the acetylacetonate, Be(acac)2, four approximately tetrahedral bonds are formed with the C—O and Be—O bond lengths equivalent. 

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