Bonding considerations group 17 elements

The organometallic chemistry of alkynylcyclopropanes involves primarily the formation and reactions of carbon-metal er-bonds. Metals come essentially from the main group elements, with lithium playing a major role. The two metallation sites are the cyclopropyl and the acetylenic positions, which are expected to differ considerably in their acidity values (t-butylacetylene, pKa = 25230, cyclopropane, pKa = 46183) but less in the reactivity of their metal conjugated bases towards electrophiles. 

Lewis acids based on boronic acid derivatives or main group elements such as mercury, tin and silicon form strong bonds to anions with considerable covalency, exemplified by hydride sponge and the anticrowns. 

The electronic structure of these small molecules could serve as the basis of a full article in another context, and our short summary of trends in MOs (or negative ionization potentials) lacks the depth the topic deserves. However, an understanding of these preliminary considerations is requisite for understanding the trends in structure and bonding observed in main group element-transition metal compounds. 

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