14.10: Properties of Organometallic Compounds

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How carbon-metal bonds are formed depends on the metal that is used. Conditions that are suitable for one metal may be wholly unsuited for another. Some organometallic compounds react very sluggishly even toward acids, whereas others react avidly with water, oxygen, carbon dioxide, and almost all solvents but the alkanes themselves. Reactivity increases with increasing polarity of the carbon-metal bond, which is determined by the electropositivity of the metal. Strongly electropositive metals, such as sodium and potassium, form largely ionic bonds to carbon, as we have mentioned in the case of alkynide salts, \(\ce{RC \equiv C}^\ominus \ce{Na}^\oplus\) (Section 11-8). Estimates of the ionic character of various carbon-metal bonds are given in Table 14-3, and it will be seen that organosodium and organopotassium compounds have the most ionic bonds and they are, in fact, among the most reactive organometallic compounds known. Many organosodium and organopotassium compounds burn spontaneously when exposed to air and react violently with water and carbon dioxide. As might be expected from their saltlike character, they are nonvolatile and do not dissolve readily in nonpolar solvents. In contrast, the more covalent, less ionic, organometallic compounds, such as \(\ce{(CH_3)_2Hg}\), are far less reactive; they are stable in air, quite volatile, and dissolve in nonpolar solvents.

Table 14-3: Percent Ionic Character of Carbon-Metal Bonds\(^a\)
Bond	Percent Ionic Chateracter	Bond	Percent Ionic Chateracter	Bond	Percent Ionic Chateracter
C-K	51%	C-Mg	35%	C-Sn	12%
C-Na	47%	C-Al	22%	C-Pb	12%
C-Li	43%	C-Zn	18%	C-Hg	9%
C-Ca	43%	C-Cd	15%
Source: L. Pauling, The Nature of the Chemical Bond, Cornell University Press, Ithaca, N.Y. 3rd, 1960, Chap. 3

All of these compounds must be handled with great care because some are dangerously reactive and others are very toxic. They seldom are isolated from the solutions in which they are prepared, but are used immediately in other reactions.

Contributors and Attributions

John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."