Page 644 - Advanced Organic Chemistry Part B - Reactions & Synthesis

7

Organometallic Compounds

of Group I and II Metals

Introduction

The use of organometallic reagents in organic synthesis had its beginning around 1900
when Victor Grignard discovered that alkyl and aryl halides react with magnesium
metal to give homogeneous solutions containing organomagnesium compounds. The
“Grignard reagents” proved to be highly reactive carbon nucleophiles and are still very
useful synthetic reagents. Organolithium reagents came into synthetic use somewhat
later, but are also very important for synthesis. The present chapter focuses on
Grignard reagents and organolithium compounds. We also consider zinc, cadmium,
mercury, indium, and lanthanide organometallics, which have more specialized places
in synthetic methodology. Certain of the transition metals, such as copper, palladium,
and nickel, which are also important in synthetic methodology, are discussed in
Chapter 8.
The composition of the organolithium compounds is RLi or more accurately
RLi . The organomagnesium compounds are usually formulated as RMgX, with X
n
being a halide. The organometallic derivatives of Group I and II metals provide reactive
carbon nucleophiles. Reactivity increases in the order Li < Na < K and MgX < CaX,
but the lithium and magnesium reactions are by far the most commonly used. Organo-
lithium and magnesium reagents react with polar multiple bonds, especially carbonyl
groups, and provide synthetic routes to a variety of alcohols. Other electrophiles, such
as acyl halides, nitriles, and CO provide routes to ketones and carboxylic acids.
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