Page 699 - Advanced Organic Chemistry Part B - Reactions & Synthesis

8

Reactions Involving

Transition Metals

Introduction

In this chapter we discuss important synthetic reactions that involve transition metal
compounds and intermediates. Reactions involving copper and palladium, the transition
metals that have the widest applications in synthesis, are discussed in the first two
sections. In the third section, we consider several other transition metals, including
nickel, rhodium, and cobalt. In contrast to lithium, magnesium, and zinc, where the
organometallic reagents are used in stoichiometric quantities, many of the transition
metal reactions are catalytic processes. The mechanisms are described in terms of
catalytic cycles that show the role of the catalytic species in the reaction and its
regeneration. Another distinguishing feature of transition metal reactions is that they
frequently involve changes in oxidation state at the metal atom. In the final two sections
we deal with transition metal–catalyzed alkene exchange (metathesis) reactions and
organometallic compounds that feature bonding of the organic component.

8.1. Organocopper Intermediates

8.1.1. Preparation and Structure of Organocopper Reagents

The synthetic application of organocopper compounds received a major impetus
from the study of the catalytic effect of copper salts on reactions of Grignard reagents
1
with -unsaturated ketones. Although Grignard reagents normally add to such
compounds to give the 1,2-addition product, the presence of catalytic amounts of Cu(I)
results in conjugate addition. Mechanistic study pointed to a very fast reaction by an
organocopper intermediate.

1
H. O. House, W. L. Respess, and G. M. Whitesides, J. Org. Chem., 31, 3128 (1966).
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