Page 700 - Advanced Organic Chemistry Part B - Reactions & Synthesis

676 H O
2
CH 3 MgBr H + CH CH CHC(CH )
3
3 2
CHAPTER 8
O OH
Reactions Involving
Transition Metals CH CH CHCCH 3
3
Cul,
MgBr H 2 O (CH ) CHCH CCH
CH 3 3 2 2 3
H +
O
Subsequently, much of the development of organocopper chemistry focused on
stoichiometric reagents prepared from organolithium compounds. Several types of
organometallic compounds can result from reactions of organolithium reagents with
2
copper(I) salts. Metal-metal exchange reactions using a 1:1 ratio of lithium reagent
and a copper(I) salt give alkylcopper compounds that tend to be polymeric and are
less useful in synthesis than the 2:1 or 3:1 “ate” compounds.

RLi + Cu(I) [RCu] n + Li +
2 RLi + Cu(I) [R 2 CuLi] + Li +
3 RLi + Cu(I) [R 3 CuLi ] + Li +
2
The 2:1 species are known as cuprates and are the most common synthetic
reagents. Disubstituted Cu(I) species have the 3d 10 electronic configuration and
would be expected to have linear geometry. The Cu is a center of high electron
density and nucleophilicity, and in solution, lithium dimethylcuprate exists as a dimer
3
LiCu CH
. The compound is often represented as four methyl groups attached
3 2 2
to a tetrahedral cluster of lithium and copper atoms. However, in the presence of LiI,
the compound seems to be a monomer of composition CH CuLi. 4
3 2
CH 3 CH
Cu 3
Li Li
Cu
CH 3 CH 3

Discrete diarylcuprate anions have been observed in crystals in which the lithium
5
cation is complexed by crown ethers. Both tetrahedral Ph Cu and linear Ph Cu
−
2
4
4
units have been observed in complex cuprates containing CH S as a ligand.
3 2
6
Ph Cu
2− units have also been observed as parts of larger aggregates. Larger
3

−
clusters of composition Ph Cu Li
and Ph Cu Mg OEt
have been characterized
6
4
2
4
6
7
by crystallography, as shown in Figure 8.1.
Cuprates with two different copper ligands have been developed. These
compounds have important advantages in cases in which one of the substituents
2
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4
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5
H. Hope, M. M. Olmstead, P. P. Power, J. Sandell, and X. Xu, J. Am. Chem. Soc., 107, 4337 (1985).
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7
S. I. Khan, P. G. Edwards, H. S. H. Yuan, and R. Bau, J. Am. Chem. Soc., 107, 1682 (1985).