Page 731 - Advanced Organic Chemistry Part B - Reactions & Synthesis

Pd II 707
RCH CH + Pd(II) RCH CH 2
2
Pd II SECTION 8.2
Nu Pd II Reactions Involving
Nu + RCH CH 2 CHCH 2 Organopalladium
Intermediates
R
[H]
Nu CHCH 3 (path a)
Nu CHCH Pd II R
2
R
–Pd(0) Nu C CH 2 (path b)
–H +
R

A second major group of organopalladium intermediates are -allyl complexes,
which can be obtained from Pd(II) salts, allylic acetates, and other compounds having
potential leaving groups in an allylic position. 98 The same type of -allyl complex
can be prepared directly from alkenes by reaction with PdCl or Pd O CCF . 99 The
2 2 3 2
reaction with alkenes occurs by electrophilic attack on the electrons followed by
loss of a proton. The proton loss probably proceeds via an unstable species in which
the hydrogen is bound to palladium. 100
Pd Pd II
+ Pd II Pd II – H –H + –
H H

These -allyl complexes are moderately electrophilic 101 in character and react
with a variety of nucleophiles, usually at the less-substituted allylic terminus. After
nucleophilic addition occurs, the resulting organopalladium intermediate usually breaks
+
down by elimination of Pd(0) and H . The overall transformation is an allylic substi-
tution.
RCH CH CH 2
2
H
H H
R H Nu – R –Pd 0
– CH 2 Nu RCH CHCH 2 Nu
H H Pd II –H +
RCHCH CH 2 Pd II
O CCH 3
2
Another general process involves the reaction of Pd(0) species with halides or
sulfonates by oxidative addition, generating reactive intermediates having the organic
group attached to Pd(II) by a bond. The oxidative addition reaction is very useful for
aryl and alkenyl halides, but the products from saturated alkyl halides often decompose
by -elimination. The -bonded species formed by oxidative addition can react with
alkenes and other unsaturated compounds to form new carbon-carbon bonds. The

98 R. Huttel, Synthesis, 225 (1970); B. M. Trost, Tetrahedron, 33, 2615 (1977).
99
B. M. Trost and P. J. Metzner, J. Am. Chem. Soc., 102, 3572 (1980); B. M. Trost, P. E. Strege, L. Weber,
T. J. Fullerton, and T. J. Dietsche, J. Am. Chem. Soc., 100, 3407 (1978).
100 D. R. Chrisope, P. Beak, and W. H. Saunders, Jr., J. Am. Chem. Soc., 110, 230 (1988).
101
O. Kuhn and H. Mayr, Angew. Chem. Int. Ed. Engl., 38, 343 (1998).