Advances in C–C and C–X Coupling Using Palladium–NHeterocyclic Carbene (Pd–NHC) Complexes - New Trends in Cross-Coupling: Theory and Applications - page 167

Pd 2 (dba) 3 ( 1 mol%)
IPr.HCl (4 mol%)

X MgBr

R

R + R'

dioxane / THF, 80°C
1-5h

R'

X=Cl,Br,I

F

HO MeO

X=I:96%
X=Cl:95%

X=Br,Cl:99% X=Cl:99%

MeO

X=Cl:95% X=Cl:0% X=Br:0%

Scheme 4.24 Kumada cross-coupling using an in situ-generated system.

Mg Br R

36 (2 mol%)
NMP / THF, RT
1h

R' + RCl R'

NN

Pd

O

OMe

O

CN

3 3 3

O

F

98% 93% 61%

O

Pd

O

COOMe N

3

N N

O

36

99% 92% 33%

Scheme 4.25 Kumada cross-coupling using the well-defined Pd(0) catalyst 36.

R'

R

R'

N

R

37a :NHC=SIPr
37b :NHC =IPr
37c : NHC = SIMes
37d :NHC =IMes

N

Cl Cl

R

R

Pd Pd

R

R

Cl

Cl

N

R

N

R'

R

R'

Figure 4.17 Structure of the [Pd(NHC)(m-Cl)Cl] 2 complexes.

In 2009, Nolan and co-workers reported the use of several [Pd(NHC)(m-
Cl)Cl] 2 complexes for Kumada coupling between aryl-Grignard reagents
and (hetero)aryl chlorides. 91 Four different NHC ligands were screened and
SIPr showed the best catalytic activity (37, Figure 4.17). For the first time,
the coupling was possible at low catalyst loadings (typically 0.2 mol%),
under mild conditions (r.t.-60 1C, Scheme 4.26). The preparation of