Advances in C–C and C–X Coupling Using Palladium–NHeterocyclic Carbene (Pd–NHC) Complexes - New Trends in Cross-Coupling: Theory and Applications - page 172

[Pd(IPent)(PEPPSI)] ( 4 )
(4 mo l%)

+

Ar(Het) X

SnBu 3 (Het)Ar

Y CsF, 1,4-dioxane

4Å molecular sieves
80 °C, 16 - 2 4 h

X

NO 2 OMe

N

N

S S S

S

N(Boc) 2

62% 92 % 67%

NN

O

N

O O S

N N

Cl Pd Cl

SO 2 Ph

O

70% 91 % 99%

N

Cl

N

N

4

N

N

N

MeO

78% 89% 90 %

N N N S N O

a

60 °C, 4 (8 mol% )

N N N N

75% a 98% a 90% a

Scheme 4.29 Arylation of heterocycles by Stille cross-coupling using [Pd(IPent)-
(PEPPSI)] (4).

Table 4.13 Comparison between phosphine and NHC ligands for Hiyama cross-
coupling.

Pd(OAc) 2 (3 mol%)
or Pd(dba) 2 (3 mol%)
Ligand (3 mol%)

Br Si(OMe) 3

+

TBAF
1,4-dioxane / THF

Yield (%) a Entry [Pd] L Time (h)

100 b

1 Pd(dba) 2 PCy 3 1.5

100 b

2 Pd(dba) 2 P(o-tol) 3 1

60 c

3 Pd(OAc) 2 IMes HCl 2

93 c

4 Pd(OAc) 2 IPr HCl 6

a

By GC.
b 80 1C, 2 equiv. Ph(SiOMe) 3 .
c

60 1C, 3 equiv. Ph(SiOMe) 3 .

1,4-dioxane-THF as solvent at 80 1C. The system proved particularly ecient
for the cross-coupling between aryl bromides and electron-deficient chlor-
ides with phenyl- or vinyltrimethoxysilane (Scheme 4.30). In terms of ligand
selection, IPr was found to be better than IMes and as ecient as PCy 3 or
P(o-tol) 3 (Table 4.13).