Advances in C–C and C–X Coupling Using Palladium–NHeterocyclic Carbene (Pd–NHC) Complexes - New Trends in Cross-Coupling: Theory and Applications - page 185

Table 4.21 Reactivity of the [Pd(SIPr)(m-Cl)Cl] 2 (37a) complex at very low catalyst
loadings.

[Pd(SIPr)( µ -Cl)Cl] 2 37a
(x mol%)

Br Ph

R + R

Ph

KHCO 3, DMF
1 20 - 140°C, 20 h

TON a Entry Aryl halide [Pd] loading (mol%) Yield (%)

499 49900

1 0.01

Br

OHC

91 9100

2 0.01 MeO Br

96 9600

Br

3 0.01

499 44950

N

4

Br

0.02

66 3300

S

5 0.02 Br

42 2100

S

6 0.02

Br

99 49 500

7 0.002

Br

a mol product/mol Pd.

N N

O

N N

H

I N O

N N

N

N

N

Pd Br Pd Br Br Pd Br

N

Ph Pd

N N

O N I

H

N

Br Br

O NN

556 557 558

Figure 4.29 Structures of caffeine- and proline-derived precatalysts.

4.3.2.5 Heck Coupling Using Pseudohalides
The use of pseudohalides is rare in the Heck reaction. However, in 2012, Yus
and co-workers reported the use of a hydroxyalkyl-functionalized NHC-
Pd(OAc) 2 mixed system to promote the Heck-Matsuda coupling between
arenediazonium salts and different alkenes (Scheme 4.36). 126 Interestingly
in this case, the reaction does not require the use of a base and cyclohexene
was found to be a suitable substrate. As an application, the preparation of
the biologically active molecule U-77863 in good yield (78%) using 0.5 mol%
of Pd(OAc) 2 and 1 mol% of the ligand was also reported. Notably, U-77863
has been reported to exhibit anti-invasive and anti-metastatic effects.