Advances in C–C and C–X Coupling Using Palladium–NHeterocyclic Carbene (Pd–NHC) Complexes - New Trends in Cross-Coupling: Theory and Applications - page 208

[Pd(IPr*)(cin)Cl] (9)
or
[Pd(IPr*)(3-Cl-pyridinyl)Cl 2 ](8 6)

R''

Cl R''

N

+

H N

R R'

R

R'

KOt Am or KOt Bu
DME , RT, [Pd] = 1 - 2 mol%
or
Toluene, Reflux, [P d] = 0.02 5 - 0.050 mol%

A t room temperature:

O

O

N

N

N

N N

Me O

9:91%
86: 92%

9:94%
86:87%

9:89%
86:93%

9:90%
86:78%

At low catalyst loadings:

O

N

N

N N

H

N

Me O

9:95%
86:96%

9:76%
86 :95%

9:93%
86: 93%

9:88%
86: 87%

N N

n-Oct

NH

9:94%
86:90%

9 :97% 9:92%

86:94%

Scheme 4.61 Reactivity of [Pd(IPr*)(cin)Cl] and [Pd(IPr*)(3-Cl-pyridinyl)Cl 2 ] in ami-
nation at room temperature and low catalyst loadings.

promote the coupling. A direct comparison between IPr* and IPr* OMe was
then conducted. The differences in reactivity were tremendous and [Pd(I-
Pr* OMe )(acac)Cl] proved to be much more active than the IPr* congener
(Scheme 4.63). The scope of the reaction was studied at very low catalyst
loadings (as low as 0.005 mol% for the coupling of p-bromotoluene and N-
methylaniline, with a yield of 72%). The catalytic system proved highly
effective, permitting the coupling of various aryl halides with a range of
amines, including challenging electron-poor anilines.
Nolan and co-workers also developed a solvent-free amination protocol
using the well-defined [Pd(IPr*)(cin)Cl] (9, Figure 4.37). 177 This complex
(1 mol%) proved particularly useful for the coupling of primary amines at
room temperature, which previously was not possible in the presence of
solvents (Scheme 4.64). Moreover, in some cases, the reaction was complete
in minutes. It is important to state that in these cases, the reaction was set