Advances in C–C and C–X Coupling Using Palladium–NHeterocyclic Carbene (Pd–NHC) Complexes - New Trends in Cross-Coupling: Theory and Applications - page 155

Table 4.4 Comparison of reactivities of various [Pd(NHC)(cin)Cl] complexes.

Cl B(OH) 2

6, 19a - d (0.02mol%)

+

F 3 C

i PrOH / THF ( 9:1)
60°C, 15 h

F 3 C

Conversion (%) a

Entry [Pd(NHC)(cin)Cl]

1 6 55

2 19a 87

3 19b 86

4 19c 85

5 19d 69

a By GC.

O

NN NN NN NN NN

n Bu

Et Oct Mes Mes

bmim-y emim-y miop-y mokt-y IMes

Small NHCs and IMes used by Trzeciak and co-workers. 57 Figure 4.13

Table 4.5 Comparison of reactivities of various [Pd(NHC) 2 X 2 ] complexes for the
Suzuki reaction at very low catalyst loadings.

[Pd(NHC) 2 Br 2 ] 21a-e
(0.0001 mol%)

Br B(OH) 2

+

NaHCO 3 , ethylene glycol
11 0°C, 1h

Entry [Pd(NHC) 2 Br 2 ] Yield (%) TON

1 [Pd(bmim-y) 2 Br 2 ](21a) 62 620 000

2 [Pd(emim-y) 2 Br 2 ](21b) 50 500 000

3 [Pd(miop-y) 2 Cl 2 ](21c) 2 20 000

4 [Pd(mokt-y) 2 Cl 2 ](21d) 76 760 000

5 [Pd(IMes) 2 Cl 2 ](21e) 86 860 000

N N

N N

N

R' R

22a :R =Me,R'=Ph
22b :R=Et,R'=Ph
22c :R= n Bu , R' = n Bu
22d :R=Mes,R'=Ph
22e :R=Mes,R'=Mes

23a :Ar=Ph,R =H
23b :Ar=Mes,R=H
23c : Ar = Dipp, R = H
23d :Ar=Dipp,R=Me
23e : Ar = Dipp, R = P h

N

Ar Ar

Cl Pd Cl

Pd

Cl

N

R

Cl

Figure 4.14 Structures of the complexes 22a-e and 23a-e.

Some 1,2,3-triazolylidene ligands were also developed by the groups
of Albrecht 58 and Fukuzawa 59 as an alternative to more common NHC lig-
ands (Figure 4.14). In the case of the PEPPSI-type precatalysts (22a-e),