Chemistry Reference
In-Depth Information
Single-crystal X-ray structure of [(p-Me
2
NC
6
H
4
(t-Bu)
2
P]
2
Pd.
50
Reprinted with permission from Journal of Organic Chemistry. Copyright
2013 American Chemical Society.
Figure 3.11
Table 3.1 P-Pd-P angles versus activities of L
2
Pd(0) precatalysts.
C
8
H
17
OMe
C
8
H
17
Pd Precatalys
ts
Cs
2
CO
3
,DMF
+
Cl
MeO
Yield
(%)
a
Pd-P bond
lengths (Å)
P-Pd-P
angle (1)
Entry
Catalyst
1
[p-Me
2
NC
6
H
4
(t-Bu)
2
P]
2
Pd
(Pd-149)
95
2.299(3); 2.299(2)
174.7(0)
2.282(4); 2.273(4)
51
2
[Ph(t-Bu)
2
P]
2
Pd (Pd-148)
69
176.8(1)
2.285(3); 2.285(3)
52
3
(t-Bu
3
P)
2
Pd (Pd-116)
48
180.0(0)
2.276(4); 2.276(4)
53
4
(Q-Phos)
2
Pd (Pd-150)
20
180.0(0)
2.276(1); 2.276(1)
48
5
[(p-tol)
3
P]
2
Pd (Pd-141)
o
5
180.0(0)
a
After 7 h.
The choice of ligand can have a profound impact on the chemoselectivity
of certain reactions. Fu and co-workers found that in Suzuki-Miyaura
coupling, different ligands have different relative reactivity with aryl chlo-
rides versus triflates. Whereas the catalyst based on the t-Bu
3
P ligand is more
selective towards chloride substrates, the Cy
3
P-based catalyst is more se-
lective for triflate substrates.
55
The same chemoselectivity trend has been
observed using preformed (t-Bu
3
P)
2
Pd and (Cy
3
P)
2
Pd,
56
which is discussed in
some detail in Chapter 2.
Varying the ligand of the L
2
Pd(0) catalyst can also have an impact on the
chemistry of a cross-coupling reaction. For example, Lautens and co-workers
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