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facile in the case of the crotyl complexes, leading to a more ecient coupling
reaction, based on the crystal structure analysis.
112
The same range of precatalysts were subsequently evaluated in a room
temperature Suzuki-Miyaura coupling (Table 3.4). Again, the Pd-crotyl com-
plexes proved superior to the corresponding Pd-allyl precatalysts (Entries 1
versus 2and3versus 4). Notably, in the case of p-Me
2
NC
6
H
4
(t-Bu)
2
P-based
complexes, both the allyl and crotyl catalysts provided very low conversions to
the desired biaryl product (Entries 5 and 6). This demonstrates the import-
ance of matching the right ligand with the right cross-coupling reaction.
Subsequently, a reaction requiring elevated temperature was investigated.
Surprisingly, in the chosen a-arylation reaction, the reactivity of the Pd-allyl
versus the Pd-crotyl complexes was observed to be the reverse of that found
in the room temperature amination and Suzuki-Miyaura reactions. The
crotyl complexes were outperformed by their allyl counterparts Q-Phos-
Pd(allyl)Cl and [p-Me
2
NC
6
H
4
(t-Bu)
2
P]Pd(allyl)Cl (Table 3.5, Entries 1 versus 2
and 4 versus 5).
Table 3.4 Room temperature Suzuki-Miyaura cross-coupling reactions.
OMe
B(OH)
2
catalyst, KO
t
-Bu
Br
+
toluene/H
2
O, rt
45 min
MeO
Conversion (%)
a
Entry
Catalyst (0.05 mol%)
1
(dtbnp)Pd(allyl)Cl
13
2
(dtbnp)Pd(crotyl)Cl
99
3
(Q-Phos)Pd(allyl)Cl
2
100
b
4
(Q-Phos)Pd(crotyl)Cl
5
[p-Me
2
NC
6
H
4
(t-Bu)
2
P]Pd(allyl)Cl
3
6
[p-Me
2
NC
6
H
4
(t-Bu)
2
P]Pd(crotyl)Cl
7
7
(t-Bu
3
P)Pd(crotyl)Cl
100
a
Conversion determined by GC analysis; average of at least two runs.
b
85% isolated yield.
Table 3.5 a-Arylation of tetralone.
OMe
O
0.05 mol %
catalyst
O
Cl
+
NaO
t
-Bu, dioxane
100 °C
MeO
Conversion (%)
a
Entry
Catalyst
Time (h)
1
(Q-Phos)Pd(allyl)Cl
3
80
2
(Q-Phos)Pd(crotyl)Cl
3
23
100
b
3
[p-Me
2
NC
6
H
4
(t-Bu)
2
P]Pd(allyl)Cl
22
4
[p-Me
2
NC
6
H
4
(t-Bu)
2
P]Pd(allyl)Cl
3
96
5
[p-Me
2
NC
6
H
4
(t-Bu)
2
P]Pd(crotyl)Cl
3
7
a
Conversion determined by GC-MS analysis. Average of two runs.
b
91% isolated yield.
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