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775
Table 2
Table 4
Cross-coupling reaction of alkyl halides and tosylates with alkyl Grignard reagents
using Ni- and Pd-containing perovskite
Ni in solution of LFNO catalyzed coupling reactions
Reaction time
0.5 h
5
1 h
7
2 h
5
4 h
8
5 h
Entry
Alkyl-X
R-MgX
Yielda (%)
Ni-perovskite Pd-perovskite
Ni concentration in solution (ppm)
8
Conditions: octyl bromide (1 mmol), nBuMgCl (1.3 mmol, 1.94 M in THF, 0.67 mL),
LFNO (10 mg; 0.8 mol %, 0.46 mg Ni), rt.
1
nOct-I
nBu-MgCl
78
73
2
3
nBu-MgCl
82
87
77
80
Br
nNon-Br
nOct-MgCl
4
5
6
7
8
9
nBu-MgCl
Et-MgBr
76
76
71
70
3
65
70
69
74
1
OTs
0.45 lm syringe filter after 1 h of stirring gave a pale yellow trans-
nOct-OTs
nOct-OTs
Et-OTs
parent solution (right), which was stirred continuously and ana-
lyzed by GC. The yields of the coupling product are shown by the
solid line along with the results obtained by similar reactions
without filtration (dotted line). It is interesting that the transparent
filtrate contains the catalytic species and showed similar perfor-
mance to the original dark suspension, indicating that coupling
proceeds in the liquid phase rather than on the bulk solid surface.
However, this is not surprising since similar results have been
reported by the Ley group.2 It is still unclear if the active catalytic
species is a single metal complex as proposed in the reaction using
Ni salts4 or small nano-particles.
In order to determine how much Ni is present in solution we
filtered the reaction mixture after stirring a mixture of LFNO, octyl
bromide, butyl Grignard reagent, and 1,3-butadiene in THF at rt
for 0.5, 1, 2, 4, and 5 h and analyzed the filtrate by ICP-AES
after quenching with water. The concentration of Ni in the liquid
phase of the resulting mixture after filtration at each stage of the
reaction is listed in Table 4, indicating that Ni in solution reached
ca. 5 ppm, corresponding to 6 Â 10À8 mmol, within 30 min
followed by a gradual increase up to 8 ppm (9 Â 10À8 mmol) over
5 h.9
These results may be explained simply by assuming an equilib-
rium between Ni in solution and Ni in perovskite, and the cross-
coupling is catalyzed in a homogeneous fashion by a complex in
solution. If so, TON of Ni in solution is calculated to be in the order
of 107. Leaching of Ni is rapid (within 30 min) but stops at low con-
centrations probably due to the presence of the reverse process.
Table 4 shows that only 1/100000 of total Ni in the bulk perovskite
(8 Â 10À3 mmol) moved into the liquid phase enabling the reuse of
the perovskite.
nBu-MgCl
nOct-MgCl
nBu-MgCl
nBu-MgCl
nOct-Cl
nOct-F
2
2
Conditions: alkyl halides or tosylate (1 mmol), catalyst (1 mol % LFPO or 0.8 mol %
LFNO), nBuMgCl (1.3 equiv); in case of LFNO, 1,3-butadiene (50 mol %), rt, 5 h. in
case of LFPO, isoprene (1.3 equiv), rt. 13 h.
a
Determined by GC.
We then checked the feasibility of recovery and reuse of the cat-
alyst by utilizing the coupling of nonyl bromide and nBuMgCl.7 It
was found that the recovery of catalysts can be achieved without
compromising the operational simplicity of the procedure, and
three catalytic runs were performed successively only by repeating
removal of the solution phase by syringe, rinsing the remaining
solids, and recharging the reagents to the reaction vessel, without
observing any appreciable loss of catalytic activity in both LFNO
and LFPO cases (Table 3).
In order to shed light on whether this reaction takes place in a
heterogeneous or homogeneous fashion, that is, on the surface of
the bulk solid catalyst or on a metal complex in the liquid phase
of the suspension, we checked the time course of the LFNO cata-
lyzed reactions carried out separately with or without filtration
( Fig. 1). Filtration of the dark black suspension (left) with
Table 3
Recycling experiments
n
n
n
n
Non- Bu
Bu-MgCl
Non-Br
+
In summary, it was demonstrated that the Ni- and Pd-contain-
ing perovskites, LaFe0.8Ni0.2O3 (LFNO) and LaFe0.95Pd0.05O3 (LFPO),
can be used as useful catalyst sources for the cross-coupling of al-
kyl halides or tosylates with Grignard reagents in the presence of
dienes. LFNO showed slightly higher reactivity than LFPO. The
present coupling reaction is catalyzed by trace amounts of Ni or
Pd in solution leached from perovskites employed with very high
TON (ca. 107). It was also proved that the remaining bulk perovsk-
ites could be reused. According to Ley’s report,2 coupling of aryl
halides with boronic acids catalyzed by palladium containing per-
ovskites is effective only in protic solvents at elevated tempera-
tures in the presence of a base. Our system works efficiently in
aprotic solvent and enables alkyl–alkyl cross coupling using Grig-
nard reagents.
1.3 equiv
Run
Yield (%)
Ni-perovskite
Pd-perovskite
1
2
3
91
90
86
78
78
75
Conditions: LFNO (0.8 mol %), 1,3-butadiene (50 mol %), rt, 5 h or LFPO (1 mol %),
isoprene (1.3 equiv), rt, 13 h.
Acknowledgments
S.P.S. expresses his sincere thanks to the Global Education and
Research Center for Bio-Environmental Chemistry at Osaka Univer-
sity for the financial support. Authors also thank Hokko Chemical
Co. LTD for the donation of perovskite catalysts.
References and notes
Figure 1. Time course of the LFNO catalyzed cross coupling of nOct-Br with
nBuMgCl at rt with (dashed line, average of two separate runs) or without (solid
line) removal of solids by filtration.8
1. (a) Misono, M. Catal. Today 2009, 144, 285–291; (b) Li, W. B.; Wang, J. X.; Gong,
H. Catal. Today 2009, 148, 81–87; (c) Zhu, J.; Thomas, A. Appl. Catal., B Environ.
2009, 92, 225–233; (d) Tsipis, E. V.; Kharton, V. V. J. Solid State Electrochem. 2008,