C. Tejel et al.
1
3
ever, this possibility is quite unlikely in our case, since 1)
the dihydride 1 is found in the solutions after the catalytic
runs even in the absence of hydrogen, 2) isolated rhodi-
(81%); H NMR (500 MHz, C
6
D
6
, 258C): d=8.33 (d, J
A
H
G
R
N
U
G
o
m+p
3
H ) and 7.12 (m, 3H; H ) (PhCOO), 8.07 (d,
H -PhB), 7.88 (m, 4H; H -Ph P ), 7.69 (m, 6H; H -Ph P , H -PhB), 7.45
2 2
t, J ACHTUNTGNERNUG( H,H)=7.2 Hz, 1H; H -PhB), 7.34 (t, J ACHTNGUERTNNUG( H,H)= J AHTCNUGTRENNUNG
J AHCTUNGTERNNUNG( H,H)=7.1 Hz, 2H;
o
o
A
o
A
3
p
3
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
um(I) complexes with the “Rh
A
T
N
T
E
N
N
(PhBP )” scaffold and labile
o
B
m+p
A
3
3
4H; H -Ph P ), 6.95 (br, 6H; H -Ph P ), 6.82 (t, J
A
H
U
G
R
N
U
G
2
2
p
B
3
m
B
p
ligands produce systematically the aldehyde decarbonilation
H -Ph
2
P ), 6.70 (t,
J
A
H
U
G
E
N
N
(H,H)=7.1 Hz , 6H; H -Ph
2
2
P , H -Ph P ), 6.64 (t,
(H,P)=11.2 Hz, 2H; CH
(H,P )=197.9, J
6 6
J ACHTUNGTRNNEUG( H,P )=8.2 Hz, 1H; Rh-H); P{ H} NMR (500 MHz, C D ,
3
m
A
2
J
A
H
U
G
R
N
U
G
2
P ), 1.79 (d,
-P ), À4.92 ppm (ddd, J
J
A
H
U
G
R
N
U
G
reaction, and 3) hydrogenation of the C=O bond requires
B
A
2
B
[16]
2
A
H
N
T
E
N
N
high pressure of hydrogen.
In summary, we disclose that a dihydridorhodium
complex [(PhBP )Rh(H) (NCMe)] is an extremely efficient
2
A
31
1
1
8.4 Hz,
58C): d=52.5 (dd, J
(P,Rh)=74, J(P,P)=20 Hz, 1P; P ); C{ H} NMR (500 MHz, C D ,
258C): d=179.8 (CO
PhCO ); elemental analysis calcd (%) for C52
.20; found: C 68.49, H 5.38.
[(PhBP )Rh(H)(OCH Py)] (4): Neat PyCHO (6.8 mL, 0.072 mmol) was
added to suspension of [(PhBP )Rh(H) (NCMe)] (1) (60 mg,
.072 mmol) in toluene (3 mL) to immediately give a yellow solution.
A
H
U
G
R
N
U
G
A
2
ACTHNGUTRENNUG( P,Rh)=123, J ACHTUNGERTNNUNG( P,P)=20 Hz, 2P; P ), 7.46 ppm (dt,
B
13
1
A
H
U
G
R
N
N
J
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
3
2
o
m
catalyst for the dimerization of both, aliphatic and aromatic,
enolizable and non-enolizable aldehydes under exceptional-
ly smooth conditions. Its outstanding activity likely results
from an operative way in which the insertion of the carbal-
dehyde group into the RhÀH bond to give an alkoxo group,
2
), 128.9 (C ), 131.7 (C ) and 128.0 ppm (C )
Rh: C 68.59, H
(
2
2 3
H47BO P
5
A
H
U
G
R
N
U
G
3
A
T
N
T
E
N
N
2
a
3
2
ACHTUNGTRENNUNG
0
and insertion of a second aldehyde into the resulting rhodi-
um alkoxide seems to be essential steps for the dismutation
of aldehydes. Most probably, the excellent effectiveness of
the lanthanide catalyst and complex 1 could be due to
common distinctive steps in spite of the divergent nature of
the metals.
This was carefully layered with pentane (12 mL) to produce pale-yellow
microcrystals in two days. The mother liquor was decanted and the solid
was washed with 2ꢆ2 mL of pentane and vacuum-dried. Yield: 50 mg
1
(
8
77%); H NMR (300 MHz, C
6
D
6
o
, 258C): d=8.44 (m, 2H; H -PhP ),
(H,H)=7.0 Hz, 2H; H -PhB), 8.15 (m, 4H; H -PhP , H -
3
.25 (d,
J
A
H
U
G
R
N
U
G
A
3
3
PhP ), 8.00 (dd, J ACHUNTGRENNUG( H,P)=11.2 Hz, J ACHTUNGTNERNUNG( H,H)=7.4 Hz, 2H; H -PhP ), 7.73
3
m
3
(t,
PhB), 7.29 (dd,
m, 6H; PhP), 6.55–6.93 (m, 16H; PhP, H and H Py), 5.86 (brd, J-
J AHCTUNRTGENNUNG( H,H)=7.5 Hz, 2H; H -PhB), 7.47 (t, J AHCTUNGTRENNUNG( H,H)=7.5 Hz, 1H; H -
3
3
J ACHUTNGRENNUG( H,P)=8.4 Hz, J ACHTUGNTRENNU(GN H,H)=7.2 Hz, 2H; H -PhP ), 7.03
3
4
(
3
A
H
U
G
R
N
U
G
2
), 5.69 (td,
J
A
H
U
G
E
N
N
(H,H)=5.9 Hz,
5
6
2
2
1
1
A
, t,
J ACHTUNGRTEN(GUNN H,P)=15.7 Hz,
Experimental Section
A
H), 1.75 (d
B
, m, J
A
H
U
G
R
N
U
G
2
-P ), 2.19 (m, 2H; CH
-P ),
-P ), À6.29 ppm
(H,P )=9.3 Hz, J(H,Rh)=
15.2 Hz, 1H; H-Rh); P{ H} NMR (300 MHz, C D , 258C): d=45.2
.96 (d , m, 1H), 1.31 (d
A
B
A
H
U
G
R
N
N
2
2
A
2
B
2
C
NMR-scale experiments: A NMR tube was charged with the catalyst,
(m, J
A
H
U
G
R
N
U
G
J
A
H
U
G
R
N
U
G
A
H
U
G
E
N
N
3
1
1
[
Rh
3 2 6 6
ACHTUNGTRENNUNG( PhBP )(H) ACHTUNGTRENNUNG( NCMe)] (1; 5.0 mg, 0.006 mmol) and dried C D
6
6
B
(
0.4 mL) under argon. For the aldehydes in Table 1, the argon atmos-
(ddd,
115 Hz, J
33 and15 Hz, P ); C{ H} NMR (300 MHz, C D , 258C): d=172.2 (C -
Py), 152.5 (C -Py), 135.5 C -Py, 119.8 (C -Py), 117.0 (C -Py), 80.9 ppm
(OCH -Py); elemental analysis calcd (%) for C H BNOP Rh: C 68.25,
J
A
H
U
G
R
N
N
A
H
U
G
R
N
N
(P,P)=42, 15 Hz, P ), 30.7 (ddd, J
C
phere was replaced by hydrogen through 3 freeze–thaw cycles and then,
dry and freshly distilled aldehyde was added (in a 100:1 mol ratio vs. cat-
alyst). The tube was introduced into the NMR probe and the mixture
A
H
U
G
R
N
U
G
A
H
U
G
E
N
N
A
13
1
6
6
6
4
5
1
31
1
was analyzed by H and P{ H} NMR spectroscopy obtaining the proton
spectrum in 2–3 min after mixing. For the aliphatic aldehydes of Table 2
no hydrogen was introduced into the NMR tube and the first proton
spectrum was obtained in about 1 min after mixing. Clean and quantita-
tive conversions to the Tishchenko esters were observed in all the cases
except for p-methoxy-benzaldehyde (55%) and for the unsaturated alde-
hydes of Table 2.
2
51 48
H 5.39, N 1.56; found: C 68.15, H 5.59, N 1.53.
Acknowledgements
Preparative-scale experiments: Only the preparation and isolation of
benzyl benzoate is reported in detail. Procedures for other aldehydes
were similar, except for acetyl acetate (see below). A solution of 1
The generous financial support from MICINN/FEDER (Project
CTQ2008-03860) and G.A. (Gobierno de Aragꢂn, Project: PM 036/2007)
is gratefully recognized. Authors also thank Dr. S. Jimꢄnez for prelimina-
ry observations and M. V. Mendoza for technical assistance. V.P. thanks
C.S.I.C. for an I3P postdoctoral contract.
(
(
9
80.0 mg, 0.096 mmol) in toluene (8 mL) was saturated with hydrogen
1 atm; freeze–thaw cycles) and then benzaldehyde (0.98 mL,
.6 mmol) was added. After stirring for 10 min the solution was analyzed
3
by GC-MS, observing the quantitative formation of benzylbenzoate. The
solution was evaporated under vacuum and the residue extracted with
hexane (2ꢆ5 mL). The extract was subjected to chromatography on a
Keywords: aldehydes · esters · homogeneous catalysis ·
hydrido ligands · rhodium · Tishchenko reaction
SiO
2
column affording a colorless solution, which was evaporated up to
dryness affording benzyl benzoate as a colorless viscous liquid. Yield
1
0
(
.83 g (81%); H NMR (500 MHz, CDCl
m, 1H), 7.55–7.38 (m, 7H), 5.45 ppm (s, 2H); C{ H} NMR (500 MHz
CDCl , 258C): d =166.4 (CO ), 136.2, 133.1, 129.8, 128.7, 128.5, 128.3,
28.3, 66.75 ppm (CH ). For ethyl acetate: after finished the catalysis,
3
, 258C): d=8.18 (m, 2H), 7.60
1
3
1
3
2
[
[
[
4] M. Haniti, S. A. Hamid, P. A. Slatford, J. M. J Williams, Adv. Synth.
Catal. 2007, 349, 1555–1575.
1
2
hexane (10 mL) was added to precipitate the catalyst and the suspension
was filtered over a silica gel column affording a colorless solution, which
was fractionally distilled to afford acetyl acetate. Yield 0.45 g (68%);
1
H NMR (500 MHz, CDCl
.94 (s, 3H), 1.16 ppm (t, J(H,H)=6.8 Hz, 3H). C{ H} NMR (500 MHz,
CDCl , 258C): d=170.8 (CO ), 60.2 (CH ), 20.8 (CH ), 14.0 ppm (CH ).
[(PhBP )Rh(H)(O CPh)] (3): Solid PhCO H (12.2 mg, 0.10 mmol) was
3
, 258C): d=4.02 (q, J ACHTUNGTENRNUG( H,H)=6.8 Hz, 2H),
[
1
3
1
1
ACHTUNGTRENNUNG
3
2
2
3
3
[
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
2
2
added to a solution of 1 (83.1 mg, 0.10 mmol) in toluene (5 mL). After
stirring for 15 min, the solution was evaporated to ca. 3 mL, layered with
hexane (15 mL), and left to stand for two days. The white-off solid that
precipitated was washed with hexane and vacuum-dried. Yield: 73.7 mg
94
ꢅ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 91 – 95