Ru-η6-benzene-phosphine complex-catalyzed transfer hydrogenation of ketones

Article abstract of DOI:10.1002/aoc.1818

Three Ru-η⁶-benzene-phosphine complexes bearing tri-(p-methoxyphenyl)phosphine, triphenylphosphine and tri-(p- trifluoromethylphenyl)phosphine were synthesized and characterized by ³¹P{¹H} NMR, ¹H NMR, ¹³C{ ¹H} NMR and elemental analyses. Complex 1 was further identified by X-ray crystallography. These complexes exhibit good to excellent activities for the transfer hydrogenation of ketones in refluxing 2-propanol, and the highest turnover frequency (TOF) is up to 5940 h^-1. The effect of electronic factors of these complexes on the transfer hydrogenation of ketones reveals that the catalytic activity is promoted by electron-donating phosphine and the catalyst stability is improved by electron-withdrawing phosphine.

Full text of DOI:10.1002/aoc.1818

Full Paper
Received: 16 March 2011
Revised: 19 May 2011
Accepted: 30 May 2011
Published online in Wiley Online Library: 8 July 2011
(wileyonlinelibrary.com) DOI 10.1002/aoc.1818
6
Ru–η -benzene–phosphine complex-catalyzed
transfer hydrogenation of ketones
Lei Wang, Qin Yang, Hai-Yan Fu, Hua Chen, Mao-Lin Yuan and Rui-Xiang Li
∗
6
Three Ru–η -benzene–phosphine complexes bearing tri-(p-methoxyphenyl)phosphine, triphenylphosphine and tri-(p-
trifluoromethylphenyl)phosphine were synthesized and characterized by 31P{ H} NMR, H NMR, C{ H} NMR and elemental
1
1
13
1
analyses. Complex 1 was further identified by X-ray crystallography. These complexes exhibit good to excellent activities for the
−
1
transferhydrogenationofketonesinrefluxing2-propanol,andthehighestturnoverfrequency(TOF)isupto5940 h .Theeffect
of electronic factors of these complexes on the transfer hydrogenation of ketones reveals that the catalytic activity is promoted
Jb oy h enl eWc ti rl eo yn -&d So on na st i, nL gt dp .hosphine and the catalyst stability is improved by electron-withdrawing phosphine. Copyright ꢀc 2011
Supporting information may be found in the online version of this article.
Keywords: ruthenium; complex; phosphine; transfer hydrogenation; ketone
Introduction
and found that all of them were highly efficient for transfer
hydrogenation of ketones.
The reduction of carbonyl compounds is an important reaction
in organic synthesis from both academic and industrial points
of view.[
1,2]
Compared with the common reduction processes
Results and Discussion
which involve high hydrogen pressure or hazardous reducing
reagents, the transfer hydrogenation is safe, highly selective
Synthesis and Characterization of Complexes 1–3
and ecofriendly.[
3–5]
The catalysts for this reaction are often
6
Ru(II) complexes, especially half-sandwich Ru complexes [(η -
The complexes were easily prepared by treating methanol
C
ꢁ[6]
(where A–B is an optically pure chiral
arene)Ru(A–B)X]
X
6
solution of [(η -benzene)RuCl2]2 with MOTPP, TPP and TFTPP,
bidentate ligand and X is a halide). For example, Noyori et al.
respectively (Scheme 1). After reaction mixtures were stirred at
room temperature for 24 h, these products were isolated as
6
originally found that [(η -arene)Ru(TsDPEN)Cl] [TsDPEN D N-(p-
tolylsulfonyl)-1,2-diphenylethylenediamine] offered high activity
and selectivity owing to the presence of N–H functionality.[
Following this pioneering work, a great variety of related ligands
and Ru complexes have been developed for this purpose.[12,13]
Compounds such as the half-sandwich arene–Ru(II) complexes
1
31
orange-red crystals in yields of 65–75%. H and P NMR of
7–11]
[26]
complex2wereconsistentwiththereportedresults. Complexes
1
and 3, as the novel complexes, were identified with elemental
1
13
31
analyses as well as H, C and P NMR characterizations. For
complex1,asingletat19.48 ppmin PNMRrevealedtheexistence
of phosphine. The two singlets of H NMR at 3.75 and 5.33 ppm
31
[
14]
bearing iminophosphorane–phosphine,
phinobenzaldehyde,
2-diphenylphos-
1
[
15]
[16]
rigid diphosphine,
N3, N3 -bis(diphenylphosphino)-2,2 -bipyridine-3,3 -
N3, N3 -di-2-hydroxybenzylidene-[2,2 ]bipyridinyl-
bispyrazoly-
were attributed to the protons of methoxy in MOTPP and the
coordinatedbenzene,respectively.Theintegrationratioofprotons
in methoxy to those in coordinated benzene and phosphine was
lazines,[
17]
0
0
0
[
18]
0
0
diamine,
0
[19]
[20]
[20]
3
,3 -diamine,
phosphinite,
aminophosphine,
bis(phosphino)amine,
BINOL-derived diphosphonites
13
1
9
: 6 : 12. Furthermore, Cf Hg NMR and the elemental analyses
[
21]
[22]
2
[23]
and k -P,N
results suggested that each complex 1 molecule contained one
benzene ring, two chlorine anions and one MOTPP. Similarly, the
structure of complex 3, which was similar to complex 1, was
confirmed by Pf Hg NMR, H NMR, Cf Hg NMR and elemental
ligands have been successfully used for transfer hydrogenation
of ketones. Although these complexes are quite effective, the
synthetic procedures of their ligands are complicated. Therefore,
there is still a strong need to develop simple and efficient catalysts
in this area. To the best of our knowledge, a little attention
is paid to arene–Ru(II) complexes with monophosphine,[24,25]
and there is no report on the effect of the electronic factors
on transfer hydrogenation of ketones. In this paper, we syn-
31
1
1
13
1
analyses.
Ł
Correspondence to: Rui-Xiang Li, Key Laboratory of Green Chemistry and
6
Technology, Ministry of Education, College of Chemistry, Sichuan University,
Chengdu, Sichuan 610064, People’s Republic of China.
E-mail: liruixiang@scu.edu.cn
thesized three simple [RuCl2(η -benzene)(monophosphine)]
6
complexes, [RuCl2(η -benzene)MOTPP] (1) [MOTPP D tri-(p-
6
methoxyphenyl)phosphine], [RuCl2(η -benzene)TPP] (2) (TPP D
6
triphenylphosphine) and [RuCl2(η -benzene)TFTPP] (3) [TFTPP
Key Laboratory of Green Chemistry and Technology, Ministry of Education,
College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, People’s
Republic of China
D
tri-(p-trifluoromethylphenyl)phosphine], investigated their
catalytic performance for transfer hydrogenation of ketones,
Appl. Organometal. Chem. 2011, 25, 626–631
Copyright ꢀc 2011 John Wiley & Sons, Ltd.

6
Ru–η -benzene–phosphine complex-catalyzed transfer hydrogenation
6
Scheme 1. Synthesis of (η -benzene)-Ru(II) complexes containing MOTPP, TPP, TFTPP.
Table 1. Crystal and results of structure refinement for complex 1
Formula
C27H27Cl2O3PRu
Formula weight (g mol 1
ꢁ
)
602.43
Temperature (K)
113(2)
Wavelength (Å)
0.71073
Crystal system, space group
Unit cell dimensions (Å, deg)
Orthorhombic, Pna21
a D 22.172(5) α D 90
b D 7.8577(17) β D 90
c D 14.422(3) γ D 90
2512.7(10)
Cell volume (Å3)
Z/calculated density
4/1.592
ꢁ
3
(
g cm
)
Absorption coefficient
0.928
ꢁ
1
(
mm
)
F(000)
1224
Crystal size (mm)
0.16 ð 0.14 ð 0.08
1.84–27.88
θ range for data collection
(
deg)
Limiting indices
ꢁ25 ꢂ h ꢂ 29, ꢁ10 ꢂ k ꢂ 9,
ꢁ
18 ꢂ l ꢂ 18
Reflections collected/unique
Completeness to θ D 27.88Ž
Absorption correction
20346/5898 (Rint D 0.0325)
99.7%
Semi-empirical from
equivalents
Maxamum and minimum
transmission
0.9294 and 0.8657
Refinement method
Full-matrix least-squares on
F
2
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
5898/1/310
0.960
Figure 1. ORTEP representation (ellipsoids at a 50% level) and labeling for
complex 1.
R1 D 0.0233, wR2 D 0.0481
R1 D 0.0267, wR2 D 0.0490
ꢁ0.025(17)
Absolute structure
parameter
elemental analyses. The single crystal X-ray diffraction studies
of complex 2 were reported by Tocher.[ In order to compare
complex 1 with complex 2, we compiled the selection of bond
distances for complexes 1 and 2 in Table 2. In both structures, the
geometry around the Ru center is pseudo-octahedral with one
27]
Largest difference peak and
0.480 and ꢁ0.570
ꢁ1
hole (e Å
)
6
η -benzene, one phosphine and two chloride atoms. Although
X-ray Diffraction
the coordinated benzene rings in complexes 1 and 2 are almost
planar, there is a significant difference in the Ru–C bond distances.
Ru(1)–C(5)[2.229(2) Å]andRu(1)–C(1)[2.221(3) Å]bonddistances
for complex 1 are significantly longer than Ru(1)–C(3) [2.193(2) Å]
and Ru(1)–C(2) [2.170(2) Å]. Similarly, the Ru–C(1) [2.228(3) Å]
The structure of complex 1 was further determined by X-ray
crystallography. Its crystal data and structure refinement results
are presented in Table 1. The ORTEP diagram is shown in Fig. 1.
The crystal structure is consistent with the results of NMR and
Appl. Organometal. Chem. 2011, 25, 626–631
Copyright ꢀc 2011 John Wiley & Sons, Ltd.
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L. Wang et al.
Table 2. Selected bond lengths (Å) for complex 1 and 2
4
6
3
6
2
5
3
5
2
1
4
1
Ru
OCH3
Ru
1Cl
P
Cl
P
2
Cl
1Cl
2
OCH3
OCH3
complex 1
complex 2
Complex 1
Complex 2
Ru(1)–P(1)
Ru(1)–Cl(1)
Ru(1)–Cl(2)
Ru(1)–C(1)
Ru(1)–C(2)
Ru(1)–C(3)
Ru(1)–C(4)
Ru(1)–C(5)
Ru(1)–C(6)
2.3536(7)
2.4136(8)
2.4052(6)
2.221(3)
2.170(2)
2.193(2)
2.196(2)
2.229(2)
2.212(3)
Ru–P
2.3637(12)
2.406(2)
2.4118(10)
2.228(3)
2.193(3)
2.201(3)
2.172(3)
2.203(3)
2.214(3)
Ru–Cl(1)
Ru–Cl(2)
Ru–C(1)
Ru–C(2)
Ru–C(3)
Ru–C(4)
Ru–C(5)
Ru–C(6)
simpler, although their catalytic activities are relatively lower than
Table 3. Transfer hydrogenation of acetophenone with 2-propanol
catalyzed by complexes 1–3
the zwitterionic Ru complex.[ Half-sandwich Ru(II) complexes
23]
a
are unstable in the process of transfer hydrogenation,[
18,20]
so the
b
ꢁ1
)
Entry
Complex
Time (min)
Yield (%)
TOF (h
relationship between the yield of phenylethanol and reaction time
was investigated with complexes 1–3 as catalysts and the results
areillustratedinFig. 2. Ontheonehand, onlymoderateyieldswere
obtained by complexes 1–3, although the reaction time was pro-
longed from 2 to 4 h. It was not clear whether the moderate yields
resultedfromtheequilibriumorthelossofcatalystactivity.Inorder
to understand this point, we introduced an additional 3 ml of iso-
propanol into the reaction mixture after complex 1 catalyzed the
transfer hydrogenation of acetophenone for 20 min. However, the
yield of phenylethanol did not increase. This suggested that these
complexes gave moderate yields even at longer reaction times,
owing to the loss of the catalyst activities. On the other hand, the
catalytic activity of complex 1 sharply declined after the reaction
progressed for 10 min, although its initial activity was the highest.
For complex 2, the obvious activity decrease was postponed to
30 min. Furthermore, the obvious activity decrease in complex 3
occurred after 1 h. Therefore, the stability order of the catalytic
species is complex 1 < 2 < 3. In other words, the stability of the
active species in this system is improved by electron-withdrawing
phosphine. Although complex 3 bearing electron-withdrawing
phosphine showed a relatively good stability and complex 1 bear-
ing electron-donating phosphine gave the highly catalytic activity,
their turnover number (TON) were almost the same. Regarding
1
2
3
1
2
3
10
10
10
91
88
71
2730
2640
2130
a
Reaction condition: acetophenone–i-PrOK–catalyst D 500 : 15 : 1.
Acetophenone,2.5 mmol;i-PrOK,75 µmol;catalyst,5 µmol;2-propanol,
Ž
3
ml; 0.1 MPa, 82 C.
GC yield of the alcohol product.
b
and Ru–C(6) [2.214(3) Å] bond distances for complex 2 are also
longer than the Ru–C(2) [2.193(3) Å] and Ru–C(4) [2.172(3) Å].
These distortions could be attributed to the steric constraints and
the stronger trans influence of electron-rich MOTPP than TPP.
According to bond distances in Table 2, we also found that the
Ru(1)–P(1) [2.3536(7) Å] bond distance in complex 1 is shorter
than the Ru–P [2.3637(12) Å] bond distance in complex 2 because
MOTPP has a stronger electron-donation than TPP.
Catalytic Transfer Hydrogenation of Ketones
The performances of complex 1–3 in the transfer hydrogenation
were investigated with acetophenone as a model substrate and
theresultsareshowninTable 3. Whenthereactionsprogressedfor
the coordinated benzene easily slipping from η to η4 mode
6
in the process of the transfer hydrogenation,[
16,28]
we suggest
1
1
0 min, the conversions of acetophenone catalyzed by complexes
–3 were up to 91, 88 and 71%, respectively. This indicated that
that the electron-donating phosphine, which has stronger trans
influence than electron-withdrawing phosphine, causes quick dis-
sociation of the coordinated benzene and subsequently results in
the deactivation of the catalyst.
As complex 1 was the most active precursor, the reductions
of a variety of ketones were carried out with complex 1 and the
results are shown in Table 4. The complex exhibited excellent
catalytic activities for the transfer hydrogenation of substituted
complexes 1–3 are quite effective catalysts for transfer hydro-
genation of acetophenone and their catalytic activities are pro-
moted by electron-donating phosphine. Their activities are much
higher than the analogous complex [RuCl2(p-cymene)PPh3][
as well as the half-sandwich Ru(II) complexes bearing bidentate
ligands.[
25]
14–22]
The synthetic method of complexes 1–3 is much
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Copyright ꢀc 2011 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2011, 25, 626–631

6
Ru–η -benzene–phosphine complex-catalyzed transfer hydrogenation
Figure 2. The yield of phenylethanol vs reaction time for complexes 1–3. Reaction conditions: acetophenone–i-PrOK–catalyst D 2000 : 15 : 1.
Ž
Acetophenone, 10 mmol; i-PrOK, 75 µmol; catalyst, 5 µmol; 2-propanol, 3 ml; 0.1 MPa, 82 C. GC yield of the alcohol product.
[
29]
acetophenones (entries 1–10). For 2-chloroacetophenone, a con-
version of 98% was achieved within 10 min (entry 1) and
TOF was up to 2940 h . Similarly, it was quite efficient for
the transfer hydrogenation of 1-acetylnaphthalene (entry 16).
Owing to the auxiliary coordination of ortho-position group, 2-
chloroacetophenone reacted much more quickly than the 3- and
Metals, China) were used as received. Other materials – MOTPP,
TFTPP[
30]
and [RuCl2(η -C6H6)]2
6
[31]
– were prepared with the
ꢁ
1
1
13
1
31
1
reported methods. H, Cf Hg and Pf Hg NMR spectra of
all complexes were recorded on Brucker Avance II 400 MHz
3
1
1
spectrometer. The chemical shifts of Pf Hg NMR were relative
1
to 85% H PO as external standard, and H NMR relative to
3
4
4
-positionanalogs(entries1–3).Incontrast,4-methacetophenone
d-tetramethylsilane (TMS) as internal standard with downfield
shifts as positive. Elemental analyses were performed using a
Carlo Erba 1106. The hydrogenation products were analyzed using
a GC Agilent 6890N equipped with an FID detector and EC-WAX
capillary column (30 m ð 0.25 mm, 0.25 µm film).
reacted more quickly than the 2- and 3-position substituted
analogs as the methyl in 2-position does not have auxiliary
coordination ability (entries 4–6). These results are better than
the half-sandwich complexes reported recently.
more, complex 1 was also highly efficient for the transfer
[
14–22]
Further-
hydrogenation of alkyl ketones and cyclic alkyl ketones (entries
Catalyst Preparation
1
2–15). For 3-heptanone, the activity of complex 1 is much
6
[21]
6
higher than [C6H4-1,3-(OPPh2fRu(η -p-cymene)Cl2g)2],
which
Preparation of [RuCl (η -C H )(MOTPP)] (1)
2
6 6
gave 34% yield with a loading of 1 mol % for 10 h. To our delight,
cyclohexanone was quantitatively reduced to its corresponding
alcohol within 5 min and the catalyst gave the highest TOF value
6
A mixture of [RuCl2(η -C6H6)]2 (0.100 g, 0.20 mmol) and MOTPP
0.155 g, 0.44 mmol) in 50 ml methanol was stirred at room
(
ꢁ
1
temperature for 24 h. The solid substances were slowly dissolved
and the color of solution changed to orange-red. At the end of
the reaction, a trace amount of insoluble substance was removed
by filtering. The filtrate was concentrated to about 5 ml and put
in a refrigerator overnight to form some red crystals. The product
was filtered, washed with diethyl ether twice, and dried under
of 5940 h (entry 14). This result is much higher than those for
ꢁ
1
[24]
6
1
[
RuCl2(p-cymene)PPh3] (TOF D 1135 h ), [Ru(η -arene)Cl2fk -
6 2
P-Ph2PCH2P( N-p-C5F4N)Ph2g] and [Ru(η -arene)Clfk -P,N-
[
14]
Ph2PCH2P( N-p-C5F4N)Ph2g][SbF6] (>99%yieldobtainedwith
6
a loading of 0.4 mol% for 24 h) and [(η -1,3,5-Me3C6H3)Ru(P-
P)Cl]CF3SO3[16] (92%yieldobtainedwith0.5 mol%for4 h).Interest-
6
vacuum to give [RuCl2(η -C6H6)(MOTPP)] as red crystals (0.173 g,
ingly, complex 1 was also efficient for the transfer hydrogenation
of pyridyl ketones (entries 19–21). Probably the competing co-
ordination between the N-donor atom and the carbonyl group
in substrate with Ru(II) metal center caused the decrease in the
catalyst activity.
3
1
1
1
7
2% yield). Pf Hg NMR (161.98 MHz, CDCl3): δ (ppm) 19.48 (s). H
NMR (400.1 MHz, CDCl3): δ (ppm) 3.75 (s, 9H, -OCH3); 5.33 (s, 6H,
C6H6); 6.81–6.84 (m, 6H, CH of -C6H4OCH3); 7.56–7.61 (m, 6H, CH
1
3
1
of -C6H4OCH3). Cf Hg NMR (100.6 MHz, CDCl3): δ (ppm) 55.27 (s,
OCH3); 89.00 (s, C6H6); 113.71 (d, J D 11.1 Hz, CH of -C6H4OCH3);
-
1
24.84 (d, J D 52.3 Hz, P-C of -C6H4OCH3); 135.64 (d, J D 11.1 Hz,
Experimental Section
CH of -C6H4OCH3); 161.10 (s, C–O of -C6H4OCH3). Anal. calc. for
C27H27Cl2O3PRu (%): C, 53.83; H, 4.52. Found: C, 53.76; H, 4.49.
General Consideration
Unless otherwise noted, all of the starting materials were
commerciallyavailableandwereusedwithoutfurtherpurification.
The catalytic reactions were carried out under a nitrogen
6
Preparation of [RuCl2(η -C6H6)(TPP)] (2)
With a similar procedures to that for complex 1, complex 2 was
obtained as red crystals (0.133 g, 65% yield) by reacting [RuCl2(η -
C6H6)]2 (0.100 g,0.20 mmol)withTPP(0.115 g,0.44 mmol). Pf Hg
6
atmosphere. All the solvents were dried prior to use. Reagent-
ž
31
1
grade PPh3 (Aldrich) and RuCl xH2O (Institute of Kunming Noble
3
Appl. Organometal. Chem. 2011, 25, 626–631
Copyright ꢀc 2011 John Wiley & Sons, Ltd.
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L. Wang et al.
Table 4. (Continued)
Table 4. Transfer hydrogenation of ketones with i-propanol cat-
alyzed by complex 1
a
Entry
13
Ketone
S/C
500
Time
1 h
Yieldb (%) TOFc (hꢁ1)
b
c
ꢁ1
93(77)
2310
Entry
1
Ketone
S/C
Time
Yield (%) TOF (h )
2940d
O
500 10 min
98
O
14
500
5 min
99
5940d
O
Cl
O
1
5
6
500 10 min
500 12 min
94
2820d
2610
O
2
500
1 h
90(78)
2340
1
O
96(87)
Cl
3
4
5
500
500
500
1.5 h
90(81)
91(64)
93(40)
2430
1920
1200
O
1
7
100
2 h
90(24)
144
O
Cl
1 h
18
200
100
5 h
9 h
91(62)
53(3)
744
18
O
O
CH3
O
1
9
0
1
O
5 h
N
2
200
100
7 h
2 h
97(21)
96(23)
252
138
O
O
CH3
N
N
6
O
500
3 h
90(80)
2400
2
CH3
7
8
200 10 min
96
1152d
1560
O
a
Reactionconditions:i-PrOK–catalystD15: 1;i-PrOK,75 µmol;catalyst,
Ž
5
µmol; 2-propanol, 3 ml; 0.1 MPa, 82 C.
b
GC yield of the alcohol product. Data in parentheses are the GC yields
Br
O
after 10 min.
c
TOF after 10 min.
Final TOF.
500
300
4 h
91(52)
d
1
NMR (161.98 MHz CDCl3): δ (ppm) 23.33 (s). H NMR (400.1 MHz,
CDCl3): δ (ppm) 5.40 (s, 6H, C6H6); 7.37–7.44 (m, 9H, CH of -C6H5);
Br
9
2 h
97(69)
98(71)
1242
2130
13
1
O
7
(
(
.73–7.77 (m, 6H, CH of -C6H5). Cf Hg NMR (100.6 MHz, CDCl3): δ
ppm) 89.21 (s, C6H6); 128.20 (d, J D 10.1 Hz, CH of -C6H5); 130.55
s, CH of -C6H5); 133.18 (d, J D 46.3 Hz, P–C of -C6H5); 134.19 (d,
Br
J D 10.1 Hz, CH of -C H ).
6
5
10
500 30 min
O
6
Preparation of [RuCl2(η -C6H6)(TFTPP)] (3)
Complex 3 was obtained as orange crystals (0.215 g, 75% yield)
by reacting [RuCl2(η -C6H6)]2 (0.100 g, 0.20 mmol) with TFTPP
OCH3
6
3
1
1
1
1
2
500
8 h
93(39)
94
1170
(0.205 g, 0.44 mmol). Pf Hg NMR (161.98 MHz, CDCl ): δ (ppm)
O
3
1
2
7
7.33 (s). H NMR (400.1 MHz, CDCl3): δ (ppm) 5.49 (s, 6H, C6H6);
.69 (d, J D 8.0 Hz, 6H, CH of -C6H4CF3); 7.90 (t, J D 8.0 Hz, 6H, CH
Et
1
3
1
of -C6H4CF3). Cf Hg NMR (100.6 MHz, CDCl3): δ (ppm) 89.72 (s,
C H ); 125.43 (d, J D 10.1 Hz, CH of -C H CF ); 128.32 (s, C–CF of
1
500 10 min
2820d
O
6
6
6
4
3
3
-
C6H4CF3); 133.06 (q, J D 30.2 Hz, -CF3); 134.54 (d, J D 10.1 Hz, CH
of -C6H4CF3); 136.48 (d, J = 45.3 Hz, P-C of -C6H4CF3). Anal. calcd
for C27H18Cl2F9PRu (%): C, 45.26; H, 2.53. Found: C, 44.96; H, 2.57.
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6
Ru–η -benzene–phosphine complex-catalyzed transfer hydrogenation
General Procedure for the Transfer Hydrogenation of Ketones
[2] G. W. Kabalka, R. S. Verma, in Comprehensive Organic Synthesis, vol.
(Eds.: B. M. Trost, I. Flemings), Pergamon Press: Oxford, 1991, 363.
[3] G. Zassinovich, G. Mestroni, S. Gladiali, Chem. Rev. 1992, 92, 1051.
[4] R. Noyori, S. Hashiguchi, Acc. Chem. Res. 1997, 30, 97.
8
Under a nitrogen atmosphere, the mixture of a ketone substrate
(
2.5 mmol), catalyst (5.0 µmol) and 2-propanol (2 ml) was intro-
Ž
[5] M. J. Palmer, M. Wills, Tetrahedron: Asymm. 1999, 10, 2045.
duced into a Schlenk tube. The solution was stirred at 82 C
[
6] T. Ohkuma, M. Koizumi, H. Doucer, T. Pham, M. Kozawa, K. Murata,
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1
998, 120, 13529.
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analysis.
1
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Single crystal X-ray diffraction studies for complex 1 were
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parameters were obtained by global refinement of the positions of
all collected reflections. Intensities were corrected for Lorentz and
polarization effects and empirical absorption. The structure was
solved by direct methods and refined by full-matrix least-squares
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2
on F . Structure solution and refinement were performed with the
SHELXL-97 package.
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Conclusions
6
The synthesis and characterization of Ru–η -benzene complexes
2
009, 694, 2488.
bearing MOTPP, TPP and TFTPP were described. The transfer
hydrogenation results indicated that they are highly efficient
catalysts for many substrates. Complex 1, bearing the electron-
donating group phosphine, gives a higher activity than the others,
but its stability in the catalytic reaction is lower.
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Acknowledgments
[
[
2
004, 2450.
We acknowledge the financial support from the National Natural
Science Foundation of China (nos 20271035 and 20371032).
25] G. A. Carriedo, P. Crochet, F. J. G. Alonso, J. Gimeno, A. Presa-Soto,
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Supporting information
Supporting information can be found in the online version of this
article. CCDC-810484 (for complex 1) contains the supplementary
crystallographic data for this paper. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data request/cif
1
990, 112, 8931.
[
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Appl. Organometal. Chem. 2011, 25, 626–631
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