Enantioselective hydride transfer hydrogenation of ketones catalyzed by [(η6-p-cymene)Ru(amino acidato)Cl] and [(η6-p-cymene)Ru(amino acidato)]3(BF4)3 complexes

Article abstract of DOI:10.1016/S0022-328X(99)00433-7

The new complexes (R_RuS_C, S_RuS_C)-[(η⁶-pCym)Ru(L-Aze)Cl] (6a, b), (R_RuS_C, S_RuS_C)-[(η⁶-pCym)Ru(L-Pip)Cl] (7a, b), (R_RuR_RuR_RuS_CS_CS_CS_NS_NS_N, S_RuS_RuS_RuS_CS_CS_CS_NS_NS_N)-[{(η⁶-pCym)Ru(L-Aze)}₃](BF₄)₃ (8a, b) and (R_RuR_RuR_RuS_CS_CS_CS_NS_NS_N, S_RuS_RuS_RuS_CS_CS_CS_NS_NS_N)-[{(η⁶-pCym)Ru(L-Pip)}₃](BF₄)₃ (9a, b) (L-Aze=L-2-azetidinecarboxylate, L-Pip=L-2-piperidinecarboxylate) were prepared, characterized and used, together with the known [{(η⁶-pCym)Ru(L-Pro)}₃](BF₄)₃, 5 and [{(η⁶-pCym)Ru(L-Ala)}₃](BF₄)₃, 10 (L-Pro=L-prolinate, L-Ala=L-alaninate), in hydride transfer reduction of acetophenone, a series of substituted acetophenones and several other ketones with moderate to high conversions and enantioselectivities up to 86% e.e.

Full text of DOI:10.1016/S0022-328X(99)00433-7

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 593–594 (2000) 299–306
Enantioselective hydride transfer hydrogenation of ketones
catalyzed by [(h6-p-cymene)Ru(amino acidato)Cl] and
[(h6-p-cymene)Ru(amino acidato)]3(BF4)3 complexes
a
b
c
c
´
Agnes Katho´ , Daniel Carmona , Fernando Viguri , Carlos D. Remacha ,
Jo´zsef Kova´cs d, Ferenc Joo´ a,d,*, Luis A. Oro b
a Institute of Physical Chemistry, L. Kossuth Uni6ersity, Debrecen 10, PO Box 7, H-4010, Hungary
b Departamento de Qu´ımica Inorga´nica, Instituto de Ciencia de Materiales de Arago´n, Uni6ersidad de Zaragoza-C.S.I.C,
E-50009 Zaragoza, Spain
c Departamento de Qu´ımica Inorga´nica, Escuela Uni6ersitaria de Ingenier´ıa Te´cnica Industrial, Instituto de Ciencia de Materiales de Arago´n,
Uni6ersidad de Zaragoza-C.S.I.C, Corona de Arago´n 35, E-50009 Zaragoza, Spain
d Hungarian Academy of Sciences, Research Group of Homogeneous Catalysis, Debrecen 10, PO Box 7, H-4010, Hungary
Received 10 June 1999; accepted 27 July 1999
Dedicated to Professor Fausto Calderazzo on the occasion of his 70th birthday.
Abstract
The new complexes (RRuSC, SRuSC)-[(h6-pCym)Ru(
L
-Aze)Cl] (6a, b), (RRuSC, SRuSC)-[(h6-pCym)Ru(
-Aze)}3](BF4)3 (8a, b) and (RRuRRuRRuSCSCSC-
-Aze= -2-azetidinecarboxylate, -Pip= -2-pipe-
-Pro)}3](BF4)3, 5 and
L-Pip)Cl] (7a, b),
(RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(h6-pCym)Ru(
SNSNSN, SRuSRuSRuSCSCSCSNSNSN)-[{(h6-pCym)Ru(
-Pip)}3](BF4)3 (9a, b) (
ridinecarboxylate) were prepared, characterized and used, together with the known [{(h6-pCym)Ru(
[{(h6-pCym)Ru(
-Ala)}3](BF4)3, 10 ( -Pro= -prolinate, -Ala= -alaninate), in hydride transfer reduction of acetophenone, a
L
L
L
L
L
L
L
L
L
L
L
L
series of substituted acetophenones and several other ketones with moderate to high conversions and enantioselectivities up to
86% e.e. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Amino acids; Asymmetric catalysis; Hydrogenation; Ketones; Ruthenium
characterization of monomeric [Cp*M(Aa)Cl] (M=
Rh, Ir) and [(h6-pCym)Ru(Aa)Cl] (pCym=4-iso-
propyltoluene, p-cymene) complexes [8,9], we have
recently shown that the cationic fragments [(h-
ring)M(Aa)]+ undergo facile trimerization upon Cl−
removal with Ag+ to afford the complexes [{(h-
ring)M(Aa)}3](BF4)3 [13]. Based on NMR and X-ray
diffraction data, it could be established, that in the
observed trimers the three metal centers all had the
same configuration, that is only two of the possible
four diastereomers were formed. As an example, with
an (S)-aminoacidate ligand only the SMSMSMSCSCSC
(s) or the RMRMRMSCSCSC (r) isomers were obtained
indicating that trimerization took place with a high
degree of self-recognition. However, in solution a
fairly fast diastereomerization of the r and s isomers
were observed.
1. Introduction
Transition metal complexes having the (h-ring)M
fragment show many interesting properties with re-
gard to both their co-ordination and structural chem-
istry as well as to their catalytic properties [1–5].
Some of these compounds are soluble in water and
display examples of aqueous organometallic chemistry
[6–12]. For example, [Cp*Rh(H2O)3]2+ (Cp*=h5-
pentamethylcyclopentadienyl) reacts with an array of
potential ligands, such as nucleobases, nucleotides,
amino acids etc. [12]. Following the preparation and
* Corresponding author. Tel.: +36-52-512900; fax: +36-52-512-
915.
E-mail addresses: dcarmona@posta.unizar.es (D. Carmona),
jooferenc@tigris.klte.hu (F. Joo´)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00433-7

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A. Katho´ et al. / Journal of Organometallic Chemistry 593–594 (2000) 299–306
300
Enantioselective reduction of prochiral ketones is a
pCym)Ru(
with -2-azetidinecarboxylic acid [(S)-(−)-azetidinecar-
boxylic acid, -Aze] and -2-piperidinecarboxylic acid
[(S)-(−)-2-piperidinecarboxylic acid, -Pip] as ligands
and their catalytic properties are discussed here, too.
Some results of the catalytic studies were already dis-
closed as a poster presentation [29].
L- or D-proline)Cl] catalyst were prepared
synthetically most valuable reaction [14] and several
catalysts and procedures have been developed such as
catalytic hydrogenation [15–17], hydrogen transfer
[1,18–21] or hydrosilylation, followed by cleavage of
the resulting silyl ether [22]. Especially notable are the
results of Noyori, Ikariya et al. who introduced the use
of chiral diamines and their derivatives (e.g. tosyl
amides) as chiral inductor ligands in various Ru-com-
plexes [1,23,24]. This highly successful approach made
possible the enantioselective hydrogenation and hydro-
gen transfer reduction of a wide array of prochiral
ketones with yields and e.e.-s close to 100% in many
cases under mild conditions. In particular, and relevant
to this study, it was shown that [(h6-pCym)-
Ru{(1S, 2S)-TsDPEN}Cl] (1; (1S, 2S)-TsDPEN=
(1S, 2S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenedi-
L
L
L
L
2. Results and discussion
2.1. Preparation of (RRuSC, SRuSC)-[(p6-pCym)Ru-
(
(
L
- Aze ) Cl ] (6a, b), (RRuSC, SRuSC ) - [ ( p6 - pCym)Ru-
L
-Pip)Cl] (7a, b), (RRuRRuRRuSCSCSCSNSNSN, SRu
-Aze)}3](BF4)3
(8a, b) and (RRuRRuRRuSCSCSCSNSNSN, SRuSRuSRuSC-
SCSCSNSNSN)-[{(p6-pCym)Ru(
-Pip)}3](BF4)3 (9a, b)
-
SRuSRuSCSCSCSNSNSN)-[{(p6-pCym)Ru(
L
L
amine) afforded
a
stable 16
e
complex, [(h6-
pCym)Ru{(1S, 2S)-TsDPENH−1}] (2) upon H+ ab-
straction from the primary amino nitrogen by base
(KOH) and concomitant Cl− loss; this further reacted
smoothly with 2-propanol to yield an 18 e hydride,
[(h6-pCym)RuH{(1S, 2S)-TsDPEN}] (3). All three
complexes were fully characterized by single crystal
X-ray diffraction. Hydride 3 is an active and highly
enantioselective catalyst of hydrogen transfer from 2-
propanol to various ketones without the need of addi-
tional base. Analogous isolobal Rh- and Ir-complexes
with Cp* as spectator ligand have been prepared by
Murata, Ikariya and Noyori [25] and by Mashima, Abe
and Tani [26,27]; these showed comparable selectivity
but somewhat less activity in the hydrogen transfer
reduction of ketones as their Ru-based analogs.
Since the best catalytic performance in our studies
was observed [13,29] with catalyst 4a, b containing
proline as a ligand of a rigid carbon skeleton, we
prepared the analogous compounds 6 and 7 with
L-Aze
and -Pip similarly (the general formulae are shown on
L
Scheme 1). The new complexes were synthesized ac-
cording to the general route described in Ref. [13], by
replacement of the acetylacetonato ligand in [(h6-
pCym)Ru(acac)Cl]. Compounds 6 and 7 were obtained
in the isomeric ratio 6a:6b=78:22 and 7a:7b=63:37.
Chloride is easily removed from these neutral chloro
complexes with Ag+ and the resulting cations undergo
trimerization to afford mixture of only two
diastereomers, in 8a:8b=75:25 and 9a:9b=90:10 ra-
tios. According to these data, compounds 6–9 resemble
the analogous Ru-complexes with various other amino
acids in that their solids contain a mixture of the r and
s isomers, in contrast to the [(h5-Cp*)Rh(Aa)] and
[(h5-Cp*)Ir(Aa)] derivatives [13], which in the solid
form were exclusively obtained as a single diastereomer.
Although it was not investigated in detail, diastereoiso-
merization of the trimers may also take place in solu-
tions with polar solvents, similar to analogous
[{(h6-pCym)Ru(Aa)}3]3+ complexes [13].
Recently we have communicated part of our results
on the catalytic activity of the trimeric [{(h-
ring)M(Aa)}3](BF4)3 and the monomeric [(h-ring)M-
(Aa)Cl] complexes in carbonyl-selective reduction of
unsaturated aldehydes and in the enantioselective re-
duction of prochiral ketones with H-transfer from 2-
propanol [13]. Among the several Ru-, Rh- and
Ir-containing catalysts, [(h6-pCym)Ru(
L- or D-pro-
line)Cl] (4a, b) and the corresponding trimers (5a, b)
gave the best combination of rate and selectivity, exem-
plified by a turnover frequency of TOF=146 h−1 and
71% e.e. in reduction of acetophenone in refluxing
2-propanol with 4. Obviously, amino acids are attrac-
tive, cheap and available ligands in catalysts inducing
chirality in reductions of prochiral substrates, such as
ketones. Such an approach, aimed mainly at synthetic
application has been recently described by Furukawa et
al. [28]. Here we present our further studies undertaken
to establish the scope of the reaction and get a deeper
insight into the reaction mechanism. To this end,
analogous compounds to the most successful [(h6-
2.2. Protic equilibria in aqueous solution
In aqueous solutions [(h6-pCym)Ru(Aa)Cl] and
[{(h6-pCym)Ru(Aa)}3]3+ complexes solvolyze to give
the [(h6-pCym)Ru(Aa)(H2O)]+ aquo species. pH-static
titrations, similar to those described in Ref. [30] indi-
cated proton dissociation processes in basic solutions of
these complexes. Using standard methods of coordina-
tion chemistry (see Section 4), we made pH-potentio-
metric titrations of [(h6-pCym)Ru(
[{(h6-pCym)Ru(
-Ala)}3](BF4)3, 10. In the 3BpHB11
range the titration curves could be well fitted with the
L
-Pro)Cl], 4 and
L

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A. Katho´ et al. / Journal of Organometallic Chemistry 593–594 (2000) 299–306
301
Scheme 1. (A) Schematic representation of the cation of the trimer 5. (B)
L-2-Azetidine carboxylic acid. (C)
L
-Proline. (D)
L-2 Piperidine
carboxylic acid.
assumption of only one protonation/deprotonation
process. The acidity constants were calculated as
pKa=8.6290.06 (4) and pKa=8.4990.04 (10). By
comparison to known p-arene-aqua complexes of
ruthenium(II) [31], e.g. to [(h6-pCym)Ru(bipy)(H2O)]+
having a pKa=7.290.1, this process can be ascribed
to the deprotonation of coordinated water:
2.3. Catalytic acti6ity
2.3.1. Hydrogen transfer from 2-propanol
Complexes of the general formula
[(h6-
pCym)Ru(Aa)Cl] or [{(h6-pCym)Ru(Aa)}3](BF4)3 are
active catalysts for the reduction of ketones by hydride
transfer from 2-propanol (Scheme 2), and in case of
prochiral substrates the reaction takes place with high
enantioselectivity. However, it deserves attention that
the observed e.e.-s never exceeded 90%. After starting
the reaction the enantioselectivity increased sharply
with increasing conversion, then leveled off or de-
creased slightly with high conversions at high substrate/
catalyst loadings [13]. Although the catalysts with
open-chain aminoacidato ligands usually show high
activity, the highest enantioselectivity was observed
[(h6−pCym)Ru(Aa)(H2O)]+
X [(h6−pCym)Ru(Aa)(OH)]+H+
(1)
A very important conclusion from these measure-
ments on proton dissociation is that in aqueous
solutions, under ambient conditions show no sign
of proton dissociation from the coordinated amine
functionality, not even at fairly high pH. This is in
contrast to what had been observed by Noyori et
al. in non-aqueous solutions and what is regarded
as a prerequisite of a high activity in hydrogen trans-
fer from 2-propanol [24]. In fact, the solutions
remained yellow throughout the titrations up to
the upper limit of the investigated pH-range, while
both the amine-deprotonated complex (2) and the hy-
dride derived from it (3) are red, as well as the cata-
lytically active solutions (in 2-propanol) of our
complexes.
with complexes of L-proline, and this was attributed to
its having a relatively bulky and rigid ring structure.
Scheme 2.

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A. Katho´ et al. / Journal of Organometallic Chemistry 593–594 (2000) 299–306
302
Table 1
Reduction of acetophenone by hydrogen transfer from 2-propanol catalyzed by 5, 8, 9 and 10 a
No.
Catalyst
t (h)
TON
e.e. (%) (configuration)
T (°C)
Remark ([catalyst]/[base]/[substrate])
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
5
5
5
5
5
5
5
5
8
8
9
9
9
10
10
10
48
1
1
1
1
1
1
1
1
1.5
0.5
1
48
1
6
20
97
78 (R)
80 (R)
75 (R)
74 (R)
69 (R)
67 (R)
70 (R)
68 (R)
55 (R)
66 (R)
60 (S)
69 (S)
76 (S)
6 (R)
21
50
83
83
83
83
83
83
83
50
83
50
21
83
83
83
A
A
A
48
(1/1/50)
(1/1/200)
(1/1/1000)
B
A, P
A
A
A
A
A
A
A, P
B
168
380
154
94
70
10
97
62
40
38
1
1
13
92
6 (R)
13 (R)
a For general conditions and for the pretreatment of the catalyst see Section 4. A, [catalyst]/[base]/[substrate]=1/1/100; B, [catalyst]/[base]/[sub-
strate]=1/2/214, P, pretreatment of the catalyst; TON, mol reacted substrate/mol catalyst.
The same complexes proved to be almost completely
inactive for the hydrogenation of ketones in aqueous/or-
ganic biphasic systems under mild conditions. There-
fore we have undertaken a detailed study of some of the
known (5, 10) and the new (8, 9) complexes with regard
to the scope and mechanism of catalysis by these
compounds. The basic findings are contained in Tables
1–3. Because of the varying [substrate]/[catalyst] ratios,
the absolute turnover numbers (TON) and not the
conversions (%) are used to characterize the extent of
the reaction.
Reduction of acetophenone, several substituted ace-
tophenones and other ketones can be accomplished
with all the catalysts investigated, showing good rates
and enantioselectivities up to 86% e.e. In general,
trimers 8 and 9 show comparable reactivity to 5, i.e. the
ring size does not exert a dramatic influence on this
catalytic property, although data of Tables 1–3 show a
8B5B9 order of reactivity towards the same sub-
strate. Strikingly, this similarity does not hold for the
enantioselectivity: 5 and 8 both catalyze the formation
of alcohols with (R)-configuration, conversely, reac-
tions with 9 as catalyst produce the (S)-alcohols. At the
moment we do not have the clue to this intriguing
observation. It is also noted, that while the catalytic
activity of 9 is close to that of 5 with all substrates, its
enantioselectivity is usually less, and in some cases even
large differences can be observed (e.g. Table 3, no. 7
and 12). In comparison to 5, 8 and 9, complex 10,
having the more flexible alaninate ligand, proved to be
a generally more active but much less enantioselective
catalyst for ketone reduction.
The reaction is applicable to a large number of
different ketonic substrates as shown by Tables 1–3.
Acetophenone and its substituted derivatives usually
show good reactivity, except 2-hydroxy-acetophenone
which is totally unreactive. Interestingly, propiophe-
none is also slow to react, however its 3- and 4-chloro-
derivatives can be easily reduced. Where applicable,
comparison of the reactivities and the Hammett sub-
Scheme 3.

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A. Katho´ et al. / Journal of Organometallic Chemistry 593–594 (2000) 299–306
303
Table 2
Reduction of substituted acetophenones by hydrogen transfer from 2-propanol catalyzed by 5, 8, 9 and 10 a
No.
Substituent
4-Methyl-
Catalyst
TON
e.e. (%) (configuration)
Remark
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
5
5
5
5
8
77
104
42
61 (R)
60 (R)
62 (R)
66 (R)
51 (R)
54 (S)
68 (S)
6 (R)
1 (R)
45 (R)
13 (S)
55 (R)
56 (R)
54 (R)
44 (R)
50 (R)
44 (S)
68 (S)
2 (R)
1 (R)
50 (R)
8 (R)
–
A
B
A, P
A
A
A
A
A, P
B
B
B
A, P
A
B
A
A
A
A
A, P
B
15 b,c
75b
91
9
9
62 b,c
13
10
10
5
10
5
5
5
8
8
94
64
84
95
4-Methoxy-
4-Chloro-
93
118
99
13 c,d
99
9
9
62 b,c
5
10
10
5
10
5
55
4-Bromo-
141
139
0
B
B
B
B
2-Hydroxy-
10
0
–
a For general conditions and for the pretreatment of the catalyst see Section 4. A, [catalyst]/[base]/[substrate]=1/1/100; B, [catalyst]/[base]/[sub-
strate]=1/2/214; P, pretreatment of the catalyst; TON, mol reacted substrate/mol catalyst.
b Reaction time, 1.5 h; temperature, 83°C.
c Reaction time, 1 h; temperature, 50°C.
d Reaction time, 2 h; temperature, 83°C.
stituent constants (|) indicates a general trend of in-
creasing rates with increasing | (Table 2, no. 2, 9:
−0.170; no. 10, 11: −0.268; no. 14, 20: 0.227, no.
21, 22: 0.232; Table 3, no. 3, 4: 0.227, no. 5, 6:
0.373), although no quantitative linear free energy re-
lationship can be established based on this limited set
of data. 3-Methyl-2-cyclohexene-1-one was reduced
with an almost complete selectivity towards the CꢀO
function and the product contained only a few per-
cent of cis/trans-3-methylcyclohexanol (Table 3). On
the other hand, benzalacetone reacted almost exclu-
sively as an olefin (Scheme 3); accordingly, in sepa-
rate experiments both methyl-benzyl-ketone and
methyl-phenethyl-ketone showed only moderate/low
reactivity (TON 12 and 26 (with 5), 15 and 69 (with
10), respectively).
Reaction rates increase sharply with the tempera-
ture in case of all catalysts. As an example, in the
hydrogenation of acetophenone with 5, only six
turnovers could be realized in 48 h at 21°C (turnover
frequency, TOF=0.125 h−1), while the TON rose to
97 in 1 h (=TOF) at 83°C (see also Table 1, no.
11–13). The reaction rate is also a function of the
substrate concentration and seems to level off at high
[substrate]/[catalyst] ratios (see e.g. Table 1, no. 3–6).
On the other hand, the enantioselecti6ity of a given
catalyst is only slightly dependent on the same
parameters. It is generally observed, that the slower
reactions at lower temperatures result in a higher op-
tical yield, and the faster reactions at higher substrate
concentrations are somewhat less selective. However,
both effects are manifested only in a range of a few
percent e.e. (e.g. Table 1, no. 4–6, Table 2 no. 1, 4,
15, 16). It seems, that the enantioselectivity provided
by catalyst 9 is somewhat more sensitive to the tem-
perature that with 5, 8 and 10 (see e.g. Table 1, no.
11–13, Table 2, no. 6–7, no. 17–18).
In related systems, Lemaire et al. [32,33] and de
Bellefon et al. [34] studied the transfer hydrogenation
of acetophenone catalyzed by p-areneꢁRh complexes
with chiral chelating diamine ligands using 2-propanol
as H-donor. It is suggested that at high substrate
concentrations the primary product of the catalytic
cycle, (R)-1-phenylethanol, while still coordinated to
Rh, serves as an H-donor for reduction of another
molecule of acetophenone. This could account for the
lower e.e.-s at high substrate concentrations and for
the increase of e.e. with increasing conversion [32] —

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304
Table 3
Reduction of various ketones by hydrogen transfer from 2-propanol catalyzed by 5, 8, 9 and 10 a
No. Substrate
Catalyst
t (h)
TON e.e. (%) (configuration)
Remark ([catalyst]/[base]/[substrate])
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Propiophenone
5
10
5
10
5
10
5
5
5
8
9
9
1
1
1
1
1
1
2
2
1
2
2
2
2
24
2
2
4
6
n.d.
n.d.
54 (R)
7 (R)
52 (R)
5 (R)
74 (R)
86 (R)
84 (R)
74 (R)
24 (S)
16 (S)
65 (R)
63 (R)
51 (R)
50 (S)
B
B
B
B
B
B
A
A, P
(1/1/50)
A
(1/1/50)
A
A
A
A
A
4-Chloro-propiophenone
3-Chloro-propiophenone
1-Indanone
103
145
135
195
60
8
24
30
35
31
17
29
10
23
3-Methyl-2-cyclohexene-1-one b
5
5
8
9
a For general conditions and for the pretreatment of the catalyst see Section 4. All reactions at 83°C. A, [catalyst]/[base]/[substrate]=1/1/100;
B, [catalyst]/[base]/[substrate]=1/2/214; P, pretreatment of the catalyst; TON, mol reacted substrate/mol catalyst; n.d., not determined.
b Reactions 13–16: conversions shown for the major product, 3-methyl-2-cyclohexene-1-ol. Minor product: cis/trans-3-methyl-cyclohexanol
(51%).
same features as found with our catalysts [13]. An
important assumption here is in that 1-phenylethanol
can be enantioselectively dehydrogenated by the same
catalyst in the presence of a suitable hydrogen accep-
tor (kinetic resolution). In fact, under conditions com-
parable to those of ketone reductions, with 5 as
catalyst and acetone as the hydrogen acceptor we ob-
served a slow dehydrogenation (TON=9 in 3.3 h) of
racemic 1-phenylethanol, however, with no sign of ki-
netic resolution.
3. Conclusions
The title complexes with chiral aminoacidate ligands,
such as prolinate, azetidine carboxylate, piperidine car-
boxylate and alaninate are useful catalysts for the enan-
tioselective reduction of prochiral ketones by hydride
transfer from 2-propanol. However, the same com-
plexes show poor hydrogenation activity for reduction
of ketones and olefinic substrates in aqueous solution.
The catalytically active species in ketone reductions in
2-propanol may be similar to the hydride 3, character-
ized by Noyori et al. [24], the formation of which
requires deprotonation of a coordinated amine group
of the ligand. However, according to the results of our
pH-metric measurements on 4 and 10 (together with the
lack of characteristic spectral changes), in the potentio-
metrically accessible pH range (511) in aqueous solu-
tions there is no such deprotonation in the
[(h6-pCym)Ru(Aa)Cl] complexes or in the correspond-
ing trimeric or solvolyzed derivatives. This may well
account for the observed lack of catalytic activity in
aqueous solutions.
2.3.2. Hydrogenation experiments
Complexes 4, 5 and 10 showed low activity in hy-
drogenation of acetophenone or substituted acetophe-
nones in organic solvents or in aqueous/organic
biphasic systems. The best result [22% conversion to
(R)-1-phenylethanol, e.e. 8%] was achieved in hydro-
genation of acetophenone with 10 in methanolic solu-
tion (0.43 mmol substrate, 0.01 mmol catalyst, 0.02
mmol base, 2 ml MeOH, 15 bar H2, room tempera-
ture, 20 h). Aqueous solutions of 4 and 10 under H2
pressure at catalytic conditions did not show the
characteristic color change to red, displayed by active
catalyst solutions in 2-propanol. Accordingly, no or
negligible conversions of acetophenone or water solu-
ble olefins (maleic, fumaric and itaconic acid) were
detected in aqueous systems under various reaction
conditions (up to 15 bar H2, 3BpHB9, 20–60°C).
Interestingly, there was a slow hydrogenation of
[HCO3]− to [HCO2]− in 0.2 M NaHCO3 solution (2
mM 10, 10 bar H2, 55°C; HPLC detection, TOF=
0.1 h−1).
4. Experimental
4.1. General
Infrared spectra were recorded on Perkin-Elmer 783,
Paragon 1000PC and 1330 spectrophotometers (range
4000–200 cm−1
)
using Nujol mulls between
polyethylene sheets or dichloromethane solutions be-
tween NaCl plates. Carbon, hydrogen, and nitrogen

´
A. Katho´ et al. / Journal of Organometallic Chemistry 593–594 (2000) 299–306
305
analyses were performed using a Perkin-Elmer 240B
microanalyzer. NMR data were recorded on a Varian
UNITY 300 spectrometer operating at 299.95 (1H) and
75.4 (13C) MHz and on a Bruker AM360 instrument.
Chemical shifts are expressed in ppm upfield from
SiMe4. Coupling constants J are given in hertz. CD
spectra were determined in 0.1 or 1 cm path length cell
by using a Jasco-710 apparatus, at concentrations ca.
5×10−4 M. Gas chromatographic measurements were
made on a Hewlett Packard 5890A equipment. The
amino acids, acetophenone, substituted acetophenones
and citral were purchased from Aldrich, cinnamalde-
hyde from Schuchardt and were used as received.
Reagent grade 2-propanol was purified with standard
methods. Other chemicals were highest grade commer-
cial products of Aldrich.
(1H, sp, CH (i-Pr)), 3.5 (1H, m, C*H), 5.42, 5.5 (2H,
AB system, J(HAHB)=6.1), 5.5, 5.62 (2H, AB system,
J(HAHB)= 5.9); 7b l 1.28, 1.30 (6H, 2×d, 2Me
(i-Pr)), 2.10 (3H, s, Me), 5.5, 5.69 (2H, AB system), 5.5,
5.70 (2H, AB system).
4.3. Preparation of the complexes [{(p6-pCym)Ru-
(Aa)}3](BF4)3 (8, 9)
An equimolar amount of AgBF4 was added to a 0.05
M solution of the corresponding [(h6-pCym)Ru(Aa)Cl]
compound in methanol (20 cm3). The mixture was
stirred for 1 h in the absence of light and the precipi-
tated AgCl was filtered off. The resulting solution was
concentrated at reduced pressure to about 2 cm3. Addi-
tion of diethylether completed the precipitation of yel-
low solids which were filtered off, washed with
diethylether, and vacuum dried. The compounds crys-
tallize with three water molecules.
4.2. Preparation of the chloride compounds [(p6-
pCym)Ru(Aa)Cl] (6, 7)
Complex 8: Yield 70%, (8a:8b molar ratio, 75:25).
Anal. Found: C, 38.6; H, 4.7; N, 3.4%. Anal. Calc.: C,
38.2; H, 5.0; N, 3.2%. C42H66N3B3F12O9Ru3. IR(Nujol):
To a solution of the acetylacetonate compound [(h6-
pCym)Ru(acac)Cl] (acac=acetylacetonate) (1.0 mmol)
in methanol (20 cm3) the appropriate amino acid (Aa)
(1.0 mmol) was added. The resulting solution was
stirred for 24 h and then filtered through Kieselguhr to
eliminate any solid residue. The solvent was then re-
moved in vacuum to leave a solid residue. Then it was
redissolved in a minimum amount of methanol and the
orange products were precipitated by addition of di-
ethylether. The solids were filtered off, washed with
diethylether and vacuum dried. They crystallize with
one molecule of water.
6(CO) 1580(vs); 6(NH) 3280(m); 6(OH) 3620(m) cm−1
.
CD spectrum (5×10−4 mol l−1, acetone) [q]l values of
maxima, minima and nodes (u, nm); +30000 (410), 0
(340), −5000 (325), 0 (315), +1000 (310), 0 (300),
1
−2000 (280), 0 (260) H-NMR (CD3)2CO, 20°C): 8a l
1.38 (3H, d, 3J(HH)=6.8, Me (i-Pr)), 1.39 (3H, d,
3J(HH)=7.1, Me (i-Pr)), 2.50 (3H, s, Me), 2.4, 2.84
(2H, m, CH2), 2.91 (1H, sp, CH (i-Pr)), 3.88 (1H, m,
C*H), 4.39, 4.58 (2H, m, CH2N), 5.89 (1H, m, NH),
5.89, 6.18 (2H, AB system, J(HAHB)=6.0), 6.08, 6.16
(2H, AB system, J(HAHB)=6.0); 8b l 1.31, 1.33 (6H,
2×d, 2 Me (i-Pr)), 1.20 (3H, d, Me(i-Pr), 7.6 (1H, m,
NH).
Complex 6: Yield 80%, (6a:6b molar ratio, 78:22).
Anal. Found: C, 44.0; H, 5.3; N, 4.0%. Anal. Calc.: C,
43.3; H, 5.7; N, 3.6%. C14H22NClO3Ru. IR (Nujol):
6(CO) 1620(vs); 6(NH) 3200(m); 3510(m) cm−1. CD
spectrum (5×10−4 mol l−1, methanol) [q]l values of
maxima, minima and nodes (u, nm); +0.15 (410), 0
(390), −0.3 (360), −0.25(340), −0.35 (320), −0.5
Complex 9: Yield 91%, (9a:9b molar ratio, 90:10).
Anal. Found: C, 41.3; H, 5.1; N, 3.2%. Anal. Calc.: C,
41.1; H, 5.6; N, 3.0%. C48H78N3B3F12O9Ru3. IR (Nu-
jol): 6(CO) 1580(vs); 6(NH) 3210(m); 6(OH) 3620(m)
cm−1. CD spectrum (5×10−4 mol l−1, methanol) [q]l
values of maxima, minima and nodes (u, nm); 36500
(410), 0 (320), −2000 (305), 0 (0), −100 (280), 0 (270),
+4000(240). 1H-NMR (CD3)2CO, 20°C): 9a l 1.28
(3H, d, 3J(HH)=6.9, Me (i-Pr)), 1.30 (3H, d,
3J(HH)=6.8, Me (i-Pr)), 1.6–2.0 (5H, m, CH2), 2.40
(1H, m, CH2N), 2.45 (3H, s, Me), 2.8 (2H, m, CH(i-Pr),
1
(290), −1 (230). H-NMR (CD3OD, 20°C): 6a l 1.25
(3H, d, 3J(HH)=6.9, Me (i-Pr)), 1.26 (3H, d,
3J(HH)=6.8, Me (i-Pr)), 2.21 (3H, s, Me), 2.2–2.3
(2H, m, CH2), 2.8 (1H, m, CH (i-Pr)), 2.8, 3.92 (2H,
2×m, CH2N), 4.08 (1H, m, C*H), 4.37 (1H, m, NH),
5.44, 5.66 (2H, AB system, J(HAHB)=5.9), 5.51, 5.61
(2H, AB system, J(HAHB)=5.6); 6b l 1.18, 1.20 (6H,
3
3
2×d, J(HH)=7.1, 2Me (i-Pr)), 2.11 (3H, s, Me).
CH2N), 3.95 (1H, d, J(HH)=11.6), C*H), 5.86, 6.02
Complex 7: Yield 94%, (7a:7b molar ratio, 63:37).
Anal. Found: C, 45.7; H, 6.2; N, 3.3%. Anal. Calc.: C,
46.1; H, 6.2; N, 3.4%. C16H26NClO3Ru. IR(Nujol):
6(CO) 1600(vs); 6(NH) 3160(m); 3520(m) cm−1. CD
spectrum (5×10−4 mol l−1, methanol) [q]l values of
maxima, minima and nodes (u, nm); +0.3 (410), 0
(380), −0.3 (360), 0 (330), +0.1 (310), 0 (290), −0.4
(2H, AB system, J(HAHB)=5.4), 6.0, 6.32 (2H, AB
system, J(HAHB)=6.0); 9b l 2.5 (3H, s, Me), 4.2 (1H,
d, C*H).
4.4. Transfer hydrogenation experiments, standard
reaction conditions
1
(230). H-NMR (CD3OD, 20°C): 7a l 1.29, 1.30 (6H,
Catalyst (0.01 mmol), HCOONa (0.02 mmol); as 100
ml 0.2 M aqueous solution, 2-propanol (10 ml), ace-
3
2×d, J(HH)=6.8, 2Me (i-Pr)), 2.13 (3H, s, Me), 3.5

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Acknowledgements
We thank the financial support provided by the
Direccio´n General de Investigacio´n Cientifica y Te´c-
nica, Spain (Grant PB96/0845) and the National Scien-
tific Research Foundation (OTKA) of Hungary (Grant
T029934). F. Joo´ is grateful to Iberdrola S.A. for a
visiting professorship at the University of Zaragoza in
1995/1996 during which this research was initiated. The
valuable experimental contribution of Ms Ma´ria Sa´gi
and the skilful technical assistance of Ms Ildiko´ Varga
are gratefully acknowledged.
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