The role of functionalized phosphines in the hydrogenation of carboxylic acids in the presence of phosphine substituted hydrido ruthenium complexes

Article abstract of DOI:10.1016/S0022-328X(99)00038-8

Hydrido ruthenium carbonyl complexes substituted by functionalized phosphines such as H₄Ru₄(CO)₈[P(CH₂OCOR) ₃]₄ have been synthesized and tested as catalysts in the hydrogenation of carboxylic acids. These complexes are more active than those reported previously, containing trialkyl- or triarylphosphines. On the basis of their behavior, their different activity has been explained in terms of an involvement of the phosphine ligand in the catalytic cycle. The ester group present in the phosphine P(CH₂OCOR)₃ is hydrogenated to produce an alcohol (RCH₂OH) and a P(CH₂OH) group which, in turn, reacts with the free acid present in solution to restore the P(CH₂OCOR) group. This hypothesis has been confirmed by the reactivity of the possible intermediate H₄Ru₄(CO)₈[P(CH₂OH) ₃]₄ with acetic acid. Another support to this statement is the almost equal catalytic activity, displayed by H₄Ru₄(CO)₈[P(CH₂OCOR) ₃]₄ complexes, whatever the R group present, in the phosphine ligand, in the hydrogenation of carboxylic acids. These complexes, on the other hand, are less active than the corresponding tributylphosphine substituted ones in the hydrogenation of alkenes and ketones. Finally when the phosphine ligand is P(CH₂CH₂COOCH₃)₃ the ester group is not reduced and consequently the catalytic activity of this complex in the hydrogenation of carboxylic acids is very low.

Full text of DOI:10.1016/S0022-328X(99)00038-8

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 582 (1999) 218–228
The role of functionalized phosphines in the hydrogenation of
carboxylic acids in the presence of phosphine substituted hydrido
ruthenium complexes
Antonella Salvini, Piero Frediani, Mario Bianchi, Franco Piacenti *, Leonardo Pistolesi,
Luca Rosi
Dipartimento di Chimica Organica della Uni6ersit a` di Firenze, 6ia Gino Capponi, 9, I-50121 Firenze, Italy
Received 7 September 1998; received in revised form 6 January 1999
Abstract
Hydrido ruthenium carbonyl complexes substituted by functionalized phosphines such as H Ru (CO) [P(CH OCOR) ] have
4
4
8
2
3 4
been synthesized and tested as catalysts in the hydrogenation of carboxylic acids. These complexes are more active than those
reported previously, containing trialkyl- or triarylphosphines. On the basis of their behavior, their different activity has been
explained in terms of an involvement of the phosphine ligand in the catalytic cycle. The ester group present in the phosphine
P(CH OCOR) is hydrogenated to produce an alcohol (RCH OH) and a P(CH OH) group which, in turn, reacts with the free
2
3
2
2
acid present in solution to restore the P(CH OCOR) group. This hypothesis has been confirmed by the reactivity of the possible
2
intermediate H Ru (CO) [P(CH OH) ] with acetic acid. Another support to this statement is the almost equal catalytic activity,
4
4
8
2
3 4
displayed by H Ru (CO) [P(CH OCOR) ] complexes, whatever the R group present, in the phosphine ligand, in the hydrogena-
4
4
8
2
3 4
tion of carboxylic acids. These complexes, on the other hand, are less active than the corresponding tributylphosphine substituted
ones in the hydrogenation of alkenes and ketones. Finally when the phosphine ligand is P(CH CH COOCH ) the ester group is
2
2
3 3
not reduced and consequently the catalytic activity of this complex in the hydrogenation of carboxylic acids is very low. © 1999
Elsevier Science S.A. All rights reserved.
Keywords: Carboxylic acids; Functionalized phosphines; Catalytic activity; Hydrogenation
docarbonyl ruthenium clusters substituted with
functionalized phosphines H Ru (CO) [P(CH OC-
1. Introduction
4
4
8
2
The hydrogenation of free carboxylic acids in homo-
OR)
(CH
3
]
)
4
[R=CH
C–(4), (S)–C
3
–(1),
C
2
H
5
–(2), (CH
3
)
2
CH–(3),
geneous phase was first achieved using ruthenium com-
plexes such as H Ru (CO) [(−)-DIOP] and
H Ru (CO) [P(CH CH CH CH ) ] [1]. Several investi-
3
3
H
2
5
CH(CH )–(5)]. These com-
3
plexes are potential catalysts for the homogeneous hy-
drogenation of unsaturated organic compounds. The
eventual presence of chiral carbon atoms in the alkyl
substituent of the phosphine (i.e. 5) might lead to
stereoselective hydrogenations.
The acyl groups in the phosphinic ligand of 1–5 react
with hydrogen at moderate temperatures (100–130°C)
with formation of the corresponding alcohol and free
hydroxy groups in the phosphine ligand (Scheme 1) [3].
The free hydroxy groups present in the phosphine
may act as new activation sites for carboxylic acids
4
4
8
2
4
4
8
2
2
2
3 3
gations on this catalytic reaction have been made in
order to elucidate its mechanism [2].
The influence of the phosphine ligand on the catalytic
activity of the ruthenium complex in this reaction is
certainly relevant. We have thought interesting to inves-
tigate the role played by the phosphine if it contains a
functional group.
We have described recently [3] the synthesis, charac-
terization and the reaction with hydrogen of hydri-
(
Scheme 2) in addition to the one operative in the
complexes containing trialkylphosphines such as
P(CH CH CH CH ) [1,2a].
*
Corresponding author. Tel.: +39-055-2757648; fax: +39-055-
2
0
757660.
2
2
2
3 3
022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00038-8

A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
219
[
Ru (CO) (CH COO) ] and P(CH OCOCH ) in
2 4 3 2 n 2 3 3
toluene were refluxed for 10 h. By crystallization from
methanol at −20°C yellow needles were obtained.
3
1
Only one singlet at 8.7 ppm is present in the P-
NMR spectrum, attributable to two magnetically
Scheme 1.
1
equivalent phosphine ligands. In the H-NMR spec-
trum a singlet at 1.85 ppm is attributable to the methyl
proton of the acetato ligand in agreement with the
1
H-NMR spectrum of analogous tributylphosphino
Scheme 2.
Scheme 3.
complex [4,5]. The other resonances in the spectrum
may be attributed to the P(CH OCOCH ) ligand: 2.07
2
3 3
(
s, 18H, CH COOCH ), 4.78 (s, 12H, CH O) ppm. In
3 2 2
13
the C-NMR spectrum the singlet at 23.0 ppm and the
triplet at 187.0 (JCP=9.0 Hz) ppm are attributable to
the carbon atom of the methyl group and to the carbon
atom of the carboxylato group of the acetato ligand, in
keeping with the C-NMR spectrum of the analogous
tributylphosphino complex [6]. The other resonances in
the spectrum may be attributed as follows: signals at
20.3 (s, CH COOCH ), 56.3 (t, CH , JCP=10.4 Hz)
13
Scheme 4.
This hypothesis has been checked by testing the
3
2
2
catalytic activity of complexes 1–5 in the hydrogena-
and 170.1 (s, PCH COO) are attributable to the
2
tion of simple monocarboxylic acids (CH COOH,
P(CH OCOCH ) ligand and the triplet at 203.8 (JCP=
3
2
3 3
CH CH COOH, CH CH CH(CH )COOH, CH CH -
4.5 Hz) ppm, in agreement with the spectroscopic data
of the analogous tributylphosphino complex [6], is as-
signed to carbonyl ligands.
3
2
3
2
3
3
2
CH CH COOH) and comparing the results obtained
2
2
with those provided by the corresponding P(CH2-
CH CH CH ) substituted complex, H Ru (CO) [P-
−
1
The IR spectrum, in the range 2200–1500 cm
,
2
2
3 3
4
4
8
(
CH CH CH CH ) ] (6).
The catalytic activity of analogous ruthenium com-
shows absorptions at 2032 (vs), 1987 (m), 1961 (vs)
2
2
2
3 3 4
−
−
1
1
cm
cm
due to terminal carbonyls, a band at 1757 (s)
attributable to the ester groups and a band at
plexes containing functionalized phosphines having a
different steric and electronic situation [P(CH OCOR)3
−
1
1573 (m) cm
due to the carboxylato ligands.
2
or P(CH CH COOCH ) ] have been compared.
These data suggest for 7 a structure similar to that
reported for Ru (CO) (CH COO) (PR ) with R= –
2
2
3 3
Ruthenium carbonyl carboxylates are present gener-
ally in the crude of the catalytic hydrogenation of
carboxylic acids performed in the presence of H Ru -
2
4
3
2
3 2
CH(CH ) ,–CH CH CH CH , –C(CH ) [7].
3
2
2
2
2
3
3 3
4
4
(
CO) [P(CH CH CH CH ) ] [1,2b]. We have therefore
8 2 2 2 3 3 4
synthesized and characterized Ru (CO) -(CH COO) -
2.1.2. Ru(CO) (CH COO) [P(CH OCOCH ) ] (8)
2
4
3
2
2
3
2
2
3 3 2
[
(
P(CH OCOCH ) ] (7) and Ru(CO) -(CH COO) [P-
Was prepared as described by Bianchi et al. [8] for
the tributylphosphine substituted analogue (Scheme 4).
Polymeric [Ru (CO) (CH COO) ] was reacted with
2
3 3 2
2
3
2
CH OCOCH ) ] (8), in order to detect their presence
2
3 3 2
in the reaction crude. The catalytic activity of 7 has also
been tested and compared with that of 1.
2
4
3
2 n
P(CH OCOCH ) in acetic acid under reflux for 90 h.
2
3 3
The catalytic activity of 5 was also tested in the
hydrogenation of CꢀC and CꢀO groups.
An oily residue was obtained after elimination of the
solvent under reduced pressure.
An octahedral structure containing two phosphine
molecules in trans position and two carboxylato and
two carbonyl groups in cis position may be attributed
to 8 on the basis of its spectroscopic data. In fact the
2. Results
31
2.1. Synthesis and characterization of rutheniumcarbon-
singlet at 26.7 ppm in the P-NMR spectrum is indica-
tive of two equivalent phosphine ligands; the presence
of two cis carbonyl ligands is in keeping with two
carbonyl stretching bands of equal intensity in the IR
yl complexes
Complexes H Ru (CO) [P(CH OCOR) ] (1–5) were
4
4
8
2
3 4
−
1
synthesized as reported previously [3]. The new com-
plexes employed were prepared as described below:
spectrum, at 2067 (vs), 2008 (vs) cm
and, in the
13
C-NMR spectrum, with the presence of only one
triplet at 193.2 ppm (JCP=12.7 Hz). A singlet at 2.04 in
1
2
.1.1. Ru (CO) (CH COO) [P(CH OCOCH ) ] (7)
Was prepared as described by Crooks et al. [4] for
the H-NMR spectrum and two singlets at 22.2 and
2
4
3
2
2
3 3 2
13
178.5 ppm in the C-NMR spectrum are attributable
to two equivalent acetato ligands.
the analogous tributylphosphine derivative (Scheme 3).

220
A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
The spectroscopic data of 8 are in keeping with those
tested it is not possible to crystallize it, to determine its
13
reported in the literature for analogous ruthenium com-
plexes [5,8]. On standing at room temperature the com-
plex turns into a new ruthenium species not yet well
characterized.
molecular weight and to collect its C-NMR spectrum.
1
31
The H- and P-NMR spectra (D O or DMSO as
2
solvent) are in keeping with those reported [5,9,10] for
analogous ruthenium complexes. Only one singlet at
31
4
4.2 ppm, present in the P-NMR spectrum, is at-
2
.1.3. H Ru (CO) [P(CH CH COOCH ) ] (9)
tributable to four magnetically equivalent phosphine
4
4
8
2
2
3 3 4
Was prepared by reacting H Ru (CO)
with
ligands. The presence of only one multiplet at −21.55
ppm in the hydrido region of the H-NMR spectrum is
4
4
12
1
P(CH CH COOCH ) in n-heptane (Scheme 5) as de-
2
2
3 3
scribed by Piacenti et al. [9] for the analogous trib-
utylphosphine substituted derivative
in agreement with the presence of four equivalent
hydrides.
1
31
13
The H-, P-, C-NMR and IR spectra are in keep-
ing with those reported [5,9,10] for analogous ruthe-
nium complexes. Only one singlet at 19.2 ppm is
The IR spectrum (KBr pellets) shows in the carbonyl
stretching region two broad bands at 2048 (vs) and
−
1
1975 (vs) cm
.
3
1
present in the P-NMR spectrum, attributable to four
magnetically equivalent phosphine ligands. At the same
The elemental analysis supports the formulation
proposed.
time the presence of only one quintet at −17.05 ppm
1
(
JHP=6.5 Hz) in the hydrido region of the H-NMR
2
.2. Hydrogenation experiments
spectra is in agreement with four equivalent hydrides
coupling with four equivalent phosphine ligands. The
other resonances in the spectrum may be attributed as
follows: 3.40 (s, 36H, CH O), 2.53 (m, 24H, CH CO),
The hydrogenation experiments were performed on
carboxylic acids, ketones and orefins. No optimization
of the yield was attempted.
3
2
2
.25 (m, 24H, PCH ) ppm. The resonances in the
2
1
3
C-NMR spectrum may be attributed as follows: 199.9
(
m, RuCO), 172.0 (t, JPC=7.2 Hz, COO), 51.6 (s,
2.2.1. Hydrogenation of carboxylic acids
OCH ), 28.1 (s, CH CO), 25.3 (t, J =10.9 Hz,
Series of hydrogenation tests of acetic acid (Table 1)
were carried out in the presence of hydrido ruthenium
complexes 1–4, 9, scanning the 80–130°C temperature
range, under 130 atm of hydrogen with a substrate/cat-
3
2
PC
1
3
1
PCH ). The attributions of the C- and H-NMR
2
spectra are confirmed by an HETCOR spectrum. These
attributions are also in agreement with the statement of
Pregosin [11] that the carbon atoms in h and k positions
couple with the phosphorous atom.
3
alyst molar ratio of 3.53×10 and a reaction time of 48
h. Samples were collected at the end of each test and
analyzed by GC and GC-MS. The residual catalyst was
also recovered from the crude after distillation of the
liquid at reduced pressure and examined by IR
spectroscopy.
The IR spectrum, in the carbonyl stretching region,
shows three absorptions at 2006 (vs), 1966 (m), 1946 (s)
−
1
cm
characteristic for these complexes [9,10].
These data support the hypothesis of a structure
similar to that of H Ru (CO) [12], based on a tetrahe-
No hydrogenation of the carboxylic group took place
at temperatures lower then 100°C.
4
4
12
dral ruthenium cluster, containing one phosphine per
ruthenium atom.
In the presence of catalysts 1–4 the product formed
at the lowest reaction temperature is ethyl acetate while
ethanol is present at higher temperatures (]120°C).
Conversions were 14–16% with hydrides 1–4 while
only ca. 4% was reached working with 9 (Table 1).
Comparative tests, performed at 130°C using 2, 9
2
.1.4. H Ru (CO) [P(CH OH) ] (10)
4
4
8
2
3 4
Was prepared by reacting H Ru (CO)
with
4
4
12
P(CH OH) in butan-2-ol (Scheme 6) as described by
2
3
Piacenti et al. [9] for the analogous tributylphosphine
substituted derivative.
and H
Ru
(CO)
[P(CH
8
CH CH
2
CH )
3
]
(6) as cata-
4
4
2
2
3
4
The residue, after distillation of the solvent was
washed with n-pentane, benzene and methylene chlo-
ride. Due to the very low solubility in all the solvents
lysts, showed a decrease of the catalytic activity in the
order 2\6\9 (Table 2).
The IR analysis of the solid residue recovered from
the crude of the tests performed at 130°C (Table 1) in
the presence of complexes 1–4 shows the disappearance
of the starting H Ru (CO) [P(CH OCOR) ] complex
4
4
8
2
3 4
and the presence, in the carbonyl stretching region, of
−
1
two broad bands at 2045 (vs) and 1975 (vs) cm
attributable to a mixture of ruthenium carbonyl com-
Scheme 5.
Scheme 6.
−
1
plexes. Other bands at 1750 (s) and 1600 (w) cm may
be attributed, respectively, to the ester group of the
phosphinic ligands and to carboxylato ligands.

A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
221
The catalytic activity of the carboxylato complex 7 in
the hydrogenation of acetic acid is almost the same of
at all temperatures tested (Table 3).
The hydrogenation of propionic acid was performed,
4). n-Propyl propionate was the main reaction product.
The conversion reached 28% in the presence of 2 at
150°C. The catalytic activity of the complexes decreases
in the order 2$3\6\9.
1
at temperatures between 130 and 150°C, in the presence
of hydrido ruthenium complexes 2, 3, 6, and 9 (Table
n-Pentanoic and 2-methylbutanoic acids were also
hydrogenated to the corresponding n-pentyl and 2-
Table 1
Hydrogenation of acetic acid in the presence of H Ru (CO) (PR ) catalysts a
4
4
8
3 4
Catalyst
T (°C)
Conv. (%)
Selectivity (%)
Ethyl acetate
Ethanol
H Ru (CO) [P(CH OCOCH ) ] (1)
100
2.0
5.0
9.0
16.0
Trace
3.9
100
100
100
94.0
100
100
94.0
91.7
100
100
ꢀ100
92.2
100
100
93.7
90.1
0
0
0
0
6.0
0
4
4
8
2
3 3 4
110
120
130
H Ru (CO) [P(CH OCOCH CH ) ] (2)
100
4
4
8
2
2
3 3 4
1
1
1
10
20
30
0
7.4
6.0
8.3
0
16.0
Trace
2.0
H Ru (CO) [P(CH OCOCH(CH ) ) ] (3)
100
4
4
8
2
3 2 3 4
110
120
130
0
6.8
Trace
7.8
0
14.3
Trace
2.9
6.3
14.0
0
H Ru (CO) [P(CH OCOC(CH ) ) ] (4)
100
4
4
8
2
3 3 3 4
110
120
130
0
6.3
9.9
0
H Ru (CO) [P(CH CH COOCH ) ] (9)
100
4
4
8
2
2
3 3 4
1
1
1
10
20
30
Trace
1.8
3.6
100
100
100
0
0
0
a
Influence of temperature. Tests performed by heating the system in subsequent steps at the temperatures indicated. Substrate 5.24 ml (91.6
mmol), catalyst 30.0 mmol, p(H ) 130 atm at 20°C, reaction time 48 h at each temperature.
2
Table 2
Hydrogenation of acetic acid in the presence of H Ru (CO) (PR ) catalysts a
4
4
8
3 4
Catalyst
Conv. (%)
Selectivity (%)
Ethyl acetate
Ethanol
H Ru (CO) [P(CH OCOCH CH ) ] (2)
10.1
1.8
92.1
100
7.9
0
4
4
8
2
2
3 3 4
H Ru (CO) [P(CH CH COOCH ) ] (9)
4
4
8
2
2
3 3 4
H Ru (CO) [P(CH CH CH CH ) ] (6)
6.1
100
0
4
4
8
2
2
2
3 3 4
a
Influence of the phosphine ligand. Substrate 45.8 mmol (2.62 ml), catalyst 15.0 mmol, T=130°C, p(H ) 130 atm at 25°C, reaction time 48 h.
2
Table 3
a
Hydrogenation of acetic acid in the presence of Ru (CO) (CH COO) [P(CH OCOCH ) ] (7): influence of temperature
2
4
3
2
2
3 3 2
Catalyst
T (°C)
Conv. (%)
Selectivity (%)
Ethyl acetate
Ethanol
Ru (CO) (CH COO) [P(CH OCOCH ) ] (7)
100
2.3
5.8
9.5
100
100
100
94.0
0
0
0
6.0
2
4
3
2
2
3 3 2
110
120
130
15.7
a
Tests performed by heating the system in subsequent steps at the temperatures indicated. Substrate 5.24 ml (91.6 mmol), catalyst 60.0 mmol,
p(H ) 130 atm at 20°C, reaction time 48 h at each temperature.
2

222
A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
Table 4
Hydrogenation of propionic acid in the presence of H Ru (CO) (PR ) catalysts a
4
4
8
3 4
Catalyst
T (°C)
R.t. b (h)
Conv. (%)
Selectivity (%)
n-Propyl propionate
Propanol
H Ru (CO) [P(CH OCOCH CH ) ] (2)
130
48
24
48
24
48
24
48
24
15.6
28.0
14.1
27.0
2.2
4.4
5.2
23.2
95.9
98.6
98.2
99.2
100
100
100
99.1
4.1
1.4
1.8
0.8
0
0
0
0.9
4
4
8
2
2
3 3 4
1
50
130
50
130
50
130
50
H Ru (CO) [P(CH OCOCH(CH ) ) ] (3)
4
4
8
2
3 2 3 4
1
H Ru (CO) [P(CH CH COOCH ) ] (9)
4
4
8
2
2
3 3 4
1
H Ru (CO) [P(CH CH CH CH ) ] (6)
4
4
8
2
2
2
3 3 4
1
a
Catalyst 15.0 mmol, substrate 3.41 ml (45.8 mmol), p(H ) 130 atm at 25°C.
2
b
R.t.: reaction time.
Table 5
Hydrogenation of 2-methylbutanoic and n-pentanoic acid to the corresponding esters (2-methylbutyl 2-methylbutanoate and n-pentyl n-pen-
a
tanoate, respectively) in the presence of (+)(S)-H Ru (CO) {P[CH OCOCH(CH )CH CH ] } (5) or H Ru (CO) [P(CH CH CH CH ) ] (6)
4
4
8
2
3
2
3 3
4
4
4
8
2
2
2
3 3 4
Substrate
Catalyst
14 h at 130°C
48 h at 150°C
116 h at 150°C
Conversion (%) Selectivity b (%) Conversion (%) Selectivity b (%) Conversion (%)
Selectivity b (%)
2
-Methylbu-
(5)
(6)
(5)
(6)
0.4
0.2
1.2
0.3
100
100
100
100
8.6
2.9
98.8
100
99.0
100
16.5
6.9
97.6
ꢀ100
99.2
tanoic acid
2-Methylbu-
tanoic acid
n-Pentanoic
acid
n-Pentanoic
acid
19.6
4.1
39.4
11.0
99.0
a
Catalytic precursor 15 mmol, substrate 45.8 mmol, p(H ) 130 atm at 20°C neat.
2
b
Selectivity to ester, the other product is the corresponding alcohol.
methylbutyl esters in the presence of 5 and 6 at tem-
2.3. Reaction of rutheniumcarbonyl complexes with
peratures higher than 130°C. The conversions reached
in the presence of 5 were higher than those found
with 6 (Table 5).
acetic acid
The reactivity of H Ru (CO) [P(CH OH) ] (10)
4
4
8
2
3 4
Trace of the RCOOCH esters were detected in the
with acetic acid has been evaluated in order to
3
crude when working at 130°C with long reaction
times or at higher temperatures, indicative of some
hydrogenolysis in a low extension of the P–C bond
of the phosphine ligand. This reactivity had not been
observed in a previous investigation on the behavior
of H Ru (CO) [P(CH OCOR) ] complexes with hy-
confirm that the P(CH OH) group formed in the cat-
alytic experiments reacts with the free acid to restore
2
the
H Ru (CO) [P(CH OCOR) ]
complex.
We
4
4
8
2
3 4
wanted also to test if hydrido ruthenium complexes
react with acetic acid to give ruthenium carbonyl car-
boxylates containing the same phosphine ligands.
4
4
8
2
3 4
drogen [3]. This new finding may be ascribed to the
more severe conditions adopted in the present work.
2.3.1. H Ru (CO) [P(CH OH) ] (10)
4
4
8
2
3 4
H Ru (CO) [P(CH OH) ] is transformed partially,
4
4
8
2
3 4
2
.2.2. Hydrogenation of olefins and ketones
The results of the hydrogenation tests on CꢀC (cy-
at reflux temperature in acetic acid for 24 h, into a
new specie containing the P(CH OCOCH ) ligand
2
3 3
−
1
clohexene, tiglic acid) and CꢀO double bonds (ace-
tophenone) in the presence of 5 and 6 are reported in
Table 6. In all cases 6 provides higher conversions
than 5. Complex 5 provides a very low enantioface
discrimination in the hydrogenation of prochiral sub-
strates.
(band at 1756 (vs) cm
in the IR spectrum and
absence of bands due to the CH OH group).
2
After heating at reflux temperature for 72 h in
acetic acid and evaporation of the unreacted acid, a
carboxylato ruthenium complex is present, containing
a phosphine in which the initial CH OH groups is
2

A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
223
Table 6
Hydrogenation of unsaturated organic substrates in the presence of (+)(S)-H Ru (CO) {P[CH OCOCH(CH )CH CH ] } (5) or
4
4
8
2
3
2
3 3 4
a
H Ru (CO) [P(CH CH CH CH ) ] (6)
4
4
8
2
2
2
3 3 4
Substrate
Catalyst
T (°C)
R.t. b (h)
Conv. (%)
Product
O.P. c (%)
mmol
Code
mmol
Acetophenone
Acetophenone
41.6
41.6
49.9
49.9
42.5
42.5
5
6
5
6
5
6
23
23
23
23
4.5
4.5
120
120
100
100
60
14
14
48
48
22
22
7.6
14.0
9.6
96.4
1.8
47.1
(+)(S)-1-Phenylethanol
1-Phenylethanol
(+)(S)-2-Methylbutanoic acid
2-Methylbutanoic acid
Cyclohexane
0.04
5.7
d
Tiglic acid
Tiglic acid
d
Cyclohexene
Cyclohexene
60
Cyclohexane
a
Neat, p(H ) 130 atm.
R.t.: reaction time.
O.P.: optical purity (%)
Solvent: 10 ml toluene/ethanol (1:1).
2
b
c
d
transformed into an ester group (band at 1754 (vs)
heating for 3 h at 40°C a colorless solution is obtained.
After elimination of acetic acid under reduced pressure
at a temperature non-exceeding 0°C, a residue is ob-
tained containing only one phosphine-substituted com-
plex having one signal at 26.4 ppm in the P-NMR
spectrum.
The spectroscopic data are in agreement with the
presence of a carboxylato ligand but a complete charac-
terization of this complex has not yet been possible due
to its rapid decomposition.
−
−
1
1
cm
cm
in the IR spectrum). The stretching at 1559 (w)
indicates the presence of the carboxylato ligand;
1
the hydride resonances in the H-NMR spectrum are
absent.
31
However the complex is not one of the ruthenium
carbonyl acetato complexes, Ru (CO) (CH COO) -
2
4
3
2
[
P(CH OCOCH ) ] (7) or Ru(CO) (CH COO) [P(CH -
2
3 3 2
2
3
2
2
OCOCH ) ] (8), but it has the same spectroscopic
3
3 2
characteristics of one of the products obtained by react-
ing H Ru (CO) [P(CH OCOCH ) ] with acetic acid
4
4
8
2
3 3 4
3
1
(
signal in the P-NMR spectrum at 35.7 ppm) (see
below).
3
. Discussion
2
.3.2. H Ru (CO) [P(CH OCOCH ) ] (1)
The results of the hydrogenation tests show that the
4
4
8
2
3 3 4
When heating 1 in acetic acid at reflux temperature
for 48 h, the starting complex is still the main product
catalytic activity of the ruthenium complexes 1–5, con-
taining a functionalized phosphine such as P(CH2-
OCOR) , is different from that of 6, the P(CH CH -
31
(
91.2%, evaluated by P-NMR spectroscopy) while a
3
2
2
small amount of 7 (2.3%) and of another complex
CH CH ) substituted analogue. This difference may be
2
3 3
3
1
(
signal at 26.4 in the P-NMR spectrum, 6.5%) are
summarized as follows:
formed. In the IR spectrum of the solution new bands
appear at 2070 (w), 2011 (sh) and 1559 (w, broad)
cm . These spectroscopic data (IR and P-NMR
spectra) are in agreement with the presence of the same
product formed by reacting 7 with acetic acid at 40°C
1. In the hydrogenation of carboxylic acids the hy-
drido ruthenium complexes 1–5 are catalytically
more active than 6 at all the temperatures tested
(100–150°C) (Tables 2, 4 and 5). A low activity is
displayed by 1–4, even below 130°C, while at the
same temperature 6 is not active (Table 1).
2. The catalytic activity of the P(CH OCOR) substi-
−
1
31
(
see below).
Compound
1
is transformed completely when
2
3
refluxed in acetic acid for 192 h: two new complexes are
present in the reaction crude, having signals at 26.4 (s,
tuted ruthenium complexes in the hydrogenation of
CꢀC or CꢀO double bonds (Table 6) is lower than
that one of 6.
31
55.3%) and 35.7 (s, 44.7%) ppm in the P-NMR
spectrum.
The nature of the catalytic species in the hydrogena-
tion of carboxylic acids is rather intriguing.
H Ru (CO) [P(CH OCOCH ) ] and some carboxylato
In the usual working up the complex giving the signal
at 26.4 ppm decomposes and a mixture of products is
4
4
8
2
3 3 4
3
1
present in solution (signals in the P-NMR spectrum at
derivatives containing the same phosphine ligand (like 7
and 8) could be involved in the catalytic cycle as found
in the hydrogenation catalyzed by H Ru (CO) -
35.7, 51.4, 64.0, 82.4 ppm).
4
4
8
2
.3.3. Ru (CO) (CH COO) [P(CH OCOCH ) ] (7)
[P(CH CH CH CH ) ] [1,2b]. Tributylphosphine sub-
2
4
3
2
2
3 3 2
2 2 2 3 3 4
Ru (CO) (CH COO) [P(CH OCOCH ) ] slowly re-
acts in the presence of acetic acid at room temperature;
stituted hydridoruthenium carbonyls have in fact been
shown to react easily with carboxylic acids, even at
2
4
3
2
2
3 3 2

224
A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
plexes 1–5 with hydrogen [3]. The formation of the
same hydrido cluster from the binuclear carboxylato
complex 7 is also suggested in consideration of almost
the same catalytic activity. The activation of the ester
moiety of the phosphine takes place by co-ordination of
its carbonyl group to a ruthenium atom of the cluster.
Activation of substrates by the breaking of a Ru–Ru
bond in cluster complexes has been reported by Lugan
[13]. The higher catalytic activity of the binuclear ruthe-
nium carboxylato complexes compared with that of the
mononuclear derivatives is in agreement with the in-
volvement of a Ru–Ru bond in the catalytically active
intermediate [2c]. This consideration suggests that the
ruthenium atom which became coordinated to the car-
bonyl group of the ester is not the same to which the
phosphine is bonded. The oxidative addition of the
ester group gives rise to the formation of an acyl and an
alkoxy ruthenium complex. The hydride moves then on
the oxygen of the acyl group forming a carbene deriva-
tive that is hydrogenated to the alcohol and a ruthe-
nium complex with a P(CH OH) group. Esterification
2
of this P(CH OH) group restore the starting complex
2
while reaction of the substrate (RCOOH) with the
alcohol formed (RCH OH) gives the corresponding
2
carboxylic acid ester. This hypothesis is supported by
the fact that H Ru (CO) [P(CH OH) ] , a model com-
4
4
8
2
3 4
plex bearing a hydroxylated phosphine, reacts easily
with acetic acid at 120°C (the temperatures adopted in
the catalytic hydrogenation) yielding ruthenium com-
plexes containing the P(CH OCOCH ) ligand (Scheme
2
3 3
2
). Working in harsh conditions the expected carboxy-
lato complexes Ru (CO) (CH COO) [P(CH OCO-
2
4
3
2
2
CH ) ] (7) and Ru(CO) (CH COO) [P(CH OCO-
3
3 2
2
3
2
2
CH ) ] (8), have not however been detected among the
3
3 2
Scheme 7.
reaction products in agreement with the behaviour of
the acetato ruthenium carbonyl 7 with acetic acid. This
complex in fact, in the presence of acetic acid, give rise
to new labile complexes not yet characterised com-
pletely, whose spectroscopic properties are identical to
those shown by the products formed from H Ru -
room temperature, in the absence of hydrogen, to give
phosphine substituted ruthenium carbonyl carboxy-
lates. Moreover, the catalytic activity shown by the
carboxylato complex 7 is very similar to that of 1.
The higher activity of the ruthenium complexes con-
taining functionalized phosphines 1–5, 7 (Tables 1–5)
in the hydrogenation of carboxylic acids may tenta-
tively be explained through the involvement of the
phosphine ligand in the activation of the substrate as
shown in the reaction pattern reported in Scheme 7.
This path can not be operative when 6 is the catalyst.
The almost equal catalytic activity shown by complexes
4
4
(
CO) [P(CH OCOCH ) ] and acetic acid (see Experi-
8 2 3 3 4
mental).
Surprisingly not only a free carboxylic acid but also
the ester group of the phosphino ligand are reduced at
a low temperature, if compared with that necessary for
the reduction of an ester, using the trialkylphosphino
derivative 6 [1a]. Analogous H Ru (CO) (PR ) com-
4
4
8
3 4
plexes containing tri(propyl)phosphine have been re-
ported to improve the catalytic activity of these clusters
in the reduction of dimethyl oxalate to methyl glycolate
H Ru (CO) [P(CH OCOR) ] (1–4) in the hydrogena-
4
4
8
2
3 4
tion of acetic acid (Table 1) suggests moreover the
formation of the same catalytic intermediates. The
[6], but the reduction of the monoester, however, can be
same species containing the P(CH OCOCH ) ligand
2
3 3
obtained only at higher temperature (180°C). Other
ruthenium complexes have been reported as efficient
catalysts in the reduction of carboxylic acid esters in
mild conditions [14,15].
may in fact be formed from all precursors 1–4 if the
reactions reported in Scheme
7
(R=CH3) are
operative.
The hydrogenation of free carboxylic acids can in-
volve the reaction path previously reported for com-
Another observation supports the suggestion that a
different path is operative in the hydrogenation of

A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
225
carboxylic acids at low temperature in the presence of
–5. The P(CH CH COOCH ) substituted complex 9
4.2. Materials
1
2
2
3 3
shows a much lower catalytic activity than 1–5 in the
hydrogenation of acetic and propionic acids, even lower
than that of 6 (Tables 1, 2 and 4): In the conditions
adopted in the catalytic tests the carbomethoxy groups
in the phosphine ligand of 9 are not hydrogenated and
therefore no new ‘sites’ for the possible engagement of
the carboxylic acid are formed.
As a final consideration the mechanism suggested
provides a justification of the insignificant enantioface
discrimination provided by 5 in the hydrogenation of
prochiral acids: the chiral center is in fact removed
from the complex by hydrogenation and substituted by
the prochiral acid used as substrate.
Reagents and solvents were purified and dried as
reported. Acetic acid was distilled under nitrogen (b.p.
118°C). Cyclohexene was eluted through activated
Al O (70–230 mesh) and rectified under nitrogen (b.p.
2
3
83°C). Acetophenone was distilled prior to use (b.p.
82°C/15 mmHg). Toluene was dried by refluxing on
sodium metal, then was refluxed and distilled on
LiAlH4· n-Heptane was purified by treatment with
conc. H SO , washed with a solution of KMnO in
2
4
4
H SO (10%), then dried on anhydrous CaCl , refluxed
2
4
2
on sodium and distilled on LiAlH Methanol, dried as
4·
reported by Vogel [16], had b.p. 65°C.
2-Methylbutyl 2-methylbutanoate was synthesized by
reacting 2-methylbutanol with 2-methylbutanoyl chlo-
ride prepared from 2-methylbutanoic acid as reported
by Vogel [16] for analogous compounds and had b.p.
4. Experimental
7
3–74°C/10 mmHg.
4.1. Instruments
n-Pentyl n-pentanoate, synthesized and purified as
reported by Vogel [16] for analogous compounds, had
b.p. 102–103°C/23 mmHg.
Elemental analyses were performed with a Perkin–
Elmer 240 C system.
P(CH OH)3 [17,18], P(CH OCOCH ) [3], P(CH2-
2
2
3 3
Gas chromatographic analyses (GC) were performed
with a Perkin–Elmer–Sigma 1 system or a Shimadzu
GC-14A chromatographic system coupled with a Shi-
madzu C-R4A computer; the packed columns (2 m)
used were: PPG (‘Polipropylenglycol’ LB-550-X on
Chromosorb W at 15%), FFAP (‘free fatty acids phase’
on Chromosorb G AW-DMCS at 5%), CW (‘Car-
bowax 20M’ on Chromosorb W at 15%). Both appara-
tuses were equipped with a FID.
OCOCH CH ) [3], P[CH OCOCH(CH ) ] [3] P[CH -
2 3 3 2 3 2 3 2
OCOC(CH ) ] [3], (−)(S)-[P(CH OCOCH(CH )CH -
3
3 3
2
3
2
CH ) ] [3] and P(CH CH COOCH ) [19,20] were syn-
3
3
2
2
3 3
thesized as reported in the literature.
Complexes H Ru (CO) [9], H Ru (CO) [P(CH -
4
4
12
4
4
8
2
CH CH CH ) ] (6) [9], H Ru (CO) [P(CH OCOR) ]
2
2
3 3 4
4
4
8
2
3 4
[R=CH –(1), C H –(2), (CH ) CH–(3), (CH ) C–(4),
3
2
5
3 2
3 3
(S)–C H CH(CH )–(5)] [3] and [Ru (CO) (CH -
2
5
3
2
4
3
-COO)2]n [4] were prepared as described in the
Conversions of carboxylic acids to esters were evalu-
ated by calibration curves.
GC-MS spectra were collected using a Shimadzu
GC-MS-QP2000 instrument, or a Carlo Erba QMD
literature.
All other solvents and chemicals were reagent grade
and used without further purification.
All reactions and manipulations were performed un-
der dry nitrogen by the Schlenk tube technique.
1000 GC-MS data system equipped with capillary
columns: a SPB-1™ (a Supelco column, 30 m, internal
diameter 0.25 mm) or a AT™-1 (Alltech column, 30 m,
internal diameter 0.25 mm).
4.3. Synthesis of ruthenium complexes
Infrared spectra were recorded with a Perkin–Elmer
model 1760-X FTIR spectrophotometer. Liquid prod-
ucts and solutions were analyzed using KBr or CaF2
cells having 0.1 mm path. Solid samples were mulled
with KBr.
4.3.1. Ru (CO) (CH COO) [P(CH OCOCH ) ] (7)
2
4
3
2
2
3 3 2
[Ru (CO) (CH COO) ] (302 mg, 1.398 mmol Ru)
2
4
3
2 n
and P(CH OCOCH ) (350 mg, 1.4 mmol) in toluene
2
3 3
(10 ml) were refluxed for 10 h. The solution was then
evaporated to dryness and the residue crystallized from
methanol at −20°C. A yellow crystalline product (396
mg, 61% yield) was recovered.
Multinuclear NMR spectra were registered using a
Varian VXR300 spectrometer operating at 299.944
1
13
MHz for H, at 75.429 MHz for C and at 121.421
3
1
MHz for P-NMR spectra, tetramethylsilane was used
Anal. Calc. for C H O P Ru : C, 33.48; H, 3.89.
26
36 20
6
4
1
13
as external reference for H- and C-NMR spectra. In
the P-NMR spectra, downfield values from external
H PO (85%) were taken as positive. C- and P-
Found: C, 33.09; H, 3.88.
The IR spectrum (toluene) shows, in the 2200–1500
3
1
13
31
−1
cm
region, bands at 2032 (vs), 1987 (m), 1961 (vs),
3
4
−
1
NMR spectra were recorded as proton decoupled
spectra.
1757 (s), 1573 (m) cm
The H-NMR spectrum (CDCl ) shows signals at
.
1
3
Optical rotations were measured with a Perkin–
Elmer model 241 polarimeter.
1.85 (s, 6H, CH COORu), 2.07 (s, 18H, CH COOCH ),
3
3
2
4.78 (s, 12H, CH O) ppm.
2

226
A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
3
1
31
The P-NMR spectrum (CDCl ) shows a singlet at
The P-NMR spectrum (C D ) shows a singlet at
6 6
3
8
.7 ppm.
19.2 ppm.
1
3
13
The C-NMR spectrum (CDCl ) shows resonances
The C-NMR spectrum (DMSO-d ) shows signals at
3
6
at 20.3 (s, CH COOCH ), 23.0 (s, CH COORu), 56.3
25.3 (t, PCH CH , J =10.9 Hz), 28.1 (s, PCH CH ),
3
2
3
2
2
CP
2
2
(
t, CH , J =10.4 Hz), 170.1 (s, PCH COO), 187.0 (t,
51.6 (s, CH O), 172.0 (t, COO, JCP=72 Hz) and 199.9
2
CP
2
3
COORu, JCP=9.0 Hz), 203.8 (t, Ru–CO, JCP=4.5
Hz) ppm.
(m, RuCO) ppm.
4
.3.4. H Ru (CO) [P(CH OH) ] (10)
H Ru (CO) (190 mg, 0.255 mmol) was reacted with
4 4 12
4
4
8
2
3 4
4
.3.2. Ru(CO) (CH COO) [P(CH OCOCH ) ] (8)
2
3
2
2
3 3 2
[
Ru (CO) (CH COO) ] (165 mg, 0.75 mmol Ru) was
2 4 3 2 n
P(CH OH) (200 mg, 1.61 mmol) in butan-2-ol (15 ml)
2 3
treated with P(CH OCOCH ) (380 mg, 1.51 mmol) in
2
3 3
by heating at 100°C for 48 h. A red solution was
formed showing bands in the IR spectrum different
from those of the starting complex. The solvent was
evaporated and the solid residue washed with n-pen-
tane, benzene and methylene chloride. The product
recovered (173 mg, 0.153 mmol, 60% yield) has a low
solubility in acetone, methanol, tetrahydrofurane and
dimethylsulfoxide.
acetic acid (5 ml) and the mixture refluxed for 90 h. The
colorless solution was evaporated to dryness and the
residue analyzed spectroscopically.
The IR spectrum (CH Cl ) shows, in the 2200–1500
2
2
−
1
cm
1
region, bands at 2067 (vs), 2008 (vs), 1754 (vs),
−
1
619 (m) cm
.
1
The H-NMR spectrum (CDCl ) shows signals at
3
2.04 (s, 6H, CH COORu), 2.09 (s, 18H, CH COOCH ),
3
3
2
Anal. Calc. for C H O P Ru : C, 21.28; H, 3.57.
20
40 20
4
4
4
.80 (s, 12 H, CH O) ppm.
2
Found: C, 21.28; H, 3.64.
The IR spectrum (KBr pellets) shows, in the 2200–
3
1
The P-NMR spectrum (CD Cl ) shows a singlet at
2
2
2
6.4 ppm.
−1
−1
1
500 cm
region, bands at 2048 (vs), 1975 (vs) cm
.
1
3
The C-NMR spectrum (CDCl ) shows resonances
1
3
The H-NMR spectrum (D O) shows signals at −
2
at 20.0 (s, CH COOCH ), 22.2 (s, CH COORu), 55.7
3
2
3
2
1.55 (m, 4H, Ru–H) and 4.01 (d, 2H, PCH , JHP=3
2
(
t, CH , J =18.0 Hz), 170.0 (s, PCH COO), 178.5 (s,
2 CP 2
Hz) ppm
COORu), 193.2 (t, Ru–CO, JCP=12.7 Hz) ppm.
31
The P-NMR spectrum (DMSO) shows a singlet at
4.2 ppm.
Prolonged standing in solution causes its transforma-
4
4
4
3
1
tion into a new product with a singlet in the P-NMR
spectrum (CD Cl ) at 35.7 ppm; its IR spectrum
2
2
.4. Reacti6ity of ruthenium complexes
−
1
(
CH Cl ) in the 2200–1500 cm region, show bands at
2 2
−
1
2
061 (vs), 1978 (broad), 1754 (vs), 1557 (m) cm
.
.4.1. Beha6ior of 9 under hydrogen
A total of 57.3 mg (0.032 mmol) of complex 9,
4
.3.3. H Ru (CO) [P(CH CH COOCH ) ] (9)
4
4
8
2
2
3 3 4
dissolved in 5 ml benzene, were introduced under dry
nitrogen in a glass vial placed in a stainless steel auto-
clave (150 ml) and hydrogen was added up to 130 atm.
The autoclave was then rocked and heated up to 130°C.
Samples of the solution were monitored by GC (using
PPG column heated to 40°C for 50 min) and IR
techniques. Methanol and methyl propionate were not
detected. The IR spectrum of the final solution was
identical to the initial one (bands at 2006 (vs), 1966 (m),
In a 25 ml round bottom flask H Ru (CO) (0.200 g,
4
4
12
0
.204 mmol), P(CH CH COOCH ) (0.355 g, 1.21
2
2
3 3
mmol) and n-heptane (12 ml) were introduced under
dry nitrogen. The mixture was heated at 100°C for 12
h, removing the CO evolved by slowly bubbling
nitrogen.
The course of the reaction was monitored by IR
spectroscopy and TLC. After 12 h the IR spectrum of
the solution showed the absorptions characteristic of
the class of compounds expected: this pattern remained
unaltered even after longer heating. The solvent was
then distilled at reduced pressure and the residue dis-
solved in methanol and crystallized by cooling at −
−
1
1
946 (s) and 1738 (vs) cm ).
4.4.2. Reaction of 10 with acetic acid
H Ru (CO) [P(CH OH) ] (24 mg, 0.021 mmol) was
4
4
8
2
3 4
refluxed for several hours in acetic acid (5 ml). The
reaction was monitored by IR spectroscopy.
A sample of the solution collected after 24 h was
distilled to dryness and the residue dissolved partially in
2
(
0°C. After two recrystallizations 0.385 g of product
77% yield) were obtained.
Anal. Calc. for C H O P Ru : C, 37.25; H, 4.92.
5
6
88 32
4
4
Found: C, 37.28; H, 5.18.
The IR spectrum (CH Cl ) shows, in the 2200–1500
methylene chloride. The IR spectrum of the solution
2
2
−
1
−1
cm region, bands at 2006 (vs), 1966 (m), 1946 (s) and
showed a band at 1756 (vs) cm
P(CH OCOCH
attributable to the carboxylato group [Ru(OCOCH
attributable to the
−
1
−1
1
738 (vs) cm
.
2
3
) group and a band at 1557 (w) cm
1
The H-NMR spectrum (C D ) shows signals at −
3
)].
were
6
6
−
1
1
7.05 (qt, 4H, HRu, JHP=6.5 Hz), 2.25 (m, 24H,
Other absorptions at 2058 (s) and 1990 (s) cm
PCH ), 2.53 (m, 24H, PCH CH ) and 3.40 (s, 36 H,
also present. No bands due to the CH OH group were
2
2
2
2
OCH ) ppm.
evident.
3

A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
227
The IR spectrum of the solid residue (KBr pellets),
The solution after heating for 3 h at 40°C becomes
colorless. This solution was evaporated to dryness at
0°C and the residue was analyzed spectroscopically.
The IR spectrum (CH Cl ) shows, in the 2200–1500
−
1
showed a band at 3430 (vs) cm
attributable to the
presence of CH OH groups. Other absorptions were at
2
−
1
2
051 (vs), 1980 (vs), 1735 (s), 1663 (s), 1559 (m) cm
.
2
2
−
1
The residue obtained after refluxing for 72 h and
cm
region, bands at 2070 (vs), 2011 (vs), 1758 (vs),
−
1
evaporation of the acetic acid was soluble completely in
methylene chloride. The spectroscopic data of this
residue were in agreement with the presence of only one
phosphino complex.
1562 (m) cm
.
1
The H-NMR spectrum (CDCl ) shows signals at
3
2.04 (s, CH COORu), 2.09 (s, CH COOCH ), 2.12 (s,
3
3
2
CH COORu), 4.81 (s, CH O) ppm.
3
2
31
The IR spectrum (CH Cl ) shows, in the 2200–1500
The P-NMR spectrum (CD Cl ) shows a singlet at
2
2
2 2
−
1
cm region, bands at 2064 (vs), 1993 (vs, broad), 1754
26.4 ppm.
−
1
13
(
vs), 1559 (w) cm
.
The C-NMR spectrum (CDCl ) shows resonances
3
1
The H-NMR spectrum (CD Cl ) shows characteris-
at 17.6 (s, CH COOCH ), 19.9 (s, CH COORu), 26.9
2
2
3
2
3
tic signals attributable to P(CH OCOCH ) group at
(s, CH COORu), 53.2 (t, CH , JCP=16.9 Hz), 167.0 (s,
2
3
3
2
2
.09 (s, CH COOCH ) and 4.53 (d, CH O, JHP=5 Hz)
PCH COO), 175.5 (s, COORu), 182.3(s, COORu),
3
2
2
2
ppm.
190.7 (m, Ru–CO) ppm.
The complex decomposes rapidly. Its complete char-
acterization is therefore difficult.
3
1
The P-NMR spectrum (CD Cl ) shows a singlet at
2
2
35.7 ppm.
1
3
The C-NMR spectrum (CD Cl ) shows resonances
2
2
attributable to the P(CH OCOCH ) group at 16.7 (s,
2
3
4.5. Catalytic hydrogenation
CH ), 54.0 (t, CH , JCP=80.1 Hz) and 166.3 (s,
3
2
PCH COO) ppm.
2
4.5.1. General procedure
The catalytic experiments were carried out in a glass
4
.4.3. Reaction of 1 with acetic acid
vial placed in a ‘Hastelloy C’ stainless steel rocking
autoclave (125 ml). Air was evacuated from the vessel
and replaced by dry nitrogen. The catalytic precursor,
the selected substrate and the solvent (when necessary)
were then introduced. The autoclave was then sealed
and hydrogen introduced up to the pressure required.
The autoclave was placed in a thermostatic oil bath set
at the desired temperature (91°C) and rocked for the
prefixed time. The amount and the identity of the
organic products in the crude were obtained by GC and
GC-MS analysis.
H Ru (CO) [P(CH OCOCH ) ]
(45 mg, 0.028
mmol) in acetic acid (5 ml) was refluxed for several
hours and the reaction monitored by IR and P-NMR
spectroscopy. After 48 h a sample of the solution was
evaporated to dryness and the residue analyzed with
spectroscopic methods: the starting complex was the
4
4
8
2
3 3 4
3
1
main product present but in the IR spectrum (CH Cl )
new bands were present at 2070 (w), 2011 (sh) and 1559
2
2
−
1
31
(
w, broad) cm . The P-NMR spectrum (CD Cl )
2 2
shows signals at 8.7 (s, 7, 2.3%), 24.5 (s, 1, 91.2%) and
2
6.4 (s, n.d.; 6.5%) ppm.
Working conditions and results are reported in Ta-
bles 1–5.
The solution was further refluxed for 144 h. The
P-NMR spectrum (CD Cl ) of a sample of the solu-
3
1
2
2
tion, after the usual work up, showed signals at 26.4 (s,
4
.5.2. Analyses of the hydrogenation products
In the hydrogenation of acetic, propanoic, 2-
55.3%) and 35.7 (s, 44.7%) ppm.
On standing at room temperature the signal at 26.4
methylbutanoic and n-pentanoic acid conversions were
evaluated by GC analyses using calibration curves ob-
tained from mixtures of known composition. In all
other tests conversions were determined without re-
sponse factors correction.
ppm decreases rapidly while there is an increase in
intensity of the signal at 35.7 ppm and the appearance
of new weak signals at 51.4, 64.0, 82.4 ppm.
The IR solution of the residue dissolved in CH Cl2
2
show bands at 2060 (vs, broad), 1998 (vs, broad), 1755
The GC analyses were performed using the following
conditions:
−
1
(
vs) and 1559 (w) cm
.
Acetic acid: a FFAP column kept at 50°C for 7 min,
−
1
4
.4.4. Reaction of 7 with acetic acid
then heated up to 130°C at a rate of 30°C min , and
kept at this temperature for 20 min.
Ru (CO) (CH COO) [P(CH OCOCH ) ] (26 mg,
2
4
3
2
2
3 3 2
0
.028 mmol) in acetic acid (5 ml) was stirred for 24 h at
Propanoic acid: a FFAP column kept at 50°C for 10
−
1
room temperature. A sample of the pale yellow solution
was evaporated to dryness. The IR spectrum of the
residue, dissolved in CH Cl , shows the bands of the
min, then heated up to 100°C at a rate of 5°C min
and kept at this temperature for 30 min.
,
2-Methylbutanoic acid: a FFAP column kept at 45°C
for 10 min, then heated up to 140°C at a rate of 10°C
2
2
starting complex and new bands at 2066 (w) and 2011
−
1
−1
(
sh) cm
.
min , and kept at this temperature for 30 min.

228
A. Sal6ini et al. / Journal of Organometallic Chemistry 582 (1999) 218–228
Matteoli, P. Frediani, C. Botteghi, J. Organomet. Chem. 188
1980) 109. (b) M. Bianchi, F. Piacenti, P. Frediani, U. Matteoli,
C. Botteghi, S. Gladiali, E. Benedetti, J. Organomet. Chem. 141
1977) 107. (c) M. Bianchi, F. Piacenti, G. Menchi, P. Frediani,
U. Matteoli, C. Botteghi, S. Gladiali, E. Benedetti, Chim. Ind. 60
(1978) 588.
n-Pentanoic acid: a FFAP column kept at 45°C for
0 min, then heated up to 140°C at a rate of 10°C
(
1
−
1
min , and kept at this temperature for 30 min.
Cyclohexene: a PPG column kept at 40°C for 25 min.
Acetophenone: a CW column kept at 60°C for 5 min,
(
−
1
[
2] (a) U. Matteoli, G. Menchi, M. Bianchi, P. Frediani, F. Piacenti,
IV Simposio Italo Cecoslovacco di Catalisi, Torino, 20–23/9/
then heated up to 160°C at a rate of 20°C min , and
kept at this temperature for 10 min. The hydrogenation
product, (+)(S)-1-phenylethanol, was recovered and
purified by distillation. Its optical purity was deter-
mined by polarimetry. When the catalytic precursor
1
983. (b) P. Frediani, U. Matteoli, G. Menchi, M. Bianchi, F.
Piacenti, Gazz. Chim. Ital. 115 (1985) 365. (c) U. Matteoli, G.
Menchi, M. Bianchi, P. Frediani, F. Piacenti, Gazz. Chim. Ital.
115 (1985) 603. (d) P. Frediani, M. Bianchi, F. Piacenti, S.
Ianelli, M. Nardelli, Inorg. Chem. 26 (1987) 1592. (e) P. Fredi-
ani, M. Bianchi, A. Salvini, F. Piacenti, S. Ianelli, M. Nardelli, J.
Chem. Soc. Dalton Trans. (1990) 165. (f) P. Frediani, M. Bi-
anchi, A. Salvini, F. Piacenti, S. Ianelli, M. Nardelli, J. Chem.
Soc. Dalton Trans. (1990) 1705. (g) P. Frediani, M. Bianchi, A.
Salvini, F. Piacenti, J. Chem. Soc. Dalton Trans. (1990) 3663. (h)
P. Frediani, C. Faggi, S. Papaleo, A. Salvini, M. Bianchi, F.
Piacenti, S. Ianelli, M. Nardelli, J. Organometal. Chem. 536
2
5
was 5 the hydrogenated product had [h]
+0.017°
D(max)
(
[
neat). Its optical purity was 0.04% based on
25
D(max)
h]
+43.6° (neat) [21,22].
Tiglic acid: a FFAP column kept at 45°C for 10 min,
−
1
then heated up to 140°C at a rate of 10°C min , and
kept at this temperature for 30 min. The hydrogenated
acid was recovered as follows: the reaction mixture was
neutralized using a saturated aqueous solution of
sodium carbonate. After extraction with diethyl ether,
the organic acid was recovered from the aqueous layer
by acidification with sulfuric acid followed by extrac-
tion with diethyl ether. The hydrogenation product,
(
1997) 123. (i) P. Frediani, C. Faggi, A. Salvini, M. Bianchi, F.
Piacenti, Inorg. Chim. Acta 272 (1998) 141.
[
[
3] M. Bianchi, P. Frediani, A. Salvini, L. Rosi, F. Piacenti, S.
Ianelli, M. Nardelli, Organometallics 16 (1997) 482.
4] G.R. Crooks, B.F.G. Johnson, J. Lewis, I.G. Williams, G.
Gamlen, J. Chem. Soc. A (1969) 2761.
5] A. Salvini, Unpublished results.
6] U. Matteoli, G. Menchi, M. Bianchi, F. Piacenti, J. Mol. Catal.
[
[
(
+)(S)-2-methylbutanoic acid, was recovered and
purified by distillation: bp 76–77°C/16 mmHg. When
the catalytic precursor was 5 the hydrogenated product
6
4 (1991) 257.
[7] U. Matteoli, G. Menchi, M. Bianchi, F. Piacenti, S. Ianelli, M.
Nardelli, J. Organomet. Chem. 498 (1995) 177.
[8] M. Bianchi, P. Frediani, U. Matteoli, G. Menchi, F. Piacenti, G.
Petrucci, J. Organomet. Chem. 259 (1983) 207.
2
D(max)
5
had [h]
on [h]
+1.128° (neat); Optical purity 5.7%, based
2
D(max)
5
+19.8° [23].
[
9] F. Piacenti, M. Bianchi, P. Frediani, E. Benedetti, Inorg. Chem.
10 (1971) 2759.
4
.6. Reco6ery of the catalyst from hydrogenation
[
[
10] S.A.R. Knox, H.D. Kaesz, J. Am. Chem. Soc. 93 (1971) 4594.
11] P.S. Pregosin, R.W. Kunziking, P. Diehl, in: E. Fluck, R.
experiments
3
1
13
Kosfeld (Eds.), P- and C-NMR of Transition Metal Phos-
phine Complexes, Springer Verlag, Germany, 1979, p. 70.
From the hydrogenation crude of acetic acid in the
presence of H Ru (CO) [P(CH OCOCH CH ) ] (Table
2
were removed by distillation at reduced pressure. The
residue was analyzed by IR spectroscopy (CH Cl as
solvent). A complex pattern (2045(vs, broad), 1975(vs,
broad), 1750(s) cm ) is present, in the 2200–1500
cm
plexes containing P(CH OCOR)3 and (PCH OH)3
groups, together with bands at 1610, 1580 and 1558
4
4
8
2
2
3 3 4
[12] R.D. Wilson, W.S. Miau, R.A. Love, R. Bau, Inorg. Chem. 17
(1978) 1271.
[
) the residual substrate and the other volatile materials
13] N. Lugan, G. Lavigne, J.J. Bonnet, R. Reau, D. Neibecker, I.
Tkatchenko, J. Am. Chem. Soc. 110 (1998) 5369.
14] (a) H.T. Teunissen, C.J. Elsevier, J. Chem. Soc., Chem. Com-
mun. (1998) 1367. (b) H.T. Teunissen, C.J. Elsevier, J. Chem.
Soc. Chem. Commun. (1997) 667.
2
2
[
−
1
−
1
range, attributable to several ruthenium com-
[15] (a) R.A. Grey, G.P. Pez, A. Wallo, J. Corsi, J. Chem. Soc.
Chem. Commun. (1980) 783. (b) R.A. Grey, G.P. Pez, A. Wallo,
J. Am. Chem. Soc. 103 (1981) 7536.
2
2
[
[
[
[
[
16] A. Vogel Vogel’s Textbook of Practical Organic Chemistry, 4th
Edn. Longmans, London, 1978.
17] K. Sasse, Houben-Weil, Methoden der Organischen Chemie,
XII/1, George Thieme Verlag, Stuttgart, 1963, p. 28.
18] M. Reuter, L. Orthner, Ger Patent no. 1 035 135 (1958); Chem.
Abstr. 54 (1960) 14124i.
19] L. Rosi, A. Bini, P. Frediani, M. Bianchi, A. Salvini, J. Mol.
Cat. A 112 (1996) 367.
20] M.M. Rauhut, I. Hechenbleikner, H.A. Currier, F.C. Schaefer,
V.P. Wystrach, J. Am. Chem. Soc. 81 (1959) 110.
21] E.L. Eliel, J. Am. Chem. Soc. 71 (1949) 3970.
22] R. MacLeod, F.J. Welch, H.S. Mosher, J. Am. Chem. Soc. 82
−
1
cm
due to carboxylato ligands.
Acknowledgements
The authors thank Ministero della Ricerca Scientifica
e Tecnologica (MURST) for financial support.
[
[
References
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1960) 876.
[
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