On the behaviour of Ru(I) and Ru(II) carbonyl acetates in the presence of H2 and/or acetic acid and their role in the catalytic hydrogenation of acetic acid

Journal of Organometallic Chemistry 690 (2005) 371–382

www.elsevier.com/locate/jorganchem

On the behaviour of Ru(I) and Ru(II) carbonyl acetates in

the presence of H and/or acetic acid and their role in the

catalytic hydrogenation of acetic acid

2

*

Antonella Salvini, Piero Frediani , Carlo Giannelli, Luca Rosi

Department of Organic Chemistry, University of Florence, Via della Lastruccia, 13-50019 Sesto Fiorentino, Italy

Received 9 September 2003; accepted 21 September 2004

Abstract

The reactivity of phosphine substituted ruthenium carbonyl carboxylates Ru(CO) (MeCOO) (PBu ) , Ru (CO) (l-

2

3 2

2

4

2 3 2 4 8 4 3 2 2

MeCOO) (PBu ) , Ru (CO) (l-MeCOO) (PBu ) with H and/or acetic acid was investigated by IR and NMR spectroscopy to clar-

ify their role in the catalytic hydrogenation of acetic acid. Evidences were collected to suggest hydride ruthenium complexes as the

catalytically active species. Equilibria among ruthenium hydrides and carboxylato complexes take place in the presence of hydrogen

and acetic acid, that is in the conditions of the catalytic reaction. Nevertheless the presence of acetic acid reduces the rate of the

6

formation of hydrides. Working at a very high temperature (180°C) polynuclear phosphido hydrides such as [Ru (l-

H) (CO) (l-PHBu)(l-PBu ) (PBu ) (l -P)] were formed. These phosphido clusters are suggested as the resting state of the catalytic

6

10

2 2

3 2

6

system.

Furthermore the bi- or tetranuclear Ru(I) carboxylato complexes react with acetic acid giving a mononuclear ruthenium complex

Ru(CO) (MeCOO)(l-MeCOO)(PBu ), containing a monodentate and a chelato acetato ligands. This complex was spectroscopically

2

3

characterised. Its identity and structure were conﬁrmed by its reactivity with stoichiometric amount of PPh

COO) (PBu )(PPh ), a new mononuclear ruthenium carbonyl carboxylate containing two diﬀerent phosphines, that was fully

characterised.

3 2

to give Ru(CO) (Me-

2

3

Keywords: Ruthenium; Carbonyl carboxylates; Acetic acid; Hydrogenation

1

. Introduction

Ru (CO) (l-MeCOO) (PBu ) (4), were detected in the

4 8 4 3 2

crude of the hydrogenation of acetic acid in the presence

of (1) as catalytic precursor [2a,3]. These carboxylato

complexes (2)–(4) are catalytically active in the hydro-

genation of acetic acid [1b].

The catalytic hydrogenation of carboxylic acids in

homogeneous phase has been investigated in our labo-

ratory for several years [1]. This reaction was achieved

using ruthenium complexes such as Ru H (CO) (P-

The behaviour of (1)–(4) with hydrogen has been

studied [1d,1e,1h] in order to understand their role in

the catalytic hydrogenations. The ruthenium carboxy-

lato complexes (2) and (3) react with hydrogen at low

temperature (50 and 100 °C, respectively) to give the

hydrido complexes RuH (CO) (PBu ) (5), Ru H -

4

8

Bu ) (1) and Ru H (CO) [(ꢀ)-DIOP] [2] as catalytic

3

4

8

2

precursors.

Ruthenium carbonyl carboxylates Ru(CO) (Me-

2

COO) (PBu ) (2), Ru (CO) (l-MeCOO) (PBu ) (3),

2

3 2

2

4

2

3 2

2

3 2

4

*

(CO) (PBu ) (6) and (1) [1h]. At higher temperature

9 3 3

Corresponding author. Tel.: +390554573522; fax: +390554573531.

E-mail address: piero.frediani@uniﬁ.it (P. Frediani).

(over 140 °C), the phosphido ruthenium clusters

0

doi:10.1016/j.jorganchem.2004.09.048

372

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

ꢀ1

by new bands at 2060(ﬀ), 1990(ﬀ) and 1575(m) cm

.

Ru4H4(CO)8(PBu3)4 (1)

5)

Ru4H4(CO)9(PBu3)3 (6)

After 48 h traces of (3) were still present. A quantitative

conversion of (3) into (11) was reached after 70 h.

No other transformations were observed increasing

the temperature up to 120 °C. At this temperature part

of the acetic acid was present in vapour phase decreasing

its concentration in solution. As a consequence the reac-

tion was reversed and (3) returned to be the main complex

present in the solution (Scheme 2). A further increase

of temperature (150 °C) reduced further the concentra-

tion of acetic acid in solution and the amount of (11).

The process is reversible because when the vessel was

cooled to room temperature and the concentration of

acetic acid restored to its initial value, the amount of

RuH2(CO)2(PBu3)2

(

H2 50˚C

H2

100˚C

Ru(CO)2(MeCOO)2(PBu3)2

2)

Ru2(CO)4(MeCOO)2(PBu3)2

(

(3)

H2

T>140˚C

Ru6H6(CO)10(PHBu)(PBu2)2(PBu3)2(P)

Ru6H6(CO)13(PBu2)(PBu3)2(P)

Ru7H8(CO)12(PBu)(PBu2)(PBu3)3(P)

Ru3H2(CO)7(PBu)(PBu3)2

(7)

(8)

(

complex present in solution.

11) increases: after 48 h (11) was the sole ruthenium

In the residue obtained removing the solvent and the

acetic acid at reduced pressure and low temperature

(10 °C), the complexes (11) and (2) were evidenced by

IR spectroscopy using n-pentane as solvent. However,

the IR spectrum of the same residue in a n-heptane/ace-

tic acid solution showed the presence of (11) as the sole

complex in solution because the absorptions of (2) in

acetic acid are shifted and overwhelmed by those of (11).

Complex (11) showed a low stability in a hydrocar-

bon solution in the absence of acetic acid.

(9)

(10)

Scheme 1.

[

(

Ru (l-H) (CO) (l-PHBu)(l-PBu ) (PBu ) (l -P)] (7),

6 6 10 2 2 3 2 6

Ru (l-H) (l-CO)(CO) (l-PBu )(PBu ) (l -P)] (8), [Ru -

6

12

2

3 2

6

7

l-H) (CO) (l -PBu)(l-PBu )(PBu ) (l -P)] (9), [Ru -

8 12 3 2 3 2 6 3

l-H) (CO) (l -PBu)(PBu ) ] (10) are formed [1d,1e]

Scheme 1).

To get more information on the role played by the

complexes (2–4) in the catalytic hydrogenation of acetic

acid we have now investigated the behaviour of these

complexes in the presence of acetic acid or acetic acid

2

7

3

3 2

2.1.1.2. NMR study. The reactivity of (3) with acetic

acid was also carried out in an NMR sample tube using

C D as solvent. After an hour at room temperature a

6

singlet at 43.5 ppm (11.7%) attributable to (11) and a

singlet at 17.2 ppm (1.2%) due to (2) were present in

and H . The reactions were monitored by ‘‘in situ’’

2

3

the P NMR spectrum. Complex (2) was not easily

1

HP-IR spectroscopy, using a cell directly connected to

the reaction vessel. Samples of the solutions were also

analysed by glc and glc-ms to identify the organic prod-

ucts formed. The new ruthenium complexes were char-

acterised by IR and NMR spectroscopy.

Some reactions were also monitored by P NMR

spectroscopy.

At the end of this investigation, the hydrogenating

identiﬁed in the IR spectrum performed in a C D /acetic

6

acid solution when (11) was the main ruthenium com-

plex because the absorptions of (2) in the presence of

acetic acid are overwhelmed by those of (11). However,

if the acetic acid was removed and the residue dissolved

in n-pentane, the presence of (11) and (2) might be easily

evidenced (see above).

3

1

activity of [Ru (l-H) (CO) (l-PHBu)(l-PBu ) (PBu ) -

(l₆-P)] (7) has been tested in order to evaluate the role

played by the phosphido clusters in the catalytic hydro-

A total conversion of (3) was reached after 56 h at

40 °C [70.4% of (11) and 29.6% of (2)]. No other signals

were present in the P NMR spectrum.

6

10

2 2

3 2

3

1

3

1

13

genation of acetic acid.

The P-, H-, and C NMR spectra (C D as sol-

6

vent) of the residue after elimination of the acetic acid

conﬁrmed the presence of (11) and (2). The NMR reso-

nances were shifted with respect to those collected from

the solution containing acetic acid. The presence of (2)

was conﬁrmed by its characteristic resonances. The com-

2

. Results and discussion

2.1. Reactivity of ruthenium carbonyl carboxylates with

acetic acid

plex (11) showed resonances due to PBu (a broad sin-

3

glet at 44.4 ppm in the P NMR spectrum) and CO

1

3

2

.1.1. Ru (CO) (l-MeCOO) (PBu ) (3)

ligands (195.9 (m) ppm in the C NMR spectrum),

two inequivalent MeCOO groups (174.5 and 183.0

2

4

2

3 2

2

n-heptane as solvent, reacted with acetic acid (Ru/

.1.1.1. IR study. Ru (CO) (l-MeCOO) (PBu ) (3), in

2

4

2

3 2

1

3

ppm in the C NMR spectrum attributable to a mono-

and a bidentate acetato ligand, respectively). These

attributions are in agreement with the resonance of the

CH COOH = 1:30) at 40 °C giving a new complex Ru-

3

(

CO) (MeCOO)(l-MeCOO)(PBu ) (11) as evidenced

2 3

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

373

Me

C

O

Bu₃P

Ru

CO CO CO CO

3)

Ru

PBu₃

PBu , MeCOO

MeCOOH

0˚C

3

4

(

1

20˚C

Me

C

OH

Me

^P^B^u3

MeCOO

C

O

MeCOO

CO

Ru

MeCOO

Bu₃P

O

OCOMe

Ru PBu₃

1

20˚C

CO

Ru

PBu₃

2)

CO CO CO CO

(

1

20˚C

PBu₃

Ru (CO) (MeCOO)

2

4

n

^H2

(12)

Me

MeCOO

C

O

^P^B^u3

O

Ru

CO

(11)

Scheme 2.

monodentate acetato group in (2) (175.9 ppm) and the

bidentate acetato ligand in Ru(l-MeCOO) [(S)-BINAP]

and giving an intermediate complex [Ru (CO) (Me-

2 4

COO) (MeCOOH) ] containing two monodentate carb-

2 2

2

3

1

(

188.1 ppm) [4], respectively. The broad signal in the

P

oxylato ligands. An analogous process involving the

formation of a Ru (MeCOO) (CO) (PBu ) containing

NMR spectrum may be due to a rapid intramolecular

rearrangement between the acetato ligands. Several

complexes containing both mono- and bidentate carb-

2

6

3 2

monodentate acetato ligands has been suggested in the

reaction of (3) with CO [1f] as a preliminary step of

the formation of Ru(CO) (PBu ).

oxylato ligands are reported, such as Ru(CO)-

0

4

3

(

p-C H NO , CF , C F , C F ) [5]. A rapid intramolecu-

RCOO)(l-O,O -RCOO)(PPh ) (R = Me, p-C H Cl,

The complexes that we are now proposing are clo-

sely related to those previously isolated by Rotem

et al. [7], containing acetic acid units directly bound

to the metal.

3

2

6

4

6

4

2

3

2

5

6 5

lar exchange between mono- and bidentate carboxylato

ligands was observed by NMR studies on these com-

plexes (R = Me, CF , C F , C F ) [6] at variable

This intermediate Ru(I) complex gives the mononu-

clear Ru(II) complex (11) and H (Scheme 2). A similar

3

2

5

6 5

temperature.

The ﬂuxional structure of the complex (11) was con-

1

ﬁrmed by the H NMR spectrum. The broad resonance

2

reactivity of the coordinated acetic acid was reported to

explain the synthesis of (2) from [Ru (CO) (l-Me-

2

4

at 2.02 ppm, attributed to the methyl group of the ace-

tato ligands, suggests a fast intramolecular rearrange-

ment of the two acetato ligands. An analogous broad

signal in the H NMR spectrum is reported by Spencer

and Wilkinson [5a] for the non-rigid Ru(MeCOO)(l-

COO) ] (12) [8]. Ruthenium (I) was oxidised by the

2 n

coordinated acetic acid and molecular hydrogen was

formed. Fachinetti et al. [9] also suggest an analogous

oxidation of Ru(0) to Ru(I) in the presence of

1

CF COOH.

3

MeCOO)(CO)(PPh ) complex.

3

The partial transformation of (11) into (2) was ob-

served by IR and NMR spectroscopy of the solution

while the contemporary formation of (12), the ruthe-

nium species without phosphinic ligands, was identiﬁed

through IR spectroscopy (KBr pellets) on the yellow res-

idue present in the NMR sample tube.

2

The low stability of (11) in the absence of acetic acid

3

was conﬁrmed by several signals present in the

NMR spectrum recorded after 24 h.

1

P

The formation of (11) is rationalised in Scheme 2.

Acetic acid is added to (3) breaking the acetato bridge

374

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

PBu₃

CO

with resonances at 23.9 (d, 1P, PBu , J = 311.6 Hz)

3 PP

^P^B^u3

MeCOO

O

CO

MeCOO

and 30.5 (d, 1P, PPh , J = 311.6 Hz) ppm. The J_P_Pva-

3

PP

Ru

+

^P^P^h3

Ru

lue is in agreement with a trans coupling between the

two phosphine [11]. The pattern of this NMR spectrum

has been well simulated using the data above reported.

CO

PPh₃

O

C

1

13

The H- and C NMR spectra are in agreement with

two equivalent acetato ligands ruling out the structures

Me

(11)

(13)

(

13c), (13d) and (13e). The pseudo triplet at 198.8 ppm

Scheme 3.

1

3

in the C NMR spectrum may be ascribed to the car-

bon atoms of two equivalent carbonyl groups coupled

with two cis phosphines. As a consequence the struc-

tures (13c), (13d) and (13f) showing two non-equivalent

carbonyl groups must be excluded. The structures (13b)

and (13e) containing the carbonyl groups in a trans posi-

tion must be also discarded because two bands of equal

intensity are present in the carbonyl stretching region of

the IR spectrum.

When the reaction was prolonged for a long time at

20 °C the Ru(II) complexes, (11) and (2), were reduced

to the Ru(I) complex (3) (Scheme 2). An acetato radical

may be involved. It reacted with n-heptane giving acetic

acid and heptenes as showed by glc. No Ru(0) species

were detected. The rearrangement of (2) into (3) at

1

20 °C was previously reported [1d] and attributed to

a thermal transformation. On the contrary a dispropor-

tionation of a polymetallic Ru(I) complex into Ru(0)

and Ru(II) species was reported by Fachinetti et al.

The MS spectrum shows a pattern of peaks centred at

m/z 740 in agreement with the Ru(CO)

(PBu )(PPh ) formulation of (13).

(MeCOO) -

2

[

9,10].

3

The elemental analysis conﬁrm the reported

formulation.

The synthesis of (13) from (11) and PPh conﬁrms

2.1.1.3. Synthesis and structure of Ru(CO) (Me-

COO) (PBu )(PPh ) (13). Complex (11) reacted at

2

3

room temperature with a stoichiometric amount of

PPh₃giving Ru(CO) (MeCOO) (PBu )(PPh ) (13)

also the structure attributed to (11).

2

3

(

Scheme 3), a ruthenium carbonyl carboxylate contain-

2.1.2. Ru

4

(CO)

2.1.2.1. IR study. The complex (4), in n-heptane as

8

(l-MeCOO) (PBu ) (4)

4 3 2

ing two diﬀerent phosphines. This new complex was iso-

lated and spectroscopically characterised.

The data collected are in agreement with an octahe-

dral structure containing a tributylphosphine trans to a

triphenylphosphine, two cis carbonyl groups and two cis

acetato ligands (Fig. 1(a)).

solvent, reacted at room temperature with an excess

of acetic acid (Ru/CH COOH = 1:23) giving (conver-

sion 60% after 24 h) a mixture of ruthenium com-

1

plexes. The new bands at 2060 and 1990 cm were

attributed to (11) while a band at 1999(w) cm sug-

gests the presence of a trace of another unidentiﬁed

product. A broadband was also present in the carboxy-

3

ꢀ

1

The other possible structures (b)–(f) (Fig. 1) have

been ruled out according to the following considera-

3

tions: the P NMR spectrum shows an AB spin system

1

ꢀ1

lato region at 1580 cm suggesting the presence of an

acetato complex. A reasonable mechanistic pathway

for the conversion of (4) into (11) is proposed in

Scheme 4 taking into account the reactivity of (4) with

CO [1f]. A preliminary coordination of acetic acid is

followed by a cleavage of the oxygen bridges between

two Ru atoms giving the complex [Ru (CO) (l-Me-

^P^B^u3

MeCOO

CO

MeCOO

OC

CO

Ru

CO

PPh₃

OCOMe

PPh₃

2

4

(13a)

(13b)

COO) (MeCOOH)(PBu )] (Scheme 4). In a subsequent

2 3

step this complex reacts with acetic acid giving the

complexes (11) and (12). This last complex was identi-

ﬁed as a yellow residue after cooling the vessel.

At higher temperature (120 °C after 24 h) (11) was the

sole complex present in the solution as shown by the IR

spectrum.

PBu₃

PPh₃

MeCOO

PPh₃

CO

MeCOO

PBu3

Ru

CO

(

13c)

(13d)

PBu₃

PBu3

2.1.2.2. NMR study. The reaction of (4) with acetic

acid was also carried out in a NMR sample tube

OC

^P^P^h3

MeCOO

OC

^P^P^h3

Ru

31

(C D as solvent) and monitored by

spectroscopy.

P NMR

6

MeCOO

CO

OCOMe

MeCOO

CO

At room temperature (11) was formed (conversion

4.5% after 1 h) together with trace of two phosphinic

(13f)

(13e)

2

compounds (singlet at 13.4 and 38.8 ppm in the

3

1

Fig. 1.

P

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

375

Me

O

Me

C

O

C

O

CO CO CO CO

C

O

Me

O

Ru

C

PBu3

r.t.

2

Bu3P

Ru

O C

^B^u3^P

Ru

O

OO

O

MeCOOH

OH

C

CO CO CO CO

Me

MeCOOH

(4)

Me

C

OH

Me

MeCOO

PBu3

C

O

MeCOO

Bu3P

O

OCOMe

2

Ru

O

Me

2

Ru

O C

CO

OH

^H2

+

Ru2(CO)4(MeCOO)2

CO CO CO CO

n

(

11)

(12)

Scheme 4.

NMR). After 8 days (11) was the main complex (75.6%)

present in the solution and (4) was still present (12.3%).

A yellow insoluble product was also formed and identi-

ﬁed by IR spectroscopy as (12).

2.2. Reactivity of ruthenium carbonyl carboxylates with

hydrogen and acetic acid

The reaction of ruthenium complexes (2–4) with

hydrogen and acetic acid, that is in the conditions em-

ployed for the hydrogenation of acetic acid, was tested

by IR spectroscopy. The organic products were identi-

ﬁed and quantiﬁed by glc and glc-ms analyses.

The conversion of (4) was complete after 15 days at

room temperature and (11) was the main product in

the solution (87.2%) together with an unidentiﬁed prod-

3

1

uct having a singlet at 38.8 ppm (12.8%) in the

NMR.

P

The IR and NMR spectra of the residue obtained

after distillation of the solvent and acetic acid at low

temperature and reduced pressure showed (11) as the

main ruthenium species. This solution was employed

to perform the spectroscopic characterisation of (11)

2.2.1. Ru (CO) (l-MeCOO) (PBu ) (3)

2

4

2

3 2

The complex (3), in a n-heptane solution, did not re-

act with acetic acid (Ru/CH COOH = 1:30) and hydro-

3

gen (100 atm) at room temperature after a long time (15

days).

(

see Section 4).

The IR spectrum of (3) was unchanged even if the

solution was heated up to 140 °C; however in these con-

ditions ethyl acetate was formed through the hydrogen-

ation of acetic acid.

Only at 180 °C after 24 h (3) was transformed into the

hydrido clusters (7), (9) and (10). The same ruthenium

complexes were formed at lower temperature from (3)

and hydrogen (50 atm) [1e]. The presence of acetic acid

reduces the rate of the transformation of (3) into phos-

phido ruthenium clusters.

This behaviour supports the hypothesis that interme-

diate hydrido ruthenium complexes must be involved in

these transformations [1h]. The presence of acetic acid

decreases the rate of the hydrogenolysis of the acetato

group in (3) because this reaction involves the formation

of ruthenium hydrides and acetic acid. Furthermore, the

presence of hydrogen hinders the formation of (11) by

reaction of (3) and acetic acid, in agreement with the

mechanism reported in Scheme 2.

2

.1.3. Ru(CO) (MeCOO) (PBu ) (2)

3 2

2

Complex (2) did not react with acetic acid at room

temperature in n-heptane solution (Ru/

CH COOH = 1:30). Only a shift of the carbonyl

stretchings of (2) to higher frequencies was due to the

presence of acetic acid. This behaviour is reversible: if

the liquids were removed and the residue dissolved in

n-heptane the starting spectrum of (2) was restored. In

the same way the resonances of (2) were shifted when

the H-, P- and C NMR spectra were recorded in a

MeCOOH/C D solution (Table 1). The multiplicity

and the coupling constants remain unchanged in all

cases.

a

3

1

31

13

6

A temperature of 140 °C was required to observe the

conversion of (2) into traces of (3); the amount of (3) in-

creased after heating at 150 °C, as expected, according

to the thermal stability of (2) [1d].

376

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

Table 1

a

Spectroscopic data of Ru(CO)

2

(MeCOO)

2

3

(PBu )

2

: inﬂuence of acetic acid

ꢀ

1

)

31

1

13

Solvent

IR m (cm

Solvent

C D

P NMR (ppm)

H NMR (ppm)

0.86 (t, 18H, CH

HH = 7.3 Hz), 1.28

(q, 12H, CH CH

HH = 7.3 Hz), 1.50

m, 12H, CH CH P),

.86 (m, 12H, CH P),

.25 (s, 6H, CH COO)

C NMR (ppm)

n-Heptane

2041(vs)

6

17.4

3

CH

2

,

13.8 (s, CH CH ), 23.7

2

3

1

971(vs)

628(m)

J

(s, CH

(t, CH

3

COO), 23.9

3

2

,

2

P, JCP = 12.7 Hz),

J

24.8 (t, CH

3 2

CH ,

(

2

JCP = 6.3 Hz), 25.4

1

2

(s, CH

2 2

CH P), 175.9

3

COO), 199.0

(

t, CO, JCP = 10.9 Hz)

n-Heptane/MeCOOH

2049(vs)

C

6

D

6

/MeCOOH

17.2

0.85 (t, 18H, CH

HH = 7.3 Hz), 1.28

(q, 12H, CH CH

HH = 7.3 Hz), 1.42

m, 12H, CH CH P),

.81 (m, 12H, CH P),

.27 (s, 6H, CH COO)

3

CH

2

,

14.1 (s, CH CH ), 23.6

2

3

1

988(vs)

575(m)

J

(s s, CH COO), 24.1

(t, CH P, JCP = 12.7 Hz),

25.0 (t, CH CH

CP = 6.3 Hz), 25.6

3

2

,

2

J

3

2

,

(

2

J

1

2

(s, CH

2

CH

2

P), 179.3

3

COO), 198.7

(

t, CO, JCP = 10.9 Hz t)

a

NMR data are partially reported [1a].

2

.3. Ru (CO) (l-MeCOO) (PBu ) (4)

gen (100 atm) at room temperature. Only a shift of the

bands in the IR spectrum was shown as observed under

nitrogen.

4

8

4

3 2

The complex (4), in n-heptane as solvent, reacted in

the presence of acetic acid (Ru/CH COOH = 1:23) and

Heating this solution for 24 h at 80 °C the complexes

(5) [1d] and RuH(CO) (MeCOO)(PBu ) (14) [13] [con-

3

hydrogen (100 atm at room temperature) at 60 °C giv-

ing (3) (traces after 72 h) as reported in Scheme 5. The

complex (12), formed as a concomitant product, was

recovered as a yellow solid and identiﬁed by IR

spectroscopy.

2

3 2

version of (2) 56%; (5)/(14) = 1/1 molar ratio] were

formed. Traces of (3) were also formed after 48 h at this

temperature.

The conversion of (2) increased when the solution

was heated at higher temperature; the dihydride (5)

was the main ruthenium complex (49%) after 24 h at

100 °C [conversion 79%; (5)/(14) = 1.6 molar ratio] and

(5) became 65% at 140 °C after 24 h [conversion 94%;

(5)/(14) = 2.2 molar ratio].

At 180 °C, (5) (78%) and (14) (22%) were present to-

gether with traces of (2) and (3): at this temperature

ethyl acetate was also formed by reduction of acetic

acid.

The same reaction takes place in a large extent at

0 °C in the presence of only hydrogen [1f] or through

6

a thermal rearrangement of (4) at 150 °C [8,12].

These data support the hypothesis that the phosphine

redistribution also takes place through hydride interme-

diates, formed in an undetectable amount. The forma-

tion of ruthenium hydrides is reduced by the presence

of acetic acid and consequently the phosphine redistri-

bution is very low. It was necessary to heat (4) at 140

°

C for 20 h to obtain a (4)/(3) molar ratio of 3:2.

The complex (4), heated at 160 °C for 25 h, was al-

The rate of the transformation of (2) into (5) was re-

duced by the presence of acetic acid according to the

equilibria reported in Scheme 6.

most completely transformed into (3) and (12). Ethyl

acetate was also present in the solution collected at this

temperature and analysed by glc.

The formation of (14) as intermediate of the reaction

of (2) with hydrogen has been previously reported work-

ing at low temperature (50 °C) in the presence of

Na CO [1h].

2

.4. Ru(CO) (MeCOO) (PBu ) (2)

2 2 3 2

2

3

The presence of an excess of acetic acid reduce the

rate of the formation of (5) and, as a consequence, in-

creases the amount of (14).

The complex (2), in a n-heptane solution, did not re-

act with acetic acid (Ru/CH COOH = 1:30) and hydro-

3

Ru (CO) (µ−MeCOO) (PBu )

Ru (CO) (µ−MeCOO) (PBu ) + 1/n[Ru (CO) (µ−MeCOO) ]

4

8

4

3 2

2

4

2

3 2

2

4

2 n

(

4)

(3)

Scheme 5.

(12)

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

377

Ru(CO) (MeCOO) (PBu ) + H

RuH(CO) (MeCOO)(PBu ) + MeCOOH

2 3 2

2

3 2

2

(

2)

(14)

RuH(CO) (MeCOO)(PBu ) + H

RuH (CO) (PBu ) + MeCOOH

2

3 2

2

3 2

(

14)

(5)

Scheme 6.

Table 2

Hydrogenation of unsaturated organic substrates in the presence of ruthenium complexes

Catalyst

Code

Hydrogenation of (yield %)

a

b

c

d

Cyclohexene

Tiglic acid

Acetophenone

Acetic acid

Ru

4

H

4

(CO)

8

(PBu

3

)

(MeCOO) (PBu )

4

(1)

(2)

(3)

(4)

(7)

47.1

2.0

21.7

15.4

98.2

79.1

0.3

9.6

45.8

65.7

14.3

1.0

40.7

16.5

34.4

29.9

2.9

Ru(CO)

2

2 3 2

Ru

2

(CO)

4

(l-MeCOO)

2

(PBu

3

)

2

22.2

88.3

0.4

4

8

4

3

[

6 6 2 2 3 2 6

Ru (l-H) (CO)10(l-PHBu)(l-PBu ) (PBu ) (l -P)]

Catalyst: 0.018 mmol Ru, substrate: 42.5 mmol, p(H

a

2

) = 130 atm, reaction time 22 h.

T = 60 °C, hydrogenated product: cyclohexane.

b

Solvent: 20 ml, toluene/ethanol (1:1), T = 100 °C, hydrogenated product: 2-methylbutanoic acid.

T = 120 °C, hydrogenated product: 1-phenylethanol.

c

d

Catalyst: 0.139 mmol Ru, substrate 433 mmol, T = 180 °C, reaction time 48 h, hydrogenated product: ethyl acetate.

2

.5. Catalytic activity of [Ru (l-H) (CO) (l-PHBu)-

(11) containing a chelato and a monodentate acetato lig-

and. The same reactivity may be involved in the synthe-

sis of (2) from (12) in the presence of acetic acid and a

6

10

(

l-PBu ) (PBu ) (l -P)] (7)

2

3 2

6

The phosphido clusters (7)–(10) were formed from

stoichiometric amount of PBu [8].

3

the catalytic precursors (1–4) when heated at high tem-

perature under hydrogen. The catalytic activity of (7),

the main cluster formed, was correlated with those of

its precursors (1–4) to evaluate the role of phosphido

clusters in the hydrogenations performed in the presence

of the ruthenium complexes (1–4) as catalytic

precursors.

The complex (11) is stable in the presence of acetic

acid but easily reacts at room temperature with PPh₃

giving a new complex containing two diﬀerent phosphi-

nic ligands (13).

The reactivity of ruthenium complexes (3) and (4)

changes when hydrogen and acetic acid are both pre-

sent: (3) does not react up to 180 °C while (4) gives (3)

and (12) at 60 °C. The high hydrogen pressure (100

atm) hinders the formation of (11) from (3) or (4) in

agreement with a process involving the formation of

molecular hydrogen (Schemes 2 and 4).

Diﬀerent substrates were hydrogenated in the

presence of (7) and the ruthenium precursors (1)–(4)

(

Table 2).

Complex (7) was catalytically active in the hydrogen-

ation of the substrates tested even if its activity was

lower than that of the other catalysts. Furthermore the

cluster (7) was recovered unaltered at the end of these

hydrogenations.

The low catalytic activity of (7) suggests the forma-

tion of phosphido clusters as the cause of the gradual

loss of activity of (1)–(4) in the course of the reduction

of acetic acid at 180 °C.

Hydride ruthenium complexes (1), (5)–(10) and (14)

are formed in the reactions of (2)–(4) with hydrogen

and acetic acid but the presence of acetic acid reduces

the rates of these reactions. These results conﬁrm the

hypothesis that hydride ruthenium complexes are the ac-

tive species in the catalytic hydrogenation of acetic acid

[1h] and suggest equilibria among H–Ru and CH COO–

3

Ru species. In the presence of a large amount of acetic

acid these equilibria are shifted towards the ruthenium

carboxylates (2), (3) and (4).

3

. Conclusions

The hydrogenation of acetic acid to ethyl acetate

takes place at 140 °C in the presence of (3), at 160 °C

with (4) and at 180 °C with (2). In these conditions (3)

is always formed even if in diﬀerent amounts from (4)

or (2) depending on the ruthenium precursor and reac-

tion temperature employed. These results support the

hypothesis that the same catalytically active intermedi-

ate is formed from (2)–(4) in the course of acetic acid

The phosphine substituted ruthenium carbonyl carb-

oxylates (3) and (4) react, at low temperature (25–40 °C)

with a large excess of acetic acid to form new complexes

containing monodentate acetato ligands. Further reac-

tion of these intermediates leads to the formation of

hydrogen and a mononuclear ruthenium (II) complex

378

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

hydrogenation. Furthermore the hydride species are

transformed into phosphido ruthenium cluster com-

plexes such as (7) in the course of the reaction.

Elemental analyses were performed with a Perkin–El-

mer model 240 C system.

Tlc separations were performed on silica gel (thick-

ness 2 mm) or alumina (thickness 1.5 mm) chromato-

The polynuclear ruthenium complex (7) shows a cat-

alytic activity lower than the precursors (1)–(4). As a

consequence the loss of catalytic activity shown by the

ruthenium complexes (1)–(4) in the reduction of acetic

acid may be ascribed to this transformation [1b]. Other

authors attribute the deactivation of catalytic systems to

the partial loss of the alkyl groups of the phosphine lig-

ands with formation of phosphido clusters [14].

graphic plate (Merck) with ﬂuorescent indicator F₂₅₄

.

4.2. Test procedure

4.2.1. Reactivity of ruthenium complexes by IR spectro-

scopy

All tests were performed in a stainless steel autoclave

(125 ml) equipped with two stopcocks and a high-

pressure gauge. Air was evacuated from the vessel, the

solution of reactants was introduced by suction then

the gas (nitrogen or hydrogen) was transferred from a

cylinder up to the pressure required.

4

. Experimental

4

.1. Instruments

The vessel was connected through a stainless-steel

low volume (2 ml) coil to the IR cell, equipped with

NaCl windows, capable of withstanding high pressure

(200 atm), which could be heated up to 200 °C. The coil

was kept at the same temperature of the system. The

solution present in the autoclave was transferred into

the IR cell under reaction conditions and examined by

IR spectroscopy. All spectra were recorded after abun-

dant ﬂushing of both coil and IR cell with the solution

present in the vessel. The solvent (n-heptane) bands were

compensated using a variable-path IR cell.

Gas chromatographyc analyses (glc) were performed

with a Perkin–Elmer Sigma 1 system coupled with a Per-

kin–Elmer Sigma 10 computer or using a Shimadzu GC-

1

4A chromatographic system coupled with a Shimadzu

C-R4A computer. Both systems were equipped with a

FID detector.

The following packed columns (2 m) were used: PPG

(

1

‘‘Polypropylenglicol’’ LB-550-X on Chromosorb W at

5%), FFAP (‘‘free fatty acids phase’’ on Chromosorb

G AW-DMCS at 5%), CW (‘‘Carbowax 20M’’ on Chro-

mosorb W at 15%).

The conversion of acetic acid to ethyl acetate was

evaluated using a calibration curve.

4.2.2. Catalytic hydrogenation experiments

A solution containing the catalytic precursor, solvent,

substrate and hydrogen was introduced into an evacu-

ated stainless steel autoclave (150 ml) containing a steel

cylinder (72 ml) to reduce the free volume. The tests of

acetic acid hydrogenation were carried out in a ‘‘Hastel-

loy C’’ stainless steel rocking autoclave (125 ml). The

vessel was placed in a thermostatic oil bath set at the de-

sired temperature (±1 °C) and rocked for the preﬁxed

time. The amounts of catalytic precursor, solvent, sub-

strate and hydrogen are reported in Table 2.

Glc-ms spectra were collected using a Shimadzu GC-

MS QP2000 instrument or a Carlo Erba QMD 1000

GC-MS system equipped with capillary columns: a

TM

SPB-1

(Supelco column, 30 m, internal diameter

TM

.25 mm) or a AT -1 (Alltech column, 30 m, internal

0

diameter 0.25 mm).

A Perkin–Elmer SCIEX API 365, a turbo ion spray

system, was employed to obtain the MS spectra of the

ruthenium complex.

Infrared spectra were recorded, at room temperature

and pressure, with a Perkin–Elmer model 1760-X FTIR

spectrophotometer. Liquid products and solutions were

At the end of the reaction, the reactor was cooled, the

gases vented and the solution analysed by glc. The iden-

tity of the products was conﬁrmed by glc-ms analysis.

analysed using KBr or CaF cells having 0.1 mm path.

2

Solid samples were mulled with KBr. The IR spectra

collected at high pressure and temperature were re-

corded with a Perkin–Elmer spectrophotometer mod.

4.3. Materials

All preparations and manipulations were routinely

performed under dry nitrogen using Schlenk tube

techniques.

5

[

80B Data System using the cell previously described

1d].

Multinuclear NMR spectra were registered using a

Varian VXR300 spectrometer operating at 299.944

Reagents and solvents were puriﬁed and dried as re-

ported. Acetic acid was distilled under nitrogen (bp

118 °C). Cyclohexene was eluted through activated

Al O (70–230 mesh) and rectiﬁed under nitrogen (bp

1

13

MHz for H, at 75.429 MHz for C and at 121.421

3

MHz for P NMR; tetramethylsilane was used as exter-

1

2

3

1

13

31

nal standard for H- and C NMR spectra. In the

NMR spectra, downﬁeld values from external H PO

31

85%) were taken as positive. C- and P NMR spectra

P

83 °C). Acetophenone was distilled prior to use (bp 82

°C/15 mmHg). Toluene was reﬂuxed on sodium metal,

then reﬂuxed and distilled on LiAlH . n-Heptane was

puriﬁed by treatment with conc. H SO , washed with

3

4

1

3

(

were recorded as proton decoupled spectra.

4

2

4

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

379

a solution of KMnO in H SO (10%), dried on anhy-

4

heated under nitrogen (5 atm at 20 °C) in the tempera-

ture range 20–150 °C.

The reaction was followed as reported in the general

2

4

drous CaCl , reﬂuxed on sodium and distilled on

2

LiAlH . Methanol, dried as reported by Vogel [15],

4

had bp 65 °C. Tri-n-butylphosphine was distilled under

nitrogen prior to use (bp 158–160 °C/60 mmHg).

All other solvents and chemicals were reagent grade

and used without further puriﬁcation.

procedure.

A sample of the solution was collected after heating

at 40 °C. After evaporation of the solvent and acetic

acid under reduced pressure the residue was dissolved

in n-heptane and analysed by IR spectroscopy: only

ꢀ

1

the bands at 2041(vs), 1971(vs) and 1628(m) cm attrib-

4

.3.1. Synthesis of ruthenium complexes

Complexes Ru H (CO) (PBu ) (1) [16], Ru(CO)₂-

1

utable to the starting complex were present. The H-,

4

8

3 4

3

1

13

P- and C NMR spectra were recorded on the residue

dissolved in C D or in C D containing the same con-

(

MeCOO) (PBu₃)₂(2) [8], Ru (CO) (l-MeCOO) (P-

2 2 4 2

Bu ) (3) [17], Ru (CO) (l-MeCOO) (PBu ) (4) [12],

6

3

2

4

8

4

3 2

centration of MeCOOH used for the reactivity tests.

The absorptions are reported in Table 1.

RuH (CO) (PBu ) (5) [1d], Ru H (CO) (PBu ) (6)

4

2

3 2

4

9

3 3

[

16], [Ru (l-H) (CO) (l-PHBu)(l-PBu ) (PBu ) (l -P)]

6 6 10 2 2 3 2 6

(

7) and [Ru (CO) (l-MeCOO) ] (12) [17] were prepared

2 4 2 n

1 31 13

4.5. Reactivity of ruthenium complexes in the presence of

acetic acid: NMR study

as described in the literature. The H-, P- and

C

NMR spectra of (1)–(4) and (6) were performed using

the same solvents (C D ) employed in experimental tests

6

4

.5.1. Ru (CO) (l-MeCOO) (PBu ) (3) with MeCOOH

with the aim to facilitate their identiﬁcation in the course

of the reactions (Table 3).

2

4

2

3 2

A solution of (3) (24 mg, 0.029 mmol) and acetic acid

0.1 ml, 1.747 mmol) in C D (1 ml) was introduced, un-

(

der nitrogen, into a NMR sample tube.

6

4.4. Reactivity of ruthenium complexes in the presence of

acetic acid: IR study

After 56 h at 40 °C two singlet at 43.5 (70.4%) and

7.2 ppm (29.6%) were present in the P NMR spec-

3

1

trum while broad bands at 2060(vs), 1990(vs), 1950(vw)

A solution of the system under examination was

introduced in the autoclave, then N (5 atm) was added.

ꢀ

1

and 1575(w) cm were present in the IR spectrum.

The solution was evaporated to dryness and the resi-

due dissolved in C D : a broad singlet was present in the

2

IR spectra were recorded under reaction conditions

after heating the solution at the pre-ﬁxed temperature

for the selected time.

6

3

1

P NMR spectrum at 44.4 ppm (70.4%), attributed to

11), together with a singlet at 17.4 ppm (29.6%), attrib-

uted to (2).

(

4

.4.1. Ru (CO) (l-MeCOO) (PBu ) (3) with MeCOOH

2

4

2

3 2

1

In the H NMR spectrum (C D ) signals attributed

6

A solution of (3) (120 mg, 0.144 mmol) and acetic

to (11) were present at d 0.77 (m, 9H, CH , PBu ),

1.16 (m, 6H, CH CH , PBu ), 1.30 (m, 6H, EtCH ,

PBu ), 1.63 (m, 6H, PCH , PBu ), 2.06 (s broad, 6H,

3

acid (0.5 ml, 8.734 mmol) in n-heptane (60 ml) was

heated under nitrogen (5 atm at 20 °C) in the tempera-

ture range 40–150 °C.

The reaction was followed as reported in the general

procedure.

3 2 3 2

3

2

3

CH COO) ppm and other resonances attributed to (2)

3

at d 0.90 (t, 18H, CH , PBu , J = 7.1 Hz), 1.30 (m,

3

HH

12H, CH CH , PBu ), 1.53 (m, 12H, EtCH , PBu ),

3 2 3 2 3

1.87 (m, 12H, PCH , PBu ), 2.27 (s, 6H, CH COO)

ppm.

2 3 3

4

.4.2. Ru (CO) (l-MeCOO) (PBu ) (4) with MeCOOH

4

8

4

3 2

A solution of (4) (119 mg, 93.8 lmol) and acetic acid

0.5 ml, 8.734 mmol) in n-heptane (60 ml) was heated

13

The C NMR spectrum (C D ) showed signals

6

(

attributed to (11) at d 13.4 (s, CH , PBu ), 20.1 (s, l-

3

under nitrogen (5 atm at 20 °C) in the temperature range

2

CH COO), 23.5 (s, CH COO), 24.1 (m, PCH , PBu ),

24.3 (s, CH CH , PBu ), 24.9 (m, EtCH , PBu ), 174.5

3

2

3

0–140 °C.

The reaction was followed as reported in the general

3 2 3 2 3

(s, COO), 183.0 (s, l-COO), 195.9 (m, CO) ppm and

procedure.

The solution recovered at the end of the experiment

was evaporated to dryness, the residue dissolved in

other resonances attributed to (2) at d 13.8 (s, CH₃,

PBu ), 23.7 (s, CH COO), 23.9 (t, PCH , PBu ,

J_P_C= 12.7 Hz), 24.8 (t, CH CH , PBu , J = 6.3 Hz),

3

2

3

2

3

PC

1

31

C D and analysed by IR, H- and P NMR. Several

6

3

singlets were present in the P NMR spectrum besides

6

25.4 (s, EtCH , PBu ), 175.9 (s, COO), 199.0 (t, CO,

J_P_C= 10.9 Hz) ppm.

2 3

1

the signals at 43.5 ppm due to (11), at 17.4 (2), 38.5,

4

The IR spectrum of the same sample dissolved in n-

pentane showed the bands of the complex (11) at

3.1, 44.6, 45.4, 53.3 ppm.

ꢀ

1

057(vs), 1987(vs), 1603(w), 1563(vw) cm and those

2

of the complex (2) at 2041(s), 1971(s), 1628(vw) cm

ꢀ

1

4

.4.3. Ru(CO) (MeCOO) (PBu ) (2) with MeCOOH

2

.

2

3 2

A solution of (2) (190 mg, 0.279 mmol) and acetic

acid (0.5 ml, 8.734 mmol) in n-heptane (60 ml) was

The sample kept for 24 h at room temperature in a

C D solution, without acetic acid, was transformed in

6

380

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

Table 3

NMR data of ruthenium complexes in C

6

D

6

as solvent

3

1

13

Complex

P NMR

H NMR

C NMR

14.0 (s, CH

24.9 (t, CH

26.6 (s, CH

a

(

1)

16.6

ꢀ16.60 (qt,4H, HRu, JHP = 6.0 Hz)

3

)

0

.91 (t, 36H, CH

.34 (q, 24H, CH

3

, JHH = 7.3 Hz)

3

CH

2

, JCP = 6.0 Hz)

1

3

CH

2

, JHH = 7.3

2 2

CH P)

Hz)

1

.52 (m, 24H, CH

.86 (m, 24H, CH

2

CH

P)

2

P)

2

31.7 (t, CH P, JCP = 10.4 Hz)

202.2 (m, CO)

1

2

b

(

3)

8.3

0.89 (t, 18H, CH

.35 (q, 12H, CH

Hz)

3

CH

2

, JHH = 6,8 Hz)

, JHH = 6.8

13.8 (s, CH

23.4 (s, CH

3

2

CH )

1

3

CH

2

3

COO)

1

.56 (m, 12H, CH

.81 (m, 12H, CH

2

CH

P)

2

P)

24.6 (t, CH

2

P, JCP = 7.9 Hz)

CH

CH P)

24.8 (t, CH

3

2

, JCP = 5.6 Hz)

.85 (s, 6H, CH

3

COO)

25.6 (s, CH

2

1

86.3 (t, COO, JCP = 7.9 Hz)

08.3 (m, CO)

2

c

(

4)

6.1

0.85 (t, 18H, CH

.28 (q, 12H, CH

Hz)

3

CH

2

, JHH = 6,8 Hz)

, JHH = 6,8

13.8 (s, CH

23.5 (s, CH

3

CH

2

)

1

3

CH

2

3

COO)

1

2

.43 (m, 12H, CH

.67 (m 12H, CH

.12 (s, 12H, CH

2

CH

P)

COO)

2

P)

23.8 (d, CH

2

P, JCP = 12.7 Hz)

CH , JCP = 6.5 Hz)

CH P)

85.3 (d, COO, JCP = 6.5 Hz)

2

24.7 (d, CH

3

2

3

25.4 (s, CH

2

1

2

03.5 (d, CO, JC–P = 10.9 Hz)

05.4 (d, CO, JC–P = 10.9 Hz)

a

(

6)

20.7

22.7

ꢀ16.85 (m, 4H, HRu)

ꢀ16.69 (m, 4H, HRu)

n.d.

0

1

3

.97 (t, 27H, CH , JHH = 7,3 Hz)

.43 (m, 18H, CH

.60 (m, 18H, CH

.89 (m, 18H, CH

3

2

CH

P)

2

)

P)

2

d

(

11)

13)

44.4

0.77 (m, 9H, CH

H, CH CH , PBu

EtCH , PBu

PBu ), 2.06 (s broad, 6H, CH

3

, PBu

3

), 1.16 (m,

13.4 (s, CH

3

, PBu

3

), 20.1 (s, l-

COO), 24.1 (m,

), 24.3 (s, CH PBu ), 24.9

PBu ), 174.5 (s, COO), 183.0

s, l-COO), 195.9 (m, CO)

13.5 (s, CH CH ), 23.2 (s, CH

24.0 (d, CH P, JCP = 22.6 Hz), 24.5

(d, CH CH , JCP = 11.3 Hz), 25.1 (s,

CH CH P), 130.3 (s, C , PPh ),

131.4 (s, C , PPh ), 132.3 (d, C

6

3

2

3

), 1.30 (m, 6H,

C

3

COO), 23.5 (s, C

PC PBu

(m, EtC

3

2

3

), 1.63 (m, 6H, PCH

2

,

2

3

C

2

3

COO)

2

3

(

n

23.0 (AB, 1P, JPP = 317.4 Hz, P Bu

3

),

0.82 (t, 9H, CH

3

CH

COO), 1.94 (m, 6H, CH

, PPh ), 7.10 (m, 6H, H

), 7.96 (m, 6H, H , PPh

2

, JHH = 7.3 Hz),

P), 1.88 (s, 6H,

P), 7.02

3

2

3

COO),

29.7 (AB, 1P, JPP = 317.4 Hz, PPh

3

)

1.24 (q, 6H, CH

3

2

1

.49 (m, 6H, CH

2

3

2

CH

3

2

m

3

(

m, 3H, H

p

3

m

,

p

3

i

,

PPh

3

o

3

)

PPh

3

, JCP = 11.3 Hz), 134.6 (d, C

o

,

3

, JCP = 9.0 Hz), 175.8 (s,

3

CH COO), 198.8 (pt, CO, JCP = 11.3

Hz)

a

b

c

NMR data are partially reported [16].

NMR data are reported in CDCl as solvent [17,18].

NMR data are partially reported [12].

3

d

43.5 in the presence of acetic acid.

several compounds as shown by various singlets present

The conversion of (4) was 24.5% after 1 h and 100%

after 15 days at room temperature. The singlet of (11) at

3

1

in the P NMR spectrum as above reported.

4

3.5 ppm was the main resonance (87.2%) and a yellow

4

.5.2. Ru (CO) (l-MeCOO) (PBu ) (4) with MeCOOH

residue was present in the sample tube. The solid was

separated and the IR spectrum recorded as nujol mull

showed bands at 2055(s), 1995(vs), 1970(vs), 1910(s)

4

8

4

3 2

A solution of (4) (18.4 mg, 0.014 mmol) and acetic

acid (0.1 ml, 1.747 mmol) in C D (1 ml) was intro-

duced, under nitrogen, into a NMR sample tube. After

6

ꢀ

1

and 1555(vs) cm attributable to (12).

The solution was evaporated to dryness and the res-

idue dissolved in C D and spectroscopically character-

1

h at room temperature new singlets were present in the

P NMR spectrum at 43.5 (11), 38.8 and 13.4 ppm.

3

1

6

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

381

ised as complex (11). NMR data are reported in

Table 2.

In the IR spectrum (n-pentane) were present bands

°C at a rate of 30 °C/min and kept at this temperature

for 10 min. The peaks due to acetic acid and ethyl ace-

tate were identiﬁed and quantiﬁed.

ꢀ

1

at 2057(vs), 1987(vs), 1563(vw, broad) cm

(

due to

11).

4.7.1. Ru (CO) (l-MeCOO) (PBu ) (3)

2

4

2

3 2

A solution of (3) (120 mg, 0.144 mmol) and acetic

acid (0.5 ml, 8.734 mmol) in n-heptane (60 ml) under

hydrogen (100 atm at 20 °C) was heated in the temper-

ature range 20–180 °C.

4

.6. Synthesis of Ru(CO) (MeCOO) (PBu )(PPh ) (13)

2 2 3 3

Triphenylphosphine (15.21 mg, 0.058 mmol) was

added to the solution containing (11) in C D (PPh /

Ru = 1/1, molar ratio) at room temperature and the

mixture monitored by P NMR.

After 3 h a second-order AB spin system with reso-

nances at d 23.9 (d, 1P, PBu , J = 311.6 Hz) and

3

the P NMR spectrum while the intensity of the singlet

The reaction was followed as reported in the general

6

3

procedure.

3

1

At the end of the reaction the vessel was cooled to

room temperature, the solvent evaporated under re-

duced pressure and the solid recovered and separated

by preparative tlc on alumina using n-hexane as eluant.

Traces of hydride clusters (7), (9) and (10) were

obtained.

3

PP

0.5 (d, 1P, PPh , J = 311.6 Hz) ppm was present in

3 PP

3

1

attributable to (11) was very low. The conversion was

9

0% after 5 h.

The solvent was evaporated and the new complex,

4.7.2. Ru (CO) (l-MeCOO) (PBu ) (4)

4

8

4

3 2

recrystallized from n-pentane at 0 °C as white crystals

and spectroscopically characterised.

The IR spectrum of (13) (n-pentane), in the 2200–

A solution of (4) (119 mg, 93.8 lmol) and acetic acid

(0.5 ml, 8.734 mmol) in n-heptane (60 ml) under hydro-

gen (100 atm at 20 °C) was heated in the temperature

range 40–180 °C.

ꢀ

1

and 1626(m) cm

500 cm region, showed bands at 2044(vs), 1982(vs)

ꢀ

1

.

In the H NMR spectrum of (13) (C D ) signals were

The reaction was followed as reported in the general

1

procedure.

6

present at d: 0.79 (t, 9H, CH , PBu , J = 7.3 Hz), 1.21

3

HH

(

EtCH , PBu ), 1.84 (s, 6H, CH COO), 1.91 (m, 6H,

q, 6H, CH CH , PBu , J = 7.3 Hz), 1.46 (m, 6H,

4.7.3. Ru(CO) (MeCOO) (PBu ) (2)

2

3

2

3

HH

2

3 2

A solution of (2) (190 mg, 0.279 mmol) and acetic

acid (0.5 ml, 8.734 mmol) in n-heptane (60 ml) under

hydrogen (100 atm at 20 °C) was heated in the temper-

ature range 20–180 °C.

2

3

PCH , PBu ), 7.02 (m, 6H, PPh ), 7.70 (m, 3H, PPh ),

2

3

7

.93 (m, 6H, PPh ) ppm.

3

1

In the C NMR spectrum of (13) (C D ) signals were

3

6

present at d: 13.5 (s, CH , PBu ), 23.2 (s, CH COO),

The reaction was followed as reported in the general

3

2

PBu , J = 11.3 Hz), 25.1 (s, EtCH , PBu ), 130.3 (s,

4.0 (d, PCH , PBu , J = 22.6 Hz), 24.5 (d, CH CH ,

2 3 CP 3 2

procedure.

3

CP

2

3

C , PPh ), 131.4 (s, C , PPh ), 132.3 (d, C_i_p_s_o, PPh₃,

m

4.8. Catalytic hydrogenation experiments: analyses of the

hydrogenation products

3

p

3

J_C_P= 11.3 Hz), 134.6 (d, C , PPh , J = 9.0 Hz),

o

3

CP

1

75.8 (s, COO), 198.5 (m, CO) ppm.

MS spectrum of (13) m/z (%): 740 (10) [M] , 712 (2)

+

The experimental conditions and the results are re-

ported in Table 2.

+

[M–CO] , 681 (100) [M–CH COO] , 653 (20) [M–

3

CH COO–CO] , 622 (5) [Ru(PPh )(PBu )(CO) ] (cen-

+

The products present at the end of the hydrogenation

were analysed by glc and their identities conﬁrmed by

glc-ms.

3

2

tres of each ruthenium cluster peaks are reported)

Elemental analysis of (13), for C H O P Ru: % C

3

6

48

6 2

5

8.3 (58.45), % H 6.6 (6.54).

The solvent, the starting substrate and the reaction

products were separated and quantiﬁed using the fol-

lowing conditions:

4.7. Reactivity of ruthenium complexes with acetic acid

and hydrogen

ꢁ

Cyclohexene: a PPG column was kept at 40 °C for 25

min.

A n-heptane solution of each ruthenium complex and

acetic acid was introduced in the autoclave under dry

ꢁ Tiglic acid: a FFAP column was kept at 140 °C per 15

nitrogen, then H (100 atm) was added.

2

min.

IR spectra were recorded in the reaction conditions

after heating the solution at the pre-ﬁxed temperature

for the selected time.

Samples of the solution examined by IR spectros-

copy, were collected and analysed by glc using a FFAP

column kept at 50 °C for 7 min, then heated up to 130

ꢁ Acetophenone: a CW column was kept at 60 °C for 5

min, then heated up to 160 °C at a rate of 20 °C/min

and kept at this temperature for 10 min.

ꢁ Acetic acid: a FFAP column was kept at 50 °C for 7

min, heated up to 130 °C at a rate of 30 °C/min and

kept at this temperature for 10 min.

382

A. Salvini et al. / Journal of Organometallic Chemistry 690 (2005) 371–382

In the hydrogenation of acetic acid the yields were eval-

uated using calibration curves obtained from mixtures

of ethyl acetate, ethanol and acetic acid of known com-

position. In all other tests conversions were evaluated

without response factors corrections.

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Article Doi

On the behaviour of Ru(I) and Ru(II) carbonyl acetates in the presence of H2 and/or acetic acid and their role in the catalytic hydrogenation of acetic acid

DOI: 10.1016/j.jorganchem.2004.09.048

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Full text of DOI:10.1016/j.jorganchem.2004.09.048

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