Catalytic studies with ruthenium clusters substituted with diphosphines. Part II. Studies with Ru3(CO)8(Ph2PCH2PPh2)2

Article abstract of DOI:10.1016/S1381-1169(99)00196-X

The catalytic reactions of Ru₃(CO)₈(dppm)₂ (dppm = Ph₂PCH₂PPh₂) under hydrogen pressure were investigated. The Ru₃(CO)₁₀(dppm) complex showed activity with 1-hexene favoring isomerixation to cis-2-hexene at lower hydrogen pressures and complete hydrogenation at higher temperature and pressure. The reaction was first order on substrate with a k_eff = 1.59 x 10^-3/min. Turnover studies implied cluster analysis. The catalytic activity was demonstrated for other unsaturated organic substrates.

Full text of DOI:10.1016/S1381-1169(99)00196-X

Ž
.
Journal of Molecular Catalysis A: Chemical 149 1999 87–97
www.elsevier.comrlocatermolcata
Catalytic studies with ruthenium clusters substituted with
diphosphines
ž / ž
/
Part II. Studies with Ru3 CO 8 Ph2 PCH2 PPh2 2
)
Bernardo Fontal , Marisela Reyes, Trino Suarez, Fernando Bellandi, Nestor Ruiz
´
Laboratorio Organometalicos, Departamento de Quimica, Facultad de Ciencias, UniÕersidad de Los Andes, Merida, Venezuela
´
Received 23 November 1998; accepted 17 March 1999
Abstract
Ž
. Ž
. Ž
.
The catalytic precursor Ru3 CO dppm dppmsPh2PCH2PPh2 shows activity with 1-hexene favoring isomerization
8
2
to cis-2-hexene at lower hydrogen pressures and complete hydrogenation at higher temperature and pressure. The reaction is
first order on substrate with a keff s1.59=10y miny1. Turnover studies indicate cluster catalysis. The catalytic activity
3
has been demonstrated for other unsaturated organic substrates. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: Ruthenium cluster; Bidentate phosphines; Hydrogenation; Isomerization catalysts
1. Introduction
with metal clusters is an area of recent research
w
x
14,15 ; the presence of ligands capable of clus-
ter stabilization is considered important during
catalytic reactions and polydentate phosphines
could be used for that task. One example of this
Ž
.
Ž
clusters with bis diphenyl-
The Ru3 CO
12
.
Ž
.
phosphino methane dppm has been synthe-
sized with one 1 and two bidentate ligands 2
as well as reports on thermal rearrangement of
the coordinated ligands 3–7 and reaction with
O2 8,9 . The diphosphine dppm has been used
in many mononuclear and cluster complexes
synthesis, a few of which has been used in
w x
w x
Ž
. Ž
.
w x
is the use of H4Ru4 CO dppm 6 , and
10
Ž .Ž
. Ž
. Ž
. w x
H2Ru3 E CO dppm EsO,S 16 in olefin
5
2
w
x
activation. In our laboratory we have been
w
x
studying the catalytic behavior of Ru complexes
w
x
with polydentate phosphines 17–22 , including
reactions of Ru carbonyl clusters with bis-
w
x
homogenous catalysis 10–13 . Catalytic studies
Ž
.
Ž
1,3 diphenylphosphino propane PPh2CH2CH2-
.
w x
CH2 PPh2 sdppp 23 . In Part I of the studies
we reported the catalytic reactions with Ru2-
Ž
. Ž
. w x
CO dppm 24 . In this paper we report the
10
Ž
. Ž
. ( )
)
reactions of Ru3 CO dppm 1 under hydro-
gen pressure.
8
2
Corresponding author. Tel.: q58-74-401380; Fax: q58-74-
401286; E-mail: fontal@ciens.ula.ve
1381-1169r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S1381-1169 99 00196-X

(
)
88
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
Ž
.
2. Experimental
freshly distilled xylene Aldrich, 15 ml in a
round bottom flask were heated to 658C with
stirring for 4 h under Ar, giving a dark red-
brown solution. After solvent evaporation, the
residue is separated on silica gel flush column
chromatography, eluted with a 3r1 volume hex-
anerCH2Cl2 mixture. The larger red-brown
band is recrystallized in CH2Cl2rhexane to give
(
) (
)
2.1. Synthesis of Ru3 CO 8 dppm 2
Several synthetic methods were tried to com-
pare the percent yield and the ease of prepara-
tion. All the gases used are high purity, reagents
are analytical grade and all solvents were appro-
priately dried before use.
Ž
. Ž
.
Ž
red-brown Ru3 CO dppm crystals 89.7%
yield . Identification similar to Section 2.1.1.
8
2
.
2.1.1. Preparation Õia diphenylketyl radical,
Ph2C2 Oy
2.1.3. Synthesis Õia photolysis
Ž
. Ž
.
2
Ž
.
Ž
The preparation of Ru3 CO dppm by this
method has been reported by Bruce et al. 2
In a typical synthesis, Ru3 CO
50 mg,
8
12
w x
.
Ž
.
0.078 mmol , dppm 60.1 mg, 0.156 mmol in
Ž
.
12
Ž
.
Ru3 CO
was prepared from RuCl3 P3H2O
THF 15 ml are heated to 408C with stirring for
several minutes under Ar. The red-orange solu-
tion is transferred to a Schlenk tube with a
water jacket, covered with Al foil under Ar; a
Ž
.
Ž
Strem Chemicals and CO Matheson, UAP
grade according to the literature method 25 .
.
w x
Sodium diphenylketyl was prepared prior to use
Ž
.
Ž
reacting benzophenone 91 mg, 0.5 mmol in
pen Hg UV lamp Ultra-Violets Products, 114
Ž
.
.
very dry THF Aldrich, 20 ml and very finely
divided metallic sodium under Ar with stirring
for 2 h. The very intense violet solution has a
V, 60 cycle, low intensity is introduced and
photolyzed for about 48 h, the reactions progress
of the reaction followed by disappearance of
Ž
.
12
concentration near 0.025 mmolrml of Ph2C2-
Ru3 CO
metal carbonyl IR bands. After the
y
Ž
.
Ž
50 mg,
12
O . In a typical synthesis, Ru3 CO
reaction is complete, the solvent is reduced
under vacuum and silica gel flush column chro-
matographed using a 3r1 volume hexaner
CH2Cl2 eluant. The red-brown band is recrys-
tallized in CH2Cl2rhexane giving red-brown
.
Ž
.
0.078 mmol and the dppm Strem Chemicals
Ž
.
ligand 60.1 mg, 0.156 mmol are dissolved in
dry THF 15 ml with stirring at 408C in Schlenk
glassware. The diphenylketyl solution 5 ml is
Ž
.
Ž
.
Ž
. Ž
.
Ž
.
added dropwise with syringe and the reaction
Ru3 CO dppm crystals 56% yield . Identi-
8
2
Ž
.
12
followed by the disappearance of Ru3 CO
fication similar to Section 2.1.1.
Ž
.
metal carbonyl IR bands P.E. 1725-X FTIR .
After solvent evaporation, the residue is sepa-
rated on silica gel flush column chromatogra-
phy, eluted with a 3r1 hexanerCH2Cl2 volume
mixture. The dark brown-red fraction is recrys-
tallized from CH2Cl2rhexane to give red-brown
crystals of Ru3 CO dppm 66.7% yield . IR:
n CO THF 2023 m , 1979 vs , 1970 s ,
1946 m cm , H NMR CD2Cl2 Varian
T-60 d 7.1–7.6 m, C6H5 , 4.2–4.3 t, CH2;
(
)
2.1.4. Synthesis Õia CH3 3 NO actiÕation
In a typical experiment Ru3 CO
0.16 mmol is dissolved in dry CH2Cl2 40 ml
in a Schlenk tube with constant Ar bubbling
during the whole reaction. The system is cooled
Ž
.
Ž
100 mg,
12
.
Ž
.
Ž
. Ž
. Ž
.
Ž .
to y788C in a Dewar flask with a CO2 s r
2
Ž
. Ž
Ž
.
8 Ž
.
Ž
.
Ž .
Ž .
acetone bath. Trimethylamine oxide, CH3 3NO
1
y
1
.
Ž
. Ž
Ž
Ž
Aldrich, sublimed three times, 47 mg, 0.64
.
Ž
.
.
Ž
.
mmol completely dissolved in CH2Cl2 15 ml
.
JPH s11 Hz . The compound decomposes be-
was added dropwise via canula to the Ru car-
bonyl solution at low temperature, the progress
of the reaction followed by disappearance of
tween 176 and 1798C.
Ž
.
2.1.2. Synthesis Õia thermal reaction
Ru3 CO metal carbonyl IR bands. The dppm
Ž
.
Ž
Ž12
.
In a typical synthesis, Ru3 CO
50 mg,
ligand 120 mg, 0.32 mmol dissolved in
CH2Cl2 15 ml was added dropwise via canula
12
.
Ž
.
Ž .
0.078 mmol , dppm 60.1 mg, 0.156 mmol and

(
)
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
89
Table 2
at low temperature. The Schlenk tube is re-
Hydrogenation and isomerization of 1-hexene: solvent effect
moved from the cold bath and allowed to warm
up slowly to room temperature, heating then to
408C during 30 min. After evaporating the sol-
vent, the residue is chromatographed in a silica
gel column and the separated fraction recrystal-
lized in a 3r1 hexanerCH2Cl2 mixture, giving
Solvent
n-Hexane cis-2-Hexeneq
Total
Ž .
%
Ž .
%
Ž
.
trans-2-hexene %
Ethanol
Methanol
2-Methoxyethanol 18.4
Acetone
THF
46.8
54.2
53.0
21.4
34.8
30.5
44.7
15.8
11.5
99.9
75.6
53.2
50.6
69.8
20.5
14.9
20.1
25.0
4.7
Ž
. Ž
.
Ž
crystals 61%
red-brown Ru3 CO dppm
8
2
Benzene
Toluene
.
yield . Identification similar to Section 2.1.1. In
Table 1, a comparison of the four synthetic
methods is presented.
3.4
Ž
.
Ž
.
Reaction conditions: solvent 5 ml , 1-hexene 1 ml, 0.67 g ,
. Ž
Ž
.
Ž
2
.
Ru3 CO dppm 2 mg , PH s500 psi, T s908C, ts2 h.
8
2
(
) (
)
2.2. Catalytic trials with Ru3 CO 2 dppm 2
strates were carried out under similar condi-
tions, adjusting the H2 pressure, solvent or reac-
tion time as required.
In a typical hydrogenation or isomerization
y
3
Ž
. Ž
.
Ž
trial, Ru3 CO dppm
2 mg, 1.54=10
8
2
.
Ž
mmol , 1-hexene Aldrich, 1 ml, 8 mmol;
5000r1 substratercatalyst ratio , 5 ml solvent
e.g., ethanol are mixed in a high pressure
.
2.2.1. Kinetic runs
Ž
.
In a 250-ml stainless steel high pressure reac-
Ž
Ž
stainless steel reactor 10 ml, glass liner, inter-
tor Parr Instruments, glass liner, internal stir-
.
nal magnetic stirrer, 20–2000 psi manometer,
ring, internal thermocouple and sample outlet
y
2
.
Ž . Ž . Ž .
Ru3 CO dppm 20 mg, 1.54=10 mmol ,
8 2
Parr Instruments . After purging with H2 three
Ž
1-hexene 10 ml, 80 mmol; 5000r1
times, the reactor is pressurized to the desired
H2 pressure, introduced in an oil bath at the
desired temperature allowing 5 min for thermal
stabilization. At the end of the run the reactor is
rapidly cooled and the liquid analyzed by gas
.
Ž
substratercatalyst ratio , ethanol solvent, 50
.
Ž
.
ml , cyclohexane 10 ml, internal standard were
mixed. After purging with H2 three times, hy-
drogen pressure adjusted to 500 psi and 5 min
Ž
Ž
.
chromatography PE AutoSystem 900, PE Nel-
allowed for thermal stabilization 908C , sam-
ples were taken every 5 min during 45 min. The
samples were immediately quenched and ana-
lyzed by gas chromatography.
son software; stainless steel column, 15% tricre-
syl phosphate on Chromosorb P, 60–80 mesh, 3
m long, 0.6 cm diameter or capillary column
Ž
.
Plot fused silica, BTR-CW Carbowax BTR ,
30 m long, 1 mm internal diameter, or GC–MS
A systematic study of several reaction condi-
tions were carried out.
Ž
.
HP 5988A GC–MS . Olefin amination was
carried out using a 10r1 ArrNH3 mixture. Test
reactions with all the other unsaturated sub-
2.2.1.1. SolÕent effect. The following solvents
were tried: ethanol, 2-ethoxyethanol, THF, to-
Table 1
Ž
. Ž .
Synthesis methods for Ru3 CO dppm
2
8
Ž
.
Synthesis method
Radical
Thermal
Photochemical
Assisted with CH3 3NO
Ž
.
Yield %
66.7
89.7
56
61
Solvent
Reaction time
Stability in solution
Product separation
Procedure
THF
30 min
good
simple
elaborate
xylene
4 h
good
simple
simple
THF
48 h
moderate
more difficult
simple
CH2Cl2
2 h
low
more difficult
elaborate

(
)
90
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
Fig. 2. Hydrogenation and isomerization of 1-hexene: temperature
Ž
.
Ž
effect. Reaction conditions: ethanol 5 ml , 1-hexene 1 ml, 0.67
. Ž
.
Ž
.
Ž
2
.
g , Ru3 CO dppm 2 mg , PH s250 psi, ts2 h.
8
2
Fig. 1. Hydrogenation and isomerization of 1-hexene: H2 pressure
Ž
.
Ž
effect. Reaction conditions: ethanol 5 ml , 1-hexene 1 ml, 0.67
. Ž
.
Ž
.
Ž
2
.
g , Ru3 CO dppm 2 mg , T s908C, ts2 h.
8
Ž
.
2 mg , PH s500 psi, Ts908C, ts2 h. The
2
Ž
luene, benzene. Reaction conditions: solvent 5
results are shown in Table 2. Ethanol was the
solvent selected for the other catalytic studies.
.
Ž
.
Ž
. Ž
.
ml , 1-hexene 1 ml, 0.67 g , Ru3 CO dppm
8
2
Table 3
Ž
.
Hydrogenation and isomerization of 1-hexene: ArqH2 pressure
effect
n-Hexane 1-Hexene cis-2-Hexene trans-2-
Ž .
%
Ž .
%
Ž .
%
Ž
.
Hexene %
(
)
Experiment 1 H2 s1 atm time, h
2
6
1.2
4.6
4.7
4.9
5.2
85.4
61.9
31.8
9.4
9.3
4.1
10.7
18.1
18.5
20.1
22.8
45.4
67.2
68.9
13
24
48
5.8
(
)
Experiment 2 500 psi ArrH2 relation
1:1
2:1
3:1
4:1
15.4
22.3
30.1
33.6
57.3
40.5
27.3
21.5
20.2
24.7
27.4
30.6
7.1
12.5
15.2
14.3
(
)
Experiment 3 ArrH2 , psi
250r250 13.8
500r500 29.1
750r750 42.3
1000r1000 48.4
60.7
32.2
9.1
19.3
26.6
35.2
36.9
6.2
12.1
13.4
12.8
1.9
Ž
.
Ž
.
Reaction conditions: ethanol 5 ml , 1-hexene 1 ml, 0.67 g ,
. Ž
Ž
.
Ž
2
.
Ž
Ru3 CO dppm 2 mg , T s908C, ts2 h experiments 1 and
Fig. 3. Hydrogenation and isomerization of 1-hexene: reaction
8
.
Ž
.
Ž
Ž
.
Ž
3 , PH s1 atm experiment 1 and Ptotal s500 psi experiment
time effect. Reaction conditions: ethanol 5 ml , 1-hexene 1 ml,
. Ž . Ž . Ž .
0.67 g , Ru3 CO dppm 2 mg , PH s250 psi, T s908C.
2
.
2 .
8
2
2

(
)
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
91
H2 pressure was selected for other catalytic
studies. H2 pressure effects were also analyzed
by the following experiments. Experiment 1:
similar conditions as above, but used 1 atm H2
pressure and 48 h total time. Experiment 2:
similar conditions as above, but used 500 psi
Ž
.
total pressure of ArqH2 with different Ar
rH2 relations. Experiment 3: similar conditions
as above, but used pressure changes of ArrH2
Ž
.
1r1 . The results are shown in Table 3.
2.2.1.3. Temperature effect. Reaction tempera-
ture change results are shown in Fig. 2. Reac-
Ž
.
Ž
tion conditions: ethanol 5 ml , 1-hexene 1 ml,
.
Ž
. Ž
.
Ž
.
0.67 g , Ru3 CO dppm
psi, ts2 h. A 908C temperature was selected
for other catalytic studies.
2 mg , PH s250
8
2
2
2.2.1.4. Reaction time effect. Reaction time
Fig. 4. Hydrogenation and isomerization of 1-hexene: amount of
change results are shown in Fig. 3. Reaction
Ž
.
Ž
catalyst effect. Reaction conditions: ethanol 5 ml , 1-hexene 1
Ž
.
Ž
conditions: ethanol 5 ml , 1-hexene 1 ml, 0.67
.
ml, 0.67 g , PH s250 psi, T s908C, ts3 h.
2
.
Ž
. Ž
.
Ž
.
g , Ru3 CO dppm
Ts908C. A 2- or 3-h reaction time was se-
2 mg , PH s250 psi,
8
2
2
2.2.1.2. PH effect. H2 pressure change results
lected for the other catalytic studies.
are shown i2n Fig. 1. Reaction conditions: ethanol
Ž
Ž
.
Ž
.
Ž
.
5 ml , 1-hexene 1 ml, 0.67 g , Ru3 CO -
2.2.1.5. Amount of catalyst effect. Amount of
catalyst change results are shown in Fig. 4.
8
.
Ž
.
dppm
2 mg , Ts908C, ts2 h. A 250-psi
2
Table 4
Catalysis study of 1-hexene with Ru3 CO 12rH2 pressure effect: in situ production of complexes
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
n-Hexane %
1-Hexene %
cis-2-Hexene %
trans-2-Hexene %
Ž .
15
Ž
.
Ž
.
a Ru3 CO 12rH2 pressure psi
2.6
15.6
26.6
55.1
66.4
93
32.1
10
1
3.2
42.0
45.1
35.6
27.7
1.2
10.3
18.3
8.3
100
200
300
500
0
5.9
Ž .
b
Ž
Ž
Ž
Ž
Ž
Ž
.
.
.
.
Ž
.
Ru3 CO 12rdppm 1:2 mole ratio r100 psi
6.4
7.1
17.6
35.2
14.9
30.2
1.4
1.4
49.8
20.6
54.7
27.6
73.2
72.4
19.2
31.9
20.2
28.6
19.0
19.1
13.4
12.3
10.2
13.6
a
Ž
.
Ru3 CO dppm r100 psi
10
Ž
Ž
.
.
Ru3 CO 12rdppm 1:4 mole ratio r100 psi
Ru3 CO 12rdppm 1:4 mole ratio r250 psi
. Ž
.
.
Ru3 CO dppm 2r100 psi
.8Ž
Ru3 CO dppm 2r250 psi
8
a
w
x
Ref. 24 .
Ž
.
Ž
.
Ž
.
Ž
.
Ž
.
Reaction conditions: ethanol 5 ml , 1-hexene 1 ml, 0.67 g , Ru3 CO or Ru3 CO 12rdppm 2 mg , Ts908C, ts2 h, PH s100 or 250
12
2
Ž
.
psi reaction b .

(
)
92
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
Table 5
Catalyst stability studies
Ž
.
Ž
.
Ž
.
Ž
.
n-Hexane %
1-Hexene %
cis-2-Hexene %
trans-2-Hexene %
Ž .
a Reaction in presence of Hg
Catalystr500 psi
47.7
43.5
60.6
55.4
1.3
10.6
2.0
38.4
35.7
29.0
27.8
12.6
10.2
8.4
CatalystqHgr500 psi
Catalystr1000 psi
CatalystqHgr1000 psi
4.3
12.5
Ž .
b Catalyst reuse
Number of reuses: 1
Number of reuses: 2
Number of reuses: 3
49.5
48.2
46.3
0.2
0
6.7
39.6
40.2
37.0
10.7
11.6
10.0
Ž
.
Ž
.
Ž
. Ž
.
Ž
2
.
Ž
.
Reaction conditions: ethanol 5 ml , 1-hexene 1 ml, 0.67 g , Ru3 CO dppm
2 mg , 1 drop Hg reaction a ; Ts908C, ts2 h,
8
Ž
.
Ž
.
PH s500 psi reactions a and b or 1000 psi reaction a .
2
Ž
.
Ž
.
Ž
. Ž
. Ž
1-hexane 1 ml, 0.67 g , Ru3 CO dppm 2
2
Reaction conditions: ethanol 5 ml , 1-hexene
8
Ž
.
.
1 ml, 0.67 g , PH s250 psi, Ts908C, ts3
mg , PH s500 and 1000 psi, 1 drop liquid Hg,
2
2
Ž
.
h. A catalyst amount of 2 mg about 5000r1
Ts908C, ts2 h . The results are shown in
.
substratercatalyst ratio was selected for other
Table 5a. In order to test the degree of catalyst
catalytic studies.
decomposition, several reactions were carried
Ž
2.2.1.6. Hydrogenation of 2-hexene. 11%
.
cisr89% trans thermodynamic isomer mixture .
A trial reaction was run with the isomer mix-
Ž
.
ture. Reaction conditions: ethanol 5 ml , 2-
Ž
.
Ž
Ž
hexene 1 ml isomer mixture , cyclohexane 1
ml, internal standard , Ru3 CO dppm
.
. Ž
.
Ž
2
2
8
.
mg , PH s250 psi, Ts908C. Product distribu-
2
Ž
.
tion: after 36 h: cis-2-hexene 68% , trans-2-
Ž
.
Ž
.
Ž
.
hexene 23% , 1-hexene 5% ; n-hexane 4% .
(
) (
)
2.2.1.7. In situ production of Ru2 CO 8 dppm 2.
( )
In order to test the possible formation of 1 in
situ, several reactions were carried out with
Ž
.
Ru3 CO
and different proportions of dppm
12
Ž
.
ligand. Reaction conditions: ethanol 5 ml , 1-
Ž
.
Ž
.
Ž
hexane 1 ml, 0.67 g , Ru3 CO 12rdppm 2 mg,
.
different molar relations , PH s100 psi, Ts
2
908C, ts2 h. The results are shown in Table 4.
(
) (
)
2.2.1.8. Stability studies of Ru3 CO 8 dppm 2. In
order to test the stability of the cluster complex
studied, reactions were carried out in the pres-
ence of small amounts of metallic mercury
Fig. 5. Hydrogenation and isomerization of 1-hexene: turnover
Ž
Ž
.
.Ž
..
frequency millimoles productr millimoles catalyst minutes vs.
Ž
Ž
amount of catalyst millimoles . Reaction conditions: ethanol 5
.
Ž
.
Ž
ml , 1-hexene 1 ml, 0.67 g , cyclohexane 1 ml, internal stan-
w
x
Ž
.
26,27 . Reactions conditions: ethanol 5 ml ,
.
dard PH s500 psi, T s908C, ts0.5 h.
2

(
)
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
93
out reusing the separated catalyst for three con-
secutive times. After the reaction, the solution
was evaporated to dryness, the residue washed
several times with pentane and vacuum dried
shows a greater amount of hydrogenation prod-
uct. This solvent behavior indicates a possible
stabilization of polar andror coordinatively un-
saturated intermediate in the catalytic cycle.
Ž
before reuse. Reaction conditions: ethanol 5
.
Ž
.
Ž
. Ž
.
ml , 1-hexene 1 ml, 0.67 g , Ru3 CO dppm
2
3.2.2. PH effect
8
2
Ž
.
initial 2 mg, then re-covered , PH s500 psi,
Ts908C, ts2 h . The results are presented in
Table 5b. Several reactions were carried out
increasing the number of millimoles of
As shown in Fig. 1, at low H2 pressure the
main products are the isomerization compounds,
favoring the cis-2-hexene isomer, that remains
an important product up to 500 psi H2 pressure.
As the H2 pressure increases the overall yield
increases and the hydrogenation product is fa-
vored, the internal isomers being hydrogenated
after the 1-hexane substrate is consumed. Al-
lowing a longer reaction time using 1 atm of H2
pressure, produces almost exclusive the isomer-
ization reaction, with a 69% cisr20% trans
2
.
Ž
. Ž
.
Ru3 CO dppm and the products analyzed
8
2
Ž
before reaching 40% total conversion reaction
conditions: ethanol 5 ml , 1-hexane 1 ml, 0.67
Ž
.
Ž
.
Ž
.
g , cyclohexane 1 ml, internal standard , PH s
2
.
500 psi, Ts908C, ts0.5 h . A plot of turnover
Ž
Ž
frequency millimoles of productr millimoles
.Ž
..
catalyst minutes vs. millimoles of catalyst is
Ž
.
presented in Fig. 5.
ratio after 48 h Table 3, experiment 1 . Dilut-
Ž
.
ing the hydrogen with an inert gas Ar has a
yield lowering effect compared with the reac-
tions with pure H2, but product relations remain
similar, that is, cis-2-hexane being favored at
lower partial pressures and increasing n-hexane
yield as H2 pressure increases and the cis iso-
3. Results and discussion
(
) (
)
3.1. Synthesis of Ru3 CO 8 dppm 2
Ž
The several synthetic methods tried for the
mer always favored over the trans Table 3,
Ž
. Ž
.
.
synthesis of Ru3 CO dppm and shown in
experiments 2 and 3 . It becomes apparent that
8
2
Table 1 indicate that the complex can be ob-
tained in good yield using the diphenylketyl
radical and thermal reaction. Lesser yields are
observed with photochemical activation and with
the isomerization route in the catalytic cycle
gets activated at a lower hydrogen pressure, and
the selectivity toward the kinetic product, cis-
2-hexene, indicates an important steric require-
ment during isomer formation. The results con-
firm that internal olefins are more difficult to
hydrogenate than terminal ones.
Ž
.
CH3 3NO there is good selectivity, but decom-
position of the trimethylamine Ru carbonyl in-
termediate lowers the overall yield. The first
two methods are thus recommended.
3.2.3. Temperature effect
3.2. Catalytic results
The reaction only proceeds at a reasonable
rate after 708C, and increases rapidly favoring
the cis isomer, obtaining complete reaction at
1108C, with almost 50% yield of cis-2-hexene
3.2.1. SolÕent effect
As shown in Table 2, under the reaction
conditions used, more polar and better coordi-
nating solvents like ethanol, methanol, THF and
2-ethoxyethanol give better overall yields, while
less polar solvents with lesser coordinating abil-
ity like toluene, benzene and acetone, give less
overall yields. All the better solvents favor the
isomerization products, except methanol that
Ž
.
Fig. 2 . Both the hydrogenation and isomeriza-
tion reaction paths require heating to overcome
activation barriers, most likely the activation of
the cluster compound by CO loss, corroborated
by the complete reaction inhibition in the pres-
ence of 1 atm of carbon monoxide gas. The
similar activation behavior could indicate the

(
)
94
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
presence of a common reaction intermediate in
the catalytic cycle.
sure shows and initial increase in isomerization
product, favoring cis-2-hexene, but after 200
psi the hydrogenation product predominates
3.2.4. Reaction time effect
Ž
.
Table 4a . After 300 psi, the Ru carbonyl
cluster decomposes under the reaction condi-
The reaction progress with time is shown in
Fig. 3. The internal cis isomer appears first in
the reaction and becomes the main product,
accounting for almost half of the reaction prod-
ucts after 3 h, when the terminal olefin is
completely consumed. After this time, the olefin
reduction product, n-hexane, keeps increasing
as the cis-2-hexene and trans-2-hexene get hy-
drogenated. The product distribution with time
indicates that the isomerization rate is faster
than the hydrogenation at 250 psi H2 pressure
and 908C.
Ž
.
tions used. A 1r2 Ru3 CO 12rdppm molar ratio
gives predominantly the cis-2-hexene isomer-
ization product and no complex decomposition
Ž
.
is observed Table 4b . The dppm substituted
cluster does not show decomposition signs up to
1000 psi H2 pressure, indicating that the biden-
tate ligand stabilizes the trinuclear cluster. This
behavior is analogous to the reaction products
Ž
. Ž
.
obtained with Ru3 CO dppm under similar
w
x10
reaction conditions 24 ; this suggests that the
compound produced in situ is similar to that
diphosphine substituted Ru cluster. Increasing
the molar ratio to 1:4 gives a different product
distribution, with less total percent yield and
more similar hydrogenationrisomerization ra-
tios. The similarity of these results and those
obtained with the catalytic precursor
3.2.5. Amount of catalyst effect
Ž
. Ž
.
2
With 2 mg of Ru3 CO dppm as catalyst
8
precursor, under the reaction conditions used,
more than 90% conversion is obtained, with
50% of the cis-2-hexene isomerization product
Ž
.
( )
Fig. 4 . As the amount of 1 is increased, more
Ž
. Ž
.
Ru3 CO dppm , including the changes ob-
8
2
hydrogenation product is observed, being the
predominant product when 20 mg of compound
are used. As the amount of catalyst is increased,
more active sites are introduced, increasing the
probability for complete olefins hydrogenation,
including the internal olefins produced more
rapidly during the isomerization process.
served when the H2 pressure changes from 100
to 250 psi, could indicate that a similar com-
pound is produced in situ when the molar rela-
tion is 1:4.
(
) (
)
3.2.8. Stability studies of Ru3 CO 8 dppm 2
In homogenous catalysis studies there is al-
ways the possibility that the reaction is carried
out by another species derived from cluster
fragmentation or metallic particles from com-
plex decomposition rather than the original clus-
ter complex. This is verified by observing the
final solution under the microscope and by run-
ning a test reaction in the presence of metallic
3.2.6. Hydrogenation of 2-hexenes
The test reaction with the thermodynamic
Ž
.
2-hexene mixture 11% cisr89% trans show
that after 36 h the isomer composition is re-
Ž
.
versed 68% cisr23% trans , indicating that the
internal olefins can enter the catalytic cycle and
be equilibrated with the other products in re-
versible reactions. The reverse reaction is slower
indicating that the internal olefins coordinate
with more difficulty due to steric reasons.
Ž
mercury with similar reaction conditions Table
.
5a . When Hg is used the change in percent
yield for the different products is less than 5%
at the two H2 pressures tried, discarding metal-
lic Ru as the active catalyst. Another test that is
useful to determine the degree of catalyst de-
composition is to separate the complex after the
catalytic reaction and reuse it under similar
reaction conditions. The results shown in Table
(
) (
)
3.2.7. In situ production of Ru3 CO 8 dppm 2
The results of the test reactions using
Ž
.
Ru3 CO
and variable amounts of dppm lig-
12
and are shown in Table 4. The reaction of
Ž
.
1-hexene with Ru3 CO and variable H2 pres-
12

(
)
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
95
5b indicate that after three catalyst reuses, the
activity has decreased only slightly.
The plot of turnover frequency vs. millimoles
of catalyst presented in Fig. 5 for isomerization
and hydrogenation results show an increase in
turnover frequency as the amount of Ru com-
plex increases, but the slopes are different. The
increasing tendency is interpreted as indicative
of cluster catalysis rather than produced by
w
x
active fragments of lower nuclearity 25 . This
supports the idea that the catalysis is being
carried out by the cluster complex. The
Ž
. Ž
.
Ru3 CO dppm complex loses CO and ben-
8
2
zene groups on thermolysis reactions in reflux-
Ž
.Ž
ing aromatic solvents giving Ru3 m-H m-
Ž
.
Ž
.Ž
..Ž
..Ž
. Ž
.
P C6H5 CHP C6H5 C6H4 CO dppm and
Ž
x
Ž
Ž
. .7Ž
. Ž
.
Ru3 m3- P C6H5 CHP C6H5 2 CO dppm
7
w
6,7 . Our reaction conditions does not favor the
Fig. 6. Hydrogenation and isomerization of 1-hexene: kinetic
thermolysis reaction, but these rearranged ther-
molysis products cannot be excluded as possible
intermediates. These complexes are presently
being tested using our reactions conditions to
investigate their catalytic behavior.
Ž
.
Ž
results. Reaction conditions: ethanol 50 ml , 1-hexene 10 ml, 6.7
. Ž
.
Ž
.
Ž
. Ž
2
g , cyclohexane 10 ml, internal standard , Ru3 CO dppm 20
8
.
mg , PH s500 psi, T s908C.
2
genation to the alkenes. 1-Hexyne hydrogenates
to 1-hexene and some n-hexane and little iso-
merization, but 2-hexyne produces mainly the
trans-2-hexene, some n-hexane and little cis-2-
hexene; this result indicates some special steric
conditions, that are presently being studied.
Aromatic compounds like benzene or carbonyl
groups as in acetone or cyclohexanone require
higher hydrogen pressures for hydrogenation to
occur with moderate reaction yield. With allylic
alcohol, double bond migration to form the
carbonyl group occurs in good proportion, but
the competing complete reduction reaction also
occur in good proportion. For a,b unsaturated
aldehydes, the hydrogenation results indicate
that both the carbon–carbon double bond and
the carbonyl group can be hydrogenated, under
stronger reaction conditions and longer times.
The results indicate that the Ru complex studied
does not show strong regioselectivity in its hy-
drogenating activity. A test reaction under hy-
droformylation conditions with 1-hexene, favors
the linear aldehyde with intermediate overall
percent yield. Hydrogenation of nitriles, such as
3.2.9. Kinetic results
The first order plot for the kinetic studies in
the isomerization and hydrogenation of 1-
hexene, following the disappearance of the sub-
strate 1-hexene is shown in Fig. 6. The results
indicate first order on substrate with an apparent
rate constant value of 1.59=10y miny for
the total reaction. This results is about 100
times slower than the value obtained for the
3
1
Ž
. Ž
.
w x
Ru3 CO dppm complex 24 , perhaps indica-
10
tive of a greater steric crowding presented by
Ž
. Ž
.
the complex Ru3 CO dppm to 1-hexene p
bonding.
8
2
3.3. Catalysis with other substrates
Ž
. Ž
.
The Ru3 CO dppm
2
complex was ex-
8
plored in its catalytic activity with other organic
substrates and the results are summarized in
Table 6. Terminal olefins like 1-hexene are
hydrogenated more rapidly than internal olefins
or cyclic olefins like cyclohexene. Alkynes re-
quire stronger conditions for the first hydro-

(
)
96
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
Table 6
Ž
. Ž .
Catalytic reactions of unsaturated organic substrates with Ru3 CO dppm
2
8
Ž
.
Ž .
Time h
Substrate
Product %
Conditions
( )
a Hydrogenation of unsaturated organic substrates
Ž
.
1-Hexene
1-Hexene
1-Hexyne
n-hexane 60.6
ethanol, 908C, 1000 psi H2
2
Ž
.
cis-2-hexene 29.0
trans-2-hexene 9.4
Ž
.
.
Ž
n-hexane 34.3
ethanol, 1108C, 250 psi H2
ethanol, 908C, 1500 psi H2
2
Ž
.
cis-2-hexene 50.0
trans-2-hexene 14.7
Ž
.
.
.
Ž
n-hexane 25.1
12
Ž
1-hexene 50.7
Ž
.
cis-2-hexene 2.2
Ž
.
.
.
.
trans-2-hexene 2.5
n-hexane 11.2
1-hexene 15.2
Ž
Ž
1-Hexyne
ethanol, 908C, 500 psi H2
6
Ž
.
cis-2-hexene 2.7
Ž
trans-2-hexene 2.3
Ž
.
2-Hexyne
2-Hexyne
n-hexane 24.9
THF, 908C, 1500 psi H2
ethanol, 908C, 500 psi H2
12
6
Ž
.
cis-2-hexene 7.7
trans-2-hexene 23.0
Ž
.
.
.
Ž
n-hexane 19.6
Ž
.
cis-2-hexene 3.0
trans-2-hexene 17.6
Ž
Ž
.
Cyclohexene
Benzene
cyclohexane 50.7
ethanol, 908C, 1500 psi H2
ethanol, 908C, 1500 psi H2
12
12
Ž
.
cyclohexadiene 4.7
Ž
.
.
cyclohexene 11.2
Ž
cyclohexene 25.7
Ž
.
Acetone
Cyclohexanone
Allylic alcohol
isopropanol 26.7
THF, 908C, 1500 psi H2
THF, 908C, 1500 psi H2
THF, 908C, 500 psi H2
12
12
12
Ž .
cyclohexanol 25.9
propanaldehyde 35.6
Ž
.
Ž
.
pronanol 23.2
( )
b Hydrogenation of a–b unsaturated aldehydes
Ž
.
Crotonaldehyde
butyraldehyde 29.2
THF, 908C, 1500 psi H2
THF, 908C, 1500 psi H2
12
12
Ž
.
butanol 21.3
Ž
.
2-butenol 22.8
3-phenylpropanal 15.6
Ž
.
Cinnamaldehyde
Ž
.
3-phenylpropanol 22.5
Ž
.
3-phenyl–2-propenol 32.3
( )
c Hydroformylation of 1-hexene
Ž
.
Ž
.
1-Hexene heptanaldehyde 47.9
THF, 1208C, 1500 psi H2rCO 1r1
12
( )
d Amine synthesis
Hydrogenation of nitrile
Acetonitrile
Ž
.
.
diethylamine 13.5
ethanol, 908C, 1500 psi H2
ethanol, 908C, 1500 psi H2
24
24
Ž
triethylamine 21.2
Ž .
benzylamine 42.4
Benzonitrile
Condensation of NH3 with alcohol
Ž
.
Ž
.
CH3OHrNH3
dimethylamine 9.4
methanol, 908C, 1000 psi ArrNH3 9r1
48
48
Ž
.
trimethylamine 12.6
Ž
.
Ž
.
CH3CH2OHrNH3
triethylamine 23.5
ethanol, 908C, 1000 psi ArrNH3 9r1
Ž
.
Ž
.
Ž
. Ž
.
Ž
2
.
Reaction conditions: solvent 5 ml , substrate 1 ml , Ru3 CO dppm 2 mgr15 mg in alcoholrNH3 reactions .
8

(
)
B. Fontal et al.rJournal of Molecular Catalysis A: Chemical 149 1999 87–97
97
w x
Ž
.
3
N. Lugan, J.J. Bonnet, J.A. Ibers, Organometallics 7 1988
1538.
acetonitrile and benzonitrile to give the ex-
pected amines requires higher H2 pressure and
longer reaction times. With acetonitrile, the
scrambling reaction allows production of trime-
thylamine in moderate yield. The condensation
reaction between NH3 and small alcohols such
a methanol and ethanol provides reasonable
amine yields under the reaction conditions tried.
w x
Ž .
4
N. Lugan, J.A. Ibers, J.J. Bonnet, JACS 107 1987 201.
M.I. Bruce, E. Horn, B. Shawkataly, M.R. Snow, E.R.T.
w x
5
Ž
.
Tiekink, M.I. Williams, J. Organomet. Chem. 316 1986
187.
w x
6
C. Bergounhou, J.J. Bonnet, P. Fompeyrine, G. Lavigne, N.
Ž
.
Logun, F. Mansilla, Organometallics 5 1985 60.
w x
Ž .
7
G. Lavigne, J.-J. Bonnet, Inorg. Chem. 20 1981 2713.
w x
Ž
.
8
G. Lavigne, N. Lugan, J.J. Bonnet, Nouv. J. Chim. 5 1981
423.
Ž
. Ž
.
The Ru3 CO dppm complex has shown good
8
2
w x
9
A. Colombie, J.J. Bonnet, P. Fompeyrine, G. Lavigne, S.
hydrogenation activity for several unsaturated
organic groups, and a strong isomerization ten-
dency for 1-hexene at low hydrogen pressures,
favoring the cis-2-hexene isomer. In general,
Ž
.
Sunshine, Organometallics 5 1986 1154.
w
w
w
w
x
10 M. Bruce, J. Hinchliffe, R. Surynt, B. Skelton, A. White, J.
Ž
.
Organomet. Chem. 469 1994 89.
x
Ž
.
11 H. Mirza, J. Vittal, J. Puddephatt, Inorg. Chem. 32 1993
1327.
x
12 A. Colombie, G. Lavigne, J.J. Bonnet, J. Chem. Soc. Dalton.
( )
the reactivity of 1 is less than that shown by
Ž
.
Trans. 1986 899.
the complex with only one dppm bidentate lig-
x
13 C. Adams, M. Bruce, P. Durkworth, P. Humphrey, O. Kuhl,
¨
Ž
. Ž
. w x
and, Ru3 CO dppm 24 , indicative of an
10
E. Tiekink, W. Cullen, P. Braunstein, C. Cea, B. Skelton, A.
Ž .
Ž
important steric condition that could have even-
tual application in regioselective or stereoselec-
tive hydrogenation reactions. The complex also
shows an interesting N–H activation capacity
that is being explored for specific amine synthe-
sis.
White, J. Organomet. Chem. 467 1994 25.
w
w
w
x
.
14 D. Shriver, H.D. Kaesz, R. Adams Eds. , The Chemistry of
Metal Cluster Complexes, VCH Publishers, New York, 1990.
x
Ž
.
15 G. Suss-Fink, G. Meister, Adv. Organomet. Chem. 35 1993
41, Academic Press.
x
16 C. Bergounhou, P. Fompeyrine, G. Commenges, J.J. Bonnet,
Ž
.
J. Mol. Catal. 48 1988 285.
w
w
w
w
x
Ž
.
17 T. Suarez, B. Fontal, J. Mol. Catal. 32 1985 191.
x
Ž
.
18 T. Suarez, B. Fontal, J. Mol. Catal. 45 1988 335.
x
Ž
.
Ž
19 T. Suarez, B. Fontal, D. Garcia, J. Mol. Catal. 34 1986 163.
Acknowledgements
x
.
20 T. Suarez, B. Fontal, H. Medina, J. Mol. Catal. 50 1989
355.
w
x
21 T. Suarez, B. Fontal, D. Garcia, Acta Cient. Venez. 34
The present work was financed by Bid-Con-
Ž
.
1983 198.
Ž
.
Ž
icit Proy. QF-04 Also Conicit Proy. F-124 for
w
w
x
x
Ž
.
22 B. Fontal, Acta Cient. Venez. 33 1982 202.
23 B. Fontal, R. Hernandez, T. Suarez, M. Reyes, F. Bellandi,
.
FTIR and Proy. S1 2338 for GC .
Ž
.
Revista Ciencia, Fac. Ingenieria, Univ. Zulia 1998 submit-
ted.
w
x
24 B. Fontal, M. Reyes, T. Suarez, F. Bellandi, J.C. Diaz, J.
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.
Ž
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.
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