Homogeneous hydrogenation of diphenylacetylene in the presence of Ru3(CO)9L3 (L=PPh3, PEt3). The crystal structure of Ru3(CO)10(PEt3)2: A reaction intermediate?

Article abstract of DOI:10.1016/S0022-328X(99)00349-6

The phosphine-substituted clusters Ru₃(CO)₉L₃ (L=PPh₃, 1; L=PEt₃, 2) are active homogeneous catalysts for the hydrogenation of diphenylacetylene. In the catalytic reactions involving complex 2, formation of Ru₃(CO)₁₀(PEt₃)₂ (3) has been observed. This complex shows a hydrogenating activity greater than that of the parent complex 2. In the light of these results and of the observed effect of dihydrogen pressure and substrate/cluster ratio, reaction mechanisms are discussed. The structure of 3 has been characterized by X-ray diffraction and is compared with those of other phosphine-substituted triruthenium clusters. Compound 3 crystallizes in the monoclinic space group P2₁ with a=9.368(7), b=12.20(2), c=13.554(9) A, β=102.63(8)° and Z=2. Refinement of 4975 data gave R₁=0.0417 and wR₂=0.1105. The two phosphorus ligands occupy equatorial positions on adjacent metal atoms so that they are trans to each other at the ends of the Ru-Ru vector. The presence of bent semi-bridging carbonyl groups makes the molecule chiral and its absolute structure was determined.

Full text of DOI:10.1016/S0022-328X(99)00349-6

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 588 (1999) 83–91
Homogeneous hydrogenation of diphenylacetylene in the presence
of Ru3(CO)9L3 (L=PPh3, PEt3). The crystal structure of
Ru3(CO)10(PEt3)2: a reaction intermediate?
Giuliana Gervasio a,*, Roberto Giordano a, Domenica Marabello a, Enrico Sappa b
a Dipartimento di Chimica IFM, Uni6ersita` di Torino, Via Pietro Giuria 7, I-10125 Turin, Italy
b Dipartimento di Scienze e Tecnologie A6anzate, Uni6ersita` del Piemonte Orientale Amedeo A6ogadro, Corso Borsalino 54,
I-15100 Alessandria, Italy
Received 8 April 1999
Abstract
The phosphine-substituted clusters Ru3(CO)9L3 (L=PPh3, 1; L=PEt3, 2) are active homogeneous catalysts for the hydrogena-
tion of diphenylacetylene. In the catalytic reactions involving complex 2, formation of Ru3(CO)10(PEt3)2 (3) has been observed.
This complex shows a hydrogenating activity greater than that of the parent complex 2. In the light of these results and of the
observed effect of dihydrogen pressure and substrate/cluster ratio, reaction mechanisms are discussed. The structure of 3 has been
characterized by X-ray diffraction and is compared with those of other phosphine-substituted triruthenium clusters. Compound
,
3 crystallizes in the monoclinic space group P21 with a=9.368(7), b=12.20(2), c=13.554(9) A, i=102.63(8)° and Z=2.
Refinement of 4975 data gave R1=0.0417 and wR2=0.1105. The two phosphorus ligands occupy equatorial positions on adjacent
metal atoms so that they are trans to each other at the ends of the RuꢀRu vector. The presence of bent semi-bridging carbonyl
groups makes the molecule chiral and its absolute structure was determined. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: Homogeneous catalysis; Hydrogenation; Phosphine-substituted ruthenium clusters; Reaction intermediates; X-ray absolute structure
did. Clusters 1 and 2, however, had not been tested as
hydrogenation catalysts for alkynes; therefore the com-
parison with the activity of other ruthenium-based sub-
stituted and unsubstituted derivatives that have been
the object of recent studies [1–4] was so far not
possible.
Here we report on the behavior of complexes 1 and 2
as homogeneous catalysts for the hydrogenation of
C2Ph2. We find that the above clusters show a consider-
able catalytic activity. In particular, under the thermal
conditions adopted, cluster 2 gives rise to complex 3,
which in turn is considerably active in hydrogenation.
This behaviour is discussed.
The structure of 3 has been determined by X-ray
diffraction and is compared with those of other tri- and
bi-substituted triruthenium derivatives. In principle
cluster bonding parameters should depend on the elec-
tron-donor ability as well as on the steric hindrance of
the phosphine ligands. The catalytic behavior of the
substituted clusters should also be related to the elec-
1. Introduction
Homo- and heterometallic ruthenium-containing car-
bonyl clusters catalyze the hydrogenation of alkynes [1]
and of cyclic dienes [2]. For some of these reactions
structure–reactivity relationships have been observed
[3] and reaction intermediates or byproducts have been
isolated and characterized [1–4]. In some instances,
reaction mechanisms based on the nature of the above
derivatives have been proposed [3b].
We had already observed that the substitution of
phosphine ligands for carbonyls may increase the cata-
lytic activity: this occurred, for example, in the hydro-
genation–isomerization reactions of linear dienes in the
presence of complexes Ru3(CO)9(PPh3)3 (1) and
Ru3(CO)9(PEt3)3 (2) [5]. We found that the presence of
CO did not inhibit these reactions, although it usually
* Corresponding author.
E-mail address: gervasio@silver.ch.unito.it (G. Gervasio)
0022-328X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00349-6

84
G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
tronic effects of the ligands. By contrast, during this
study we have found that catalytic activity is mainly
influenced by the chemical reactivity of clusters (e.g.
tendency to fragmentation and/or disproportionation);
this kind of reactivity, however, cannot be directly
related to the observed structural parameters.
2.3. Identification of the organometallic products in the
reaction solutions
All the (clear) solutions of the catalytic experiments
involving cluster 1 changed over time from red to pale
yellow. IR spectra showed the presence of some unal-
tered 1 together with bands at 2060, 2029, 2011 and
1960 cm−1 that could belong to (not isolated)
Ru3(CO)10(PPh3)2; in the experiment under CO/H2
these signals were more intense.
2. Experimental
All the solutions of the catalytic experiments with
cluster 2 changed from dark orange to pale yellow;
after the experiments under 1 atm of H2, with decreas-
ing amounts of dihydrogen or by changing substrate/
cluster (S/C) ratios, IR spectra showed the presence of
unaltered cluster 2 together with cluster 3 in nearly
equal amounts. After the experiments under CO/H2,
however, only weak signals for cluster 2 and no signals
for 3 were observed.
The solutions of the experiments involving cluster 3
turned from dark orange to yellow; the change in
colour was slow when CO/H2 was used. IR spectra
showed the presence of unaltered complex 3 and some
complex 2, together with bands attributable to uniden-
tified (mononuclear?) complexes.
2.1. Synthesis of complexes 1 and 2
The syntheses of complexes 1 and 2 have already
been described [6]. Complex 1 was obtained by reflux-
ing for 1 min Ru3(CO)12 with a 1.5/1 M excess of
triphenylphosphine in hexane under N2 in the presence
of Me3NO. A deep red solution (and a violet insoluble
residue) was obtained, which, after thin-layer chro-
matography (TLC) separation, gave some unreacted
parent
cluster,
Ru3(CO)11(PPh3)
(ca.
10%),
Ru3(CO)10(PPh3)2 (ca. 50%) and complex 1 (ca. 30%).
IR (C6H14): 2046 s, 1980 vs, 1967 vs, cm−1 31P-NMR:
.
+31.3 s.
Complex 2 was obtained by refluxing for 30 s in
hexane under N2 Ru3(CO)12 with an excess of PEt3 and
Me3NO. TLC of the clear, red solution, yielded 75% of
2 slightly contaminated by 3 (see below) and about 15%
of an unidentified yellow product, together with some
decomposition. IR(C6H14): 2061 s*, 2016 w, 1986 s,
2.4. Independent synthesis of complex 3
A sample of complex 2 was heated at reflux in hexane
under N2 for 3–5 min. The red colour of the solution
remained unaltered. TLC separation showed the pres-
ence of the unreacted parent complex (about 20%),
complex 3 (about 60%) and some unidentified yellow
products. IR (C6H14): 2061 vs, 2011 vs, 2001 vs, 1966
1968 s, 1947 vs, cm−1 31P-NMR: +11.71 s*,+32.69
.
s. (The signals marked with * are presumably due to
impurities, e.g. complex 3).
m, cm−1 31P-NMR: +11.71 s. This complex was
.
crystallized from hexane for X-ray analysis and for
catalytic experiments. Satisfactory elemental analyses
were obtained for 3 as well as for 1 and 2.
2.2. Homogeneous catalytic reactions
Catalytic reactions were performed, as previously
described [1,2], in 25 ml sealed glass vials each contain-
ing 2 ml of an n-octane solution of the complex and
diphenylacetylene under the appropriate pressure of
dihydrogen. The vials were sealed and then warmed in
an oven at 120°C for the required reaction time. Details
of the reagent concentration and of the reaction condi-
tions are given as footnotes to Table 1.
The organic products in the reaction solutions were
analyzed with a Carlo Erba FID 4200 gas chro-
matograph equipped with a (2 m×0.6 mm i.d.) SE 30
5% on Chromosorb WAW (60/80 mesh) column oper-
ated under the following conditions: N2 flow 46 ml
min−1, 60°C (6 min) then 10°C min−1 up to 240°C.
The reaction solutions were analyzed by means of IR
spectroscopy (Bruker Equinox 55, KBr cells) then chro-
matographed on TLC preparative plates on which the
organometallic products were separated. These were
analyzed by IR spectroscopy.
2.5. X-ray analysis of complex 3
The data were collected at room temperature on a
Siemens P4 diffractometer using graphite monochroma-
tized MoꢀKa radiation. Three standard reflections mea-
sured every 50 reflections showed no decay. Cell
constants were obtained from least-squares refinement
based on the setting angles of 26 reflections in the range
20°B2qB35°. Empirical absorption correction was
performed according to the method of reference [7].
The structure was solved by direct methods and
refined using the programs SHELXS-86 and SHELXL-93
(PC version), respectively. The absolute structure was
determined using the Flack parameter (Table 2) [8].
Crystal data and refinement parameters are reported in
Table 2.

G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
85
Table 1
Hydrogenation of diphenylacetylene in the presence of clusters 1–3 a
Experiment
Reaction time (min)
Conversion
TON
Selectivity
cis-SB
trans-SB
C2Ph2H4
Cluster 1
A
15
30
45
9.0
25.3
15.4
68.6
192.9
116.9
33.7
57.7
60.2
41.4
33.9
32.8
24.9
8.4
7.0
B
30
30
30
12.9
5.5
4.9
98.5
41.9
37.2
57.9
28.0
31.2
34.2
52.6
54.0
7.9
19.3
14.8
C’
C’’
D
30
30
30
17.7
25.0
28.3
205.4
140.8
82.8
40.5
40.3
40.3
54.4
54.1
54.1
5.1
5.5
5.6
30
30
30
30.1
24.7
18.1
56.7
93.0
136.3
40.8
48.3
56.6
50.5
43.4
35.3
8.7
8.3
8.1
15
30
45
7.0
8.2
5.0
26.8
31.1
19.1
43.2
61.1
51.4
37.7
22.7
27.1
19.1
16.2
21.5
Cluster 2
E
15
30
45
10.9
63.7
58.5
16.7
97.7
89.6
53.8
59.1
51.2
36.7
40.2
48.1
9.4
0.6
0.7
F
30
30
30
67.0
36.4
1.6
103.9
56.4
2.4
52.7
55.9
27.6
46.2
43.5
62.2
1.1
0.5
10.3
G’
G’’
H
30
30
30
42.9
80.6
99.4
72.9
69.9
50.6
53.6
50.3
14.1
45.3
49.2
85.0
1.0
0.5
0.8
30
30
30
93.5
79.2
56.7
119.2
202.0
289.2
55.7
61.5
65.4
43.5
37.9
34.0
0.8
0.6
0.6
15
30
45
12.1
16.2
21.1
20.6
27.6
35.9
88.6
86.4
87.9
9.9
12.5
11.3
1.5
1.0
0.8
Cluster 3
J
15
30
45
3.3
42.0
52.1
9.3
117.2
145.4
50.4
55.6
62.5
37.6
43.6
37.1
11.9
0.8
0.4
K
I’
30
30
30
51.4
27.1
21.7
143.4
75.7
60.6
57.3
54.6
54.1
42.2
44.1
43.9
0.5
1.2
2.0
30
30
30
37.3
69.8
98.6
57.2
56.6
36.4
54.1
56.1
46.6
44.7
42.6
52.2
1.1
1.3
1.2
I’’
L
30
30
30
89.1
68.5
41.8
102.4
157.5
192.2
55.4
58.3
64.8
43.2
40.5
34.3
1.4
1.2
0.9
15
30
45
11.5
21.7
27.9
17.7
33.6
43.1
87.9
91.2
91.7
8.4
7.1
7.0
3.7
1.7
1.2
a Experimental conditions: t always 120°C. (A) Substrate/cluster (S/C)=761.1, H2=1 atm. (B) S/C=763.8, H2=1.0, 0.5, 0.25 atm. (C’)
S/C=1158.3, 563.1, 292.6, H2=1 atm. (C’’) S/C=188.3, 376.5, 753.0, H2=1 atm. (D) S/C=381.2, CO/H2 50/50 (0.5/0.5 atm). (E) S/C=153.3,
H2=1 atm. (F) S/C=154.9, H2=1.0, 0.5, 0.25 atm. (G’) S/C=170.0, 86.7, 50.9, H2=1 atm. (G’’) S/C=127.5, 255.0, 510.0, H2=1 atm. (H)
S/C=170.0, H2/CO 50/50. (J) S/C=278.9, H2=1 atm. (K) S/C=278.9, H2=1.0, 0.50, 0.25 atm. (I’) S/C=153.3, 81.1, 36.9, H2=1 atm. (I’’)
S/C=115.0, 229.9, 459.8, H2=1 atm. (L) S/C=154.4, H2/CO 50/50.

86
G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
Table 2
Crystal
3. Results and discussion
data
and
structure
refinement
parameters
for
Ru3(CO)10(PEt3)2 (complex 3)
3.1. Hydrogenation reactions
Identification code
Complex 3
The results of the hydrogenation experiments are
collected in Table 1. The observed order of activity is
Empirical formula
Formula weight
Temperature (K)
Wavelength (MoꢀKa) (A)
Crystal system
Space group
C22H30O10P2Ru3
819.61
293(2) K
0.71073
Monoclinic
P21
Ru3(CO)9(PPh3)3
(1)\(Ru3(CO)10(PEt3)2
(3)\
,
(Ru3(CO)9(PEt3)3 (2). This behavior could point to the
possibility that the electron-donor ability of the phos-
phine ligands plays a role in affecting catalytic activi-
ties. For example, the electron-withdrawing PPh3 would
weaken the cluster frame and favor fragment catalysis,
whereas the electron-donating PEt3 would strengthen
the cluster and favor cluster catalysis. Indeed, fragment
catalysis (as discussed below) would explain the ob-
served lower activity of 3 with respect to 1.
Unit cell dimensions
,
a (A)
9.368(7)
12.20(2)
13.554(9)
102.63(8)
1511(2)
2
1.801
1.632
,
b (A)
,
c (A)
i (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
Absorption coefficient (mm−1
)
F(000)
Crystal size (mm)
Color
808
Table 3
Atomic coordinates (×104) and equivalent isotropic displacement
parameters (A2×103) for Ru3(CO)10(PEt3)2 (complex 3) a
0.30×0.42×0.48
Black
1.54–31.41
q range for data collection (°)
Scan type
ꢀ
x
y
z
Ueq
Scan speed (° min−1
Scan range (°)
)
Variable; 4.00–20.00
1.6
3 measured every 50
reflections
−15h513, −15k517,
−195l518
5823
4975 [Rint=0.0385]
Semi-empirical from
psi-scans
Ru(1)
Ru(2)
Ru(3)
P(1)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
−7085(1)
−4271(1)
−3963(1)
−2467(1)
−5739(2)
−5903(8)
−6790(11)
−7107(7)
−7319(10)
−5706(8)
−4735(10)
−1177(2)
−1594(8)
−1735(12)
−773(10)
113(12)
−3224(1)
−1074(1)
−2353(1)
−3632(1)
−2862(6)
−3202(9)
−3559(7)
−4388(9)
−4931(6)
−5204(7)
−1576(1)
−448(7)
491(7)
−2461(7)
−2118(10)
−1197(8)
−2045(11)
−4572(5)
−5378(5)
−3293(5)
−3362(5)
−2859(6)
−2691(6)
−911(6)
−771(7)
−1220(6)
−1209(6)
320(5)
41(1)
Standard reflections
−6399(1)
−8313(1)
−5708(2)
−3863(8)
−2899(10)
−6505(9)
−7881(10)
−5404(9)
−4606(12)
−9586(2)
−10262(11)
−9093(15)
−11318(10)
−12200(12)
−8670(11)
−8333(14)
−8117(8)
−8732(8)
−5534(8)
−4633(7)
−8506(8)
−9330(7)
−6304(9)
−6287(11)
−4384(9)
−3194(7)
−5919(9)
−5590(8)
−8512(8)
−9556(6)
−8420(8)
−8478(9)
−6425(8)
−5457(7)
−10134(7)
−11237(6)
47(1)
43(1)
45(1)
57(2)
81(3)
62(2)
86(3)
62(2)
81(3)
49(1)
69(2)
94(4)
72(2)
101(4)
73(2)
101(4)
56(2)
93(3)
49(2)
70(2)
55(2)
85(2)
61(2)
98(3)
62(2)
94(3)
57(2)
82(2)
55(2)
67(2)
55(2)
90(2)
64(2)
82(2)
50(2)
76(2)
Limiting indices
Reflections collected
Independent reflections
Absorption correction
Max. and min. transmission
Refinement method
0.258 and 0.178
Full-matrix least-squares on
F2
P(2)
C(7)
C(8)
C(9)
Data/restraints/parameters
Goodness-of-fit on F2 a
Final R indices [4492 data with
I\2|(I)]
R indices (all data)
Absolute structure parameter
Extinction coefficient
4975/1/336
0.977
bR1=0.0353, cwR2=0.0988
C(10)
C(11a)
C(12a)
C(11)
O(11)
C(12)
O(12)
C(13)
O(13)
C(21)
O(21)
C(22)
O(22)
C(23)
O(23)
C(24)
O(24)
C(31)
O(31)
C(32)
O(32)
C(33)
O(33)
110(8)
785(11)
bR1=0.0417, cwR2=0.1105
−0.04(5)
0.0111(7)
−4044(8)
−3906(9)
−3218(6)
−2646(6)
−5273(7)
−5868(7)
−5508(9)
−6423(7)
−3698(9)
−3542(9)
−3529(8)
−3344(8)
−3903(8)
−4160(6)
−1660(7)
−1180(8)
−1817(9)
−1255(7)
−3239(7)
−3618(7)
Largest diff. peak and hole
0.779 and −0.941
(e A−3
)
a Goodness-of-fit=[S[w(Fo2−Fc2)2]/(n−p)]1/2
b R1=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ.
.
c wR2=[S[w(Fo2−Fc2)2]/([w(F2o)]2]1/2
.
1165(4)
−1090(5)
−826(4)
−3555(6)
−4297(5)
−1728(7)
−1481(6)
−2905(5)
−3207(5)
All non-hydrogen atoms were anisotropically refined.
The H atoms of the triethylphosphine ligands were
calculated and refined riding on the corresponding car-
bon atoms with the isotropic temperature factors fixed
at 1.2Ueq of the carbon atoms to which they are linked.
Table 3 lists atomic coordinates and equivalent
isotropic displacement parameters for all non-hydrogen
atoms, with the corresponding estimated S.D.s in
parentheses.
a Ueq is defined as one third of the trace of the orthogonalized Uij
tensor.

G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
87
In the experiments under 1 atm of dihydrogen, a
regular increase of the turnover numbers (TONs) with
time is observed, except for cluster 1 that gives a
maximum after 30 min, then a decrease. In all experi-
ments an increase in the amount of cis-stilbene is also
observed; this is particularly evident for cluster 1. A
decrease of dihydrogen pressure results in a gradual
decrease of TON for all of the clusters; a decrease of
the amount of cis-stilbene and an increase of the fully
hydrogenated product is also observed.
In the experiments performed varying the amount of
C2Ph2, a decrease of the S/C ratio results in a regular
decrease of TON for all of the clusters suggesting
fragment catalysis; however, for 1 and 3 the cis/trans-
stilbene ratio remains constant or changes only very
little, whereas for 2 a sharp decrease in the amount of
cis-stilbene is observed. Moreover, in the experiments
performed varying the amount of the clusters, the TON
increases as the metal concentration decreases, pointing
to the possibility that all of the clusters examined
fragment partially to mononuclear species and/or
smaller clusters and that some or all of the species
become catalytically active. Finally, the use of CO
results in lower catalytic activities for all of the clusters;
this could also be due, in part, to the lower pressure of
dihydrogen present (H2/CO 50:50). However, increasing
TONs with time were observed in the experiments
involving cluster 2 as well as cluster 3. This behavior
could suggest that CO favors dismutation and forma-
tion of active precursors. Formation of mononuclear
fragments (active in isomerization) would be instead
disfavored; this would be accounted for by the strong
decrease of trans-stilbene when CO is used.
Fig. 1. An ORTEP plot (30% probability ellipsoids) of the molecular
structure for complex Ru3(CO)10(PEt3)2 (3). Hydrogen atoms and
selected labels have been omitted for clarity.
carbonyl ligands positions are distorted with respect to
those observed in the parent complex Ru3(CO)12 [11].
In fact only the ligands on Ru(1) maintain the equato-
rial and axial positions found in Ru3(CO)12, while
CO(21), CO(22) and CO(24) rotate nearly 25° around
Ru(2) in order to accommodate themselves to the en-
trance of the bulky phosphine (see Fig. 2).
The rotation around Ru(2) also induces a rotation
around Ru(3) and gives rise to the semi-bridging
CO(24) and CO(32) (Ru(2)ꢀC(24)ꢀO(24) 154.1(7)° and
Ru(3)ꢀC(32)ꢀO(32) 165.4(9)°). The two Ru(CO)3P moi-
eties are related to each other by a twisting round the
Ru(1)ꢀRu(3) bond of about 31°. The presence of the
two bent semi-bridging COs makes the molecule un-
symmetrical and chiral. Some of the other complexes
reported in Table 6 show analogous behavior [L=
PPh3, PPh(OMe)2] [15,16] or a similar trend [L=
PiPr2(C6H5Cr(CO)3)] [21]; the complexes with
L=P(OMe)3 [12] and L=P(OCH2CF3)3 [15] show the
same type of distortion, yet the disorder observed per-
mits no consideration about the carbonyls. In the com-
plex with L=P(C4H3S)3 [17] no distortion occurs
owing to the great dimensions of the Ru3 cluster. The
great RuꢀRu distances are probably due to the great
bulkiness of the ligands.
3.2. Formation of complex 3
It is known that Ru3(CO)12−nLn complexes undergo
thermal ‘disproportionation’ reactions under conditions
comparable with those adopted in this work. Favored
final products are Ru3(CO)10L2 derivatives, closely re-
lated to complex 3. Two hypotheses have been set forth
about these reaction mechanisms; one consists in inter-
or intramolecular phosphine exchange [9], but kinetic
studies indicate that fragmentation does occur and that
there is an equilibrium between mono-, bi- and trinu-
clear fragments or complexes [10].
We have considered tri- and di-substituted phosphine
derivatives of triruthenium dodecacarbonyl reported up
to now in the literature in order to verify whether the
substitution of phosphines for carbonyls modifies the
electronic and steric properties of these clusters, thus
making them more or less active in homogeneous
catalysis.
3.3. Structure of complex 3 — a comparison with
other phosphine-substituted ruthenium complexes
The examination of Tables 5 and 6 shows that phos-
phine ligands are always in equatorial position and that
for bi- and trisubstituted derivatives only structures of
type 1 are found. Complexes of type 2 occur only when
phosphine ligands are bidentate (e.g. dppm). The great
variability of RuꢀRu distances even in two molecules in
the asymmetric unit does not allow a correlation with
The structure of complex 3 is shown in Fig. 1 and
relevant distances and angles are reported in Table 4.
The molecular structure of complex 3 consists of a
triangle of Ru atoms, with the two phosphine ligands
equatorially bonded to two different Ru atoms in ap-
proximately trans configuration (type 1, Table 6). The

88
G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
the electronic properties of phosphine ligands and is in
keeping with a high degree of flexibility of the metallic
cluster. It seems to be more likely that molecular struc-
tures are a consequence of a minimization of steric
inter- and intramolecular repulsions.
3.4. Catalytic reaction mechanisms
In a previous study on the catalytic activity of phos-
phine-substituted ruthenium clusters in homogeneous
hydrogenation–isomerization of 1,4-pentadiene, we ob-
served that clusters 1 and 2 are considerably active and
selective, giving TOF values of 946.5 and 379.5 and
selectivities to 1,3-pentadiene of 79.6 and 86.9, respec-
tively. Attempts had been made to correlate the activity
to the number and to the pKa of the phosphines. It has
Fig. 2. A diagram of the molecular structure of complex 3 showing
the orientations of the carbonyls with respect to the Ru3 plane.
Table 4
,
Selected bond lengths (A) and angles (°) for Ru3(CO)10(PEt3)2 (com-
plex 3)
also been observed that the trisubstutituted derivatives
are more active than less substituted complexes and
that CO does not inhibit the reactions, whereas an
excess of free phosphine initially results in lower activi-
ties, but gives, after a while, the same results obtained
without it [5].
Finally, we found that disproportionation, CO and
phosphine displacement and formation of fragments
occurred either during the synthesis of complexes 2 and
3 and during catalytic reactions [6]; the same apparently
occurred during these catalytic reactions.
In the present work, we have observed that com-
plexes 1, 2 show good activity in the hydrogenation of
diphenylacetylene and that their activity is apparently
related to the type of phosphinic substituent (complex 1
is considerably more active than 2). Moreover complex
3, formed upon disproportionation during the catalytic
reactions of 2, is also an active catalytic species. A
disproportionation and/or fragmentation mechanism
can also be inferred from the findings of Bhaduri and
coworkers; they found that complex 1 shows a modest
catalytic activity in the homogeneous catalytic hydro-
genation of cyclohexene [18]; under dihydrogen ‘dispro-
portionation’ occurs leading to H4Ru4(CO)12−n(PPh3)n
derivatives, thus indicating, once again, formation and
reassembly of metal fragments. By raising the tempera-
ture Ru3(CO)7(PPh2)2(C6H4) (complex 4) was obtained;
this complex was considered as a catalytic hydrogena-
tion intermediate. These observations do also accord
with our recent findings on the catalytic activity of 4 [4].
Interestingly, complex 3 could be the precursor of
structures such as 4. Unfortunately, we did not observe
any such complex in our experiments. Their presence
would indeed have pointed to the occurrence of cluster
catalysis.
,
Bond lengths (A)
Ru(1)ꢀRu(2)
Ru(1)ꢀRu(3)
Ru(2)ꢀRu(3)
Ru(1)ꢀP(1)
2.868(2)
2.855(2)
2.863(2)
2.343(3)
2.358(3)
1.892(7)
1.957(6)
1.949(7)
1.898(11)
1.967(9)
1.918(7)
2.762(9)
1.976(7)
1.887(8)
1.954(7)
1.950(7)
2.485(9)
1.133(9)
Ru(3)ꢀP(2)
Ru(1)ꢀC(11)
Ru(1)ꢀC(12)
Ru(1)ꢀC(13)
Ru(2)ꢀC(21)
Ru(2)ꢀC(22)
Ru(2)ꢀC(23)
Ru(2)···C(32)
Ru(2)ꢀC(24)
Ru(3)ꢀC(31)
Ru(3)ꢀC(32)
Ru(3)ꢀC(33)
Ru(3)···C(24)
CꢀO av.
Bond angles (°)
Ru(1)ꢀRu(3)ꢀRu(2)
Ru(1)ꢀRu(2)ꢀRu(3)
Ru(2)ꢀRu(1)ꢀRu(3)
Ru(2)ꢀC(24)ꢀO(24)
Ru(3)ꢀC(32)ꢀO(32)
RuꢀCꢀO av.
C(11)ꢀRu(1)ꢀP(1)
C(12)ꢀRu(1)ꢀP(1)
C(13)ꢀRu(1)ꢀP(1)
C(11)ꢀRu(1)ꢀC(12)
C(11)ꢀRu(1)ꢀC(13)
C(21)ꢀRu(2)ꢀC(22)
C(21)ꢀRu(2)ꢀC(23)
C(21)ꢀRu(2)ꢀC(24)
C(22)ꢀRu(2)ꢀC(23)
C(23)ꢀRu(2)ꢀC(24)
C(31)ꢀRu(3)ꢀP(2)
C(32)ꢀRu(3)ꢀP(2)
C(33)ꢀRu(3)ꢀP(2)
C(31)ꢀRu(3)ꢀC(32)
C(31)ꢀRu(3)ꢀC(33)
60.22(6)
59.75(6)
60.03(4)
154.1(7)
165.4(9)
176.6(8)
94.3(3)
92.1(2)
91.3(3)
94.9(3)
96.0(4)
98.8(4)
99.5(4)
93.4(4)
91.7(3)
91.1(3)
95.8(3)
92.0(3)
90.4(2)
92.1(4)
92.5(3)
The structural parameters of complexes 1 and 2 and
of the other phosphine-substituted complexes discussed

G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
89
above point to a low tendency to release metal frag-
ments and could indicate that formation of cluster 3
could occur only through inter- and intramolecular
exchange of phosphines and CO [9] rather than through
a dismutation path requiring cluster fragmentation and
reassembly of metal fragments. On the other hand, we
cannot exclude that the phosphines present on all the
ruthenium atoms of such trinuclear derivatives could
favor fragmentation by keeping in solution mononu-
clear fragments. Indeed, it was recently found that
phosphine substitution for CO on the metallacyclic
cluster Os3(CO)9(C4Ph4) at room temperature gives
monosubstituted products via associative adduct for-
mation only for small phosphines (Tolman’s cone angle
below 143°). Indeed, bulky phosphines cause fragmen-
tation to mono- and dinuclear products [19]. Finally,
the presence of bent semi-bridging carbonyls on com-
plex 2 would favor fragmentation [20].
complex 3 and the ‘disproportionation’ occurring dur-
ing the catalytic experiments suggest the possibility that
fragmentation occurs together with the formation of
some smaller cluster or mononuclear species active in
the catalytic cycle. A possible reaction scheme is envis-
aged in Scheme 1.
Finally, it is worth noting that substitution of SMe2
for CO at a ruthenium atom of the Ru3 triangle that
contains a bridging C2Ph2 ligand in the layer segregated
cluster Pt3Ru6(CO)20(C2Ph2)(m3-H)(m-H) results in a
higher activity in the hydrogenation of diphenyl-
acetylene [21]. It was proposed that the enhanced activ-
ity could be due to the lability of the SMe2 ligand,
which would easily be displaced, leaving a free coordi-
nation site; when this site is occupied again by CO, the
activity is reduced to that of the parent cluster. It was
also proposed that all catalytic transformations occur
at the triruthenium triangle and that platinum exerts a
promotional effect by donating electronic density, i.e. a
‘metal-to-metal ligand’ effect. We have found that an
extra CO in place of a phosphine ligand does increase
the activity (cluster 3 versus 2); we suggest that this
In conclusion, the observed results (effect of dihydro-
gen pressure and S/C ratio), the inhibition of the reac-
tions when CO is used, the high catalytic activity of
Table 5
Structural parameters for Ru3(CO)9L3 derivatives
,
L
RuꢀRu (A)
Type
Tolman’s cone angle (°)
Ref.
a
b
c
CO
PMe3
2.8595(4)
2.860(1)
2.851(1)
2.860(2) a
2.863(1)
2.900(2)
2.887(1)
2.884(1)
2.882(4)
2.857(2)
2.9396(8) a
2.844(1)
2.857(2)
2.851(1)
2.846(1)
2.8512(4)
2.862(2)
2.864(1)
2.8518(4)
2.854(1)
2.860(1)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
[11]
[12]
[13]
[13]
[13]
[13]
118
122
120
109
115
PMe2Ph
PMe2(CH2Ph)
P(OEt)3
2.852(2)
2.870(1)
2.894(1)
2.876(1)
2.874(2)
2.866(2)
2.851(1)
2.887(2)
2.876(2)
2.882(1)
2.885(1)
2.852(2)
P(OMe)2Ph b
P(OCH2CF3)
PCy3
P(OMe)3
110
170
107
[13]
[14]
[23]
c
2.849(1)
2.863(1)
2.846(1)
2.848(1)
2.869(1)
2.885(2)
2.838(1)
2.838(1)
AsMe2Ph d
120
[13]
a The molecule lies on a threefold axis.
b Four independent molecules.
c Two polimorphs (triclinic and monoclinic).
d Two independent molecules.

90
G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
Table 6
Structural parameters for Ru3(CO)10L2 complexes
a
L
RuꢀRu
Type
Tolman’s cone angle
Ref.
A
b
c
b
b
PPh3
PPh3
PEt3
2.852(1)
2.893(3)
2.846(3)
2.893(3)
2.855(2)
2.845(1)
2.860(1)
2.831(2)
2.880(1)
2.8914(8)
2.833(3)
2.863(3)
2.842(4)
2.873(3)
2.868(2)
2.859(1)
2.865(1)
2.847(2)
3.003(1)
2.8927(6) c
2.823(3)
2.873(3)
2.838(4)
2.881(3)
2.863(2)
2.845(1)
2.868(1)
2.861(2)
2.945(1)
1
1
1
1
1
1
1
1
1
1
145°
145°
[16]
[15]
132°
107°
115°
110°
150°
164°
tw
P(OMe)3
P(OMe)2Ph
[12]
[15]
[15]
[17]
[22]
P(OCH2CF3)3
P(SC4H5)3
PiPr[C6H5Cr(CO)3]
a See annexed scheme.
b Two independent molecules.
c The molecule lies on a 2-fold axis.
could be due to the better coordinating properties
of phosphine ligands with respect to dimethyl
sulphide.
In Table 7 the catalytic results observed for clusters
1–3 are compared with those for other ruthenium
clusters, unsubstituted and/or substituted with phos-
phine and phosphido-ligands. The activity observed for
clusters 1, 2 and 3 is indeed rather high; only complexes
containing benzyne or alkyne ligands show higher ac-
tivity. It is worth noting that for such derivatives cluster
catalysis was observed [4].
Scheme 1.
In this work we have observed that phosphine-substi-
tuted triruthenium clusters are rather active in the
hydrogenation of diphenylacetylene: as for structure–
reactivity relationships, we have found that the bonding
parameters of such clusters cannot be linked to their
hydrogenation activity. However, the phosphine sub-
stituents may play a role either in determining catalytic
activity (cluster catalysis) and in promoting fragmenta-
tion of the clusters (fragment catalysis).
angles are available on request from the Cambridge
Crystallographic Data Centre as supplementary publi-
cation CCDC No. 117035. Copies of the data can be
obtained free of charge on application to: The Director,
CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(Fax: +44-1223-336-033; email: deposit@ccdc.cam.
ac.uk or www: http://www.ccdc.cam.ac.uk).
4. Supplementary material
Acknowledgements
Full tables of anisotropic thermal parameters, of
hydrogen atomic coordinates, of bond distances and
Support for this work has been obtained from
MURST (Italy) under the form of a cofinancing pro-

G. Ger6asio et al. / Journal of Organometallic Chemistry 588 (1999) 83–91
91
Table 7
[4] M. Castiglioni, S. Deabate, R. Giordano, P.J. King, S.A.R.
Knox, E. Sappa, J. Organomet. Chem. 571 (1998) 251.
[5] M. Castiglioni, R. Giordano, E. Sappa, J. Organomet. Chem.
342 (1988) 111.
Comparison between the catalytic activities of clusters 1–3 and those
of other ruthenium-based trinuclear complexes — hydrogenation of
diphenylacetylene
[6] M. Castiglioni, R. Giordano, E. Sappa, J. Organomet. Chem.
342 (1988) 97.
a
Cluster
S/C ratio
TOF b Selectivity c
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A
B
C
D
49.4
60.3
97.4
117.3
99.1
100
100
99.3
100
93.0
99.3
99.6
98.7
81.1
[6]
[6]
[6]
[6]
this work
this work
this work
[6]
100.0
108.0
761.1
153.3
278.9
194.6
559.2
90.1
Cluster 1
Cluster 2
Cluster 3
E
155.9
119.5
193.9
700.8
250.8
F
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Ru3(CO)7(PPh2)2(HC2Ph).
(E)
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(F)
b TOF=Turnover frequency (TON h−1).
c To monoenes.
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