Ru3(CO)12 in Acidic Media. Intermediates of the Acid-Cocatalyzed Water-Gas Shift Reaction (WGSR)

Article abstract of DOI:10.1021/ic960630v

The elucidation of the WGSR promoted by ruthenium carbonyls in acidic media started with the detection of the Ru(0), Ru(I), and Ru(II) intermediate complexes, namely Ru₃(CO)₁₂, Ru₂[μ-η²-OC(CF₃)O]₂(CO) ₆, and fac-[Ru(CF₃-COO)₃(CO)₃]^-, which accumulate when CF₃COOH is employed as an acid cocatalyst. Under catalytic conditions, the three were found to interconvert through elementary steps which produce CO₂ and H₂. In fact, Ru(0) is oxidized by H⁺ to Ru(I) and half the hydrogen of the catalytic cycle is supplied by this reaction. On the other hand, Ru(I) disproportionates to Ru(0) and Ru(II), and this latter species undergoes nucleophilic attack by H₂O. The decomposition of the metallacarboxylic acid intermediate gives back Ru(I), while H₂ and CO₂ are produced in a 1/2 molar ratio. The two alternating pathways for dihydrogen formation, namely Ru(0) oxidation by H⁺ and the decomposition of a metallacarboxylic acid intermediate, involve H₂ reductive elimination from the same RuHCF₃COO(CO)₂L₂ intermediate (L = H₂O, ethers). These findings define an acid-cocatalyzed WGSR whose distinctive features are (i) the intervention of a disproportionation reaction to generate a Ru(II) electron poor complex, whose CO ligands can undergo nucleophilic attack by water, (ii) the generation of the hydrido intermediate for dihydrogen production through two distinct reaction patways, and (iii) the reductive elimination of H₂ from the hydrido intermediate without involving H⁺ from the medium.

Full text of DOI:10.1021/ic960630v

Inorg. Chem. 1996, 35, 7217-7224
7217
Ru3(CO)12 in Acidic Media. Intermediates of the Acid-Cocatalyzed Water-Gas Shift
Reaction (WGSR)
Giuseppe Fachinetti,* Tiziana Funaioli,* Lorenzo Lecci, and Fabio Marchetti
Dipartimento di Chimica e Chimica Industriale, Universita` di Pisa, via Risorgimento 35,
I-56126 Pisa, Italy
ReceiVed May 28, 1996X
The elucidation of the WGSR promoted by ruthenium carbonyls in acidic media started with the detection of the
Ru(0), Ru(I), and Ru(II) intermediate complexes, namely Ru3(CO)12, Ru2[µ-η2-OC(CF3)O]2(CO)6, and fac-[Ru(CF3-
COO)3(CO)3]-, which accumulate when CF3COOH is employed as an acid cocatalyst. Under catalytic conditions,
the three were found to interconvert through elementary steps which produce CO2 and H2. In fact, Ru(0) is
oxidized by H+ to Ru(I) and half the hydrogen of the catalytic cycle is supplied by this reaction. On the other
hand, Ru(I) disproportionates to Ru(0) and Ru(II), and this latter species undergoes nucleophilic attack by H2O.
The decomposition of the metallacarboxylic acid intermediate gives back Ru(I), while H2 and CO2 are produced
in a 1/2 molar ratio. The two alternating pathways for dihydrogen formation, namely Ru(0) oxidation by H+ and
the decomposition of a metallacarboxylic acid intermediate, involve H2 reductive elimination from the same
RuHCF3COO(CO)2L2 intermediate (L ) H2O, ethers). These findings define an acid-cocatalyzed WGSR whose
distinctive features are (i) the intervention of a disproportionation reaction to generate a Ru(II) electron poor
complex, whose CO ligands can undergo nucleophilic attack by water, (ii) the generation of the hydrido intermediate
for dihydrogen production through two distinct reaction patways, and (iii) the reductive elimination of H2 from
the hydrido intermediate without involving H+ from the medium.
NaBPh4 from Aldrich. The ethers were further purified by distilling
them from LiAlH4, with THF and THF-d8 under an Ar atmosphere
Introduction
In acidic media Ru3(CO)12 is a catalyst precursor for
homogeneous WGSR,1 for the addition of carboxylic acids to
alkynes,2 and, under conditions of high temperature and pressure,
for the production of ethylene glycol derivatives from syngas3
and for the syngas homologation of CH3OH,4 esters,5 and
carboxylic acids.6 On the other hand, the known fundamental
chemistry of ruthenium carbonyls in acidic solutions is unsuf-
ficient for the complete understanding of these catalytic reac-
tions: all are believed to involve hydrido intermediates whose
origin and nature were not demonstrated, however. Moreover,
in the case of the here disclosed acid-cocatalyzed WGSR, not
only the nature of the dihydrogen yielding hydrido complex
but also the origin and the nature of the mandatory intermedi-
ates,7 bearing CO ligands susceptible of attack by water in acidic
solutions, still remained obscure. On trying to characterize
them, we met with some new aspects of the chemistry of
ruthenium carbonyls, which are fundamental for a better
understanding of catalytic reactions.
and diglyme under vacuum; CF3COOCs was anhydrified under vacuum
at 120 °C. Ruthenium trichloride hydrate was used as received from
Chimet SpA. The ruthenium complex Ru3(CO)12 was prepared by
literature methods.8 The IR spectra were recorded on a Perkin-Elmer
Model FT-IR 1725-X, and 1H and 19F NMR spectra on a Varian Model
Gemini-200. Liquid samples for infrared spectra were taken off with
a syringe and transferred to a 0.1 mm CaF2 cell. Analyses of H2 in
gas samples from catalysis run were performed by a DANI Model 3200
gas chromatograph equipped with HW detector and a molecular sieve
column with Ar as carrier gas. A calibration curve was prepared
periodically. CO2 was determined by bubbling the reaction gases
through 25 mL aliquots of a 0.098 N Ba(OH)2 solution and back-
titration (phenolphthalein end point) of Ba(OH)2 excess. The apparatus
and procedures for the gas volumetric measurements were those
described in the literature.9
Batch Reactor Procedures. Catalytic activity runs were carried
out at 95 °C, PCO ) 0.8 atm in an all glass vessel with a volume of
316 mL, similar to that described in the literature.10 During a typical
run, gas samples (1 mL) were removed at 1.5-h intervals and analyzed
by GC.
Ru2[µ-η2-OC(CF3)O]2(CO)6 (1a). Ru3(CO)12 (5.0 g, 7.82 mmol)
was suspended in diglyme containing 8 M H2O and 0.8 M CF3COOH
(total volume ) 100 mL) and heated to 100 °C during 12 h. The
resulting orange solution was concentrated under vacuum (20 mmHg,
100 °C) leaving a deep red oil which was treated with toluene (200
mL). This homogeneous solution was stirred under CO atmosphere at
40 °C during 2 h and then stored 24 h at -20 °C. A 5.9 g amount of
pale yellow crystals of 1a (85% yield) was obtained and gave
satisfactory analytical data. FT-IR (Nujol mull): νCO 2102 vs, 2051
Experimental Section
General Methods. Unless otherwise specified, all operations were
carried out under argon by standard Schlenk techniques. CO (<0.1%
H2) was purchased from Matheson, and AR grade toluene, py, iso-
PrOH, THF, THF-d8, diglyme, CF3COOH, CF3COOCs, CF3SO3H, and
X Abstract published in AdVance ACS Abstracts, November 1, 1996.
(1) Yarrow, P.; Cohen, H.; Ungermann, C.; Vanerberg, D.; Ford, P. C.;
Rinker, R. G. J. Mol. Catal. 1983, 22, 239.
(2) Rothem, M.; Shvo, Y. J. Organomet. Chem. 1993, 448, 189.
(3) Dombek, B. D. AdV. Catal. 1983, 32, 325.
(4) Braca, G.; Sbrana, G.; Valentini, G.; Andrich, G.; Gregorio, G. J. Am.
Chem. Soc. 1978, 100, 6238.
vs, 2017 vs, 1993 s, and 1665 s cm-1 11
.
Ru2[µ-η2-OC(CF3)O]2(CO)4L2 (L ) H2O, Diglyme) (1b). A 0.350
g amount of 1a was dissolved in diglyme containing 8 M H2O (total
(5) Braca, G.; Sbrana, G.; Gregorio, G. U.S. Patent 4,189,441, 1980.
(6) (a) Knifton, J. F. J. Mol. Catal. 1981, 11, 91. (b) Knifton, J. F. Chem.
Techn. 1981, 609. (c) Knifton, J. F. Hydr. Proc. 1981, 60, 113.
(7) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Princples
and Applications of Organotransition Metal Chemistry; University
Science Book: Mill Valley, CA, 1987.
(8) Braca, G.; Sbrana, G.; Pino, P. Chim. Ind. (Milan) 1964, 46, 206;
Chim. Ind. (Milan) 1968, 50, 121.
(9) Calderazzo, F.; Cotton, F. A. Inorg. Chem. 1962, 1, 30.
(10) Pardey, A. J.; Ford, P. C. J. Mol. Catal. 1989, 53, 247.
(11) Rotem, M.; Goldberg, I; Shmueli, U; Shvo, Y. J. Organomet. Chem.
1986, 314, 185.
S0020-1669(96)00630-1 CCC: $12.00 © 1996 American Chemical Society

7218 Inorganic Chemistry, Vol. 35, No. 25, 1996
Table 1. Crystal Data and Details of Structure Refinements
Fachinetti et al.
empirical formula
fw
temp, K
C9CsF9O9Ru
657.07
293(2)
C10H8F6O8Ru
471.23
293(2)
C41H36BN3O2Ru
714.61
293(2)
wavelength, Å
cryst system
space group
a, Å
0.71073
monoclinic
P21/c (No. 14)
8.3839(5)
0.71073
monoclinic
P21/c (No. 14)
12.486(2)
1.54178
hexagonal
P65 (No. 170)
9.7604(6)
b, Å
14.450(3)
10.228(2)
9.7604(9)
c, Å
16.079(1)
90
102.951(5)
90
12.286(2)
90
107.76(2)
90
64.244(8)
90
90
120
R, deg
â, deg
γ, deg
V, Å3
1898.4(4)
1494.2(5)
5300.3(9)
Z
4
4
6
D(calc), Mg/m3
abs coeff, mm-1
F(000)
2.299
2.840
1224
2.095
1.159
920
1.343
3.892
2208
cryst size, mm
θ range for data collcn, deg
h ranges
k ranges
l ranges
reflcns collcd
indepdt reflcns
refinement method
data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole, e‚Å-3
0.34 × 0.24 × 0.22
0.25 × 0.25 × 0.08
0.21 × 0.21 × 0.48
1.92-24.99
2.63-20.99
5.23-59.85
-1 to 9
-12 to 12
-8 to 0
0 to 10
-72 to 64
5129
-1 to 17
-10 to 1
-19 to 18
-1 to 12
4312
2134
3248 [Rint ) 0.022]
full-matrix least squares on F2
3240/30/239
1.029
R1 ) 0.0526, wR2 ) 0.1278
R1 ) 0.0727, wR2 ) 0.1863
1.110 and -0.794
1596 [Rint ) 0.057]
full-matrix least squares on F2
1596/16/150
1.069
R1 ) 0.0890, wR2 ) 0.2200
R1 ) 0.1633, wR2 ) 0.2865
1.212 and -0.981
5129
full-matrix least squares on F2
5129/5/436
1.108
R1 ) 0.0343, wR2 ) 0.0764
R1 ) 0.0735, wR2 ) 0.0886
0.841 and -1.178
volume ) 20 mL), and the solution was briefly evacuated. Under an
inert atmosphere the IR spectrum consisted of the absorptions of 1b at
diglyme (total volume ) 20 mL) in the vessel for catalytic runs. After
45 min CO2 formation ceased; the atmosphere was replaced by pure
argon and the temperature raised to 65 °C. Gas samples (1 mL) were
periodically taken off, and H2 was determined by GC (Figure 6). After
24 h the IR spectrum of the liquid phase showed only the absorptions
of 1b (νCO: 2043 s, 1989 m, 1958 s cm-1). An identical solution ([Ru]
) 0.05 M, [H2O] ) 8 M in diglyme, total volume ) 20 mL) in the
same 316 mL reaction vessel was treated with 130 µL (1.5 mmol) of
CF3SO3H at the end of CO2 formation and then warmed to 65 °C. The
H2 formed at various times was determined as before.
{fac-Ru(OCOCF3)2(CO)3[(CH3)2CHOH]} (4). Ru3(CO)12 (5.0 g,
7.82 mmol) was suspended in diglyme containing 8 M H2O and 2.2 M
CF3COOH (total volume ) 50 mL) and warmed to 100 °C during 12
h. The resulting orange solution of 1a was stirred under a PCO ) 1
atm at room temperature for 5 days. As a consequence of the
disproportionation reaction, Ru3(CO)12 separated out and was removed
by filtration. The mother liquor was evaporated to dryness under
vacuum at 100 °C, leaving an orange oil which was dissolved in 15
mL of iso-PrOH. A 200 mL volume of toluene was then added and
the solution concentrated under vacuum at room temperature, till the
precipitation of colorless crystals of 4 occurred (3.43 g, 7.28 mmol,
31% yield; νCO (Nujol) 2153 s, 2094 vs, 2078 vs, and 1676 s, broad,
cm-1). Satisfactory analytical data were obtained. The molecular
structure is shown in Figure 3.
2043 s, 1989 m, and 1958 vs cm-1 11
By restoration of a CO
.
atmosphere, gas absorption took place and absorptions of 1a, together
with those of 1b became evident.
[fac-Ru(OCOCF3)3(CO)3]Cs (2). A catalytic run was carried out
by employing Ru3(CO)12 (0.250 g, 0.39 mmol) in diglyme containing
8 M H2O, 3 M CF3COOH, and 0.4 M CF3COOCs (total volume ) 20
mL). The run was protracted overnight and then stopped by lowering
the temperature to 20 °C. Colorless crystals of 2 (0.310 g, 40% yield),
suitable for an X-ray investigation, separated out within 1 day.
Satisfactory analytical data were obtained. FT-IR (Nujol mull): νCO
2145 s, 2084 vs 2067 vs, and 1693 s cm-1. The molecular structure is
reported in Figure 2.
Disproportionation Reaction of 1a. 1a (0.650 g, 1.09 mmol) and
CF3COOCs (0.270 g, 1.09 mmol) were dissolved in 20 mL of anhydrous
THF and placed under a CO atmosphere at 30 °C. Within 8 h, 1.07
mmol of gas was absorbed while orange Ru3(CO)12 separated out (0.220
g, 0.34 mmol, 95% yield; νCO (n-hexane) 2061 s, 2031 s, and 2013 m
cm-1). On evaporation of the mother liquor to dryness under vacuum,
a pale yellow residue of 2 was obtained (0.710 g, 1.08 mmol, 99%
yield; νCO (Nujol): 2145 s, 2084 vs, 2067 vs, and 1693 s cm-1).
Reaction between 2 and H2O. (a) At 95 °C, in the Presence of
CF3COOH. A 20 mL aliquot of a 8 M H2O, 0.5 M CF3COOH, and
0.036 M 2 (0.470 g, 0.71 mmol) solution in diglyme was placed under
an Ar atmosphere in the 316 mL reaction vessel used for the catalytic
runs. By the increase of the temperature up to 95 °C, the colorless
solution turns yellow. After 1 hour the H2 (0.35 mmol, 99% yield)
and the CO2 (0.69 mmol, 97% yield) were quantitatively determined.
The IR spectrum of the liquid phase showed only the absorptions of
1H NMR Spectra. 2 (0.130 g, 0.20 mmol) was dissolved in THF-
d8 containing 8 M H2O (total volume 0.5 mL) and allowed to stand for
1 h. The spectrum of Figure 4a was then obtained. 4 (0.095 g, 0.20
mmol) was dissolved in THF-d8 containing 8 M H2O (total volume
0.5 mL) and allowed to stand for 1 h. The spectrum of Figure 4b was
obtained and was converted into that of Figure 4a by addition of 0.052
g (0.21 mmol) of solid CF3COOCs, directly in the NMR tube. In
another experiment 4 was reacted with 8 M H2O in THF-d8 at the same
concentration as before. By means of a syringe, increasing amounts
of CF3SO3H were then added directly into the NMR tube. The spectra
of Figure 4c-f were obtained at CF3SO3H/Ru ) 0.42, 0.72, 1.36, and
2.40 molar ratios, respectively.
[fac-RuH(CO)2(py)3][BPh4] (5). 4 (1.32 g, 2.8 mmol) was dissolved
in 25 mL of THF, and 5 mL of H2O was added at room temperature.
After 1 h, 1.3 g (3.8 mmol) of NaBPh4 in 20 mL of py was added, and
the product was precipitated by addition of 150 mL of CH3OH. After
1 week at 4 °C 1.7 g (2.38 mmol, 85% yield) of 517 was collected as
colorless crystals. The molecular structure is reported in Figure 5.
1b. νCO: 2043 s, 1989 m, 1958 s cm-1
.
(b) At Room Temperature. 2 (0.443 g, 0.67 mmol) was dissolved
in diglyme containing 8 M H2O (total volume ) 20 mL) under an Ar
atmosphere in the 316 mL reaction vessel used for the catalytic runs.
A pale yellow color was immediately observed, and the reaction was
monitored by IR spectroscopy. After 45 min at room temperature, only
the IR absorptions of a 3a-c mixture of hydrido complexes became
detectable (νCO: 2041 and 1957 cm-1). Only trace amounts of H2 were
detected in the gas phase, while quantitative determination of the
produced CO2 gave 0.62 mmol (92% yield).
Dihydrogen Formation from a 3a-c Mixture of Hydrides.
4
(0.470 g, 1 mmol) was reacted at room temperature with 8 M H2O in

Ru3(CO)12 in Acidic Media
Inorganic Chemistry, Vol. 35, No. 25, 1996 7219
X-ray Structure Determinations. The crystals of [fac-Ru(OCOCF3)3-
(CO)3]Cs are colorless monoclinic prisms defined by the form {011}
closed by the pinacoid {100}. One of them was glued at the end of a
glass fiber and was mounted on a Siemens P4 automatic single-crystal
diffractometer, equipped with a graphite-monochromatized Mo KR
radiation. Cell parameters were calculated on the accurately centered
setting angles of 25 strong reflections with 12.5° e θ e 13°. Details
about the crystal parameters and intensity data collection are sum-
marized in the second column of Table 1. The Laue class was
established by an automatic procedure contained in the diffractometer
control program.12 A redundant set of data was collected to estimate
the collection accuracy. Three standard reflections measured every 97
measurements showed no decay in the crystal. The space group was
univocally established as P21/c on the basis of systematic absences.
The collected intensities were corrected for Lorentz and polarization
effects and for absorption by a Gaussian integration method.13 The
equivalent reflections present in the set were then merged resulting in
The final reliability parameters are shown in Table 1, where R1, wR2,
and S have the same meaning as in the preceeding column and w )
2
2
1/[σ2(Fo ) + (0.1454P)2 + 15.38P], where P ) [max(Fo ,0) + 2Fc2]/3.
The reliability appears acceptable considering the poor quality of the
crystal and the presence of disorder.
The crystals of [RuH(CO)2(py)3][BPh4] are colorless hexagonal
prisms closed by hexagonal bipyramids. One of them was glued at
the end of a glass fiber, and its diffraction pattern was studied on a
Weissenberg camera using Cu KR radiation (λ ) 1.541 78 Å). The
pattern showed well-shaped spots displaying hexagonal symmetry and
a very long c period. The systematic extinctions suggested a primitive
lattice with a 61 or 65 operator.
Accurate cell parameters and intensity data were collected on a
Nonius CAD4 single-crystal diffractometer equipped with graphite-
monochromatized Cu KR radiation. Crystal parameters and collection
details are summarized in the fourth column of Table 1. Collection of
three standard reflections every 97 measurements allowed one to
exclude any crystal decay. The collected data were corrected for
Lorentz and polarization effects and for absorption by using a ψ-scan
method. The structure was solved by standard Patterson and Fourier
methods in the P65 space group, and the absolute configuration of the
crystal was chosen on the basis of Flack index.14 The hydrogen atoms
were introduced in calculated positions and were allowed to ride on
the connected carbon atoms. The final reliability indexes obtained in
the last least-squares cycles, with all the heavy atoms with anisotropic
thermal parameters, are shown in the last column of Table 1, where w
an internal R value (Rint ) ∑|Fo2 - Fo (mean)|/∑(Fo )) of 0.022. The
structure was solved by the automatic Patterson method contained in
the SHELXTL2 program, and the molecule was completed by means
of the next Fourier map. Disorder in the positions of the CF3 groups
was suggested by electron density maps. The disorder was explained
as a statistical distribution of the trifluoroacetate groups on two different
conformations, and two different CF3 groups were introduced in each
position imposing the sums of occupancies equal to 1.
2
2
The final refinement cycles were made with anisotropic thermal
factors for Cs, Ru, O, and C atoms and isotropic for F atoms and
imposing geometrical constraints to the CF3 modifications. The final
reliability factors are showed in Table 1, where R1 ) ∑||Fo| - |Fc||/
2
2
) 1/[σ2(Fo ) + (0.0427P)2 + 0.09P] with P ) [max(Fo ,0) + 2Fc2]/3.
All calculations and drawings were performed by using the
SHELXTL13 program.
2
2
2
∑|Fo|, wR2 ) [w(Fo - Fc2)2/w(Fo )2]1/2, and w ) 1/[σ2 (Fo ) +
2
2
(0.0636P)2 + 12.34P], with P ) [max(Fo ,0) + 2Fc2]/3 and S ) [w(Fo
Results and Discussion
- Fc2)2/(N - P)]1/2
.
The crystals of {fac-Ru(OCOCF3)2(CO)3[(CH3)2CHOH]} (4) are
colorless milky, with a prismatic shape. Some of them were sealed
within glass capillaries under a nitrogen atmosphere and were examined
on a Siemens P4 single-crystal diffractometer. All the samples appeared
to be crystalline, but not one presented a good diffraction profile. In
fact some profiles appeared to be exceedingly large and some other
showed a depression in the central part of the profile as they
corresponded to two different single crystals slightly misaligned. The
third column of Table 1 summarizes the relevant crystal data and
intensity data collection details. Cell parameters were calculated from
the setting angles of 13 accurately centered strong reflections having
8.9° e θ e 9.6°. The choice of such a low value for max, here and in
the intensities collection, has been called for by the lack of intense
diffractions at high angles.
A redundant set of data was collected to verify, on merging, the
collection reliability. Three standard reflections measured every 97
measurements allowed one to exclude any crystal decay. The collected
data were corrected for Lorentz and polarization effects, but not for
absorption, since a scanning around the ψ angle of 5 intense reflections
showed a slight effect on the measured intensity.
The space group was univocally established as P21/c by systematic
extinctions, and the structure was solved by direct methods contained
in the TREF13 procedure. However, the two CF3 groups of the
trifluoroacetate ligands and two methyl groups of isopropyl alcohol
could not be reliably localized in a rather smeared electron density
that appeared on the Fourier map. We explained this fact with the
presence of disorder both in -CF3 and in -CH(CH3)2 groups. As in
the case of the cesium salt, we have introduced two distinct idealized
-CF3 groups in each expected position of trifluoroacetate ligand and
two different -CH(CH3)2 groups in the isopropyl alcohol, assuming a
total occupancy equal to 1 for each group. The atoms found in the
Fourier map were refined with anisotropic thermal factors, while
isotropic factors have been used for the disordered atoms that have
been introduced in geometrically calculated positions and have been
refined as rigid groups. The hydrogen atoms were not introduced.
Direct Detection of Intermediates during the CF3COOH-
Cocatalyzed WGSR. We recently evidenced that the nature
of conjugated base affects the acid-cocatalyzed WGSR promoted
by Rh4(CO)12.15 A role of the conjugated base is apparent also
in the case, examined here, of the Ru3(CO)12 precursor in H2O/
diglyme solution: by comparison of two strong acids, i.e.
sulfuric and triflic, as cocatalysts for the WGSR under the same
conditions, only the former resulted in activity. Moreover, by
the employment of CF3COOH as cocatalyst in the 8 M H2O/
diglyme medium ([Ru] ) 0.036 M, [CF3COOH] ) 0.5 M, PCO
) 0.8 atm, T ) 95 °C) the TOF(H2) (TOF(H2) ) mol of H2/
mol of Ru/day) was 3 and increased to 18 on adding CF3COOCs
in a 1/5 molar ratio with respect to the acid. Such a sharp
increase of TOF(H2) demonstrates the beneficial role of
CF3COO- and can be understood by considering that CF3COOH
behaves as a weak acid in the reaction medium (κa ) 2 × 10-2
at 25 °C).16 Therefore, the addition of CF3COOCs, although
only in a 1/5 molar ratio with respect to the acid, strongly
increases the concentration of its conjugated base.
Remarkably, the CF3COO- concentration also affects the
nature of the intermediate carbonyl complexes which accumulate
during WGSR. At the low CF3COO- concentration arising
from the dissociation of CF3COOH, only dimeric Ru(I) carbo-
nyls, namely a PCO-depending equilibrium mixture of Ru2[µ-
η2-OC(CF3)O]2(CO)6 (1a) and Ru2[µ-η2-OC(CF3)O]2(CO)4L2
(L ) H2O, diglyme) (1b),11 can be detected by IR analysis after
the early stages of catalysis (Figure 1a). When the CF3COO-
concentration is substantially increased by the addition of CF3-
COOCs, however, two new absorptions (νCO 2136 and 2065
(14) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
(15) Fachinetti, G.; Fochi, G.; Funaioli, T. Inorg. Chem. 1994, 33, 1719.
(16) This value was determined by fitting the 19F NMR chemical shift data
of progressively diluted CF3COOH solutions (5 × 10-1 to 5 × 10-4
M, 25 °C) in diglyme containing 8 M H2O, to equation which describes
the dependence of the concentration Co on the measured chemical
shift (Dimicoli, J. L.; Helene, C. J. J. Chem. Soc. 1973, 95, 1036),
(12) XSCANS: X-ray Single Crystal Analysis System, rel. 2.1; Siemens
Analytical X-ray Instruments Inc.: Madison, WI, 1994.
(13) Sheldrick, G. M. SHELXTL-Plus, Rel. 5.03; Siemens Analytical X-ray
Instruments Inc.: Madison, WI, 1994.
affords the value of 2 × 10-2
.

7220 Inorganic Chemistry, Vol. 35, No. 25, 1996
Fachinetti et al.
cm-1; Figure 1b) point out the accumulation of a new electro-
philic carbonyl.
Figure 2. ORTEP projection of the structure of the anionic moiety of
[fac-Ru(OCOCF3)3(CO)3]Cs (2). Ru, C, and O atoms are represented
by thermal ellipsoids at 50% probability. The disordered F atoms have
been refined with isotropic thermal displacement factors and are here
represented by spheres. For clarity, only one of the two limit positions
of the fluorine atoms is shown.
Table 2. Bond Lengths (Å) and Angles (deg) for the Anion
[fac-Ru(OCOCF3)3(CO)3]-
Ru-C(1)
Ru-C(2)
Ru-C(3)
Ru-O(8)
Ru-O(4)
Ru-O(6)
C(1)-O(1)
C(2)-O(2)
C(3)-O(3)
1.896(10)
1.914(10)
1.925(10)
2.088(6)
2.091(6)
2.096(6)
1.142(11)
1.130(11)
1.107(11)
O(4)-C(4)
O(5)-C(4)
C(4)-C(5)
O(6)-C(6)
O(7)-C(6)
C(6)-C(7)
O(8)-C(8)
O(9)-C(8)
C(8)-C(9)
1.267(10)
1.198(11)
1.520(11)
1.269(10)
1.213(11)
1.552(12)
1.280(10)
1.194(11)
1.543(12)
C(1)-Ru-C(2)
C(1)-Ru-C(3)
C(2)-Ru-C(3)
C(1)-Ru-O(8)
C(2)-Ru-O(8)
C(3)-Ru-O(8)
C(1)-Ru-O(4)
C(2)-Ru-O(4)
X(3)-Ru-O(4)
O(8)-Ru-O(4)
C(1)-Ru-O(6)
C(2)-Ru-O(6)
C(3)-Ru-O(6)
O(8)-Ru-O(6)
O(4)-Ru-O(6)
89.5(4)
92.8(4)
90.2(4)
174.1(3)
93.2(3)
92.5(3)
92.8(4)
95.6(3)
172.0(3)
81.7(2)
93.7(3)
175.5(3)
92.8(4)
83.4(2)
81.1(2)
O(1)-C(1)-Ru
O(2)-C(2)-Ru
O(3)-C(3)-Ru
C(4)-O(4)-Ru
O(5)-C(4)-O(4)
O(5)-C(4)-C(5)
O(4)-C(4)-C(5)
C(6)-O(6)-Ru
O(7)-C(6)-O(6)
O(7)-C(6)-C(7)
O(6)-C(6)-C(7)
C(8)-O(8)-Ru
O(9)-C(8)-O(8)
O(9)-C(8)-C(9)
O(8)-C(8)-C(9)
177.1(10)
177.4(9)
178.2(8)
122.7(6)
129.1(9)
119.6(8)
111.2(7)
123.1(6)
127.7(9)
119.5(8)
112.7(7)
121.1(5)
129.0(9)
120.0(8)
111.0(7)
Figure 1. (a) IR spectrum in the CO stretching region of samples
withdrawn during the WGSR in diglyme containing 8 M H2O ([Ru] )
0.036 M, [CF3COOH] ) 0.5 M, PCO ) 0.8 atm, T ) 95 °C). (b) IR
spectrum in CO stretching region of samples withdrawn during the
WGSR at increased [CF3COO-] by addition of CF3COOCs in a 1/5
molar ratio with respect to CF3COOH. For a comparison, the spectrum
of 0.015 M 2 in diglyme containing 8 M H2O and 0.5 M CF3COOH
has been inserted (dashed line). The absorptions of the H2O/CF3COOH/
diglyme medium have been subtracted. Key: (*) absorptions of 1a;
(+) absorptions of (1b); (O) absorptions of 2.
of Ru3(CO)12 in the presence of carboxylic acids.2
In order to characterize this latter species, WGSR was carried
out in a more concentrated solution at 95 °C. On cooling of
the sample to room temperature, a colorless precipitate, suitable
for a single-crystal X-ray analysis, separated out. The IR spectra
of this product in the solid state (νCO 2145 s, 2084 vs, and 2067
vs, cm-1) and in an acidic H2O/diglime solution (Figure 1b,
dashed line) confirm that it is the same carbonyl complex which
is found to accumulate when the homogeneous catalysis is
carried out in the presence of excess CF3COO-. The molecular
structure shows that it is the cesium salt of [fac-Ru(OCOCF3)3-
(CO)3]- (2) (Figure 2); the main bond distances and angles are
summarized in Table 2.
2Ru3(CO)12 + 6CF3COOH
3H2 + 3Ru2[µ-η2-OC(CF3)O]2(CO)6 + 6CO
(1)
1a
–CO
+L
3Ru2[µ-η2-OC(CF3)O]2(CO)4L2
1b
L = H2O, diglyme
More surprising is the accumulation of the Ru(II) carbonyl 2
during the catalytic process with added CF3COOCs. On the
other hand, the high wavenumbers for the CO stretching
vibrations of 2 indicate electrophilic character of the CO ligands
as required for the WGSR mandatory intermediate undergoing
Reactions Interconverting the Intermediates and Produc-
ing CO2 and H2. The formation of the equilibrium mixture of
1a,b, the only products found to accumulate at low CF3COO-
concentration (eq 1), parallels a number of well-known reactions

Ru3(CO)12 in Acidic Media
Inorganic Chemistry, Vol. 35, No. 25, 1996 7221
Scheme 1. Overall Reactions Resulting in the
Acid-Cocatalyzed WGSR Promoted by Ruthenium Carbonyls
intermediates in the two reductions of the proton respectively
in the left- and right-hand branches of Scheme 1.
(a) From Ru3(CO)12 and HX. In the case of H2 being
formed from Ru3(CO)12 and CF3COOH, it has been shown that
the mononuclear hydrido Ru(II) complex [RuH(OCOCF3)(CO)2-
(py)2] can be trapped when the N-donor ligand pyridine is
present.17 By analogy, we assume that the more labile RuH-
(OCOCF3)(CO)2L2 (L ) H2O or diglyme) (3b) is formed Via
oxidative addition of CF3COOH to Ru3(CO)12 under the
conditions of catalysis and constitutes the intermediate for the
dihydrogen production of the left-hand branch of Scheme 1.
More details on dihydrogen evolution from 3b are given in
section b, since the low-temperature reaction between 2 and
H2O in neutral solution allows this intermediate to be synthe-
sized and, thus, its properties to be separately investigated.
(b) From 2 and H2O. As mentioned before, reaction 3
between 2 and 8 M H2O in diglyme requires high temperatures
to occur when tested in the same medium of catalysis, i.e. in
the presence of 0.5 M CF3COOH. However, in the absence of
acid, 2 undergoes nucleophilic attack by H2O already at room
temperature, and hydrido intermediates can be detected under
these milder conditions. The addition of water to 0.036 M 2 in
diglyme at 20 °C brings about modifications in the IR spectrum
of the solution: the absorptions of 2 are replaced by two bands
at 2041 and 1957 cm-1, indicative for a cis-dicarbonyl complex,
and one at 2338 cm-1, this latter being due to the produced
CO2. The reaction is complete in 45 min; no dihydrogen is
formed under these conditions, thus suggesting that the produc-
tion of CO2 leaves a stable hydrido cis-dicarbonyl complex of
Ru(II). Any attempt to isolate this species failed, and its nature
was ascertained by chemical and spectroscopic methods.
When the reaction between 2 and H2O was carried out in
THF-d8 ([2] ) 0.4 M, [H2O] ) 8 M), the 1H NMR spectrum of
the resulting solution showed a hydridic peak at -13.8 ppm,
accompanied by two minor resonances at -13.4 and -14.0 ppm
(Figure 4a).
attack by H2O. An investigation on the origin of 2 and on its
reaction with H2O was then undertaken. As a result, we found
that 2 is the product of a hitherto unrecognized disproportion-
ation reaction of 1a. In anhydrous THF, 1a is stable under CO,
while, under an inert atmosphere, 1b is unaffected by excess
CF3COO-. When both these ligands are present, however, gas
absorption takes place at room temperature; the disproportion-
ation reaction is pointed out by the formation of orange insoluble
Ru3(CO)12, while the characteristic IR absorptions of 2 become
evident in the solution. Quantitative recovery of Ru3(CO)12 and
2 as well as gas volumetric measurement of reacted CO, indicate
the stoichiometry of eq 2.
+ 3CF3COO- +
3Ru2[µ-η2-OC(CF3)O]2(CO)6
1a
3CO THF8
(2)
Ru3(CO)12 + 3[fac-Ru(OCOCF3)3(CO)3]-
2
The reactions 1 and 2 account for the formation of the
intermediates 1a,b and 2, which were found to accumulate
during the catalytic process. Under catalytic conditions,
Ru3(CO)12 becomes a labile intermediate. At low CF3COO-
concentrations, the disproportionation reaction 2 constitutes the
slow step of the WGSR; on the other hand, CF3COO- together
with CO promotes the conversion of 1a into the more labile 2,
till the enhanced process rate at high CF3COO- concentrations
is controlled by the reaction consuming 2, i.e. by the reaction
with H2O which produces CO2 and H2. As a matter of fact,
when 2 was warmed under an inert atmosphere to the same
temperature (95 °C) and in the same medium of the catalytic
process, H2 and CO2 were produced in a 1/2 ratio, together with
1b which was identified on the basis of its IR spectrum (eq 3).
By analogy with the recently reported case of the hydridosul-
fonatocarbonyl(pyridine)ruthenium(II),17 the three resonances
were tentatively attributed to an equilibrium mixture of anionic,
neutral, and cationic Ru(II) hydrido dicarbonyl complexes
formed by different degrees of substitution of trifluoroacetato
by neutral H2O or THF ligands (eq 4).
THF
[fac-Ru(OCOCF3)3(CO)3]– + H2O
2
2[fac-Ru(OCOCF3)3(CO)3]-
+
CO2 + [RuH(OCOCF3)2(CO)2L]– + CF3COOH
(4)
2
3a
[CF3COOH] ) 0.5 M, 8 M H2O in diglyme
–CF3COO–
+L
2H2O ssssssssssssssssssssssssssf
inert atmosphere, 95 °C
2
RuH(OCOCF3)(CO)2L2
H + 2CO +
+
Ru2[µ-η -OC(CF3)O]2(CO)4L2
2
2
3b
1b
2CF3COO- + 2CF3COOH (3)
–CF3COO–
+L
[RuH(CO)2L3]+
Reactions 1-3 result altogether in a catalytic cycle (Scheme
1) producing CO2 and H2 from CO and H2O.
3c
Origins and Nature of the Hydrido Intermediates for
Dihydrogen Formation. The distinctive aspect of such a
WGSR (Scheme 1) is that Ru(0) and a CO ligand in a Ru(II)
complex alternate in supplying electrons for dihydrogen forma-
tion. Since the knowledge of the ruthenium hydrides which
arise from Ru3(CO)12 in acidic media can be of general utility
for a better understanding of several catalytic reactions besides
WGSR, we devoted a particular effort to identify the hydrido
L = THF, H2O
In order to confirm that, we examined how the CF3COO-
relative concentration affects the three resonances. The case
of [CF3COO-]/[Ru] ) 2 was investigated by reacting with H2O
(17) Fachinetti, G.; Funaioli, T.; Marchetti, F. J. Organomet. Chem. 1995,
498, C20.

7222 Inorganic Chemistry, Vol. 35, No. 25, 1996
Fachinetti et al.
in ethers {fac-Ru(OCOCF3)2(CO)3[(CH3)2CHOH]} (4), whose
molecular structure is reported in Figure 3.
Figure 4. 1H NMR spectra of hydrides accumulating at room
temperature in the reaction between Ru(II) carbonyls and H2O in THF-
d8: (a) Same spectrum obtained directly from 2 or on adding
CF3COOCs to the hydride mixture arising from 4; (b) spectrum obtained
directly from 4; (c-f) spectra showing the modifications induced on
adding increasing amounts of triflic acid to the solution of spectrum b.
Figure 3. 3. ORTEP projection of the molecular structure of {fac-
Ru(OCOCF3)2(CO)3[(CH3)2CHOH]} (4). Thermal ellipsoids are rep-
resented at 30% probability. The disordered CF3 and C(CH3)2 groups
have been refined with isotropic thermal parameters and are represented
by spheres. Moreover, to limit superposition, only one of the two limit
positions is shown. The distances and angles around the metal are as
follows: Ru-C(2) 1.85(3), Ru-C(1) 1.86(3), Ru-C(3) 1.91(3), Ru-
O(4) 2.02(2), Ru-O(6) 2.06(2), Ru-O(8) 2.092(13), C(2)-Ru-C(1)
88.0(12), C(2)-Ru-C(3) 90.9(11), C(1)-Ru-C(3) 91.6(12), C(2)-
Ru-O(4) 96.9(9), C(1)-Ru-O(4) 94.4(9), C(3)-Ru-O(4) 170.3(9),
C(2)-Ru-O(6) 97.1(10), C(1)-Ru-O(6) 174.7(8), C(3)-Ru-O(6)
89.8(10), O(4)-Ru-O(6) 83.6(6), C(2)-Ru-O(8) 175.6(9), C(1)-
Ru-O(8) 90.9(9), C(3)-Ru-O(8) 93.4(9), O(4)-Ru-O(8) 79.0(6),
O(6)-Ru-O(8) 83.9(6).
The neutral electrophilic carbonyl complex 4 (νCO (Nujol):
2153 s, 2094 vs, and 2078 vs cm-1) reacted at room temperature
with 8 M H2O in diglyme at a rate comparable to 2; the IR
spectrum of the solution at the end of the reaction (νCO: 2041
and 1957 cm-1) shows only minor modifications with respect
to that arising from the reaction between 2 and H2O.
When the reaction between 4 and H2O is carried out in THF-
1
d8, however, the H NMR spectrum of the resulting solution
shows only the two hydridic resonances at -13.4 and -13.8
ppm (Figure 4b), while the third resonance at -14.0 ppm
becomes evident only when CF3COOCs is added to the
solution: the three NMR resonances, in a ratio identical to that
in Figure 4a from the reaction between 2 and H2O, are observed
when CF3COOCs is added in equimolar amount with respect
to Ru. In a separate experiment we examined the effect of the
added strong acid CF3SO3H onto the spectrum of Figure 4b.
Under the hypothesis that the equilibria in (4) are responsible
for the three hydridic resonances, it is expected that the addition
of an acid (strong enough to protonate the trifluoroacetate ions
released in the solution) results in the accumulation of the
cationic species. Accordingly, the addition of increasing
amounts of triflic acid enhances the most downfield resonance,
as shown in Figure 4c-f. Being that the molar ratio CF3SO3H/
Ru ) 2.40, the two IR bands at 2041 and 1957 cm-1 observed
at the end of the reaction between 4 (or 2) and H2O are shifted
to higher frequencies (2047 and 1963 cm-1), as a consequence
of the CF3SO3H-promoted accumulation of the cationic species.
These findings demonstrate the intervention of CF3COO-
ligands in generating the three hydrido species from 2 and H2O,
and it is likely that the three resonances at -14.0, -13.8, and
-13.4 ppm (Figure 4a) are attributable to 3a, 3b, and 3c,
Figure 5. Projection of the cation in the structure of [RuH(CO)2(py)3)]-
[BPh4]. Thermal ellipsoids are represented at 50% probability.
respectively. All the three are cis-dicarbonyl hydrido com-
plexes; moreover, hydride chemical shifts of less than -10 ppm
exclude the presence of CO groups trans to the hydrido ligand.18
Remarkably, while the neutral 3b is the dominant species in a
neutral solution, the addition of a strong acid to the mixture of
hydrido complexes converts 3a and 3b into 3c, a conclusion
which will be reviewed again in the next section.
Finally, the nature of the hydrido complexes arising from the
nucleophilic attack of H2O onto 2 or 4 has been proven by
treating their mixture with pyridine, which nearly quantitatively
converts 3a-c into the isolable and structurally characterized
hydrido cationic complex [fac-RuH(CO)2(py)3]+,17 whose struc-
ture is shown in Figure 5 with the main bond distances and
angles in Table 3.
Dihydrogen Formation from 3a-c. As required in the
overall reaction 3, dihydrogen production from the mixture of
(18) Kaesz, H. D.; Saillant, R. B. Chem. ReV. 1972, 72, 231.

Ru3(CO)12 in Acidic Media
Inorganic Chemistry, Vol. 35, No. 25, 1996 7223
Table 3. Bond Lengths (Å) and Angles (deg) for the Cation
[RuH(CO)2(py)3]+
Ru-C(1)
1.850(7)
1.861(7)
2.149(5)
2.185(5)
2.284(4)
1.58a
1.141(8)
1.145(7)
1.343(7)
1.350(7)
1.361(9)
1.361(9)
1.363(9)
C(6P)-C(7P)
N(2)-C(12P)
N(2)-C(8P)
1.362(9)
1.334(7)
1.339(7)
1.379(9)
1.351(9)
1.379(9)
1.369(8)
1.330(8)
1.344(8)
1.387(7)
1.347(11)
1.376(11)
1.380(8)
Ru-C(2)
Ru-N(1)
Ru-N(2)
C(8P)-C(9P)
C(9P)-C(10P)
C(10P)-C(11P)
C(11P)-C(12P)
N(3)-C(13P)
N(3)-C(17P)
C(13P)-C(14P)
C(14P)-C(15P)
C(15P)-C(16P)
C(16P)-C(17P)
Ru-N(3)
Ru-H(1)
C(1)-O(1)
C(2)-O(2)
N(1)-C(3P)
N(1)-C(7P)
C(3P)-C(4P)
C(4P)-C(5P)
C(5P)-C(6P)
C(1)-Ru-C(2)
C(1)-Ru-N(1)
C(2)-Ru-N(1)
C(1)-Ru-N(2)
C(2)-Ru-N(2)
N(1)-Ru-N(2)
C(1)-Ru-N(3)
(C2)-Ru-N(3)
N(1)-Ru-N(3)
N(2)-Ru-N(3)
O(1)-C(1)-Ru
O(2)-C(2)-Ru
87.2(3) C(7P)-C(6P)-C(5P)
170.2(2) N(1)-C(7P)-C(6P)
94.2(3) C(12P)-N(2)-C(8P)
93.7(2) C(12P)-N(2)-Ru
171.0(2) C(8P)-N(2)-Ru
83.4(2) N(2)-C(8P)-C(9P)
97.5(2) C(10P)-C(9P)-C(8P)
119.3(6)
123.6(6)
117.1(5)
124.5(4)
118.5(4)
121.9(6)
120.5(6)
Figure 6. Dihydrogen evolution at 65 °C from the mixture of hydrides
3a-c ([Ru] ) 0.05 M). Plots of the H2/Ru molar ratio Vs time, with
(0) and without (() added 0.075 M CF3SO3H.
Scheme 2. Fundamental Chemistry of Ruthenium Carbonyls
in Acidic Media
95.5(2) C(9P)-C(10P)-C(11P) 118.1(6)
92.0(2) C(12P)-C(11P)-C(10P) 118.8(6)
93.3(2) N(2)-C(12P)-C(11P)
174.5(5) C(13P)-N(3)-C(17P)
175.2(6) C(13P)-N(3)-Ru
123.6(6)
117.3(5)
121.4(4)
120.6(4)
122.8(7)
C(3P)-N(1)-C(7P) 115.4(5) C(17P)-N(3)-Ru
C(3P)-N(1)-Ru
C(7P)-N(1)-Ru
123.0(4) N(3)-C(13P)-C(14P)
121.2(4) C(15P)-C(14P)-C(13P) 119.0(7)
N(1)-C(3P)-C(4P) 123.6(6) C(14P)-C(15P)-C(16P) 119.8(6)
C(5P)-C(4P)-C(3P) 119.6(6) C(15P)-C(16P)-C(17P) 118.2(8)
C(4P)-C(5P)-C(6P) 118.4(6) N(3)-C(17P)-C(16P)
122.9(6)
a The H(1) atom coordinates have been refined with constraints.
hydrides 3a-c is expected, and we investigated the required
conditions for that. Under an inert atmosphere, 0.05 M 4 was
reacted at room temperature with 8 M H2O in diglyme, till CO2
production ceased. By the increase of the temperature to 65
°C, dihydrogen evolved from the solution, and the reaction was
monitored by determining the H2/Ru molar ratio at various
stages. It can be seen from Figure 6 that its limit value is 0.5,
thus indicating the reductive elimination (eq 5), which involves
only hydrido ligands and no active hydrogen atoms from the
medium.
bridged diruthenium dihydrido complex, whose sulfinate-bridged
analog has been fully characterized.19
Conclusions. By including the findings on the origin and
stability of the hydrido intermediates into the cycle drawn in
Scheme 1, we can summarize the chemistry of ruthenium
carbonyls in acidic media20 as in Scheme 2.
The same hydrido intermediate 3b is formed in two distinct
reactions, namely the oxidative addition of the acid to Ru3(CO)12
and the nucleophilic attack by H2O onto a CO ligand in 2,
followed by CO2 elimination from the metal hydroxycarbonyl.
The role attributed to an acidic cocatalyst for WGSR is generally
the protonation of a hydrido intermediate to produce dihydro-
gen.21 On the contrary, in the present case H+ hampers
dihydrogen evolution from the mixture of hydrides 3a-c as
well as nucleophilic attack by water onto 2: the only role here
recognized for acidity is in the oxidative addition of HX to
Ru3(CO)12. On the other hand, the hitherto neglected interven-
tion of the conjugated base is critical in promoting the
disproportionation reaction of 1a, and is required for the
formation of the higher oxidation state complex 2, whose CO
ligands can undergo nucleophilic attack by water. The need
for a coordinating conjugated base which assists the dispropor-
tionation reaction renders the exceptionally strong acid CF3SO3H
65 °C, H O/diglyme8
2
2RuH(OCOCF3)(CO)2L2
-2L
3b
H2 + Ru2[µ-η2-OC(CF3)O]2(CO)4L2
(5)
1b
L ) H2O, diglyme
According to reaction 5, IR absorptions at 2043, 1989, and
1958 cm-1 after a long reaction time revealed that 1b is the
product accompanying dihydrogen formation. The intervention
of active hydrogen atoms from the medium was excluded even
in acidic solution. As mentioned before, rather than giving rise
to H2, CF3SO3H converts hydrides 3a,b into the cationic species
3c, which was found inert toward H2 formation. As a matter
of fact, we observed that at 65 °C dihydrogen production slows
down on increasing the amount of added acid (Figure 6). It
stops for [CF3SO3H]/[Ru] ) 5; a temperature of 95 °C was
then required for restoring slow H2 production.
(19) Siedle, A. R.; Newmark, R. A.; Pignolet, L. H. Inorg. Chem. 1986,
25, 1345.
(20) The conclusions of the present work are likely to apply also in the
case of H2SO4, the first employed acidic cocatalyst for the WGSR. In
fact, IR absorptions due to dinuclear Ru(I) carbonyl complexes
analogous to 1a or 1b (νCO: 2063 m, 2042 s, 2004 m, and 1959 s
cm-1) and to a Ru(II) carbonyl complex analogous to 2 (νCO: 2154
m and 2083 s cm-1) were detected during a catalytic run carried out
in diglyme under the following conditions: [Ru] ) 0.036 M, [H2O]
) 8 M, [H2SO4] ) 0.8 M, T ) 95 °C, PCO ) 0.9 atm.
On these grounds we exclude that dihydrogen formation in
the overall reaction 3 is the result of simple protonation of the
hydrido intermediate complexes. More probably, the dihydro-
gen-eliminating intermediate has the nature of a trifluoroacetato-
(21) (a) Ford, P. C.; Ungermann, C.; Landis, V.; Moya, S. A.; Rinker, R.
C.; Laine, R. M. AdV. Chem. Ser. 1979, No. 173, 81. (b) Laine, R. C.;
Crawford, E. J. J. Mol. Catal. 1988, 44, 357.

7224 Inorganic Chemistry, Vol. 35, No. 25, 1996
Fachinetti et al.
unsuitable as a cocatalyst for WGSR, contrary to H2SO4, because
of the coordinating power of SO42-. A similar role for the
disproportionation reaction was ascertained also in the acid-
cocatalyzed WGSR promoted by rhodium carbonyls in pyri-
dine.15
dissociation constant, Dr. U. Englert, Aachen University,
Aachen, Germany, for intensity data collection on a [RuH(CO)2-
(py)3][BPh4] single crystal, Mr. F. Del Cima for technical
assistence, and Chimet SpA for a gift of ruthenium.
Supporting Information Available: Three X-ray crystallographic
files, in CIF format, are available. Access information is given on
any current masthead page.
Acknowledgment. This work was supported by the Minis-
tero della Ricerca Scientifica e Tecnologica (MURST). We
thank Prof. S. Merlino and Dr. G. Fochi for helpful discussions,
Dr. G. Uccello-Barretta for helping in determining an acid
IC960630V