Promoting role of [PtI2(CO)]2 in the iridium-catalyzed methanol carbonylation to acetic acid and its interaction with involved iridium species

Article abstract of DOI:10.1021/om060282x

The catalytic activity of the iridium complexes involved in methanol carbonylation is significantly enhanced when the carbonyliodoplatinum dimer [PtI₂(CO)]₂ (10′) is added to the reaction mixture. Under CO this complex readily affords the monomeric species [PtI ₂(CO)₂] (10). The turnover frequency value, which is 1450 h^-1 for iridium alone, reaches 2400 h^-1 for a Pt/Ir = 3/7 molar ratio, under 30 bar of CO and at 190 °C. To get a deeper insight into the role of the platinum cocatalyst, model conditions (dinitrogen, ambient temperature, CH₂Cl₂, PPN⁺ as counterion) have been adopted. [PtI₂(CO)]₂ (10′ interacts with [PPN][IrI₃(CH₃)(CO)₂] (4-PPN), affording the monoiodo-bridged anionic species [IrI₂(CH₃)(CO) ₂(μ-I)-PtI₂(CO)]^- (11), which undergoes cleavage under CO to provide [IrI₂(CH₃)(CO)₃] (6) and PtI₃(CO)]^- (9). Although we have to take into account the possible iodide dissociation from 4 in the polar reaction medium (CH₃COOH, CH₃OH, CH₃I, HI, H₂O), which can be scavenged by platinum to give 9, we should not discard the intermediacy of 11, even under working catalytic conditions. The crystal structures of [PPN][IrI₃(COCH₃)(CO)₂] (8-PPN) and [PPN][PtI₃(CO)] (9-PPN), which are both involved in the overall process, were determined by X-ray diffraction analysis. A catalytic cycle is herein proposed, in which the cooperative effect between the platinum promoter and the iridium catalyst is depicted.

Full text of DOI:10.1021/om060282x

5894
Organometallics 2006, 25, 5894-5905
Promoting Role of [PtI2(CO)]2 in the Iridium-Catalyzed Methanol
Carbonylation to Acetic Acid and Its Interaction with Involved
Iridium Species
Samuel Gautron,†,‡ Nicolas Lassauque,† Carole Le Berre,† Laurent Azam,†
Roberto Giordano,† Philippe Serp,† Ga´bor Laurenczy,§ Jean Claude Daran,|
Carine Duhayon,| Daniel Thie´baut,‡ and Philippe Kalck*,†
Laboratoire de Catalyse, Chimie Fine et Polyme`res, Ecole Nationale Supe´rieure d’Inge´nieurs en Arts
Chimiques Et Technologiques (ENSIACET), 118 route de Narbonne, F-31077 Toulouse Cedex 4, France,
ACETEX CHIMIE, Acetic Acid Task Force One, AATF1, Usine de Pardies, BP 17, 64150 Mourenx,
France, Institut des Sciences et Inge´nierie Chimiques, BCH-LCOM, Ecole Polytechnique Fe´de´rale de
Lausanne, CH-1015 Lausanne, Switzerland, and Laboratoire de Chimie de Coordination du CNRS, 205
route de Narbonne, 31077 Toulouse Cedex, France
ReceiVed March 30, 2006
The catalytic activity of the iridium complexes involved in methanol carbonylation is significantly
enhanced when the carbonyliodoplatinum dimer [PtI2(CO)]2 (10′) is added to the reaction mixture. Under
CO this complex readily affords the monomeric species [PtI2(CO)2] (10). The turnover frequency value,
which is 1450 h-1 for iridium alone, reaches 2400 h-1 for a Pt/Ir ) 3/7 molar ratio, under 30 bar of CO
and at 190 °C. To get a deeper insight into the role of the platinum cocatalyst, model conditions (dinitrogen,
ambient temperature, CH2Cl2, PPN+ as counterion) have been adopted. [PtI2(CO)]2 (10′) interacts with
[PPN][IrI3(CH3)(CO)2] (4-PPN), affording the monoiodo-bridged anionic species [IrI2(CH3)(CO)2(µ-I)-
PtI2(CO)]- (11), which undergoes cleavage under CO to provide [IrI2(CH3)(CO)3] (6) and [PtI3(CO)]-
(9). Although we have to take into account the possible iodide dissociation from 4 in the polar reaction
medium (CH3COOH, CH3OH, CH3I, HI, H2O), which can be scavenged by platinum to give 9, we should
not discard the intermediacy of 11, even under working catalytic conditions. The crystal structures of
[PPN][IrI3(COCH3)(CO)2] (8-PPN) and [PPN][PtI3(CO)] (9-PPN), which are both involved in the overall
process, were determined by X-ray diffraction analysis. A catalytic cycle is herein proposed, in which
the cooperative effect between the platinum promoter and the iridium catalyst is depicted.
in this process is the high energy costs to separate water from
acetic acid by distillation;3 indeed, below a 14 wt % water
concentration, precipitation of a rhodium iodide salt occurs. At
low water concentrations, Celanese has shown that the introduc-
tion of large amounts of LiI significantly stabilizes the rhodium
catalyst.6
Iridium is also capable of catalyzing methanol carbonylation,
but, although it tolerates low water concentrations and low CO
pressures, its activity is too low in comparison to that of rhodium
to anticipate any industrial application.7 BP Chemicals discov-
ered that the addition of a ruthenium promoter enabled a viable
mixed catalytic system.8 Addition of such a compound increases
both the stability and the catalytic activity.9,10a Experiments
conducted on the Ir-Ru system showed that the main role of
[RuI2(CO)4] is to act as an iodide abstractor, facilitating con-
version of [IrI3(CH3)(CO)2]- (4) into the key species [IrI2(CH3)-
(CO)3] (6), which in turn rapidly undergoes CO insertion with
Introduction
To ensure the annual worldwide production of more than 8
million tons of acetic acid, methods other than carbonylation
of methanol are economically obsolete.1 Among the group VIII
metals that have been recognized as catalysts for this reaction,
cobalt diiodide, which was the first catalytic precursor to be
discovered and then used in a small plant in the 1960s, requires
harsh conditions of 680 bar of CO and 250 °C and is now only
of historical interest.2,3 In 1970, Monsanto developed a new low-
pressure process, based on both rhodium and an iodide promoter,
characterized by very mild conditions (30 bar, 190 °C).4
Oxidative addition of CH3I to the H[RhI2(CO)2] active species
was shown to be the rate-determining step.5 The main concern
* To whom correspondence should be addressed. E-mail:
Philippe.Kalck@ensiacet.fr.
† Ecole Nationale Supe´rieure d’Inge´nieurs en Arts Chimiques Et Tech-
nologiques (ENSIACET).
‡ ACETEX CHIMIE.
(6) Smith, B. L.; Torrence, G. P.; Aguilo, A.; Alder, S. (Hoechst Celanese
Corp.) U.S. Patent 5,001,259, 1991.
(7) Jones, J. H. Platinum Met. ReV. 2000, 44, 94.
(8) Vercauteren, C. J. E.; Clode, K. E.; Watson, D. J. Eur. Patent 616,-
997, 1994.
§ Ecole Polytechnique Fe´de´rale de Lausanne.
| Laboratoire de Chimie de Coordination du CNRS.
(1) Weissermel, K.; Arpe, H. J. In Industrial Organic Chemistry, 3rd
ed.; VCH: Weinheim, Germany, 1997.
(2) Torrence, P. In Applied Homogeneous Catalysis with Organometallic
Conpounds; Cornils B., Herrmann W. A., Eds.; Wiley-VCH: Weinheim,
Germany, 2002; p 104.
(3) Noriyuki, Y.; Kusano, S.; Yasui, M.; Pujado, P. W. Appl. Catal. 2001,
221, 253.
(4) Paulik, F. E.; Hersman, A.; Knox, W. R.; Roth, J. F. (Monsanto Co.)
U.S. Patent 3,769,329, 1973.
(5) Forster, D. AdV. Organomet. Chem. 1979, 17, 225.
(9) Whyman, R.; Wright, A. P.; Iggo, J. A.; Heaton, B. T. Dalton Trans.
2002, 771.
(10) (a) Haynes, A.; Maitlis, P. M.; Morris, G. E.; Sunley, G. J.; Adams,
H.; Badger, P. W.; Bowers, C. M.; Cook, D. B.; Elliott, P. I. P.; Ghaffar,
T.; Green, H.; Griffin, T. R.; Payne, M.; Pearson, J. M.; Taylor, M. J.;
Vickers, P. W.; Watt, R. J. J. Am. Chem. Soc. 2004, 126, 2847. (b) Maitlis,
P. M.; Haynes, H.; Sunley, G. J.; Howard, M. J. J. Chem. Soc., Dalton
Trans. 1996, 2187.
10.1021/om060282x CCC: $33.50 © 2006 American Chemical Society
Publication on Web 11/08/2006

Promising Role of [PtI2(CO)]2
Organometallics, Vol. 25, No. 25, 2006 5895
formation of the acyl complex 8.10a,b The Ru promoter can also
act as a scavenger of free HI released during catalysis.
Scheme 1. Catalytic Cycle for the Iridium-Catalyzed
Methanol Carbonylation to Acetic Acid
During our studies of the promoting effect of the platinum
dimer [PtI2(CO)]2 on the iridium-catalyzed methanol carbonyl-
ation at low water concentrations,11a,b which showed catalytic
efficiency close to that of ruthenium, we gained spectroscopic
and FAB-MS evidence of the formation of a heterobimetallic
monoiodo-bridged [Ir-Pt] species having structural features
similar to those detected and characterized by Whyman et al.9
Results and Discussion
In most literature reports, the catalytically active iridium
species is considered to be H[IrI2(CO)2] (1-H).12 We have
directly generated it in situ by heating in an autoclave an acetic
acid/water solution containing a suspension of an iridium iodide
salt (a mixture of IrI3 and IrI4), under 6 bar of CO at 190 °C
for 25 min. After this preformation treatment, the carbonylation
of methanol/methyl iodide mixtures to acetic acid was performed
under 30 bar of CO under the very conditions used in the
industrial Monsanto process, except for a 6 wt % water
concentration. This iridium system gives only modest car-
bonylation rates, since the maximum turnover frequency
observed is 1450 h-1. Under the same catalytic conditions, the
addition of the dimer [PtI2(CO)]2 (10′) significantly enhances
the catalytic activity. The TOFs calculated exclusively on the
basis of the iridium concentrations in the medium reach 2400
h-1. The highest activity was obtained for a Pt/Ir molar ratio of
3/7 and a water concentration between 5 and 6 wt %.11a These
results approach those obtained with the iridium-ruthenium
system used in the Cativa process, which is now being
implemented in industrial plants.7
We have also monitored the formation of the hydride complex
by HP-NMR under the same preformation conditions, at 90 °C.
In the 1H NMR spectrum (Figure 1), a hydride signal is observed
at δH -11.6 ppm, very close to the -11.7 ppm value already
reported for 2-PPN, thus confirming the presence of 2-H in
the medium.14
By separate experiments we have demonstrated that the
carbonyliodoplatinum dimer alone presents no catalytic activ-
ity: in the same way as ruthenium, it plays the role of cocatalyst.
We performed other series of experiments under conditions
as close as possible to those of catalysis, so as to obtain valuable
information about the long-lived complexes involved in the
catalytic cycle. For this purpose we avoided the use of stabilizing
counterions, such as PPN+ and AsPh4+, and/or the use of
deuterated organic solvents. Indeed, HP-NMR experiments were
performed in acetic acid/water (90/10) solutions under 30 bar
of CO and at 90 °C, with the IrI3/IrI4 salt. This salt reacts within
30 min to provide almost exclusively 2-H (characterized by δH
-11.5 ppm and δC 156.0 ppm). In addition, two weak 13C NMR
signals were detected at 163.4 and 151.3 ppm (Figure 2) and
assigned to the presence of cis- and trans-[H][IrI4(CO)2] (3-
H). We also observed an intense signal at 125.0 ppm, due to
the presence of significant amounts of dissolved CO2, which
points to the fact that iridium catalyzes the WGSR in the absence
of iodomethane. Moreover, and unexpectedly, complex 1-H is
not observed as the resting state in the preformation process.
Presumably, as the medium contains some amounts of HI,
released through the reduction of IrI3/IrI4 by CO, the oxidative
addition of HI to 1-H occurs so quickly that 2-H becomes the
resting state in the WGSR.
1. Mechanistic Studies of the Preformation of Iridium
Active Species. It is largely admitted in the literature13 that two
anionic catalytic cycles are interconnected for iridium (Scheme
1), one for the carbonylation of methanol and the other for the
WGSR (water-gas shift reaction), which constitutes an undesir-
able side process. These two cycles are linked by the active
species H[IrI2(CO)2] (1-H). We have followed by high-pressure
IR (CIR) and high-pressure NMR the in situ preformation of
complex 1-H. The commercial salt IrI3/IrI4 was reacted in a
20/1 chlorobenzene/water mixture (w/w) at 130 °C and under
5 bar of CO. Infrared spectra show the progressive appearance
of four bands at 2163 w, 2112 vs, 2064 vs, and 1982 m cm-1
,
which we can assign to the presence of both H[Ir(H)I3(CO)2]
(2-H: νIrH 2163 cm-1; νCO 2112, 2064 cm-1) and 1-H (νCO
2064, 1982 cm-1) by comparison with the spectra of [PPN]-
[Ir(H)I3(CO)2] (2-PPN) and [PPN][IrI2(CO)2] (1-PPN), respec-
tively, which were also fully characterized by X-ray diffrac-
tometry.14
The νIrH and νCO bands of 2-PPN and 1-PPN slightly differ
from those observed for 2-H and 1-H, respectively (Table 1).
2. Behavior of 1-PPN and 1-H under Carbonylation
Conditions. 2.1. Schlenk Experiments on 1-PPN Reactivity.
We have reported previously14 that 1-PPN reacts preferentially
with HI to give 2-PPN, even in the presence of a 40-fold excess
of CH3I, so that the shift from WGSR to methanol carbonylation
occurs only at a slow rate. The oxidative addition of CH3I to 1
proceeds reversibly at elevated temperature,12 producing the
anionic methyliridium species 4. In a previous study we had
isolated the complex 4-PPN, the X-ray crystal structure of which
is consistent with that of a fac,cis isomer.14 The rate-determining
(11) (a) Le Berre, C.; Serp, P.; Kalck, P.; Layeillon, L.; Thiebaut, D.
(Acetex Chimie) Fr. Patent 9,813,954, 1998. (b) Gautron, S.; Lassauque,
N.; Le Berre, C.; Serp, P.; Azam, L.; Giordano, R.; Laurenczy, G.; Thie´baut,
D.; Kalck P. Eur. J. Inorg. Chem. 2006, 6, 1121.
(12) (a) Forster, D. J. Chem. Soc., Dalton Trans. 1979, 1639. (b) Vickers,
P. W.; Pearson, J. M.; Ghaffar, T.; Adams, H.; Haynes, A. J. J. Phys. Org.
Chem. 2004, 17, 1007.
(13) Forster, D.; Singleton, T. C. J. Mol. Catal. 1982, 299.
(14) Gautron, S.; Giordano, R.; Le Berre, C.; Jaud, J.; Daran, J.-C.; Serp,
P.; Kalck, P. Inorg. Chem. 2003, 42, 5523.

5896 Organometallics, Vol. 25, No. 25, 2006
Gautron et al.
1
Table 1. 13C and H NMR Data and FAB/MS Values for the Ir and Pt Complexes Studied
MS-FAB
(m/z)
Ir complex
13C NMR (ppm)
169.9 (s, CO)
1H NMR (ppm)
IR (νCO, cm-1
2046 (vs), 1967 (s)
2157 (w, νIrH
)
[PPN][IrI2(CO)2] (1-PPN)
[PPN][IrHI3(CO)2] (2-PPN)
503
631
155.0 (s, CO)
-11.65 (s, Ir-H)
)
2103 (s), 2052 (vs)
2112 (s), 2068 (s)
2100 (s), 2048 (s)
[PPN][IrI4(CO)2] (3-PPN)
[PPN][IrI3(CH3)(CO)2] (4-PPN)
149.7 (s, CO)
156.0 (s, CO); -16.6
(q, JC-H ) 141 Hz, CH3)
157.1 (s, CO); -15.2
(q, JC-H ) 141 Hz, CH3)
152.5, 150.4, 150.1 (s, CO);
2.15 (s, CH3)
646
H[IrI3(CH3)(CO)2] (4-H)
[IrI2(CH3)(CO)2]2 (5′)
1.90, 1.85 (s, CH3)
2120 (s), 2074 (s)
-5.3, -8.76 (q, JC-H
140 Hz, CH3)
)
[IrI2(CH3)(CO)3] (6)
146.9 (s); -22.3 (q, JC-H
)
2.08 (s, CH3)
3.13 (s, CH3)
2156 (s), 2116 (s),
2096 (s)
2111 (s), 2061 (s),
1679 (m), 1660 (m)
140 Hz)
cis-[PPN][IrI3(COCH3)(CO)2]
(8-PPN)a
196.2 (s, COCH3);
151.4 (s, Ir-CO); 49.5
(s, CH3CO)
trans-[PPN][IrI3(COCH3)(CO)2]
(8-PPN)
201.5, (s, COCH3);
162.7 (s, Ir-CO);
52.2 (s, CH3CO)
203.4, (s, COCH3);
161.5 (s, Ir-CO);
50.6 (s, CH3CO)
2.76 (s, CH3)
3.04 (s, CH3)
2114 (w), 2070 (vs),
1655 (s)
trans-H[IrI3(COCH3)(CO)2] (8-H)
2176 (w), 2115 (s),
1708 (m)
195Pt and 1H NMR
MS-FAB
(m/z)
other complexes
13C NMR (ppm)
(ppm)
IR (νCO, cm-1
)
H[PtI3(CO)] (9-H)
156.8 (s, CO, JC-Pt ) 1649 Hz)
195Pt: -5450
2068 (vs)
(JC-H ) 1649 Hz)
[PPN][PtI3(CO)] (9-PPN)
[PtI2(CO)]2 (10')
152.8 (s, CO, JC-Pt ) 1759 Hz)
154.5 (JC-Pt ) 1843 Hz)
166.0 (JC-Pt ) 1466 Hz)
195Pt: -5460
2075 (vs)
2111 (vs)
2127 (vs)
603
(JC-Pt ) 1759 Hz)
195Pt: -5328
(JC-Pt) 1843 Hz)
[PtI2(CO)2] (10)
195Pt: -5790
(JC-Pt ) 1466 Hz)
1H: 2.28 (s, CH3)
[PPN][Ir2I5(CH3)2(CO)4] (13-PPN)
154.68 (s, CO); -14.83 (q, CH3);
JH-C ) 141 Hz
2117 (s), 2061 (s)
2107 (s), 2050 (s)
1161
1121
[PPN][IrI(CH3)(CO)2(µ-I)2PtI2(CO)]
(11-PPN)
155.4 (s, CO-Ir); 154.91 (s, CO-Pt,
JPt-C) 1650 Hz); -14.09 (q, CH3,
JH-C) 141 Hz); -14.18
1H: 2.36 (s, CH3)
195Pt: -5462
(JPt-C ) 1650 Hz)
(q, CH3, JH-C ) 141 Hz)
a See ref 16.
ized and gives, under CO, the tricarbonyl complex [IrI2(CH3)-
(CO)3] (6) (Scheme 1).14,16 These authors, as Forster12 did
previously, have proposed that migratory CO insertion in 6
occurs readily under CO to give the neutral acyl species [IrI2-
(COCH3)(CO)3] (7). In a medium from which iodide ions had
notbeenremoved,thestableanioniccomplex[IrI3(COCH3)(CO)2]-
was isolated as the [AsPh4]+ salt 8-AsPh4 and characterized as
the fac,cis isomer.10a Theoretical studies show that the latter
species is formed through kinetic control, while the trans isomer
is the thermodynamic product.17
2.2. Stoichiometric Carbonylation of 4-PPN. By using a
water/methanol mixture, we reacted [PPN][IrI3(CH3)(CO)2] (4-
PPN) under 5 bar of CO and succeeded in obtaining and
crystallizing the trans-8-PPN isomer. Its structure was deter-
mined by X-ray diffraction (Figure 3). The crystal structure of
complex 8 with AsPh4+ as counterion was recently reported by
Volpe et al.18
In the salt [PPN][IrI3(COCH3)(CO)2] (8-PPN) the anion
adopts a trans geometry for the two CO ligands. The trans
influence effect of the acetyl group is shown by the increased
Figure 1. 1H HP-NMR spectrum of complex 2-H under preforma-
tion conditions (30 bar, 90 °C).
step in the iridium catalytic cycle is migratory CO insertion,15
and the preliminary formation of the neutral pentacoordinated
intermediate [IrI2(CH3)(CO)2] (5) is needed to account for that.
Haynes et al. have demonstrated that iodide abstraction from 4
to afford 5 is favored by addition of methanol or a Lewis acid,
such as InI3.16 Under dinitrogen, dimerization of 5 occurs and
provides [Ir2(µ-I)2I2(CH3)2(CO)4] (5′), which has been character-
(16) Ghaffar, T.; Adams, H.; Maitlis, P. M.; Sunley, G. J.; Baker, M. J.;
Haynes, A. Chem. Commun. 1998, 1023.
(17) (a) Kinnunen, T.; Laasonen, K. J. Organomet. Chem. 2001, 628,
222. (b) Kinnunen, T.; Laasonen, K. J. Mol. Struct. 2001, 542, 273.
(18) Volpe, M.; Wu, G.; Iretskii, A.; Ford, P. C. Inorg. Chem. 2006, 45,
1861.
(15) Pearson, J. M.; Haynes, H.; Morris, G. E.; Sunley, G. J.; Maitlis, P.
M. J. Chem. Soc., Chem. Commun. 1995, 1045.

Promising Role of [PtI2(CO)]2
Organometallics, Vol. 25, No. 25, 2006 5897
Figure 2. 13C HP-NMR spectrum of a solution from preformation treatment (30 bar, 90 °C).
bond length of Ir(1)-I(2) ) 2.8147(8) Å by comparison with
the two other Ir-I bonds (ca. 2.70 Å). In addition, the C(4)
carbon atom and the O(3) oxygen atom are approximately in
the same plane as the Ir(1) and I(2) atoms and the two CO
ligands. Most of the distances are in the same range as those
for the fac,cis isomer,10a except for those in the acetyl ligand,
in which the Ir-CO bond is longer for the cis isomer than for
the trans one (2.058(12) Å). Indeed, all the other distances and
angles shown by the present X-ray crystal structure fit well those
observed for the cis isomer and are very close to those calculated
by Kinnunen and Laasonen.17 The compound trans-8-PPN was
at 3.60 ppm is due to traces of methanol presumably present in
the crystal lattice, even after treatment in vacuo of the relevant
8-PPN salts. Methanol would cause solvolysis of one iodide
ligand followed by readdition of that very ligand, after a
rearrangement process has occurred, thus giving the thermo-
dynamic isomer. Moreover, worthy of note is that significant
quantities of complex 4-PPN (δ 2.18 ppm) are still seen in
Figure 4a, which would also show that fac,cis-8-PPN is formed
through kinetic control.
2.3. 13C HP-NMR Experiments on the Catalytic Behavior
of 1-H. We performed 13C HP-NMR experiments under CO at
high temperature, in the absence of any stabilizing counterion.
The medium was the same as that used for our previous
carbonylation batch experiments.11
1
also characterized by IR and 13C and H NMR spectroscopy
(Table 1).
By reacting [PPN][IrI3(CH3)(CO)2] (4-PPN) with CO (5 bar,
1h, 25 °C) in a CH2Cl2/CH3OH mixture, we produced mainly
fac,cis-8-PPN instead (Figure 4a). Then we studied the effect
of methanol concentration on the cis/trans ratio in this reaction
and observed that the increase in the polarity and in the protic
nature of the solvent plays a prominent role on this ratio. Indeed,
we have seen by 1H NMR, on the products isolated after
reaction, that the addition of increasing quantities of methanol
results in the production of higher amounts of the mer,trans-
8-PPN isomer (signal at δ 2.77 ppm; see Figure 4). The signal
13C HP-NMR spectra reveal several carbonyl signals (Figure
5). First, the hydride complex 2-H, which arises from WGSR,
is still present, but the low intensity of its carbonyl signal at δC
156.4, as well as that of the signals due to carbon dioxide and
3-H, all point to a small WGSR contribution. We can observe
a rather intense signal at δC 157.1 ppm that, combined with the
presence of a quartet at -15.2 ppm, indicates the presence of
the methyl complex 4-H. During a 4 h reaction we observed
the progressive appearance of new signals at δC 203.4 (not

5898 Organometallics, Vol. 25, No. 25, 2006
Gautron et al.
Figure 3. Ortep diagram of [PPN][IrI3(COCH3)(CO)2] (mer,trans-
8-PPN). The PPN+ counterion is omitted for clarity purposes.
Ellipsoids are at the 50% probability level. Selected bond lengths
(Å): Ir(1)-I(1) ) 2.6849(8), Ir(2)-I(2) ) 2.8147(8), Ir(1)-I(3)
) 2.6984(9), Ir(1)-C(1) ) 1.929(11), Ir(1)-C(2) ) 1.915(13),
Ir(1)-C(3) ) 2.058(12), C(1)-O(1) ) 1.116(13), C(2)-O(2) )
1.104(14), C(3)-O(3) ) 1.183(14), C(3)-C(4) ) 1.487(18).
Selected bond angles (deg): I(1)-Ir(1)-I(2) ) 91.85(3), I(1)-
Ir(1)-I(3) ) 174.65(3), I(2)-Ir(1)-I(3) ) 93.07(3), I(1)-Ir(1)-
C(1) ) 89.8(3), I(2)-Ir(1)-C(1) ) 89.8(3), I(3)-Ir(1)-C(1) )
88.1(3), I(1)-Ir(1)-C(2) ) 91.6(4), I(2)-Ir(1)-C(2) ) 86.1(3),
I(3)-Ir(1)-C(2) ) 90.8(4), C(1)-Ir(1)-C(2) ) 175.7(5), I(1)-
Ir(1)-C(3) ) 87.4(3), I(2)-Ir(1)-C(3) ) 178.3(3), I(3)-Ir(1)-
C(3) ) 87.7(3), C(1)-Ir(1)-C(3) ) 88.7(5), C(2)-Ir(1)-C(3) )
95.5(5), Ir(1)-C(1)-O(1) ) 177.8(11), Ir(1)-C(2)-O(2) )
175.4(12), Ir(1)-C(3)-C(4) ) 117.9(9), Ir(1)-C(3)-O(3) )
119.9(9), C(4)-C(3)-O(3) ) 122.0(12).
Figure 4. 1H NMR spectra showing the variation in the amounts
of the cis/trans acyl species resulting from three separate carbonyl-
ation experiments on 4-PPN, performed at different CH2Cl2/CH3OH
ratios: (a) CH2Cl2/CH3OH 35 mL/5 mL; (b) CH2Cl2/CH3OH 20
mL/20 mL; (c) CH2Cl2/CH3OH 5 mL/35 mL.
shown), 161.7, and 50.6 ppm (Figure 5), which correspond to
the anionic acyl species trans-8-H. This observation confirms
that the slowest step in the iridium-catalyzed methanol car-
bonylation is CO migratory insertion, affording 8-H.
compound the anion presents a distorted-square-planar geometry
(Figure 7), with a very small trans influence of the carbonyl
ligand.19
3. Platinum Cocatalyst Activity. 3.1. Characterization and
Role of the Species Formed under Dinitrogen at Ambient
Temperature. We studied the promoting effect of [PtI2(CO)]2
by employing a model system based on the use of PPN+ salts
of the relevant Ir anions and by running experiments under
dinitrogen at ambient temperature, with CH2Cl2 as solvent.
Addition of [PtI2(CO)]2 (10′) during the catalytic runs dramati-
cally enhances the reaction rate. We have checked the activity
of the compound itself and observed that it does not catalyze
methanol carbonylation. Hence, the increased activity can be
attributed to the direct involvement of the carbonyliodoplatinum
dimer in the CO migratory insertion step.
13C-195Pt
The second peak at -5462 ppm (d, J
) 1650 Hz)
can be assigned to the heterobimetallic compound [PPN]-
[IrI2(CH3)(CO)2(µ-I)PtI2(CO)] (11-PPN), in which the anion has
a structure with one iodide bridge. A diiodo-bridged structure
could also be hypothesized, involving a five-coordinate platinum
center, but as Pt(II) preferentially adopts a square-planar
geometry, the former isomeric form would be the preferred one.
The subsequent cleavage by CO of this anionic species would
accelerate the slowest step in the iridium catalytic cycle,
providing the iridium neutral species 6, within which methyl
cis migration is favored under CO (Scheme 2). Indeed, 11-PPN
is detected at room temperature in CH2Cl2 solution upon
instantaneous reaction of the promoter with the 4-PPN salt.
Although the major role played by the promoter in abstracting
an iodide ligand from 4-PPN via the intermediate formation of
11-PPN is evident under model conditions, another important
aspect of its behavior under operating catalytic conditions should
not be disregarded: [PtI2(CO)]2 could also act as scavenger of
the I- ions released by Ir-I bond rupture at elevated temperature
in polar/coordinating solvents, thus moderating10a their concen-
In order to elucidate its role as promoter, addition of labeled
[PtI2(13CO)]2 (10′) to a dichloromethane solution of the labeled
salt [PPN][IrI3(CH3)(13CO)2] (4-PPN) (Pt/Ir ) 0.3/1) was
conducted under dinitrogen. The room-temperature reaction is
instantaneous, and the 195Pt NMR spectra reveal two signals at
13C-195Pt
-5460 and -5462 ppm. The signal at -5460 ppm (d, J
) 1759 Hz) corresponds to the salt [PPN][PtI3(CO)] (9-PPN)
(Figure 6), which we have characterized independently by X-ray
diffraction.
By a separate synthesis, suitable crystals of 9-PPN were
obtained by reacting the dimeric species [PtI2(CO)]2 with HI,
followed by addition of [PPN]Cl under dinitrogen. In this
(19) Hartley, F. R. In ComprehensiVe Organometallic Chemistry; Wilkin-
son, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K.,
1982; p 490.

Promising Role of [PtI2(CO)]2
Organometallics, Vol. 25, No. 25, 2006 5899
Figure 7. Ortep diagram of [PPN][PtI3(CO)] (9-PPN). Ellipsoids
are at the 50% probability level. Selected bond lengths (Å): Pt(1)-
C(1) ) 1.822(8), Pt(1)-I(1) ) 2.6068(4), Pt(1)-I(2) ) 2.6110(4),
Pt(1)-I(3) ) 2.6127(5), C(1)-O(1) ) 1.135(7). Selected bond
angles (deg): C(1)-Pt(1)-I(1) ) 87.54(18), C(1)-Pt(1)-I(2) )
179.33(18), C(1)-Pt(1)-I(3) ) 88.57, I(1)-Pt(1)-I(2) ) 92.402(15),
I(1)-Pt(1)-I(3) ) 176.017, I(2)-Pt(1)-I(3) ) 91.494(16), O(1)-
C(1)-Pt(1) ) 178.6(6).
Figure 5. 13C HP-NMR spectra of solutions from batch experi-
ments on the Ir-catalyzed methanol carbonylation.
Scheme 2. Schematic Pathway Showing the Reaction of 10′
with 4
(CH3)2(CO)4] (5′), which is likely to form from 12 in weakly
coordinating solvents.
The two signals at 1.90 and 1.85 ppm increase simultaneously
at high Pt/Ir molar ratios (1/1.8), pointing to the formation of
the two isomers of the neutral homobimetallic dimer 5′.14 As
for the two signals at 2.36 and 2.28 ppm, we observed that their
relative intensities varied with the Pt/Ir molar ratio. Hence, we
Figure 6. Platinum species identification by 195Pt NMR spectros-
copy.
tration in solution to aid the displacement of iodide by CO in
[IrI3(CH3)(CO)2]-, with generation of the neutral species [IrI2-
(CH3)(CO)3].
1
recorded for every each Pt/Ir value the H NMR spectrum in
tandem with its FAB/MS spectrum. As shown in Figure 9, two
anionic complexes were detected at m/z 1121 and 1161,
respectively. For a relatively high platinum to iridium ratio of
1/2.65, we observed that the signal at 2.36 ppm in the 1H NMR
spectrum increases simultaneously with the peak at m/z 1121
in the FAB/MS, pointing to the presence of the compound 11-
PPN. For a lower Pt/Ir ratio of 1/4.75 the signal at m/z 1121
almost completely disappears from FAB/MS, as well as the 1H
NMR signal at 2.36 ppm, so that the two signals at 2.28 ppm
and m/z 1161 can be unambiguously attributed to 13-PPN. It
turns out that this monoiodo-bridged anionic diiridium species
and the dimer proposed as a possible intermediate in the Ir-
Ru system9 are one and the same.
1H NMR spectra of the aforementioned reaction solution
showed the formation of the dimer [Ir2(µ-I)2I2(CH3)2(CO)4] (5′),
of the salt [PPN][IrI2(CH3)(CO)2(µ-I)PtI2(CO)] (11-PPN), of
the complex [IrI2(CH3)(CO)2(solv)] (12), and of [PPN][Ir2I4(µ-
I)(CH3)2(CO)4] (13-PPN). To assign all of the relevant signals,
we studied the changes in their relative intensities by varying
the concentrations of 10′ and 4-PPN: signals at 2.36, 2.28, 2.14,
2.09, 1.90, and 1.85 ppm were observed (Figure 8). The signal
at 2.14 ppm corresponds to unreacted 4-PPN and presents a
significant intensity even at low Pt/Ir molar ratios. The signal
at 2.09 ppm could be attributed to the pentacoordinated, or
hexacoordinated solvated, neutral species [IrI2(CH3)(CO)2(solv)]
(12), “solv” being presumably either a CD2Cl2 molecule, since
Ir-CH2Cl2 complexes are known,20 or H2O present as traces
in the solvent. Such attribution can indeed be made in view of
the concomitant presence (see below) of the dimer [Ir2I2(µ-I)2-
1
We also recorded H and 13C NMR spectra of the same
reaction mixtures in order to assign the 13C signals (Table 1).
Figure 10 shows two examples relevant to two different Pt/Ir
molar ratios (1/2.65 and 1/4.75, respectively). We compared
the variations in the 1H NMR signals to those in the 13C signals.
Thus, we could note that the intensity of the peak at 2.36 ppm,
attributed to the compound 11-PPN, varies in the same way as
(20) Crabtree, R. H. In The Organometallic Chemistry of the Transition
Metals; 3rd ed.; Wiley-Interscience: New York, 2001; p 109.

5900 Organometallics, Vol. 25, No. 25, 2006
Gautron et al.
Figure 8. 1 H NMR studies showing the influence of the Pt/Ir ratio on the nature of the species observed in the reaction of 10′ with 4-PPN.
that of the two CO peaks at 155.41 and 154.94 ppm. Owing to
the presence of the two 195Pt satellites (not shown in Figure 10
for clarity purposes), we assigned the signal at 154.94 ppm to
the CO ligand bound to the platinum center; thus, the signal at
155.41 ppm was attributed to the two CO ligands coordinated
to iridium. Similarly, the signal at 155.56 ppm, present only at
lower Pt/Ir molar ratios, is assigned to unreacted 4-PPN, and
By 13C NMR spectroscopy we compared the intensity of the
acetic acid and iodomethane signals and, in particular, their
ratios. We could reasonably make such a comparison, since the
iodomethane formed during the carbonylation is not labeled,
so that the signal observed does actually decrease only when
labeled iodomethane (i.e., the reactant) is consumed. We
observed, for the same reaction times (20 min), that the Ir-Pt
system leads to the consumption of larger amounts of 13CH3I
than does the Ir system (Figure 11). We also noted the formation
of 13CO2 (125.0 ppm) and 13CH4 (-4.2 ppm, quintet) as
byproducts (Figure 12). As for the formation of iridium or
platinum species, we detected 4-H (Figure 12), identified as
the major product, together with 8-H and 9-H, the presence of
the last compound being confirmed by 195Pt NMR. We also
observed that under 30 bar of CO the monomer [PtI2(CO)2] (10),
which is the stable carbonyliodoplatinum species formed by
[PtI2(CO)]2 under carbon monoxide, is regenerated from H[PtI3-
(CO)] in the presence of a HI scavenger (molecular sieves).
1
the 13C NMR signal at 154.69 ppm, related to the H NMR
signal at 2.28 ppm, can be associated with the dimer 13-PPN.
From the 13C NMR spectrum in Figure 10b the presence of
9-PPN (152.75 ppm) is evident, as well as that of 5′ (152.14,
150.00, 149.68 ppm).
Hence, from the identification of the various species produced
by reaction of 10′ with 4 we can propose the mechanistic
pathway depicted in Scheme 3. The anionic monoiodo-bridged
[Ir-Pt] heterobimetallic species 11 is possibly an intermediate
through which the platinum promoter exerts its role as iodide
abstractor and accelerating agent.
1
3.2. H HP-NMR Experiments on the Reaction between
Thus, it appears that the role of the platinum promoter is to
abstract iodide from the methyliridium complex 4-H via a
monoiodo-bridged species and/or to scavenge iodide ions
coming from rupture of Ir-I bonds under more drastic condi-
tions. Under CO such a Ir-Pt dimer undergoes rapid cleavage
to give the neutral methyltricarbonyliridium complex [IrI2(CH3)-
(CO)3] (6). Then migratory CO insertion occurs within this
active intermediate to produce the neutral coordinatively
unsaturated species [IrI2(COCH3)(CO)2] (7), from which
10′ and the Ir Species Formed by Carbonylation of 1-H. We
were also interested in elucidating the reactivity under CO of
H[IrI2(CO)2] (1-H) in the presence of the Pt cocatalyst to
compare the HP-NMR results to those obtained using 1-H alone.
A sapphire tube was charged with IrI3/IrI4 and [PtI2(CO)]2
(Pt/Ir ) 1/4) in CH3COOH (64 wt %), CH3COOCH3 (20 wt
%), H2O (6 wt %), and labeled 13CH3I (10 wt %) and then
pressurized under 30 bar of 12CO/13CO and heated to 86 °C.

Promising Role of [PtI2(CO)]2
Organometallics, Vol. 25, No. 25, 2006 5901
1
Figure 9. Correlations between FAB-MS and H NMR spectra for the reaction of 10′ with 4-PPN: at Pt/Ir ) 1/4.75 (a) and at Pt/Ir )
1/2.65 (b). Comparisons with calculated mass spectra are shown to the right.
[IrI3(COCH3)(CO)2]- (8) is formed by subsequent coordination
of an iodide ion. On the basis of the evidence found by
employing a model system, we tentatively propose the catalytic
cycle shown in Scheme 4, which also highlights another possible
pathway involving the mononuclear unsaturated species 5.
In Scheme 4 the interconnected platinum cycle is also depic-
ted. Compound 9-H, which has been observed by IR and NMR,
is directly formed by cleavage of 11-H, slowly regenerating 10
by substitution of CO for iodide. The species detected by HP-
NMR are shown in boldface characters in the catalytic cycle.
We have included the water-gas shift reaction, which involves
the protonated species 1-H, 2-H, and 3-H. With regard to the
amounts of methane found, it may arise from the reaction of
CH3I with 2-H, as shown in the cycle, but also from the reaction
between 4-H and HI.
have obtained; however, the possible intervention of mono-
nuclear species and iodide transfer from Ir to Pt by a stepwise
dissociation/coordination mechanism would provide an alterna-
tive pathway for the promoting effect of carbonyliodoplatinum
species under operating conditions.
Experimental Section
1. Materials. All reactions and manipulations of Ir and Pt
complexes were performed under an argon or dinitrogen atmo-
sphere. Dichloromethane was distilled using CaH2. Other reagents
were used as supplied: the salt IrI3/IrI4, denoted IrI3,4 (Johnson-
Matthey), platinum(II) iodide, bis(triphenylphosphoranylidene)
chloride ([PPN]Cl), 13C-labeled methyl iodide, and triphenylphos-
phine (Aldrich), acetyl chloride, methyl iodide, and indium triiodide
(Acros), acetone, acetic acid, chlorobenzene, chloroform, dichloro-
methane, dimethylformamide, n-hexane, n-heptane, methanol, n-
pentane, and toluene (Scharlau), chloroform-d3, dichloromethane-
d2, methanol-d4, and toluene-d8 (Eurisotop), argon, dinitrogen,
carbon monoxide, and 13C-labeled carbon monoxide (Air Liquide),
and hydriodic acid (Merck). Labeling experiments were performed
by stirring the relevant dissolved complex under a 13CO atmosphere
for a few hours.
2. Instrumentation. IR spectra were recorded on a Perkin-Elmer
1710 Fourier Transform spectrophotometer using either a solution
cell with CaF2 windows or CsI salt for solid pellet analysis.
1H, 13C, and 195Pt NMR spectra were recorded on a Bruker AC250
or on a AMX400 spectrometer. Mass spectra were recorded
by the negative FAB method on a NERMAG R10-10 mass
spectrometer.
Conclusion
In this study we have shown that [PtI2(CO)]2 exerts a
promoting effect on the catalytic activity of the Ir-based
methanol carbonylation to acetic acid. The role of the promoter
is to abstract an iodide ligand by reaction with the anionic resting
state [IrI3(CH3)(CO)2]- and/or to scavenge iodide ions released
in solution. Under model conditions, a heterobimetallic complex,
which could be considered as an intermediate, has been detected
and characterized by coupled NMR and FAB/MS; then, under
CO, this anionic monoiodo-bridged [Ir-Pt] species undergoes
cleavage to [PtI3(CO)]- and [IrI2(CH3)(CO)3], the latter produc-
ing an acyl species and then acetyl iodide, which is in turn
hydrolyzed to acetic acid.
X-ray crystallographic data for the compounds 8-PPN and 9-PPN
were collected on an Oxford-Diffraction Xcalibur diffractometer.
Final unit cell parameters were obtained by the least-squares
In summary, we propose the intermediacy of [IrI2(CH3)(CO)2-
(µ-I)PtI2(CO)]- on the basis of all the experimental data we

5902 Organometallics, Vol. 25, No. 25, 2006
Gautron et al.
1
Figure 10. Correlations between H and 13C spectra for the reaction of 10′ with 4-PPN: (a) Pt/Ir ) 1/4.75; (b) Pt/Ir ) 1/2.65.
Scheme 3. Iodide Abstraction Pathway
refinement of a large number of selected reflections. Structures were
solved by direct methods (SIR97)21 and refined by least-squares
procedures either on F2 using SHELXL-9722 for 9-PPN or on F
using CRYSTALS23 for 8-PPN. In all of the compounds, all H
atoms were introduced at calculated positions as riding atoms
(d(CH) ) 0.99-0.98 Å) with a displacement parameter equal to
1.2 (C6H5) or 1.5 (CH3) times that of the parent atom.
Calculations were carried out with the SHELXL-97 program
using the integrated system WINGX (version 1.63)24 or the
CRYSTALS package. Molecular views were obtained with the help
of ORTEPIII25 or CAMERON.26 Fractional atomic coordinates,
anisotropic thermal parameters for non-hydrogen atoms, and atomic
coordinates for H atoms have been deposited with the Cambridge
Crystallographic Data Center. Copies of the data can be obtained
free of charge on application to the Director, CCDC, 12 Union
Road, Cambridge CB2 IE2, U.K.
(21) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C., Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. SIR97-a program for automatic solution of crystal structures by direct
methods. J. Appl. Crystallogr. 1999, 32, 115.
(22) Sheldrick, G. M. SHELXL97: Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(23) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.
(24) Farrugia, L. J. WinGX. J. Appl. Crystallogr. 1999, 32, 837.
(25) Farrugia, L. J. ORTEP-3 for Windows, J. Appl. Crystallogr. 1997,
30, 565.
(26) Watkin, D. J.; Prout, C. K.; Pearce, L. J. CAMERON; Chemical
Crystallography Laboratory, Oxford, U.K., 1996.

Promising Role of [PtI2(CO)]2
Organometallics, Vol. 25, No. 25, 2006 5903
Figure 11. Comparison of the CH3COOH/CH3I ratio between the Ir-Pt system (left) and that of Ir alone (right).
the IR beam onto the rod placed across a Hastelloy B2 (Top
Industrie) batch 100 mL autoclave and to refocus the IR beam onto
the detector. Spectra were recorded on a Perkin-Elmer GXII
spectrophotometer. The reactor can be pressurized up to 50 bar
with CO and heated up to 200 °C. A solution can be added into
the reactor under pressure using a liquid feed line.
5. High-Pressure NMR Analyses. Batch carbonylation experi-
ments were monitored in situ by high-pressure NMR spectroscopy
using sapphire tubes (10 mm e.d.), pressure rated to 100 bar, fitted
with a titanium valve. Reaction mixtures can be heated up to 100
°C.
All high-pressure NMR experiments were performed on a Bruker
DRX400 spectrometer. The NMR tube was charged with IrI3,4
,
[PtI2(CO)]2, and the reaction mixture. Once the tube was sealed,
the medium was flushed several times with 12CO and then
pressurized to 10 bar with 13CO. The pressure was then adjusted
to 30 bar with 12CO.
6. Synthesis of Iridium Compounds. 6.1. [PPN][IrI2(CO)2]
(1-PPN). This compound was prepared from IrI3,4 (2 g, 3.21 mmol)
in a mixture of DMF (150 mL) and water (1.5 mL). The solution
was stirred under a gentle CO bubbling at 160 °C for 3 h. The
initially dark red solution turned yellow due to the presence of
[NH2Me2][IrI2(CO)2]. [PPN]Cl (1.84 g, 3.21 mmol) was then added,
and the solution was cooled to room temperature. Cold water (750
mL, 1-3 °C) was then slowly added in order to precipitate
[PPN][IrI2(CO)2] (1-PPN). The yellow powder was filtered and
washed three times with 50 mL of cold water. This product was
dried under vacuum and crystallized at -18 °C in a bilayered
mixture of CH2Cl2 and n-hexane (1/1). After a few hours yellow
needle-shaped crystals were obtained (2.67 g, 80%). IR (CH2Cl2):
ν(CO)/cm-1 2046, 1967. IR (CsI): ν(CO)/cm-1 2045, 2034, 1968,
1960. 13C{1H} NMR (CD2Cl2): δ 169.9 (Ir-CO). MS (FAB-):
m/z 503. Anal. Calcd for C38H30IrI2NO2P2: C, 43.86; H, 2.91; N,
1.35. Found: C, 43.69; H, 2.81; N, 1.38.
6.2. [PPN][IrHI3(CO)2] (2-PPN). This compound was prepared
from [PPN][IrI2(CO)2] (1-PPN; 0.5 g, 0.48 mmol) dissolved in 20
mL of dichloromethane by dropwise addition of HI (57% in water,
0.1077 g, 0.48 mmol). The slow addition of HI was monitored by
IR, and after a few minutes CO bands corresponding to [PPN][Ir-
(H)I3(CO)2] (2-PPN) were observed, while those corresponding to
1-PPN had completely disappeared. The solvent was then removed
under vacuum, and an orange-red solid was obtained. This product
was crystallized in an acetone/n-heptane (1/1) bilayered mixture
to afford small reddish orange crystals (0.55 g, 98%) not suitable
for X-ray analysis. IR (CH2Cl2): ν(CO)/cm-1 2157, 2103, 2052.
1H NMR (CD2Cl2): δ -11.7 (s, H-Ir). 13C{1H} NMR (CD2Cl2):
δ 155.0 (s, Ir-CO). MS (FAB-): m/z 631. Anal. Calcd for C38H31-
IrI3NO2P2: C, 39.06; H, 2.67; N, 1.20. Found: C, 39.21; H, 2;63;
N, 1.22.
Figure 12. 13C NMR spectra for the Ir-Pt-catalyzed methanol
carbonylation.
3. Batch Experiments. High-pressure batch carbonylation
experiments were performed in a Hastelloy B2 100 mL autoclave
(Top Industrie) equipped with a stirring axis. The reactor can be
pressurized up to 90 bar from a gas reservoir and can be heated up
to 200 °C. Pressure can be maintained in the reactor. We measured
carbon monoxide consumption in the reservoir and then calculated
the carbonylation rate at 20% of unreacted methyl acetate. The
reactor is equipped with a feed line to introduce liquids under
pressure. All batch experiments were started with the IrI3,4 salt in
a mixture of acetic acid and water (10/1); the reactor was closed
and flushed several times with carbon monoxide and then pressur-
ized at 5 bar and heated to 190 °C, and the mixture was stirred at
1000 rpm to preform the iridium active species. After 25 min,
[PtI2(CO)]2 was dissolved in the liquid component and added
through the liquid feed line overpressurized with carbon monoxide.
The pressure was then adjusted to 30 bar. It can be maintained
constant by supplying gas from the reservoir during the experiments.
A glassware reactor (Top Industrie) was used for some experiments.
Technical features and working conditions were the same as those
used for the Hastelloy autoclave, except for the maximum operating
pressure, which was 8 bar. With such a reactor it was possible to
observe the reaction mixture during the experiments and perform
crystallizations afterward.
4. High-Pressure/High-Temperature IR Analyses. Batch ex-
periments were monitored in situ by high-pressure IR spectroscopy
in an autoclave equipped with a cylindrical internal reflectance
(CIR) silicon rod: a “Cassegrain” lens system was used to focus

5904 Organometallics, Vol. 25, No. 25, 2006
Scheme 4. Proposed Catalytic Cycle for the Ir-Pt-Catalyzed Methanol Carbonylation
Gautron et al.
6.3. [PPN][IrI4(CO)2] (3-PPN). The salt [PPN][IrI2(CO)2] (1
g, 0.96 mmol) was dissolved in 50 mL of dichloromethane, and
iodine (0.24 g, 0.96 mmol) was added to the solution. The mixture
was stirred for 10 min, and then the solvent was removed under
vacuum to obtain a red powder (1.01 g, 80%). IR (CH2Cl2): ν(CO)/
cm-1: 2112, 2068. 13C{1H} NMR (CD2Cl2): δ 149.7 (s, Ir-
CO).
6.4. [PPN][IrI3(CH3)(CO)2] (4-PPN). This compound was
prepared by starting from [PPN][IrI2(CO)2] (1 g, 0.96 mmol)
dissolved in 10 mL of dichloromethane. Methyl iodide (5.45 g,

Promising Role of [PtI2(CO)]2
Organometallics, Vol. 25, No. 25, 2006 5905
38.4 mmol) was added to the medium, and the solution was stirred
at room temperature for 1 h. The solvent was removed under
vacuum, and the yellow-orange powder obtained was crystallized
from a CH2Cl2/n-hexane (1/1) bilayered mixture to yield orange
crystals (1.08 g, 95%). IR (CH2Cl2): ν(CO)/cm-1 2100, 2048. IR
7. Synthesis of Platinum Complexes. 7.1. [PtI2(CO)2] (10) and
[PtI2(CO)]2 (10′). According to the literature,28 [PtI2(CO)2] was
prepared by addition of PtI2 (2 g, 4.45 mmol) to 125 mL of n-hexane
in an autoclave. The mixture was pressurized with 12 bar of CO
and stirred for 1 h at 75 °C. By using a high-pressure IR cell reactor,
we observed the formation of the complex. The solution was cooled
to room temperature in the reactor and then depressurized. A 1.69
g amount (80% yield) of a red solid was obtained and dried under
reduced pressure, corresponding to the dimer [PtI2(CO)]2.
1
(CsI): ν(CO)/cm-1 2088, 2034. H NMR (CD2Cl2): δ 2.15 (s,
CH3). 13C NMR (CD2Cl2): δ 156 (s, Ir-CO), -16.6 (q, CH3, 1JC-H
) 141 Hz). MS (FAB-): m/z 646. Anal. Calcd for C39H33IrI3-
NO2P2: C, 39.61; H, 2.81; N, 1.18. Found: C, 39.51; H, 2.72; N,
1.23.
Under CO this compound reverts to [PtI2(CO)2] in 100% yield.
[PtI2(CO)]2 spectral data: IR (CH2Cl2) ν(CO)/cm-1 2111; 13C NMR
6.5. [Ir2I2(CH3)2(µ-I)2(CO)4] (5′). This dimeric species can be
prepared according to the procedure described by Ghaffar et al.27
via abstraction of an iodide ligand from [PPN][IrI3(CH3)(CO)2].
To 2 g (1.69 mmol) of the starting compound dissolved in 20 mL
of dichloromethane was added InI3 (0.83 g, 1.69 mmol). The
mixture was stirred for 30 min at room temperature, and then the
solvent was removed under vacuum to obtain a mixture of
[IrI2(CH3)(CO)2]2 and [PPN][InI4]. The dimer 5′ was repeatedly
extracted from this powder using hot cyclohexane. The solvent was
then removed under vacuum to obtain an orange-red powder (0.45
g, 25%). IR (CH2Cl2): ν(CO)/cm-1 2120, 2074. 1H NMR
(CD2Cl2): δ 1.90, 1.85 (s, Ir-CH3). 13C NMR (CD2Cl2): δ 152.5,
150.4, 150.1 (s, Ir-CO), -5.3, -8.76, (q, CH3, 1JC-H ) 140 Hz).
1
(CD2Cl2) δ 154.5 (s + satellites (d), CO, JPt-C 1843 Hz); 195Pt
NMR (CD2Cl2) δ -5328 (1JPt-C ) 1843 Hz). [PtI2(CO)2] spectral
data: IR (CH2Cl2) ν(CO)/cm-1 2127; 13C NMR (CD2Cl2) δ 166.0
(s + satellites (d), CO, 1JPt-C ) 1466 Hz); 195Pt NMR (CD2Cl2) δ
-5790 (1JPt-C ) 1466 Hz).
7.2. [PPN][PtI3(CO)] (9-PPN). [PtI2(CO)]2 (1 g, 1.05 mmol)
was dissolved in 50 mL of dichloromethane, and HI (0.26 g, 2.10
mmol) was added to give rapidly, at room temperature, the complex
H[PtI3(CO)].28 Then, [PPN]Cl (1.20 g, 2.10 mmol) was added to
the solution. The solvent was removed under vacuum to give a
yellow product. Crystallization of this compound in a 1/1 CH2Cl2/
n-hexane bilayered mixture gave yellow crystals of [PPN][PtI3(CO)]
(1.08 g, 45%). IR (CH2Cl2): ν(CO)/cm-1 2075. 13C NMR
(CD2Cl2): δ 152.8 (s + satellites (d), CO, 1JPt-C ) 1759 Hz). 195Pt
NMR (CD2Cl2): δ -5460 (1JPt-C ) 1759 Hz). MS (FAB-): m/z
603. Anal. Calcd for C37H30I3NOPtP2: C, 38.90; H, 2.65; N, 1.23.
Found: C, 39.02; H, 2.61; N, 1.28.
Crystallographic data for 9-PPN: C37H30I3NOP2Pt, crystal
dimensions 0.47 × 0.34 × 0.2 mm, monoclinic, space group P21/
c, a ) 13.6476(7) Å, b ) 17.9405(9) Å, c ) 15.4626(9) Å, â )
104.570(5)°, V ) 3664.2(3) Å3, T ) 293(2) K, Z ) 4, Dc ) 2.071
Mg/m3, µ ) 6.474 mm-1. A total of 22 953 reflections was collected
(Rint ) 0.0302), with θmax ) 26.32°. Semiempirical from equivalent
absorption correction. Final R indices (I > 2σ(I)) were R1 ) 0.0345
and wR2 ) 0.0741.
8. Characterization of the Hetero- and Homobimetallic
Complexes [PPN][IrI2(CH3)(CO)2(µ-I)PtI2(CO)] and [PPN]-
[Ir2I4(µ-I)(CH3)2(CO)4]. We did not succeed in isolating these two
compounds, but by correlating FAB/MS and NMR analyses we
were able to characterize them in solution. [PPN][IrI3(Me)(CO)2]
(4-PPN; 0.12 g, 0.10 mmol) was dissolved in 50 mL of dichloro-
methane, and [PtI2(CO)]2 (0.03 g, 0.016 mmol) was added to the
solution; IR analysis revealed that the reaction is almost instanta-
neous and gives a mixture of [PPN][IrI2(CH3)(CO)2(µ-I)PtI2(CO)]
(11-PPN) and [PPN][Ir2I4(µ-I)(CH3)2(CO)4] (13-PPN).
6.6. [IrI2(CH3)(CO)3] (6). The dimer [Ir2I2(CH3)2(µ-I)2(CO)4]
(5′; 1 g, 0.97 mmol) was dissolved in 20 mL of dichloromethane
and placed in a glass reactor, which was then pressurized to 5 bar
of CO and heated to 30 °C. The solution was stirred for 10 min
and then cooled to -30 °C with an acetone/liquid nitrogen mixture.
A 15 mL portion of n-heptane was added by the liquid feed line.
After a few hours we observed the formation of microcrystals not
suitable for X-ray analysis. IR (CH2Cl2): ν(CO)/cm-1 2156, 2116,
2096. 1H NMR (CD2Cl2): δ 2.08 (s, CH3). 13C NMR (CD2Cl2): δ
1
146.9 (s, Ir-CO), -22.3 (q, CH3, JC-H ) 140 Hz).
6.7. mer,trans-[PPN][Ir(COCH3)I3(CO)2] (8-PPN). This com-
plex was prepared by addition of H2O (2 g, 0.11 mol) to a solution
of [PPN][IrI3(CH3)(CO)2] (0.5 g, 0.42 mmol) in 30 mL of methanol.
The solution was placed in a glass reactor and stirred for 1 h under
5 bar of CO at room temperature. Then 20 mL of n-hexane was
added by a liquid feed line overpressurized with CO and the reactor
was cooled to 0 °C. After 2 h we observed the formation of orange
crystals (0.38 g, 75% yield) suitable for X-ray analysis, corre-
sponding to mer,trans-[PPN][Ir(COCH3)I3(CO)2]. IR (CH2Cl2):
ν(CO)/cm-1 2114, 2070, 1655. 1H NMR (CD2Cl2): δ 2.76 (s, CH3).
13C{1H} NMR (CD2Cl2): δ 201.5 (COMe), 162.7 (s, Ir-CO), 52.2
1
(q, Me, JC-H ) 140 Hz).
Crystallographic data for mer,trans-[PPN][Ir(COCH3)I3-
(CO)2] (8-PPN): C40H33I3IrNO3P2, crystal dimensions 0.19 × 0.23
× 0.40 mm, monoclinic, space group P21/c, a ) 14.605(1) Å, b )
18.580(1) Å, c ) 15.176(1) Å, â ) 95.168(6)°, V ) 4101.4(5) Å,3
T ) 180(2)K, Z ) 4, Dc ) 1.96 Mg/m3, µ ) 5.628 mm-1. A total
of 39 257 reflections was collected (Rint ) 0.05), with θmax ) 32°.
Semiempirical from equivalent absorption correction. Final R
indices (I > 2σ(I)) were R1 ) 0.0397 and wR2 ) 0.0436.
8.1. [PPN][IrI2(CH3)(CO)2(µ-I)PtI2(CO)] (11-PPN). IR (CH2-
Cl2): ν(CO)/cm-1 2107, 2050. 1H NMR (CD2Cl2): δ 2.36 (s, CH3).
13C NMR (CD2Cl2): δ 155.4 (s, CO), 154.91 (s + satellites (d),
1
1
Pt-CO, JPt-C ) 1650 Hz), -14.09 (q, CH3, JC-H ) 141 Hz),
-14.18 (q, CH3, 1JC-H ) 141 Hz). 195Pt NMR (CD2Cl2): δ -5462
(1JPt-C ) 1650 Hz). MS (FAB-): m/z 1121.
8.2. [PPN][Ir2I4(µ-I)(CH3)2(CO)4] (13-PPN). IR (CH2Cl2):
ν(CO)/cm-1 2117, 2061. 1H NMR (CD2Cl2): δ 2.28 (s, CH3). 13
C
1
6.8. fac,cis-[PPN][Ir(COCH3)I3(CO)2] (8-PPN). The salt [PPN]-
[IrI3(CH3)(CO)2] (0.5 g, 0.42 mmol) was dissolved in 40 mL of
dichloromethane containing 5 mL of methanol. The solution was
placed in a glass reactor and stirred for 90 min under 5 bar of CO
at room temperature. Then 20 mL of n-hexane was added by a
liquid feed line and the reactor was cooled to 0 °C. After 2 h we
observed the formation of yellow crystals (380 mg, 75% yield),
corresponding to fac,cis-[PPN][Ir(COCH3)I3(CO)2]. IR (CH2Cl2):
NMR (CD2Cl2): δ 154.68 (s, CO), -14.83 (q, CH3, JC-H ) 141
Hz). MS (FAB-): m/z 1161.
Acknowledgment. This work was supported by Acetex
Chimie and by the “Ministe`re de la Recherche et de la
Technologie”. G.L. thanks the Swiss National Science Founda-
tion (Grant 200020-105335/1).
Supporting Information Available: CIF files giving X-ray
crystallographic data for mer,trans-8-PPN and 9-PPN. This material
is available free of charge via the Internet at http://pubs.acs.org.
1
ν(CO)/cm-1 2111, 2061, 1679, 1660. H NMR (CD2Cl2): δ 3.13
(s, CH3). 13C{1H} NMR (CD2Cl2): δ 196.2 (COMe), 151.4 (s, Ir-
1
CO), 49.5 (q, Me, JC-H ) 140 Hz).
OM060282X
(27) Ghaffar, T.; Adams, H.; Maitlis, P. M.; Sunley, G. J.; Baker, M. J.;
Haynes, A. Chem. Commun. 1998, 1023.
(28) Andreini, B. P.; Dell’Amico, D. B.; Calderazzo, F.; Venturi, M. G.
J. Organomet. Chem. 1988, 357.