Isolation and structural characterization of anionic and neutral compounds resulting from the oxidative addition of HI or CH3I to [IRI 2(CO)2]-

Article abstract of DOI:10.1021/ic0340938

The active iridium species in the methanol carbonylation reaction has been crystallized as the [PPN][IrI₂(CO)₂] complex and the X-ray structure solved, showing a cis-geometry and a square planar environment. Hydriodic acid reacts very quickly with this compound to provide [PPN][IrHI ₃(CO)₂], the X-ray crystal structure of which has been determined. The two CO ligands remain in mutual cis-position in a pseudooctahedral environment. The same cis-arrangement has been observed from the X-ray structure for [PPN][IrI₃(CH₃)(CO)₂] resulting from the slower oxidative addition of CH₃I to [PPN][IrI₂(CO)₂]. By iodide abstraction with InI ₃, the anionic methyl complex gave rise to the dimeric neutral complex [Ir₂(μ-I)₂I₂(CH₃) ₂(CO)₄]. An X-ray structure showed that the methyl ligands are in the equatorial positions of the two octahedrons sharing an edge, formed by the two bridging iodide ligands. All these four complexes have been fully characterized by mass spectrometry, ¹H and ¹³C NMR, and infrared both in solution and in the solid state. When necessary, the ¹³CO- or ¹³CH₃-enriched complexes have been prepared and analyzed.

Full text of DOI:10.1021/ic0340938

Inorg. Chem. 2003, 42, 5523−5530
Isolation and Structural Characterization of Anionic and Neutral
Compounds Resulting from the Oxidative Addition of HI or CH I to
3
[IrI2(CO)2]-
Samuel Gautron,† Roberto Giordano,† Carole Le Berre,† Joe1l Jaud,‡ Jean-Claude Daran,§
,†
Philippe Serp,† and Philippe Kalck*
Laboratoire de Catalyse, Chimie Fine et Polyme`res, Ecole Nationale Supe´rieure des Inge´nieurs en
Arts Chimiques et Technologiques, 118 route de Narbonne, 31077 Toulouse Cedex 4, France,
Centre d’Elaboration des Mate´riaux et Etudes Structurales, BP 4347, 31055 Toulouse Cedex,
France, and Laboratoire de Chimie de Coordination du CNRS, 205 route de Narbonne,
31077 Toulouse Cedex, France
Received January 29, 2003
The active iridium species in the methanol carbonylation reaction has been crystallized as the [PPN][IrI2(CO)2]
complex and the X-ray structure solved, showing a cis-geometry and a square planar environment. Hydriodic acid
reacts very quickly with this compound to provide [PPN][IrHI3(CO)2], the X-ray crystal structure of which has been
determined. The two CO ligands remain in mutual cis-position in a pseudooctahedral environment. The same
cis-arrangement has been observed from the X-ray structure for [PPN][IrI3(CH )(CO)2] resulting from the slower
3
oxidative addition of CH I to [PPN][IrI2(CO)2]. By iodide abstraction with InI3, the anionic methyl complex gave rise
3
to the dimeric neutral complex [Ir2(µ-I)2I2(CH ) (CO)4]. An X-ray structure showed that the methyl ligands are in the
3 2
equatorial positions of the two octahedrons sharing an edge, formed by the two bridging iodide ligands. All these
four complexes have been fully characterized by mass spectrometry, 1H and 13C NMR, and infrared both in solution
and in the solid state. When necessary, the 13CO- or 13CH -enriched complexes have been prepared and analyzed.
3
Introduction
concerned, is a much faster addition to Ir(I) than to Rh(I),
while the rate of migration of the methyl group onto the
coordinated CO ligand is 105-106 higher for Rh(III) than
for Ir(III).4
Forster5 proposed that two catalytic cycles do coexist, one
involving anionic and the other neutral iridium iodo carbonyl
complexes, and that the predominance of one over the other
could depend on iodide-ion levels and particularly HI
concentration.6 Variables such as water, methanol, and MeI
content do furthermore influence which of the two cycles is
likely to make the major contribution; the possibility of a
competitive water-gas shift reaction should not be disre-
garded as well.
The square-planar 16-electron d8-complex cis-[IrI2(CO)2]-
(anion of 1) is an intermediate species in the iridium-
ruthenium CATIVA process for methanol carbonylation,1 in
that it undergoes a rapid oxidative addition by methyl iodide
to afford [IrI3(CH3)(CO)2]-, the resting state in the catalytic
cycle. This iridium(I) complex was originally and indepen-
dently proposed as the active catalytic species operating in
the reaction mixtures by Forster2 and Pannetier.3
The mechanistic feature that distinguishes the Ir-catalyzed
reaction from the classical Rh-based Monsanto process, as
far as the oxidative addition of MeI to the metallic center is
* To whom correspondence should be addressed. E-mail: Philippe.
Kalck@ensiacet.fr. Tel: 0033562885690. Fax: 0033562885600.
† Ecole Nationale Supe´rieure des Inge´nieurs en Arts Chimiques et
Technologiques.
(4) (a) Bassetti, M.; Monti, D.; Haynes, A.; Pearson, J. M.; Stanbridge, I.
A.; Maitlis, P. M. Gazz. Chim. Ital. 1992, 122, 391. (b) Griffin, T. R.;
Cook, D. B.; Haynes, A.; Pearson, J. M.; Monti, D.; Morris, G. E. J.
Am. Chem. Soc. 1996, 118, 3029. (c) Ellis, P. R.; Pearson, J. M.;
Haynes, A.; Adams, H.; Bailey, N. A.; Maitlis, P. M. Organometallics
1994, 13, 3215. (d) Maitlis, P. M.; Haynes, A.; Sunley, G. J.; Howard,
M. J. J. Chem. Soc., Dalton Trans. 1996, 2187.
‡ Centre d’Elaboration des Mate´riaux et Etudes Structurales.
§ Laboratoire de Chimie de Coordination du CNRS.
(1) Haynes, A.; Mann, B. E.; Morris, G. E.; Maitlis, P. M. J. Am. Chem.
Soc. 1993, 115, 4093.
(5) Forster, D. J. Chem. Soc., Dalton Trans. 1979, 1639.
(2) Forster, D. J. Am. Chem. Soc. 1976, 98, 846.
(3) Brodzki, D.; Denise, B.; Pannetier, G. J. Mol. Catal. 1977, 2, 149.
(6) (a) Forster, D. AdV. Organomet. Chem. 1979, 17, 255. (b) Forster,
D.; Hershman, A.; Morris, D. E. Catal. ReV.sSci. Eng. 1981, 23, 89.
10.1021/ic0340938 CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/08/2003
Inorganic Chemistry, Vol. 42, No. 18, 2003 5523

Gautron et al.
Three different regimes were envisaged, all of them
pointing to the very important role played by iodide con-
centration in determining whether an anionic or a neutral
catalytic cycle is actually operating.7 In addition, the im-
portance of I- concentration, first recognized to exert a
powerful catalytic effect on the rate of the oxidative addition
of alkyl halides to Rh(I) complexes,8 was also observed in
H+ containing mixtures in which HI is generated. In fact,
HI is able to compete with MeI, giving in its turn oxidative
addition onto [IrI2(CO)2]- to form the hydride [IrHI3(CO)2]-.5
More recently, Ghaffar et al.9 and Churlaud et al.10 detected
the latter hydridic species in their reaction mixtures under
catalytic conditions, thus confirming the early proposal by
Forster.5 In their study, Churlaud et al.10 reported that when
the temperature is raised, [IrHI3(CO)2]- slowly gives
[IrI4(CO)2]- and restores [IrI2(CO)2]- after H2 evolution as
previously pointed out.5 Both cis-[IrI2(CO)2]- and the
aforementioned hydrido iodo carbonyl species, together with
[IrI3(CO)3],11 are involved in the water-gas shift reaction,
which represents a significant side reaction in the methanol
carbonylation process.11,12a,b
As far as halo carbonyl complexes of iridium are con-
cerned, oxidative addition reactions onto [IrX2(CO)2]- anions
were studied with regard to either mechanism and stereo-
chemical course.12,13 Interestingly, hydrogen halides were
found to add to the square-planar Ir(I) complexes in a
stereospecific cis-fashion: the geometry of the oxidative
addition-derived iridium complexes is fac,cis while the same
reactions onto [RhI2(CO)2]- afford mer,trans analogues.
The major formal difference between the oxidative addi-
tion of HI and that of MeI consists of a mechanistic one.
Indeed, the first step of the former process is the protonation
of the electron-rich iridium center via an electrophilic
addition, which explains the faster reaction rate observed for
HI; by contrast, kinetic evidence and theoretical calculations4a,b
indicate a classical SN2 reaction pathway for MeI, by which
the nucleophile cis-[IrI2(CO)2]- slowly attacks the carbon
atom, giving rise to a linear transition state with iodide as a
leaving group. Moreover, a density functional study of the
oxidative addition of MeI onto the Ir(I) precursor14a,b showed
that the only cis form of [IrI2(CO)2]- undergoes this type of
reaction.4c On energy grounds the trans isomer would react
faster than the cis one (the difference in energy being 3.7
kcal in favor of the trans form), but that is not the case since
the cis to trans conversion is unlikely to occur (difference
in energy of 10.39 kcal, the cis isomer being the more stable).
Therefore, we were interested in studying the competition
between HI and MeI for cis-[IrI2(CO)2]- and to determine
the structures of the so-generated anionic complexes.
Furthermore, anionic dimeric halogeno carbonyls of iri-
dium have been known for many years,15 and neutral dimeric
complexes such as [Ir(µ-Cl)Cl(CH3)(CO)2]216 and [Ir(µ-Cl)-
17
(Cl)H(CO)2]2 were also prepared. As the neutral dimeric
complex [Ir(µ-I)I(CH3)(CO)2]2 has been reported18 to react
with CO to give the tricarbonyl species [IrI2(CH3)(CO)3],
an intermediate in the iridium-catalyzed methanol carbony-
lation, our goal was also to synthesize the related iridium
dinuclear complexes that could be generated from the
Ir(III) anionic species detected and/or isolated in the course
of this work, via reaction with iodide-abstraction agents.
Experimental Section
General Procedures. All manipulations were carried out with
standard vacuum and dry-argon techniques. Dimethylformamide
(DMF, Scharlau, 99.8%), iodomethane (CH3I, Acros, 99%), hy-
driodic acid (HI, Merck, 57%), indium triodide (InI3, Acros, 99.9%),
n-hexane (Scharlau, 96%), IrI3 (iridium iodide (Johnson-Mathey)
is sold as IrI3.4, which is a mixture of IrI3 and IrI4), and carbon
C-13-enriched carbon monoxide (Air Liquide, 99%) were used as
received, and dichloromethane (CH2Cl2, Aldrich) was dried with
1
CaH2. H and 13C spectra were recorded with Bruker AC250 or
AMX 400 spectrometers. Mass spectra were recorded on a
NERMAG R10-10 (FAB negative mode; gas: Xe). The reference
for the NMR chemical shifts was SiMe4. Solution infrared spectra
were recorded on a Perkin-Elmer 1710 spectrophotometer with a
0.1 mm cell equipped with CaF2 windows and when necessary with
a high-pressure infrared cell (Autoclave Top Industrie).
X-ray Crystallographic Study. Data for compounds 1, 3, and
4 were collected on an Oxford-Diffraction Xcalibur diffractometer
whereas a Nonius Kappa CCD was used for compound 2. The final
unit cell parameters were obtained by the least-squares refinement
of a large number of selected reflections. For all compounds, only
statistical fluctuations were observed in the intensity monitors over
the course of the data collections.
The structure was solved by direct methods (SIR97)19 and refined
by least-squares procedures on F2. In all compounds, all H atoms
were introduced at calculated positions as riding atoms [d(CH) )
0.99-0.98 Å], using AFIX43 for C6H5 and AFIX137 for CH3
groups, with a displacement parameter equal to 1.2 (C6H5) or 1.5
(CH3) times that of the parent atom. In compound 3, one of the
CO’s and the methyl were disordered on two sites with an
occupation factor ratio of 0.67/0.33. Least-squares refinements
2
2 2
were carried out by minimizing the function Σw(Fo - Fc ) ,
where Fo and Fc are the observed and calculated structure factors.
The weighting scheme used in the last refinement cycles was w )
2
2
1/[σ2(Fo ) + (aP)2 + bP], where P ) (Fo + 2Fc2)/3. Models
(7) Forster, D.; Singleton, T. C. J. Mol. Catal. 1982, 17, 299.
(8) Forster, D. J. Am. Chem. Soc. 1975, 97, 951.
(9) Ghaffar, T.; Charmant, J. P. H.; Sunley, G. J.; Morris, G. E.; Haynes,
A.; Maitlis, P. M. Inorg. Chem. Commun. 2000, 3, 11.
(10) Churlaud, R.; Frey, U.; Metz, F.; Merbach, A. E. Inorg. Chem. 2000,
39, 4137.
(11) Jones, J. H. Platinum Met. ReV. 2000, 44, 94.
(12) (a) Forster, D. Inorg. Chem. 1972, 11, 473. (b) Haak, S.; Haynes, A.;
Maitlis, P. M.; Morris, G. E.; Watt, R. J. 12th International Symposium
on Homogeneous Catalysis, Stockholm, Sweden, Aug 23-29, 2000.
(13) Haynes, A.; McNish, J.; Pearson, J. M. J. Org. Chem. 1998, 551,
339.
(14) (a) Kinnunen, T.; Laasonen, K. J. Mol. Struct. (THEOCHEM) 2001,
542, 273. (b) Kinnunen, T.; Laasonen, K. J. Mol. Struct. (THEOCHEM)
2001, 540, 91.
reached convergence with R ) Σ(||Fo| - |Fc||)/Σ(|Fo|) and wR2
2
2 2
) {Σw(Fo - Fc2)2/Σw(Fo ) }1/2, having values listed in Table 1.
(15) Cleare, M. J.; Griffith, W. P. J. Chem. Soc. A 1970, 2788.
(16) Bailey, N. A.; Jones, C. J.; Shaw, B. L.; Singleton, E. Chem. Commun.
1967, 1051.
(17) Shaw, B. L.; Singleton, E. J. Chem. Soc. A 1967, 1683
(18) Ghaffar, T.; Adams, H.; Maitlis, P. M.; Sunley, G. J.; Baker, M. J.;
Haynes, A. Chem. Commun. 1998, 1023.
(19) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giaco-
vazzo, 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.
5524 Inorganic Chemistry, Vol. 42, No. 18, 2003

Hydrido- and Methyliodocarbonyliridium Complexes
Table 1. Crystal Data and Structure Refinement Parameters
The calculations were carried out with the SHELXL-97 pro-
gram20 using the integrated system WINGX(1.63).21 A molecular
view was realized with the ORTEP program.22 Fractional atomic
coordinates, anisotropic thermal parameters for non-hydrogen atoms,
and atomic coordinates for H atoms have been deposited as
Supporting Information.
param
1
2
empirical formula
fw
C38H30I2IrNO2P2
1040.57
C38H31I3IrNO2P2
1168.48
temp, K
180(2)
293(2)
wavelength, Å
cryst system
space group
a, Å
b, Å
c, Å
0.710 73
triclinic
P1h
0.710 73
monoclinic
P21/c
9.3661(3)
16.4735(6)
25.2247(5)
90.0
94.713(2)
90.0
3878.8(2)
4
2.001
5.945
2192
Synthesis of [PPN][IrI2(CO)2] (1). In a two-necked flask (250
mL) equipped with gas inlet and a reflux condenser was placed 2
g (3.21 mmol) of IrI3.4 in a mixture of DMF (150 mL) and water
(1.5 mL); CO was passed through the stirred solution, and the
temperature was raised to 160 °C. After 4 h, the solution color
changed from dark to yellow. After the solution was cooled to room
temperature, PPNCl was added (1 molar equiv/Ir) to the limpid
solution; further addition of cold deionized water caused the
precipitation of [PPN][IrI2(CO)2] (1). Careful washing of the
resulting salt with water gave a yellow solid, which was dried in
vacuo. Recrystallization from bilayered CH2Cl2/n-heptane gave
yellow needles suitable for X-ray determination (m ) 1.67 g;
yield: 50%). IR (CH2Cl2): 2046 (s), 1967 (s) cm-1. IR (KI
pellets): 2045 (s), 2034 (s), 1968 (s), 1960 (s) cm-1. MS: m/z )
503. 13C NMR (CD2Cl2): δ ppm 169.9 ppm (s, CO).
10.0352(15)
17.363(2)
21.899(3)
76.120(10)
88.430(10)
80.460(10)
3652.7(8)
4
R, deg
â, deg
γ, deg
V, Å3
Z
D(calcd), Mg/m3
abs coeff, mm-1
F(000)
1.892
5.467
1976
cryst size, mm
0.34 × 0.07 ×
0.15 × 0.17 ×
0.063
0.20
θ range, deg
3.41-25.68
-7 e h e 12,
-21 e k e 21,
-26 e l e 26
26 163
13 731 (0.0796)
98.9
analytical
0.578 and 0.876
13 731/730/829
0.911
R1 ) 0.0580,
wR2 ) 0.0930
R1 ) 0.1245,
wR2 ) 0.1137
1.236 and -1.973
2.58-27.46
0 e h e 12,
0 e k e 21,
-32 e l e 32
9607
8852 (0.063)
99.6
semiempirical
0.541 and 0.378
8852/0/428
0.801
R1 ) 0.0399,
wR2 ) 0.0799
R1 ) 0.0820,
wR2 ) 0.0942
1.014 and -1.281
index ranges
Synthesis of [PPN][IrHI3(CO)2] (2). Differently from the early
report by Forster,5 who prepared the above hydridoiridium species
via the addition of slightly more than 1 equiv of HI to [IrI2(CO)2]-
in nitromethane, we found that large amounts of [IrI4(CO)2]- were
formed as a side product when adapting his synthetic procedure to
CH2Cl2 reaction mixtures.
reflecns collcd
unique reflecns (Rint
completeness, %
abs corr
max and min transm
data/restraints/params
goodness-of-fit on F2
final R indices
)
Hence we modified the synthetic method as follows: In a
Schlenk tube, 20 mL of CH2Cl2 was placed and degassed with a
flow of N2 ; the [PPN][IrI2(CO)2] salt was added (500 mg; 0.48
mmol), and then HI was added dropwise with a microsyringe and
very slowly to the well-stirred solution of the Ir(I) anion, while
monitoring the disappearance of the reactant IR bands after every
addition of HI. When the IR spectrum signaled that the reaction
had reached completion, addition of HI was stopped and a bright
orange-red limpid solution was obtained. The solution was evapo-
rated and the residual dried in vacuo to afford an orange-red solid
(m ) 549 mg; yield 98%), which was dissolved in 20 mL of
degassed acetone; n-heptane was then slowly added to give a
bilayered mixture suitable for recrystallization. Indeed, after 1 month
at -18 °C, large dark orange crystals could be found, suitable for
X-ray diffractometry; they were dried by bubbling N2 through the
solution and kept under inert atmosphere. IR (CH2Cl2): 2157 (vw,
[I > 2σ(I)]
R indices (all data)
resid density, e Å-3
param
3
4
empirical formula
C39H33I3IrNO2P2‚
CH2Cl2
C3H3I2IrO2
fw
1267.43
517.05
temp, K
wavelength, Å
cryst system
space group
a, Å
180(2)
0.710 73
180(2)
0.710 73
triclinic
P1h
6.6629(18)
7.6766(19)
8.710(2)
102.94(2)
110.72(3)
90.52(2)
404.19(18)
2
4.248
monoclinic
P21/c
10.6554(5)
26.6621(14)
14.9769(9)
90.0
98.809(4)
90.0
4204.7(4)
4
b, Å
c, Å
R, deg
â, deg
ν
Ir-H), 2103, 2052 (s, νCO) cm-1. MS: m/z ) 631. 1H NMR
γ, deg
(CD2Cl2): δ -11.65 ppm. 13C NMR (CD2Cl2): δ 155.0 ppm (s,
CO).
V, Å3
Z
D(calcd), Mg/m3
abs coeff, mm-1
F(000)
2.002
5.616
2392
Synthesis of [PPN][IrI3(CH3)(CO)2] (3). In a 20 mL Schlenk
tube 10 mL of CH2Cl2 was degassed with a flow of N2; [PPN]-
[IrI2(CO)2] (1) (1 g; 0.96 mmol) was added together with 40 equiv
of CH3I. After the mixture was stirred for 1 h at room temperature,
an orange solution was obtained. Drying in vacuo afforded an
orange solid. Recrystallization from a bilayered CH2Cl2/n-heptane
mixture gave orange crystals suitable for X-ray analysis (m ) 0.68
g; yield 60%). IR (CH2Cl2): 2100 (s), 2048 (s) cm-1. IR (KI
pellets): 2088 (s), 2034 (s) cm-1. MS: m/z ) 646. 1H NMR
(CD2Cl2): δ 2.15 ppm. 13C NMR (CD2Cl2): δ 156.0 (s, CO),
-15.75 ppm (s, CH3).
24.078
440
cryst size, mm
0.317 × 0.317 ×
0.204 × 0.138 ×
0.186
0.057
θ range, deg
2.99-26.31
-9 e h e 13,
-33 e k e 33,
-18 e l e 18
29 700
4.07-26.37
-8 e h e 8,
-9 e k e 9,
-10 e l e 10
2468
index ranges
reflecns collcd
unique reflecns (Rint
completeness, %
abs corr
max and min transm
data/restraints/params
goodness-of-fit on F2
final R indices
)
8588 (0.0360)
99.8
analytical
0.6059 and 0.3207
8588/421/491
0.956
R1 ) 0.0322,
wR2 ) 0.0641
R1 ) 0.0471,
wR2 ) 0.0683
1.170 and 1.095
1541 (0.0461)
93.1
analytical
0.2578 and 0.0726
1541/0/75
1.084
R1 ) 0.0338,
wR2 ) 0.0874
R1 ) 0.0385,
wR2 ) 0.0900
1.437 and 1.875
(20) Sheldrick, G. M. SHELX97, Programs for Crystal Structure Analysis
(Release 97-2); Institu¨t fu¨r Anorganische Chemie der Universita¨t:
Tammanstrasse 4, D-3400 Go¨ttingen, Germany, 1998.
(21) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837-838.
(22) (a) Burnett, M. N.; Johnson, C. K. ORTEP-III; Report ORNL-6895;
Oak Ridge National Laboratory: Oak Ridge, TN, 1996. (b) Farrugia,
L. J. ORTEP3 for Windows. J. Appl. Crystallogr. 1997, 30, 565.
[I > 2σ(I)]
R indices (all data)
resid density, e Å-3
Inorganic Chemistry, Vol. 42, No. 18, 2003 5525

Gautron et al.
Synthesis of [Ir2(µ-I)2I2(CH3)2(CO)4] (4). Addition of an
equimolecular amount of InI3 to a CH2Cl2 solution (20 mL) of
[PPN][IrI3CH3(CO)2] (3) (m ) 2 g; 1.69 mmol) and drying in vacuo,
followed by extraction with hot cyclohexane from the [PPN][InI4]
residual, afforded a dark orange solution. Drying in vacuo gave an
orange solid that was dissolved in CH2Cl2 ; further addition of
n-heptane afforded a bilayered mixture from which crystals were
obtained after 1 week in the refrigerator (-20 °C) (0.22 g; yield
1
25%). IR (CH2Cl2): 2120 (s), 2074 (s) cm-1. H NMR (CD2Cl2):
δ 1.96, 1.90 ppm. 13C NMR (CD2Cl2): δ 152.5, 150.4, 150.1 ppm
(CO).
Results and Discussion
Since the iridium-based catalytic system for the carbony-
lation of methanol involves the production of MeI in aqueous
acidic media through the reaction of HI on CH3OH, we
studied the reactivity of HI and of MeI toward the precursor
cis-[IrI2(CO)2]-. We at first followed the formation of the
cis-H[IrI2(CO)2] precursor by CO reduction of the iridium
iodide salt in water-containing reaction mixtures. To compare
their reactivity, we performed the oxidative addition reactions
of HI and of MeI in chlorobenzene, which lead to the
formation of the corresponding species H[IrHI3(CO)2] and
H[IrI3(CH3)(CO)2], respectively.
We could prepare, isolate, and crystallize these anionic
complexes as their PPN+ salts and determined their X-ray
structures, together with that of the precursor [PPN]-
[IrI2(CO)2].
Starting from the above oxidative addition-derived anionic
species, we also prepared, by reaction with InI3, a iodide-
abstraction agent, the neutral dimer [Ir2(µ-I)2(I)2(CH3)2(CO)4],
fully characterized both by spectroscopy and X-ray diffrac-
tometry.
Figure 1. ORTEP view of [PPN][IrI2(CO)2] (1) with atomic labeling
scheme for the anion and showing mainly the two phosphorus and the
nitrogen atoms of the cation. Ellipsoids are at the 50% probability level.
in molecule A the two Ir(1)-I(11) and Ir(1)-I(12) bond
lengths correspond to 2.6755(10) and 2.6273(10) Å, respec-
tively, which well accords with the Ir(2)-I(21) and
Ir(2)-I(22) bond distances of 2.6581(11) and 2.6551(10) Å.
In molecule B, the thermal parameters of one iodine atom
appear to be larger than the other, whereas the CO ligand
trans to this iodide presents ellipsoids smaller than expected.
This phenomenon might be due to a disorder between I-
and CO ligands. However, no correct model can be defined
for this disorder. Apparently the isomer shown is present in
greater than 90%. The four angles around the iridium atoms
vary from 84.1(4) to 94.0(5)° and do therefore deserve some
further discussion. The I-Ir-I values of 90.99(3) and
92.31(3)° are close to a right angle. The C(11)-Ir(1)-C(12)
angle measures 94.0(5)°, the C(21)-Ir(2)-C(22) one reaches
91.9(6)°, and the values of 84.1(4)° for I(12)-Ir(1)-C(12)
and 86.1(4)° for I(22)-Ir(2)-C(21) are essentially due to
the lack of linearity along the Ir-C-O bonds.
[PPN][IrI2(CO)2] (1). The anionic iridium(I) precursor
[IrI2(CO)2]-, which directly intervenes in the catalytic cycle,
curiously has never been described in the solid state. We
succeeded in isolating and crystallizing this anionic complex
as its PPN+ salt.
Carbonylation of DMF solutions of IrI3.4 affords quanti-
tatively [NH2Me2][IrI2(CO)2] after 3-4 h, as shown by
infrared spectroscopy. The ammonium cation results from
the decarbonylation of DMF and its protonation by HI.23
After PPN+ addition (see Scheme 1) and recrystallization
from a CH2Cl2/n-heptane mixture, yellow needles of [PPN]-
[IrI2(CO)2] were obtained, suitable for X-ray crystal structure
determination.
The structure of the rhodium analogue complex [PyMe]-
[RhI2(CO)2] has been reported very recently.24 In the two
disordered structures solved with two different counterca-
tions, the bond distances and angles compare well with those
found here, since the mean Rh-I distance is ca. 2.66 Å,
Rh-C is 1.85 Å, and C-O is 1.125 Å.
The mean value calculated for the iridium-iodine bond
length is 2.654 Å. It is worth mentioning that previous ab
initio calculations carried out by Kinnunen and Laasonen14
on cis-[IrI2(CO)2]- indicate a 2.778 Å value for both the Ir-I
bond distances, i.e. 0.124 Å overestimated compared to that
measured in this work.
Scheme 1. Rapid Preparation of [PPN][IrI2(CO)2] from a
Commercial Iridium Salt
IR spectra of KI pellets of [PPN][IrI2(CO)2] show a pattern
of four CO bands possessing almost the same intensity, at
2045, 2034, 1968, and 1960 cm-1: they do actually cor-
respond to two systems of two bands each, arising from the
Crystal data for complex [PPN][IrI2(CO)2] (1) are listed
in Table 1. Its X-ray structure is shown in Figure 1, and
bond lengths and angles of interest are listed in Table 2.
The geometry of the above anionic species 1 presents a
square-planar environment for the iridium metal center, and
the two CO ligands are in a cis arrangement. Two nearly
identical molecules coexist in the asymmetric unit; indeed,
(23) Serp, P.; Hernandez, M.; Richard, B.; Kalck, P. Eur J. Inorg. Chem.
2001, 2327.
(24) Haynes, A.; Maitlis, P. M.; Quyoum, R.; Pulling, C.; Adams, H.; Spey,
S. E.; Stange, R. W. J. Chem. Soc., Dalton Trans. 2002,
2565.
5526 Inorganic Chemistry, Vol. 42, No. 18, 2003

Hydrido- and Methyliodocarbonyliridium Complexes
Table 2. Bond Lengths (Å) and Bond Angles (deg) within the Anions
with Esd’s Referring to the Last Significant Digit
this study. Indeed, dissolution of the solid material in
dichloromethane, monitored by infrared spectroscopy, does
only afford the two CO bands at 2046(s) and 1967(s) cm-1,
peculiar to the cis-complex in solution. In 13C NMR spectra
the two equivalent CO ligands appear as one singlet at 169.9
ppm, in CD2Cl2 solution.
Molecule A
Molecule B
Compound 1
Ir(1)-C(11)
1.813(7)
1.815(7)
Ir(2)-C(21)
1.802(7)
1.808(7)
2.6551(10)
2.6575(11)
1.092(7)
1.114(7)
Ir(1)-C(12)
Ir(1)-I(12)
Ir(1)-I(11)
O(11)-C(11)
O(12)-C(12)
Ir(2)-C(22)
2.6268(10) Ir(2)-I(22)
Moreover, in the absence of a stabilizing countercation,
the reductive carbonylation of IrI3.4 has been also monitored
by IR spectroscopy in a pressurized cylindrical internal
reflectance (CIR) cell. Chlorobenzene/water mixtures (20:
1) were employed for this purpose, at 130 °C and 5 bar of
carbon monoxide for 2 h, leading to the formation of a
mixture of species characterized by four bands at 2163 (w),
2112 (vs), 2064 (vs), and 1982 (m) cm-1. Except for a shift
due to the nature of the countercation, these bands could be
attributed to H[IrHI3(CO)2] at 2163 (νIr-H), 2112 and 2064
(νCO); and to H[IrI2(CO)2] at 2064 and 1982, with the 2064
cm-1 band deriving from the contribution from (and super-
imposition of) the common band shown by both of the
complexes. Therefore, we became interested in isolating this
anionic [IrHI3(CO)2]- complex, which is reported as an
intermediate species of the water-gas shift reaction in the
literature, being slowly transformed into a mixture of
[IrI4(CO)2]- and [IrI2(CO)2]- with H2 evolution through a
disproportionation process.5 With rhodium, this side reaction
takes a significant place and a mechanism has been proposed
by Eisenberg and co-workers25 from kinetic studies and
quenching experiments. More recently, [RhHI3(CO)2]- was
isolated and characterized.26
[PPN][IrHI3(CO)2] (2). A rapid and quantitative synthesis
of this compound was accomplished via the slow addition
of 1 equiv of aqueous HI to a CH2Cl2 solution of [PPN]-
[IrI2(CO)2]. The reaction proceeds very cleanly (see Scheme
2). However, it is worth mentioning that Forster reported
on the formation of significant amounts of [IrI4(CO)2]- when
a slight excess of HI was added to the anionic iridium
precursor in nitromethane.5 We can confirm this piece of
observation, i.e. that in CH2Cl2, after formation of equimo-
lecular amounts of complex 2, addition of even a slight
excess of HI results in the generation of [IrI4(CO)2]-, thus
leading, with 1 mol in excess, to the complete transformation
of the hydride species at the end of the reaction. Complex 2
has been crystallized as large dark orange crystals, and its
X-ray crystal structure determined. The unit cell contains
four PPN+ cations and four [IrHI3(CO)2]- anions, the
structure of which is discussed (Figure 2).
2.6759(10) Ir(2)-I(21)
1.114(7)
1.118(7)
O(21)-C(21)
O(22)-C(22)
C(11)-Ir(1)-C(12) 92.2(5)
C(11)-Ir(1)-I(12) 84.6(4)
C(12)-Ir(1)-I(12) 173.3(4)
C(11)-Ir(1)-I(11) 174.2(4)
C(12)-Ir(1)-I(11) 92.6(4)
C(21)-Ir(2)-C(22)
C(21)-Ir(2)-I(22)
C(22)-Ir(2)-I(22)
C(21)-Ir(2)-I(21)
C(22)-Ir(2)-I(21)
I(22)-Ir(2)-I(21)
O(21)-C(21)-Ir(2)
O(22)-C(22)-Ir(2)
90.9(6)
88.4(4)
179.2(4)
178.1(4)
88.4(4)
92.36(3)
175.9(12)
178.0(14)
I(12)-Ir(1)-I(11)
91.00(3)
O(11)-C(11)-Ir(1) 177.3(12)
O(12)-C(12)-Ir(1) 176.2(11)
Compound 2
Ir(1)-C(11)
Ir(1)-C(12)
C(11)-O(11)
C(12)-O(12)
1.913(10)
1.858(8)
1.042(9)
1.127(8)
Ir(1)-I(1)
Ir(1)-I(2)
Ir(1)-I(3)
2.6964(6)
2.6927(5)
2.8360(6)
C(11)-Ir(1)-C(12) 95.3(3)
C(12)-Ir(1)-I(2)
C(12)-Ir(1)-I(1)
C(11)-Ir(1)-I(3)
171.4(2)
84.7(3)
88.9(3)
96.7(2)
95.749(18)
C(11)-Ir(1)-I(2)
C(11)-Ir(1)-I(1)
I(2)-Ir(1)-I(1)
I(2)-Ir(1)-I(3)
87.2(2)
175.3(3)
92.049(19) C(12)-Ir(1)-I(3)
91.563(18) I(1)-Ir(1)-I(3)
Compound 3a
I(1)-Ir(1)
2.7005(4)
2.7658(4)
2.7177(4)
1.830(10)
2.131(10)
1.132(11)
Ir(1)-C(11)
1.870(5)
1.118(6)
I(2)-Ir(1)
C(11)-O(11)
I(3)-Ir(1)
Ir(1)-C(12)
Ir(1)-C(1)
C(12)-O(12)
Ir(1)-C(12A)
Ir(1)-C(1A)
1.829(15)
2.156(16)
1.135(16)
89.98(15)
94.9(9)
91.7(9)
91.8(12)
82.0(9)
87.82(16)
88.5(12)
87.6(8)
179.1(11)
93.168(13)
175.0(9)
87.4(10)
C(12A)-O(12 A)
C(11)-Ir(1)-I(2)
C(12A)-Ir(1)-C(11)
C(12A)-Ir(1)-C(1A)
C(11)-Ir(1)-C(1A)
C(12A)-Ir(1)-I(1)
O(11)-C(11)-Ir(1) 178.0(5)
C(12)-Ir(1)-C(11) 92.6(6)
C(12)-Ir(1)-C(1)
C(11)-Ir(1)-C(1)
C(12)-Ir(1)-I(1)
C(11)-Ir(1)-I(1)
C(1)-Ir(1)-I(1)
C(12)-Ir(1)-I(3)
C(1)-Ir(1)-I(3)
I(1)-Ir(1)-I(3)
94.2(6)
89.8(4)
87.7(6)
176.85(16) C(11)-Ir(1)-I(3)
87.1(4)
179.5(6)
86.2(4)
C(1A)-Ir(1)-I(1)
C(12A)-Ir(1)-I(3)
C(1A)-Ir(1)-I(3)
91.885(12) I(1)-Ir(1)-I(2)
86.2(6)
179.5(4)
C(12)-Ir(1)-I(2)
C(1)-Ir(1)-I(2)
C(12A)-Ir(1)-I(2)
C(1A)-Ir(1)-I(2)
O(12A)-C(12A)-Ir(1) 179(2)
O(12)-C(12)-Ir(1) 176.7(16)
I(3)-Ir(1)-I(2)
93.397(14)
Compound 4b
Ir(1)-C(1)
1.872(12)
1.872(12)
2.165(11)
2.6874(11) C(1)-O(1)
2.7156(11)
96.3(5)
87.7(5)
89.6(4)
85.6(4)
177.4(4)
88.7(3)
174.7(4)
86.4(4)
87.7(3)
Ir(1)-I(3)
I(3)-Ir(1)
O(2)-C(2)
2.8021(11)
2.8021(11)
1.107(14)
1.123(15)
Ir(1)-C(2)
Ir(1)-C(3)
Ir(1)-I(2)
Ir(1)-I(3)
C(1)-Ir(1)-C(2)
C(1)-Ir(1)-C(3)
C(2)-Ir(1)-C(3)
C(1)-Ir(1)-I(2)
C(2)-Ir(1)-I(2)
C(3)-Ir(1)-I(2)
C(1)-Ir(1)-I(3)′
C(2)-Ir(1)-I(3)′
C(3)-Ir(1)-I(3)′
I(2)-Ir(1)-I(3)′
91.50(4)
98.8(3)
91.1(3)
173.3(3)
90.38(4)
85.70(3)
94.30(3)
176.7(10)
176.4(11)
C(1)-Ir(1)-I(3)
C(2)-Ir(1)-I(3)
C(3)-Ir(1)-I(3)
I(2)-Ir(1)-I(3)
I(3)-Ir(1)-I(3)′
Ir(1)-I(3)-Ir(1)′
O(1)-C(1)-Ir(1)
O(2)-C(2)-Ir(1)
The two iodine atoms trans to the CO ligands, which can
be considered as belonging to the equatorial plane, present
two iridium-iodine distances of 2.6964(6) Å for Ir(I)-I(I)
and 2.6927(5) Å for Ir(1)-I(2), i.e. about 0.05 Å longer
than the mean Ir-I bond length in complex 1. The axial
Ir(1)-I(3) bond shows some lengthening due to the large
trans-influence of the hydride ligand (Ir(1)-I(3) ) 2.8360-
(6) Å). The three I-Ir-I angles, which are 91.563(18),
a A refers to the disordered distribution of CH3 and CO. b Symmetry
transformations used to generate equivalent atoms: ′, -x + 1, -y + 1,
-z + 1.
two slightly different iridium moieties observed in the unit
cell in their environment, both of them having a cis-
arrangement of the ligands, and definitely not from the
presence of the trans isomer, never detected in the course of
(25) Baker, E. C.; Hendriksen, D. N.; Eisenberg, R. J. Am. Chem. Soc.
1980, 102, 1020.
(26) Roe, D. C.; Sheridan, R. E.; Bunel, E. E. J. Am. Chem. Soc. 1994,
116, 1163.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5527

Gautron et al.
Table 3. Selected Infrared and NMR Data for Complexes 1-4
CO, cm-1 a
ν
CO, cm-1 b
δ
CO, ppma
δ
H, ppma
13
1
complex
ν
1
2046 s, 1967 s
2045 s, 2034 s,
1968 s, 1960 s
169.9
2
3
4
2157 w, 2103 s,
2052 s
2100 s, 2048 s
155.0
-11.65
2088 s, 2034 s
156.0, 15.75 2.15
(CH3)
152.5, 150.4, 1.96, 1.90
150.1
2120 s, 2074 s
a In CH2Cl2. b In KI.
Figure 2. ORTEP drawing of [PPN][IrHI3(CO)2] (2). Ellipsoids are at
the 50% probability level. The hydride ligand Hy1 has been positioned in
its ideal position at 1.6 Å from Ir1.
Scheme 2. Schematic Diagram Showing the Whole Reactivity of the
Anion [IrI2(CO)2]- toward HI and CH3I and Then the Formation of the
Neutral Dimer by Iodide Abstraction
Figure 3. ORTEP plot of the mononuclear structure of [PPN][IrI3(CH3)-
(CO)2] (3) (major form), with the labeling scheme for the anion. Ellipsoids
are at the 50% probability level.
95.749(18), and 92.049(19)°, respectively, slightly deviate
from 90° and are not very far to constitute a right-angled
trihedron. Besides these three heavy atoms, the three re-
maining ligands are less precisely positioned in the rele-
vant octahedron. As for the two CO’s, the two iridium-
oxygen distances are close one to the other, i.e., 2.955 Å for
Ir(1)-O(11) and 2.985 Å for Ir(1)-O(12); the two carbon-
iridium and two carbon-oxygen bond distances, as already
observed in [IrI2(CO)2]-, show the following values:
Ir(1)-C(12) ) 1.852(18) Å, C(12)-O(12) ) 1.127(8) Å;
Ir(1)-C(11) ) 1.913(10) Å, C(11)-O(11) ) 1.042(9) Å.
The hydride ligand has been positioned in its ideal position,
the sixth of the octahedron, and lies at a distance of about
1.6 Å from the iridium atom. Due to the uncertainty in the
position of this hydrogen atom in the final refinements, it
could be safer not to comment further on the Ir-H bond
length, although it would have been interesting to compare
this distance in an anionic mononuclear moiety to other ones
that mainly belong to cationic structures. Indeed, in the three
Ir(III) cationic complexes [IrH(OH)(PMe3)4]+, [IrH(OMe)-
(PMe3)4]+, and [IrH(SH)(PMe3)4]+, the Ir-H distances are
1.71(8), 1.81(8), and 1.64(5) Å, respectively.27 These bond
distances lie in the range 1.5-2.0 Å reported for a mean
iridium-hydride bond length.
than the two CO bands of the precursor 1 (2046 and 1967
cm-1), the difference of 51 cm-1 being consistent with the
two CO ligands being in a mutual cis position.
The corresponding rhodium hydride complex [RhHI3(CO)2]-
was previously reported26 to be stable only below -20 °C
and to undergo disproportionation at room temperature to
provide [RhI4(CO)2]-, [RhI2(CO)2]-, and dihydrogen. The
same disproportionation path has been proposed by Forster5
for the iridium analogue. Relevant NMR data for the rhodium
complex that are worthy of note are -10.45 ppm for the
hydride and 177.9 ppm for the 13CO ligands; infrared data
do only show a CO band at 2080 cm-1, and the Rh-H band
has not been detected. All the shifts of the hydride and the
CO’s observed in NMR spectra point to a more nucleophilic
character of the iridium metal center than that of the rhodium
one.
All of the NMR data obtained (Table 3) are in agree-
ment with those recently reported by Merbach et al.10 for
this complex in solution, pointing to a fac,cis geometry.
FAB-MS spectra in negative mode show the molecular peak
at m/z 631 and two main signals corresponding to the
successive loss of two CO ligands.
[PPN][IrI3(CH3)(CO)2] (3). In accordance with earlier
reports,12a complex 1 reacts quickly with an excess (40 equiv)
of iodomethane to provide [IrI3(CH3)(CO)2]- quantitatively.
This orange compound crystallizes in the space group P21/c
(Z ) 4), the asymmetric unit containing one PPN cation,
the anion [IrI3(CH3)(CO)2]-, and a CH2Cl2 solvent mole-
cule. In the anion there is a disorder between one CO and
the methyl ligands which corresponds to the ratio 0.67:0.33.
The [IrI3(CH3)(CO)2]- moiety shows a fac arrangement
with a pseudooctahedral geometry. The two iridium-iodine
1
In H NMR the hydride resonates at -11.63 ppm (-40
°C) in CD2Cl2. 13C-enriched 2 gives a signal at 155.0 ppm,
but no coupling between the hydrogen nucleus and the two
CO ligands has been observed.
As for IR spectra, the two CO stretching bands appear at
2103(s) and 2052(s) cm-1, i.e. quite at higher frequencies
(27) Milstein, D.; Calabrese, J. C.; Williams, I. D. J. Am. Chem. Soc. 1986,
108, 6387.
5528 Inorganic Chemistry, Vol. 42, No. 18, 2003

Hydrido- and Methyliodocarbonyliridium Complexes
Figure 5. ORTEP drawing of [Ir(µ-I)2I2(CH3)2(CO)4] (4) with the labeling
scheme, the primed atoms being deduced from the first half-molecule
through the inversion center. Ellipsoids are at the 50% probability level.
Figure 4. Kinetic measurements of the formation of 2 or 3 resulting from
the oxidative addition of HI or CH3I to [IrI2(CO)2]- (anion of 1).
bond distances trans to the two CO ligands, which measure
2.7005(4) and 2.7177(4) Å, respectively, are slightly in-
creased (∼0.05-0.06 Å) with respect to the mean value of
2.65 Å observed in [IrI2(CO)2]- . Far more significant is the
lengthening of the Ir(1)-I(2) bond trans to the methyl ligand
since its distance, which can be accounted for by the trans-
influence of the methyl group, is 2.7658(4) Å. The infrared
spectra of [PPN][IrI3(CH3)(CO)2] (3) present two stretching
bands at 2100(s) and 2048(s) cm-1 in CH2Cl2 solutions, the
difference of 52 cm-1 between the two wavenumbers being
consistent with two CO ligands in mutual cis-position.
on heating at 160 °C the same reaction mixture, addition of
CH3I slowly occurs to form 3 at the expense of 2. Thus, the
regeneration of 1 from 2 described by Forster5 might occur
only at relatively high temperatures. It constitutes a very
important step within the mechanism of methanol carbony-
lation, which intervenes prior to the commonly accepted
oxidative addition of CH3I. Moreover, the presence of water
under a CO atmosphere is also a way to restore [IrI2(CO)2]-
from [IrHI3(CO)2]- via the water-gas shift reaction.5
[Ir2(µ-I)2I2(CH3)2(CO)4] (4). Concerning the iridium
mechanism of the catalytic methanol carbonylation, two
cycles are interconnected which involve anionic and neu-
tral intermediate species, respectively. Maitlis et al. have
shown that the cis-migratory insertion of carbon monoxide
into the iridium-methyl bond occurs faster in the neutral
intermediate.28,29 Under the operative conditions of the
Cativa process, one of the main roles of the ruthenium halo
carbonyl complex is to promote the formation of the neutral
species [IrI2(CH3)(CO)3], via iodide abstraction.30 Thus, by
adding InI3 (1 equiv/Ir) as iodide scavenger, we prepared
[Ir2(µ-I)2I2(CH3)2(CO)4] (4) with moderate yields. Extraction
with hot cyclohexane, followed by recrystallization, gave
orange crystals of 4, albeit in poor yields, suitable for X-ray
analysis. This complex crystallizes in the P1h space group
with half of the dinuclear moiety in the asymmetric unit
(Figure 5).
The dimer is centrosymmetric, with two iodide and two
CO ligands in the axial positions and two methyl and two
CO groups in the equatorial terminal ones. The two
octahedrons are completed and bridged by two iodide ligands.
Bond lengths are consistent with those observed for com-
plex 3, except for the distances Ir-I of the bridging iodides,
for which a slight lengthening is observed. In particular, the
Ir(1)-I(3) trans to CO and Ir(1)-I(3′) trans to CH3 bond
distances are 2.7156 (11) and 2.8021 (11) Å, respectively.
It should be mentioned that Haynes et al., in a preliminary
communication, reported the synthesis of 4 performed by
1
In H NMR 3 is characterized by a singlet at 2.15 ppm
(CD2Cl2), and the 13C NMR spectra for [IrI3(CH3)(13CO)2]-
and [IrI3(13CH3)(CO)2]- present a singlet at -15.75 ppm for
the methyl group and a singlet at 156.0 ppm for the carbonyl
group. These values fit those previously reported.21
Competitive Oxidative Addition Reactions of HI and
CH3I on [PPN][IrI2(CO)2]. As previously proposed by
Forster,5 although the complex [IrI3(CH3)(CO)2]- is usually
considered as the resting state in the iridium-catalyzed
carbonylation of methanol, the competitive oxidative addition
of HI is a very fast process that gives a relatively unstable
species, whereas the reaction of CH3I onto [IrI2(CO)2]-
occurs at a relatively slower rate to produce the stable 3
complex.
Even on addition of 40 equiv of CH3I, the reaction rate of
the oxidative addition to 1 is slower than that observed when
using the stoichiometric quantity of HI required to react with
the anion [IrI2(CO)2]-. Experimental evidence concerning a
reaction mixture of HI/CH3I/[IrI2(CO)2]- (1:40:1) clearly
indicates that HI reacts faster than CH3I, the kinetic curve
being superimposed on that of HI alone, the hydride 2 being
the only one detected (Figure 4).
To shed light on these markedly different reaction rates,
we carried out competitive experiments using a reaction
mixture of HI/CH3I/[PPN][IrI2(CO)2] (1:40:1). Infrared moni-
toring of this experiment followed by comparison with the
two independent oxidative additions gave confirmation that
complex 1 reacts quickly and exclusively with HI to provide
2. Even with solutions standing overnight at room temper-
ature, CH3I does not add to form complex 3, and [PPN]-
[IrI4(CO)2] and 2 are the only observed species. However,
(28) Pearson, J. M.; Haynes, A.; Morris, G. E.; Sunley, G. J.; Maitlis, P.
M. J. Chem. Soc., Chem. Commun. 1995, 1045.
(29) Haynes, A.; Pearson, J. M.; Vickers, P. W.; Charmant, J. P. H.; Maitlis,
P. M. Inorg. Chim. Acta 1998, 382.
(30) Whyman, R.; Wright, A. P.; Iggo, J. A.; Heaton, B. T. J. Chem. Soc.,
Dalton Trans. 2002, 771.
Inorganic Chemistry, Vol. 42, No. 18, 2003 5529

Gautron et al.
reacting InI3 with [NBu4][IrI3(CH3)(CO)2] and described its
reactivity with carbon monoxide to provide [IrI2(CH3)-
(CO)3];22 in a note, they indicated that an X-ray structure of
4 was in progress and that the iridium-(bridging) iodide
distances were 2.799 (2) and 2.716 (2) Å with a methyl and
a CO ligand in trans-position, respectively.
different intensities, these three signals might be assigned
to two isomers of the main complex, the structure of which
has been determined.
Conclusion
The oxidative addition of HI to the square-planar complex
[PPN][IrI2(CO)2] is a very fast reaction that affords the
hydrido iodo carbonyl derivative [PPN][IrHI3(CO)2]. The
corresponding methyl complex [PPN][IrI3(CH3)(CO)2] has
been prepared by addition of MeI to the Ir(I) precursor.
Removal of one iodide ligand from the latter complex does
afford the neutral dimeric species [Ir2(µ-I)2I2(CH3)2(CO)4].
All the aforementioned four compounds have been fully
characterized by X-ray diffractometry besides IR and 1H and
13C NMR spectroscopies.
Infrared spectra in CH2Cl2 solutions show two CO bands
at 2120 (vs) and 2074 (vs) cm-1 corresponding to the 2 Au
IR-active modes for the dinuclear complex. Thus, the
positions of these two stretching frequencies relevant to the
centrosymmetric dimer cannot be compared with the two
corresponding CO bands for 3 (A′ and A′′ modes), which
1
are observed at 2100 and 2048 cm-1. In H NMR spectra
the methyl groups give a singlet mainly at 1.96 ppm and
one peak of lower intensity at 1.90 ppm, which could be
assigned to a different isomer of the centrosymmetric
complex 4. In 13C NMR spectra for 13CO-enriched 4, a strong
signal is obtained at 152.5 ppm together with a less intense
one at 150.4 and a third peak of weak intensity at 150.1
ppm. No coupling has been detected between the two
differently positioned cis 13CO ligands. Due to their quite
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0340938
5530 Inorganic Chemistry, Vol. 42, No. 18, 2003