Electron-rich Vaska-type complexes trans-[Ir(CO)Cl(2-Ph2PC 6H4COOMe)2] and trans-[Ir(CO)Cl(2-Ph 2PC6H4OMe)2]: Synthesis, characterisation and reactivity

Article abstract of DOI:10.1002/ejic.201001005

The in-situ-generated dimeric precursor [Ir(CO)₂Cl]₂ reacts with four molar equivalents of the ligands 2-Ph₂PC ₆H₄COOMe (a) and 2-Ph₂PC₆H ₄OMe (b) to afford tetracoord

Full text of DOI:10.1002/ejic.201001005

FULL PAPER
DOI: 10.1002/ejic.201001005
Electron-Rich Vaska-Type Complexes trans-[Ir(CO)Cl(2-Ph2PC6H4COOMe)2]
and trans-[Ir(CO)Cl(2-Ph2PC6H4OMe)2]: Synthesis, Characterisation and
Reactivity
Dipak Kumar Dutta,*[a] Biswajit Deb,[a] Bhaskar Jyoti Sarmah,[a] J. Derek Woollins,[b]
Alexandra M. Z. Slawin,[b] Amy L. Fuller,[b] and Rebecca A. M. Randall[b]
Keywords: Iridium / Phosphanes / Carbonyl ligands / Oxygen / Oxidative addition / Vaska’s complex
The in-situ-generated dimeric precursor [Ir(CO)2Cl]2 reacts
with four molar equivalents of the ligands 2-Ph2PC6H4-
COOMe (a) and 2-Ph2PC6H4OMe (b) to afford tetracoordi-
nated complexes of the type trans-[Ir(CO)ClL2] (1a, 1b),
where L = a and b. The IR spectra of 1a and 1b in CHCl3
solution show the terminal υ(CO) bands at around 1957 and
1959 cm–1, respectively, which are significantly lower in fre-
quency compared to Vaska’s complex, trans-[Ir(CO)Cl-
(PPh3)2] (1965 cm–1) and substantiate the enhanced electron
density at the metal centre. The single-crystal X-ray struc-
ture of 1a indicates iridium–oxygen (ester group) distances
[Ir···O(2) 3.24 Å, Ir···O(5) 3.29 Å] and angle [O(5)···Ir···O(2)
157.25°] suggesting a long-range intramolecular “second-
ary” Ir···O interaction resulting in a pseudo-hexacoordinated
complex. Complex 1b reacts with O2 to generate [Ir(O2)(CO)-
Cl(2-Ph2PC6H4OMe)2] (2b), while 1a remains unreactive.
Complex 2b shows a distorted octahedral structure with per-
oxo O–O linkage (O2–O3 1.47 Å). The kinetic study of the
reaction of 1b and Vaska’s complex towards dioxygen ad-
dition reveals that the rate of dioxygen addition to 1b is about
three times faster than Vaska’s complex. Complexes 1a and
1b undergo oxidative addition with small molecules like
CH3I and I2 to produce IrIII carbonyl species of the type
[Ir(CO)Cl(CH3)IL2] (3a, 3b) and [Ir(CO)ClI2L2] (4a, 4b), where
L = a, b.
and well characterised.[7,8] The factors that influence these
reactions have been the subject of much interesting dis-
cussion which has mainly been concerned with the elec-
tronic properties of the ligands.[9–11] The importance of geo-
metric aspects of the metal environment has also increas-
ingly been recognised as evidenced by several publications
in the last few decades.[9,12,13]
The stereochemical properties of metal complexes de-
pend mainly on the coordinating ligands as evidenced by
the observation that some electronically similar iridium
complexes show considerably different reactivities towards
O2, H2 and other related molecules.[12] The title compounds,
trans-[Ir(CO)Cl(2-Ph2PC6H4COOMe)2] and trans-[Ir(CO)-
Cl(2-Ph2PC6H4OMe)2] in the present study are striking ex-
amples, in which the former complex has been found to be
inert towards molecular oxygen at room temperature, while
the latter is found to be about three times more reactive
than Vaska’s complex in oxygen uptake, although the physi-
cal properties of both complexes closely resemble Vaska’s
complex. As part of our continuing research activity,[11,14]
herein we report the structural and electronic characteristics
of two new Vaska-type iridium complexes of P,O donor li-
gands, (2-Ph2PC6H4COOMe) and (2-Ph2PC6H4OMe), and
their reactivity with small molecules such as O2, CH3I and
I2.
Introduction
Vaska’s complex, trans-[Ir(CO)Cl(PPh3)2], occupies a
central position of pivotal importance in the discovery of
oxidative addition (OA) reactions of transition-metal com-
plexes.[1] The activation of small molecules such as CO,
CH3I, H2, O2, etc., by metal complexes[2] is important and
interesting due to their catalytic reactions; for instance oxi-
dative addition of CH3I is an important step in the rho-
dium-catalysed Monsanto[3] and iridium-based Cativa[4]
process for acetic acid production. Activation of molecular
oxygen by metal complexes has attracted great interest in
recent years producing model oxidation catalysts for chemi-
cal processes in terms of cost, atom economy and the po-
tential for limited by-products.[2f,5] Vaska’s discovery of the
reversible molecular oxygen carrier[6] [Ir(CO)Cl(PPh3)2] is
of great importance, since the 1:1 oxygen adduct [Ir(O2)-
(CO)Cl(PPh3)2] can be recrystallised and is extremely stable
[a] Materials Science Division, Council of Scientific and Industrial
Research, North-East Institute of Science and Technology,
Jorhat 785006, Assam, India
Fax: +91-376-2370011
E-mail: dipakkrdutta@yahoo.com
[b] School of Chemistry, University of St. Andrews,
St. Andrews, KY16 9ST, UK
Eur. J. Inorg. Chem. 2011, 835–841
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
835

D. K. Dutta et al.
FULL PAPER
show characteristic downfield shifts at δ = 29.0 and
19.5 ppm compared to their corresponding free ligands δ =
–3.71 (a) and –16.13 (b) ppm. 13C NMR spectra of 1a show
terminal CO resonance at δ = 181.3 ppm, and the chemical
shifts due to the phenylic and methyl carbon atoms are
found in the range δ = 126.3–135.8 and 51.76 ppm, respec-
tively. Similar to 1a, the 13C NMR spectrum of 1b also exhi-
bits the characteristic resonance of terminal CO at around
δ = 180.1 ppm, and the resonance due to the phenyl and
methyl carbon atoms are found in the range δ = 123.3–138.6
and 55.73 ppm, respectively.
Results and Discussion
Synthesis and Characterisation of 1a and 1b
In situ-generated dimeric precursor [Ir(CO)2Cl]2 reacts
with four molar equivalent of the ligands, L (a, b) by the
cleavage of the chloro-bridge to afford tetracoordinated P-
bonded complexes of the type trans-[Ir(CO)ClL2] (1a, 1b)
(Scheme 1).
The crystal structure of 1a (Figure 1, Tables 2 and 3) re-
veals that the iridium atom lies in an approximately square-
planar environment formed by the two phosphorus donors,
Ir, C (of CO) and Cl atoms. The ester carbonyl oxygen atom
of the two phosphane ligands points towards the iridium
centre from above and below the vacant axial sites of the
Scheme 1. Synthesis of 1a and 1b.
The observed elemental analyses data of the complexes
agree well with their molecular composition. The IR spec-
tra of 1a and 1b in nujol exhibit intense ν(CO) bands at
1940 and 1942 cm–1 respectively, indicating the presence of
terminal carbonyl groups. These νCO bands occur at signif-
icantly lower frequencies than those of the well-known Vas-
ka’s complex, (Table 1) and other related Vaska-type com-
plexes[12] like trans-[{(C6H4-2-CH3)3P}2-Ir(CO)Cl], trans-
[{(C6H4-3-CH3)3P}2Ir(CO)Cl] and trans-[{(C6H4-4-CH3)3-
P}2Ir(CO)Cl]. The low ν(CO) values of 1a and 1b may be
due to the formation of long-range intramolecular Ir···O
secondary interactions by which the ester and ether oxygen
atoms donate electron density to the metal centre, which in
turn donates electron density to the antibonding π* orbital
of CO and consequently lowers the CO bond order. In or-
der to obtain evidence for this intramolecular secondary in-
teraction, the IR spectra of 1a, 1b and Vaska’s complex
were recorded in CHCl3 solution where 1a and 1b exhibited
Figure 1. X-ray crystal structure of 1a. Hydrogen atoms are omitted
for clarity.
Table 2. Summary of X-ray single-crystal data and structure refine-
intense terminal ν(CO) bands at 1957 and 1959 cm–1 respec- ment parameters for 1a and 2b.
tively, both frequencies being significantly lower than that
1a
2b
recorded for Vaska’s complex, 1965 cm–1 (Table 1).
Empirical formula
Crystal colour
Molecular mass
Temperature [K]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C41H34ClIrO5P2
Yellow
896.34
125
monoclinic
P21/n
14.6003 (10)
16.8562 (9)
14.7687 (10)
90
70.483(2)
90
C40H36Cl3IrO5P2
Orange
957.25
Table 1. IR stretching[a] of 1a, 1b and Vaska’s complex, and their
oxidative addition adducts.
125
Electrophiles
–
1a
1b
Vaska’s complex
triclinic
¯
P1
1940[b]
1957
2042
2063
–
1942[b]
1959
2040
2060
2011
1952[b]
1965
2047
2067
2015
9.8000(6)
10.5916(17)
19.381(3)
79.736(15)
79.570(18)
76.321(17)
2
1903.0(3)
1.549
0.71075
3.778
878.0
26.37
7548
0.0685(6956)
0.1952(7548)
CH3I
I2
O2
[a] In CHCl3 solution, unless otherwise stated. [b] In Nujol.
γ [°]
Z
4
The 1H NMR spectrum of 1a shows a characteristic
phenylic multiplet in the region δ = 7.34–8.21 ppm and
methyl singlet at δ = 3.47 ppm. Similar to 1a, 1b also shows
the phenylic multiplet in the range δ = 6.83–7.95 ppm and
methyl singlet at around δ = 3.59 ppm. The appearance of
upfield shifts of CH3 protons compared to free ligands [δ =
3.73 (a) and 3.72 (b) ppm] further substantiate the forma-
tion of Ir···O bonds. 31P{1H} NMR spectra of 1a and 1b
Volume [Å3]
ρcalcd. [gcm–3]
λ [Å]
3529.8(4)
1.687
0.71075
4.005
1776.0
26.37
7013
0.0324 (6663)
0.1265 (7013)
μ [mm–1]
F(000)
θmax. [°]
Reflections collected
R (obsd. data)
wR2 (all data)
836
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 835–841

Electron-Rich Vaska-Type Complexes
1
planar complex. The spectroscopic evidence (FTIR and H Such steric inhibition towards dioxygen addition was also
NMR spectroscopic data) as well as the observed iridium– reported by Vaska and co-workers[6b,12] for the complex
oxygen distances [Ir(1)···O(2) 3.246 Å; Ir(1)···O(5) 3.290 Å] trans-[{(C6H4-2-CH3)3P}2Ir(CO)Cl], in which the steric ef-
(sum of the van der Waals radius of Ir–O ≈ 3.52 Å) indicate fect caused by –CH3 groups was explained with the help of
long-range intramolecular “secondary” Ir···O interactions both molecular models and a single-crystal X-ray structure
leading to a pseudo-hexacoordinated complex. A similar determination.
type of long-range interaction was earlier reported by us[11]
On the other hand, complex 1b was found to be very
for a rhodium complex of the 2-Ph2PC6H4COOMe ligand, reactive towards dioxygen and even more reactive than Vas-
where the Rh···O distances were 3.08 and 3.18 Å. Another ka’s complex. It is interesting to note that the related com-
long-range interaction was earlier reported for a palladium plex trans-[{(C6H4-2-CH3)3P}2Ir(CO)Cl] shows no activity
complex of 2-phenyl phosphanyl anisole, where the Pd···O towards dioxygen[6b,12] although both complexes have sim-
distance was 3.17 Å.[15] Miller and Shaw also indicated a ilar configuration apart from their ortho substituents. In or-
typical long-range interaction for the complex trans-[Ir- der to explain the origin of such completely different behav-
(CO)Cl{PMe2(2-MeOC6H4)}2] in which an Ir···O “second- iours of the title complexes, one should consider a few
ary” bond with the methoxy oxygen was reported.[16]
points which might alter the reactivity of the central metal
atom.[17] For complexes of the same metal, reactivity is in-
creased by strong σ-donor and polarisable ligands. Partial
and total deactivation is caused by strong π-acceptor li-
gands or electronegative ligands or a positive charge on the
complex. In addition to the above electronic factors, steric
effects of the ligand environment also have a profound in-
fluence on the reactivity of the metal centre.[12,17,18] The in-
ertness of 1a towards O2 addition may be caused by the
strong steric influence of ligand a as demonstrated (vide
supra). However, in order to substantiate the significantly
high reactivity of 1b, one should consider the combined ef-
fect of electronic as well as steric factors of the ligand. The
higher electron density of the metal centre influenced by the
OCH3 group of b may enhance the susceptibility of the cen-
tral metal atom towards dioxygen addition. In respect of
the steric effect of b, it is likely that during dioxygen ad-
dition, the Ph2PC6H4-2-OCH3 ligands may rotate and re-
adjust in such a way that the incoming molecules suffer less
steric hindrance. This may be partially substantiated by the
observed Ir···OCH3 spatial distances [O(5)···Ir(1) 3.546 Å,
O(4)···Ir(1) 3.551 Å, C(39)···Ir(1) 4.563 Å, C(20)···Ir(1)
4.409 Å] as obtained from the X-ray crystal structure of 2b
(Figure 2).
Table 3. Selected bond lengths [Å] and bond angles [°] of 1a and 2b.
1a
Bond lengths
P1–Ir1
Cl1–Ir1
C1–O1
Ir1···O5
2.3174(16)
2.3670(13)
0.972(7)
3.29
P2–Ir1
C1–Ir1
Ir1···O2
2.3360(16)
1.903(5)
3.24
Bond angles
P2–Ir1–P1
Ir1–C1–O1
177.13(4)
175.1(5)
C1–Ir1–Cl1
O5···Ir1···O2
172.69(15)
157.25
2b
Bond lengths
P1–Ir1
Cl1–Ir1
C1–O1
O2–Ir1
2.354(3)
2.412(3)
1.134(13)
1.994(8)
P2–Ir1
C1–Ir1
O2–O3
O3–Ir1
2.356(3)
1.883(12)
1.469(12)
2.047(8)
Bond angles
C1–Ir1–O2
O2–Ir1–O3
C1–Ir1–Cl1
O3–O2–Ir1
109.4(4)
42.6(3)
96.9(4)
70.6(5)
C1–Ir1–O3
P1–Ir1–P2
O1–C1–Ir1
O2–O3–Ir1
152.0(4)
172.06(8)
172.8(10)
66.8(5)
Reactivity of 1a and 1b with Molecular Oxygen
An interesting characteristic of square-planar IrI com-
plexes is that they bind O2 reversibly through side-on bond-
ing. However, the stereochemical behaviour of the Ir centre
is affected by the presence of different coordinating ligands.
In the present investigation, complex 1a is found to be unre-
active towards dioxygen, even after prolonged treatment
with O2. The reactivity of 1a was also tested under harsh
conditions, i.e. in the temperature range 50–100 °C and O2
pressure 5–10 bar, in an autoclave using toluene as solvent.
Under these conditions, only 5–8% dioxygen adduct was
detected spectroscopically. The dioxygen adduct was found
to be stable only in solution. The lack of reactivity of 1a
may be due to the steric effect of the ligand 2-
Ph2PC6H4COOMe as revealed by the crystal and molecular
structure of 1a (Figure 1). The two COOCH3 groups, one
from each phosphane, are located near the apical positions
[(Ir(1)···O(2) 3.246 Å; Ir(1)···O(5) 3.290 Å)] of the planar
trans-[Ir(CO)ClP2] unit, which may effectively protect the
Figure 2. X-ray crystal structure of 2b. Hydrogen atoms and uncoor-
central iridium atom from the attacking molecular oxygen. dinated solvent molecules are omitted for clarity.
Eur. J. Inorg. Chem. 2011, 835–841
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
837

D. K. Dutta et al.
FULL PAPER
It is interesting to mention here that attempts to develop
single crystals of 1b in CH2Cl2 or in any other solvent in
air result in the formation of dioxygen adduct [Ir(O2)(CO)-
Cl(2-Ph2PC6H4OMe)2] (2b), which indicates that 1b is very
susceptible to dioxygen addition when it is kept in solution,
however, it is very stable in the solid state for a longer
period. The dioxygen adduct 2b has been characterised by
elemental analysis, IR, NMR and single-crystal X-ray dif-
fraction. The appearance of IR bands at around 2011 and
858 cm–1 indicate the presence of CO and O–O groups,
1
respectively, in the compounds. The H NMR spectrum of
2b shows the chemical shift for the –OCH3 group at around
3.71 ppm which is closer to the –OCH3 shift of the free
ligand [1H NMR (CDCl3): δ = 3.72 (b) ppm] indicating that
the iridium–oxygen secondary interaction disappears after
O2 addition (Figure 3). The single-crystal X-ray structure
of 2b (Tables 2 and 3, Figure 2) reveals that the iridium
atom lies in a distorted octahedral environment formed by
the two phosphorus donors, O–O (peroxo), C (of CO) and
Cl atoms. The O–O [O2–O3 1.469(12) Å] and Ir–O [O2–Ir1
1.994(8) Å, O3–Ir1 2.047(8) Å] bond lengths, and O–Ir–O
[O2–Ir1–O3 42.6(3)°] bond angle in 2b are similar to the
Vaska dioxygen adduct reported by Lebel et al.[8]
Figure 4. Series of UV/Vis spectra illustrating the reaction of 1b with
molecular O2 at 25 °C. The arrows indicate the behaviour of each
band as the reaction progresses.
In order to check the correctness of the experimental rate
constant as obtained from UV/Vis spectroscopy, similar ki-
netic experiments were carried out using FTIR spec-
troscopy by monitoring the changes in the ν(CO) bands
with known concentration of 1b as used in UV/Vis spec-
troscopy. In this experiment, when 1b reacts with O2 in tolu-
ene as solvent at 25 °C, an IR band appears at around
1955 cm–1 which then decays with a new band appearing at
2010 cm–1 which finally replaces the former band. A plot of
ln(A0/At) vs. time indicates a pseudo-first-order reaction in
which the rate constant was found to be almost the same as
Figure 3. 1H NMR spectra of b, 1b and 2b show the significant
chemical shifts of –OCH3 protons.
The rate of reactivities of 1b and Vaska’s complex
towards O2 addition were monitored by both UV/Vis and
IR spectroscopy. Figure 4 shows a typical series of UV/Vis
spectra for the reaction of 1b with O2 at 25 °C, in which the
bands appearing in the visible (λmax = 434.5, 382.5 nm) and
near-visible (λmax = 331.4 nm) region undergo decay until
equilibrium is attained. The appearance of an isosbestic
point close to the peak 331.4 nm indicates that the O2 up-
take reaction is proceeding without forming an intermedi-
ate or multiple products.
An absorbance vs. time plot for the decay of λmax
382.5 nm is shown in Figure 5a. A linear fit of pseudo-first
order was observed for the entire course of the reaction of
O2 with 1b as is evidenced from the plot of ln(A0/At) vs.
time, where A0 and At are the absorbance at time t = 0 and
t, respectively (Figure 5b). From the slope of the plot, the
Figure 5. [a] Kinetic plot for 1b showing the decay of the UV/Vis
band at λmax = 382.5 nm during the reaction of 1b with molecular
O2. [b] Plot of ln(A0/At) vs. time for the reaction of 1b with molecu-
rate constant was calculated and found to be 2.53ϫ10–3 s–1. lar O2 at 25 °C.
838
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 835–841

Electron-Rich Vaska-Type Complexes
that obtained by UV/Vis spectroscopy. The rate of dioxygen towards dioxygen addition revealed that the rate of di-
addition towards Vaska’s complex was also measured by oxygen addition to 1b is about three times faster than for
UV/Vis spectroscopy and the rate constant was found to be Vaska’s complex.
9.1ϫ10–4 s–1, which reveals that the rate of dioxygen ad-
dition in 1b is about three times faster than that of Vaska’s
complex and this enhanced reactivity may be due to the
higher nucleophilicity of the iridium centre in the former.
Experimental Section
General: All operations were carried out under nitrogen. All sol-
vents were distilled under N2 prior to use. IrCl3·xH2O was pur-
chased from M/S Arrora Matthey Ltd., Kolkota.
Reactivity of 1a and 1b with CH3I and I2
Elemental analyses were performed with a Perkin–Elmer 2400 ele-
Complexes 1a and 1b are coordinatively unsaturated and
undergo OA reactions with different electrophiles like CH3I
and I2 to afford six-coordinate IrIII complexes of the type
trans-[Ir(CO)(CH3)ClIL2] (3a, 3b) and trans-[Ir(CO)I2ClL2]
(4a, 4b) (Scheme 2). The IR spectra of all the complexes in
CHCl3 show a single intense terminal ν(CO) absorption in
the range 2040–2063 cm–1 indicating the formation of the
mental analyser. UV/Vis spectra were recorded with a UV/Vis spec-
trophotometer model Shimadzu 1610 PC. IR spectra (4000–
400 cm–1) were recorded in CHCl3 solution and nujol with a Per-
kin–Elmer system 2000 FT-IR spectrophotometer. The 1H, 13C and
31P NMR spectra were recorded in CDCl3 solution with a Jeol
Delta 270 MHz spectrometer at room temperature (r.t.) and chemi-
cal shifts were reported relative to SiMe4 and 85% H3PO3 as in-
ternal and external standards, respectively.
1
oxidised IrIII products. The H NMR spectra of 3a and 3b
Synthesis of the Ligands 2-Ph2PC6H4COOCH3 (a) and 2-
Ph2PC6H4OCH3 (b): The ligands were prepared according to lit-
erature methods.[19]
show a singlet at around δ = 3.09–3.12 ppm for the methyl
proton of the Ir–CH3 group and other characteristic bands
for COOCH3/OCH3 and phenylic protons are obtained in
1
Synthesis of the Starting Complex [Ir(COE)2Cl]2 (COE = cis-cyclo-
octene): The starting complex [Ir(COE)2Cl]2 was prepared by re-
fluxing IrCl3·xH2O and cis-cyclooctene in 2-propanol for about 3 h
under nitrogen.[20]
their respective ranges. The H NMR spectra of 4a and 4b
do not show any major changes in their chemical shifts
compared to the parent complexes (1a, 1b). 31P NMR spec-
tra of each of the complexes 3a, 3b, 4a and 4b exhibit char-
acteristic 31P{1H} NMR resonances in the range δ = 1.5–
4.3 ppm, and the 13C NMR spectra show different charac-
teristic resonances for terminal CO in the range δ = 182.3–
186.4 ppm, methyl carbon atoms in the range δ = 48.3–
58.5 ppm and phenylic carbon atoms in the range δ =
122.5–141.3 ppm.
Synthesis of the Complexes trans-[Ir(CO)Cl(2-Ph2PC6H4COOMe)2]
(1a) and trans-[Ir(CO)Cl(2-Ph2PC6H4OMe)2] (1b): [Ir(COE)2Cl]2
(0.223 mmol, 200 mg) was dissolved in acetonitrile. The solution
was then stirred at r.t. for about 10 min under a nitrogen atmo-
sphere. After that the flow of N2 was stopped and CO gas was
passed to the solution until a clear greenish yellow solution was
obtained. A stoichiometric amount (Ir/ligand = 1:2) of the ligand
[0.897 mmol, 287 mg (a), 262 mg (b)] in DCM was then added to
the solution and the mixture was stirred for about another 30 min.
The solvent was evaporated under vacuum and washed with diethyl
ether. The bright yellow compound thus obtained was recrystallised
from DCM/hexane and stored over silica gel in a desiccator.
Analytical Data for 1a: Yield 90%. IR: ν = 1940 (nujol), 1957
˜
(CHCl3) [ν(CO)], 1721 [ν(COOCH3)] cm–1. 1H NMR (CDCl3): δ =
3.47 (s, 6 H, COOCH3), 7.34–8.21 (m, 28 H, Ph) ppm. 13C NMR
(CDCl3): δ = 51.76 (s, CH3), 126.3–135.8 (m, Ph), 166.98 (s,
COester), 181.3 (s, COt) ppm. 31P NMR (CDCl3): δ = 28.97 (s, 1
P) ppm. C41H34ClIrO5P2 (895.7): calcd. C 54.93, H 3.79; found C
54.78, H 3.71.
Scheme 2. Oxidative addition of different electrophiles towards 1a
and 1b.
1b: Yield 88%. IR (CHCl ): ν = 1942 (nujol), 1959 (CHCl )
˜
3
3
[ν(CO)] cm–1. 1H NMR (CDCl3): δ = 3.59 (s, 6 H, OCH3), 6.83–
7.95 (m, 28 H, Ph) ppm. 13C NMR (CDCl3): δ = 55.8 (s, CH3),
123.3–138.6 (m, Ph), 168.3 (s, C-O Ph), 180.1 (s, CO)t ppm. 31P
NMR (CDCl3): δ = 19.49 (s, 1 P) ppm. C39H34ClIrO3P2 (839.7):
calcd. C 55.73, H 4.05; found C 55.58, H 3.97.
Conclusions
Two new Vaska-type complexes 1a and 1b have been syn-
thesised and characterised, which undergo oxidative ad-
dition with small molecules like CH3I and I2 to produce
IrIII carbonyl species trans-[Ir(CO)(CH3)ClIL2] (3a, 3b) and
trans-[Ir(CO)ClI2L2] (4a, 4b). The X-ray crystal structure of
1a shows long-range “secondary” Ir···O bonding. Complex
1a is found to be inert towards dioxygen addition; on the
other hand, 1b reacts rapidly with O2 to generate 2b. The
Synthesis of trans-[Ir(O2)(CO)ClL2] (2b): Complex 1b (100 mg) was
dissolved in DCM (25 cm3) and the solution was then placed into
a 50 mL beaker. The reaction mixture was stirred at r.t. and air
was passed into the mixture for about 6 h to allow dioxygen uptake.
The solvent was evaporated under vacuum and the orange com-
pound so obtained was recrystallised from hexane/DCM and
stored over silica gel in a desiccator.
However, 1a does not react with molecular oxygen under similar
kinetic study of the reaction of 1b and Vaska’s complex experimental conditions.
Eur. J. Inorg. Chem. 2011, 835–841
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
839

D. K. Dutta et al.
FULL PAPER
Analytical Data for 2b: IR (CHCl ): ν = 2011 [ν(CO)], 858 [ν(O–
made after a regular interval of time by UV/Vis spectroscopy in the
˜
3
O)] cm–1. 1H NMR (CDCl3): δ = 3.71 (s, 6 H, OCH3), 7.03–7.79 region 600–300 nm. After completion of the experiment, absorbance
(m, 28 H, Ph) ppm. 13C NMR (CDCl3): δ = 56.3 (s, CH3), 122.8–
139.3 (m, Ph), 170.3 (s, C-OPh), 180.8 (s, COt) ppm. 31P NMR
(CDCl3): δ = 1.52 (s, 1 P) ppm. C39H34ClIrO5P2 (871.7): calcd. C
53.69, H 3.90; found C 53.50, H 3.89.
vs. time data for the decay of an appropriate wavelength (λmax =
380–390 nm) were analysed offline using OriginPro 7.5 software. The
pseudo-first-order rate constants were determined from the gradient
of the plot of ln(A0/At) vs. time, where A0 is the initial absorbance
and At is the absorbance at time t.
Synthesis of [Ir(CO)(CH3)ClIL2] (3a, 3b) [L = 2-Ph2PC6H4COOMe
(a), 2-Ph2PC6H4OMe (b)]: [Ir(CO)ClL2] (100 mg) was dissolved in
DCM (15 cm3) and to that solution CH3I (6 cm3) was added. The
reaction mixture was then stirred at r.t. for about 10 min. The solu-
tion changed from yellow to orange and the solvent was evaporated
under vacuum. The compound so obtained was washed with diethyl
ether and stored over silica gel in a desiccator.
In order to correlate the results obtained from the UV/Vis spectra,
the kinetic experiment was again carried out with FTIR spec-
troscopy. FTIR spectra (4.0 cm–1 resolution) were scanned in the
ν(CO) region (2200–1600 cm–1) and saved at regular time intervals
using the spectrometer software. Kinetic measurements were made
by following the decay of the ν(CO) bands of the complexes in the
region 1955–1965 cm–1. The pseudo-first-order rate constants were
determined as mentioned above.
3a: IR (CHCl ): ν = 2042 [ν(CO)] cm–1. 1H NMR (CDCl ): δ = 3.12
˜
3
3
(s, 3 H, CH3), 3.63 (s, 6 H, -COOCH3), 7.05–8.16 (m, 28 H,
Ph) ppm. 13C NMR (CDCl3): δ = 48.3, 53.6 (s, CH3), 125.8–138.3
(m, Ph), 165.8 (s, COester), 184.9 (s, COt) ppm. 31P NMR (CDCl3):
δ = 2.6 (s, 1 P) ppm. C42H37ClIIrO5P2 (1037.6): calcd. C 48.56, H
3.57; found C 48.08, H 3.48.
Acknowledgments
The authors are grateful to the Director, North East Institute of
Science and Technology (CSIR) Jorhat 785006, Assam, India, for
his kind permission to publish this work. The Department of Science
and Technology (DST), New Delhi (grant number SR/S1/IC-05/
2006), the Royal Society of Chemistry (RSC), UK and the Council
of Scientific and Industrial Research (CSIR), India (International
Joint Project, 2007/R2-CSIR) are acknowledged for partial financial
grants. B. D. and B. J. S. thank the CSIR, New Delhi, for providing
Senior Research Fellowships.
3b: IR (CHCl ): ν = 2040 [ν(CO)] cm–1. 1H NMR (CDCl ): δ = 3.09
˜
3
3
(s, 3 H, CH3), 3.78 (s, 6 H, -OCH3), 6.97–7.83 (m, 28 H, Ph) ppm.
13C NMR (CDCl3): δ = 49.6, 58.5 (s, CH3), 122.5–139.4 (m, Ph),
171.3 (s, C-OPh), 182.3 (s, COt) ppm. 31P NMR (CDCl3): δ = 1.5 (s,
1 P) ppm. C40H37ClIIrO3P2 (981.6): calcd. C 48.90, H 3.77; found C
48.62, H 3.69.
Synthesis of [Ir(CO)ClI2L2] (4a, 4b): [Ir(CO)ClL2] (100 mg) was dis-
solved in DCM (15 cm3) and to that solution I2 (50 mg) was added.
The reaction mixture was then stirred at r.t. for about 2 h. The sol-
vent was evaporated under vacuum and the brown compound so
obtained was washed with hexane several times and stored over silica
gel in a desiccator.
[1] L. Vaska, Acc. Chem. Res. 1968, 1, 335–344.
[2] a) G. J. Sunley, D. J. Watson, Catal. Today 2000, 58, 293–307;
b) P. R. Ellis, J. M. Pearson, A. Haynes, H. Adams, N. A. Bailey,
P. M. Maitlis, Organometallics 1994, 13, 3215–3226; c) T. R.
Griffin, D. B. Cook, A. Haynes, J. M. Pearson, D. Monti, G. E.
Morris, J. Am. Chem. Soc. 1996, 118, 3029–3030; d) M. Lei, W.
Zhang, Y. Chen, Y. Tang, Organometallics 2010, 29, 543–548; e)
R. D. Adams, B. Captain, L. Zhu, J. Organomet. Chem. 2008,
693, 819–833; f) W. B. Tolman, E. I. Solomon, Inorg. Chem.
2010, 49, 3555–3556; g) W. B. Tolman, Activation of Small Mole-
cules, Wiley-VCH, Weinheim, Germany, 2006; h) A. J. Muller, J.
Conradie, W. Purcell, S. S. Basson, J. A. Venter, South African J.
Chem. 2010, 63, 11–19.
4a: IR (CHCl ): ν = 2063 [ν(CO)] cm–1. 1H NMR (CDCl ): δ = 3.53
˜
3
3
(s, 6 H, COOCH3), 7.21–8.14 (m, 28 H, Ph) ppm. 13C NMR
(CDCl3): δ = 52.3 (s, CH3), 128.5–141.3 (m, Ph), 165.8 (s,
CO)ester, 186.4 (s, COt) ppm. 31P NMR (CDCl3): δ = 4.3 (s, 1
P) ppm. C41H34ClI2IrO5P2 (1149.5): calcd. C 42.80, H 2.96; found
C 42.54, H 2.89.
4b: IR (CHCl ): ν = 2060 [ν(CO)] cm–1. 1H NMR (CDCl ): δ = 3.79
˜
3
3
(s, 6 H, OCH3), 6.93–7.89 (m, 28 H, Ph) ppm. 13C NMR (CDCl3):
δ = 55.9 (s, CH3), 124.2–139.5 (m, Ph), 168.5 (s, C-OPh), 185.9 (s,
COt) ppm. 31P NMR (CDCl3): δ = 3.5 (s, 1 P) ppm. C39H34ClI2-
IrO3P2 (1093.5): calcd. C 42.80, H 3.11; found C 42.35, H 3.03.
[3] a) D. Forster, J. Am. Chem. Soc. 1976, 98, 846–848; b) D. For-
ster, Adv. Organomet. Chem. 1979, 17, 255–267; c) D. Forster,
T. C. Singleton, J. Mol. Catal. 1982, 17, 299–303.
[4] a) G. J. Sunley, D. J. Watson, Catal. Today 2000, 58, 293–307;
b) J. H. Jones, Platinum Met. Rev. 2000, 44, 94–105.
X-ray Structural Analysis: Single crystals of 1a and 2b were grown
by layering a CH2Cl2 solution of 1a and 2b with n-hexane. The inten-
sity data for the compounds were collected with a Rigaku Saturn
CCD using Mo-Kα radiation (λ = 0.71073 Å) at 125 K. The struc-
tures were solved with SHELXS-97 and refined by full-matrix least-
squares on F2 using the SHELXL-97 computer program.[21] Hydro-
gen atoms were idealised by using the riding models.
[5] a) D. B. Williams, W. Kaminsky, J. M. Mayer, K. I. Goldberg,
Chem. Commun. 2008, 4195–4197; b) L. I. Simandi, Dioxygen
Activation and Homogeneous Catalytic Oxidation, Elsevier, New
York, 1991; c) J.-U. Rohde, M. R. Kelley, W.-T. Lee, Inorg.
Chem. 2008, 47, 11461–11463; d) M. Costas, A. Llobet, J. Mol.
Catal. A 1999, 142, 113–124; e) P. A. Shapley, in: Activation and
Functionalization of C–H Bonds (Eds.: K. I. Goldberg, A. S.
Goldman), chapter 22, ACS Symposium Series 885, 2004; f) C.
Limberg, J. H. Telesb, Adv. Synth. Catal. 2001, 343, 447–449; g)
A. Bakac, Inorg. Chem. 2010, 49, 3584–3593.
[6] a) L. Vaska, Science 1963, 140, 809–810; b) L. Vaska, L. S.
Chen, J. Chem. Soc., Chem. Commun. 1971, 1080–1081.
[7] a) Y. B. Lee, W. T. Wong, Chem. Commun. 2007, 3924–3926; b)
L. Vaska, Acc. Chem. Res. 1976, 9, 175–178.
CCDC-737947 (for 1a) and -755360 (for 2b) contain the supplemen-
tary crystallographic data for this paper. These data can be obtained
free of charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Kinetic Experiment: Kinetic experiments of the OA reaction of com-
plexes 1b and Vaska’s complex with dioxygen were carried out using
UV/Vis and FTIR spectroscopy in a solution cell. In order to obtain
the pseudo-first-order condition, a dilute solution of the complexes
(4ϫ10–4 m) was prepared in toluene. 50 cm3 of the stock solution
was placed in a 100 mL beaker and the solution was stirred in an
open atmosphere to allow dioxygen uptake. Measurements were
[8] H. Lebel, C. Ladjel, F. B. Gariepy, F. Schaper, J. Organomet.
Chem. 2008, 693, 2645–2648.
[9] A. Roodt, S. Otto, G. Steyl, Coord. Chem. Rev. 2003, 245, 121–
137.
[10] a) N. F. Stuurman, J. Conradie, J. Organomet. Chem. 2009, 694,
259–268; b) C. E. Johnson, R. Eisenberg, J. Am. Chem. Soc.
840
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 835–841

Electron-Rich Vaska-Type Complexes
1985, 107, 3148–3160; c) X. Li, T. Vogel, C. D. Incarvito, R. H.
Crabtree, Organometallics 2005, 24, 62–76.
[11] D. K. Dutta, J. D. Woollins, A. M. Z. Slawin, D. Konwar, P.
Das, M. Sharma, P. Bhattacharyya, S. M. Aucott, Dalton Trans.
2003, 2674–2679.
[12] R. Brady, W. H. D. Camp, B. R. Flynn, M. L. Schneider, J. D.
Scott, L. Vaska, M. F. Werneke, Inorg. Chem. 1975, 14, 2669–
2675.
Deb, A. L. Fuller, A. M. Z. Slawin, J. D. Woollins, D. K. Dutta,
Inorg. Chim. Acta 2010, 363, 1539–1546; d) B. Deb, P. P. Sar-
mah, D. K. Dutta, Eur. J. Inorg. Chem. 2010, 1710–1716; e) B.
Deb, D. K. Dutta, J. Mol. Catal. A 2010, 326, 21–28.
J. Blin, P. Braunstein, J. Fischer, G. Kickelbick, M. Knorr, X.
Morise, T. Wirth, J. Chem. Soc., Dalton Trans. 1999, 2159–2169.
[15]
[16]
E. M. Miller, B. L. Shaw, J. Chem. Soc., Dalton Trans. 1974,
480–485.
[13] a) S. C. Zinner, C. F. Rentzsch, E. Herdtweck, W. A. Herr-
mann, F. E. Kühn, Dalton Trans. 2009, 7055–7062; b) A. A.
Bowden, J. D. Atwoot, J. Coord. Chem. 1998, 46, 203–209; c) T.
Osswald, H. Ruegger, A. Mezzeti, Chem. Eur. J. 2010, 16, 1388–
1397; d) S. Perez, C. Lopez, R. Bosque, X. Solans, M. F. Bardia,
A. Roig, E. Molins, P. W. N. M. van Leeuwen, G. P. F.
van Strijdonck, Z. Freixa, Organometallics 2008, 27, 4288–4299.
[14] a) D. K. Dutta, J. D. Woollins, A. M. Z. Slawin, D. Konwar, M.
Sharma, P. Bhatacharyya, S. M. Aucott, J. Organomet. Chem.
2006, 691, 1229–1234; b) D. K. Dutta, J. D. Woollins, A. M. Z.
Slawin, A. L. Fuller, B. Deb, P. P. Sarmah, M. G. Pathak, D.
Konwar, J. Mol. Catal. A 2009, 313, 100–106; c) D. Bora, B.
[17]
[18]
J. S. Valentine, Chem. Rev. 1973, 73, 235–245.
B. L. Shaw, R. E. Stainbank, J. Chem. Soc., Dalton Trans. 1972,
223–228.
[19] a) B. M. Trost, D. L. V. Vranken, C. Bingel, J. Am. Chem. Soc.
1992, 114, 9327–9343; b) H. K. Reinius, R. H. Latinen, A. O. I.
Krause, J. T. Puriainen, Catal. Lett. 1999, 60, 65–70.
[20] J. L. Herde, J. C. Lambert, C. V. Senoff, Inorg. Synth. 1974, 15,
18–20.
[21] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
Received: September 20, 2010
Published Online: January 12, 2011
Eur. J. Inorg. Chem. 2011, 835–841
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
841