Photochemical reaction of CpIr(CO)2 with C6F 5X (X = CN, F): Formation of diiridium(II) complexes

Article abstract of DOI:10.1021/om301055h

Visible light irradiation of CpIr(CO)₂ (1) in pentafluorobenzontrile resulted in the formation of the two isomeric diiridium(II) complexes [CpIr(μ-CO)(C₆F₄CN)] ₂ (3) and [CpIr(CO)(C₆F₄CN)]₂ (4), while the analogous reaction of 1 in hexafluorobenzene to give [CpIr(μ-CO)(C₆F₅)]₂ (3a) required UV irradiation. Complex 4 isomerizes to 3 under visible light irradiation. A reaction pathway to 4 involving aromatic nucleophilic substitution has been proposed on the basis of experimental and computational data. The isomerization of 4 to 3 is believed to proceed via a radical species resulting from homolytic fission of the Ir-Ir bond.

Full text of DOI:10.1021/om301055h

Article
pubs.acs.org/Organometallics
Photochemical Reaction of Cp*Ir(CO)2 with C6F5X (X = CN, F):
Formation of Diiridium(II) Complexes
Kar Hang Garvin Mak,† Pek Ke Chan,† Wai Yip Fan,*,† Rakesh Ganguly,‡ and Weng Kee Leong*,‡
†Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543
‡Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
S
* Supporting Information
ABSTRACT: Visible light irradiation of Cp*Ir(CO)2 (1) in pentafluorobenzontrile resulted in the formation of the two
isomeric diiridium(II) complexes [Cp*Ir(μ-CO)(C6F4CN)]2 (3) and [Cp*Ir(CO)(C6F4CN)]2 (4), while the analogous
reaction of 1 in hexafluorobenzene to give [Cp*Ir(μ-CO)(C6F5)]2 (3a) required UV irradiation. Complex 4 isomerizes to 3
under visible light irradiation. A reaction pathway to 4 involving aromatic nucleophilic substitution has been proposed on the
basis of experimental and computational data. The isomerization of 4 to 3 is believed to proceed via a radical species resulting
from homolytic fission of the Ir−Ir bond.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
The reaction of 1 in dry C6F5CN (scrupulously predried or in the
presence of molecular sieves) under irradiation with a tungsten
lamp (or more slowly under ambient light) gave a dark red
suspension. Spectroscopic analysis indicated the presence of one
major product, the diiridium(II) species [Cp*Ir(μ-CO)-
(C6F4CN)]2 (3) and the minor isomer 4; the yield of the latter
could be increased by shortening the reaction time (Scheme 2).
The two isomers decomposed on silica and could not be separated by
fractional crystallization, but fractional crystallization afforded
diffraction-quality crystals of both. In the presence of even
adventitious moisture, complex 2 was obtained quantitatively instead.
In contrast, while 1 reacted with C6F5CN and water under
ambient conditions to yield the metallocarboxylic acid 2, there
was no analogous reaction with C6F6. Complex 1 did react with
C6F6 (10 mg/mL), however, under UV irradiation to give
Cp*Ir(CO)(η2-C6F6) (5) and [Cp*Ir(CO)(C6F5)]2 (3a) in a
5/1 ratio; a similar UV irradiation of 1 in C6F5CN gave an
intractable mixture. Both 3a and 5 have also been characterized
by spectroscopy and by single-crystal X-ray crystallographic
studies (Scheme 3). These products were also unstable on silica
gel. Irradiation of a more dilute solution (4.4 mg/mL) gave only
5, and prolonging the irradiation caused precipitation of a tan
solid which contained a mixture of unidentified products.
Heating the reaction mixture containing 1 and 5 at 80 °C also
Iridium complexes generally have the oxidation states +1 and +3;
Ir(II) complexes are uncommon, and those containing diiridium-
(II) are rarer still. In the reported examples, they are typically
synthesized via oxidative addition of a substrate across the two
iridium centers of a diiridium(I) species, and the resulting
iridium(II) atoms are bridged by a ligand such as acetato, sulfido,
sulfonylamido, or pyrazolato.1−4 To date, there are only five
known examples of diiridium(II) complexes containing no
bridging ligands across the Ir−Ir bond, three of which contain
large chelating ligands that seemingly stabilize the iridium(II)
centers;5−7 the fourth contains a chelating ligand that is
apparently too bulky to bridge the metal centers,8 and the fifth
was synthesized via deprotonation of a bridged cationic dimeric
species (Figure 1).9
Sometime ago, we reported that the reaction of Cp*Ir(CO)2
(1) with pentafluorobenzonitrile in the presence of water gave
the metallocarboxylic acid species Cp*Ir(CO)(COOH)-
(C6F4CN) (2),10 and a reaction pathway based on the
nucleophilicity of 1,11 and the susceptibility of perfluorinated
aromatic rings toward nucleophilic aromatic substitution,12 was
proposed (Scheme 1). Our earlier attempts at trapping the
intermediate A were unsuccessful, which we presumed may be
due to its susceptibility to hydrolysis. Under scrupulously dry
conditions, however, we observed an unusual reaction leading to
the formation of diiridium(II) complexes, which we wish to
report here.
Received: November 6, 2012
Published: February 6, 2013
© 2013 American Chemical Society
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Figure 1. The only five known diiridium(II) complexes without a ligand bridging the Ir−Ir bond.
Scheme 1
Scheme 2
did not result in the formation of 3a. These results suggested that
5 was unlikely to be the precursor to 3a.
The decarbonylation of 1 under UV photoexcitation to form
Cp*Ir(CO) (1*)13 has been well studied in relation to C−H
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Scheme 3
Figure 2. Relative energies of 3 and 4 and their hypothetical isomers 3′ and 4′.
bond activation13−15 and was thus a possible precursor to 3a and
5. However, the fact that the UV−vis spectrum of 1 showed that a
strong absorption band at 297 nm but absorbed poorly in the
350−500 nm (visible) region suggested that 1* was unlikely to
be responsible for the formation of 3 and 4 from C6F5CN. This
difference in reactivity may be attributed to the increased
susceptiblility to nucleophilic attack of C6F5CN in comparison to
C6F6; the latter could only react with the highly reactive 16e
species 1* (to form 5) or a UV-photoexcited 1 having increased
nucleophilicity (to eventually form 3a).16
Conversion of 4 to 3. NMR analyses showed that, with
increasing irradiation time, the amount of unreacted 1 and 4
decreased relative to 3 until only the latter remained, suggesting
that 4 converted irreversibly to 3 upon visible light irradiation.
Synchronous opening of the two bridging carbonyls does not
result in any change of the relative stereochemistry about the two
iridium centers. The conversion of 4 to 3 must therefore involve
cleavage of the Ir−Ir bond. Homolytic cleavage of the Ir−Ir bond
to give the radical species [Cp*Ir(CO)(C6F4CN)]• (C) rather
than a [Cp*Ir(CO)(C6F4CN)]+[Cp*Ir(CO)(C6F4CN)]− ion
pair was supported by the observation that 3 reacted quantitatively
in the presence of visible light with CHCl3 to form Cp*Ir(CO)-
(C6F4CN)(Cl) (6). The reaction failed to proceed in the absence
of visible light irradiation, and a species such as Cp*Ir(CO)-
(C6F4CN)(CHCl2), which may be expected from heterolytic
cleavage of the Ir−Ir bond, was not observed.
The Gibbs free energies for 3 and 4 and for their respective
stereoisomers 3′ and 4′ were computed (Figure 2). Compound 3
was computed to be 29.6 kJ/mol higher in energy than 4 in the
gas phase, but the situation was reversed on solvation; it was
12.3 kJ/mol lower in energy in C6F5CN. This can be rationalized
by the high polarity of 3 (19.6 D) and low polarity of 4 (0.0024 D)
and accounted for the reason 3 was the major product in the
reaction and why it was energetically favored in a polar
environment; irradiation of a solution of 1 in a less polar mixture
of C6F5CN and C6F6 (1/1, v/v) for 24 h gave a 9/1 mixture of 3
and 4. The computed energies suggested that 4 first splits
homolytically into two [Cp*Ir(CO)(C6F4CN)]• radicals, which
would recombine, effectively with rotation of one of them about
the Cp*−Ir axis, to generate 3′ but subsequent bridging of the
Ir−Ir bond by the CO ligands to 3 was favored.
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Scheme 4
Mechanistic Investigations. The most likely reaction
pathway by which 3 and 4 were formed was via reductive
coupling of the acyl fluoride intermediate B with the elimination
of oxalyl fluoride, either directly or via some other
intermediate(s). However, our attempts to detect oxalyl fluoride
or its hydrolysis product, oxalic acid, were unsuccessful. The
reaction of 1 with C6F5CN (and molecular sieves) in the dark
showed ∼90% conversion after 24 h. The IR spectrum did not
contain any absorption peak indicative of a −COF group, nor
was there any resonance at around −53 ppm in the 19F NMR
spectrum, which would have been indicative of a −COF group
attached to an Ir(III) center.17 These ruled out the presence of B,
but the spectroscopic data were assignable to a mixture of two
unknown compounds D and E, in a 5/2 ratio. Variable-
temperature 19F NMR experiments showed no evidence of
exchange between their signals, suggesting that they were
separate species.
Both D and E were converted quantitatively to 6 upon
standing in chloroform over an extended period of time and,
upon visible light irradiation in C6F5CN, completely converted
to 3 after 24 h. Freshly prepared 3 in C6F5CN showed no
reaction upon stirring in complete darkness for 24 h. These
observations indicated that D and E were precursors to 3.
Although we have not been able to assign definitive identities to
them, we propose that they may be zwitterionic Meisenheimer-
type complexes of the formula Cp*Ir(CO)2(CFC5F4CN), from
which loss of a CO and light-activated dissociation of a fluorine
atom would lead to C (Scheme 4). We have studied the
formation of such a complex computationally and found that the
Gibbs free energy for its formation from 1 and C6F5CN was
+83 kJ mol−1.
Crystallographic Discussion. The X-ray crystal structures
of 3, 3a, 4, and 5 have all been determined; the ORTEP plots for
3 and 4 are shown in Figure 3. There are two crystallographically
independent molecules found in the crystals of 3 and 3a; a
common atomic numbering scheme and selected bond
parameters are given in Table 1. The molecular structures of 3
and 3a are essentially the same; the perfluoroaryl rings are
oriented perpendicular to the plane defined by the bridging
carbonyls and are eclipsed and parallel to each other.
Figure 3. ORTEP plots of one of the crystallographically independent
molecules of 3 (top) and 4 (bottom). Thermal ellipsoids are drawn at
the 50% probability level. Hydrogen atoms have been omitted for clarity.
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diiridium(II) complexes containing no bridging ligands; the next
closest is that found in the complex containing tetracyanobisi-
midazole ligands (2.826(2) Å).9
Table 1. Common Atomic Numbering Scheme and Selected
Bond Parameters for 3 and 3a
The ORTEP plot for 5 is shown in Figure 5, together with
selected bond parameters. The molecule has a η2-coordinated
3 (X = CN)
3a (X = F)
a
param
molecule A
molecule B
molecule A
molecule B
Ir(1)−Ir(2)
Ir(1)−C(1)
Ir(1)−C(2)
Ir(2)−C(1)
Ir(2)−C(2)
Ir(1)−C(3)
Ir(2)−C(4)
C(1)−O(1)
C(2)−O(2)
ϕ
2.7655(5)
2.059(14)
2.024(11)
2.024(11)
2.050(10)
2.025(9)
2.050(10)
1.153(12)
1.185(12)
89.0
2.7485(5)
2.049(11)
2.049(11)
2.027(11)
2.017(11)
2.046(14)
2.048(14)
1.159(11)
1.165(11)
89.5
2.7576(8)
2.008(14)
2.034(13)
2.028(14)
2.011(14)
2.094(13)
2.090(15)
1.182(16)
1.175(16)
89.0
2.7583(8)
2.040(14)
2.014(14)
2.001(14)
2.035(13)
2.059(13)
2.078(13)
1.192(16)
1.161(16)
89.7
Figure 5. ORTEP plot showing the molecular structure of 5, with
thermal ellipsoids drawn at the 50% probability level. Hydrogen atoms
have been omitted for clarity. Selected bond distances (Å) and angles
(deg): Ir(1)−C(4) = 1.863(9); Ir(1)−C(1) = 2.071(6); C(4)−O(4) =
1.124(11); F(1)−C(1) = 1.390(6); F(2)−C(2) = 1.340(8); F(3)−
C(3) = 1.351(7); C(1)−C(1A) = 1.465(11); C(1)−C(2) = 1.469(9);
C(2)−C(3) = 1.317(10); C(3)−C(3A) = 1.428(13); C(1)−C(2)−
C(3)−C(3A) = 1.4(6).
a
Bond lengths are given in Å; ϕ is the angle between the C(1)−Ir(1)−
Ir(2)−C(2) and C(3)−Ir(1)−Ir(2)−C(4) planes, given in deg.
The molecule of 4 sits on a crystallographic inversion center,
and the C6F4CN rings are also parallel but trans with respect to
each other across the Ir−Ir bond. Unlike in 3 and 3a, the CO
ligands are in terminal positions. Interestingly, they are also
oriented essentially perpendicular to the plane defined by the
carbonyls and the iridium atoms (ϕ = 87.3°). This mutually trans
arrangement of the ligands is unique; the four known
diiridium(II) complexes containing no bridging ligands that
have been crystallographically studied have their ligands arranged
in a staggered conformation,6−9 and we believe that it can be
traced to the HOMO-2 orbital, which was computed to have
π-type symmetry, thus restricting rotation about the Ir−Ir bond
(Figure 4). The Ir−Ir bond of 4 (2.8442(6) Å) is clearly longer
C6F6 ligand, and the associated bond parameters are similar to
those of three other group 9 complexes containing such a moiety
which have been structurally characterized: viz., CpIr(C2H4)(η2-
C6F6) (5a),18 CpRh(PMe3)(η2-C6F6) (5b),19 and (η5:η1-
C5H5SiMe2CH2PPh2)Rh(η2-C6F6) (5c).20 An almost planar
C6F4 unit is retained; the C(1)−C(2)−C(3)−C(3A) dihedral
angle is only 1.4°, and F(2) and F(3) are bent out of the arene
ring plane by 2.9 and 5.5°, respectively. The coordinated CC
bond (C(1)−C(1A) = 1.465(11) Å) is significantly lengthened
compared to that of free C6F6 (1.394 Å), and the C−C bond
lengths for the rest of the ring resemble those of a free diene, with
a short (C(2)−C(3)), medium (C(3)−C(3A)), short (C(3A)−
C(2A)) pattern, as observed for 5a−c. The fluorine atoms (F(1)
and F(1A)) on the carbon atoms bonded to the Ir atom bend
strongly away from the plane of the aromatic ring; the dihedral
angle between the C6 ring plane and the F(1)−C(1)−C(1A)−
F(1A) plane is 47.0°, similar to that reported for 5a (47.9°) but
larger than those for the Rh complexes (43.8 and 38.0°, for 5b,c,
respectively), and is probably a consequence of the larger size of
Ir compared to Rh. Thus, the C6F6 ligand resembles a
coordinated alkene in geometry.
CONCLUDING REMARKS
■
We have reported here the unusual formation of two isomeric
diiridium(II) complexes 3 and 4 from the visible light irradiation
of Cp*Ir(CO)2 in pentafluorobenzonitrile; the generation of an
analogue from hexafluorobenzene occurred less readily.
Complex 4 is one of the few examples of such a species that
does not contain a bridging ligand across the Ir−Ir bond, and it
appears to be the less stable isomer. The reaction pathway is
believed to proceed via initial nucleophilic attack on the aromatic
Figure 4. Computed molecular structures of 4 (left) and its HOMO-2
(right).
than those in 3 (2.7655(5) and 2.7485(5) Å) and 3a (2.7576(8)
and 2.7583(8) Å). It is also longer than those of the other known
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Anal. Found: C, 40.68; H, 2.79; N, 2.74. Calcd: C, 40.83; H, 2.86; N,
2.65.
Data for 4 are as follows. Yield (spectroscopic): maximum ∼50%. IR
νCO (CH2Cl2): 2051 (vs). 1H NMR: δ 1.49 (s, 30H) ppm. 19F NMR: δ
−34.5 (m, 2F, Fortho), −59.9 (m, 2F, Fmeta) ppm.
In an attempt to detect formation of oxalic acid via IR spectroscopy,
three cycles of freeze−pump−thaw were performed on the crude
reaction mixture at the end of the reaction. The Carius tube was then
exposed to air and left to thaw. After the mixture thawed, volatiles were
removed under reduced pressure, and the residue was extracted with
ether. The ether extract was dried and an IR spectrum was collected
using the KBr pellet method. No oxalic acid was observed.
A similar procedure was employed to monitor the ratio of 3 to 4
under varying irradiation times. After reaction for the designated
number of hours, volatiles were removed under reduced pressure, and
1H and 19F NMR spectra were recorded.
ring followed by generation of an organometallic radical species
C. Although the precise role of irradiation in the reaction remains
unclear, it has a decided role in the isomerization of 4 to 3, which
is believed to proceed via C resulting from homolytic fission of
the Ir−Ir bond. Complex 4, and probably 3 as well, is therefore a
ready precursor for the organometallic radical [Cp*Ir(CO)-
(C6F4CN)]•, and we are in the process of further exploration of
its chemistry.
EXPERIMENTAL SECTION
■
General Procedures. All reactions and manipulations were
performed under argon using standard Schlenk techniques unless stated
otherwise. Visible light irradiation was carried out using a Phillips 60 W
commercial light bulb. UV irradiation was carried out using a 450 W
medium-pressure mercury lamp (peak emission at 254 nm). NMR
spectra were recorded on a JEOL ECA400 or ECA400SL NMR
spectrometer as CDCl3 solutions unless otherwise stated; 1H chemical
shifts reported were referenced against the residual proton signals of
the solvent. 19F chemical shifts reported were referenced against external
trifluoroacetic acid; designations of the F atoms are with respect to the
iridium atom. Electrospray ionization (ESI) mass spectra were obtained
on a Thermo Deca Max (LCMS) mass spectrometer with an ion-trap
mass detector at 15 eV and 40 °C using direct injection of the sample.
Fast atom bombardment (FAB) mass spectra were obtained on a
Finnigan MAT95XL-T spectrometer in a 3NBA matrix (FAB). All
elemental analyses were performed by the microanalytical laboratory at
NUS. Cp*Ir(CO)2 (1)21 and Cp*Ir(CO)(COOH)(C6F4CN) (2)9
were prepared according to their published methods. All other reagents
were from commercial sources and used without further purification.
Computational Studies. The reaction energetics for the reactions
were studied by DFT theory utilizing Becke’s three-parameter hybrid
function22 and Lee, Yang, and Parr’s gradient-corrected correlation
function (B3LYP).23 The LANL2DZ (Los Alamos effective core
potential double-ζ) basis set was employed for all atoms.24 Excited state
calculations were carried out with the TD method using the same basis
set.25 For calculations involving solvated species, the Onsager model was
employed. The dielectric constant for the solvent C6F5CN was
estimated as 21, on the basis of its polarity of 2.4 D in comparison to
that of 2.9 D in acetone, which has a dielectric constant of 20.7.
Harmonic frequencies were calculated at the optimized geometries to
characterize stationary points as equilibrium structures with all real
frequencies and to evaluate zero-point energy (ZPE) corrections. All
calculations were performed using the Gaussian 09 suite of programs.26
Optimization of the structure of the solvated Meisenheimer
zwitterion was first carried out in the gas phase to give a structure in
which the C6F4CN ring was oriented parallel to the Cp* ring. The cavity
radius (a0) of this was used to optimize the zwitterion in the solvated
phase to the structure depicted in Scheme 4. The cavity volume for this
was then calculated and the new value of a0 employed to reoptimize the
structure.
Reaction of 1 with C6F5CN in the Dark. In a Carius tube
containing dried 4 Å molecular sieves (7 pieces) was added 1 (10 mg,
0.026 mmol) and C6F5CN (0.25 mL, 0.383 g, 1.98 mmol). The reaction
vessel containing the yellow solution was wrapped in aluminum foil and
placed inside a wooden box, and the mixture was stirred slowly at room
temperature for 24 h. An orange solution was formed. Volatiles were
1
removed under reduced pressure, and a H NMR spectrum of the
remaining oil showed that D and E were obtained in a 5/2 ratio.
Data for D are as follows. IR νCO (hexane): 2019 cm−1. 1H NMR: δ
1.73 (s) ppm. 19F NMR: δ −29.3 (m, 1F), −40.6 (m, 1F), −60.3 (m,
1F), −60.8 (m, 1F) ppm.
Data for E are as follows. IR νCO (hexane): 2002. 1H NMR: δ 1.76 (s)
ppm. 19F NMR: δ −30.5 (m, 1F), −39.3 (m, 1F), −64.1 (m, 1F) ppm.
Photochemical Reaction of 1 and C6F6. In a quartz Carius tube
containing 1 (20 mg, 0.0522 mmol) was added C6F6 (2 mL). The
mixture was degassed by three cycles of freeze−pump−thaw and then
irradiated for 20 h. An orange-brown solution was formed. Volatiles
were removed under reduced pressure, and the remaining residue was
extracted with cyclohexane (20 mL). The cyclohexane extract was dried
in vacuo to give a brown-yellow oil (26.9 mg). The 1H NMR spectrum of
the oil showed the presence of 5 and 3a (5/1 ratio by integration) and
small amounts of unidentified products. Recrystallization from toluene
and cyclopentane gave a larger proportion of 5 in the supernatant, but
complete separation was not obtained. Prolonged irradiation led to slow
precipitation of a tan solid containing a mixture of unidentified products.
X-ray diffraction quality crystals of 5 and 3a were grown from a
toluene/hexane solution of the mixture at 5 °C.
Data for 3a are as follows. Yield (spectroscopic): ∼15%. IR νCO
(cyclohexane): 1778 (vs). 1H NMR: δ 1.82 (s, 30H) ppm. 19F NMR: δ
−39.0 (m, 2F, Fortho), −85.2 (t, 1F, Fpara), −88.5 (m, 2F, Fmeta) ppm.
FAB-MS+ (m/z): 523 [M/2].
Data for 5 are as follows. Yield (spectroscopic): ∼80%. Yield
1
(isolated): 28%. IR νCO (cyclohexane): 2027 (vs). H NMR: δ 1.89
(s, 15H) ppm. 19F NMR: δ −71.4 (m, 2F, F2 and F2A), −77.9 (m, 2F, F1
and F1A), −97.9 (m, 2F, F3 and F3A) ppm. FAB-MS+ (m/z): 523 [M −
F], 495 [M − F − CO], 356 [M − C6F6]. Anal. Found: C, 39.90; H, 3.13.
Calcd for C17H15F6IrO·1/4C6H12: C, 39.50; H, 3.23.
Synthesis of [Cp*Ir(μ-CO)(C6F4CN)]2 (3 and 4). In a Carius tube
containing dried 4 Å molecular sieves (7 pieces), 1 (25 mg, 0.0653
mmol) and C6F5CN (0.25 mL, 0.383 g, 1.98 mmol) were added. The
yellow solution was irradiated with a tungsten lamp and stirred slowly at
room temperature for 24 h. A red suspension was formed. Volatiles were
removed under reduced pressure, and the remaining red residue was
resuspended in ether (10 mL). After collection of a reddish orange
powder via filtration, it was washed with ether (5 mL) and dried under
reduced pressure to yield spectroscopically pure 3.
When the reaction was only carried out for 4 h, the terminal CO
isomer [Cp*Ir(CO)(C6F4CN)]2 (4) was obtained together with 3 as a
side product. X-ray diffraction quality crystals of 4 were grown from a
dichloromethane/hexane solution of a mixture of 3 and 4 at room
temperature.
Reaction of 3 with Chloroform. In a Carius tube containing 3
(10 mg, 0.0095 mmol) was added CHCl3 (1 mL). The red solution was
irradiated for 12 h under a tungsten lamp, with stirring. A yellow solution
was formed within 4 h. Volatiles were removed under reduced pressure,
and a 1H NMR spectrum showed quantitative conversion to Cp*Ir(CO)-
(C6F4CN)(Cl) (6). The same observations could be made when an
NMR sample of 3 was left in CDCl3 for a few hours. The product could
be purified by TLC with dichloromethane/hexane (2/1, v/v) as the
eluent. When the reaction was performed in the dark, no reaction
occurred.
Data for 6 are as follows. IR νCO (CH2Cl2): 2053 (vs). 1H NMR: δ
1.94 (s, 15H) ppm. 19F NMR: δ −35.1 (s, br, 2F, Fortho), −58.8 (m, 2F,
Fmeta) ppm. FAB-MS+ (m/z): 538 [M − CO + H], 530 [M − Cl]. HR-
FAB: calcd for C18H15F4NO193Ir ([M − Cl]) 530.0714, found 530.0697.
Crystal Structure Determinations. Crystals were mounted on
quartz fibers. X-ray data were collected on a Bruker AXS APEX system,
using Mo Kα radiation, with the SMART suite of programs.27 Data were
Data for 3 are as follows. Yield (spectroscopic): ∼90% to
1
quantitative. IR νCO (CH2Cl2): 1770 (vs). H NMR: δ 1.83 (s, 30H)
ppm. 19F NMR: δ −36.2 (m, 2F, Fortho), −60.9 (m, 2F, Fmeta) ppm. FAB-
MS+ (m/z): 1058 [M], 1030 [M − CO], 530 [M/2], 502 [M/2 − CO].
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processed and corrected for Lorentz and polarization effects with
SAINT28 and for absorption effects with SADABS.29 Structural solution
and refinement were carried out with the SHELXTL suite of
programs.30 The structures were solved by direct methods to locate
the heavy atoms, followed by difference maps for the light, non-
hydrogen atoms. Organic hydrogen atoms were placed in calculated
positions and refined with a riding model. All non-hydrogen atoms were
given anisotropic displacement parameters in the final model. The
crystal of 3a contained a disordered hexane solvate. This was modeled
with two alternative sites of equal occupancies (0.25), with all the carbon
atoms assigned a common isotropic thermal parameter and appropriate
bond restraints applied. The molecule of 5 was located across a
crystallographic mirror plane and exhibited disorder of the Cp* ring
about this plane.
(18) Bell, T. W.; Helliwell, M.; Partridge, M. G.; Perutz, R. N.
Organometallics 1992, 11, 1911.
(19) (a) Belt, S. T.; Duckett, S. B.; Helliwell, M.; Perutz, R. N. J. Chem.
Soc., Chem. Commun. 1989, 928−930. (b) Belt, S. T.; Helliwell, M.;
Jones, W. D.; Partridge, M. G.; Perutz, R. N. J. Am. Chem. Soc. 1993, 115,
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AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
■
This work was supported by an A*STAR grant (Research Grant
No. 012 101 0035). K.H.G.M. thanks the National University of
Singapore for Research Scholarships.
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dx.doi.org/10.1021/om301055h | Organometallics 2013, 32, 1053−1059