Reactions of Cp Ir(CO)2 with pentafluorobenzonitrile: Half-sandwich iridium complexes Cp Ir(CO)(p-C6F4CN)(X)

Article abstract of DOI:10.1016/j.jorganchem.2013.05.038

The reaction of Cp*Ir(CO)₂ (1) with pentafluorobenzontrile in the presence of a base afforded the diaryl complex Cp*Ir(CO)(p-C ₆F₄CN)₂ (4). The reaction proceeds via the metallacarboxylic acid Cp*Ir(CO)(p- C₆F₄CN)(COOH) (2). The latter can be decarboxylated in the presence of a base to the hydrido species Cp*Ir(CO)(p-C₆F₄CN)(H) (5), which can then undergo hydrideechloride exchange to Cp*Ir(CO)(p-C₆F ₄CN)(Cl) (6a). In the presence of air and water, the reaction of 1 with pentafluorobenzontrile afforded a complex formulated as Cp*Ir(CO)(p-C₆F₄CN){C(OH)(NH₂)C ₆F₅} (7a); this is also available from the reaction of 2 with pentafluorobenzamide in the presence of aqueous NaOH.

Full text of DOI:10.1016/j.jorganchem.2013.05.038

Journal of Organometallic Chemistry 741-742 (2013) 176e180
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Reactions of Cp*Ir(CO)2 with pentafluorobenzonitrile: Half-sandwich
iridium complexes Cp*Ir(CO)(p-C6F4CN)(X)
,
b
,
b
Kar Hang Garvin Mak a, Pek Ke Chan a, Wai Yip Fan a , Weng Kee Leong , Yongxin Li
**
*
a Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore
b Division of Chemistry and Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of Cp*Ir(CO)2 (1) with pentafluorobenzontrile in the presence of a base afforded the diaryl
complex Cp*Ir(CO)(p-C6F4CN)2 (4). The reaction proceeds via the metallacarboxylic acid Cp*Ir(CO)(p-
C6F4CN)(COOH) (2). The latter can be decarboxylated in the presence of a base to the hydrido species
Cp*Ir(CO)(p-C6F4CN)(H) (5), which can then undergo hydrideechloride exchange to Cp*Ir(CO)(p-
C6F4CN)(Cl) (6a). In the presence of air and water, the reaction of 1 with pentafluorobenzontrile afforded
a complex formulated as Cp*Ir(CO)(p-C6F4CN){C(OH)(NH2)C6F5} (7a); this is also available from the re-
action of 2 with pentafluorobenzamide in the presence of aqueous NaOH.
Received 20 March 2013
Received in revised form
27 May 2013
Accepted 27 May 2013
Keywords:
Iridium
Pentafluorobenzonitrile
Restricted rotation
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
ORTEP plot, together with selected bond parameters, are given in
Fig. 1. The closest known analogue is Cp*Ir(CO)(C6H5)2, for which
The iridium carbonyl complex Cp*Ir(CO)2 (1) holds a special
place in the development of organometallic chemistry as it was
among the earliest example of an organometallic complex that
could activate, under photochemical conditions, the CeH bond in
alkanes [1]. In our own studies, we had recently reported that it
reacted with pentafluorobenzonitrile, in the presence of water, to
afford the metallocarboxylic acid species Cp*Ir(CO)(p-
C6F4CN)(COOH) (2) [2]. In subsequent attempts at elucidating the
reaction pathway for this, we found that visible light irradiation
under anhydrous conditions led to the formation of two isomeric
the crystal structure has not yet been reported [4]
The possible precursors to 4 included 2 and 3, but the latter was
ruled out on the basis that the formation of 4 did not require visible
light irradiation (but see later). On the other hand, the reaction of 2
with C6F5CN in the presence of aqueous NaOH afforded 4 as the
only iridium-containing product. Decarboxylation of 2 occurred in
the presence of aqueous NaOH to afford the hydrido species
Cp*Ir(CO)(p-C6F4CN)(H) (5) quantitatively. Although leaving a so-
lution of 5 in chloroform to stand eventually gave complete con-
version to Cp*Ir(CO)(p-C6F4CN)(Cl) (6a), it did not react with
C6F5CN. Complex 6a could also be obtained quantitatively from the
reaction of 3 in the presence of visible light with CHCl3; reaction
with CH3I afforded the iodo analogue Cp*Ir(CO)(p-C6F4CN)(I) (6b)
(Scheme 1). The structures of both 6a and 6b have been confirmed
by single crystal X-ray crystallographic studies; the ORTEP plot for
6b, together with selected bond parameters, is given in Fig. 2.
The complexes 2, 5 and 6a also failed to give 3 even in a reducing
environment (zinc powder), indicating that these may also be
excluded as possible precursors to 3. It is therefore plausible that
the formation of 4 proceeded via an anionic intermediate [Cp*Ir(-
CO)(p-C6F4CN)]ꢀ (A) (Scheme 2). Intermediate A is analogous to the
reported anionic complex [Cp*Ir(PMe3)(H)]Li, which has been re-
ported to be active in CeF activation [5].
diiridium(II) complexes [Cp*Ir(m-CO)(p-C6F4CN)]2 (3) and [Cp*Ir(-
CO)(p-C6F4CN)]2 (30) [3]. In the presence of other additives, how-
ever, different Cp*Ir(III)-containing products were obtained. We
wish to report here our findings for these, as well as the related
reactivity of 2 and 3.
2. Results and discussion
Stirring a solution of 1 in C6F5CN in the presence of basic
alumina or NaOH pellets gave quantitative conversion to Cp*Ir(-
CO)(p-C6F4CN)2 (4), which has been completely characterised,
including by a single crystal X-ray crystallographic study; the
We believe that generation of the proposed anionic intermediate
A also accounted for the observation that the reaction of 1 with
C6F5CN in the presence of air yielded a mixture containing a
* Corresponding author. Tel.: þ65 6592 7577.
** Corresponding author.
E-mail address: chmlwk@ntu.edu.sg (W.K. Leong).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.05.038

K.H.G. Mak et al. / Journal of Organometallic Chemistry 741-742 (2013) 176e180
177
Fig. 2. ORTEP plot of 6b showing the atomic numbering scheme, with thermal ellip-
soids drawn at 50% probability level and hydrogen atoms omitted for clarity. Selected
ꢀ
bond lengths (A) and angles (deg): Ir(1)eI(1) ¼ 2.6967(5); Ir(1)eC(11) ¼ 1.891(7);
Ir(1)eC(12)
¼
2.084(6); O(1)eC(11)
¼
1.108(8); C(16)eN(1)
¼
1.122(9); C(15)e
C(16) ¼ 1.441(9); C(12)eIr(1)eI(1) ¼ 91.58(16); C(11)eIr(1)eC(12) ¼ 91.9(2).
Fig. 1. ORTEP plot of 4 showing the atomic numbering scheme, with thermal ellipsoids
The room temperature 19F{1H} NMR spectrum of 6a showed one
small broad signal for the F atoms ortho to the iridium atom and a
sharp multiplet for the meta F’s, while that of 6b showed two broad
signals for the ortho F atoms and one sharp multiplet for the meta F
atoms; these were suggestive of restricted rotation of the C6F4CN
ring. The 19F{1H} NMR spectra of 6a over the temperature 20 ꢁC
to ꢀ60 ꢁC are shown in Fig. 3, and shows that on cooling to 0 ꢁC, the
Fortho signal at ꢀ35.1 ppm collapsed into the baseline and gradually
re-emerged as two sharp signals at ꢀ32.7 and ꢀ37.8 ppm as the
temperature was decreased to below about ꢀ20 ꢁC. Similarly, the
Fmeta signal was also split into two sharp signals, at ꢀ57.7
and ꢀ58.8 ppm, at temperatures below about ꢀ30 ꢁC. Since the
room temperature spectrum of 6b clearly showed two signals for
the ortho F’s, it indicated that the restricted rotation increased with
the size of the halogen ligand on the iridium centre. Restricted
rotation of perfluorinated rings have been studied with C6F5S [7],
(C6F5)3P [8], and the C6F5 ligands [9]
drawn at 50% probability level and hydrogen atoms omitted for clarity. Selected bond
distances [A] and angles [deg]: Ir(1)eC(11), 1.866(4); Ir(1)eC(19), 2.068(3); Ir(1)e
C(12), 2.095(3); C(11)eIr(1)eC(19), 97.24(14); C(11)eIr(1)eC(12), 90.42(15); C(19)e
Ir(1)eC(12), 84.00(12).
ꢀ
species which has been formulated as Cp*Ir(CO)(p-C6F4CN)
[C(OH)(NH2)(C6F5)] (7a) and C6F5CONH2, in w1:1 molar ratio. The
identity of the amide was confirmed by a single crystal X-ray crys-
tallographic study [6], and was likely the result of base catalysed
hydrolysis of C6F5CN; stirring a mixture of C6F5CN with one equiva-
lent of aqueous NaOH gave C6F5CONH2 in w48% yield, but no reac-
tion occurred in the absence of a base.
The species 7a decomposed on silica gel and on standing, and its
formulationwas proposed on the basis of its spectroscopic evidence.
It was also obtained as the major product when freshly prepared 2
was reacted with one equivalent of C6F5CONH2 in the presence of
aqueous NaOH. As hemiaminal groups typically undergo dehydra-
tion to an imine, this may likely be the reason for the precipitation of
unidentified solids upon leaving a solution of 7a to stand. The
involvement of 3 or 5 as intermediates can also be ruled out as we
have found that 5 did not react with C6F5CONH2, and that the for-
mation of 7a did not depend on visible light irradiation. It was thus
likely that under the reaction conditions, the intermediate A that
was formed also acted as a base to generate C6F5CONH2 from
C6F5CN. Consistent with this was the observation that 2 reacted with
PhCONH2 and tBuCONH2 in the presence of aqueous NaOH to afford
the analogues Cp*Ir(CO)(p-C6F4CN)[(C(OH)(NH2)(R))] (R ¼ Ph (b)
and tBu (c)).
Although it has not proven possible to separate the complexes 7
cleanly from the amide and small amounts of 4, their 19F{1H} NMR
spectra also clearly indicated restricted rotation of the C6F4CN ring.
At ambient temperature, only the meta F resonances were visible
but at ꢀ60 ꢁC, for example, that for 7a showed a total of seven
resonances in a 1:1:1:1:2:1:2 integration ratio. On the basis of the
observed coalescence temperatures (Tc) and the differences in fre-
quency of the Fortho resonances in the absence of exchange (dn) [10],
the free energies of activation (
perfluoroarene ring in 6a, 7a and 7b have been estimated (Table 1).
D
Gz) for the restricted rotation of the
O
C
F
F
visible light
Ir
Ir
+ CHCl3 (a)
or CH3I (b)
F
Ir
Cl
C
O
F
F
OC
F
F
F
F
C
N
C
N
C
N
F
F
F
3
6
Scheme 1.

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K.H.G. Mak et al. / Journal of Organometallic Chemistry 741-742 (2013) 176e180
Scheme 2.
The values are consistent with the increased steric bulk of X in the
complexes Cp*Ir(CO)(p-C6F4CN)(X).
NaOH, the diaryl complex Cp*Ir(CO)(p-C6F4CN)2 was formed. In the
absence of the base, the metallacarboxylic acid Cp*Ir(CO)(p-
C6F4CN)(COOH) was obtained, the decarboxylation of which gave
the hydrido species Cp*Ir(CO)(p-C6F4CN)(H), which may undergo
hydrideechloride exchange with halogenated solvents to form the
halide species Cp*Ir(CO)(p-C6F4CN)(X). In the presence of air and
water, the reaction afforded a complex formulated as Cp*Ir(CO)(p-
C6F4CN)[C(OH)(NH2)C6F5] (7a), presumably via hydrolysis of some
of the nitrile to the amide. These reactions presumably proceeded
via the formation of a carbonylate intermediate [Cp*Ir(CO)(p-
C6F4CN)]ꢀ.
3. Conclusion
We have found that the reaction of Cp*Ir(CO)2 with penta-
fluorobenzontrile followed a complex network of pathways that
depended on the conditions used. In the presence of aqueous
4. Experimental section
4.1. 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. NMR spectrawere recorded on a Jeol ECA400 or ECA400SL
NMR spectrometer as CDCl3 solutions; 1H chemical shifts reported
were referenced against the residual proton signals of the solvent.19F
chemical shifts reported were referenced against external trifluoro-
acetic acid; designations of the F atoms are with respect to the
iridium atom. Solution IR spectra were obtained with CH2Cl2 as
solvent on a Bruker ALPHA FTIR spectrometer at a resolution of
2 cmꢀ1 using a solution IR cell with NaCl windows and a pathlength
of 0.1 mm. Electrospray ionization (ESI) mass spectra were obtained
Table 1
Free energy of activation for the eC6F4CN ring restricted rotation.
Compound
Tc of Fortho dn at 213 K (Hz) D )
Gz at Tc (kJ molꢀ1
signals (K)
Cp*Ir(CO)(p-C6F4CN)(Cl), 6a 273
Cp*Ir(CO)(p-C6F4CN)[C(OH) 293
(NH2)(C6F5)], 7a
1915
5451
þ48
þ49
Cp*Ir(CO)(p-C6F4CN)[C(OH) 253
(NH2)(Ph)], 7b
5964
þ42
Fig. 3. Variable temperature 19F NMR spectra of 6a.

K.H.G. Mak et al. / Journal of Organometallic Chemistry 741-742 (2013) 176e180
179
on a Thermo Deca Max (LCMS) mass spectrometer with an ion-trap
mass detector at 15 eV, 40 ꢁC using direct injection of sample. Fast
atom bombardment (FAB) mass spectra were obtained on a Finnigan
MAT95XL-T spectrometer in a 3NBA matrix (FAB). All elemental an-
alyses were performed by the microanalytical laboratory at NUS. The
complexes 1 [11], 2 [2], and 3 [3], were prepared according to the
published methods. All other reagents were from commercial sour-
ces and used without further purification.
(vs) cmꢀ1.1H NMR:
d
2.08 (s,15H, CH3), ꢀ14.72 (s,1H, IreH).19F NMR:
d
ꢀ32.3 (m, 2F, Fortho), ꢀ60.2 (m, 2F, Fmeta).
4.5. Synthesis of Cp*Ir(CO)(C6F4CN)[C(OH)(NH2)C6F5], 7a
To a carius tube containing 2, freshly prepared from 1 (10 mg,
0.0261 mmol), sodium hydroxide pellets (200 mg, 5.00 mmol), ether
(1 ml), C6F5CONH2 (6 mg, 0.0284 mmol) and deionized water
(0.25 ml) were added. Effervescence was observed immediately. The
resulting orange mixture was stirred for 24 h, after which the organic
layer was orange in colour. Volatiles were removed under reduced
pressure to obtain an orange oil. The 1H and 19F NMR spectra showed
the presence of 4 and 7a, in a 1:9 ratio. The presence of 4 was
attributed to incomplete removal of C6F5CN after the synthesis of 2.
Leaving a solution of 7a in CDCl3 to stand resulted in precipitation
and apparent decomposition to unidentified compounds. Repeating
4.2. Reaction of 3 with alkyl halides
To 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)(p-
C6F4CN)(Cl) (6a). The same observations can be made if an NMR
sample of 3 was left in CDCl3 for a few hours. Replacing CHCl3 with
CH3I (1 ml) gave Cp*Ir(CO)(p-C6F4CN)(I) (6b). Both products 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.
t
the procedure with PhCONH2 (3 mg, 0.0248 mmol) or BuCONH2
(3 mg, 0.0297 mmol) in place of C6F5CONH2 yielded 7b or 7c,
respectively, as the major product.
Data for 7a: Yield (spectroscopic) ¼ w90%. nCO: 2054 (vs); nNH
3402 (w), 3686 (w) cmꢀ1. 1H NMR:
4.56 (s, br, 1H, OH),1.96 (s, 15H,
CH3). 19F NMR:
,
:
d
d
ꢀ58.5 (m, 1.5F, Fmeta, C6F4CN), ꢀ66.4 (m, 2F, Fortho
Data for 6a: Yield ¼ quantitative (spectroscopic); 10 mg,
C6F5), ꢀ78.8 (t, 1F, Fpara, C6F5), ꢀ85.6 (m, 2F, Fmeta, C6F5). ESI-MS:
0.018 mmol (94%, isolated). nCO: 2053 (vs) cmꢀ1. 1H NMR:
d 1.94 (s,
ESI: þ741 [M ꢀ H]þ.
15H, CH3). FAB-MS: þ538 [Mꢀ CO þ H], þ530 [Mꢀ Cl]þ. HR-FAB-MS:
calcd for C18H15F4NO193Ir: [M ꢀ Cl]þ: 530.0714, found: 530.0697.
Data for 6b: Yield ¼ quantitative (spectroscopic); 11 mg,
Data for 7b: Yield (spectroscopic) ¼ w90%. 1H NMR:
d 7.68 (m,
3H, C6H5), 7.35 (m, 2H, C6H5), 1.94 (s, 15H, CH3). 19F NMR: 20 ꢁC
d
ꢀ58.7 (m, 2F, Fmeta); ꢀ60 ꢁC: ꢀ32.1 (s, br,1F, Fortho), ꢀ48.0 (s, br,1F,
0.017 mmol (89%, isolated). nCO: 2046 (vs) cmꢀ1. 1H NMR:
d 2.07 (s,
Fortho), ꢀ58.1 (s, br, 2F, Fmeta). ESI-MS: ESI: þ651 [M ꢀ H]þ
15H, CH3). ESI-MS: þ689 [M þ MeOH]þ, þ530 [M ꢀ I]þ. Anal. Calcd
for C18H15F4IIrNO: C, 32.93; H, 2.30; N, 2.13. Found: C, 32.71; H 2.29;
N, 2.00.
Data for 7c: Yield (spectroscopic) ¼ w60%. 1H NMR:
d 1.88 (s,
15H, CH3), 1.13 (s, 9H, Bu). 19F NMR: ꢀ59.2 (m, 2F, Fmeta). ESI-MS:
t
ESI: þ631 [M ꢀ H]þ
4.3. Synthesis of Cp*Ir(CO)(p-C6F4CN)2, 4
4.6. Crystal structure determinations
To a carius tube containing 2, freshly prepared from 1 (10 mg,
0.0261 mmol), C6F5CN (0.25 ml, 0.383 g, 1.98 mmol), sodium hy-
droxide pellets (200 mg, 5.00 mmol), ether (1 ml) and deionized
water (0.25 ml) were added. Effervescence was observed immedi-
ately. The resulting orange mixture was stirred for 24 h, after which
a cream colour paste was obtained. The paste was shaken with
dichloromethane (5 ml) and deionized water (5 ml), after which the
organic layer was filtered through Celite to obtain a pale yellow
solution. Volatiles were removed from the filtrate under reduced
pressure to give pale yellow solids. A 1H NMR spectrum showed
only the presence of 4. A 19F{1H} NMR spectrum showed that a
small amount of C6F5CONH2 was obtained as a side product.
Yield ¼ quantitative (spectroscopic); 15 mg, 0.021 mmol (82%,
Crystals were mounted on quartz fibres. X-ray data were
collected at 103(2) K on a Bruker AXS APEX system, using Mo K
a
radiation, with the SMART suite of programs [12]. Data were pro-
cessed and corrected for Lorentz and polarization effects with
SAINT [13], and for absorption effects with SADABS [14]. Structural
solution and refinement were carried out with the SHELXTL suite of
programs [15]. The structures were solved by direct methods to
locate the heavy atoms, followed by difference maps for the light,
non-hydrogen atoms. There was a disordered CH2Cl2 solvate found
in the crystals of both 6a and 6b. In the former, this was modelled
with five alternative sites with equal occupancies, while in the
latter, it was modelled with two alternative sites with occupancies
summed to unity; appropriate restraints were placed on the bond
and thermal displacement parameters. Organic hydrogen atoms
were placed in calculated positions, and refined with a riding
model. All non-hydrogen atoms were given anisotropic displace-
ment parameters in the final model.
isolated). nCO: 2045 (vs) cmꢀ1 1H NMR: 2.02 (s, 15H, CH3). 19F
. d
NMR:
d
ꢀ33.6 (m, 2F, Fortho), ꢀ59.3 (m, 2F, Fmeta). ESI-MS: þ705
[M þ H]þ. Anal. Calcd for C25H15F8IrN2O: C, 42.68; H, 2.15; N, 3.98.
Found: C, 42.46; H 2.09; N, 3.85.
4.4. Synthesis of Cp*Ir(CO)(p-C6F5CN)(H), 5
Acknowledgements
To a carius tube containing 2, freshly prepared from 1 (10 mg,
0.0261 mmol), sodium hydroxide pellets (200 mg, 5.00 mmol), ether
(1 ml) and deionized water (0.25 ml) were added. Effervescence was
observed immediately. The resulting orange mixture was stirred for
1 h with no colour change. The mixture was extracted with ether
(2 ꢂ 2 ml), after which the organic layer was filtered through Celite
to obtain an orange solution. Volatiles were removed from the
filtrate under reduced pressure to give an orange residue. A 1H NMR
spectrum showed the presence of 5 and 6a. After the solution was
left to stand in CDCl3 for a longer period of time, only 6a could be
observed in the spectrum. Yield (spectroscopic) ¼ w90%. nCO: 2014
This work was supported by Nanyang Technological University
and the Ministry of Education with
a research grant (No.
T208B1111/M45110000) and two of us (K.H.G.M. and P.K.C.) would
like to thank the National University of Singapore for Research
Scholarships.
Appendix A. Supplementary material
CCDC 940727e940729 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of

180
K.H.G. Mak et al. / Journal of Organometallic Chemistry 741-742 (2013) 176e180
[5] T.H. Peterson, J.T. Golden, R.G. Bergman, Organometallics 18 (1999) 2005e
2020.
[6] The X-ray crystal structure has been reported earlier by others:
M. Gdaniec Acta Crystallogr. Sect. E Struct. Rep. Online 59 (2003) o1642e
o1644.
charge from The Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary data
[7] (a) M. Arroyo, C. Mendoza, S. Bernès, H. Torrens, H. Morales-Rojas, Polyhedron
28 (2009) 2625e2634;
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.05.038.
(b) W.A.W. Abu Bakar, J.L. Davidson, W.E. Lindsell, K.J. McCullough,
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(c) J.L. Davidson, J. Chem. Soc. Dalton Trans. (1986) 2423e2431.
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