Reaction of Cp*Ir(CO)2 with activated perfluoroaromatic compounds: Formation of metallocarboxylic acids via aromatic nucleophilic substitution

Article abstract of DOI:10.1021/om701078q

The reaction of Cp*Ir(CO)₂ with activated perfluoroaromatic compounds such as pentafluoropyridine and -benzonitrile afforded the metallocarboxylic acids Cp*Ir(COOH)(L)(CO), L = C ₅F₄N or C₆F₄CN, respe

Full text of DOI:10.1021/om701078q

Organometallics 2008, 27, 1247–1253
1247
Reaction of Cp*Ir(CO)2 with Activated Perfluoroaromatic
Compounds: Formation of Metallocarboxylic Acids via Aromatic
Nucleophilic Substitution
Pek Ke Chan and Weng Kee Leong*
Department of Chemistry, National UniVersity of Singapore, 3 Science DriVe 3, Singapore 117543
ReceiVed October 26, 2007
The reaction of Cp*Ir(CO)2 with activated perfluoroaromatic compounds such as pentafluoropyridine
and -benzonitrile afforded the metallocarboxylic acids Cp*Ir(COOH)(L)(CO), L ) C5F4N or C6F4CN,
respectively. The reaction probably proceeds via aromatic nucleophilic substitution followed by nucleophilic
attack by water at one of the carbonyl ligands.
Cp*Ir(CO)2, 1a, and its related derivatives are known to
undergo photochemical C-H activation with alkanes.7 In an
attempt to study its C-F activation potential, we have examined
the reaction of 1a with neat pentafluorobenzonitrile (C6F5CN).
The reaction proceeded at room temperature to precipitate
Cp*Ir(COOH)(p-C6F4CN)(CO), 2a, as a white solid. In this
paper, we present our study on the reaction of 1a with C6F5CN
and other fluoroaromatic compounds.
Introduction
Activation of the strong C-F bond remains a very important
goal, and several examples of cleavage of C-F bonds in
fluoroaromatics and fluoropyridines by the platinum group
metals are known.1 For group 9 transition metal complexes,
activation of C-F bonds in fluoroaromatics often involves
photolytic or thermal conditions.2 Thus the photolysis of
Cp*Rh(PMe3)(C2H4) in hexafluorobenzene affords Cp*Rh-
(PMe3)(η2-C6F6), which upon further irradiation results in C-F
activation to form Cp*Rh(PMe3)(C6F5)(F).2a Ru, Rh, and Ir
dihydride complexes are also known to activate C-F bonds in
fluoroaromatics.1,3 For Cp*Rh(PMe3)(H)2, a mechanism that
involves initial deprotonation and nucleophilic attack by the
resultant anion [Cp*Rh(PMe3)(H)]- on the fluoroaromatic
compounds was proposed.
Results and Discussion
Reaction of 1a with Fluoroaromatic Compounds. The
reaction of 1a with C6F5CN proceeded at room temperature,
leading to the slow precipitation of 2a as a white powder. The
19F NMR spectrum of the solid crude showed that C-F bond
cleavage of C6F5CN occurred exclusively at the para position.
The reaction is accelerated in the presence of a small amount
of water, to afford 2a in essentially quantitative yield (Scheme
1).
Compound 2a has been completely characterized, including
by a single-crystal X-ray crystallographic study; the ORTEP
plot showing the molecular structure of 2a, together with
selected bond parameters, is given in Figure 1.
For the nickel triad, activation of C5F5N, for example, occurs
predominantly at the 2-position for Ni and at the 4-position for
Pt and Pd. The difference in regiochemistry has been accounted
for with differing mechanisms.4 For nickel complexes, the
observed preference for C-F activation at the 2-position
suggests that the reaction takes place via a three-center transition
state in a concerted oxidative addition reaction. Reaction via a
tight ion pair, or a Meisenheimer intermediate, would result in
activation at the 4-position as observed for platinum5 and
palladium4b complexes, and in nucleophilic substitution by
various transition metal anions.6
The most important structural feature of 2a is probably the
M-COOH moiety. The earliest reported example appears to be
also an iridium species,8 although there have since been a
(6) (a) Kiplinger, J. L.; Richmond, T. G.; Osterberg, C. E. Chem. ReV.
1994, 94, 373–431. (b) Chambers, R. D.; Martin, P. A.; Waterhouse, J. S.;
Williams, D. L. H. J. Fluorine Chem. 1982, 20, 507–514. (c) Bruce, M. I.;
Stone, F. G. A. Angew. Chem., Int. Ed. 1968, 7, 747–753. (d) Booth, B. L.;
Haszeldine, R. N.; Perkins, I. J. Chem. Soc. (A) 1971, 927–929. (e) Booth,
B. L.; Haszeldine, R. N.; Perkins, I. J. Chem. Soc., Dalton Trans. 1975,
1843–1846. (f) Booth, B. L.; Haszeldine, R. N.; Taylor, M. B. J. Chem.
Soc. (A) 1970, 1974–1978.
(1) Torrens, H. Coord. Chem. ReV. 2005, 249, 1957–1985.
(2) (a) Belt, S. T.; Helliwell, M.; Jones, W. D.; Partridge, M. G.; Perutz,
R. N. J. Am. Chem. Soc. 1993, 115, 1429–1440. (b) Selmeczy, A. D.; Jones,
W. D. Organometallics 1994, 13, 52–532. (c) Edelbach, B. L.; Jones, W. D.
J. Am. Chem. Soc. 1997, 119, 7734–7742. (d) Ballhorn, M.; Partridge, M. G.;
Perutz, R. N.; Whittlesey, M. K. Chem. Commun. 1996, 961–966.
(3) Burdeniuc, J.; Jedlicka, B.; Crabtree, R. H. Chem. Ber. 1997, 130,
145–154.
(7) (a) Chan, P. K.; Leong, W. K.; Krummel, K. I.; Garland, M. V.
Eur. J. Inorg. Chem. 2006, 1568–1572. (b) Dunwoody, N.; Sun, S.; Lees,
A. J. Inorg. Chem. 2000, 39, 4442–4451. (c) Lees, A. J. J. Organomet.
Chem. 1998, 554, 1–11. (d) Bromberg, S. E.; Lian, T.; Bergman, R. G.;
Harris, C. B. J. Am. Chem. Soc. 1996, 118, 2069–1072. (e) Bengali, A. A.;
Schultz, R. H.; Moore, C. B.; Bergman, R. G. J. Am. Chem. Soc. 1994,
116, 9585–9589. (f) Buchanan, J. M.; Stryker, J. M.; Bergman, R. G. J. Am.
Chem. Soc. 1986, 108, 1537–1550. (g) Janowicz, A. H.; Periana, R. A.;
Buchanan, J. M.; Kovac, C. A.; Stryker, J. M.; Wax, M. J.; Bergman, R. G.
Pure Appl. Chem. 1984, 56, 13–23. (h) Janowicz, A. H.; Bergman, R. G.
J. Am. Chem. Soc. 1982, 104, 352–354. (i) Hoyano, J. K.; Graham, W. A. G.
J. Am. Chem. Soc. 1982, 104, 3723–3725.
(4) (a) Burling, S.; Elliott, P. I. P.; Jasim, N. A.; Lindup, R. J.; McKenna,
J.; Perutz, R. N.; Archibald, S. J.; Whitwood, A. C. Dalton Trans. 2005,
3686–3695. (b) Jasim, N. A.; Perutz, R. N.; Whitwood, A. C.; Braun, T.;
Izundu, J.; Neumann, B.; Rothfeld, S.; Stammler, H.-G. Organometallics
2004, 23, 6140–6149. (c) Cronin, L.; Higgitt, C. L.; Karch, R.; Perutz, R. N.
Organometallics 1997, 16, 4920–4928. (d) Braun, T.; Perutz, R. N. Chem.
Commun. 2002, 2749–2757. (e) Braun, T.; Perutz, R. N. In Routes to
Fluorinated Organic DeriVatiVes by Nickel Mediated C-F ActiVation of
Heteroaromatics; Screttas,C. G., Steele, B. R., Eds.;PerspectiVes in Orga-
nometallic Chemistry; Royal Society of Chemistry: U. K., 2003; pp 136–
151.
(5) Hintermann, S.; Pregosin, P. S.; Rûegger, H.; Clark, H. C. J.
Organomet. Chem. 1992, 435, 225–234.
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Vol’pin, M. E. IzV. Akad. Nauk SSSR, Ser. Khim. 1972, 2371.
10.1021/om701078q CCC: $40.75
2008 American Chemical Society
Publication on Web 02/09/2008

1248 Organometallics, Vol. 27, No. 6, 2008
Chan and Leong
Scheme 1
number of related examples; these were generally obtained via
attack of a base, such as OH-, on a carbonyl ligand.9 Although
there is no evidence of H-bonding in the solid-state structure
of 2a, the solid-state infrared spectrum, however, shows two
broad νOH bands at 3447 and 2700 cm-1, which suggest that
both the monomeric and dimeric forms exist in the solid. The
latter band is typical of organic carboxylic acids, which exist
Figure 1. Molecular structure of 2a. ORTEP plot with thermal
ellipsoids drawn at the 50% probability level. The hydrogen atoms
have been omitted for clarity. Selected bond distances [Å] and
angles [deg]: Ir(1)-C(1), 2.090(8); Ir(1)-C(7), 2.040(6); Ir(1)-C(31),
1.906(10);C(7)-O(7),1.227(9);C(7)-O(8),1.330(10);C(7)-Ir(1)-C(1),
88.9(3); C(31)-Ir(1)-C(1), 89.8(4) C(31)-Ir(1)-C(7), 86.9(3);
O(7)-C(7)-O(8),118.8(6);O(7)-C(7)-Ir(1),122.9(5);O(8)-C(7)-Ir(1),
118.3(5).
1
as H-bonded dimers in the solid state. The H NMR spectrum
of 2a displayed one signal at δ 1.95 for the methyl protons of
the Cp* ligand and a broad peak at δ 8.45 for the carboxylic
group; the latter was confirmed by its disappearance when D2O
was added to the NMR sample. This signal is typical of a
metallocarboxylic acid (7–11 ppm) and is upfield of that for
organic carboxylic acids (10–13 ppm),9e suggesting that the
iridium center is still relatively electron-rich despite the presence
of an electron-withdrawing perfluorinated ligand.
A similar reaction occurred with some other fluoroaromatic
compounds such as pentafluoropyridine (C5F5N), pentafluo-
robenzaldehyde (C6F5CHO), and 1-fluoro-4-nitrobenzene (p-
FC6H4NO2), to afford the corresponding metallocarboxylic acids
Cp*Ir(COOH)(L)(CO) (where L ) p-C5F4N (2b), p-C6F4CHO
(2c), or p-C5H4NO2 (2d)), although only for 2b was the product
isolated in analytically pure form. The spectroscopic data for
2b confirm that substitution also occurred exclusively at the
para position. Compound 2d was obtained in low yield (7%),
but the site of substitution of the arene at the para position was
suggested on the basis of the absence of resonances in the 19F
NMR spectrum. The reaction with 1,3-C6F4(CN)2 afforded the
hydride species Cp*Ir(H){2,4-C6F4(CN)2}(CO), 4, instead,
presumably via decarboxylation of the initially formed metal-
locarboxylic acid Cp*Ir(COOH){2,4-C6F3(CN)2}(CO). Attempts
at the reaction of 1a with a number of other fluoroaromatics
carrying a substituent less electron-withdrawing than CN, viz.,
C6F5X (where X ) OMe, NH2, H, Cl, F, COOMe, CH2CN,
CF3, in order of increasing electron-withdrawing ability) under
similar conditions failed.
Figure 2. Molecular structure of 3a. ORTEP plot with thermal
ellipsoids drawn at the 50% probability level. The hydrogen atoms
have been omitted for clarity. Selected bond distances [Å] and
angles [deg]: Ir(1)-C(11), 1.873(3); Ir(1)-C(21), 2.068(3);
Ir(1)-C(31), 2.047(3); O(31)-C(31), 1.200(4); O(32)-C(31),
1.369(4); O(32)-C(32), 1.441(4); C(11)-Ir(1)-C(21), 93.41(13);
C(11)-Ir(1)-C(31), 89.09(12); C(31)-Ir(1)-C(21), 88.84(11)
O(31)-C(31)-Ir(1), 126.3(2); O(32)-C(31)-Ir(1), 113.84(19);
O(31)-C(31)-O(32), 119.9(3); C(31)-O(32)-C(32), 117.2(2).
The reaction of 1a with C6F5CN in alcoholic solvents, namely,
methanol or 2-propanol, produced the corresponding esters,
Cp*Ir(COOR)(p-C6F4CN)(CO) (R ) Me (3a); iPr, (3b)). These
esters can also be formed by stirring a solution of 2a in the
respective alcohol. The carbonyl vibration of the ester group
appears at 1661 and 1652 cm-1 for 3a and 3b, respectively,
which is shifted to higher frequencies than that for the carboxylic
acid group in 2a (1630 cm-1), consistent with the expected
increase in carbonyl stretching frequency on going from a
carboxylic acid to an ester. The reaction of 1a with C5F5N in
methanol similarly produced Cp*Ir(COOMe)(p-C5F4N)(CO), 3c.
All three complexes 3a-c were isolated as white powders that
were moderately air-stable in their solid state, but air-sensitive
in solution. Compound 3a has been completely characterized,
including by single-crystal X-ray crystallographic study; the
ORTEP plot showing the molecular structure of 3a, together
with selected bond parameters, are given in Figure 2. The bond
parameters for 3a are very similar to those in 2a.
Mechanistic Studies. As mentioned above, there are two
principal reaction pathways leading from 1a to 2a that can be
considered: (a) oxidative addition into a C-F bond or (b)
nucleophilic aromatic substitution. These alternative pathways
are depicted for C6F5CN in Scheme 2. There are a number of
alternatives to the first intermediate A for the oxidative addition
pathway, including prior CO dissociation followed either by
(9) (a) Pinkes, J. R.; Masi, C. J.; Chiulli, R.; Steffey, B. D.; Cutler,
A. R. Inorg. Chem. 1997, 36, 70–79. (b) Gibson, D. H.; Mehta, J. M.; Ye,
M.; Richardson, J. F.; Mashuta, M. S. Organometallics 1994, 13, 1070–
1072. (c) Mandal, S. K.; Ho, D. M.; Orchin, M. J. Organomet. Chem. 1992,
439, 53–64. (d) Gibson, D. H.; Ong, T. S. J. Am. Chem. Soc. 1987, 109,
7191–7193. (e) Bennett, M. A. J. Mol. Catal. 1987, 41, 1–20. (f) Gibson,
D. H.; Owens, K.; Ong, T. S. J. Am. Chem. Soc. 1984, 106, 1125–1127.
(g) Carlos, F.; Barrientos, P.; Gilchrist, A. B.; Sutton, D. Organometallics
1983, 2, 1265–1266. (h) Sweet, J.; Graham, W. A. G. Organometallics
1982, 1, 982–986. (i) Grice, N.; Kao, S. C.; Pettit, R. J. Am. Chem. Soc.
1979, 101, 1627–1628.

Reaction of Cp*Ir(CO)2 with Perfluoroaromatic Compounds
Organometallics, Vol. 27, No. 6, 2008 1249
Scheme 2
direct insertion into a C-F bond or via formation of an Ir-(η2-
C6F6) intermediate (either with prior CO loss or via a 20-electron
species such as Cp*Ir(CO)2(η2-C6F6), or a ring slippage complex
(η3-Cp*)Ir(CO)2(η2-C6F6)). The resultant intermediate B, which
contains an Ir-F bond, may then undergo hydrolysis to form
an Ir-OH bond followed by CO insertion; the last step has
been reported for Ni, Pt, and Pd complexes,9e,10 Although
complexes such as LRh(PMe3)(C6F5)(F) (where L ) Cp or Cp*)
may be obtained photochemically from the reaction of
LRh(PMe3)(C2H4) with C6F6,2a CO dissociation is not likely to
be so facile at room temperature in the absence of photoacti-
vation. UV irradiation should promote CO dissociation and
hence increase the rate of reaction. However, UV irradiation of
a solution of 1a in C6F5CN did not give 2a but a mixture of
other products, suggesting that the oxidative addition pathway
is unlikely.
Highly fluorinated aromatic compounds are susceptible to
nucleophilic substitution because fluoride is a good leaving
group, and the presence of electron-withdrawing substituent(s)
favors the reaction by stabilizing the negative charge in the
intermediate;11 nucleophilic attack occurs predominantly at the
position para to the functional group present.12 That the reaction
between 1a and C6F5CN or C5F5N is highly regioselective is
therefore consistent with a nucleophilic substitution pathway.
Nucleophilic aromatic substitutions by organic and organome-
tallic nucleophiles are known,6 although the organometallic
nucleophiles employed to date are metal anions. The order of
nucleophilicity has previously been established on the basis of
empirical observations: [Re(CO5)]– ∼ [CpFe(CO)2]– > [CpRu-
(CO)2]– [Mn(CO)4(PPh3)]– > [Mn(CO5)]– > [CpMo(CO)3]– >
[Fe(CO4)]2- > [Co(CO4)]–.6c Strong nucleophiles react with
hexafluorobenzene to afford stable complexes, while weaker
nucleophiles are unreactive. Thus [Mn(CO5)]- has been reported
to react with C6F5CN and C5F5N, but [Co(CO4)]– failed to
react.6f Although neutral transition metal carbonyls have been
known to act as nucleophiles in oxidative addition reactions
with simple alkyl halides,13 to our knowledge this is the first
report on nucleophilic substitution in fluoroarenes by a neutral
transition metal carbonyl.
The effects of different substituents and the position of
substitution were also tested with a number of other ligands,
including 2,3,5,6-tetrafluoropyridine, 2,4,5,6-tetrafluoropyridine,
2,3,5,6-tetrafluoro-4-pyridinecarbonitrile, and 4-fluorobenzoni-
trile, which showed no reaction. The observations may be
summarized as follows: (i) Reaction only proceeded when there
was one or more highly electron-withdrawing substituent(s). For
fluoroarenes containing a substituent less electron-donating than
CN, no reaction occurred at room temperature, while those
carrying a substituent more electron-donating than CN gave
rapid reaction. (ii) The reaction was highly regioselective. When
the para position was not available, substitution at other
positions did not occur even when there were highly electron-
withdrawing substituents. (iii) Reaction occurred only for highly
activated compounds. (iv) The reaction rate was enhanced if
there was a second electron-withdrawing substituent that was
not para to the first substituent. Such high regioselectivity and
substituent dependence is again uncharacteristic of oxidative
addition. For example, the reaction of CpRh(PMe3)(C2H4) with
pentafluoroanisole (p-C6F5OMe) was found to be nonregiose-
lective and occurred under photoirradiation to give two isomeric
η2-arenes.14
Although C6F5CN and C5F5N are different ring systems and
hence the electron-withdrawing ability of the substituents cannot
be compared directly, the reaction of 1a with a 1:1 molar ratio
of C6F5CN and C5F5N at room temperature gave, after 16 h, a
19F NMR spectrum that shows that 2a and 2b were formed in
a 1.4:1 molar ratio, indicating that C6F5CN was more susceptible
to nucleophilic attack compared to C5F5N. As mentioned earlier,
a large number of other fluoroaromatic compounds failed to
react with 1a, while others with more electron-withdrawing
groups than CN afforded mixtures, presumably from further
substitution. Although it may appear surprising that 1a did not
react with octafluorotoluene (C6F5CF3), this is, however,
consistent with an earlier report that the rate of nucleophilic
substitution on C6F5CF3 by ammonia at 80 °C is 42 times slower
than that on C5F5N.6b
(10) Campora, J.; Palma, P.; Rio, D. D.; Alvarez, E. Organometallics
2004, 23, 1652–1655.
There are suggestions from the literature that 1a may be very
nucleophilic. For instance, CpIr(CO)2 is known to act as a two-
electron donor in several iridium-osmium complexes;15 thus the
more electron-donating Cp* should therefore make the iridium
(11) Berdeniuc, J.; Jedlicka, B.; Crabtree, R. H. Chem. Ber. 1997, 130,
145–154.
(12) (a) Reinhold, M.; McGrady, J. E.; Perutz, R. N. J. Am. Chem. Soc.
2004, 126, 5268–5276. (b) Bosque, R.; Clot, E.; Fantacci, S.; Maseras, F.;
Eisenstein, O.; Perutz, R. N.; Renkema, K. B.; Caulton, K. G. J. Am. Chem.
Soc. 1998, 120, 12634–12640.
(13) (a) Hart-Davis, A. J.; Graham, W. A. G. Inorg. Chem. 1970, 9,
2658–2662. (b) Oliver, A. J.; Graham, W. A. G. Inorg. Chem. 1970, 9,
243–247. (c) Hart-Davis, A. J.; Graham, W. A. G. Inorg. Chem. 1971, 10,
1653–1657.
(14) Ballhorn, M.; Partridge, M. G.; Perutz, R. N.; Whittlesey, M. K.
Chem. Commun. 1996, 961–962.
(15) Jiang, F.; Biradha, K.; Leong, W. K.; Pomeroy, R. K.; Zaworotko,
M. J. Can. J. Chem. 1999, 77, 1327–1335.

1250 Organometallics, Vol. 27, No. 6, 2008
Chan and Leong
center more electron-rich and hence nucleophilic. A nucleophilic
iridium center was also proposed recently for the formation of
an Ir(III) metallocarboxylic acid starting from Tp′Ir(CO)2 [Tp′
) hydrotris(pyrazolyl)borate or hydrotris(3,5-dimethylpyra-
zolyl)borate], one proposed mechanism involving initial pro-
tonation of the iridium center by water. The reaction showed a
kinetic isotope effect of kH O/kD O ) 1.4 at 20 °C, indicating
or a nucleophilic attack by fluoride ion may occur to form a
fluoroacyl species such as Cp*Ir(L)(COF)(CO), E, which would
then be expected to undergo hydrolysis of the COF moiety to
COOH.18 In contrast to a number of precedents for the formation
of metallocarboxylic acid via nucleophilic attack of water or
hydroxide ions on cationic metal–carbonyl complexes,9,19 there
is no precedent for a fluoroacyl intermediate. A similar pathway
is proposed for the formation of the iridium alkoxycarbonyls
3a and 3b, and we believe that the transformation from D to 2
or 3 is the rate-determining step. The latter is supported by the
observation that the rate of formation of the acid 2a is faster
than for the methyl ester 3a, followed by the isopropyl ester
3b: the reaction of 1a with C6F5CN in the presence of water to
form 2a took 8 h to complete, while the same reaction in the
presence of methanol or 2-propanol to form their corresponding
esters 3a and 3b gave a 98% and 82% conversion, respectively,
after 22 h of stirring at room temperature; complete conversion
was obtained after approximately 2 days. Similarly, the reaction
2
2
that an O-H or O-D bond cleavage was involved in the rate-
determining step.16 We have also attempted to test the nucleo-
philicity of 1a by its reaction with BF3 · OEt2. Thus we have
found that immediate precipitation of a white solid occurred
when an ether solution of BF3 · OEt2 was added to a solution of
1a in hexane. The white solid was soluble in dcm initially but
decomposed to a yellow insoluble solid upon standing. This
white solid showed two CO stretching vibrations, which were
blue-shifted by ca. 100 cm-1 from that for 1a (νCO 2118 (s),
2078 (s) cm-1 cf. νCO 2009, 1937 cm-1 for 1a), consistent with
formation of an adduct. The 1H NMR spectrum also showed a
downfield shift in the Cp* resonance from δ 2.18 to δ 2.26,
and the 11B NMR spectrum showed a resonance upfield of that
of BF3 · OEt2 by 1.18 ppm, consistent with adduct Cp*Ir-
(CO)2fBF3, 5, formed being a slightly stronger coordination
complex than BF3 · OEt2. The MS (FAB+) showed a low-
intensity cluster of peaks around m/z 451, which corresponded
to the formulation Cp*Ir(CO)2(BF3). In contrast, the rhodium
analogue of 1a, viz., Cp*Rh(CO)2, 1b, failed to react with
C6F5CN. This is consistent with the fact that rhodium, being
above iridium in the same group, should be less electron-rich
and hence less nucleophilic.
i
of 1a with C6F5CN in a 1:1 molar ratio of MeOH to PrOH
under anhydrous condition gave a 7:1 ratio of 3a to 3b (from
19F NMR integration). Thus the rate followed the acidicity of
the nucleophile;20 if the rate-determining step (rds) involved
nucleophilic attack by F-, the reaction time required for all the
alcohols would have been similar.
We attempted to obtain more information on this step by
making a rough measure of the kinetic isotope effect (kH O/
2
kD O); if the rds was a general base-catalyzed attack by H2O,
2
the reaction in H2O would have been expected to be faster than
in D2O. In contrast, an rds involving nucleophilic attack by OH-
would give a kH O/kD O generally close to unity or even the
Nucleophilic aromatic substitution by 1a would lead to a
cationic intermediate D, similar to the reaction of CpIr-
(CO)(PPh3) with alkyl halides (RX) to form the stable ionic
species [CpIr(CO)(PPh3)(R)]+[X]– via a bimolecular mech-
anism.13a We found that the reaction of 1a with C6F5CN at room
temperature, in the presence of molecular sieves to remove
water, gave an off-white precipitate. The IR spectrum of the
crude mixture (taken in C6F5CN) showed only weak IR bands
for 2a, presumably resulting from trace amounts of moisture.
The residue obtained after removal of solvent and other volatiles
was not soluble in C6D6 or CDCl3, but dissolved in methanol
to give 3a, suggesting that it was ionic and may possibly be
the ionic intermediate [Cp*Ir(CO)2(p-C6F4CN)]+[F]–, D. Un-
fortunately, attempts to stabilize this putative intermediate by
salt exchange with AgBF4 were unsuccessful, although the
reaction of 2a with HBF4 yielded a compound that analyzed as
[Cp*Ir(CO)2(C6F4CN)]+[BF4]–, 6. We also attempted to stabilize
the intermediate by reducing the electrophilicity of the remaining
CO ligand toward nucleophilic attack by water or hydroxide
ion via phosphine substitution.16 Thus the reaction of the
phosphine-substituted complex Cp*Ir(CO)(PPh3), 7, with
C6F5CN afforded a brown oil, which still contained a CO (by
IR spectrum) and a phosphine ligand (from the 1H NMR
spectrum). The FAB-MS spectrum showed a molecular ion peak
corresponding to the formulation [Cp*Ir(CO)(PPh3)(C6F4CN)]+,
and the 19F NMR spectrum showed three resonances in a 2:2:1
relative integration ratio; the chemical shift for the fluoride ion
is known to vary over a wide range.17 The data are thus
consistent with the formulation [Cp*Ir(CO)(PPh3)(C6F4-
CN)]+[F]–, 8, suggesting that species such as D can indeed be
formed in the reaction leading to 2a.
2
2
inverse because OD- is a better nucleophile that OH-.21 If the
rds involved nucleophilic attack by F-, no kinetic isotope effect
would be expected. We observed a kinetic isotope effect of ∼1.2
at room temperature. The observed value was thus relatively
small compared to the generally observed value of 2 or above
for general base catalysis,21b,22 although there have been reports
of a kinetic isotope effect much smaller than 2 for reactions
that proceeded via general base catalysis. For example, a kinetic
isotope effect of 1.38 was observed in the transesterification
(ethanolysis) of 2′/3′-O-peptidyl adenosine where the molecule
acted as a general base in its own external peptidyl transfer,
and it was interpreted to suggest significant movement of a
proton toward the base concurrent with the attack of the neutral
ethanol molecule.23 In our case, there may be strong hydrogen
(17) (a) Chambers, R. D.; Gray, W. K.; Sandford, G.; Vaughan, J. F. S.
J. Fluorine Chem. 1999, 94, 213–215. (b) Bassindale, A. R.; Pourny, M.;
Taylor, P. G.; Hursthouse, M. B.; Light, M. E. Angew. Chem., Int. Ed.
2003, 42, 3488–3490. (c) Christe, K. O.; Wilson, W. W.; Wilson, R. D.;
Bau, R.; Feng, J. J. Am. Chem. Soc. 1990, 112, 7619–7625.
(18) (a) Blake, A. J.; Cockman, R. W.; Ebsworth, E. A. V.; Holloway,
J. H. J. Chem. Soc., Chem. Commun. 1988, 529–530. (b) Ebsworth, E. A. V.;
Robertson, N.; Yellowlees, L. J. J. Chem. Soc., Dalton Trans. 1993, 1031–
1037.
(19) (a) Katz, N. E.; Szalda, D. J.; Chou, M. H.; Creutz, C.; Sutin, N.
J. Am. Chem. Soc. 1989, 111, 6591–6601. (b) Catellani, M.; Halpern, J.
Inorg. Chem. 1980, 19, 566–568.
(20) The true rate-determining step is most likely to be that for the
aromatic nucleophilic substitution. However, under the reaction condition
used, the fluoroarene is the solvent and hence is present in large excess.
(21) (a) Slebocka-Tilk, H.; Neverov, A. A.; Brown, R. S. J. Am. Chem.
Soc. 2003, 125, 1851–1858. (b) Bender, M. L.; Pollock, E. J.; Neveu, M. C.
J. Am. Chem. Soc. 1962, 84, 595–599.
The cationic intermediate D may undergo attack by water or
(22) Fife, T. H.; Singh, R.; Bembi, R. J. Org. Chem. 2002, 67, 3179–
3183.
OH– on one of the carbonyl carbons to form the COOH moiety,9
(23) Changalov, M. M.; Ivanova, G. D.; Rangelov, M. A.; Acharya, P.;
Acharya, S.; Minakawa, N.; Foldesi, A.; Stoineva, I. B.; Yomtova, V. M.;
Roussev, C. D.; Matsuda, A.; Chattopadhyaya, J.; Petkov, D. D. Chem-
BioChem 2005, 6, 1–6.
(16) Elliot, O. I. P.; Haslam, C. E.; Spey, S. E.; Haynes, A. Inorg. Chem.
2006, 45, 6269–6275.

Reaction of Cp*Ir(CO)2 with Perfluoroaromatic Compounds
Organometallics, Vol. 27, No. 6, 2008 1251
Scheme 3
Table 1. Crystal and Refinement Data for 2a and 3a
2a
3a
empirical formula
fw
C19H16F4IrNO3
574.53
C20H18F4IrNO3
588.55
temperature
213(2)
223(2)
cryst syst
space group
monoclinic
C2/m
triclinic
P1
j
a, Å
13.3143(8)
8.2139(5)
b, Å
8.8432(6)
9.1750(6)
c, Å
16.7447(10)
14.0581(9)
R, deg
90
73.4480(10)
84.5460(10)
75.8680(10)
984.45(11)
ꢀ, deg
108.601(3)
90
1868.5(2)
γ, deg
volume, Å3
Z
4
2
density calc, Mg m-3
absorp coeff, mm-1
F(000)
2.042
7.204
1096
1.986
6.839
564
cryst size, mm3
θ range for data collection, deg
no. of reflns collected
no. of indep reflns
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole (e Å-3
0.17 × 0.10 × 0.06
2.57 to 30.50
8728
2879 [R(int) ) 0.0358]
0.6718 and 0.3739
2879/0/256
0.42 × 0.32 × 0.24
2.38 to 26.37
15 037
4034 [R(int) ) 0.0231]
0.2906 and 0.1613
4034/0/268
1.076
1.063
R1 ) 0.0346, wR2 ) 0.0719
R1 ) 0.0386, wR2 ) 0.0737
1.800 and -1.355
R1 ) 0.0171, wR2 ) 0.0422
R1 ) 0.0177, wR2 ) 0.0424
1.001 and -0.439
)
bonding and significant H-F bond formation in the transition
state, leading to the small kinetic isotope effect.
Experimental Section
General Procedures. All manipulations of air-sensitive materials
were carried out with rigorous exclusion of oxygen and moisture
in Schlenk-type glassware or Carius tubes on a dual-manifold
Schlenk line under an atmosphere of argon. Solvents were purified,
dried, distilled, and stored under argon prior to use. NMR spectra
The effect of fluoride ions on the rate of reaction was also
studied. Reaction of 1a with C6F5CN in the presence of water
and tetrabutylammonium fluoride (Bu4NF) or tetramethylam-
monium fluoride (Me4NF), which will be reported elsewhere,
resulted in the formation of the decarboxylated product Cp*Ir-
(H)(p-C6F4CN)(CO). However, the reaction of 1a with C6F5CN
in methanol to give 3a proceeded to completion in 8 h in the
presence of 5 equiv of [Me4N]F, but failed to complete even
after 22 h in the absence of [Me4N]F. This result suggested
that the formation of D from 1a and C6F5CN was reversible,
with the equilibrium lying to the left; the addition of F-
promoted the second step (nucleophilic attack on carbonyl
carbon) by partial abstraction of proton from H2O or ROH
(Scheme 3).
1
were measured on a Bruker 300 MHz FT NMR spectrometer. H
chemical shifts were referenced to residual CHCl3 proton signal
(δ 7.26) in CDCl3. 19F chemical shifts were referenced to external
CF3COOH (δ 0.00). Elemental analyses were carried out by the
elemental analysis laboratory in the department. Solvents were
purified, dried over the appropriate drying agents, distilled, and
stored under argon in flasks fitted with Teflon valves prior to use.
Pentafluorobenzonitrile and pentafluoropyridine (Aldrich) were
stored as degassed solutions in Carius tubes and used without further
purification. All other reagents were also purchased commercially
and used as supplied. Compounds 1a and 7 were synthesized by
the literature methods;24,25 the former was purified by column
chromatography (neutral alumina, 50–200 µm, hexane as eluant).
Reaction of 1 with Fluoroarenes and Fluoropyridines in
the Presence of Water. In a typical reaction, to a Carius tube
containing 1a (10 mg, 26 µmol) was added the fluoroarene or
fluoropyridine (0.5 mL) and deionized H2O (0.1 mol). The reaction
mixture was degassed by three cycles of freeze–pump–thaw and
stirred at room temperature. Details on the amount of substrates
used are given in Table S1.
Conclusion
We have reported here that the reaction of 1a with C6F5CN
proceeded with high regioselectivity in the presence of water
or alcohols to produce the metallocarboxylic acid or esters
Cp*Ir(COOR)(p-C6F4CN)(CO), 2 or 3, where the substituent
in the arene ring was in the para position. Similar reactions
with perfluoroarenes carrying one or more highly electron-
withdrawing groups and with pentafluoropyridine also yielded
para-substituted products. Experimental evidence suggested that
the formation of 2 or 3 occurred via aromatic nucleophilic
substitution by 1a on the fluoroarene followed by nucleophilic
attack by water or alcohol, probably via a general base-catalyzed
route, on one of the carbonyl ligands to form the carboxylic
group.
With Pentafluorobenzonitrile, C6F5CN. Cp*Ir(CO)(COOH)(p-
C6F4CN), 2a, precipitated out of solution as a white solid. The
(24) Ball, R. G.; Graham, W. A. G.; Heinekey, D. M.; Hoyano, J. K.;
McMaster, A. D.; Mattson, B. M.; Michel, S. T. Inorg. Chem. 1990, 29,
2023–2025.
(25) Wang, D.; Angelici, R. J. Inorg. Chem. 1996, 35, 1321–1331.

1252 Organometallics, Vol. 27, No. 6, 2008
Chan and Leong
mixture was filtered via a cannula, and the solvent was removed
from the supernatant under reduced pressure. Additional product
was recovered from the supernatant by addition of a hexane-
dichloromethane solution followed by slow evaporation. Combined
yield: 76.6 mg (99%). X-ray diffraction quality crystals of 2a were
obtained by slow evaporation from a C6F5CN solution. IR (KBr):
Reaction of 1 with C6F5CN in Methanol. To a Carius tube
containing 1a (19.1 mg, 49.8 µmol) was added methanol (1.0 mL)
and C6F5CN (0.5 mL). The resultant mixture was degassed by three
cycles of freeze–pump–thaw and left to stand at room temperature
for 2 days. The volatiles were removed under reduced pressure,
and the residual solid was recrystallized from methanol to give white
crystals of Cp*Ir(COOCH3)(p-C6F4CN)(CO), 3a. Yield: 27.4 mg
(93%). X-ray diffraction quality crystals of 3a were grown from a
concentrated methanol solution at 5 °C.
A similar procedure was followed for a reaction using 1a (19.5
mg, 50.9 µmol) with 2-propanol (1.0 mL) and C6F5CN (0.5 mL)
to afford white crystals of Cp*Ir(COOiPr)(p-C6F4CN)(CO), 3b.
Yield: 20.5 mg (65%).
A similar reaction using 1a (19.6 mg, 51.1 µmol) in methanol
(1.0 mL) and C5F5N (0.5 mL) afforded unreacted 1a (0.9 mg, 5%),
which was recovered by washing the residue with hexane and a
white crystalline solid of Cp*Ir(COOCH3)(p-C5F4N)(CO), 3c, by
recrystallization of the residue from methanol. Yield: 25.7 mg
(89%).
νOH 3447 (br), 2700 (br, w), νCN 2237 (w), νCO 2036 (s), 1624 (m)
cm-1. 1H NMR (CDCl3): δ 8.45 (brs, 1H, IrCOOH), 1.96 (s, 15H,
Cp*CH3). 19F NMR (CDCl3): δ -34.27 (m, 2F, Fmeta), -59.17 (m,
2F, Fortho). MS FAB+ (m/z): 576 [M + H]+, 558 [M - OH]+, 530
[M - OH - CO]+, 502 [M - OH - 2CO]+. Anal. Calcd for
C19H16F4NO3Ir: C, 39.72; H, 2.81; F, 13.23; N, 2.44. Found: C,
39.84; H, 2.60; F, 13.20; N, 2.68. HR-MS FAB+ (m/z): calcd for
C19H17F4NO3Ir [M + H]+ 576.0774, found 576.0757.
With Pentafluoropyridine, C5F4N. Cp*Ir(COOH)(p-C5F4N)-
(CO), 2b, precipitated out of solution as a white solid. The mixture
was filtered through a cannula, the solvent removed under reduced
pressure, and the residue washed with hexane (3 × 1 mL) to remove
unreacted 1a (7.9 mg, 35%). Combined yield of 2b: 19.4 mg (59%).
IR (KBr): νOH 3448 (br), 2705 (br, w), νCO 2040 (s), 1628 (m)
3a: IR (KBr): νCN 2236 (w), νCO 2038 (s), 1650 (m) cm-1. IR
(dcm): νCN 2239 (w), νCO 2041, 1659 (s) cm-1. 1H NMR (CDCl3):
δ 3.44 (s, 3H, OCH3), 1.95 (s, 15H, Cp*CH3). 1H NMR (CH2Cl2):
δ 3.36 (s, 3H, OCH3), 1.91 (s, 15H, Cp*CH3). 19F NMR (CDCl3):
δ -35.07 (m, 2F, Fmeta), -59.35 (m, 2F, Fortho). 19F NMR (CH2Cl2):
δ -36.32 (m, 2F, Fmeta), -62.53 (m, 2F, Fortho). Anal. Calcd for
C20H19F4NO3Ir: C, 40.81; H, 3.08; N, 2.38. Found: C, 41.29; H,
3.22; N, 2.19. MS FAB+ (m/z): 590 [M + H]+, 558 [M -
(OCH3)]+, 530 [M - (OCH3) - (CO)]+. HR-MS FAB+ (m/z):
calcd for C20H19F4NO3Ir [M + H]+ 590.0930, found 590.0926.
cm-1 1H NMR (CDCl3): δ 1.98 (s, 15H, Cp*CH3). 19F NMR
.
(CDCl3): δ -20.60 (m, 2F, Fmeta), -42.88 (m, 2F, Fortho). MS FAB+
(m/z): 552 [M + H]+, 534 [M - OH]+, 506 [M - OH - CO]+,
478 [M - OH - 2CO]+. Anal. Calcd for C17H16F4NO3Ir: C, 37.09;
H, 2.93; F, 13.80; N, 2.54. Found: C, 37.20; H, 2.83; F, 13.62; N,
2.82. HR-MS FAB+ (m/z): calcd for C17H17F4NO3Ir [M + H]+
552.0774, found 552.0777.
With 2,3,4,5,6-Pentafluorobenzaldehyde, C6F5CHO. The reac-
tion mixture turned from yellow to pale brown. Removal of volatiles
under reduced pressure yielded a brown oil, which contained
Cp*Ir(COOH)(C6F4CHO)(CO), 2c, as the major product and a
mixture of unknown compounds in minor quantities. IR (dcm): νCO
2046 (s), 1719 (m), 1700 (m), 1652 (s), 1627 (m) cm-1. 1H NMR
(CDCl3): 10.27 (s, 1H, CHO), 1.98 (s, 15H, Cp*CH3). 19F NMR
(CDCl3): δ -37.16 (m, 2F, Fmeta), -71.13 (m, 2F, Fortho). MS FAB+
(m/z): 561 [M - (OH)]+, 533 [M - (COOH)]+, 505 [M - (COOH)
- (CO)]+. HR-MS FAB+ (m/z): calcd for C19H16O3F4193Ir [M -
(OH)]+ 561.0683, found 561.066.
1
3b: IR (dcm): νCN 2238 (w), νCO 2040 (s), 1652 (m). H NMR
(CDCl3): δ 5.02 {sep, 3JHH ) 6.2, 1H, OCH(CH3)2} 1.95 (s, 15H,
Cp*CH3), 1.05, 0.95 (dd, 6H, OCH(CH3)2. 19F NMR (CDCl3): δ
-34.58 (m, 2F, Fmeta), -59.81 (m, 2F, Fortho). Anal. Calcd for
C22H22F4NO3Ir · ½IPA: C, 43.65; H, 4.05; N, 2.17. Found: C, 43.81;
H, 3.87; N, 2.30. MS FAB+ (m/z): 618 [M + H]+, 558 [M -
(OC3H7)]+, 530 [M - (COOC3H7)]+, 502 [M - (COOC3H7) -
(CO)]+. HR-MS FAB+ (m/z): calcd for C22H23F4NO3Ir [M + H]+
618.1244, found 618.1255.
1
3c: IR (dcm): νCN 2236 (w), νCO 2042 (s), 1661(m) cm-1. H
With 1-Fluoro-4-nitrobenzene, p-FC6H4(NO2). The reaction
mixture turned slightly brown. Removal of volatiles under reduced
pressure gave yellow solids. The integration ratio of the methyl
resonance of the Cp* ligand in Cp*Ir(COOH)(p-C5H4NO2)(CO),
2d, to 1a in the 1H NMR spectrum was 1:14 (7% conversion). 1H
NMR (CDCl3): 1.94 (s, 15H, Cp*CH3) and other small peaks.
With Tetrafluoroisophthalonitrile 1,3-C6F4(CN)2. To a Carius
tube containing 1a (10.0 mg, 26.1 µmol) and 1,3-C6F4(CN)2 (7.0
mg, 35.0 µmol) was added C6D6 (1 mL) and deionized H2O (0.1
mL). The reaction mixture was degassed by three cycles of
freeze–pump–thaw, sonicated, and stirred for 40 h at room
temperature. Half the solution was syringed into an NMR tube
containing 1,3,5-triphenylbenzene (6.0 mg, 19.5 µmol) as internal
standard. NMR yield of Cp*Ir(H){2,4-C6F4(CN)2}(CO), 4, was
92%. IR (dcm): νCN 2252, 2242(w), νCO 2052 (s) cm-1. 1H NMR
(C6D6): 1.53 (s, 15H, Cp*CH3), -14.39 (s, 1H, Ir-H). 19F NMR
NMR (CDCl3): δ 3.45 (s, 3H, OCH3), 1.96 (s, 15H, Cp*CH3). 19
F
NMR (CDCl3): δ -20.88 (m, 2F, Fmeta), -43.64 (m, 2F, Fortho).
Anal. Calcd for C18H18F4NO3Ir: C, 38.29; H,3.21; 2.48. Found: C,
38.54; H, 3.33; N, 2.43. MS FAB+ (m/z): 566 [M + H] +, 534 [M
- (OCH3)]+, 506 [M - (OCH3) - (CO)]+. HR-MS FAB+ (m/z):
calcd for C18H19F4NO3Ir [M + H]+ 566.0925, found 566.0936.
Formation of 3a from 2a. Complex 2a (5.0 mg, 13.0 µmol)
was dissolved in methanol and stirred at room temperature for 16 h.
1
The H NMR spectrum showed partial conversion to 3a (82%).
Continued stirring of the solution at room temperature for 3 days
did not increase the amount of 3a.
Reaction of 1a with BF3 · OEt2. To a dcm solution (2 mL) of
1a (10.0 mg, 26.1 µmol) was added BF3 · OEt2 dropwise until the
solution turned colorless. Attempts to crystallize out the product
from dcm/cyclopentane or dcm/hexane solutions were unsuccessful.
The solution slowly turned yellow upon standing. A similar reaction
using a hexane solution (2 mL) of 1a (10.0 mg, 26.1 µmol) resulted
in the formation of a fine white precipitate. The solid was soluble
in dcm and slowly turned into an insoluble yellow solid upon
standing.
An NMR scale reaction was carried out as follows: Complex 1a
(7.0 mg, 18.3 µmol) was dissolved in CDCl3 (0.4 mL) in an NMR
tube fitted with a rubber septum. BF3OEt2 (0.1 mL, 8.1 µmol
withdrawn from a 10 µg/mL BF3OEt2 solution in CDCl3) was added
immediately prior to NMR analysis. An IR spectrum taken after
3
3
(C6D6): δ -28.72 (d, JFF ) 14.4, 1F, 3-F), -31.65 (dd, JFF
)
15.5, 2JFF ) 26.8, 1F, 5-F), -48.68 (d, 3JFF ) 28.9, 1F, 6-F). MS
FAB- (m/z): 537 [M - H].
Competitive Reaction in C6F5CN/C5F5N. To a Carius tube
containing 1a (5.4 mg, 14.1 µmol) was added C5F5N (0.250 mL),
C6F5CN (0.274 mL) (1:1 molar ratio), and deionized H2O (0.2 mL).
The reaction mixture was degassed by three cycles of freez-
e–pump–thaw and stirred at room temperature for 16 h. The
1
volatiles were removed under reduced pressure, and the H NMR
spectrum of the residue was taken in CDCl3. The integration ratio
of the fluorine resonances of 2a:2b in the 19F NMR spectrum was
1.4:1.
NMR analysis showed
a mixture of unreacted 1a and
Cp*Ir(CO)2(BF3), 5. IR (dcm): νCO 2118 (s), 2078 (s) cm-1. IR
(CDCl3): νCO 2106 (s), 2065 (s) cm-1. H NMR (CDCl3): δ 2.26
1

Reaction of Cp*Ir(CO)2 with Perfluoroaromatic Compounds
Organometallics, Vol. 27, No. 6, 2008 1253
(s, Cp*). 19F NMR (CDCl3): δ -77.12 (s. 4F, BF4). 1H NMR (dcm,
no-d)*: δ 2.35 (s, Cp*). 11B NMR (CDCl3): δ -1.18. MS FAB+
(m/z): 451 [M]+. *A reference NMR tube containing the same
volume of CDCl3 was locked and shimmed in the usual manner
and then replaced with the “no-d” sample (crude aliquot in
CH2Cl2).26 1H chemical shifts were referenced with the resonance
of CH2Cl2 set to δ 5.30.
Reaction of 1b with C6F5CN. Compound 1b (6.0 mg, 20.4
µmol) was dissolved in C6F5CN (0.5 mL) and stirred at room
temperature for 16 h. The IR spectrum shows only peaks due to
unreacted 1b.
the 1H NMR spectrum was ∼1:1.5. (ii) To a Carius tube containing
1 (10.0 mg, 26.1 µmol) were added C6F5CN (0.5 mL) and deionized
H2O (0.2 mL). The reaction mixture was degassed by three cycles
of freeze–pump–thaw and stirred at room temperature for 2¾ h.
The volatiles were removed under reduced pressure, and a 1H NMR
spectrum of the residue taken in CDCl3 showed that the integration
ratio of the Cp* resonance of 1a:2a was ∼1:1.8.
Rate of Formation of Methyl vs Isopropyl Ester. (i) To a
Carius tube containing 1a (10.0 mg, 26.1 µmol) were added C6F5CN
(0.25 mL) and methanol (0.5 mL). The reaction mixture was
degassed by three cycles of freeze–pump–thaw and stirred at room
temperature. Aliquots (0.3 mL) for 1H NMR analyses (CDCl3
solutions) taken out after 8 and 22 h reaction time showed that the
percentage conversion of 1a to 3a was 63% and 98%, respectively
(from integration ratio of the Cp* resonance). (ii) A similar
procedure with 2-propanol showed that the percentage conversion
of 1a to 3b after 8 and 22 h was 57% and 82%, respectively.
Competitive Reaction in Methanol/2-Propanol. A mixture of
methanol (0.500 mL), 2-propanol (0.945 mL), and C6F5CN (0.500
mL) was predried with molecular sieves and syringed into a Carius
tube containing 1a (10.0 mg, 26.1 µmol). The reaction mixture was
degassed by three cycles of freeze–pump–thaw and stirred at room
temperature for 22 h. 19F NMR analysis of the residue (CDCl3
solutions) showed that the ratio 3b:3a was ∼1:7.
Reaction of 2a with HBF4. To a Carius tube containing 2a (10.0
mg, 17.4 µmol) in dcm (4 mL) was added HBF4 (3 drops). The
reaction mixture was stirred at room temperature for 16 h, and the
volatiles were then removed under reduced pressure. The oily
residue obtained was sparingly soluble in dcm and completely
soluble in acetone and was identified to be [Cp*Ir(CO)2(p-
C6F4CN)]+[BF4]-, 6. IR (dcm): νCN 2246 (w), νCO 2124 (s), 2090
(s) cm-1 1H NMR (d6-acetone): δ 2.27 (s, 15H, Cp*CH3). 19F
.
NMR (d6-acetone): δ -33.92 (m, 2F, Fmeta), -58.88 (m, 2F, Fortho),
-74.02 (s, 4F, BF4). MS FAB+ (m/z): 558 [M]+, 530 [M - (CO)]+,
502 [M – 2(CO)]+. HR-MS FAB+ (m/z): calcd for C19H15O2-
F4N[193]Ir [M]+: 558.0663, found 558.0662.
Attempted Salt Exchange Reactions with AgBF4. (i) To a
Carius tube containing 1a (20.0 mg, 52.2 µmol) was added
anhydrous C6F5CN (1.0 mL). The solution was degassed by three
cycles of freeze–pump–thaw and stirred at room temperature for 2
days. To half the solution, anhydrous AgBF4 (10.0 mg, 51.3 µmol)
was added under an argon atmosphere and the mixture was stirred
for 3 h. Immediate precipitation of a tan solid was observed.
Volatiles were removed under reduced pressure to afford a residue
that was soluble in methanol but did not convert to 3a. (ii) To a
Carius tube containing 1a (10.0 mg, 26.1 µmol) and anhydrous
AgBF4 (8.0 mg, 41.1 µmol) was added anhydrous C6F5CN (0.5
mL). The solution was degassed by three cycles of freez-
e–pump–thaw and stirred at room temperature for 16 h. A tan
precipitate in an orange solution was obtained. The 1H and 19F
NMR spectra showed complicated mixtures. The expected cationic
dicarbonyl species [Cp*Ir(CO)2(p-C6F4CN)]+[BF4]-, 5, was not
detected (1H NMR, 19F NMR, and IR).
Reaction of 1a with C6F5CN in the Presence of 5 equiv of
Me4NF. To a Carius tube containing 1a (10.0 mg, 26.1 µmol) and
Me4NF (25.0 mg, 269 µmol) was added anhydrous C6F5CN (0.25
mL) and methanol (0.5 mL). The mixture was degassed by three
cycles of freeze–pump–thaw and stirred at room temperature for
1
8 h. The volatiles were removed under reduced pressure, and H
NMR analysis (CDCl3 solution) of the residue showed complete
conversion of 1a to 3a.
Crystal Structure Determinations. The crystals were mounted
on quartz fibers. X-ray data were collected on a Bruker AXS APEX
system, using Mo KR radiation, with the SMART suite of
programs.27 Data were processed and corrected for Lorentz and
polarization effects with SAINT,28 and for absorption effects with
the program 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. Crystal and
refinement data are summarized in Table 1.
Reaction of 7 with C6F5CN. To a Carius tube containing 7 (5.0
mg, 8.09 µmol) was added C6F5CN (0.5 mL) and distilled H2O
(0.1 mL). The reaction mixture was degassed by three cycles of
freeze–pump–thaw and stirred for 40 h. The volatiles were removed
under reduced pressure to give 7 as a pale brown oil. IR (dcm):
. This work was supported by an A*STAR grant (Research
Grant No. 012 101 0035), and one of us (P.K.C.) thanks
ICES for a Research Scholarship.
1
νCN 2248 (w), 2210 (w), νCO 2062 (s), 2019 (w) cm-1. H NMR
(CDCl3): δ 7.8–7.3 (m, 15H, aromatic), 1.87 (s, 15H, Cp*CH3).
19F NMR (CDCl3): δ - 31.7 (m, 2F), - 58.0 (m, 2F), -64.4 (s,
1F). MS FAB+ (m/z): 792 [M]+. HR-MS FAB+ (m/z): calcd for
C36H30F4NOP193Ir 792.1625, found 792.1649.
Rate of Reaction in D2O vs H2O. (i) To a Carius tube containing
1a (10.3 mg, 26.9 µmol) was added C6F5CN (0.5 mL) and D2O
(0.2 mL). The reaction mixture was degassed by three cycles of
freeze–pump–thaw and stirred at room temperature for 2¾ h. The
volatiles were removed under reduced pressure and the integration
ratio of the Cp* resonance of 1a against that of deuterated 2a in
Supporting Information Available: Crystallographic data in
CIF format for 2a and 3a, and 19F NMR spectra of 2a, 2b, and 3a.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OM701078Q
(27) SMART, version 5.628; Bruker AXS Inc.:Madison, WI, 2001.
(28) SAINT+, version 6.22a; Bruker AXS Inc.:Madison, WI, 2001.
(29) Sheldrick, G. M. SADABS; 1996.
(26) Hoye, T. R.; Eklov, B. M.; Ryba, T. D.; Voloshin, M.; Yao, L. J.
Org. Lett. 2004, 6, 953–956.
(30) SHELXTL version 5.1; Bruker AXS Inc.:Madison, WI, 1997.