[Cp*IrCl2]2-assisted C=C bond cleavage with water: An experimental and computational study

Article abstract of DOI:10.1021/om0610445

Reaction of the dimeric species [Cp*IrCl₂]₂ with a number of organic substrates carrying a terminal alkyne functionality (RCCH) in the presence of water leads to C=C bond cleavage to form Cp*IrCl-(CH₂R)(CO). The reaction pathway has been studied both experimentally and computationally.

Full text of DOI:10.1021/om0610445

Organometallics 2007, 26, 1173-1177
1173
[Cp*IrCl2]2-Assisted CtC Bond Cleavage with Water:
An Experimental and Computational Study
Venugopal Shanmugham Sridevi, Wai Yip Fan, and Weng Kee Leong*
Department of Chemistry, National UniVersity of Singapore, 3 Science DriVe 3, Singapore 117543
ReceiVed NoVember 13, 2006
Reaction of the dimeric species [Cp*IrCl2]2 with a number of organic substrates carrying a terminal
alkyne functionality (RCCH) in the presence of water leads to CtC bond cleavage to form Cp*IrCl-
(CH2R)(CO). The reaction pathway has been studied both experimentally and computationally.
Scheme 1
Introduction
Several instances of the metal-assisted CtC bond cleavage
reaction of 1-alkynes with water have been reported; metal
systems known include ruthenium,1 osmium,2 and iridium.3 The
related reaction of metal-acetylides or vinylidenes with water
is also known.4 For the reactions with 1-alkynes, the CtC bond
cleavage mostly resulted in the formation of complexes contain-
ing a carbonyl and an η1-alkyl with one less carbon atom. In
this article, we present our studies on this reaction using the
readily accessible dimeric iridium complex [Cp*IrCl2]2, 1.
Results and Discussion
diffraction quality crystal resulted in conversion to [Cp*Ir(CO)-
The reaction of 1 with a number of different 1-alkynes in
the presence of water at ambient temperature leads rapidly to
complexes of the general formula [Cp*IrCl(CH2R)(CO)], 2, in
modest to high yields (Scheme 1).
Cl2] via â-hydride elimination.6
The ORTEP plot for 2a is shown in Figure 1, and selected
bond parameters together with a common atomic numbering
scheme are given in Table 1. Of the four structures, two of them
(2f and 2g) showed disorder of the carbonyl and the chloro
ligands over each other.
The reaction did not occur in the absence of water, and we
have found that a similar reaction did not occur with the rhodium
analogue, [Cp*RhCl2]2. A similar reaction with Me3SiCtCH
afforded the analogous compound in which the Me3Si group
has been replaced by H, viz., [Cp*IrCl(CH3)(CO)], 2i, in 97%
yield; this compound has been obtained by earlier workers via
other routes.5 Interestingly, the same compound was also
obtained as the sole product in the reaction with Me3SiCt
CSiMe3. The reaction, however, did not proceed for Ph3SiCt
CH, PhCtCSiMe3, or the diyne Me3SiCtCCtCSiMe3. All the
compounds have been completely characterized, and for 2a, 2f,
2g, and 2i also by single-crystal X-ray crystallographic studies.
Compound 2c was rather unstable; attempts at growing a
Reaction of 1 with PhCCD showed that the deuterium was
not incorporated, pointing to cleavage of the tCH bond in the
course of the reaction. The source of the carbonyl oxygen was
confirmed to be water, as carrying out the reaction in the
presence of H218O afforded [Cp*IrCl(CH2Ph)(C18O)], 18O-2a.
Water was also the source of the hydrogens in the IrCH2 group,
since reaction of 1 with PhCCH in the presence of D2O afforded
[Cp*IrCl(CD2Ph)(CO)], d-2a. Water also accounted for all three
hydrogens in the methyl group in 2i, as carrying out the reaction
in the presence of D2O afforded [Cp*IrCl(CD3)(CO)], d-2i, the
identity of which has been established; the Me3Si group was
lost as trimethylsilanol, detected as a δ 0.04 resonance in the
1H NMR spectrum of the reaction mixture.7
(1) (a) Mountassir, C.; Ben Hedda, T.; Le Bozec, H. J. Organomet. Chem.
1990, 388, C13. (b) Bianchini, C.; Casares, J. A.; Peruzzini, M.; Romerosa,
A.; Zanobini, F. J. Am. Chem. Soc. 1996, 118, 4585.
A mechanism, based on a vinylidene intermediate, for such
metal-assisted cleavage of CtC bonds in 1-alkynes has first
been studied for the ruthenium system [L3RuCl2(PPh3)], where
L3 ) CH3CH2CH2N(CH2CH2PPh2)2;1b a similar mechanism was
also proposed for the iridium system [IrHCl2(PPh3)3]3d and for
the water-soluble [Cp*IrCl2(PAr3)].3c The possibility of alkyne
hydration to an unbound aldehyde in any part of the reaction
pathway was ruled out by the following observations: (a) no
PhCH2CHO was observed in the formation of 2a, (b) dimer 1
(2) Sullivan, B. P.; Smythe, R. S.; Kober, E. M.; Meyer, T. J. J. Am.
Chem. Soc. 1982, 104, 4701.
(3) (a) O’Connor, J. M.; Pu, L. J. Am. Chem. Soc. 1990, 112, 9013. (b)
Jimenez, M. V.; Sola, E.; Martinez, A. P.; Lahoz, F. J.; Oro, L. A.
Organometallics 1999, 18, 1125. (c) Chin, C. S.; Chong, D.; Maeng, B.;
Ryu, J.; Kim, H.; Kim, M.; Lee, H. Organometallics 2002, 21, 1739. (d)
Albertin, G.; Antoniutti, S.; Bacchi, A.; Pelizzi, G.; Piasente, F. J. Chem.
Soc., Dalton Trans. 2003, 2881.
(4) (a) Abu Salah, O. M.; Bruce, M. I. J. Chem. Soc., Dalton Trans.
1974, 2302. (b) Bruce, M. I.; Swincer, A. G. Aust. J. Chem. 1980, 33, 1471.
(c) Knaup, W.; Werner, H. J. Organomet. Chem. 1991, 411, 471. (d) Buil,
M. L.; Esteruelas, A.; Lopez, A. M.; Onate, E. Organometallics 1997, 16,
3169.
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Soc. 1983, 105, 7190. (b) Monti, D.; Franchey, G.; Bassetti, M.; Haynes,
A.; Sunley, G. J.; Maitlis, P. M.; Cantoni, A.; Bocelli, G. Inorg. Chim.
Acta 1995, 240, 485.
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Mcmaster, A. D.; Mattson, B. M.; Michel, S. T. Inorg. Chem. 1990, 29,
2023.
(7) Cella, J. A.; Carpenter, J. C. J. Organomet. Chem. 1994, 480, 23.
10.1021/om0610445 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/30/2007

1174 Organometallics, Vol. 26, No. 5, 2007
SrideVi et al.
Scheme 2
Figure 1. ORTEP plot of 2a (50% thermal ellipsoids drawn, all
hydrogen atoms omitted).
Scheme 3a
Table 1. Common Atomic Numbering Scheme and Selected
Bond Parameters for 2a, 2f, 2g, and 2i
2a
2fa
2ga
2i
R
Ph
Fc
Bond Lengths (Å)
2.3892(16) 2.378(17) 2.382(2)
(CH2)4CCH
H
Ir(1)-Cl(1)
Ir(1)-C(1)
Ir(1)-C(2)
C(1)-O(1)
C(2)-R
2.3637(12)
1.931(6)
2.084(5)
0.998(7)
1.897(8)
2.147(6)
1.048(9)
1.497(9)
1.928(19) 1.825(9)
2.135(11) 2.137(4)
1.06(3)
1.177(13)
1.497(15) 1.519(6)
a Ir ) blue; Cl ) green; O ) red; C ) large, gray; H ) small, gray.
Bond Angles (deg)
Ir(1)-C(1)-O(1) 177.4(7)
173.0(19) 176.8(9)
177.6(6)
Ir(1)-C(2)-R 117.7(4)
117.4(7)
102.6(18) 93.9(16)
87.6(6) 85.4(3)
116.8(3)
presumably via the monomeric [Cp*IrCl2]; an equilibrium
between 1 and its solvent-stabilized monomeric species has been
suggested by earlier workers,9 and consistent with this, we have
found that the dimer to monomer step involved a relatively small
∆G° (+12.6 kJ mol-1). The binding of the alkyne (step I) was
associated with a small, negative ∆G° (-2.5 kJ mol-1).
The alternative to a vinylidene, viz., the acetylide [Cp*Ir-
(Cl)2(H)(CCPh)], is unlikely; we have computed it to lie at
+120.9 kJ mol-1 higher than the vinylidene. In fact, it also lies
at a higher energy (+75.4 kJ mol-1) to A. The precise pathway
for the η2-alkyne to vinylidene rearrangement (step II) is
uncertain. However, the fact that there was no deuterium
incorporation in the reaction with PhCtCD ruled out an
intramolecular pathway such as a 1,2-shift.10 A plausible
mechanism could be a 1,3-shift or a deprotonation/protonation
involving water.11 However, consistent with earlier proposals,3c,d
the rearrangement step (II) to the vinylidene B was associated
with a large, negative ∆G° (-45.5 kJ mol-1). Since we have
found that 1 did not react with PhCtCH under anhydrous
Cl(1)-Ir(1)-C(1) 94.1(2)
Cl(1)-Ir(1)-C(2) 83.94(17)
a Disorder of Cl and CO.
93.64(15)
85.61(15)
did not react with PhCH2CHO to form 2a, and (c) the reaction
of 1 with a mixture of PhCH2CHO and PhCtCH in the presence
of D2O afforded only d-2a but no 2a; 1H NMR analysis showed
that while all the phenylacetylene was consumed, the aldehyde
remained unreacted. Our proposed mechanism for the reaction
is given in Scheme 2.
We have also investigated the cycle computationally, at the
DFT level of theory with the LANL2DZ basis set; this level of
theory has been widely used for computational studies on
transition metal sysems.8 The model reaction studied was that
between 1 and PhCCH, and the computed energetics from A
onward are shown in Scheme 3; the computed reaction free
energies are given in kJ mol-1. The formation of A is
(8) (a) Su, M.-D.; Chu, S.-Y. J. Am. Chem. Soc. 1997, 119, 10178. (b)
Mainz, D. T.; Klicic, J. J.; Friesner, R. A.; Langlois, J.-M.; Perry, J. K.
J. Comput. Chem. 1997, 17, 1863. (c) Su, M.-D.; Chu, S.-Y. J. Am. Chem.
Soc. 1999, 121, 1045. (d) Alexeev, Y.; Gordon, M. S. Organometallics
2003, 22, 4111. (e) Wada, K.; Pamplin, C. B.; Legzdins, P.; Patrick, B. O.;
Tsyba, I.; Bau, R. J. Am. Chem. Soc. 2003, 125, 7035. (f) Branchadell, V.;
Crevisy, C.; Gree, R. Chem.-Eur. J. 2004, 10, 5795. (g) Sakaki, S.;
Takayama, T.; Sumimoto, M.; Sugimoto, M. J. Am. Chem. Soc. 2004, 126,
3332. (h) Berezin, K. V.; Nechaev, V. V. Appl. Spectrosc. 2004, 71, 164.
(i) Chung, L. W.; Wu, Y.-D. J. Theor. Comput. Chem. 2005, 4, 737. (j)
Krompiec, S.; Pigulla, M.; Krompiec, M.; Marciniec, B.; Chadyniak, D.
J. Mol. Catal. A 2005, 237, 17. (k) Lev, D. A.; Grotjahn, D. B.; Amouri,
H. Organometallics 2005, 24, 14232. (l) Martin, M.; Sola, E.; Tejero, S.;
Andres, J. L.; Oro, L. A. Chem.-Eur. J. 2006, 12, 4043.
(9) (a) Gill, D. S.; White, C.; Maitlis, P. M. J. Chem. Soc., Dalton Trans.
1978, 617. (b) Mirabelli, M. G. L.; Sneddon, L. G. J. Am. Chem. Soc. 1998,
110, 449. (c) Esteruelas, M. A.; Ferna´ndez-Alvarez, F. J.; Lo´pez, A. M.;
On˜ate, E.; Ruiz-Sa´nchez, P. Organometallics 2006, 25, 5131.
(10) Wakatsuki, Y. J. Organomet. Chem. 2004, 689, 4092.
(11) (a) Wakatsuki, Y.; Koga, N.; Werner, H.; Morokuma, K. J. Am.
Chem. Soc. 1997, 119, 360. (b) Blanchini, C.; Peruzzini, M.; Vacca, A.;
Zanobini, F. Organometallics 1991, 10, 3697.
(12) (a) Birdwhistell, K. R.; Tonker, T. L.; Templeton, J. L. J. Am. Chem.
Soc. 1987, 109, 1401. (b) Birdwhistell, K. R.; Tonker, T. L.; Templeton,
J. L. J. Am. Chem. Soc. 1985, 107, 4474. (c) Birdwhistell, K. R.; Nieter
Burmayer, S. J.; Templeton, J. L. J. Am. Chem. Soc. 1983, 105, 7789. (d)
Tatsumi, K.; Hoffmann, R.; Templeton, J. L. Inorg. Chem. 1982, 21, 466.

[Cp*IrCl2]2-Assisted CtC Bond CleaVage with Water
Organometallics, Vol. 26, No. 5, 2007 1175
were purified, dried, distilled, and stored under nitrogen prior to
use, except for ClCH2CH2Cl, which was used as supplied unless
otherwise stated. Oxygen-18-labeled water (95 atom % 18O) was
conditions, or with LiCtCPh, it would appear that the driving
force for the reaction involved attack of water; the water-
catalyzed formation of vinylidene is known.12 Consequently,
we believe that steps I and II probably lie far to the left in the
absence of water.
1
purchased from Aldrich and used as received. H NMR spectra
were recorded on a Bruker ACF300 or AV300 NMR spectrometer
as CDCl3 solutions; chemical shifts reported were referenced against
the residual proton signals of the solvent. Mass spectra were
obtained on a Finnigan MAT95XL-T spectrometer in a 3NBA
matrix (FAB) or a Finnigan MAT LCQ spectrometer with MeOH
as solvent (ESI). All elemental analyses were performed by the
microanalytical laboratory at NUS. [Cp*IrCl2]2, 1, was prepared
according to the published method.6 All other reagents were from
commercial sources and used without further purification.
The attack of water at CR of the vinylidene (step III) is in
accord with the LUMO being concentrated at this carbon
atom.10,13 The step involving a formal reductive elimination of
HCl (step IV) was associated with a large, positive ∆G° (+50.6
kJ mol-1), consistent with the formation of a 16-electron species.
However, the computational study did not take into account any
possible solvation effect of the HCl, which may be expected to
lower the associated energetics. Although intermediates B and
C are relatively uncommon Ir(V) species, nevertheless we have
found that when 1 was reacted with PhCtCH in the presence
of methanol, a species that can be identified spectroscopically
as [Cp*Ir{dCOCH3(CH2Ph)}Cl2], 3, was formed (together with
another as-yet unidentified species that increased with time);
the 1H NMR and FAB-MS data were consistent with the
formulation, together with the observation of a singlet signal at
171 ppm in the 13C NMR assignable to the presence of an Ird
C moiety. The use of PhCCD in the presence of MeOH did not
result in any incorporation of deuterium, while reactions in the
presence of d3- or d4-methanol afforded [Cp*Ir{dCOCD3(CH2-
Ph)}Cl2], d3-3, or [Cp*Ir{dCOCD3(CD2Ph)}Cl2], d5-3, respec-
tively; the formation of d3-3 further confirmed the source of
the protons in the CH2 moiety as the solvent (CD3OH). Although
attempts at the isolation of pure 3 were unsuccessful, as it turned
out to be rather unstable, we were able to characterize
Reaction of 1 with Phenyl Acetylene. A dichloroethane solution
(4 mL) of [Cp*IrCl2]2, 1 (36.3 mg, 45.6 µmol), and phenylacetylene
(10 µL, 91.2 µmol) was stirred at room temperature for 0.5 h. The
solvent was then removed under reduced pressure and the residue
obtained was dissolved in the minimum amount of dichloromethane
and chromatographed on silica gel TLC plates. Elution with hexane/
CH2Cl2 (1:1, v/v) yielded [Cp*IrCl(CH2Ph)(CO)], 2a, as a yellow
solid.
A similar procedure was employed with the other alkynes.
Product yields and characterization data are given in Table 2.
Reaction of 1 with Phenyl Acetylene in Methanol. A dichlo-
roethane solution (1 mL) of 1 (36.3 mg, 45.6 µmol), PhCCH (10
µL, 91.2 µmol), and methanol (0.1 mL) was allowed to stand at
room temperature for 0.5 h. The solvent was then removed under
reduced pressure and redissolved in CDCl3. Analysis of the mixture
showed the presence of 3 and a small quantity of an unidentified
product.
1H NMR (δ, CDCl3): 1.67 (s, 15H, Cp*), 4.64 (s, 2H, CH2),
4.82 (d, 3H, OCH3), 7.16-7.52 (m, aromatic). FAB-MS: 532 [M]+,
497 [M - Cl]+.
An analogous reaction using tBuCtCH afforded, after removal
of solvent and volatiles under reduced pressure and extraction with
ether, an orange-yellow solid identified as [Cp*Ir(dC(OCH3)(CH2-
But))Cl2], 3a. Yield ) 86%.
1H NMR (δ, CDCl3): 1.67 (s, 15H, Cp*), 1.02 (s, 9H, CH3),
3.23 (s, 2H, CH2), 4.88 (s, 3H, OCH3). 13C NMR (δ, CDCl3): 292.7
(s, IrdC), 92.9 (s, Cp*), 72.7 (s, OCH3), 69.1 (s, CH2), 30.3 (s,
C(CH3)3), 8.9 (s, Cp*), 1.0 (s, CH3). FAB-MS: 512 [M]+, 477
[M - Cl]+. Anal. Calcd for C17H29Cl2O1Ir1: C, 39.84; H, 5.70.
Found: C, 40.09; H, 5.73.
t
spectroscopically and analytically the Bu analogue, [Cp*Ir{d
t
COCH3(CH2 BuPh)}Cl2], 3a, from the analogous reaction
t
employing BuCtCH. The identitication of 3a, we believe,
corroborates the intermediacy of C in the reaction.
The final step (V), a migratory deinsertion, is energetically
favorable and is consistent with observation that deinsertion at
iridium is generally more favorable than on rhodium.14 Such
deinsertion has been observed in other related systems.15
Conclusion
We have reported here the very facile reaction of the readily
available dimeric species [Cp*IrCl2]2 with 1-alkynes in the
presence of water leading to CtC bond cleavage to form
compounds of the general formula [Cp*IrCl(CH2R)(CO)]. This
represents a very useful way to access thermally unstable
transition metal alkyls. The mechanistic pathway has been
studied using a combination of experimental and computational
means, and the proposed mechanism involved redox chemistry
between Ir(III) and Ir(V) intermediates.
X-ray Crystallographic Studies. Crystals were grown from
dichloromethane/hexane solutions and mounted on quartz fibers.
X-ray data were collected on a Bruker AXS APEX system, using
Mo KR radiation, at 223 K with the SMART suite of programs.16
Data were processed and corrected for Lorentz and polarization
effects with SAINT17 and for absorption effects with SADABS.18
(18) Sheldrick, G. M. SADABS; 1996.
Experimental Section
(19) SHELXTL version 5.1; Bruker AXS Inc.: Madison, WI, 1997.
(20) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.;
Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.;
Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.;
Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.;
Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels,
A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson,
B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03;
Gaussian Inc.: Wallingford, CT, 2004.
General Procedures. All reactions and manipulations were
performed under argon using standard Schlenk techniques. Solvents
(13) Delbecq, F. J. Organomet. Chem. 1991, 406, 171.
(14) (a) Milstein, D. Acc. Chem. Res. 1984, 17, 221. (b) Milstein, D.;
Fultz, W. C.; Calabrese, J. C. J. Am. Chem. Soc. 1986, 108, 1336.
(15) (a) Alexander, J. J.; Wojcicki, A. J. Organomet. Chem. 1968, 15,
P23. (b) Alaimo, P. J.; Arndtsen, B. A.; Bergman, R. G. J. Am. Chem. Soc.
1997, 119, 5269. (c) Crevier, T. J.; Mayer, J. M. Inorg. Chim. Acta 1998,
270, 202. (d) Alaimo, P. J.; Arndtsen, B. A.; Bergman, R. G. Organome-
tallics 2000, 19, 2130. (e) Kataoka, Y.; Shibahara, A.; Yamagata, T.; Tani,
K. Organometallics 2001, 20, 2431. (f) Klei, S. R.; Golden, J. T.; Burger,
P.; Bergman, R. G. J. Mol. Catal. A 2002, 189, 79.
(16) SMART version 5.628; Bruker AXS Inc.: Madison, WI, 2001.
(17) SAINT+ version 6.22a; Bruker AXS Inc.: Madison, WI, 2001.

1176 Organometallics, Vol. 26, No. 5, 2007
Table 2. Product Yields and Characterization Data
SrideVi et al.
elemental
analysis found
(calcd)
FAB-MS [M]+,
product
alkyne
PhCCH
ν
CO (CH2Cl2)/cm-1
1H NMR (δ, CDCl3)
[M - Cl]+
2a
2011(vs)
1.79 (s, 15H, Cp*), 3.02 (d, 1H,
482, 447
C, 45.27 (44.85)
H, 4.28 (4.60)
2JHH ) 9.3 Hz, CH2), 3.98 (d, 1H, CH2),
6.94-6.99 (m, 1H, aromatic), 7.13-7.26
(m, 4H, aromatic)
d-2a
PhCCH
PhCCH
2010(vs)
1.79 (s, 15H, Cp*), 6.94-6.99 (m, 1H,
aromatic), 7.13-7.26 (m, 4H, aromatic)
1.79 (s, 15H, Cp*), 3.02 (d, 1H,
484, 449
484, 449
C, 44.81 (44.66)
H, 4.39 (4.16)
18O-2a
2011(w), 1968(vs)
2JHH ) 9.4 Hz, CH2), 3.98 (d, 1H, CH2),
6.94-6.99 (m, 1H, aromatic), 7.13-7.26
(m, 4H, aromatic)
2b
2c
p-BrC6H4CCH
2011(vs)
2003(vs)
1.80 (s, 15H, Cp*), 3.02 (d, 1H, J ) 9.2 Hz,
CH2), 3.78 (d, 1H, CH2), 7.11-7.41 (m,
4H, aromatic)
561
C, 39.03 (38.54)
H, 4.18 (3.77)
CyCCH
1.83 (s, 15H, Cp*), 1.92 (s, 2H, CH2),
1.05-1.34 (m, 2H, Cy), 1.55-1.90 (m, 8H,
Cy), 2.52-2.58 (m, 1H, C-H, Cy)
1.82 (s, 15H, Cp*), 2.02 (d, 1H, 2JHH ) 9.6 Hz,
CH2), 2.73 (d, 1H, CH2), 1.01 (s, 9H, CH3)
1.85 (s, 15H, Cp*), 2.49-2.41 (m, 2H,
CH2), 1.67-1.62 (m, 2H, CH2), 1.35-1.32
(m, 4H, CH2), 0.88 (t, 3H, CH3)
488, 453
C, 47.00 (47.49)
H, 6.26(6.6)a
2d
2e
tBuCCH
nBuCCH
1995(vs)
2004(vs)
462, 427
461, 427
low yield
C, 43.50 (43.46)
H, 6.10 (6.15)
2f
FcCCH
2007(vs)
1.79 (s, 15H, Cp*), 4.19 (s, 5H, Cp), 4.27 (m,
2H, Cp), 4.52 (m, 2H, Cp), 5.22 (d, 1H,
2JHH ) 1.1 Hz, CH2), 5.44 (d, 1H, CH2)
1.85 (s, 15H, Cp*), 1.41-1.69 (m, 8H,
CH2), 1.92-1.93 (m, 1H, CH2), 1.99 (s,
1H, tC-H), 2.32-2.42 (m, 1H, CH2).
590, 555
487, 453
452
C, 45.22 (44.79)
H, 4.38 (4.44)
2g
2h
HCC(CH2)4CCH
3-C4H3SCCH
2116(w), 2004(vs)
2007(vs)
C, 44.82 (44.48)
H, 5.64 (5.39)
1.76 (s, 15H, Cp*), 2.91 (d, 1H, 2JHH
)
C, 41.54 (41.24)
H, 4.17 (4.65)b
10.2 Hz, CH2), 3.96 (d, 1H, CH2),
6.83 (m, 1H, thiophene), 7.01-7.20 (m,
1H, thiophene), 7.43-7.67 (m, 1H, thiophene)
1.87 (s, 15H, Cp*), 1.07 (s, 3H, CH3)
2i
Me3SiCCH
2010(vs), 1962(w)
406, 371
C, 35.50 (35.50)
H, 4.47 (4.56)
1
a Based on 0.5 hexane solvate. Presence of hexane in sample verified by H NMR. b Based on 0.25 hexane solvate.
Table 3. Crystal Data and Structure Refinement for 2a and 2d-f
2a
2f
2g
2i
empirical formula
fw
C18H22ClIrO
482.01
C22H26ClFeIrO
589.93
C18H26ClIrO
486.04
C12H18ClIrO
405.91
cryst system
space group
a, Å
b, Å
monoclinic
P21/n
14.0317(5)
7.0962(3)
18.1574(7)
90
110.5740(10)
90
1692.65(11)
4
triclinic
P1h
triclinic
P1h
triclinic
P1h
7.5593(5)
10.4598(8)
13.2612(9)
98.916(2)
103.329(2)
98.601(2)
989.07(12)
2
7.0618(6)
10.9572(9)
12.0565(10)
94.249(2)
105.388(2)
96.320(2)
888.78(13)
2
7.6284(10)
8.0215(11)
12.0085(16)
77.503(2)
80.148(2)
66.855(2)
656.63(15)
2
c, Å
R, deg
â, deg
γ, deg
volume, Å3
Z
density (calcd), Mg/m3
absorp coeff, mm-1
F(000)
1.891
8.042
928
1.981
7.597
572
1.816
7.659
472
2.053
10.344
384
cryst size, mm3
no. of reflns collected
no. of indep reflns
completeness, % (to θ, deg)
max. and min. transmn
no. of data/restraints/params
goodness-of-fit on F2
final R indices [I > 2σ(I)]
0.24 × 0.12 × 0.04
0.12 × 0.06 × 0.01
0.25 × 0.21 × 0.08
0.28 × 0.22 × 0.12
26 021
10 685
10 451
9453
4983 [R(int) ) 0.0413]
96.5 (30.50)
0.74 and 0.25
4983/0/195
1.292
R1 ) 0.0463,
wR2 ) 0.0942
R1 ) 0.0493,
wR2 ) 0.0955
2.216 and -2.354
4042 [R(int) ) 0.0555]
99.9 (26.37)
0.93 and 0.46
4042/3/250
1.318
R1 ) 0.0676,
wR2 ) 0.1304
R1 ) 0.0741,
wR2 ) 0.1330
2.298 and -5.635
4648 [R(int) ) 0.0265]
90.3 (29.92)
0.58 and 0.25
4648/8/227
1.062
R1 ) 0.0285,
wR2 ) 0.0644
R1 ) 0.0318,
wR2 ) 0.0658
1.730 and -0.900
2683 [R(int) ) 0.0278]
100.0 (26.37)
0.37 and 0.16
2683/0/197
1.049
R1 ) 0.0202,
wR2 ) 0.0501
R1 ) 0.0214,
wR2 ) 0.0508
1.055 and -0.467
R indices (all data)
largest diff peak and hole, e Å-3
Structural solution and refinement were carried out with the
SHELXTL suite of programs.19 Crystal and refinement data are
summarized in Table 3.
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. The structures of 2f and 2g
exhibited disorder of the CO with the Cl ligands. These were
modeled with two alternative sites each, with appropriate restraints
placed on bond and thermal parameters and occupancies summed
to unity. All non-hydrogen atoms were given anisotropic displace-
ment parameters in the final model.

[Cp*IrCl2]2-Assisted CtC Bond CleaVage with Water
Organometallics, Vol. 26, No. 5, 2007 1177
Computational Studies. The reaction energetics for the reaction
of 1 with PhCCH was studied using DFT theory together with the
LANL2DZ basis set. Spin-restricted calculations were used for
determining the structures of the organic, inorganic, and organo-
metallic reactants, intermediates, and products, fully optimized at
the DFT/LANL2DZ level. 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) correction. All calculations were performed
using the Gaussian 03 suite of programs.20
Acknowledgment. This work was supported by an A*STAR
grant (Research Grant No. 012 101 0035), and one of us (V.S.S.)
thanks ICES for a Research Scholarship.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM0610445