Cycloiridation of α,β-unsaturated ketones, esters, and acetophenone

Article abstract of DOI:10.1021/om050441x

C-H activation of acetophenone and cyclic and acyclic α,β- unsaturated ketones or esters occurs with [IrH₂(acetone) ₂(PPh₃)₂]⁺. In the case of acyclic α,β-unsaturated ketones or esters, the β-C-H bond was activated to afford iridafuran hydrides as cyclometalation products. For cyclopentenone, a cyclic α,β-unsaturated ketone, the C-H activation affords an η⁵-hydroxycyclopentadienyl iridium hydride. The activation of the ortho C-H bonds in acetophenone affords orthometalated products structurally related to the iridafuran hydrides. Plausible mechanisms are proposed for reactions in each case. In particular, the formation of iridafurans is believed to proceed by a mechanism analogous to that previously proposed for the RuH ₂(CO)(PPh₃)₃-catalyzed Murai reaction.

Full text of DOI:10.1021/om050441x

4810
Organometallics 2005, 24, 4810-4815
Cycloiridation of r,â-Unsaturated Ketones, Esters, and
Acetophenone
Xingwei Li, Peng Chen, Jack W. Faller,* and Robert H. Crabtree*
Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107
Received June 2, 2005
C-H activation of acetophenone and cyclic and acyclic R,â-unsaturated ketones or esters
occurs with [IrH2(acetone)2(PPh3)2]+. In the case of acyclic R,â-unsaturated ketones or esters,
the â-C-H bond was activated to afford iridafuran hydrides as cyclometalation products.
For cyclopentenone, a cyclic R,â-unsaturated ketone, the C-H activation affords an
η5-hydroxycyclopentadienyl iridium hydride. The activation of the ortho C-H bonds in
acetophenone affords orthometalated products structurally related to the iridafuran hydrides.
Plausible mechanisms are proposed for reactions in each case. In particular, the formation
of iridafurans is believed to proceed by a mechanism analogous to that previously proposed
for the RuH2(CO)(PPh3)3-catalyzed Murai reaction.
Introduction
We recently reported the insertion of various termi-
nal, internal, and nitro-functionalized alkynes into
iridium hydrides, where mechanistic studies have shown
that different alkynes react differently even with the
same iridium hydride.12 Furthermore, we also found
that these iridium hydrides are stable and highly active
catalysts for the cyclization of hydroxylaryl and amino-
aryl alkynes to afford isochromenes and indoles, respec-
tively, which will be published elsewhere. These iridium
hydrides were synthesized through the cyclometalation
of acetophenone and enones, as briefly mentioned
previously.12a We now present a full report of the cyclo-
iridation of cyclic and acyclic R,â-unsaturated ketones,
esters, and acetophenones using [IrH2(acetone)2(PPh3)2]+.
Activation of C-H bonds through chelation assistance
(cyclometalation) allows the synthesis of metal hydrides
that have been of great interest recently.1 These initially
generated metal hydrides can be further elaborated by
reaction with unsaturated molecules to afford syntheti-
cally useful C-C coupling products.2-10 Catalytic reac-
tions involving cyclometalation have been reported for
various metals including ruthenium,2,3 rhodium,4-7
cobalt,8 zirconium,9 iridium,10 and palladium.11
(1) For reviews, see: (a) In Activation of Unreative Bonds and
Organic Synthesis; Murai, S., Ed.; Springer: Berlin, 1999. (b) Kakiuchi,
F.; Murai, S. Acc. Chem. Res. 2002, 35, 826. (c) Ritleng, V.; Sirlin, C.;
Pfeffer, M. Chem. Rev. 2002, 102, 1731. (d) Dyker, G. Angew. Chem.,
Int. Ed. 1999, 38, 169. (e) Guari, Y.; Sabo-Etienne, S.; Chaudret, B.
Eur. J. Inorg. Chem. 1999, 1047. (f) Omae, I. Coord. Chem. Rev. 2004,
248, 995. (g) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103,
1759. (h) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001,
40, 3750.
(2) (a) Murai, S.; Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani,
A.; Sonoda, M.; Chatani, N. Nature 1993, 266, 529. (b) Chatani, N.;
Asaumi, T.; Yorimitsu, S.; Ikeda, T.; Kakiuchi, F.; Murai, S. J. Am.
Chem. Soc. 2001, 123, 10935. (c) Kakiuchi, F.; Tsujimoto, T.; Sonoda,
M.; Chatani, N.; Murai, S. Synlett 2001, 948. (d) Chatani, N, Kamitani,
A.; Murai, S. J. Org. Chem. 2002, 67, 7014.
(3) (a) Trost, B. M.; Imi, K.; Davies, I. W. J. Am. Chem. Soc. 1995,
117, 5371. (b) Ko, S.; Na, Y.; Chang, S. J. Am. Chem. Soc. 2002, 124,
750. (c)
Results and Discussion
C-H Activation of Acyclic R,â-Unsaturated Ke-
tones and Esters. Synthesis. Iridium readily gives
cyclometalation,13 and [IrH2(acetone)2(PPh3)2]+ had
proven effective in a number of other catalytic reactions
involving C-H activation;14 therefore, it seems to be a
reasonable choice of starting material. Indeed, reflux
of [IrH2(acetone)2(PPh3)2]+ (1) in acetone with 2 equiv
of R,â-unsaturated ketones or esters for 4-14 h leads
to a color change to orange or yellow. Removal of the
solvent under reduced pressure, followed by addition of
diethyl ether, afforded off-white to yellow precipitates,
which were then filtered to give the cyclometalated
(4) (a) Jun, C.-H.; Hong, J.-B.; Lee, D.-Y. Synlett 1999, 1. (b) Jun,
C.-H.; Hong, J.-B.; Kim, Y.-H.; Chung, K.-Y. Angew. Chem., Int. Ed.
2000, 39, 3440.
(5) (a) Lim, Y.-G.; Kang, J.-B.; Kim, Y. H. Chem. Commun. 1996,
585. (b) Lim, Y.-G.; Lee, K.-H.; Koo, B. T.; Kang, J.-B. Tetrahedron
Lett. 2001, 42, 7609.
(6) (a) Tan, K. L.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc.
2001, 123, 2685. (b) Lewis, J. C.; Wiedemann, S. H.; Bergman, R. G.;
Ellman, J. A. Org. Lett. 2004, 6, 35. (c) Tan, K. L.; Bergman, R. G.;
Ellman, J. A. J. Am. Chem. Soc. 2002, 124, 13964. (d) Tan, K. L.; Park,
S.; Ellman, J. A.; Bergman, R. G. J. Org. Chem. 2004, 69, 7329. (e)
Wiedemann, S. H.; Bergman, R. G.; Ellman, J. A. Org. Lett. 2004, 6,
1685.
(7) Lenges, C. P.; Brookhart, M. J. Am. Chem. Soc. 1999, 121, 6616.
(8) (a) Halbritter, G.; Knoch, F.; Wolski, A.; Kisch, H. Angew. Chem.,
Int. Ed. 1994, 33, 1603. (b) Halbritter, G.; Knoch, F.; Wolski, A.; Kisch,
H. J. Organomet. Chem. 1995, 492, 87.
(9) Rodewald, S. Jordan, R. F. J. Am. Chem. Soc. 1994, 116, 4491.
(10) Dorta, R.; Togni, A. Chem. Commun. 2003, 760.
(11) (a) Dick, A. R.; Hull, K. L.; Sanford, M. S. J. Am. Chem. Soc.
2004, 126, 2300. (b) Desai, L. V.; Hull, K. L.; Sanford, M. S. J. Am.
Chem. Soc. 2004, 126, 9542.
(12) (a) Li, X.; Incavito, C. D.; Crabtree, R. H. J. Am. Chem. Soc.
2003, 125, 3698. (b) Li, X.; Vogel, T.; Incarvito, C. D.; Crabtree, R. H.
Organometallics 2005, 24, 62. (c) Li, X.; Incarvito, T.; Vogel, T.;
Crabtree, R. H. Organometallics 2005, 24, 3066.
(13) (a) Davies, D. L.; Al-Duaij, O.; Fawcett, J.; Giardiello, M.; Hilton,
S. T.; Russel, D. R. Dalton Trans. 2003, 4143. (b) Dorta, R.; Goikhman,
R.; Milstein, D. Organometallics 2003, 22, 2806. (c) Santos, L. L.;
Mereiter, K.; Paneque, M.; Slugovc, C.; Carmona, E. New J. Chem.
2003, 27, 107. (d) Danopoulos, A. A.; Winston, S.; Hursthouse, M. B.
J. Chem. Soc., Dalton Trans. 2002, 3090. (e) Slugovc, C.; Mereiter, K.;
Trofimenko, S.; Carmona, E. Angew. Chem., Int. Ed. 2000, 39, 2158.
(14) (a) Crabtree, R. H.; Parnell, C. P. Organometallics 1985, 4, 519.
(b) Crabtree, R. H.; Dion, R. P. J. Chem. Soc., Chem. Commun. 1984,
1260. (c) Burk, M. J.; Crabtree, R. H.; Parnell, C. P.; Uriarte, R. J.
Organometallics 1984, 3, 816.
10.1021/om050441x CCC: $30.25 © 2005 American Chemical Society
Publication on Web 08/24/2005

Cycloiridation of R,â-Unsaturated Ketones
Organometallics, Vol. 24, No. 20, 2005 4811
Scheme 1. Cyclometalation of r,â-Unsaturated
Scheme 2 Proposed Mechanism for the Formation
Ketones or Esters
of Hydrides 2a-e
Mechanistic Aspects. In the reaction between 1 and
2 equiv of trans-PhCHdCHC(O)Me, the saturated ke-
tone PhCH2CH2C(O)Me was isolated (92%) together
with complex 2a. In a reaction of 1 with 1 equiv of trans-
PhCHdCHC(O)Me in acetone-d6 (70 °C, 4 h), 1H NMR
spectroscopy showed that the reaction mixture contains
starting material 1, product 2a, and coproduct PhCH2-
CH2C(O)Me in a ratio of 1:1:1, and only 50% of 1 was
converted.
These results suggest that the role of the R,â-
unsaturated ketone is twofold: 1 equiv acts as a
hydrogen acceptor to generate the saturated ketone and
an Ir(I) species, which reacts with the second equivalent
of substrate to afford the cyclometalation product. If so,
other hydrogen acceptors, such as tert-butylethylene
(TBE), a hydrogen acceptor with very high driving force,
should also dehydrogenate 1. Indeed, 1 equiv of trans-
PhCHdCHC(O)Me reacts (acetone, reflux) with a mix-
ture of 15 equiv of TBE and 1 to afford 2a in nearly
quantitative yield.
To further understand the mechanism, we probed the
reaction using 2 equiv of commercially available methyl
methacrylate-d5 [CD2dC(CD3)CO2CH3, MMA-d5]. Both
1H and 2H NMR spectroscopy indicate that the organo-
metallic product 2c-d5 contained >98% Ir-D. MMA-d5
acts as a hydrogen acceptor, as indicated by the detec-
tion of free CD2HCH(CD3)CO2CH3 in 1H NMR spectros-
copy.
iridium hydrides 2a-e in high yields (Scheme 1). These
products are stable toward air and moisture in both
solution and solid forms, and specially dry acetone
solvent is not necessary. The same products were
observed with excess (up to 6 equiv) R,â-unsaturated
ketones or esters.
The cyclometalation of R,â-unsaturated ketones is
relatively fast, and the reaction is complete within 5 h
(2a,b), while the reaction of R,â-unsaturated ester is
much slower and requires as long as 14 h for 2d. The
formation of 2e is of interest; the organic starting
material can be regarded as both an R,â-unsaturated
ketone and an R,â-unsaturated ester. Since the cyclo-
metalation of esters is much slower than that of ketones,
we observed only 2e as a result of the cyclometalation
of the ketone moiety.
NMR Spectroscopy. Hydrides 2a-e were fully
1
characterized by H, 13C, and 31P{1H} NMR spectros-
copy. The 1H NMR spectra (acetone-d6) of 2a-e show a
high-field triplet resonance at δ 20-23, assigned to the
hydride due to its coupling to two equivalent phos-
phines. More interestingly, resonances were observed
for 2b (δ 10.22, 1H) and 2c (δ 9.09, 1H) that appear at
too low a field for assignment to vinyl protons, but are
reasonably assigned to R-protons of metal carbenes. This
is best explained by resonance between the two struc-
tures shown in Scheme 1, the five-membered iridacycle
being essentially an iridafuran.15-17 A contribution from
the carbenoid form was also indicated by 13C{1H} NMR
spectra of hydrides 2a-e, where a low-field triplet
resonance (δ 159-199) is observed for each complex. In
general, the Ir-C of the products from R,â-unsaturated
ketones (2a,b,e) appears to have more carbenoid char-
acter, because they give a lower field Ir-C resonance in
13C NMR spectroscopy than those in esters 2c,d. The
31P{1H} NMR spectrum of each of these hydrides simply
shows a singlet, indicating a trans arrangement of the
phosphines. In complexes 2a, 2b, and 2e, a long-range
coupling (5JPH ) 1.2 Hz) is observable between the
phosphines and the CH3 (R3 group).
A plausible mechanism for this transformation is
proposed in Scheme 2 based on these observations.
Dihydride 1 is first dehydrogenated by the R,â-unsatur-
ated ketone to generate an iridium(I) species. The
carbonyl group of the R,â-unsaturated ketone coordi-
nates to the iridium(I) to bring the â-C-H bond into
the vicinity, where it may interact via agostic bonds.18
Another possible intermediate, an η4-π-species, was
proposed in a closely related report.17 C-H activation
of this species and coordination of the solvent would lead
to the formation of hydrides 2. This mechanism is
analogous to that proposed for RuH2(CO)(PPh3)3-
catalyzed C-C coupling reactions between acetophe-
none and alkenes (Murai-type catalysis).1a Syntheses of
iridafurans through C-H activation have previously
been reported.16,17
Failure of Murai-Type Catalysis. Hydrides 2a-e
(5 mol % loading) proved inactive as catalysts for
the Murai-type coupling between the corresponding
R,â-unsaturated ketones or esters and a variety of
alkenes (styrene, 1-hexene, triethoxylvinylsilane, TBE,
and allylbenzene). The failure is probably an indication
of the high activation barrier of the final C-C coupling
step, since the alkene insertion step is generally low in
barrier and we did observe the isomerization of allyl-
(15) Sunley, G. J.; Menanteau, P. C.; Adams, H. Bailey, N. A.;
Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1989, 2415.
(16) (a) Castarlenas, R.; Esteruelas, M. A.; Martin, M.; Oro, L. A.
J. Organomet. Chem. 1998, 564, 241. (b) Bleeke, J. R.; New, P. R.;
Blanchard, J. M. B.; Haile, T.; Rhode, A. M. Organometallics 1995,
14, 5127.
(18) (a) Matsubara, T.; Koga, N.; Musaev, D. G.; Morokuma, K. J.
Am. Chem. Soc. 1998, 120, 12692. (b) Matsubara, T.; Koga, N.; Musaev,
D. G.; Morokuma, K. Organmetallics 2000, 19, 2318.
(17) Grotjahn, D. B.; Hoerter, J. M.; Hubbard, J. L. J. Am. Chem.
Soc. 2004, 126, 8866.

4812 Organometallics, Vol. 24, No. 20, 2005
Li et al.
benzene to trans-MeCHdCHPh when allylbenzene was
heated with a catalytic amount of 2a, showing that
insertion is possible. C-C reductive elimination from
iridium centers is usually difficult, and only a few
examples have been reported.17,19 The barrier for this
reductive elimination is expected to be even higher when
it involves a carbon with carbenoid character.
C-H Activation of Cyclopentenone, a Cyclic r,â-
Unsaturated Ketone. Synthesis and Spectroscopy.
On the basis of the mechanism proposed in Scheme 2,
the cyclometalation of enones is expected only when the
carbonyl group is syn to the â-C-H bond, but not in an
anti arrangement as in 2-cyclohexen-1-one.
Indeed, a different pathway was now observed. When
2 equiv of 2-cyclopenten-1-one and hydride 1 were
heated under reflux in acetone for 10 h, hydride 3 was
isolated (eq 1) and characterized by NMR spectroscopy
Figure 1. ORTEP diagram of the cation of 3 shown with
50% thermal ellipsoids. The hydride position is calculated.
1
and X-ray crystallography. In the H NMR spectrum
(CD2Cl2), a high-field triplet at δ -15.33 (2JPH ) 26.4
Hz) was assigned to the hydride. The CH protons in the
Cp ring give two slightly broadened singlets at δ 5.01
(2H) and 4.69 (2H). Another broad singlet at δ 7.76,
which disappeared upon addition of D2O, was assigned
to the -OH. Accordingly, the IR spectroscopy confirmed
the presence of a hydroxyl group (νOH ) 3293 cm-1). In
the 31P{1H} NMR spectrum, only a singlet was observed,
indicating the phosphines were equivalent. 13C{1H}
NMR spectroscopy showed no virtual coupling for the
ipso aryl carbons of the phosphines, in contrast to those
in hydrides 2a-e (see Experimental Section). This
result together with the relatively large P-Ir-H coupling
constant (26.4 Hz) agrees well with the proposed
structure of 3, where the two phosphines and the
hydride are cofacial.
Table 1. Selected Bond Lengths and Angles for
Complex 3
Bond Lengths (Å)
Ir(1)-P(1)
Ir(1)-P(2)
Ir(1)-C(1)
Ir(1)-C(2)
Ir(1)-C(3)
Ir(1)-C(4)
Ir(1)-C(5)
2.286(2)
2.286(2)
2.348(10)
2.314(10)
2.213(10)
2.238(8)
2.216(10)
Bond Angles (deg)
P(1)-Ir(1)-P(2)
P(1)-Ir(1)-C(1)
P(1)-Ir(1)-C(2)
P(1)-Ir(1)-C(3)
P(1)-Ir(1)-C(4)
P(1)-Ir(1)-C(5)
99.36(7)
99.5(2)
127.9(3)
158.2(3)
131.5(3)
99.5(2)
mechanism.20 In contrast, Ba¨ckvall et al. has shown that
the hydrogen transfer from the complex to an imine goes
via a stepwise inner sphere mechanism.21 A catalytic
version of this type of hydrogen transfer was also
reported by Ba¨ckvall et al.22 Complex 3, however, fails
to transfer any hydrogen to aldehydes. This is probably
because (1) the Ir-H bond is stronger than the Ru-H
bond and/or (2) the product from the hydrogen transfer
would be an iridium(I) species and would need π-acidic
ligands to be stable.
Mechanistic Aspects. In a proposed mechanism
shown in Scheme 3, the first equivalent of cyclopenten-
one may be hydrogenated by the dihydride 1 to generate
a reactive iridium(I) species. The cyclopentenone is
proposed to undergo tautomerization to form a hydroxy-
cyclopentadiene, which probably binds to the iridium
in an η4 mode to stabilize this iridium(I) species.
Activation of the allylic C-H bonds of the hydroxy-
cyclopentadiene finally leads to the formation of 3. In
closely related examples, Crabtree et al.23 reported the
C-H activation of unfunctionalized cyclopentadiene,
cyclopentene, and indene using the same iridium dihy-
Crystallographic Studies of Hydride 3. Single
crystals of 3 suitable for X-ray crystallography were
obtained by slow diffusion of diethyl ether into its
acetone solution. As shown in Figure 1, complex 3 has
a distorted octahedral geometry assuming the Cp ring
occupies three coordination positions. The pentahaptic-
ity of the functionalized Cp ring follows from the Ir(1)-
C(1-5) distances ranging from 2.211 to 2.357 Å. The
phosphines are in a cis arrangement (P(1)-Ir(1)-P(2)
) 99.38(8)°), enforced by the Cp ring. Selected bond
lengths and angles are displayed in Table 1.
This appears to be a remarkably simple synthesis of
this functionalized Cp complex. Casey et al. recently
studied a related ruthenium-substituted hydroxycyclo-
pentadienyl hydride and proposed hydrogen transfer
from this complex to ketones or aldehydes through a
novel outer sphere concerted proton-hydride transfer
(20) Casey, C. P.; Singer, S. W.; Powell, D. R.; Hayashi, R. K.;
Kavana, M. J. Am. Chem. Soc. 2001, 123, 1090.
(21) Samec, J. S. M.; EÄ ll, A. H.; Ba¨ckvall, J.-E. Chem. Commun.
2004, 2748.
(22) (a) Pa`mies, O.; Ba¨ckvall, J. E. Chem.-Eur. J. 2001, 7, 5052. (b)
Samec, J. S. M.; Ba¨ckvall, J. E. Chem.-Eur. J. 2002, 8, 2955.
(23) (a) Crabtree, R. H.; Mihelcic, J. M.; Quirk, J. M. J. Am. Chem.
Soc. 1979, 101, 7738. (b) Crabtree, R. H.; Parnell, C. P. Organometallics
1984, 3, 1727.
(19) (a) Ananikov, V. P.; Musaev, D. J.; Morokuma, K. J. Am. Chem.
Soc. 2002, 124, 2839. (b) Navarro, J.; Sola, E.; Martin, M.; Dobrinovitch,
I. T.; Lahoz, F. J.; Oro, L. A. Organometallics 2004, 23, 1908. (c) Chin,
C. S.; Won, G.; Chong, D.; Kim, M.; Lee, H. Acc. Chem. Res. 2002, 35,
218. (d) Schwiebert, K. E.; Stryker, J. M. J. Am. Chem. Soc. 1995, 117,
8275.

Cycloiridation of R,â-Unsaturated Ketones
Organometallics, Vol. 24, No. 20, 2005 4813
Scheme 3 Proposed Mechanism for the C-H
Scheme 4 Proposed Mechanism for the Formation
of 4a
Activation of Cyclopentenone
dride to give cyclopentadienyl or indenyl iridium hy-
drides, with aromatization being an obvious driving
force.
proposed in Scheme 3, and molecular hydrogen should
be a coproduct. In a plausible mechanism (Scheme 4),
the acetophenone coordinates at the carbonyl group
when the acetone ligand is substituted. The carbonyl
coordination guides the ortho C-H bonds to interact
with the iridium, probably via a C-H agostic intermedi-
ate. C-H activation is then proposed to generate an
iridium(III) aryl hydride dihydrogen species; loss of
dihydrogen and substitution by acetone affords the final
orthometalation product. Although this iridium(III) aryl
hydride dihydrogen species was not detected, a related
iridium(III) alkyl hydride dihydrogen species was previ-
ously proposed.24 The driving force of this acceptor-
less C-H activation is probably the formation of a
strong Ir-aryl bond that favors C-H over H-H bond
metathesis.24b
C-H Activation of Acetophenone and Its De-
rivatives. Synthesis and Spectroscopy. Acetophe-
none, structurally related to R,â-unsaturated ketones,
reacts with dihydride 1 in acetone under reflux to afford
a greenish yellow solution. Upon addition of diethyl
ether, 4a was obtained as a yellow precipitate (eq 2).
In contrast to the synthesis of 2a-e, 1 equiv of aceto-
phenone is enough to afford 4a in nearly quantitative
yield. Similarly, R-tetralone reacts with 1 to afford 4b
through a directly analogous synthesis. Both 4a and 4b
are stable toward air and moisture in solid or solution
form and were characterized spectroscopically. In par-
ticular, the 1H NMR spectrum of 4a gives the resonance
of the hydride at δ -21.95 as a triplet (2JPH ) 14.6 Hz),
the 13C{1H} NMR spectrum (acetone-d6) shows a triplet
(2JPC ) 8.2 Hz) at δ 149.0, assigned to the Ir-C, and the
coordinated acetone gives resonances at δ 215.8 and
31.0. The 31P{1H} NMR spectrum gives a singlet. All
these NMR data are similar to those observed in
hydrides 2a-e, except for the Ir-C resonance, which is
simply an aryl carbon with little carbenenoid character.
The stereochemistry of 4a,b, together with 2a-e, with
H cis to the aryl or vinyl group, was assigned by analogy
with the great number of Ir(III) derivatives having two
high trans effect ligands mutually cis. These include a
broad range of [IrH2(L)2(PPh3)2]BF4 derivatives (L )
acetone, 2,2′-dipyridyl, OH2).23,24
Conclusions
Various iridium hydrides can be synthesized from the
C-H activation of acetophenone and both cyclic and
acyclic R,â-unsaturated ketones or esters. In the case
of acyclic R,â-unsaturated ketones or esters, the â-C-H
bond was activated to afford iridafuran hydrides as
cyclometalation products, in which case 2 equiv of such
R,â-unsaturated ketones are necessary. For cyclopen-
tenone, a cyclic R,â-unsaturated ketone, the C-H
activation affords a hydroxycyclopentadienyl hydride.
The activation of the ortho C-H bonds in acetophenone
affords orthometalated products structurally related to
the iridafuran hydrides, but only 1 equiv of acetophe-
none is needed. Plausible mechanisms are proposed for
reactions in each case. In particular, the formation of
iridafurans is believed to go by a mechanism analogous
to that previously proposed for the RuH2(CO)(PPh3)3-
catalyzed Murai reaction.
Experimental Section
Interestingly, complex
1 failed to react with
1-indanone (acetone, reflux, 14 h), the five-membered
ring analogue of R-tetralone, and only starting materials
were returned (eq 3).
General Considerations. All reactions were carried out
under argon, although all the products proved to be air stable.
Acetone was used without any treatment. All R,â-unsaturated
ketones and esters, acetophenone, and tert-butylethylene
were purchased from Aldrich and used without purification.
R-Tetralone was distilled before use. 1H and 13C NMR spectra
(24) (a) Lee, D.-H.; Chen, J.; Faller, J. W., Crabtree, R. H. Chem.
Commun. 2001, 213. (b) Albeniz, A. C.; Schulte, G.; Crabtree, R. H.
Organometallics 1992, 11, 242.
Since this reaction proceeds without any hydrogen
acceptor, the mechanism must be different from that

4814 Organometallics, Vol. 24, No. 20, 2005
Li et al.
were recorded on Bruker 400 or 500 spectrometers. 31P{1H}
NMR spectra were recorded on Bruker 400 spectrometers with
external 85% H3PO4 standard. Elemental analyses were
(s, CH3COCH3), 14.9 (s, OCH2CH3). The signal for coordinated
CH3COCH3 may well be obscured by the solvent signal.
31P{1H} NMR (acetone-d6, 161.9 MHz, 296 K): δ 20.83 (s).
Anal. Calcd for C45H46BF4IrO3P2: C, 55.39; H, 4.75. Found:
C, 55.17; H, 4.64.
performed at the Atlantic Microlab.
-
Synthesis of 2a (BF4-). To a flask charged with 1 (BF4
,
0.490 g, 0.532 mmol) and acetone (9 mL) was added trans-4-
phenyl-3-buten-2-one (0.156 g, 1.067 mmol). This mixture was
heated under reflux for 4 h, during which time the solution
changed from light yellow to orange. The solution was then
cooled to room temperature and concentrated to ca. 0.5 mL
under reduced pressure, followed by slow precipitation using
diethyl ether (15 mL). The bright yellow powder was filtered,
washed with diethyl ether (15 mL), and dried in vacuo. Yield:
0.496 g (0.492 mmol, 93%). 1H NMR (acetone-d6, 400 MHz,
Complex 2e (SbF6-). Complex 2e (SbF6-) was synthe-
sized through a method directly analogous to that for 2a, using
1 (SbF6-, 200 mg, 0.187 mmol) and trans-MeC(O)CHd
CHCO2Me (42 mg, 0.375 mmol). Yield: 200 mg (0.178 mmol,
95%). 1H NMR (acetone-d6, 500 MHz, 296 K): δ 7.49-7.61 (m,
30H, PPh3), 6.48 (s, 1H, iridafuran CH), 3.38 (s, 3H, OCH3),
5
2.10 (s, 6H, CH3COCH3), 1.85 (t, JPH ) 1.2 Hz, 3H, CH3),
2
-21.78 (t, JPH ) 14.0 Hz, Ir-H, 1H). 13C{1H} NMR (acetone-
d6, 100.6 MHz, 296 K): δ 214.8 (s, CO), 180.3 (t, 8.0 Hz, Ir-C),
172.2 (CO), 139.8 (s, CH), 135.7 (virtual t, 5.6 Hz, PPh3), 132.5
(s, PPh3), 129.8 (virtual t, 5.3 Hz, PPh3), 128.6 (virtual t, 26.4
Hz, ipso-PPh3), 52.6 (s, OCH3), 36.3 (s, CH3), 31.0 (s, CH3-
COCH3), 26.6 (s, CH3). The signal for coordinated CH3COCH3
may well be obscured by the solvent signal. 31P{1H} NMR
(acetone-d6, 161.9 MHz, 296 K): δ 22.91 (s). Anal. Calcd for
3
296 K): δ 7.59 (d, JHH ) 7.6 Hz, 2H), 7.40-7.52 (m, 30H,
PPh3), 7.19 (t, 3JHH ) 7.3 Hz, 1H), 7.03 (t, 3JHH ) 7.6 Hz, 2H),
6.50 (s, 1H, iridafuran C-H), 2.09 (s, 6H, overlapping with
5
solvent signal, CH3COCH3), 1.90 (t, JPH ) 1.5 Hz, 3H, CH3),
-20.82 (t, 2JPH ) 14.1 Hz, Ir-H, 1H). 13C{1H} NMR (acetone-
d6, 100.6 MHz, 296 K): δ 211.1 (s, CO), 198.8 (t, 6.5 Hz, Ir-C),
145.05 (s), 135.55 (virtual t, 5.5 Hz, PPh3), 132.8 (s), 132.4 (s),
132.2 (s), 132.0 (s), 129.7 (virtual t, 5.1 Hz, PPh3), 128.9 (s),
128.6 (virtual t, 27.3 Hz, ipso-PPh3), 31.09 (s, CH3COCH3),
26.04(s, CH3). The signal for coordinated CH3COCH3 may well
be obscured by the solvent signal. 31P{1H} NMR (acetone-d6,
161.9 MHz, 296 K): δ 20.85 (s). Anal. Calcd for C49H46BF4-
IrO2P2: C, 58.39; H, 4.60. Found: C, 58.03; H, 4.63. Evapora-
tion of ether from the ethereal solution afforded PhCH2CH2C-
(O)Me (72 mg, 0.486 mmol, 92%).
C45H44F6IrO4P2Sb: C, 47.46; H, 3.89. Found: C, 47.57; H, 3.93.
-
Complex 3 (BF4-). To an acetone solution (8 mL) of 1 (BF4
,
370 mg, 4.01 mmol) was added 2-cyclopenten-1-one (66 mg,
8.04 mmol) via syringe. The solution was heated under reflux
for 12 h, followed by concentration of the solution to ca. 0.5
mL. Diethyl ether (20 mL) was added, and a light yellow
precipitate formed, which was filtered and washed with diethyl
ether (10 mL). The yellow precipitate was recrystallized using
acetone-ether (1:4). Yield: 0.280 g (0.316 mmol, 79%). 1H
NMR (CD2Cl2, 400 MHz, 296 K): δ 7.76 (br s, 1H, exchange-
Complex 2b (BF4-). Complex 2b was synthesized through
a method directly analogous to that for 2a, using 1 (BF4-, 300
mg, 0.326 mmol) and methyl vinyl ketone (68 mg, 0.971 mmol).
able with D2O, OH), 7.22-7.40 (m, 30H, PPh3), 5.01 (br s, 2H,
2
Cp ring C-H), 4.69 (br s, 2H, Cp ring C-H), -15.33 (t, JPH
)
1
Yield: 264 mg (0.283 mmol, 87%). H NMR (acetone-d6, 400
26.4 Hz, 1H, Ir-H). 13C NMR (CD2Cl2, 125.8 MHz, 300 K): δ
149.0 (s, C-OH), 134.4 (virtual t, 5.5 Hz, PPh3), 133.2 (d, 60.0
Hz, ipso-PPh3), 131.4 (s), 128.9 (virtual t, 5.3 Hz, PPh3), 82.8
(s, Cp ring C), 70.4 (s, Cp ring C). 31P{1H} NMR (CD2Cl2, 161.9
MHz, 296 K): δ 6.51 (s). IR (CH2Cl2 film): 3293 cm-1 (br, νOH),
2173 cm-1 (w, νIr-H). Anal. Calcd for C41H36BF4IrOP2: C, 55.60;
H, 4.10. Found: C, 55.72; H, 4.12.
3
MHz, 296 K): δ 10.21 (d, JHH ) 7.3 Hz, 1H, Ir-CH), 7.50-
7.64 (m, 30 H, PPh3), 6.15 (d, 3JHH ) 7.3 Hz, 1H, Ir-CHdCH),
5
2.10 (s, 6H, CH3COCH3), 1.64 (t, JPH ) 1.5 Hz, 3H, CH3),
2
-20.77 (t, JPH ) 14.8 Hz, 1H, Ir-H). 13C{1H} NMR (acetone-
d6, 100.6 MHz, 296 K): δ 211.6 (s, CO), 184.1 (t, 8.8 Hz, Ir-C),
136.3 (s, CH), 135.3 (virtual t, 6.0 Hz, PPh3), 132.4 (s), 130.0
(virtual t, 5.1 Hz, PPh3), 129.8 (virtual t, 27.5 Hz, ipso-PPh3),
31.0 (s, CH3COCH3), 25.4 (s, CH3). The signal for coordinated
CH3COCH3 may well be obscured by the solvent signal.
31P{1H} NMR (acetone-d6, 161.9 MHz, 296 K): δ 23.79 (s).
Anal. Calcd for C43H42BF4IrO2P2: C, 55.43; H, 4.54. Found:
C, 55.34; H, 4.67.
Complex 4a (BF4-). Complex 4a was synthesized through
a method directly analogous to that for 2a, using 1 (BF4-, 250
mg, 0.271 mmol) and acetophenone (33 mg, 0.275 mmol).
1
Yield: 236 mg (0.241 mmol, 89%). H NMR (acetone-d6, 400
3
MHz, 296 K): δ 7.49 (t, JHH ) 7.4 Hz, 6H, PPh3), 7.30-7.41
3
3
(m, 24H, PPh3), 7.17 (d, JHH ) 7.6 Hz, 1H), 7.10 (dd, JHH
)
4
3
Complex 2c (BF4-). Complex 2c was synthesized through
a method directly analogous to that for 2a, using 1 (BF4-, 300
mg, 0.326 mmol) and methyl methacrylate (82 mg, 0.975
7.6 Hz, JHH ) 1.0 Hz, 1H), 6.79 (t, JHH ) 7.6 Hz, 1H), 6.66
(td, 3JHH ) 7.6 Hz, 4JHH ) 1.0 Hz, 1H), 2.10 (s, 3H, CH3), 2.09
2
(s, 6H, CH3COCH3), -21.95 (t, JPH ) 14.6 Hz, Ir-H, 1H).
1
mmol). Yield: 255 mg (0.270 mmol, 83%). H NMR (acetone-
13C{1H} NMR (acetone-d6, 100.6 MHz, 296 K): δ 215.8 (s, CO),
149.0 (t, 8.2 Hz, Ir-C), 145.3 (s), 141.9 (s), 136.0 (s), 135.2
(virtual t, 5.5 Hz, PPh3), 133.8 (s), 132.1 (s, PPh3), 129.8
(virtual t, 5.0 Hz, PPh3), 128.8 (virtual t, 26.8 Hz, ipso-PPh3),
122.2 (s), 31.0 (s, CH3COCH3), 24.5 (s, CH3). The signal for
coordinated CH3COCH3 may well be obscured by the solvent
signal. 31P{1H} NMR (acetone-d6, 161.9 MHz, 296 K): δ 22.12
(s). Anal. Calcd for C47H44BF4IrO2P2: C, 57.50; H, 4.52.
Found: C, 57.26; H, 4.77.
d6, 400 MHz, 296 K): δ 9.09 (s, 1H, Ir-CH), 7.50-7.65 (m, 30H,
PPh3), 3.45 (s, 3H, OMe), 2.11 (s, 6H, CH3COCH3), 1.04 (s,
3H, CH3), -22.83 (t, 2JPH ) 14.1 Hz, Ir-H, 1H). 13C{1H} NMR
(acetone-d6, 100.6 MHz, 296 K): δ 206.3 (s, CO), 182.3 (CO),
159.6 (t, 9.0 Hz, Ir-C), 135.2 (virtual t, 5.8 Hz, PPh3), 132.3
(s, PPh3), 130.0 (virtual t, 26.7 Hz, ipso-PPh3), 129.9 (virtual
t, 5.1 Hz, PPh3), 129.3 (s), 54.3 (s, OMe), 31.0 (s, CH3COCH3),
18.5 (s, CH3). 31P{1H} NMR (acetone-d6, 161.9 MHz, 296 K):
δ 23.49 (s). Anal. Calcd for C44H44BF4IrO3P2: C, 54.95; H, 4.61.
Found: C, 54.50; H, 4.59.
Complex 4b (BF4-). Complex 4b was synthesized through
a method directly analogous to that for 2a, using 1 (BF4-, 250
mg, 0.271 mmol) and R-tetralone (40 mg, 0.274 mmol). Yield:
232 mg (0.230 mmol, 85%). 1H NMR (acetone-d6, 400 MHz,
296 K): δ 7.48-7.55 (m, 6H, PPh3), 7.30-7.43 (m, 24H, PPh3),
Complex 2d (BF4-). Complex 2d was synthesized through
a method directly analogous to that for 2a, using 1 (BF4-, 200
mg, 0.217 mmol) and trans-CHMedCHCO2Et (42.6 mg, 0.434
1
3
3
mmol). Yield: 189 mg (0.197 mmol, 91%). H NMR (acetone-
7.08 (d, JHH ) 7.6 Hz, 1H), 6.79 (t, JHH ) 7.6 Hz, 1H), 6.67
3
3
d6, 400 MHz, 296 K): δ 7.50-7.63 (m, 30H, PPh3), 5.47 (s,
(t, JHH ) 7.6 Hz, 1H), 6.58 (d, JHH ) 7.2 Hz, 2H), 2.36 (t,
3
1H, iridafuran CH), 4.13 (q, JHH ) 7.0 Hz, 2H, OCH2CH3),
3JHH ) 6.0 Hz 2H, CH2), 2.20 (t, 3JHH ) 6.2 Hz 2H, CH2), 2.09
2.10 (s, 6H, CH3COCH3), 1.67 (s, 3H, CH3), 1.10 (t, 3JHH ) 7.0
(s, 6H, CH3COCH3), 1.34 (quintet, JHH ) 6.2 Hz, CH2CH2-
3
2
2
Hz, 3H, OCH2CH3), -23.58 (t, JPH ) 14.3 Hz, Ir-H, 1H).
CH2), -22.25 (t, JPH ) 14.2 Hz, Ir-H, 1H). 13C{1H} NMR
13C{1H} NMR (acetone-d6, 100.6 MHz, 296 K): δ 188.1 (t, 8.4
Hz, Ir-C), 183.4 (CO), 135.6 (virtual t, 5.5 Hz, PPh3), 132.6 (s,
PPh3), 129.9 (virtual t, 4.9 Hz, PPh3), 128.8 (virtual t, 26.7
Hz, ipso-PPh3), 120.7 (s), 63.6 (s, OCH2CH3), 36.3 (s, CH3), 31.1
(acetone-d6, 100.6 MHz, 296 K): δ 215.8 (s, CO), 150.0 (s),
148.6 (t, 8.1 Hz, Ir-C), 143.1 (s), 139.5 (s), 136.5 (s), 135.2
(virtual t, 5.8 Hz, PPh3), 132.1 (s, PPh3), 129.7 (virtual t, 5.0
Hz, PPh3), 129.0 (virtual t, 26.9 Hz, ipso-PPh3), 121.8 (s), 38.0

Cycloiridation of R,â-Unsaturated Ketones
Organometallics, Vol. 24, No. 20, 2005 4815
Table 2. Crystallographic Data for Complex 3
Crystallography. Single crystals of 3 suitable for X-ray
diffraction analysis were obtained by slow diffusion of diethyl
ether into an acetone solution of 3. X-ray diffraction for single
crystals was measured on a Nonius Kappa CCD diffractometer.
Data collection was carried out at -90 °C. The structure was
solved by direct methods and expanded using Fourier tech-
niques. All non-hydrogen atoms in the cation were refined
anisotropically, while owing to disorder, the tetrafluoroborate
atoms were refined isotropically as a rigid group. Hydrogen
atoms (with the exception of the hydroxyl hydrogen atom,
which could not be located) were included in calculated
positions but not refined. The Ir-H distance was fixed at 1.60
Å and the vector oriented on the basis of residual density
observed in the difference Fourier. The crystal parameters and
other experimental details of the data collection are sum-
marized in Table 2.
empirical formula
C41H36BF4IrP2O
885.71
molecular weight (g mol-1
)
radiation, λ (Å)
T (°C)
Mo KR (monochr), 0.71073
-90
cryst syst
space group
a (Å)
monoclinic
P21/c (No. 14)
14.5538(6)
14.2109(7)
17.5636(8)
101.834(3)
3555.3(3)
4
1.655
39.1
0.07 × 0.12 × 0.12
21 196, 8382
0.058
b (Å)
c (Å)
â (deg)
V (Å3)
Z
Dcalcd (g cm-3
)
µ (Mo KR) (cm-1
cryst size (mm)
)
total, unique no. of rflns
Rint
no. of observations used
no. of variables
4650
417
0.051, 0.060
1.39
-2.11, 4.35
Acknowledgment. Funding from the U.S. Depart-
ment of Energy (R.H.C.), National Science Foundation
(J.W.F.), and the Johnson Matthey Co. (X.L.) is grate-
fully acknowledged.
Ra, Rw
b
GOF
min., max. resid dens (e Å -3
)
a R ) ∑||Fo| - |Fc||/∑|Fo|, for all I > 3σ(I). b Rw ) [∑w(|Fo| -
2
1/2
|Fc|)2/∑wFo
]
Supporting Information Available: Tables providing
atomic positional parameters, bond distances and angles,
anisotropic thermal parameters, and calculated hydrogen atom
positions for complex 3. A CIF file is also available. This
material is available free of charge via the Internet at
http://www.pubs.acs.org.
.
(s, CH2), 31.0 (s, CH3COCH3), 29.2 (s, CH2), 24.2 (s, CH2). The
signal for coordinated CH3COCH3 may well be obscured by
the solvent signal. 31P{1H} NMR (acetone-d6, 161.9 MHz, 296
K): δ 21.84 (s). Anal. Calcd for C49H46BF4IrO2P2: C, 58.39; H,
4.60. Found: C, 58.46; H, 4.59.
OM050441X