Catalytic C-H activation of hydrocarbons by rhodium (I) and iridium (I) complexes with hemilabile quinolyl-Cp ligands

Article abstract of DOI:10.1021/om050438d

The rhodium(I) and iridium(I) complexes 3a-6a contain the hemilabile Cp-quinoline chelate ligands 1 and 2, respectively, where the hard nitrogen donor does not displace the good acceptor ligand ethylene. After irradiation with visible light, intensely colored complexes are obtained, where the N-donor coordinates to the metal centers. Depending on the metal atom and on the substitution pattern at the Cp rings, the mono-ethene complex with N-metal coordination can be observed spectroscopically (e.g., 3b) or C-H addition products are probable intermediates. The iridium complex 6a is able to activate the aliphatic C-H bond in cyclohexane. With the rhodium complex 5a as the precatalyst, catalytic H/D exchange reactions have been performed with olefinic substrates. With linear α-olefins a fast double-bond isomerization dominates. The hemilabile ligands stabilize the catalytically active metal complexes without suppressing their activity significantly.

Full text of DOI:10.1021/om050438d

4774
Organometallics 2005, 24, 4774-4781
Catalytic C-H Activation of Hydrocarbons by
Rhodium(I) and Iridium(I) Complexes with Hemilabile
Quinolyl-Cp Ligands†
Gerald Kohl, Ralph Rudolph, Hans Pritzkow, and Markus Enders*
Anorganisch-Chemisches Institut der Universita¨t, Im Neuenheimer Feld 270,
69120 Heidelberg, Germany
Received June 1, 2005
The rhodium(I) and iridium(I) complexes 3a-6a contain the hemilabile Cp-quinoline
chelate ligands 1 and 2, respectively, where the hard nitrogen donor does not displace the
good acceptor ligand ethylene. After irradiation with visible light, intensely colored complexes
are obtained, where the N-donor coordinates to the metal centers. Depending on the metal
atom and on the substitution pattern at the Cp rings, the mono-ethene complex with N-metal
coordination can be observed spectroscopically (e.g., 3b) or C-H addition products are
probable intermediates. The iridium complex 6a is able to activate the aliphatic C-H bond
in cyclohexane. With the rhodium complex 5a as the precatalyst, catalytic H/D exchange
reactions have been performed with olefinic substrates. With linear R-olefins a fast double-
bond isomerization dominates. The hemilabile ligands stabilize the catalytically active metal
complexes without suppressing their activity significantly.
Introduction
ligands often leads to complexes that are no longer able
to activate C-H bonds. Therefore, stabilizing ligands
must balance the complex reactivity in such a way that
the activation of substrates is still possible. This is even
more important in catalytic transformations where a
stabilizing ligand must coordinate and decoordinate
several times. To allow for a sufficient concentration and
proximity of the additional donor ligands, so-called
hemilabile chelate ligands are ideal.6 This concept has
been applied to Cp ligands where neutral Werner-type
donors with N, P, O, or S atoms are attached to the five-
membered ring by a suitable spacer (e.g., a C2 or C3
chain).7 We have incorporated the C2 spacer as well as
an sp2 nitrogen atom into a rigid heterocycle by using
quinolyl-functionalized Cp ligands such as 1 or 2.8,9
These ligands have a predefined geometry so that the
nitrogen donor atom is in a suitable position for the
coordination to the metal center. However, the N atom
in 1 or 2 is a typical donor ligand with poor acceptor
properties and will therefore not bind strongly to
electron-rich metals in low oxidation states such as RhI
The selective activation of C-H bonds of saturated
or unsaturated hydrocarbons can be realized by coor-
dinatively unsaturated transition metal complexes. A
further important step following the C-H activation is
the selective transformation of the hydrocarbon into
functionalized molecules.1 The formation of a free
coordination site in a transition metal complex can be
accomplished by the photochemically induced dissocia-
tion of a ligand. Some cyclopentadienyl rhodium and
iridium complexes of the type CpRMLn (CpR ) substi-
tuted cyclopentadienyl; M ) RhI, IrI) are well studied
examples that are able to activate C-H bonds.2 After
dissociation of a neutral two-electron ligand (L) the
resulting 16 valence electron species were characterized
using matrix isolation techniques.3 In solution such
unsaturated species often undergo side reactions, which
can lead to a decomposition of the active complex.4,5
Stabilization of the unsaturated species by external
† Dedicated to Professor Gottfried Huttner.
* To whom correspondence should be addressed. E-mail:
markus.enders@uni-hd.de.
(4) Belt, S. T.; Duckett, S. B.; Haddleton, D. M.; Perutz, R. N.
Organometallics 1989, 8, 748-759.
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J. Chem. 1989, 13, 725-736.
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(b) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Peterson, T. H.
Acc. Chem. Res. 1995, 28, 154-162. (c) Schwartz, J. Acc. Chem. Res.
1985, 18, 302-308. (d) Parshall, G. W. Acc. Chem. Res. 1975, 8, 113-
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34, 633-639. (f) Guari, Y.; Sabo-Etienne, S.; Chaudret, B. Eur. J. Inorg.
Chem. 1999, 1047. (g) Dyker, G. Angew. Chem., Int. Ed. 1999, 38,
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(7) (a) Jutzi, P.; Redeker, T. Eur. J. Inorg. Chem. 1998, 663-674,
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Butenscho¨n, H. Chem. Rev. 2000, 100, 1527-1564.
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3832-3839.
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10.1021/om050438d CCC: $30.25 © 2005 American Chemical Society
Publication on Web 08/20/2005

C-H Activation by Rh(I) and Ir(I) Complexes
Organometallics, Vol. 24, No. 20, 2005 4775
Scheme 1. Preparation of the Rhodium and
Iridium Complexes 3a-6a
or IrI. As a consequence, it has a hemilabile character
and should not completely decrease the reactivity of
unsaturated complexes with these metals. As the sta-
bilizing ligand will always remain in close proximity, a
stabilization of the low-coordinate species will always
be possible. This prevents decomposition pathways of
the active system, which is necessary in catalytic
transformations.
Figure 1. Solid-state molecular structure of 3a (only one
molecule of the asymmetric unit is shown). The structure
of the Ir complex 4a is very similar (see Supporting
Information).
Results and Discussion
The reaction of [(C2H4)2MCl]2 (M ) Rh, Ir) with [η5-
(8-quinolyl)cyclopentadienyl]sodium (1Na) and [2,3,4,5-
tetramethyl-1-(8-quinolyl)cyclopentadienyl]potassium
(2K), respectively, yields the rhodium and iridium bis-
ethene complexes 3a-6a after column chromatography
in high purity and good yields (Scheme 1).
1
The H NMR spectra of the four complexes 3a-6a
show that two molecules of ethene are coordinated to
the metal centers. Therefore, the nitrogen atom of the
quinolyl moiety does not bind to the metal atom in these
complexes. The proton NMR spectra of the rhodium
complexes show two broad featureless signals for the
ethene hydrogen atoms at room temperature. The
ethene units in the iridium complexes exhibit the two
well-resolved multiplets of an AA′BB′ spin system.
Similar multiplicity patterns were found in other ethene
rhodium and iridium complexes of cyclopentadienyl
ligands.10,11
The embedment of the donor function into the rigid
aromatic system in the ligand 1 or 2 leads to a good
crystallization behavior of their metal complexes, re-
gardless of whether the donor group coordinates. Crys-
tals of 3a-6a could be obtained from solutions in
toluene (3a, 4a, 6a) or dichloromethane (5a) at -28 °C.
The X-ray analyses affirm the conclusions of the NMR
spectra. The complexes 3a and 4a with the ligand 1
crystallize in the monoclinic space group P21/n with two
independent but very similar molecules in the asym-
metric unit (Figure 1). Their tetramethyl-substituted
analogues 5a and 6a crystallize in the triclinic space
group P1h (Figure 2).
Figure 2. Solid-state molecular structure of 5a (H atoms
omitted for clarity). The structure of the Ir complex 6a is
very similar (see Supporting Information).
the complexes with the ligand 1 the angles between the
cyclopentadienyl and the quinoline planes are ap-
proximately 170°. This nearly coplanar orientation is
not possible in the methyl-substituted derivatives 5a
and 6a. In these compounds the best planes of the two
cycles form angles of 63°.
Photochemical induced removal of a ligand such as
CO or ethene is a known method to generate reactive
species. We irradiated the complexes 3a-6a with visible
light in solvents such as benzene or cyclohexane.
Depending on the substitution pattern and on the
nature of the metal atom, the reactivity of the complexes
after their activation with visible light differs and the
nature of the solvent is also very important. The
irradiation of the related carbonyl complex 2Rh(CO)2
in chloroform or dichloromethane leads to an oxidation
of the central metal and the formation of the Rh(III)
The distances of the metal atoms to the carbon atoms
of the five-membered rings lie between 2.2 and 2.3 Å
for all four complexes. The ethene ligands are somewhat
closer, with metal carbon distances of 2.1-2.15 Å. In
(10) (a) Moseley, K.; Kang, J. W.; Maitlis, P. M. Inorg. Chim. Acta
1971, 5, 528-530. (b) Moseley, K.; Kang, J. W.; Maitlis, P. M. J. Chem.
Soc. A 1970, 2875-2883.
(11) Jutzi, P.; Kirsten, M. O.; Neumann, B.; Stammler, H.-G.
Organometallics 1994, 13, 3854-3861.

4776 Organometallics, Vol. 24, No. 20, 2005
Kohl et al.
Figure 3. Photochemical transformation of 3a into 3b and 1H NMR spectra of 3a and 3b in C6D6. *Signal due to C6D5H;
(a) coordinated C2H4; (b) noncoordinated C2H4.
chloro complex 2RhCl2.12 In contrast, the irradiation of
the rhodium complex 3a in deuterated benzene or
cyclohexane leads to an intensely colored new compound
(3b), which in the absence of light reacts slowly back to
3a. The color of the solution changes from pale yellow
to dark blue [3b in toluene: λmax ) 612 nm (ꢀ ) 688
L‚mol-1‚cm-1)]. This band is an indicator for a coordina-
tion of the nitrogen atom to the metal center in 3b
caused by metal-quinolyl charge-transfer absorptions.
A similar behavior has been described by us for related
manganese and rhenium carbonyl complexes.13 The 1H
NMR spectrum of 3b shows a complete set of new
signals compared to 3a. Between δ ) 1.86-2.03 and
3.49-3.67 the two broad resonances of only one ethene
ligand are found. The liberated ethene is detected as a
singlet at 5.24 ppm. The protons of the cyclopentadienyl
ring could be detected as two multiplets between 4.65-
4.70 and 6.33-6.38 ppm, respectively. The signals in
the aromatic region differ significantly from those in the
bis-ethene complex 3a. The signal of the H2 atom, which
is close to the nitrogen atom, is shifted from 8.67 ppm
in 3a to 6.99 ppm in 3b. Its coupling pattern proves the
nitrogen-rhodium interaction present in 3b due to its
splitting into a doublet of doublets of doublets with
observation is in agreement with the reactivity of CpRh-
(C2H4)2, which is described to be photostable under an
atmosphere of ethene but decomposes to a red-brown,
uncharacterized product by photolysis in a vacuum or
in an atmosphere of argon.4
The complex CpIr(CO)(C2H4) reacts photochemically
with deuterated benzene or deuterated cyclohexane to
the complexes CpIr(CO)(C2H3)H and CpIr(CO)(R)H (R
) C6D5; C6D11). The formation of CpIr(CO)(C6D5)H
instead of the expected deuterido complex CpIr(CO)-
(C6D5)D formed by direct C-D bond activation of one
molecule of d6-benzene indicates a fast H/D exchange,
which leads to the exclusive formation of the hydrido
complex.14
However, the irradiation of 4a in C6D12 does not lead
to an activation of the C-D bond, and therefore no H/D
exchange occurs. The color of the solution turns from
yellow to blue, and after 6 h a new set of signals is
observed in the proton NMR spectrum, similar to the
spectrum of the mono-ethene complex 3b. Between δ )
1.04-1.16 and 2.94-3.04 two multiplets with the in-
tensity of one ethene ligand are found. The liberated
ethene is detected as a singlet at 5.37 ppm. The protons
of the cyclopentadienyl ring could be detected as two
pseudotriplets at 4.83 and 5.09 ppm, respectively. The
signals of the quinolyl ring are found at 6.69, 7.23, 7.44,
and between 7.71 and 7.78 ppm. The intense blue color
and the changes of the chemical shifts in the proton
NMR spectrum, which have the same tendencies as
found for the system 3a/3b, indicate that the newly
formed compound is the mono-ethene complex 4b,
similar to 3b.
3
4
coupling constants of J(H2,H3) ) 5.1 Hz, J(H2,H4) )
3
1.4 Hz, and J(H,Rh) ) 2.5 Hz (Figure 3).
The mono-ethene complex 3b reacts slowly in the
dark with the liberated ethene to give the bis-ethene
complex 3a. However, removal of the ethene atmosphere
leads to a slow decomposition of the blue mono-ethene
compound 3b. This decomposition reaction was also
observed after prolonged irradiation of a solution of 3a
in benzene with visible light for several days. This
By performing the photochemical reaction in C6D6 the
color of the solution turns from yellow to red. After 3.5
(12) Enders, M.; Kohl, G.; Pritzkow, H. J. Organomet. Chem. 2004,
689, 3024-3030.
(13) Enders, M.; Kohl, G.; Pritzkow, H. J. Organomet. Chem. 2001,
622, 66-73.
(14) Bell, T. W.; Brough, S.-A.; Partridge, M. G.; Perutz, R. N.;
Rooney, A. D. Organometallics 1993, 12, 2933-2941.

C-H Activation by Rh(I) and Ir(I) Complexes
Organometallics, Vol. 24, No. 20, 2005 4777
1
h of irradiation the signals in the H NMR spectrum
The photolysis of (C5H5)Rh(C2H4)2 carried out in a
vacuum or under argon leads to the formation of a red-
brown precipitate of unknown composition.4,15 This
shows the importance of the quinolyl moiety in 5a,
which can coordinate to the rhodium center after the
elimination of one molecule of ethene and thus stabilizes
the resulting unsaturated mono-ethene species.
The mechanism of the H/D exchange was investigated
by several working groups.2c,5,16,17 On this basis we can
predict the following mechanism for the H/D exchange
reaction (Scheme 2).
disappeared nearly completely, which shows the high
reactivity of 4a toward aromatic and olefinic C-H bond
activation, leading to a fast H/D exchange reaction. The
different colors that appear after the irradiation of 4a
in C6D12 and C6D6, respectively, indicate the presence
of different reaction products in these two cases, but
neither NMR investigation in deuterated and nondeu-
terated aromatic solvents nor mass spectrometric mea-
surements gave further indications of the composition
of the red irradiation product of 4a.
The first step is the dissociation of an ethene ligand.
The unsaturated mono-ethene complex is then stabilized
by an intramolecular coordination of the quinolyl ni-
trogen atom. The RhI-N bond in 5b is weak so that a
C-D bond of the solvent can add oxidatively (compound
A or B) followed by the insertion of the olefin ligand
into the Rh-D bond. The reductive elimination of a
hydrogen atom from the ethyl rhodium species C
followed by the reductive elimination of a molecule of
benzene regenerates the mono-ethene complex 5b.
Several such cycles cause complete deuterium incorpo-
ration into the ethene molecules. In addition, a second
complex can add oxidatively via a C-H bond so that
D-incorporation occurs also in the ligand. In the case of
the mono-ethene complex 3b we proved the coordination
of the quinolyl moiety to the rhodium center by NMR
investigation. At present we cannot prove whether the
N-coordination is also present in compound C.
The irradiation of 5a in deuterated cyclohexane leads
also to the formation of the green compound 5b, but an
H/D exchange does not occur. In an atmosphere of
ethene 5b reacts back to unchanged 5a. This process is
completely reversible without any decomposition of the
complex. In the 1H NMR spectrum recorded directly
after irradiation in C6D12 apart from the signals of 5a
additional signals of the green product are detected.
These are two singlets of the four methyl groups at δ )
1.57 and 2.15 and two less intense multiplets at δ )
1.19-1.21 and 1.54-1.57, respectively. The integral
ratios show that only one ethene ligand is coordinated.
Therefore, the green compound 5b is a mono-ethene
complex probably stabilized by intramolecular coordina-
tion of the quinolyl nitrogen atom as in 3b. The signals
of the quinolyl protons between 6.67 and 8.82 ppm of
5b and 5a partly overlap. Therefore, a full assignment
of these resonances is not possible.
The irradiation of the rhodium complex 5a in deu-
terated benzene leads to a change in color from yellow
to deep green. The absorption maximum in the visible
region lies at λmax ) 701 nm (ꢀ ) 4535 L‚mol-1‚cm-1) in
toluene and at λmax ) 719 nm (ꢀ ) 4129 L‚mol-1‚cm-1
)
in cyclohexane. The solvatochromic effect is again an
indication of a coordination of the quinolyl moiety
leading to intramolecular MLCT bonds.13 In the 1H
NMR spectrum a new set of signals can be detected.
However, a complete conversion into the new green
compound 5b is possible only in diluted solutions. This
is due to an intense absorption band of 5b with an
absorption maximum appearing in toluene at λmax ) 356
nm (ꢀ ) 7491 L‚mol-1‚cm-1) and in cyclohexane at λmax
) 366 nm (ꢀ ) 7794 L‚mol-1‚cm-1). This so-called inner
filter effect inhibits a quantitative formation of 5b in
concentrated solutions of 5a [5a in toluene: λmax ) 391
nm (ꢀ ) 2268 L‚mol-1‚cm-1); 5a in cyclohexane: λmax
394 nm (ꢀ ) 2285 L‚mol-1‚cm-1)].
)
In the absence of light and under an atmosphere of
ethene the color of the green solution turns to yellow.
The proton NMR spectrum shows some remarkable
differences compared with the spectrum before the
irradiation. The resonances of the ethene ligands are
much less intense, and some signals of the quinolyl
moiety are found to have a different coupling pattern
and lower intensity especially in the ring containing the
heteroatom. The investigation by mass spectrometry
shows that these changes in the NMR spectrum result
from an exchange of the hydrogen atoms by deuterium
atoms occurring in the quinolyl moiety and in the ethene
ligands. The base peak that comes from the fragment
[2Rh]+ shows a broad isotopic distribution with a
maximum at m/z ) 354 and not at m/z ) 351 as before
the irradiation (see Supporting Information).
Such reactions with a H/D exchange of the solvent
C6D6 and a coordinated olefin ligand are also known
after thermal activation in the cases of (C5H5)Rh(C2H4)2
and (C5Me5)Rh(C2H4)2. Whereas with (C5H5)Rh(C2H4)2
some decomposition of the complex was found after 20
h at 100 °C, (C5Me5)Rh(C2H4)2 was found to remain
stable even when the temperature is raised to 140 °C.2c,5
When a solution of 5a in benzene is heated under reflux
for 3 h, the proton NMR spectrum shows some changes
in the signal intensities and coupling patterns but not
in the chemical shifts. The intensity of the ethene
signals drops from 4 to approximate 2 for each signal.
Further heating for 6 h does not lead to a complete H/D
exchange in the olefinic ligands. The analysis of the
resonances of the quinolyl protons indicates a deuterium
incorporation into the H2 (70%) and H3 (30%) position.
Irradiation of the iridium complex 6a in deuterated
benzene leads to a rapid change in color from pale yellow
to red, but no significant changes could be detected in
the proton NMR spectrum within 15 min of irradiation.
After 2 days of photochemical induced reaction nearly
1
all signals in the H NMR spectrum had disappeared;
even the two singlets of the methyl groups of the
cyclopentadienyl ring could be detected only in low
intensity. The mass spectrum proves the existence of a
multiple deuterated product that results in a very broad
isotopic pattern. A similar but somewhat lower reactiv-
(15) A decomposition reaction was also observed by photolysis of a
solution of (C5Me5)Rh(C2H4)2 in C6D6.
(16) (a) Poli, R.; Harvey, J. N.; Smith, K. M. Chem. Eur. J. 2001, 7,
1679-1690. (b) Ritleng, V.; Sirlin, C.; Pfeffer, M. Chem. Rev. 2002,
102, 1731-1769.
(17) (a) Lenges, C. P.; White, P. S.; Marshall, W. J.; Brookhart, M.
Organometallics 2000, 19, 1247-1254. (b) Lenges, C. P.; White, P. S.;
Brookhart, M. J. Am. Chem. Soc. 1999, 121, 4385-4396.

4778 Organometallics, Vol. 24, No. 20, 2005
Kohl et al.
Scheme 2. Proposed Catalytic Cycle for H/D Exchange in Ethene Ligands with Complexes 5a/5ba
a The formulas A and B (A′ and B′, respectively) represent possible equilibria with noncoordinated (A and A′) or coordinated
quinolyl ligand during the catalytic cycle.
ity of 6a is found when the irradiation is performed in
irradiated in the presence of 1-hexene. However, a fast
isomerization of the double bond occurred in this case.
This can be explained by the formation of allylic
rhodium hydride complexes followed by the reductive
elimination of the isomerized hexene. A GC-MS analysis
of the reaction mixture shows 2- and 3-hexene in a ratio
of 75% to 25%, respectively, beside traces of 1-hexene.
The isotopic patterns in the obtained mass spectra of
the 2- and 3-hexene show that only a very few H/D
exchanges occurred. Therefore, the isomerization reac-
tion is much faster than the H/D exchange reaction.
Furthermore, 1,2-substituted olefins are sterically too
hindered to act as substrates for an oxidative addition
to the rhodium metal center.
For a successful exchange of a hydrogen atom with a
deuterium atom, olefins are needed that do not bear
hydrogen atoms in the allylic position because of the
fast formation of allylic complexes. The irradiation of a
degassed benzene solution of 2,2-dimethylbutene and
vinyltrimethylsilane, respectively, containing a catalytic
amount of 5a leads to a H/D exchange of the hydrogen
atoms (Scheme 3).
C6D12. After 2 days of irradiation the signal intensity
1
in the H NMR spectrum is significantly reduced but
still more intense than in the case of C6D6 as the solvent.
This shows that the iridium complex 6a is more reactive
toward the activation of C-H bonds than its rhodium
analogue 5a. It even allows the activation of the low-
reactive aliphatic C-H bonds of cyclohexane.
The rhodium complex 5a can activate selectively only
aromatic and olefinic C-H bonds during its irradiation
with visible light. Its ethene ligands are completely
deuterated after some hours of irradiation when the
reaction is performed in C6D6. Therefore, we tried to use
5a as a deuteration catalyst for olefinic substrates.
Due to the fact that a complete deuteration of the
olefin ligands occurs, the irradiation of a benzene
solution of 5a was performed in an atmosphere of ethene
(1 bar ethene pressure) in order to synthesize deuterated
ethene. However, in an atmosphere of ethene the
deuteration reaction is suppressed. The solution re-
1
mains yellow and no changes are observed in the H
NMR spectrum after several days of irradiation. The
excess of ethene inhibits the formation of 5b, and
therefore no free coordination site is generated, which
is necessary for the activation of C-H bonds and for
H/D exchange reactions.
Substituted olefins usually coordinate more weakly
than ethene. Therefore, the rhodium complex 5a was
In the case of 2,2-dimethylbutene the resonance of the
R-hydrogen atom integrates to 45% of its original
intensity after one week of irradiation, whereas the
â-hydrogen atoms still show 95% of its initial integrated
intensity. After approximate two weeks of further
irradiation only 28% of the original intensity of the

C-H Activation by Rh(I) and Ir(I) Complexes
Organometallics, Vol. 24, No. 20, 2005 4779
Table 1. Selected Bond Lengths (Å) for 3a-6a
3a (M ) Rh) 4a (M ) Ir) 5a (M ) Rh) 6a (M ) Ir)
Scheme 3. H/D Exchange in Vinyltrimethylsilane
and 2,2-Dimethylbutene Catalyzed by 5a
M-C10
M-C11
M-C12
M-C13
M-C14
M-C15
M-C16
M-C17
M-C18
C15-C16
C17-C18
Cp-Mb
2.288(2)
2.291(3)
2.201(3)
2.196(3)
2.251(3)
2.249(3)
2.252(3)
2.240(3)
2.244(3)
2.240(3)
2.123(3)
2.129(3)
2.115(3)
2.124(3)
2.130(3)
2.126(3)
2.127(3)
2.133(3)
1.409(5)
1.409(5)
1.413(4)
1.404(4)
1.890
2.270(5)
2.275(5)
2.200(5)
2.186(6)
2.244(6)
2.230(6)
2.256(6)
2.242(6)
2.242(5)
2.258(5)
2.116(6)
2.112(6)
2.097(6)
2.113(6)
2.125(6)
2.117(6)
2.118(5)
2.121(5)
1.428(11)
1.425(9)
1.433(8)
1.432(8)
1.883
2.249(5)
2.225(6)
2.272(5)
2.277(5)
2.216(6)
2.127(7)
2.135(6)
2.123(6)
2.125(7)
1.401(9)
1.404(9)
1.887
2.228(4)
2.221(5)
2.269(4)
2.295(5)
2.214(5)
2.117(6)
2.118(5)
2.117(5)
2.110(5)
1.428(9)
1.421(8)
1.880
signal of the R-hydrogen atom is left. The intensity of
the resonances of the â-hydrogen atoms still amounts
to 93%. Beside the resonances of the nondeuterated 2,2-
dimethylbutene in the 13C NMR spectrum the signal of
the R-C atom in the deuterated compound is somewhat
shifted and split into a triplet due to the coupling with
the deuterium atom. Due to the low deuterium incor-
poration into the â-position, no such coupling could be
detected in this case.
Vinyltrimethylsilane was found to be more reactive
than 2,2-dimethylbutene. A total of 50% of deuterium
was determined in the R-position after 3 days of irradia-
tion, whereas the â-hydrogen atoms still show 92-95%
of the initial integrated intensity. After approximately
two weeks the intensity of the resonance of the R-hy-
drogen atom decreased to only 24%. After this period a
significant loss in intensity was also found for the
signals of the â-hydrogen atoms (between 36% and 41%).
The preferential R-hydrogen exchange has been ob-
served in related systems, and it is also a support for
the general catalytic cycle described in Scheme 2 with
olefin insertion into a metal hydride bond.17
1.892
1.882
a For 3a and 4a the values for both independent molecules in
the unit cell are given. b Shortest distance between the plane
defined by the Cp ring and the metal atom.
dirhodium(I),18 and di-µ-chlorotetrakis(ethene)diiridium(I)19
were prepared according to the literature procedures. All other
reagents were used as purchased. NMR: Bruker DRX 200
(200.13 MHz for 1H, 50.32 MHz for 13C). The 1H NMR spectra
were calibrated using signals of residual protons from the
solvent referenced to SiMe4. The 13C spectral chemical shifts
are reported relative to the 13C solvent signals. MS: JEOL
JMS-700 and VG ZAB-2F.
Conclusion
It has been known for a long time that rhodium(I)
and iridium(I) complexes with a cyclopentadienyl spec-
tator ligand and one or two neutral and labile ligands
can be activated thermally or photochemically. The
resulting complexes are highly reactive, and some of
them allow for the activation of C-H bonds. By using
the hemilabile, quinoline-functionalized Cp ligands 1
and 2 we were able to stabilize the reactive intermedi-
ates without suppressing their reactivity too much.
After irradiation of the rhodium complexes 3a and 5a
the mono-ethene complexes 3b and 5b, respectively,
Bis(η2-ethene)[η5-(8-quinolyl)cyclopentadienyl]rhod-
ium(I) (3a). A total of 530 mg (2.46 mmol) of [η5-(8-quinolyl)-
cyclopentadienyl]sodium (1Na) dissolved in 25 mL of thf was
added dropwise to a solution of 479 mg (1.23 mmol) of di-µ-
chlorotetrakis(ethene)dirhodium(I) in 25 mL of toluene. The
resulting mixture was stirred overnight. The solvents were
evaporated. Column chromatography on Al2O3/5% H2O using
toluene as eluent yielded 578 mg (1.65 mmol, 67%) of 3a as a
1
yellow solid. H NMR (CDCl3): δ 1.16 (br, 4H, ethene-CH2);
2.66 (br, 4H, ethene-CH2); 5.31 (pt, 2H, Cp-CH); 6.34 (pt, 2H,
Cp-CH); 7.36 (dd, 3J(H3,H2) ) 4.1 Hz, 3J(H3,H4) ) 8.2 Hz, 1H,
H3); 7.48 (dd, J(H,H) ) 8.0 Hz, J(H,H) ) 7.3 Hz, 1H, H6);
3
3
1
were identified by H NMR. Irradiation of the corre-
7.65 (dd, J(H,H) ) 8.1 Hz, J(H,H) ) 1.5 Hz, 1H, H5 or H7);
3
4
sponding Ir complexes 4a and 6a leads to more reactive
complexes. The presence of the oxidative addition
products is probable in these cases. The iridium complex
6a is able to activate the aliphatic C-H bond in
cyclohexane. A high concentration of coordinating ligands
such as ethene suppresses the reactivity of the com-
plexes. Linear R-olefins are quickly isomerized into
internal olefins. If no H atom is present in the â-position
relative to the double bond of the olefin, a catalytic H/D
exchange reaction occurs in the presence of photochemi-
cally activated complex 5a. In this reaction the R-posi-
tion is the more reactive one, and in the case of 2,2-
dimethylbutene the H/D exchange is nearly stereospecific.
7.80 (dd, J(H,H) ) 7.3 Hz, J(H,H) ) 1.4 Hz, 1H, H5 or H7);
8.11 (dd, 3J(H,4H3) ) 8.3 Hz, 4J(H,4H2) ) 2.0 Hz, 1H, H4); 8.92
(dd, 3J(H2,H3) ) 4.1 Hz, 4J(H2,H4) ) 1.9 Hz, 1H, H2). 13C NMR
3
4
1
(CDCl3): δ 39.3 (d, J(Rh,C) ) 13.3 Hz, ethene-CH2); 86.9 (d,
1J(Rh,C) ) 4.4 Hz, Cp-CH); 89.4 (d, 1J(Rh,C) ) 3.9 Hz, Cp-
1
CH); 104.5 (d, J(Rh,C) ) 3.9 Hz, quart. Cp-C); 120.9, 126.2,
126.7, 128.1, 136.3, 149.4 (quinoline-CH); 128.9, 132.5, 145.9
(quart. Cquinoline). MS (EI): m/z (%) 351 (1) [M+]; 323 (16) [M+
- C2H4]; 295 (100) [M+ - 2 C2H4]. Anal. Calcd for C18H18NRh
(351.25): C 61.55, H 5.17, N 3.99. Found: C 61.28, H 5.19, N
3.97.
Bis(η2-ethene)[η5-(8-quinolyl)cyclopentadienyl]iridium-
(I) (4a). A total of 228 mg (1.06 mmol) of [η5-(8-quinolyl)-
cyclopentadienyl]natrium(I) (1Na) dissolved in 20 mL of thf
was added dropwise to a solution of 300 mg (0.53 mmol) of
di-µ-chlorotetrakis(ethene)diiridium(I) in 20 mL of toluene
cooled at -78 °C. The resulting mixture was warmed to room
Experimental Section
General Procedures. All experiments were carried out
under an atmosphere of dry argon. Solvents were dried by
using standard procedures and distilled prior to use. [η5-(8-
Quinolyl)cyclopentadienyl]sodium (1Na),8 2,3,4,5-tetramethyl-
1-(8-quinolyl)cyclopentadiene (2H),9a di-µ-chlorotetrakis(ethene)-
(18) (a) Cramer, R. Inorg. Chem. 1962, 1, 722-723. (b) Cramer, R.
Inorg. Synth. 1990, 29, 86-88.
(19) Onderdelinden, A. L.; van der Ent, A. Inorg. Chim. Acta 1972,
6, 420-426.

4780 Organometallics, Vol. 24, No. 20, 2005
Table 2. Crystal Data and Experimental Details
3a 4a 5a
18H18NRh C22H26NRh
Kohl et al.
6a
C22H26IrN
empirical formula
fw
C
C18H18IrN
440.53
351.24
407.35
triclinic
P1h
496.64
triclinic
P1h
cryst syst
monoclinic
monoclinic
P21/n
space group
P21/n
unit cell dimens
a, Å
14.5264(8)
6.9596(4)
14.5137(8)
6.9902(4)
7.310(5)
7.2888(1)
11.0309(2)
12.0453(2)
81.382(1)
78.660(1)
72.152(1)
899.69(3)
2
b, Å
11.092(6)
c, Å
27.986(2)
27.8759(15)
90
12.134(7)
R, deg
90
81.36(4)
â, deg
93.454(1)
93.593(1)
78.19(5)
γ, deg
90
90
72.32(5)
volume, Å3
2824.2(3)
2822.6(3)
913.4(10)
Z
8
8
2
density(calc), g/cm3
F(000)
1.652
2.073
1.481
1.833
484
1424
1680
420
cryst size, mm3
θ range for data collection, deg
index ranges
0.38 × 0.27 × 0.16
1.62 to 32.02
-21 e h e 21,
0 e k e 10,
0 e l e 41
47 841
0.36 × 0.10 × 0.07
1.54 to 32.04
-18 e h e 21,
-10 e k e 10,
-38 e l e 41
24 556
0.10 × 0.17 × 0.35
1.72 to 25.06
-8 e h e 8,
-12 e k e 13,
0 e l e 14
3226
0.51 × 0.44 × 0.10
1.73 to 28.29
-9 e h e 9,
-14 e k e 14,
-16 e l e 15
11 993
no. of reflns collected
no. of indep reflns
9719 [R(int) ) 0.0284]
9719/0/505
1.341
R1 ) 0.0394,
wR2 ) 0.0857
R1 ) 0.0409,
wR2 ) 0.0862
2.183 and -1.953
9540 [R(int) ) 0.0304]
9540/0/426
1.156
R1 ) 0.0408,
wR2 ) 0.0825
R1 ) 0.0471,
wR2 ) 0.0846
4.048 and -3.618
3226 [R(int) ) 0.0000]
3226/0/278
1.063
R1 ) 0.0453,
wR2 ) 0.1014
R1 ) 0.0728,
wR2 ) 0.1096
0.571 and -0.504
4392 [R(int) ) 0.0446]
4392/0/316
no. of data/restraints/params
goodness-of-fit on F2
1.115
final R indices [I > 2σ(I)]
R1 ) 0.0372,
wR2 ) 0.0989
R1 ) 0.0379,
wR2 ) 0.0995
2.337 and -3.856
R indices (all data)
largest diff peak and hole, e Å-3
temperature overnight. The solvents were evaporated. Column
chromatography on Al2O3/5% H2O using toluene as eluent
yielded 270 mg (0.61 mmol, 56%) of 4a as a dark yellow solid.
1H NMR (CDCl3): δ 0.67-0.77 (m, 4H, ethene-CH2); 2.35-
2.45 (m, 4H, ethene-CH2); 5.32 (pt, 2H, Cp-CH); 6.35 (pt, 2H,
Cp-CH); 7.35 (dd, 3J(H3,H2) ) 4.1 Hz, 3J(H3,H4) ) 8.2 Hz, 1H,
1.72 (br, 4H, ethene-CH2); 1.77 (d, 3J(Rh,H) ) 0.5 Hz, 6H, CH3);
2.13-2.19 (br, 4H, ethene-CH2); 6.73 (dd, 3J(H3,H2) ) 4.0 Hz,
3J(H3,H4) ) 8.2 Hz, 1H, H3); 7.37 (dd, 3J(H,H) ) 6.6 Hz,
3J(H,H) ) 8.2 Hz, 1H, H6); 7.45 (dd, 3J(H,H) ) 8.2 Hz, 4J(H,H)
) 2.0 Hz, 1H, H5 or H7); 7.58 (dd, 3J(H,4H3) ) 8.3 Hz, 4J(H4,H2)
3
4
) 1.9 Hz, 1H, H4); 8.63 (dd, J(H,H) ) 6.6 Hz, J(H,H) ) 1.9
3
3
H3); 7.47 (dd, J(H,H) ) 8.0 Hz, J(H,H) ) 7.3 Hz, 1H, H6);
3
4
Hz, 1H, H5 or H7); 8.65 (dd, J(H2,H3) ) 4.0 Hz, J(H2,H4) )
3
4
7.67 (dd, J(H,H) ) 8.2 Hz, J(H,H) ) 1.5 Hz, 1H, H5 or H7);
1.9 Hz, 1H, H2). 13C NMR (CDCl3): δ 8.9, 10.2 (CH3); 44.8 (d,
3
4
7.73 (dd, J(H,H) ) 7.2 Hz, J(H,H) ) 1.5 Hz, 1H, H5 or H7);
8.10 (dd, 3J(H,4H3) ) 8.3 Hz, 4J(H,4H2) ) 1.8 Hz, 1H, H4); 8.91
(dd, 3J(H2,H3) ) 4.1 Hz, 4J(H2,H4) ) 1.8 Hz, 1H, H2). 13C NMR
(CDCl3): δ 20.1 (ethene-CH2); 81.9, 84.6 (Cp-CH); 100.3 (quart.
Cp-C); 121.0, 126.2, 127.1, 128.7, 136.2, 149.4 (quinoline-CH);
128.7, 131.5, 145.8 (quart. Cquinoline). MS (EI): m/z (%) 413 (54)
[M+ - C2H4]; 385 (100) [M+ - 2 C2H4]; 359 (22) [M+ - 2 C2H4
- C2H2]; 192.5 (18) [M2+ - 2 C2H4]. HR-MS (EI): calcd for
C16H14N193Ir 413.0756; found 413.0751. Anal. Calcd for C18H18-
NIr (440.57): C 49.07, H 4.12, N 3.18. Found: C 49.27, H 4.30,
N 3.31.
1J(Rh,C) ) 13.7 Hz, C2H4); 97.8 (d, J(Rh,C) ) 3.8 Hz, quart.
1
C
Cp); 98.3 (d, 1J(Rh,C) ) 3.8 Hz, quart. CCp); 106.5 (d, 1J(Rh,C)
) 4.6 Hz, quart. CCp); 120.5 126.2, 127.4, 136.1, 138.0, 149.9
(quinoline-CH); 128.3, 134.0, 147.9 (quart. Cquinoline). MS (EI):
m/z (%) 407 (6) [M+]; 379 (15) [M+ - C2H4]; 351 (100) [M+ - 2
C2H4]; 175.5 (9) [M2+ - 2 C2H4]; 103 (5) [Rh+]. Anal. Calcd for
C22H26NRh (407.37): C 64.87, H 6.43, N 3.44. Found: C 65.21,
H 6.38, N 3.33.
Bis(η2-ethene)[η5-2,3,4,5-tetramethyl-1-(8-quinolyl)cy-
clopentadienyl]iridium(I) (6a). To a suspension of 37 mg
(0.92 mmol) of potassium hydride in 25 mL of thf was added
233 mg (0.93 mmol) of 2,3,4,5-tetramethyl-1-(8-quinolyl)-
cyclopentadiene (2H). After stirring for 3 h at room temper-
ature the violet suspension was added to a solution of 265 mg
(0.47 mmol) of di-µ-chlorotetrakis(ethene)diiridium(I) in 25 mL
of toluene, which was kept at -78 °C. The resulting mixture
was warmed to room temperature overnight. The solvents were
evaporated. Column chromatography on Al2O3/5% H2O using
toluene as eluent yielded 205 mg (0.41 mmol, 45%) of 6a as a
dark yellow solid. 1H NMR (CDCl3): δ 0.88-0.98 (m, 4H,
ethene-CH2); 1.35 (s, 6H, CH3); 1.58-1.68 (m, 4H, ethene-CH2);
Bis(η2-ethene)[η5-2,3,4,5-tetramethyl-1-(8-quinolyl)cy-
clopentadienyl]rhodium(I) (5a). To a suspension of 103 mg
(2.6 mmol) of potassium hydride in 25 mL of thf was added
641 mg (2.3 mmol) of 2,3,4,5-tetramethyl-1-(8-quinolyl)cyclo-
pentadiene (2H). After stirring for 3 h at room temperature
the violet suspension was transferred to a solution of 500 mg
(1.3 mmol) of di-µ-chlorotetrakis(ethene)dirhodium(I) in 25 mL
of toluene via cannula. The resulting brown solution was
stirred overnight. The solvents were evaporated and the
residue suspended in toluene. The precipitated inorganic salts
were separated by filtration with a reversal frit (G4), and the
dark filtrate was chromatographed on Al2O3/5% H2O with
toluene as eluent to give 870 mg (2.14 mmol, 83%) of 5a as a
yellow solid. 1H NMR (CDCl3): δ 1.32 (s, 6H, CH3); 1.36-1.47
(br, 4H, ethene-CH2); 1.90-1.97 (br, 4H, ethene-CH2); 1.98 (d,
3J(Rh,H) ) 0.5 Hz, 6H, CH3); 7.33 (dd, 3J(H3,H2) ) 4.2 Hz,
3J(H3,H4) ) 8.1 Hz, 1H, H3); 7.55 (dd, 3J(H,H) ) 7.1 Hz,
3J(H,H) ) 8.1 Hz, 1H, H6); 7.77 (dd, 3J(H,H) ) 8.1 Hz, 4J(H,H)
) 1.5 Hz, 1H, H5 or H7); 8.15 (dd, 3J(H,4H3) ) 8.1 Hz, 4J(H4,H2)
3
3
2.03 (s, 6H, CH3); 7.34 (dd, J(H3,H2) ) 4.2 Hz, J(H3,H4) )
8.3 Hz, 1H, H3); 7.47-7.58 (m, 1H, H6); 7.79 (dd, J(H,H) )
3
8.2 Hz, J(H,H) ) 1.2 Hz, 1H, H5 or H7); 8.15 (dd, J(H,H) )
4
3
8.2 Hz, J(H,H) ) 1.6 Hz, 1H, H4); 8.26 (dd, J(H,4H3) ) 7.1
4
3
Hz, J(H,4H2) ) 1.2 Hz, 1H, H5 or H7); 8.91 (dd, J(H2,H3) )
4.2 Hz, 4J(H2,H4) ) 1.6 Hz, 1H, H2). 13C NMR (CDCl3): δ 8.2,
10.1 (Cp-CH3); 24.9 (ethene-CH2); 93.8, 95.0, 100.4 (quart. CCp);
120.6, 126.5, 127.8, 136.1, 139.4, 150.1 (quinoline-CH); 128.2,
132.9, 147.3 (quart. Cquinoline). MS (EI): m/z (%) 497 (6) [M+],
469 (63) [M+ - C2H4], 441 (100) [M+ - 2 C2H4], 249 (54) [M+
- 2 C2H4 - Ir], 234 (69) [M+ - 2 C2H4 - Ir - CH3]. Anal.
4
3
3
4
) 1.7 Hz, 1H, H4); 8.42 (dd, J(H,H) ) 7.1 Hz, J(H,H) ) 1.5
3
4
Hz, 1H, H5 or H7); 8.91 (dd, J(H2,H3) ) 4.2 Hz, J(H2,H4) )
1.7 Hz, 1H, H2). H NMR (C6D6): δ 1.32 (s, 6H, CH3); 1.66-
1

C-H Activation by Rh(I) and Ir(I) Complexes
Organometallics, Vol. 24, No. 20, 2005 4781
Calcd for C22H26NIr (496.68): C 53.20, H 5.28, N 2.82. Found:
C 53.78, H 5.32, N 2.98.
pressure lamp for 6 h, during which the color of the solution
turned to blue. The solution was investigated directly by NMR
spectroscopy. H NMR (C6D12): δ 1.04-1.16 (m, 2H, ethene-
CH2); 2.94-3.04 (m, 2H, ethene-CH2); 4.83 (pt, 2H, Cp-CH);
5.37 (s, free ethene); 5.95 (pt, 2H, Cp-CH); 6.69 (dd, 3J(H3,H2)
) 5.5 Hz, 3J(H3,H4) ) 8.4 Hz, 1H, H3); 7.23-7.44 (m, 3H,
quinoline-CH); 7.71-7.78 (m, 2H, quinoline-CH).
(η2-Ethene)[η5-(8-quinolyl)cyclopentadienyl]rhodium-
(I) (3b). A solution of 5 mg (14 µmol) of 3a in 0.5 mL of C6D6
was added to a NMR tube closed by a Teflon valve. The yellow
solution was irradiated with the light of a 150 W Hg high-
pressure lamp for 8 h, during which the color of the solution
turned to blue. The solution was investigated directly by NMR
spectroscopy. 1H NMR (C6D6): δ 1.86-2.03 (m, 2H, ethene-
CH2); 3.49-3.67 (m, 2H, ethene-CH2); 4.65-4.70 (m, 2H, Cp-
CH); 5.24 (s, free ethene); 6.04 (dd, 3J(H3,H2) ) 5.1 Hz,
3J(H3,H4) ) 8.3 Hz, 1H, H3); 6.33-6.38 (m, 2H, Cp-CH); 6.87
(d, 1H, H5 or H7); 6.88 (d, 1H, H5 or H7); 6.94 (dd, 3J(H4,H3) )
8.3 Hz, 3J(H,4H2) ) 1.4 Hz, 1H, H4); 6.99 (ddd, 3J(H2,H3) )
1
Acknowledgment. This work was supported by the
Deutsche Forschungsgemeinschaft (SFB 623). The au-
thors thank Degussa AG for donation of rhodium(III)
chloride. G.K. thanks the Landesgraduiertenfo¨rderung
Baden-Wu¨rttemberg for a scholarship.
4
3
5.1 Hz, J(H2,H4) ) 1.4 Hz, J(H,Rh) ) 2.5 Hz, 1H, H2); 7.48
Supporting Information Available: Molecular struc-
(dd, J(H,H) ) 3.4 Hz, J(H,H) ) 5.2 Hz, 1H, H6).
3
3
1
tures of 4a and 6a; CIF files for 3a, 4a, 5a, and 6a; H NMR
(η2-Ethene)[η5-(8-quinolyl)cyclopentadienyl]iridium-
(I) (4b). A solution of 5 mg (11 µmol) of 4a in 0.5 mL of C6D12
was added to a NMR tube closed by a Teflon valve. The yellow
solution was irradiated with the light of a 150 W Hg high-
and 13C NMR spectra; and UV/vis spectra are available free
of charge via the Internet at http://pubs.acs.org.
OM050438D