Ruthenium dihydrogen complex for C-H activation: Catalytic H/D exchange under mild conditions

Article abstract of DOI:10.1002/ejic.200800359

Catalytic H/D-exchange reactions were studied with [Ru(dtbpmp) (η²-H₂)(H)₂] (1) as catalyst. Under mild reaction conditions (25-75°C) a wide range of arenes and olefins undergo H/D exchange with [D₆]benzene. A p

Full text of DOI:10.1002/ejic.200800359

FULL PAPER
DOI: 10.1002/ejic.200800359
Ruthenium Dihydrogen Complex for C–H Activation: Catalytic H/D Exchange
under Mild Conditions
Martin H. G. Prechtl,[a,b] Markus Hölscher,[a] Yehoshoa Ben-David,[c] Nils Theyssen,[b]
David Milstein,[c] and Walter Leitner*[a,b]
Keywords: Ruthenium dihydrogen complexes / H/D exchange / CH activation / Deuteration / DFT calculations
Catalytic H/D-exchange reactions were studied with
[Ru(dtbpmp)(η2-H2)(H)2] (1) as catalyst. Under mild reaction
conditions (25–75 °C) a wide range of arenes and olefins un-
dergo H/D exchange with [D6]benzene. A preference for pro-
tons at sp2 carbons was observed with conversions up to
Ͼ90% and significant regioselectivity in certain cases. For
nism were investigated by means of DFT calculations for
both model complexes (PMe2 donor sites) and real catalysts
(PtBu2 donor sites). The calculations resulted in Gibb’s free
activation energies in the range of 10–16 kcalmol–1, indicat-
ing H/D exchange at the β-position of naphthalene to be
clearly favoured over the α-position, which is in full accord-
more reaction insights NMR-based kinetic studies were per- ance with the experimental observations.
formed with naphthalene as substrate, revealing an acti-
vation energy of 15.8 kcalmol–1 for the H/D exchange at the
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
β-position. Furthermore, the key steps of the reaction mecha-
Germany, 2008)
As part of our ongoing interest in the catalytic properties
of non-classical ruthenium hydrides, we have investigated
several complexes of that type in recent years.[11,12] For mo-
nomeric complexes we included bulky mono-dentate phos-
phanes and carbenes of NHC-type.[11,12a] With chelating bi-
dentate phosphane ligands binuclear complexes were ob-
tained, instead, bulky tridentate pincer ligands led to mono-
meric complexes.[12] For example [Ru(IMes)(PCy3)(η2-H2)2-
H2] (2a) (IMes = 1,3-dimesityl-1,3-dihydro-2H-imidazol-2-
ylidene) and [Ru(IMes)2(η2-H2)2H2] (2b) as carbene ana-
logues of Chaudret’s hexahydride [Ru(PCy3)2(η2-H2)2H2]
(3).[11] In contrast to 3, complexes 2a and 2b showed a very
high activity for the H/D exchange between [D6]benzene
and several arenes. As recently communicated, we focus on
the investigation in catalysis of ruthenium dihydrogen com-
plexes bearing pincer-ligands with constrained geome-
try.[10,12b] The complex [Ru(dtbpmp)(η2-H2)H2] (1)
Introduction
Activation of C–H bonds in hydrocarbons is one of the
prominent challenges in modern homogeneous catalysis.
For early evaluation of the potential of new catalyst precur-
sors for this type of reaction, H/D-exchange processes are
found to be useful for C–H bond cleavage and forma-
tion.[1–3] Other application fields of isotopic exchange reac-
tions are well established, for example, in medicinal research
and drug discovery processes where deuterated and tritiated
labeled compounds are used to investigate metabolisms.[4–6]
Furthermore, there is an increasing interest in mild and se-
lective catalytic H/D-exchange processes from a fundamen-
tal and application-oriented view.
H/D exchanges catalyzed by transition metals are usually
performed with D2 or in deuterated organic solvents such
as [D6]benzene or [D6]acetone, and in some cases deuterium
oxide or [D4]methanol can be used, unfortunately, in most
cases the reaction temperatures are well above 100 °C or
higher catalyst loadings are necessary.[4,7,8,9,10] Organome-
tallic complexes of iridium, rhodium, and ruthenium show
a particular promising potential as catalysts.[4,8a,b,9c,d,10]
(dtbpmp
=
2,6-bis[(di-tert-butylphosphanyl)methyl]pyr-
idine) is readily accessible in good yields using the direct
hydrogenation route shown in Scheme 1.[12] Complex 1 was
found to catalyze the H/D exchange efficient at 50 °C. It
should be noted that catalytic deuterium incorporation into
[a] Institute of Technical and Macromolecular Chemistry, RWTH
Aachen University,
Worringer Weg 1, 52074 Aachen, Germany
Fax: +49-241-8022177
E-mail: leitner@itmc.rwth-aachen.de
[b] Max-Planck-Institut für Kohleforschung,
Kaiser-Wilhelm-Platz 1, 45470 Mülheim/Ruhr, Germany
[c] Department of Organic Chemistry, Weizmann Institute of Sci-
ence,
76100 Rehovot, Israel
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Scheme 1. Synthesis of 1.[12b]
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hetero aromatic compounds such as thiophene, 2,5-dimeth- 1 at 50 °C within three days. The incorporation took place
ylfuran and indol occurred very efficiently with D2O as the with a clear preference for the meta position (87%), while
deuterium source.[10]
the para protons was much lower deuterated (28%) and no
During these studies, it was observed that complex 1 is significant incorporation was detected in the ortho position.
also an active catalyst for the H/D exchange between [D6]- The methyl group remained unreactive under the present
benzene and aromatic substrates such as toluene
4
conditions. In accordance to this observation, also other
(Scheme 2).[10,12b] In the present work we discuss the results arenes were deuterated by treatment with 1 under similar
of catalytic H/D exchange reactions between arenes and conditions. Again, a significant chemo- and regio-selectivity
[D6]benzene with the non-classical hydride complex was observed in certain cases. o-Xylene 5 was exclusively
[Ru(dtbpmp)(η2-H2)H2] (1) as catalyst precursor. At 50 °C, deuterated in the positions which are meta to the methyl
deuterium is effectively transferred from the solvent C6D6, groups (Ͼ95%). In case of m-xylene 6 the regio-selectivity
into arenes with a significant regioselectivity for certain is largely the same. The proton in the position that is meta
cases. The substrate scope included arenes, olefins and fer- to both methyl groups undergoes almost completely H/D
rocene and we complemented our previous mechanistic in- exchange (93%). The total sum of the deuterium incorpora-
vestigations,[10] by including NMR kinetics and additional tion is low (15%) for all other aromatic positions as well
DFT calculations.
for methyl groups (6%). No H/D exchange was detectable
with mesitylene 7 as substrate, even at higher catalyst load-
ings (2 mol-%). The treatment of naphthalene 8 under the
same conditions as for 4 resulted preferably in β-deuteration
(90%) with a low amount of α-deuteration (18%).
The deuterium incorporation in phenanthrene 9 is also
high and occurs almost exclusively in the two positions C3
and C4 (94%). Interestingly, the heteroaromatic isoquin-
oline 10 was not deuterated under the conditions used in
this study. This might be a result of the stronger coordina-
tion of the nitrogen functionality in isoquinoline 10 sup-
ported by DFT calculations for the two isomeric complexes
10a and 10b (Figure 1).
Figure 1. The isomeric complexes 10a and 10b.
The two isomers should be the ones that compete in the
reaction mechanism for the H/D exchange (vide infra).[10]
The calculations show 10b to be more stable than 10a by
19.6 kcal/mol. As a result the reaction only can take place
if 10b isomerizes to 10a, which is an event that involves de-
coordination of isoquinoline and re-coordination in C–H
binding mode, which does not seem to be possible under
the reaction conditions used in this work.
Aromatic substrates like styrene 11 or indene 12 are also
highly deuterated with a very different chemo- and regio-
selectivity. The olefinic double bond is deuterated preferen-
tially in styrene 11, with terminal positions being most reac-
tive. Almost complete deuteration was observed in both ter-
minal vinylic positions under standard conditions (86–
88%). Very high incorporation (75%) was also obtained in
the ortho and para positions of the aromatic ring. For in-
Scheme 2. Catalytic H/D exchange of aromatic compounds using
C6D6 as the deuterium source and complex 1 as catalyst precursor.
Reaction conditions (under argon): substrate 4–13: 1.0–1.6 mmol;
1 mol-% Ru-cat. 1, C6D6 (0.6 mL), C6H12 (0.05 mL), t = 3 d; reac-
tion temperature: T = 50 °C; see Exp. Sect. for details. The values
give the overall incorporation at the indicated positions.
Results and Discussion
As depicted in Scheme 2, selective H/D exchange oc- dene 12 the deuteration is higher in the five-membered ring
curred when treating toluene 4 with 1 mol-% of precatalyst (69–89%) than in the six-membered ring. Also the incorpo-
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Catalytic H/D Exchange under Mild Conditions
Figure 2. Time-resolved 1H-NMR-monitoring of the H/D exchange in naphthalene 8. Catalyst loading for 1: 4 mol-%, T = 70 °C; conver-
sion: 24% (α), 90% (β) after 240 min.
ration at the sp3 carbon is with 76% higher than in the
positions of the six-membered ring. Finally, the treatment
of ferrocene 13 showed also significant H/D exchange and
about every fourth hydrogen was replaced by deuterium.
The properties of the catalytic system were studied in
more detail with naphthalene 8. As previously reported for
the D2O system, also in the present system the reaction was
not influenced by the addition of mercury.[10] This indicates
a molecular organometallic mechanism.[13] Under the con-
ditions of Scheme 2 the results were identical within the ex-
perimental order in the presence of mercury (Hg/Ru = 10:1;
α: 18%; β: 92%).[13] The kinetics of the reaction were than
investigated by monitoring the H/D exchange at the β-posi-
Figure 3. Logarithmic plot of the β-deuteration at different catalyst
loadings at 50 °C.
tion by 1H NMR spectroscopy at different temperatures
and catalyst loadings. Figure 2 shows the strong signal de-
crease of the β-positions, the lower decrease of the α-posi-
tions and the increase of the benzene signal due to the H/
D exchange. The increase of the deuterium incorporation
at the β-position with precatalyst 1 (7 mol-%) at 50 °C re-
sulted in deuterium incorporation of 79% after 6.5 h and
90% at 24 h respectively. In a second independent run a
deuterium incorporation of 87% (6.5 h) and 95% (24 h) was
obtained. Only 18% of the α-positions were exchanged at
that stage.
A detailed analysis of the spectra between 20 and 70 min
reaction time (Ͻ 30% conversion) revealed an initial rate of
1.23ϫ10–6 molL–1 min–1 for a reaction with 2 mol-%
of
1
at 50 °C (Figure 3). The rate increased to
2.77ϫ10–6 molL–1 min–1 upon doubling the catalyst load-
ing to 4 mol-%. Further increase to 7 mol-% gave a rate of
3.31ϫ10–6 molL–1 min–1. From a double logarithmic plot
of these data (Figure 4), a formal reaction order of 0.8 can
be deduced for catalyst 1. The data are most consistent with
a first-order dependence up to concentrations correspond-
Figure 4. Double logarithmic plot to determine of the data from
Figure 2 to determine the formal reaction order.
The influence of the reaction temperature was investi-
ing to 4 mol-% and a deviation at higher loadings. This may gated at 4 mol-% loading of 1 in the range of 40–70 °C (Fig-
be at least attributed to the formation of unreactive hydride ure 5). The slope of the nearly linear increase between 20
bridged dimers.[12a,14]
and 80 min reaction time was used to determine the acti-
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vation energy of the process. From the Arrhenius plot, also play a role in this reaction. Scheme 3 shows the key
shown in Figure 6, the apparent activation energy is derived steps of the exchange process for both ligand types: [Ru-
as EA = 15.8 kcalmol–1.
(dMepmp)(η2-H2)(C10H8)] (14m) (m for model ligand) as well
as the real catalyst complex [Ru(dtbpmp)(η2-H2)(C10H8)]
(14r) (r for real ligand). Key structural parameters of the
real complexes are shown in Figure 7.
Figure 5. Temperature-dependent conversion/time profiles of the β-
deuteration of naphthalene 8 catalysed by [Ru(dtbpmp)(H2)H2] (1).
Conditions: time-resolved 1H-NMR-monitoring, catalyst loading:
4 mol-%, T = 40–70 °C.
Scheme 3. Relative energies (∆G, ∆G‡, kcal/mol) of reactants, prod-
ucts and transition states (not shown) involved in H/H exchange at
naphthalene in α and β-positions (top to bottom) for model (m)
and real (r) complexes (with basis sets B1 and B2, respectively). All
calculations were carried out employing the B3LYP hybrid func-
tional. ∆G and ∆G‡ values for calculations in the presence of sol-
vent (IEF-PCM; solvent: benzene; only for complexes with the real
ligand) are given in italics.
Complexes with the real ligand are discussed first (reac-
tion of 14ar and 14br to 15ar and 15br, respectively, Figure 7):
for the real complexes the relative stabilities of the reactants
show the α-isomer to be slightly more unstable than the β-
Figure 6. The Arrhenius plot of the β-deuteration catalyzed by
[Ru(dtbpmp)(H2)H2] (1).
We have very recently reported a reaction mechanism for isomer. However, this difference is small, i.e. at the reaction
the H/D exchange for benzene and toluene based on DFT temperature chosen in this work both the α- and the β-
calculations.[10] The mechanism relies on σ-bond metathesis isomer should be present in solution. In the transition states
as the key step. In a four-centre transition-state, one arene the planes of the naphthalene rings are rotated relative to
bonded hydrogen centre reacts with a metal bonded hydride the planes which are formed by the ruthenium centre, the
centre forming metal bonded H2, while the carbon atom of two hydrogen centres attached to it and the nitrogen atom
the arene forms a single bond with the metal. In the present of the pincer backbone (i.e. rotation about the Ru–C bond
study, we have extended these calculations to the exchange that is being formed, Figure 7). This rotation is necessary
of naphthalene as substrate in order to validate the consist- for the molecules to generate the appropriate geometry that
ency of this mechanistic model with the experimental re- enables hydrogen transfer. For the β-isomer (TS14br-15br)
sults. Our previous study had shown that the difference be- the naphthalene ring is rotated about the C1–C2–H1–H2
tween the activation energies of a H,H-transfer is roughly bond by 94°. However, for the α-isomer (TS14ar-15ar) the
1 kcal/mol lower than a H,D-transfer. Therefore only H,H- naphthalene ring can only be rotated up to a value of 83°,
transfer processes are considered in this work for simplicity. on further rotation the repulsive interactions between the
The corresponding local minima (reactants [14a, 14b] and remote phenyl ring of that naphthalene unit and the methyl
products [15a, 15b], a for α isomer, b = β isomer) as well as groups of one tBu substituent will become too strong. Ac-
transition states (TS14a,b-15a,b) were located for complexes cordingly, the transition state geometry of the α-isomer is
containing the real ligand and for a model ligand, in which less ideal resulting in a significantly higher activation energy
the tBu groups of the real ligand were replaced by Me (15.0 kcal/mol relative to the reactant) compared to the β-
groups. The reason for computing the same reaction step isomer (10.4 kcal/mol relative to the reactant).[15]
for both types of ligands was to assess the steric influence
Upon replacement of the tBu groups in the real ligands
of the real ligand and/or to find out if electronic reasons by Me groups in the model ligands the steric strain should
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Catalytic H/D Exchange under Mild Conditions
Figure 7. Calculated structures (B3LYP/B2) of key intermediates and transition states for H/H exchange at the α- (top) and β-positions
(bottom) of naphthalene with selected atom distances [Å] and angles [°].
be minimized, i.e. the steric influence on the activation ener- the real complexes the Ru–C distance of the forming Ru–C
gies should be lowered. For the reaction of 14am to 15am the bond is significantly longer (2.239 Å) in the α-isomer than
calculated Gibb’s free activation energy amounts to in the β-isomer (2.207 Å). The H–H bond, which is being
7.4 kcal/mol (relative to the reactant), while for the β-iso- formed reflects this tendency as well. In the α-isomer the
mer it is 5.1 kcal/mol (Scheme 3), which indicates the steric H–H distance is 1.603 Å, while in the β-isomer the distance
factors play indeed a role in this reaction. Additionally and is slightly shorter (1.592 Å) indicating as well that the pro-
in contrast to the real complexes in the model complexes cess of bond formation has advanced further. Re-optimiza-
the naphthalene units of both isomers are rotated signifi- tion of the real complexes in the presence of benzene as the
cantly further than the rotation in the real complexes. Also solvent showed no significant changes in the energy profiles,
the rotation in the model complexes reaches approximately indicating the solvent to have no drastic influence on the
the same extent (100° and 103° for the α- and the β-isomer, reaction. According to these results one would expect a sig-
respectively; not shown in Figure 7). These values are very nificantly higher deuterium incorporation in the β-position,
similar to the corresponding benzene complex (100°, not with no significant incorporation in the α-position. This is
shown) indicating that in the model complexes there is no in full accord with our experiments which showed that there
sterically induced hindrance for this rotation that is associ- is a clear preference of the β-position (up to Ͼ95% deutera-
ated with the remote part of the naphthalene ring. This is tion) with respect to α-deuteration (Ͻ 20%), which can be
reflected in the energy difference of the two transition influenced by catalyst loadings, temperature and reaction
states: In the model complexes the difference is 2.3 kcal/ time as previously discussed.[10] Overall the experimental
mol, while for the real complexes (vide supra) the difference and computational data generate a consistent picture and
is 4.6 kcal/mol. Therefore it is reasonable to assume that show that the process is facile. Also the computationally
both electronic and steric factors play a role in this reaction. derived activation barriers reflect the experimentally re-
The structures of the transition states indicate further- gioselectivity nicely. This regioselectivity has electronic
more that in the case of the α-isomer the reaction has not grounds which are further improved by steric hindrance ex-
made as much progress as for the β-isomer. For instance, in erted by the tBu groups at the ligand.
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C6H12/[D6]benzene, 25 °C, before H/D exchange): δ = 7.0 (48.6, α/
β), 2.0 (120, Me), 1.3 (100.0, C6H12, internal standard) ppm. 1H
NMR (300 MHz, C6H12/[D6]benzene, 25 °C, after H/D exchange):
Conclusions
We have shown that the non-classical ruthenium hydride
complex 1 is an effective catalyst for the H/D exchange be- δ = 7.0 (25.9 α/β), 2.0 (117.7, Me), 1.3 (100.0, C6H12, internal stan-
dard) ppm. 2H NMR (600 MHz, C6H12/[D6]benzene, 25 °C, after
tween arenes, olefins and [D6]benzene at mild conditions.
The incorporation shows significant chemo- and regio se-
H/D exchange): δ = 6.9 (β-CD), 2.0 (residue, Me) ppm. 13C NMR
(75 MHz, C6H12/[D6]benzene, 25 °C): δ = 136.5 (CMe), 130.1 (α-
CH, β-D1-isotopomer), 130.1 (α-CH, meta-D2-isotopomer), 126.3
lectively in certain cases which is in agreement with our
previous investigations with D2O as deuterium source.[10]
(β-CH, β-D1-isotopomer), 126.0 [β-CD, β-D2-isotopomer, t,
In conclusion, the H/D exchange is independent from the
deuterium source. The DFT calculations show significant
differences in activation energies for the H/D exchange on
naphthalene and support the experimentally observed pref-
erence for the deuteration in β-position. The NMR-kinetics
resulted in an activation energy of 15.8 kcal/mol for the H/
D exchange of the β-position in naphthalene. Further pre-
parative studies towards catalytic applications of 1 and re-
lated complexes are underway.
1J(C,D) = 24.2 Hz] ppm.
m-Xylene 6: Ru-cat 1 (8 mg, 0.016 mmol, 1 mol-%), T = 50 °C, sub-
strate: 170 mg (1.6 mmol), 0.5 mL C6D6, 0.1 mL C6H12, t = 3 d;
conversion: 93% (β), 15% (α), 6% (Me). 1H NMR (300 MHz,
C6H12/[D6]benzene, 25 °C, before H/D exchange): δ = 7.1 (10.8, β),
6.9 (31.2, α), 2.1 (90.0, Me), 1.3 (100.0, C6H12, internal standard)
ppm. 1H NMR (300 MHz, C6H12/[D6]benzene, 25 °C, after H/D
exchange): δ = 7.1 (0.75, β), 6.9 (26.4, α), 2.1 (84.7, Me), 1.3 (100.0,
2
C6H12, internal standard) ppm. H NMR (600 MHz, C6H12/[D6]-
benzene, 25 °C, after H/D exchange): δ = 7.1 (s, β-CD), 7.0 (residue,
α-CD), 2.1 (residue, Me) ppm.
Experimental Section
Mesitylene 7: Ru-cat 1 (8 mg, 1.6 mmol, 1 mol-%), T = 50 °C, sub-
strate: 192 mg (1.6 mmol), 0.5 mL C6D6, 0.1 mL C6H12, t = 3 d.
No conversion detectable.
General: All reactions were performed under Ar and H2 atmo-
spheres using Schlenk or glove box techniques. Solvents and sub-
strates were purchased from Aldrich, Acros and Strem and were
purified according to standard procedures.[16] The PNP ligand
dtbpmp was synthesised according the procedures by Milstein and
Hartwig.[17,18] The syntheses of the ruthenium complexes were car-
ried out in a thick-walled Büchi Miniclave made of glass, similar
to a Fischer–Porter bottle, via the direct-hydrogenation route start-
ing from the [Ru(cod)(η3-C4H7)2] complex.[10,12]
Naphthalene 8: The experiments c–j were analysed by 1H NMR
every ten minutes. a) Ru-cat 1 (5 mg, 0.01 mmol, 1 mol-%), T =
50 °C, substrate: 128 mg (1.0 mmol), 0.6 mL C6D6, 0.05 mL C6H12,
t = 68 h. – a) Ru-cat 1 (5 mg, 0.01 mmol, 1 mol-%), T = 50 °C,
substrate: 128 mg (1.0 mmol), 0.6 mL C6D6, 0.05 mL C6H12, t =
68 h; conversion: 18% (α), 90% (β). – b) Whitesides test: mercury
(20 mg, 0.1 mmol, 10 mol-%) was added to the reaction with a
100 µL Hamilton Micro Syringe without a cannula; conversion:
18% (α), 92% (β). 1H NMR (300 MHz, C6H12/[D6]benzene, 25 °C,
before H/D exchange): δ = 7.6 (17.1, α), 7.2 (16.3, β), 1.4 (100.0,
Caution! The use of pressurised gases can be hazardous and must
only be carried out with suitable equipment and under appropriate
safety precautions.
1
C6H12, internal standard) ppm. H NMR (300 MHz, C6H12/[D6]-
The deuterium incorporation was quantified by integration of the
substrate/product signals in the 1H NMR spectra in ratio to in-
ternal standard cyclohexane. The deuteration were verified by com-
bination of 13C-NMR and 2H NMR spectroscopy. The NMR spec-
tra were recorded on Bruker AMX-300, Bruker AMX-400 (NMR
kinetics) and Bruker DMX 600 (2H NMR) spectrometer.
benzene, 25 °C, after H/D exchange): δ = 7.6 (14.1, α), 7.1 (1.6, β),
1.4 (100.0, C6H12, internal standard) ppm. 2H NMR (600 MHz,
C6H12/[D6]benzene, 25 °C, after H/D exchange): δ = 7.7 (residue,
α), 7.3 (β) ppm. 31P NMR (122 MHz, C6H12/[D6]benzene, 25 °C,
after H/D exchange): δ = 108.0 (s, main signal) ppm. – c) Ru-cat 1
(7 mol-%), T = 50 °C, substrate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL
C6H12; conversion: 79% (β)/6.5 h, 90% (β)/24 h. – d) Ru-cat 1
(7 mol-%), T = 50 °C, substrate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL
C6H12; conversion: 87% (β)/6.5 h, 95% (β)/24 h. – e) Ru-cat 1
(4 mol-%), T = 70 °C, substrate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL
C6H12; conversion: 65% (β)/1.3 h, 90% (β)/4 h. – f) Ru-cat 1
(4 mol-%), T = 60 °C, substrate 0.5 mmol, 0.6 mL C6D6, 0.05 mL
C6H12; conversion: 30% (β)/1.3 h, 64% (β)/4 h. – g) Ru-cat 1
(4 mol-%), T = 45 °C, substrate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL
C6H12; conversion: 21% (β)/1.3 h, 48% (β)/4 h. – h) Ru-cat 1
(4 mol-%), T = 40 °C, substrate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL
C6H12; conversion: 11% (β)/1.3 h, 22% (β)/4 h. i) Ru-cat 1 (2 mol-
%), T = 50 °C, substrate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL C6H12;
conversion: 15% (β)/1.2 h. – j) Ru-cat 1 (4 mol-%), T = 50 °C, sub-
strate: 0.5 mmol, 0.6 mL C6D6, 0.05 mL C6H12; conversion: 28%
(β)/1.3 h, 54% (β)/4 h.
Procedure for Catalytic H/D Exchange between Arenes and [D6]Ben-
zene with [Ru(dtbpmp)(η2-H2)H2] as Catalyst, Exemplified for Tolu-
ene 4: A Teflon®-capped Young NMR tube was filled with the cata-
lyst 1 (5 mg, 0.01 mmol, 1 mol-%), then 0.6 mL of C6D6 was added.
The substrate 4 (92 mg, 1.0 mmol) and 0.05 mL cyclohexane (in-
ternal standard) were added. The 1H NMR spectrum was measured
immediately in order to determine the substrate/internal standard
ratio as starting point of the reaction. The mixture was kept for
three days at 50 °C, afterwards it was cooled to room temp. and
1
2
the H- and H NMR spectra were measured (manual lock to [D6]
benzene; conversion: 87% (meta), 28% (para), Ͻ 5% (ortho), 1%
1
(Me). H NMR (300 MHz, C6H12/[D6]benzene, 25 °C, before H/D
exchange): δ = 7.1 (23.5, meta-H), 7.0 (32.5, ortho/para-H), 2.1
(48.4, Me), 1.3 (100.0, C6H12, internal standard), –7.5 (Ru-H) ppm.
1H NMR (300 MHz, C6H12/[D6]benzene, 25 °C, after H/D ex-
change): δ = 7.07 (3.0, meta-H), 6.8 (23.4, ortho/para-H), 2.1 (47.8,
Me), 1.3 (100.0, C6H12, internal standard) ppm. 2H NMR
(600 MHz, C6H12/[D6]benzene, 25 °C, after H/D exchange): δ = 7.3
(meta-D), 7.2 (ortho/para-D), 2.4 (weak, Me) ppm.
Phenanthrene 9
o-Xylene 5: Ru-cat 1 (8 mg, 0.016 mmol, 1 mol-%), T = 50 °C, sub-
strate: 170 mg (1.6 mmol), 0.5 mL C6D6, 0.1 mL C6H12, t = 3 d;
1
conversion: 95% (β), Ͻ 5% (α), Ͻ 5% (Me). H NMR (300 MHz,
3498
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3493–3500

Catalytic H/D Exchange under Mild Conditions
Ru-cat 1: 5 mg (0.01 mmol, 1 mol-%), T = 50 °C, substrate: 178 mg basis set by Ahlrichs et al.[21] in the implementation that is used in
(1.0 mmol), 0.5 mL C6D6, 0.05 mL C6H12, t = 3 d; conversion: Ͻ
5% (C1), 7% (C2), 40% (C3, C4), Ͻ 5% (C5). 1H NMR (300 MHz,
C6H12/[D6]benzene, 25 °C, before H/D exchange): δ = 8.4 (17.6,
C5), 7.6 (15.9, C2), 7.4 (16.4, C1), 7.3 (31.5, C3/C4), 1.4 (100.0,
C6H12, internal standard) ppm. H NMR (300 MHz, C6H12/[D6]-
benzene, 25 °C, after H/D exchange): δ = 8.4 (16.9, C5), 7.6 (13.2,
the Gaussian03 program, while for ruthenium the Stuttgart/
Dresden (311111/22111/411) basis set and associated ECP was
used.[22] This basis set is denoted B1. For real complexes (i.e. tBu
substituents at P) all nonmetal atoms were calculated using the 6-
31G(d) basis set.[23] For the hydrogen centres bonded to the metal
(2 centres) and the hydrogen centre of the naphthalene taking part
1
C2), 7.4 (15.7, C1), 7.2 (1.9, C3/C4), 1.4 (100.0, C6H12, internal in the reaction (1 centre) polarization functions were added, so that
standard) ppm. 2H NMR (600 MHz, C6H12/[D6]benzene, 25 °C, af-
ter H/D exchange): δ = 7.3 (C3/C4) ppm.
these 3 hydrogen centres were calculated with the 6-31G(d,p) basis-
set. For the ruthenium centre a (441/2111/31/1) basis set[24a] in com-
bination with a nonrelativistic small core ECP was used.[24b] This
basis set is denoted B2. All stationary points were checked by fre-
quency calculations to prove the existence of local minima (zero
imaginary frequencies) or saddle points of order 1 (one imaginary
frequency). Calculations (geometry optimization followed by fre-
quency calculation, B3LYP/B2) in the presence of a solvent (ben-
zene) were carried out using the self-consistent reaction field
(SCRF) formalism, as implemented in Gaussian 03 employing the
IEF-PCM (integral equation formulation of the polarizable contin-
uum model).[25] together with the united atom topological model
for radii. Extra spheres for hydrogen were added for the hydrogen
centres present at the Ru center and the hydrogen centre of the
naphthalene involved in the reaction. During the geometry optimi-
zations and the subsequent frequency calculations, the calculation
of dispersion solute–solvent interaction energy, of repulsion solute–
solvent interaction energy, and of the cavitation energy were
switched off.
Isoquinoline 10: Ru-cat 1 (5 mg, 0.01 mmol, 1 mol-%), T = 50 °C,
substrate: 129 mg (1.0 mmol), 0.5 mL C6D6, 0.05 mL C6H12, t =
3 d. No conversion detectable.
Styrene 11
Ru-cat 1: 5 mg (0.01 mmol, 1 mol-%), T = 50 °C, substrate: 104 mg
(1.0 mmol), 0.5 mL C6D6, 0.05 mL C6H12, t = 3 d; conversion: 14%
1
(m), 74% (o/p), 35% (x), 86% (a), 88% (b). H NMR (300 MHz,
C6H12/[D6]benzene, 25 °C, before H/D exchange): δ = 7.0 (33.7, m),
6.8 (50.3, o/p), 6.3 (15.9, x), 5.3 (18.1, a), 4.8 (17.1, b), 1.2 (100.0,
1
C6H12, internal standard) ppm. H NMR (300 MHz, C6H12/[D6]-
benzene, 25 °C, after H/D exchange): δ = 7.0 (29.0, m), 6.8 (12.8,
o/p), 6.3 (10.4, x), 5.3 (2.5, a), 4.8 (2.0, b), 1.3 (100.0, C6H12, in-
ternal standard) ppm. 2H NMR (600 MHz, C6H12/[D6]benzene,
25 °C, after H/D exchange): δ = 7.3 (m), 7.1 (o/p), 6.6 (x), 5.6 (a),
5.1 (b) ppm.
Acknowledgments
The Mynott group (R. Ettl, C. Wirtz, W. Wisniewski, M. Stachel-
haus, B. Waßmuth and R. Mynott) is acknowledged for NMR and
IR experiments. RWTH Aachen, Max-Planck-Gesellschaft and
German–Israeli Project Cooperation (DIP G7.1) are gratefully ac-
knowledged for financial support. We are also grateful for generous
allocation of computer time by the Computation and Communica-
tion Centre of the RWTH Aachen.
Indene 12
Ru-cat 1: (5 mg, 0.01 mmol, 1 mol-%), T = 50 °C, substrate: 116 mg
(1.0 mmol), 0.5 mL C6D6, 0.05 mL C6H12, t = 3 d; conversion: 62%
(C1, C2), 27% (C3, C6), 69% (C7), 89% (C8), 76% (C9). 1H NMR
(300 MHz, C6H12/[D6]benzene, 25 °C, before H/D exchange): δ =
[1] P. J. Jessop, R. H. Morris, Coord. Chem. Rev. 1992, 121, 155–
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[2] S. Sabo-Etienne, B. Chaudret, Coord. Chem. Rev. 1998, 178–
7.3 (31.6, C1, C2), 7.3–7.1 (33.2, C3, C6), 6.7 (17.1, C7), 6.2 (14.9,
180, 381–407.
1
C8), 3.0 (42.0, C9), 1.4 (100.0, C6H12, internal standard) ppm. H [3] F. Kakiuchi, S. Murai, Acc. Chem. Res. 2002, 35, 826–834.
[4] a) J. T. Golden, R. A. Andersen, R. G. Bergman, J. Am. Chem.
Soc. 2001, 123, 5837–5838; b) S. R. Klei, J. T. Golden, T. D.
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NMR (300 MHz, C6H12/[D6]benzene, 25 °C, after H/D exchange):
δ = 7.3 (23.1, C1, C2), 7.3–7.1 (12.7, C3, C6), 6.7 (5.3, C7), 6.2
(1.6, C8), 3.0 (10.0, C9), 1.4 (100.0, C6H12, internal standard) ppm.
2H NMR (600 MHz, C6H12/[D6]benzene, 25 °C, after H/D ex-
change): δ = 7.3 (C1, C2), 7.1–7.0 (C3, C6), 6.7 (C7), 6.2 (C8), 3.0
(C9) ppm.
Ferrocene 13: Ru-cat 1 (5 mg, 0.01 mmol, 1 mol-%), T = 50 °C, sub-
strate: 186 mg (1.0 mmol), 0.6 mL C6D6, 0.05 mL C6H12, t = 3 d;
[5] A. F. Thomas, Deuterium Labelling in Organic Chemistry 1971,
Meridith Cooperation, New York.
1
conversion: 25%. H NMR (300 MHz, C6H12/[D6]benzene, 25 °C,
[6] T. H. Lowry, K. S. Richardson, Mechanism and Theory in Or-
ganic Chemistry 1987, Harper and Row, New York.
[7] B. Rybtchinski, R. Cohen, Y. Ben-David, J. M. L. Martin, D.
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[8] a) C. P. Lenges, P. S. White, M. Brookhart, J. Am. Chem. Soc.
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before H/D exchange): δ = 4.0 (35.2, Cp-H), 1.4 (100.0, C6H12,
internal standard) ppm. H NMR (300 MHz, C6H12/[D6]benzene,
25 °C, after H/D exchange): δ = 3.7 (26.5, Cp-H), 1.4 (100.0, C6H12,
internal standard) ppm. 2H NMR (600 MHz, C6H12/[D6]-
benzene, 25 °C, after H/D exchange): δ = 4.0 (Cp-D) ppm.
1
Computational Studies: The calculations reported herein were car-
ried out with the Gaussian 03 program series (revision C02).[19]
Local minima and transition states were calculated employing the
B3LYP hybrid functional.[20] For model complexes (i.e. Me substit-
uents at P) all nonmetal atoms were calculated using the TZVP
Eur. J. Inorg. Chem. 2008, 3493–3500
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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Received: April 8, 2008
Published Online: June 25, 2008
3500
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3493–3500