Reactivity of the chiral metallic Bronsted acid [(η6- p -MeC6H4 i Pr)Ru(κ3 P, O,O'- POH)][SbF6]2 (POH = (S C1, R C2)-Ph2PC(Ph)HC(OH)HCH2OMe) toward aldimines

Article abstract of DOI:10.1021/om501018r

Dichloromethane solutions of complex 1 catalyze both the aza-Diels-Alder (ADA) reaction of aldimines with cyclopentadiene and the aza-Friedel-Crafts (AFC) reaction between aldimines and indoles. Racemic adducts were obtained in both cases. NMR measurements of mixtures of the aldimine N-(4-methylbenzylidene)aniline (I) and 1, in a 20/1 molar ratio, reveal the formation of the deprotonated compound 2 and the corresponding iminium cation HI⁺ (H-N⁺). This cation is responsible for the achiral catalysis. Below 273 K, in 1/1 molar ratio mixtures of 1 and I, the chiral species 1·I (O-H···N) and 2·HI⁺ (O^-···H-N⁺) were formed by intermolecular hydrogen bonding and proton transfer, respectively. The latter solutions catalyze stoichiometrically the ADA reaction between aldimine I and HCp with 16% ee. With 5 mol % of catalyst loading, a 6% ee can be obtained if the aldimine is slowly added to the solution (20 equiv in 60 h). Above 273 K, solutions containing 1 and aldimine I irreversibly evolve to the aniline complex 3, which was isolated as a racemic mixture. The molecular structure of 3 has been determined by X-ray diffractometric methods. Hydride 5, an intermediate in this reaction, has been isolated and spectroscopically characterized. On the basis of synthetic and spectroscopic studies, a plausible pathway for the formation of 3 from 1 is proposed.

Full text of DOI:10.1021/om501018r

Article
pubs.acs.org/Organometallics
Reactivity of the Chiral Metallic Brønsted Acid
[(η6‑p‑MeC6H4iPr)Ru(κ3P,O,O′-POH)][SbF6]2 (POH =
(SC1,RC2)‑Ph2PC(Ph)HC(OH)HCH2OMe) toward Aldimines
́
Pilar Pardo, Daniel Carmona,* Pilar Lamata,* Ricardo Rodrıguez,* Fernando J. Lahoz,
́
Pilar Garcıa-Orduna, and Luis A. Oro
̃
́
́
́
Departamento de Quımica Inorganica, Instituto de Sıntesis Quımica y Catalisis Homogenea (ISQCH), CSIC-Universidad
́
́
́
de Zaragoza, Pedro Cerbuna 12, 50009 Zaragoza, Spain
S
* Supporting Information
ABSTRACT: Dichloromethane solutions of complex 1
catalyze both the aza-Diels−Alder (ADA) reaction of
aldimines with cyclopentadiene and the aza-Friedel−Crafts
(AFC) reaction between aldimines and indoles. Racemic
adducts were obtained in both cases. NMR measurements of
mixtures of the aldimine N-(4-methylbenzylidene)aniline (I)
and 1, in a 20/1 molar ratio, reveal the formation of the deprotonated compound 2 and the corresponding iminium cation HI+
(H−N+). This cation is responsible for the achiral catalysis. Below 273 K, in 1/1 molar ratio mixtures of 1 and I, the chiral species
1·I (O−H···N) and 2·HI+ (O−···H−N+) were formed by intermolecular hydrogen bonding and proton transfer, respectively. The
latter solutions catalyze stoichiometrically the ADA reaction between aldimine I and HCp with 16% ee. With 5 mol % of catalyst
loading, a 6% ee can be obtained if the aldimine is slowly added to the solution (20 equiv in 60 h). Above 273 K, solutions
containing 1 and aldimine I irreversibly evolve to the aniline complex 3, which was isolated as a racemic mixture. The molecular
structure of 3 has been determined by X-ray diffractometric methods. Hydride 5, an intermediate in this reaction, has been
isolated and spectroscopically characterized. On the basis of synthetic and spectroscopic studies, a plausible pathway for the
formation of 3 from 1 is proposed.
Chart 1. Brønsted Acid Catalyst 1
INTRODUCTION
■
Brønsted acid catalysis constitutes an important branch of
organocatalysis that has grown at a dramatic pace over the past
few years.1 Activation of the substrate takes place through either
proton transfer or hydrogen bonding. As one of the most
representative examples, imines, carbonyl, and nitro compounds
have been efficiently activated by highly acidic chiral Brønsted
acids derived from binol.2
On the other hand, chiral catalysts based on transition metals
are among the most efficient and versatile for the preparation of
enantioenriched compounds.3 Metallic catalysts usually activate
organic substrates acting as Lewis acids, and therefore, the
catalytic reaction occurs when at least one of the substrates is
coordinated to the metallic fragment.4
However, we have recently reported the activation of the
carbonyl of trifluoromethyl pyruvates toward the hydroxyalkyl-
ation of indoles through the protons of a molecule of water
coordinated to a chiral cationic Ir(III) fragment. Experimental
and theoretical calculations indicate that catalysis takes place
without coordination of the substrates to the metal.5 Also
recently, we have prepared and characterized the 18-electron
ruthenium complex (RRu,SC1,RC2)-[(η6-p-MeC6H4iPr)Ru-
(κ3P,O,O′-POH)][SbF6]2 (POH = (SC1,RC2)-Ph2PC(Ph)HC-
(OH)HCH2OMe; Chart 1). This complex activates CC and
CO bonds toward Diels−Alder and Friedel−Crafts hydroxy-
alkylation reactions by acting as a Brønsted acid through its OH
functionality. Enantiomeric excesses of up to 81% were
achieved.6 The acidic properties of the OH group are enhanced
by coordination to the metallic cation, resulting in a Lewis acid
assisted Brønsted acid catalyst (LBA).7
Application of Brønsted acid metal complexes in catalysis is
scarce,7,8 and as far as we know, activation of imines has not been
attempted with catalysts of this class. We anticipated that the
study of metal-based Brønsted acid/imine systems would also
contribute to a better understanding of the nature of the catalyst/
substrate complexes involved in Brønsted acid organocatalysis.
In the present paper, we report on the results obtained when
attempting the activation of the CN bond of aldimines by 1.
Special attention has been paid to the detection and character-
ization of the intermediates involved in the process.
Received: October 6, 2014
Published: November 17, 2014
© 2014 American Chemical Society
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Scheme 1. Catalytic Aza-Diels−Alder Reactions
Scheme 2. Catalytic Aza-Friedel−Crafts Reactions
To obtain information about the catalytic processes, mixtures
of the imine N-(4-methylbenzylidene)aniline (I) and compound
1 were studied by NMR spectroscopy. Chart 2 collects the new
species potentially present in the solutions. The RRu,SC1,RC2
diastereomer of compound 2, obtained by deprotonation of 1,
has been recently reported.6 While complex 1·I would result
from O−H···N hydrogen bond formation between compound 1
and aldimine I, compound 2·HI+ is formed by proton transfer
from 1 to I, leading to an O−···H−N+ interaction. The iminium
cation HI+, which would proceed from the protonation of the
aldimine by complex 1, most likely would afford the hydrogen-
bonded species I···HI+ in the presence of excess imine.
RESULTS AND DISCUSSION
■
Catalysis. Dichloromethane solutions of complex 1 catalyze,
at room temperature, the aza-Diels−Alder (ADA) reaction
of aldimines I−III with cyclopentadiene (Scheme 1), as well
as the aza-Friedel−Crafts (AFC) reaction between aldimines I,
IV, and V and indoles (Scheme 2). The molar ratios 1/20/120
catalyst/imine/HCp and 1/20/30 catalyst/indole/imine were
employed for the ADA and AFC reactions, respectively.
In general, good conversions were obtained after some hours
of reaction, with endo/exo molar ratios of up to 94/6 for
the ADA reaction. Important amounts of the corresponding
bis(indole) derivative (up to 97%) were obtained for the AFC
reaction. In spite of 1 being enantiopure, racemic adducts were
obtained in all cases. Racemic products were also obtained
when the catalytic reactions were performed at 248 K.
The chemical shifts of the acidic proton for the hydrogen-
bonded species I···HI+ (10.70 ppm, vbr) and for the iminium
HI+ (11.49 ppm, vbr) were measured, at 183 K, from CD2Cl2
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9.71 ppm together with a set of peaks with chemical shifts and
multiplicities close to those expected for the free imine (see the
Supporting Information). Thus, the spectra9 are compatible with
the existence of an equilibrium between the free aldimine I and
the hydrogen-bonded cation I···HI+, free imine being the most
abundant species. This equilibrium is detected in the entire range
of temperatures measured (193−293 K).
Chart 2. Species Derived from the Interaction of Catalyst 1
with Imine I, Including Its Deprotonation Product 2
In summary, under catalytic conditions, complex 1, acting as a
Brønsted acid, activates the aldimine by protonation. Obtaining
racemic adducts could be accounted for by assuming that the
resulting achiral iminium cation is the key compound for
the catalytic activity. In independent experiments, it has been
shown that, as expected, at room temperature, HBF4 catalyzes
the reaction between imine I and HCp or 1,2-dimethylindole at
rates similar to those shown in Schemes 1 and 2, respectively.
Bis(indole) was also formed in the AFC reaction, and obviously,
racemic adducts were obtained in both cases (see the Supporting
Information).
To obtain a deeper insight regarding the interaction between
compound 1 and imines, mixtures of this compound and
aldimine I in a 1/1 molar ratio were studied by NMR
1
spectroscopy (Figure 2). Above 233 K, the H NMR spectra
Figure 2. Selected region of the 1H NMR spectra of a 1/1 molar ratio
mixture of imine I and complex 1, at different temperatures. The asterisk
denotes the aldehydic proton of 4-methylbenzaldehyde.
Figure 1. 31P{1H} NMR spectra of a 20/1 molar ratio mixture of imine I
and complex 1, at different temperatures. Trace A corresponds to
starting complex 1.
showed only one broad averaged signal, centered at about
11.7 ppm, for the acidic proton. Below 203 K, this signal splits
into three resonances at around 13.4, 11.5, and 10.6 ppm.10 The
three resonances are broad even at 183 K, the lowest attained
temperature, with full widths at half-height of 179, 50, and
102 Hz, respectively. The broadness of the proton signals
hampers the detection of magnetization transfer. Thus, at 183 K,
cross-peaks were not observed in either the 1H, 15N HMQC or
the 1H, 31P HMBC spectra. The proton signal at 11.5 ppm is very
close to that measured for the iminium HI+ cation (11.49 ppm),
and we suspect that the metallic hydrogen-bonded species 1·I
(O−H···N) and the ion pair complex 2·HI+ (O−···H−N+)
(Chart 2) are the other two compounds involved in the equilibria
that generate the three broad acidic signals observed. Above
273 K, the progressive formation of 3 was observed.
solutions of imine I with 0.5 equiv and 1.0 equiv of HBF4,
respectively (see the Supporting Information).
Figure 1 shows the 31P{1H} NMR spectra of a 20/1 molar ratio
mixture of I and 1 (the ratio employed in the ADA catalytic
reactions) at different temperatures, together with the 31P{1H}
NMR spectrum of the starting complex 1 (trace A). From 193 to
253 K (traces B−E), the spectra consist of only one resonance
at around 59.0 ppm. The chemical shift value and the gradual
small upfield shift of the resonance as the temperature increases
are identical with those found for pure samples of the de-
protonated compound 2 (Chart 2).6 At temperatures ≥273 K
(traces F and G) the progressive formation of a new metallic
compound 3 (δ(P) 63.66 ppm, 293 K) at the expense of 2 was
observed. After 2 h at 293 K (trace H), compound 3 is the only
phosphorus-containing species present in the solution. The
characterization of 3 as well as its formation pathway from 1 is
discussed below. In independent experiments, it has been shown
that neither complex 2 nor complex 3 catalyzes the reactions
between imine I and HCp or indole.
However, in the 31P{1H} NMR spectra, from 183 to 273 K,
only one averaged singlet around 59.1 ppm was detected. This
resonance is shifted downfield only 0.2 ppm with respect to that
obtained for complex 2. These 31P{1H} NMR data are also
compatible with the existence of an equilibrium between
compound 2 and the metallic species 1·I and 2·HI+.
At 193 K, the proton NMR spectra of these mixtures (I/1,
20/1 molar ratio) present a low-field resonance centered at
To give support to the presence of the chiral metallic species
1·I and 2·HI+, the DA reaction between imine I and HCp was
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carried out stoichiometrically (I/1, 1/1 molar ratio), at 248 K. A
16% ee was obtained, showing the presence of chiral species in
the reaction medium.
of the complex is depicted in Figure 3, and selected structural
parameters are summarized in Table 1.
The observed structural features are similar to those reported
for parent complex 1.6 The metal atom is pseudotetrahedral,
being coordinated to a p-MeC6H4iPr group and to the phos-
phorus and to the two oxygen atoms of the PO fragment in a
κ3P,O,O′ coordination mode. The ruthenium retains its R
configuration.11 The five-membered metallacycles (Ru−P(1)−
C(23)−C(24)−O(1) and Ru−O(1)−C(24)−C(25)−O(2))
exhibit envelope conformations in both complexes with similar
deviations from a planar geometry.12
Concerning the intramolecular geometry, deprotonation of
the POH ligand seems to only affect the Ru−O(1) bond length,
which is shortened in complex 4 with respect to that in com-
pound 1 (2.130(5) and 2.063(5) Å in 1 and 4, respectively). As
shown in Figure 3, the most interesting feature of the cation of
4 is the encountered interaction between the oxygen O(1) and
the iminium cation resulting from the proton transfer to the
4-methylpyridine nitrogen atom. The strength of this O···H−N
interaction is borne out by its geometrical parameters (N−H,
0.88(2) Å; H···O, 1.85(7) Å; N···O, 2.605(9) Å; N−H···O,
144(6)°), specially by the short N···O distance.
From these NMR data, we realized that only at low imine
concentrations (and preferably below 273 K) would species
containing interactions between the ruthenium complex 1
and imines be present in the solution. To obtain asymmetric
induction, these species have to be involved in the catalysis. We
therefore anticipated that enantioenriched products could be
obtained by slow addition of the imine to a solution containing
complex 1 and HCp or indoles. In fact, at 248 K, the slow
addition of the imine I (20 equiv over 60 h) to a solution of 1 and
120 equiv of HCp resulted in a 98% conversion to the
corresponding Diels−Alder adduct with a 91/9 endo/exo ratio
and 6% ee.
A model for the 2·HI+ (O−···H−N+) species (Chart 2) has
been isolated and completely characterized from the reaction
between 1 and 4-methylpyridine. Thus, the addition of 1 equiv of
the pyridine to dichloromethane solutions of complex 1 affords
compound 4 (Figure 3) in 85% isolated yield. The complex was
Reaction Pathway from 1 to 3. Complex 3 was isolated by
treating 1 with the imine I in wet CH2Cl2. It was characterized
by analytical and spectroscopic means (see the Experimental
Section) as well as by X-ray analysis. Selected structural param-
eters are given in Table 1. Compound 3 crystallizes as a racemate
in the centrosymmetric space group P21/c. Its molecular
structure (Figure 4) reveals the κ2P,O coordination of the new
Figure 3. Molecular structure of complex 4 showing the interaction
between the O and the NH group. Hydrogen atoms, except for the atom
involved in the hydrogen bond, are omitted to aid clarity. Ellipsoids are
drawn at the 50% probability level.
characterized by microanalysis and IR and NMR spectroscopy.
At room temperature, the acidic proton of complex 4 resonates at
11.76 ppm and its 31P{1H} NMR spectrum consists of one
singlet at 58.71 ppm, very close to that attributed to the
phosphorus nucleus in complex 2 under the same conditions.
Single crystals suitable for X-ray diffraction analysis of complex 4
were obtained by slow diffusion of diethyl ether into dichloro-
methane solutions of the compound. A molecular representation
Figure 4. Molecular representation of the cation of 3. Hydrogen
atoms are omitted to aid clarity. Ellipsoids are drawn at the 50%
probability level.
Ph2PC(Ph)C(O)CH2OMe fragment and the presence of
coordinated aniline. The presence of a CC double bond
between the C(23) and C(24) carbon of this fragment is clear
Table 1. Selected Bond Lengths (Å) and Angles (deg) for Complexes 4 and 3
4
3
4
3
Ru−P(1)
Ru−O(1)
Ru−O(2)
2.3328(19)
2.063(5)
2.170(5)
2.3282(9)
2.066(2)
Ru−N(1)
Ru−Ct
C(23)−C(24)
2.066(2)
1.729(3)
1.371(6)
a
1.690(3)
1.558(10)
P(1)−Ru−O(1)
P(1)−Ru−O(2)
P(1)−Ru−N(1)
P(1)−Ru−Ct
77.85(16)
78.75(15)
81.30(8)
O(1)−Ru−N(1)
O(1)−Ru−Ct
N(1)−Ru−Ct
O(2)−Ru−Ct
82.39(11)
124.75(13)
130.97(13)
129.56(19)
134.55(19)
85.04(8)
135.24(13)
78.3(2)
133.96(11)
O(1)−Ru−O(2)
a
Ct is the centroid of the ring of the p-MeC6H4iPr group.
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from the bond length (1.371(6) Å) and the significantly smaller
deviation from planarity found in the Ru−P(1)−C(23)−
C(24)−O(1) metallacycle, which adopts an arrangement
between envelope E2 and twist 3T2 conformations.12
or 2 equiv of NaHCO3 afforded the neutral hydride complex
[(η6-p-MeC6H4iPr)Ru(κ2P,O-Ph2PC(Ph)C(O)CH2OMe)H]
(5), which was isolated and spectroscopically characterized (see
the Experimental Section). In particular, a doublet centered at
−7.79 ppm (2J(PH) = 44.9 Hz) in its 1H NMR spectrum and a
singlet at 72.96 ppm in its 31P{1H} NMR spectrum denote the
presence of the hydride and phosphorus ligands, respectively. We
suggest that imines, acting as bases, also give 5 from 1. Notably,
isolated 5 reacts with the iminium cation prepared from imine
I and aqueous HSbF6 rendering complex 3 (see the Experimental
Section).
1
On the other hand, inspection of the H NMR spectra of
mixtures of complex 1 with excess of the imine I, at room
temperature, gave us an insight into the mechanism of the
formation of 3 from 1. The spectra reveal the presence of (i) a
singlet at 9.92 ppm attributed to the aldehydic proton of
4-methylbenzaldehyde, (ii) a signal at 9.71 ppm (at 193 K)
attributed to the excess of imine most likely in equilibrium with a
small proportion of the hydrogen-bonded species I···HI+, and
(iii) a small amount of 1-(p-tolylmethyl)phenylamine, most
probably derived from the hydrogenation of the imine.
According to the NMR data, eq 1 can be proposed for the
formation of 3 upon treatment of 1 with I.
The reaction pathway depicted in Scheme 4 accounts for all of
the above observations. While the methoxy arm of the POH
ligand is tightly bonded to the metal in complex 1,13 it dissoci-
ates easily in the deprotonated monocation 2. Then, the inter-
mediate hydride A would be formed by a β-elimination reaction.
Epimerization at the metal must precede this β-elimination: only
in the RRu,SC1,RC2 epimer is the required interaction between
the involved β-hydrogen and the metal possible (Scheme 5).
Intermediate B is the enolic form of hydride A, which in turn can
be deprotonated by a second molecule of imine, rendering
hydride 5. The acidic proton of the iminium cations, formed over
the process, reacts with the hydridic Ru−H hydrogen atom,
leading to hydrogen loss. Furthermore, this iminium cation
affords aniline and 4-methylbenzaldehyde, by hydrolysis. Taking
advantage of the vacancy generated by the elimination of H2, the
amine coordinates the metal, affording the final complex 3.
According to Scheme 5, the formation of A from 2 is com-
pletely diastereoselective: starting from the RRu,SC1,RC2 isomer of
complex 2, only the isomer RRu,SC1-A can be formed. Although
chirality could be eroded on going from intermediate A to hydride
5, the circular dichroism (CD) spectrum of 5 shows maxima
centered at 434, 331, and 316 nm whose intensity decreases
with time. This behavior indicates that 5 was obtained as an
enantioenriched complex and that it slowly racemizes in solution.
However, the CD spectrum of 3 is silent, showing that either it
quickly racemizes or racemization occurs on going from 5 to 3.
A plausible catalytic cycle that accounts for the observed
hydrogenation of the imine I is depicted in Scheme 6. The imine
CN double bond interacts with intermediate B (Scheme 4),
affording the outer-sphere Noyori type intermediate D.14
Transfer of the O−H and Ru−H hydrogen atoms to the imine
reduces the double bond and gives the unsaturated species C.
Activation of molecular hydrogen by C regenerates B, which
restarts the catalytic cycle.
On examination of the reaction products, the role of the imine
is 2-fold. On the one hand, it deprotonates the POH ligand acting
as a base; on the other, it provides the aniline ligand present in
3 as well as the detected 4-methylbenzaldehyde, by hydrolysis.
In addition, the hydrogen produced in the reaction hydro-
genates the imine CN bond. In fact, when 3 equiv of imine
I and 10 bar of H2 were added to a solution containing the
products of eq 1, hydrogenation of the aldimine was apparent by
proton NMR. A catalytic cycle for this hydrogenation reaction is
proposed below.
To establish the role of the aldimine as a base, the reactivity of
complex 1 with inorganic bases was studied (Scheme 3).
Addition of 1 equiv of Na2CO3 or equimolar amounts of
NaHCO3 to methanolic solutions of 1 gave complex 2 in high
yield.6 However, the addition of equimolar amounts of Na2CO3
Scheme 3. Reactions of 1 and 2 with Inorganic Bases
When the reactions between complex 1 and aldimine I or
N-benzylidenebenzylamine (VI) were carried out under strictly
Scheme 4. Plausible Pathway for the Reaction of 1 with Imine I in the Presence of Water
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Scheme 5. β-Elimination Reaction
crystallographically determined compound 3 (see the Exper-
imental Section).
Scheme 6. Proposed Catalytic Cycle for the Hydrogenation of
Imine I
CONCLUSIONS
■
The Brønsted acid complex 1 activates aldimines for ADA
and AFC reactions through a proton-transfer process. Using
5 mol % of catalyst (I/1 molar ratio 20/1), the catalytically active
species present in the solution is the achiral iminium cation
HI+ (Chart 2). Therefore, racemic adducts were obtained. It is
likely that, at low temperatures, under stoichiometric conditions
(I/1 molar ratio 1/1) significant amounts of the chiral metallic
species 1·I (O−H···N) and 2·HI+ (O−···H−N+) (see Chart 2)
were present in the catalytic solutions. Consequently, under
these conditions, measurable ee values were obtained for the
ADA reaction between I and HCp. At 248 K, slow addition of
aldimine I to solutions containing complex 1 and HCp also
generates the chiral metallic species mentioned above, and
therefore, ee values were obtained for the catalytic process.
Isolation and X-ray characterization data of the related proton-
transfer species 4 provide support for the formation of the 2·HI+
(O−···H−N+) compounds. At temperatures higher than 273 K,
in the presence of imine I and traces of water, complex 1 evolves
to the amine-containing derivative 3, through the deprotonated
complex 2. It has been shown that the hydride complex 5 is
another intermediate in this transformation. Under strictly
anhydrous conditions the related imino derivative 6 was obtained
instead. A plausible pathway for the evolution from 1 to 3, which
includes successive β-hydride elimination and keto−enol
tautomerie steps, was proposed.
Chart 3. Imine Complexes 6 and 7
EXPERIMENTAL SECTION
■
Measurements. All preparations have been carried out under argon.
All solvents were treated in a solvent purification system and degassed
prior to use. Most measurements were conducted with standard
commercial instruments, as detailed in the Supporting Information. In
1H NMR and 13C NMR, the chemical shifts are expressed in ppm
anhydrous conditions, complexes 6 and 7 (analogous to complex
3 containing an imine coordinated to the ruthenium) were
isolated (Chart 3). The complexes were characterized by IR and
NMR spectroscopy (see the Experimental Section). Proton
and carbon assignments were accomplished through NOE
experiments and two-dimensional homonuclear and hetero-
nuclear correlations. As the formation of the amine through
hydrolysis of the corresponding aldimine has been avoided,
imines I or VI, present in the reaction medium, coordinate to the
metal instead.
The formation of complexes related to 3 by reaction of
compound 1 with aldimines, under wet conditions, is more
general. Thus, complex 1 reacts with aldimine VI to give the
benzylamine analogue of complex 3, [(η6-p-MeC6H4iPr)Ru-
(κ2P,O-Ph2PC(Ph)C(O)CH2OMe)(benzylamine)][SbF6]
(8). Complex 8 has been characterized by the usual analyti-
cal and spectroscopic methods, taking advantage of the
similarity of its spectroscopic properties to those of the
downfield from SiMe4. The 31P NMR chemical shifts are relative to
85% H3PO4. J values are given in Hz. NOESY and 13C, 31P, 1H
correlation spectra were obtained using standard procedures.
General Catalytic Procedure for the Aza-Diels−Alder Re-
action. Under argon, in a Schlenk flask equipped with a magnetic stirrer,
complex 1 (31.7 mg, 0.03 mmol) was dissolved in dry CH2Cl2 (3 mL), at
room temperature, and the corresponding imine I−III (0.60 mmol) was
added. After the mixture was stirred for 10 min, freshly distilled
cyclopentadiene (0.3 mL, 3.60 mmol) in 1 mL of dry CH2Cl2 was added.
The reaction was monitored by TLC chromatography. After the
appropriate reaction time, the solution was concentrated under vacuum
to dryness and the residue was extracted with 3 × 10 mL of diethyl ether.
The resulting suspension was filtered over Celite and evaporated to
dryness. The crude product was purified by column chromatography
with silica as a stationary phase and an n-hexane/ether (8/2) mixture as
1
eluent. The conversion and endo/exo ratio were determined by H
NMR. The enantiomeric excess (ee) was determined by HPLC.
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2-Phenyl-3-p-tolyl-2-azabicyclo[2.2.1]hept-5-ene.
and 18.8 min (endo adducts)). HRMS (ESI): m/z 421.9592 (calcd
421.9574 C18H16Br2NO [M + H]+).
General Catalytic Procedure for the Aza-Friedel−Crafts
Reaction. Under argon, in a Schlenk flask equipped with a magnetic
stirrer, complex 1 (31.7 mg, 0.03 mmol) was dissolved in dry CH2Cl2
(2 mL), at room temperature, and the corresponding imine I, IV, or
V (0.90 mmol) was added. After the mixture was stirred for 10 min, the
corresponding indole (0.60 mmol) was added. The reaction was
monitored by TLC chromatography. After the appropriate reaction
time, the solution was concentrated under vacuum to dryness and the
residue was extracted with 3 × 10 mL of diethyl ether. The resulting
suspension was filtered over Celite and evaporated to dryness. The
crude product was purified by column chromatography with silica as a
stationary phase and an n-hexane/ethyl acetate (from 9/1 to 5/5)
mixture as eluent. Conversion was determined by 1H NMR.
Enantiomeric excess was determined by HPLC.
Endo/exo molar ratio: 89/11. Data for the endo diastereomer are as
follows. H NMR (300.13 MHz, CDCl3, room temperature, ppm):
1
δ 7.45−6.55 (m, 9H, HAr), 5.89 (dtd, J = 5.6, 2.8, 1.5 Hz, 1H, H4), 5.70
(m, 1H, H5), 4.65 (d, J = 3.1 Hz, 1H, H1), 4.15 (d, J = 8.7 Hz, 1H, H3),
3.04 (qd, J = 9.0, 3.3 Hz, 1H, H2), 2.69 (dddd, J = 16.4, 9.3, 4.6, 2.4 Hz,
1H, H7), 2.41 (s, 3H, Me), and 1.88 (dddd, J = 16.3, 8.7, 2.4, 1.6 Hz, 1H,
H6). 13C{1H} NMR (75.47 MHz, CDCl3, room temperature, ppm):
δ 145.72, 139.80, 136.79 (Cipso), 133.99 (C4), 130.37 (C5), 129.84−
111.95 (CHAr), 57.84 (C1), 46.41 (C3), 46.04 (C2), 31.49 (C6), and
21.07 (Me). ee: 0%, determined by HPLC with a Daicel Chiralpak
OD-H column (90/10, n-hexane/iPrOH; 1.00 mL/min; tR 18.9 and
23.0 min (endo adducts); tR 14.8 and 20.8 min (exo adducts)). HRMS
(ESI): m/z 262.1595 (calcd 262.1590 C19H20N [M + H]+).
2,4-Dichloro-6-(2-phenyl-2-azabicyclo[2.2.1]hept-5-en-3-yl)-
phenol.
[(1,2-Dimethylindol-3-yl)-p-tolylmethyl]phenylamine.
1H NMR (400.16 MHz, CDCl3, room temperature, ppm): δ 7.32−6.38
(m, 13H, HAr), 5.54 (s, 1H, H1), 3.55 (s, 3H, Me1), 3.51 (s, 1H, NH),
2.22 (s, 3H, Me3), and 2.16 (s, 3H, Me2). 13C{1H} NMR (100.62 MHz,
CDCl3, room temperature, ppm): δ 144.18, 141.61, 136.64, 134.78
(d, J = 73.2 Hz), 133.57, 127.30, 113.99 (Cipso), 130.51−107.60 (CHAr),
46.79 (C1), 29.43 (Me1), 20.98 (Me3), and 10.67 (Me2). ee: 0%,
determined by HPLC with a Daicel Chiralpack OD−H column (80/20,
n-hexane/iPrOH; 1.00 mL/min; tR 15.4 and 16.8 min). HRMS (ESI):
m/z: 339.1854 (calcd 339.1856 C24H23N2 [M − H]−).
3,3′-((p-Tolyl)methylene)bis(1,2-dimethylindole).15
Endo/exo molar ratio: 93/7. Data dor the endo diastereomer are as
follows. 1H NMR (400.16 MHz, CDCl3, room temperature, ppm): δ 7.96
(br s, 1H, OH), 7.48−6.59 (m, 7H, HAr), 5.83 (dtd, J = 5.7, 2.9, 1.4 Hz, 1H,
H4), 5.63 (m, 1H, H5), 4.76 (d, J = 3.5 Hz, 1H, H1), 4.02 (d, J = 8.4 Hz, 1H,
H3), 3.04 (ddd, J = 18.5, 8.8, 3.5 Hz, 1H, H2), 2.55 (dddd, J = 16.6, 9.8, 4.7,
2.4 Hz, 1H, H7), and 1.93 (dddd, J = 16.3, 8.7, 2.5, 1.5 Hz, 1H, H6).
13C{1H} NMR (100.62 MHz, CDCl3, room temperature, ppm): δ 149.26,
142.87, 129.36, 126.68, 124.89 (Cipso), 133.59 (C4), 130.51 (C5), 129.34−
116.97 (CHAr), 55.53 (C1), 45.64 (C3), 43.57 (C2), and 31.43 (C6). ee:
0%, determined by HPLC with a Chiralpak IC column (70/30, n-hexane/
iPrOH; 1.00 mL/min; tR 16.0 and 19.5 min (endo adducts)). HRMS
(ESI): m/z 332.0610 (calcd 332.0609 C18H16Cl2NO [M + H]+).
2,4-Dibromo-6-(2-phenyl-2-azabicyclo[2.2.1]hept-5-en-3-yl)-
phenol.
1H NMR (400.16 MHz, CDCl3, room temperature, ppm): δ 7.22 (d, J =
8.2 Hz, 2H, HAr), 7.13 (d, J = 7.9 Hz, 2H, HAr), 7.09−7.00 (m, 4H, HAr),
6.92 (d, J = 7.9 Hz, 2H, HAr), 6.82 (ddd, J = 8.0, 7.0, 1.0 Hz, 2H, HAr),
6.01 (s, 1H, H1), 3.63 (s, 6H, Me1), 2.33 (s, 3H, Me3), and 2.15 (s, 6H,
Me2). 13C{1H} NMR (100.62 MHz, CDCl3, room temperature, ppm):
δ 140.96, 136.55, 135.14, 133.50, 127.88, 113.17 (Cipso), 128.88, 128.71,
119.95, 119.60, 118.49, 108.25 (CHAr), 39.32 (C1), 29.43 (Me1), 21.07
(Me3), and 10.70 (Me2). HRMS (ESI): m/z 391.2192 (calcd 391.2169
C28H27N2 [M − H]−).
3,3′-((p-Tolyl)methylene)bis(indole).16
1H NMR (400.16 MHz, CDCl3, room temperature, ppm): δ 7.86 (br s,
2H, NH), 7.39 (d, J = 7.9 Hz, 2H, HAr), 7.33 (dt, J = 8.1, 0.8 Hz, 2H,
HAr), 7.23 (d, J = 8.1 Hz, 2H, HAr), 7.20−7.12 (m, 2H, HAr), 7.08 (d, J =
7.8 Hz, 2H, HAr), 7.00 (ddd, J = 8.0, 7.1, 1.0 Hz, 2H, HAr), 6.64 (dd, J =
2.4, 0.9 Hz, 2H, H1), 5.85 (s, 1H, H2), and 2.32 (s, 3H, Me). 13C{1H}
NMR (100.62 MHz, CDCl3, room temperature, ppm): δ 140.94,
136.65, 135.45, 127.07, 119.88 (Cipso), 128.88, 128.53, 121.84, 119.91,
119.15, 110.96 (CHAr), 123.51 (C1), 39.74 (C2), and 21.06 (Me).
HRMS (ESI): m/z 335.1521 (calcd 335.1543 C24H19N2 [M − H]−).
NMR study of the Interaction of 1 with Aldimine I. At 183 K, in
an NMR tube, to a solution of 1 (15.0 mg, 0.014 mmol) in 0.6 mL
Endo/exo molar ratio: 94/6. Data for the endo diastereomer are as
follows. H NMR (300.13 MHz, CDCl3, room temperature, ppm):
1
δ 8.37 (br s, 1H, OH), 7.63−6.69 (m, 7H, HAr), 5.93 (dtd, J = 5.6, 2.7,
1.4 Hz, 1H, H4), 5.72 (d, J = 4.3 Hz, 1H, H5), 4.83 (d, J = 3.4 Hz, 1H,
H1), 4.11 (d, J = 8.7 Hz, 1H, H3), 3.12 (ddd, J = 18.4, 8.8, 3.5 Hz, 1H,
H2), 2.64 (dddd, J = 16.6, 9.8, 4.5, 2.3 Hz, 1H, H7), and 2.04 (dd, J =
15.3, 8.7 Hz, 1H, H6). 13C{1H} NMR (75.47 MHz, CDCl3, room
temperature, ppm): δ 150.80, 142.63, 129.52, 126.69, 112.03 (Cipso),
133.54 (C4), 130.55 (C5), 130.14−117.06 (CHAr), 55.87 (C1), 45.58
(C3), 43.75 (C2), and 31.38 (C6). ee: 0%, determined by HPLC with a
Chiralpak IC column (70/30, n-hexane/iPrOH; 1.00 mL/min; tR 15.4
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of CD2Cl2, were added the appropriate amount of imine I (2.8 mg,
0.014 mmol or 55.4 mg, 0.284 mmol) and 15.0 mg of MS 4 Å. Then,
1H and 31P{1H} NMR spectra were measured at different temperatures
141.56−126.16 (m, 15C, CHAr), 135.65 (Cipso Ph), 132.36 (d, J =
5.2 Hz, Cipso Ph), 128.77 (CH5), 122.99 (d, J = 47.1 Hz, Cipso Ph), 112.61
(d, J = 5.5 Hz), 99.57 (MeC, iPrC p-MeC6H4iPr), 87.10 (d, J = 7.0 Hz,
CHB′), 82.54 (CHA′), 81.14 (CHA, C2), 78.94 (CHB), 77.10 (C3), 69.25
(OMe), 52.05 (d, J = 27.5 Hz, C1), 31.56 (CHi), 22.95 (Mei), 22.88
(Me′), 21.70 (Mei′), and 19.07 (Me). 31P{1H} NMR (121.42 MHz,
CD2Cl2, room temperature, ppm): δ 58.71 (s).
(from 183 to 293 K).
Preparation of the Complex [(η6-p-MeC6H4iPr)Ru(κ2P,O-
Ph2PC(Ph)C(O) CH2OMe)(aniline)][SbF6] (3). To a solution of
complex 1 (150.0 mg, 0.142 mmol), in 20 mL of CH2Cl2, was added
55.5 mg (0.284 mmol) of N-(4-methylbenzylidene)aniline (I). The
resulting yellow solution was stirred for 7 h, and then it was filtered to
remove some insoluble impurities. The solution was concentrated
under reduced pressure to ca. 2 mL. The slow addition of n-hexane led to
the precipitation of an orange solid which was washed with n-hexane
(3 × 10 mL) and vacuum-dried. The crude product was purified
by column chromatography with silica as a stationary phase and a
CH2Cl2/n-hexane (9/1) mixture as eluent.
General Catalytic Procedure for the Aza-Diels−Alder Re-
action with 2 or 3 as a Catalyst. Under argon, in a Schlenk flask
equipped with a magnetic stirrer, the corresponding metal complex 2 or
3 (0.03 mmol) was dissolved in dry CH2Cl2 (3 mL), at room tem-
perature, and the imine I (117.2 mg, 0.60 mmol) was added. After the
mixture was stirred for 10 min, freshly distilled cyclopentadiene (0.3 mL,
3.60 mmol) in 1 mL of dry CH2Cl2 was added. The reaction was
monitored by TLC chromatography. After several days, the solution was
concentrated under vacuum to dryness and the residue was extracted
with 3 × 10 mL of diethyl ether. The resulting suspension was filtered
over Celite and evaporated to dryness. According to 1H NMR data, the
crude product does not contain products from the ADA reaction.
General Catalytic Procedure for the Aza-Friedel−Crafts
Reaction with 2 or 3 as a Catalyst. Under argon, in a Schlenk
flask equipped with a magnetic stirrer, the corresponding metal complex
2 or 3 (0.03 mmol) was dissolved in dry CH2Cl2 (2 mL), at room
temperature, and imine I (175.7 mg, 0.90 mmol) was added. After the
mixture was stirred for 10 min, the corresponding indole (0.60 mmol)
was added. The reaction was monitored by TLC chromatography. After
several days, the solution was concentrated under vacuum to dryness
and the residue was extracted with 3 × 10 mL of diethyl ether. The
resulting suspension was filtered over Celite and evaporated to dryness.
No AFC products were detected by 1H NMR of the crude product.
General Catalytic Procedure for the Stoichiometric Aza-
Diels−Alder Reaction. Under argon, in a Schlenk flask equipped with a
magnetic stirrer, complex 1 (52.9 mg, 0.05 mmol) was dissolved in dry
CH2Cl2 (3 mL), at 248 K, and imine I (9.7 mg, 0.05 mmol) was added.
After the mixture was stirred for 10 min, freshly distilled cyclopentadiene
(0.25 mL, 3.0 mmol) in 1 mL of dry CH2Cl2 was added. The reaction was
monitored by TLC chromatography. After 65 h, the solution was
concentrated under vacuum to dryness and the residue was extracted with
3 × 10 mL of diethyl ether. The resulting suspension was filtered over
Celite and evaporated to dryness. The crude product was purified by
column chromatography with silica as a stationary phase and ann-hexane/
ether (8/2) mixture as eluent. A conversion of >99% and an endo/exo
Yield: 77.7 mg, 60%. Anal. Calcd for C38H41F6NO2PRuSb·H2O: C,
49.1; H, 4.4; N, 1.5. Found: C, 48.6; H, 4.7; N, 1.2. IR (cm−1): ν(NH2)
3303, 3254 (s), ν(SbF6) 653 (s). 1H NMR (300.13 MHz, CD2Cl2, room
temperature, ppm): δ 7.78−6.83 (m, 20HAr), 5.15 (m, 2H, HA′, HB′),
4.77 (d, J = 6.0 Hz, 1H, HB), 4.65 (dd, J = 5.8, 3.2 Hz, 1H, HA), 4.23, 3.62
(2 × d, J = 9.8, 10.7 Hz, 2H, NH2), 3.95 (AB system, J = 10.9 Hz, 2H,
H3), 3.36 (s, 3H, OMe), 2.66 (m, 1H, Hi), 2.08 (s, 3H, Me), 1.24 (d, J =
7.0 Hz, 3H, Mei), and 1.11 (d, J = 6.9 Hz, 3H, Mei′). 13C{1H} NMR
(75.47 MHz, CD2Cl2, room temperature, ppm): δ 183.97 (d, J =
20.5 Hz, C2), 145.49 (Cipso aniline), 136.92 (Cipso Ph), 134.62 (d, J =
51.8 Hz, Cipso Ph), 134.17−120.09 (m, 20C, CHAr), 126.34 (d, J =
52.5 Hz, Cipso Ph), 115.68 (d, J = 3.1 Hz), 97.84, (MeC, iPrC
p-MeC6H4iPr), 97.21 (d, J = 50.8 Hz, C1), 91.71 (d, J = 7.6 Hz), 79.68,
(CHA′, CHB′), 90.94 (d, J = 2.0 Hz, CHA), 89.30 (CHB), 72.13 (d, J =
12.0 Hz, C3), 59.30 (OMe), 31.52 (CHi), 21.83, 21.78, (Mei, Mei′), and
18.26 (Me). 31P{1H} NMR (121.42 MHz, CD2Cl2, room temperature,
ppm): δ 63.66 (s).
Preparation of the Complex [(η6-p-MeC6H4iPr)Ru(κ3P,O,O′-
PO)]·HNC5H4Me[SbF6]2 (4). To a solution of complex 1 (200.0 mg,
0.189 mmol), in 20 mL of CH2Cl2, was added 18.4 μL (0.189 mmol) of
4-methylpyridine. The resulting yellow solution was stirred for 2 h, and
then it was concentrated under reduced pressure to ca. 2 mL. The slow
addition of n-hexane led to the precipitation of a yellow-orange solid
which was washed with n-hexane (3 × 10 mL) and vacuum-dried.
1
ratio of 90/10 were determined by H NMR. ee: 16%, determined by
HPLC with a Daicel Chiralpak OD-H column (90/10, n-hexane/iPrOH;
1.00 mL/min; tR (minor) 13.2 min; tR (major) 16.3 min (endo adducts)).
General Catalytic Procedure for Slow Addition in the Aza-
Diels−Alder Reaction. Under argon, in a Schlenk flask equipped with a
magnetic stirrer, complex 1 (31.7 mg, 0.03 mmol) was dissolved in dry
CH2Cl2 (2 mL), at 248 K. After the mixture was stirred for 10 min, freshly
distilled cyclopentadiene (0.3 mL, 3.60 mmol) in 1 mL of dry CH2Cl2 was
added. After that, 117.2 mg of imine I (0.60 mmol) was added by slow
addition in 1 mL of dry CH2Cl2 over 60 h. After 68 h, the solution was
concentrated under vacuum to dryness and the residue was extracted with
3 × 10 mL of diethyl ether. The resulting suspension was filtered over
Celite and evaporated to dryness. The crude was purified by column
chromatography with silica as a stationary phase and an n-hexane/ether
(8/2) mixture as eluent. A conversion of 75% and an endo/exo ratio of
91/9 were determined by 1H NMR. ee: 6%, determined by HPLC with a
Daicel Chiralpak OD-H column (90/10, n-hexane/iPrOH; 1.00 mL/min;
tR (minor) 12.9 min; tR (major) 15.9 min (endo adducts)).
Yield: 184.8 mg, 85%. Anal. Calcd for C38H44F12NO2PRuSb2: C, 39.7;
H, 3.85; N, 1.2. Found: C, 39.8; H, 3.85; N, 1.25. IR (cm−1): ν(SbF6)
1
652 (s). H NMR (300.13 MHz, CD2Cl2, room temperature, ppm):
NMR Study of the Hydrogenation of I. At 298 K, in an NMR
δ 11.76 (br s, 1H, HN), 8.61 (d, J = 6.4 Hz, 2H, H4), 7.87 (d, J = 5.9 Hz,
2H, H5), 7.74−6.30 (m, 15HAr), 5.88 (d, J = 6.0 Hz, 1H, HB′), 5.50 (d, J =
6.1 Hz, 1H, HA′), 4.96 (d, J = 5.8 Hz, 1H, HB), 4.46 (dd, J = 5.4, 2.0 Hz,
1H, HA), 4.16 (ddd, J = 35.1, 6.7, 3.0 Hz, 1H, H2), 4.00 (s, 3H, OMe),
3.88 (dd, J = 14.3, 6.7 Hz, 1H, H1), 3.45 (d, J = 8.5 Hz, 1H, H3), 3.07
(dd, J = 8.5, 2.9 Hz, 1H, H3), 2.79 (m, 1H, Hi), 2.72 (s, 3H, Me′),
2.14 (s, 3H, Me), 1.35 (d, J = 6.9 Hz, 3H, Mei′), and 1.29 (d, J = 6.9 Hz,
3H, Mei). 13C{1H} NMR (75.47 MHz, CD2Cl2, room temperature,
ppm): δ 162.57−162.51 (Cipso 4-methylpyridine), 140.83 (CH4),
pressure tube, to a solution of 1 (15.0 mg, 0.014 mmol) in 0.4 mL of
CD2Cl2 was added the imine I (9.1 mg, 0.047 mmol). The H NMR
1
spectrum shows the presence of imine in equilibrium with the I···HI+
cation. Then, H2 gas at 10 bar of pressure was added. The gradual
formation of N-(4-methylbenzyl)phenylamine at the expense of imine
I was observed. After 4 h of treatment, the conversion was completed.
Preparation of the Complex [(η6-p-MeC6H4iPr)Ru(κ2P,O-Ph2PC-
(Ph)C(O)CH2OMe)H] (5). To a solution of complex 1 (150.0 mg,
0.142 mmol), in 20 mL of MeOH, was added 23.8 mg (0.284 mmol) of
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NaHCO3. The resulting yellow solution was stirred for 3 h. After this
time, it was concentrated under vacuum to dryness and the residue was
extracted with 2 × 10 mL of toluene. The resulting suspension was
filtered through a cannula and concentrated under reduced pressure to
ca. 2 mL. The slow addition of n-hexane led to the precipitation of a
yellow-green solid which was washed with n-hexane (3 × 10 mL) and
vacuum-dried. This complex was also prepared by reacting complex 1
with an equimolar amount of Na2CO3, following the same procedure.
6.9 Hz, 3H, Mei), and 1.28 (d, J = 6.8 Hz, 3H, Mei′). 13C{1H} NMR
(75.47 MHz, CD2Cl2, room temperature, ppm): δ 184.32 (d, J =
19.8 Hz, C2), 173.97 (d, J = 3.1 Hz, C4), 150.42 (Cipso N-(4-
methylbenzyliden)aniline), 144.79 (Cipso N-(4-methylbenzylidene)-
aniline), 137.41 (Cipso Ph), 134.93 (d, J = 49.8 Hz, Cipso Ph), 134.16−
120.86 (m, 24C, CHAr), 129.18 (Cipso N-(4-methylbenzylidene)aniline),
126.90 (d, J = 53.1 Hz, Cipso Ph), 116.49 (d, J = 2.4 Hz), 98.48 (MeC,
iPrC p-MeC6H4iPr), 96.57 (d, J = 52.1 Hz, C1), 93.88 (d, J = 2.0 Hz,
CHA), 91.82 (CHA′), 89.37 (d, J = 7.6 Hz, CHB), 81.87 (CHB′), 71.64
(d, J = 12.1 Hz, C3), 59.25 (OMe), 31.48 (CHi), 22.19 (Mei′), 21.79
(Mei), 21.58 (Me′), and 18.11 (Me). 31P{1H} NMR (121.42 MHz,
CD2Cl2, room temperature, ppm): δ 63.63 (s).
Complex 7.
Yield: 68.0 mg, 82%. Anal. Calcd for C32H35O2PRu·1/2H2O: C, 64.85;
H, 6.1. Found: C, 64.5; H, 5.85. CD (CH2Cl2, 3.6 × 10−4 M, 20 °C; λ, nm
(Δε)): 434 (+0.36), 380 (0), 331 (−1.91), 316 (−1.94), 283 (0).
1H NMR (300.13 MHz, MeOD, room temperature, ppm): δ 7.67−6.91
(m, 13H, HAr), 6.74 (d, J = 7.2 Hz, 2H, HAr), 5.52 (d, J = 5.3 Hz, 1H, HB),
5.16 (d, J = 5.1 Hz, 1H, HA′), 5.07 (d, J = 4.6 Hz, 1H, HA), 4.82 (1H, HB′),
3.70 (AB system, J = 11.3 Hz, 2H, H3), 3.18 (s, 3H, OMe), 2.36 (m, 1H,
Hi), 1.87 (s, 3H, Me), 1.22 (d, J = 6.7 Hz, 3H), 1.20 (d, J = 6.7 Hz, 3H),
(Mei, Mei′), and −7.79 (d, J = 44.9 Hz, 1H, H). 13C{1H} NMR (75.47
MHz, MeOD, room temperature, ppm): δ 180.05 (d, J = 20.8 Hz, C2),
141.79 (d, J = 40.0 Hz, Cipso Ph), 139.26 (Cipso Ph), 135.04 (d, J = 63.7 Hz,
Cipso Ph), 136.93−126.15 (m, 15C, CHAr), 111.36, 102.74 (MeC, iPrC
p-MeC6H4iPr), 102.05 (d, J = 50.3 Hz, C1), 89.43−88.74 (m, CHA′,
CHB), 87.21 (CHA), 81.04 (CHB′), 72.17 (d, J = 11.8 Hz, C3), 58.16
(OMe), 32.96 (CHi), 24.16, 23.57 (Mei, Mei′), and 19.24 (Me). 31P{1H}
NMR (121.42 MHz, MeOD, room temperature, ppm): δ 72.96 (s).
Reaction of the Complex [(η6-p-MeC6H4iPr)Ru(κ2P,O-Ph2PC-
(Ph)C(O)CH2OMe)H] (5) with HI+. At room temperature, in a NMR
tube, to a solution of the compound N-(4-methylbenzylidene)aniline
(I; 10.0 mg, 0.05 mmol), in 0.6 mL of CD2Cl2, was added 6.1 μL
(0.05 mmol) of HSbF6·6H2O. Then, 30.0 mg of complex 5 was added.
After 20 min, 1H and 31P{1H} NMR spectra revealed complete
conversion to complex 3.
Yield: 100.7 mg, 70%. Anal. Calcd for C46H47F6NO2PRuSb·H2O: C,
53.55; H, 4.8; N, 1.35. Found: C, 53.65; H, 4.6; N, 1.4. IR (cm−1):
ν(SbF6) 653 (s). 1H NMR (300.13 MHz, CD2Cl2, room temperature,
ppm): δ 7.74−6.67 (m, 25HAr + H4), 5.07 (m, 2H, HA, HB′), 4.95 (d, J =
6.2 Hz, 1H, HA′), 4.68 (d, J = 5.8 Hz, 1H, HB), 4.60 (d, J = 14.0 Hz, 1H,
H5), 4.41 (d, J = 14.0 Hz, 1H, H5), 4.07 (AB system, J = 10.1 Hz, 2H,
H3), 3.47 (s, 3H, OMe), 2.55 (m, 1H, Hi), 1.99 (s, 3H, Me), 1.20 (d, J =
7.1 Hz, 3H), and 1.18 (d, J = 7.1 Hz, 3H), (Mei, Mei′). 13C{1H} NMR
(75.47 MHz, CD2Cl2, room temperature, ppm): δ 183.37 (d, J = 20.2
Hz, C2), 175.55 (d, J = 3.1 Hz, C4), 137.52 (Cipso N-benzylidenbenzyl-
amine), 136.23 (Cipso N-benzylidenbenzylamine), 134.03 (d, J = 49.2
Hz, Cipso Ph), 133.23−126.36 (m, 25C, CHAr), 131.78 (d, J = 5.8 Hz,
Cipso Ph), 126.34 (d, J = 52.8 Hz, Cipso Ph), 115.92 (d, J = 2.0 Hz), 97.10
(MeC, iPrC p-MeC6H4iPr), 98.06 (d, J = 52.2 Hz, C1), 92.81 (d, J =
2.2 Hz, CHA′), 91.38 (d, J = 1.8 Hz, CHB′), 88.69 (d, J = 8.0 Hz, CHA),
81.13 (CHB), 72.58 (d, J = 12.2 Hz, C3), 59.34 (OMe), 58.06 (C5),
31.28 (CHi), 21.89, 21.80, (Mei, Mei′), and 17.74 (Me). 31P{1H} NMR
(121.42 MHz, CD2Cl2, room temperature, ppm): δ 62.33 (s).
Preparation of the Complexes [(η6-p-MeC6H4iPr)Ru(κ2P,O-
Ph2PC(Ph)C(O)CH2OMe)(imine)][SbF6] (imine = N-(4-
Methylbenzylidene)aniline (6), N-Benzylidenebenzylamine
(7)). To a solution of complex 1 (150.0 mg, 0.142 mmol), in 20 mL of
dry CH2Cl2, were added 0.284 mmol of the corresponding imine and
100.0mgof MS4 Å. The resulting yellowsolutionwas stirredfor 24 h, and
then it was filtered to remove the MS 4 Å and other insoluble impurities.
The solution was concentrated under reduced pressure to ca. 2 mL. The
slow addition of n-hexane led to the precipitation of a yellow solid which
was washed with n-hexane (3 × 10 mL) and vacuum-dried. The crude
product was purified by column chromatography with silica as a stationary
phase and a CH2Cl2/n-hexane (9/1) mixture as eluent.
Preparation of the Complex [(η6-p-MeC6H4iPr)Ru(κ2P,O-
Ph2PC(Ph)C(O)CH2OMe)(benzylamine)][SbF6] (8). To a solution
of complex 1 (150.0 mg, 0.142 mmol), in 20 mL of CH2Cl2, was added
54.0 μL (0.284 mmol) of N-benzylidenebenzylamine. The resulting
yellow solution was stirred for 7 h, and then it was filtered to remove
some insoluble impurities. The solution was concentrated under re-
duced pressure to ca. 2 mL. The slow addition of n-hexane led to the
precipitation of an orange solid which was washed with n-hexane (3 ×
10 mL) and vacuum-dried. The crude product was purified by column
chromatography with silica as a stationary phase and a CH2Cl2/n-hexane
(9/1) mixture as eluent.
Complex 6.
Yield: 73.6 mg, 56%. Anal. Calcd for C39H43F6NO2PRuSb: C, 50.6; H,
4.7; N, 1.5. Found: C, 50.6; H, 5.0; N, 1.6. IR (cm−1): ν(NH2) 3318,
Yield: 103.6 mg, 72%. Anal. Calcd for C46H47F6NO2PRuSb: C, 54.5; H,
4.7; N, 1.4. Found: C, 54.4; H, 4.7; N, 1.4. IR (cm−1): ν(SbF6) 653 (s).
1H NMR (300.13 MHz, CD2Cl2, room temperature, ppm): δ 7.85−6.61
(m, 24HAr + H4), 5.85 (d, J = 6.1 Hz, 1H, HB), 5.27 (dd, J = 4.6, 3.3 Hz,
1H, HA′), 4.94 (d, J = 6.0 Hz, 1H, HA), 4.84 (d, J = 5.8 Hz, 1H, HB′), 3.83
(d, J = 11.4 Hz, 1H, H3), 3.41 (d, J = 11.5 Hz, 1H, H3), 3.22 (s, 3H,
OMe), 2.73 (m, 1H, Hi), 2.26 (s, 3H, Me′), 2.08 (s, 3H, Me), 1.35 (d, J =
1
3262 (s), ν(SbF6) 651 (s). H NMR (300.13 MHz, CDCl3, room
temperature, ppm): δ 7.63−6.69 (m, 20HAr), 5.82 (d, J = 6.2 Hz, 1H,
HA′), 5.77 (d, J = 6.0 Hz, 1H, HB′), 5.04 (d, J = 6.0 Hz, 1H, HB), 4.51 (dd,
J = 5.2, 3.8 Hz, 1H, HA), 4.13 (m, 1H, NH), 3.98 (m, 2H, H4), 3.88 (AB
system, 2H, H3), 3.35 (s, 3H, OMe), 2.86 (m, 1H, Hi), 2.08 (s, 3H, Me),
1.75 (m, 1H, NH), 1.35 (d, J = 7.0 Hz, 3H, Mei), and 1.31 (d, J = 6.9 Hz,
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Organometallics
Article
3H, Mei′). 13C{1H} NMR (75.47 MHz, CDCl3, room temperature,
ppm): δ 182.61 (d, J = 20.6 Hz, C2), 138.47 (Cipso benzylamine), 136.81
(d, J = 22.2 Hz, Cipso Ph), 136.46 (d, J = 27.0 Hz, Cipso Ph), 134.63−
126.01 (m, 20C, CHAr), 124.94 (d, J = 54.3 Hz, Cipso Ph), 116.20 (d, J =
4.1 Hz), 97.34 (MeC, iPrC p-MeC6H4iPr), 96.83 (d, J = 50.1 Hz, C1),
91.45 (d, J = 1.6 Hz, CHA), 89.75 (d, J = 7.8 Hz, CHB′), 86.49 (CHA′),
80.31 (CHB), 71.88 (d, J = 12.0 Hz, C3), 59.21 (OMe), 53.49 (C4),
31.31 (CHi), 22.19, 21.83 (Mei, Mei′), and 18.10 (Me). 31P{1H} NMR
(121.42 MHz, CDCl3, room temperature, ppm): δ 64.93 (s).
(7) Yamamoto, H.; Futatsugi, K. Angew. Chem., Int. Ed. 2005, 44,
1924−1942.
(8) (a) Ishibashi, H.; Ishihara, K.; Yamamoto, H. Chem. Rec. 2002, 2,
177−188. (b) Ishihara, K.; Nakashima, D.; Hiraiwa, Y.; Yamamoto, H. J.
Am. Chem. Soc. 2003, 125, 24−25. (c) Cheon, C. H.; Imahori, T.;
Yamamoto, H. Chem. Commun. 2010, 46, 6980−6982. (d) Cheon, C.
H.; Kanno, O.; Toste, F. D. J. Am. Chem. Soc. 2011, 133, 13248−13251.
́
(e) Dıez, J.; Gimeno, J.; Lledos
́ ́
, A.; Suarez, F. J.; Vicent, C. ACS Catal.
2012, 2, 2087−2099.
(9) For a more complete description of the 1H NMR spectra, see the
next section.
ASSOCIATED CONTENT
* Supporting Information
■
(10) A comparable behavior has been reported for the species detected
in the reaction between diphenylphosphate and 15N-labeled imine I:
Fleischmann, M.; Drettwan, D.; Sugiono, E.; Rueping, M.; Gschwind, R.
M. Angew. Chem., Int. Ed. 2011, 50, 6364−6369.
(11) (a) Cahn, R. S.; Ingold, C.; Prelog, V. Angew. Chem., Int. Ed. Engl.
1966, 5, 385−415. (b) Prelog, V.; Helmchen, G. Angew. Chem., Int. Ed.
Engl. 1982, 21, 567−583. (c) Lecomte, C.; Dusausoy, Y.; Protas, J.;
Tirouflet, J.; Dormond, A. J. Organomet. Chem. 1974, 73, 67−76.
(d) Stanley, K.; Baird, M. C. J. Am. Chem. Soc. 1975, 97, 6598−6599.
(e) Sloan, T. E. Top. Stereochem. 1981, 12, 1−36.
S
Text, figures, and CIF files giving details of the NMR study of the
interaction of 1 with 20 equiv of I, general catalytic procedure for
the ADA and AFC reactions with HBF4·Et2O as a catalyst, NMR
study of the interaction of 1 with 1 equiv of I, NMR study of the
formation of HI+ and I···HI+, and X-ray crystallographic data and
full details of the structural analysis of complexes 3 and 4. This
material is available free of charge via the Internet at http://pubs.
acs.org.
(12) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354−1358.
Ru−P(1)−C(23)−C(24)−O(1): q2 = 0.663(5) Å, ϕ2 = −34.8(5), E5
conformation (1); q2 = 0.631(6) Å, ϕ2 = −31.5(6), E5 conformation (4);
q2 = 0.045(3) Å, ϕ2 = 47(4), E2/3T2 conformation (3). Ru−O(1)−
C(24)−C(25)−O(2): q2 = 0.503(6) Å, ϕ2 = 64.7(6), 3E conformation
(1); q2 = 0.487(6) Å, ϕ2 = 71.6(7), 3E conformation (4).
(13) The bond distances Ru−OH and Ru−OMe were 2.130(5) and
2.178(5) Å, respectively, in the crystal of complex 1.6
AUTHOR INFORMATION
Corresponding Authors
*D.C.: e-mail, dcarmona@unizar.es; tel, 34-976-762027; fax,
34-976-761187.
*P.L.: e-mail, plamata@unizar.es.
*R.R.: e-mail, riromar@unizar.es.
Notes
■
(14) (a) Haack, K. J.; Hashiguchi, S.; Fuji, A.; Ikariya, T.; Noyori, R.
Angew. Chem., Int. Ed. Engl. 1997, 36, 285−288. (b) Yamakawa, M.; Ito,
H.; Noyori, R. J. Am. Chem. Soc. 2000, 122, 1466−1478. (c) Noyori, R.;
Yamakawa, M.; Hashiguchi, S. J. Org. Chem. 2001, 66, 7931−7944.
(15) Vahdat, S. M.; Khaksar, S.; Baghery, S. World Appl. Sci. J. 2012, 19,
1003−1008.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
We thank the Ministerio de Economıa y Competitividad of Spain
(16) Xie, W.; Bloomfield, K. M.; Jin, Y.; Dolney, N. Y.; Wang, P. G.
Synlett 1999, 4, 498−500.
(CTQ2012-32095) and Gobierno de Aragon
́
(Grupo Con-
icos Enantioselectivos) for
financial support. This work was supported by the CONSOL-
solidado: Catalizadores Organometal
́
́
IDER INGENIO 2010 program under the project “Factorıa de
Crystalizacion” (CSD2006-0015). R.R. and P.P. acknowledge
́
the CSIC and European Social Fund for JAE grants. The authors
acknowledge financial support from the Scientific Policy Vice
Chancellor of Zaragoza University for X-ray measurements. The
authors acknowledge Prof. Anton Vidal for his help with the
POH ligand employed in this work.
REFERENCES
■
(1) For recent reviews see: (a) Brak, N.; Jacobsen, E. N. Angew. Chem.,
Int. Ed. 2013, 52, 534−561. (b) Rueping, M.; Nachtsheim, B. J.;
Ieawsuwan, W.; Atodiresei, I. Angew. Chem., Int. Ed. 2011, 50, 6706−
6720. (c) Yu, J.; Shi, F.; Gong, L.-Z. Acc. Chem. Res. 2011, 44, 1156−
1171. (d) Rueping, M.; Kuenkel, A.; Atodiresei, I. Chem. Soc. Rev. 2011,
40, 4539−4549. (e) Terada, M. Bull. Chem. Soc. Jpn. 2010, 83, 101−119.
(2) Rueping, M.; Nachtsheim, B. J.; Ieawsuwan, W.; Atodiresei, I.
Angew. Chem., Int. Ed. 2011, 50, 6706−6720.
(3) Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer: New York, 1999; Vols. I−III and Suppl. 1
and 2 (2004).
(4) (a) Lewis Acids in Organic Synthesis, Yamamoto, H., Ed.; Wiley-
VCH: Weinheim, Germany, 2000. (b) Transition Metals for Organic
Synthesis: Building Blocks and Fine Chemicals; Beller, M., Bolm, C.,
Carsten, B., Eds.; Wiley-VCH: Weinheim, Germany, 2004.
́
(5) Carmona, D.; Lamata, M. P.; San
́
chez, A.; Viguri, F.; Rodrıguez, R.;
́
Oro, L. A.; Liu, C.; Dıez-Gonzal
́
ez, S.; Maseras, F. Dalton Trans. 2014,
43, 11260−11628.
́
(6) Carmona, D.; Lamata, M. P.; Pardo, P.; Rodrıguez, R.; Lahoz, F. J.;
Garcıa-Orduna, P.; Alkorta, I.; Elguero, J.; Oro, L. A. Organometallics
́
̃
2014, 33, 616−619.
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