Pyridine- A nd Quinoline-Derived Imines as N, N-Bidentate Directing Groups in Palladium versus Platinum C-H Bond Activation Reactions

Article abstract of DOI:10.1021/acs.organomet.0c00703

The C-H activation by Pd(II) and Pt(II) compounds of a wide range of imines related to 2-pyridinecarboxaldehyde, ArCHaNCH2(CH2)nPh (Ar = 2-pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1), which can be useful for bond functionalization assisted by bidentate directing groups, has been studied. The results indicate that the presence of two methyl groups at the α-carbon, relative to the imine nitrogen atom, facilitates the metalation. The heterocyclic fragment of the chelating ligand also shows a relevant influence on the full process, the cyclometalated compounds being more easily formed for the 2-picolinyl than for the 2-quinolinyl derivatives, while for the 2-pyridinyl derivatives the reaction is less favored. These effects have been found to be determinant for both palladium and platinum compounds. The preparative results can be explained by a steric enhancement of the metalation process, the reaction being strongly favored when bulky substituents are located in the proximity (α-carbon) of the coordinating nitrogen atoms (with both palladium and platinum). Furthermore, surprisingly the formation of six-membered platinacycles is especially favored. The kinetico-mechanistic studies of the C-H activation reaction, on some equivalent Pd(II) and Pt(II) coordination complexes of the family, have shown that the nature of the d8 metal center plays a determinant role in the reactivity observed. In this respect, the Pt(II) square-planar center has been found to be much more involved in the energetics of the reaction than the Pd(II) equivalent. The full process can be seen as a mechanistic continuum that goes from an electrophilic substitution (Pd(II) centers) to an oxidative addition/reductive elimination sequence (Pt(II) centers). The observation is directly associated with the fact that the Pt(II) center is prone to the existence of oxidatively added Pt(IV) hydrido complexes.

Full text of DOI:10.1021/acs.organomet.0c00703

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Article
Pyridine- and Quinoline-Derived Imines as N,N‑Bidentate Directing
Groups in Palladium versus Platinum C−H Bond Activation
Reactions
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Hector Torralvo, Joan Albert, Xavier Ariza,* Merce Font-Bardia, Jordi Garcia, Jaume Granell,*
and Manuel Martinez
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ABSTRACT: The C−H activation by Pd(II) and Pt(II) compounds of a
wide range of imines related to 2-pyridinecarboxaldehyde, ArCH
NCH2(CH2)nPh (Ar = 2-pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1),
which can be useful for bond functionalization assisted by bidentate
directing groups, has been studied. The results indicate that the presence of
two methyl groups at the α-carbon, relative to the imine nitrogen atom,
facilitates the metalation. The heterocyclic fragment of the chelating ligand
also shows a relevant influence on the full process, the cyclometalated
compounds being more easily formed for the 2-picolinyl than for the 2-
quinolinyl derivatives, while for the 2-pyridinyl derivatives the reaction is less
favored. These effects have been found to be determinant for both palladium
and platinum compounds. The preparative results can be explained by a
steric enhancement of the metalation process, the reaction being strongly
favored when bulky substituents are located in the proximity (α-carbon) of the coordinating nitrogen atoms (with both palladium
and platinum). Furthermore, surprisingly the formation of six-membered platinacycles is especially favored. The kinetico-mechanistic
studies of the C−H activation reaction, on some equivalent Pd(II) and Pt(II) coordination complexes of the family, have shown that
the nature of the d8 metal center plays a determinant role in the reactivity observed. In this respect, the Pt(II) square-planar center
has been found to be much more involved in the energetics of the reaction than the Pd(II) equivalent. The full process can be seen
as a mechanistic continuum that goes from an electrophilic substitution (Pd(II) centers) to an oxidative addition/reductive
elimination sequence (Pt(II) centers). The observation is directly associated with the fact that the Pt(II) center is prone to the
existence of oxidatively added Pt(IV) hydrido complexes.
critical challenge in organic chemistry. An interesting approach
to address this issue involves the use of substrates that contain
directing groups that bind to the metal center in a first step.7 A
further rearrangement of the molecules allows the C−H bond
activation, this latter process being called cyclometalation.
Although ligand-directed catalytic reactions have been histor-
ically focused mainly on monodentate directing groups, in the
past decade an increasing number of reports on carbon−
hydrogen bond functionalization assisted by bidentate directing
groups have appeared.8 The easy metal coordination and
tunability of properties of a bidentate directing group, versus
those of a monodentate ligand, have resulted in an increase in
INTRODUCTION
■
Cyclometalation processes have received considerable attention
because they permit the regioselective activation of strong
aromatic or even aliphatic carbon−hydrogen bonds.1 Further-
more, the metallacycles obtained have potential applications in
many areas, such as organic synthesis and homogeneous
catalysis2 or bioorganometallic chemistry. In the last area, the
biological activity of these types of complexes has led to the
discovery of an important number of cyclometalated com-
pounds having a high potential as anticancer metallodrugs.3
In addition, these complexes have also been employed in
materials science. Some remarkable examples are its use in
photophysical devices,4 for light harvesting and energy transfer
in photovoltaic cells,5 and as liquid crystals.6 Moreover, the
development of catalytic C−H functionalization processes by
ligand-directed reactions has also led to a renewed interest in the
study of the cyclometalation reactions and the reactivity of their
derivatives.3
Received: November 3, 2020
Published: January 12, 2021
The direct conversion of carbon−hydrogen bonds into
carbon−heteroatom and carbon−carbon bonds remains a
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their use as directing groups in catalytic C−H functionalization
processes. In addition, the use of bidentate directing groups can
also have an important effect on the catalytic process by
producing important changes in the reaction mechanism.
Finally, when monodentate directing groups are used,
unexpected secondary reactions may occur due to the relatively
weaker coordination capabilities of these functional groups to
the metal center in comparison with bidentate units.
We have already reported the synthesis of 2,2-disubstituted
indolines via Pd-catalyzed C−H activation of imines derived
from 2-pyridinecarboxaldehyde using PhI(OAc)2 as an oxidant.9
The ability of the pyridine moiety to coordinate to the Pd(II)
center seems to be essential for this catalytic process involving a
new bidentate Nimine,Npyridine directing group. The absence of
hydrogens in the α-position of the amine fragment is also a
requirement for the formation of indolines.
Here we report the study of a wide range of imines related to
2-pyridinecarboxaldehyde, ArCHNCH2(CH2)nPh (Ar = 2-
pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1), in order to evaluate
the relative importance of different factors in the C−H
activation by Pd(II) and Pt(II) compounds in these imine
systems. The group of imines selected presents the additional
advantage that it is possible to obtain a great number of ligands
with different features by means of standard organic synthesis. A
set of kinetico-mechanistic studies on selected representative
Pd(II) and Pt(II) complexes of the new bidentate ligands has
also been carried out in order to establish possible effects of the
metal center, the nature of the substituents on the [N,N′] and
organometallic [C−N] fused final [C,N,N′] cycles, and the final
metalated ring size.
affected by the previous coordination reaction of the directing
groups of the ligand. In this respect, it should be noted that
palladium acetate, the most useful reagent for catalytic or
stoichiometric C−H bond activation reactions, presents a huge
variety of structures in solution, depending on the solvent used
and the presence of moisture, making the study of the metalation
process very difficult.12 In addition, these imines can be useful
systems in the field of C−H bond functionalization assisted by
bidentate ligands, a new and attractive area of research.8 In fact,
we have previously shown that this system is useful in the
synthesis of 2,2-disubstituted indolines via Pd-catalyzed C−H
activation.9
Synthesis of Palladium Compounds. The imines
described in Figure 1 were reacted with palladium(II) acetate
under mild conditions (toluene, room temperature, 1 h of
reaction) in order to obtain the corresponding coordination
derivatives. Imines 1, 3−5, 9, 11, and 12 afforded the expected
coordination complexes containing the imines in a chelate N,N′-
bidentate coordination mode in good yields, and the
compounds were characterized by elemental analysis, NMR
spectroscopy, and mass spectrometry (Scheme 1).
a
Scheme 1. Synthesis of Palladium Compounds
RESULTS AND DISCUSSION
■
As part of an ongoing research project on the study of
stoichiometric10 and catalytic9,11 C−H bond activation
processes, we have conducted the study of the reaction between
palladium(II) acetate or cis-bis(dimethyl sulfoxide)-
dichloridoplatinum(II) with imines ArCHNCH2(CH2)nPh
(Ar = 2-pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1), in which
the CH2(CH2)n fragment presents methyl groups in different
positions (see Figure 1). The synthesis of all these imines is
a
Reagents and conditions: (i) Pd(OAc)2, toluene, room temperature,
1 h; (ii) Pd(OAc)2, toluene, 90 °C, 1 h.
Figure 1. Imines studied.
While the coordination compounds were obtained from all of
the [N,N′] bidentate imines containing the pyridinyl fragment,
imines 2 and 10, which have a picolinyl fragment and methyl
substituents at the α-carbon (relative to the imine nitrogen),
behave in a rather distinct manner. In these latter cases, the
palladacycles with the imines coordinated in a [C,N,N′]
terdentate coordination mode were obtained in good yields.
Even the use of the mild conditions indicated in Scheme 1 do not
allow the detection of the corresponding [N,N′] coordination
compounds. Interestingly, imines 6 and 13, also containing the
picolinyl moiety but without any methyl substituents at the α-
straightforward and is easily accomplished by condensation of
the corresponding primary amines and the suitable aldehydes
under dehydrating conditions.
These imines show the presence of two nitrogen atoms that
would facilitate the isolation of the corresponding bidentate
coordination compounds. These complexes have been proposed
as intermediates for the cyclometalation reaction leading to a
[C,N,N′] terdentate final structure. This fact allows the study of
the cyclometalation process separately: that is, without being
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carbon (relative to the imine nitrogen), do allow the synthesis of
the corresponding [N,N′] coordination compounds. Finally,
when the reaction was performed under mild conditions with
imines containing the quinolinyl fragment (7 and 14), mixtures
of [N,N′] coordination and [C,N,N′] cyclometalated com-
pounds were obtained. All of these results suggest that the
presence of two methyl groups at the α-position relative to the
imine nitrogen donor facilitates metalation and that the
heterocyclic fragment also shows an important effect on the
outcome of the process. That is, the trend of these imines to
experience the cyclometalation follows the sequence picolinyl >
quinolinyl > pyridinyl for the same imine metalating moiety.
The cyclopalladated 2-pyridinyl derivatives 1mPd and 9mPd
were obtained in good yields when their corresponding
coordination compounds 1cPd and 9cPd, which present two
methyl groups at the carbon at the α-position relative to the
imine nitrogen atom, were treated in toluene at 90 °C. When the
same reaction was performed with the 2-pyridinyl coordination
compound 5cPd, which presents only one methyl group at the
carbon at the α-position relative to the imine nitrogen atom, the
cyclometalated derivative 5mPd was detected but in very low
yield (5%). No metalated compounds were obtained from
coordination compounds 3cPd, 6cPd, 11cPd, and 13cPd,
which do not present any methyl substituent in the (CH2)nCH2,
fragment. Finally, the 2-pyridyl complex 4cPd, which presents
two methyl groups at the β-position in the CH2CH2 chain, and
2-picolinyl complex 12cPd, which presents only one methyl at
the α position relative to the nitrogen atom in the CH2CH2
fragment, do not experience cyclopalladation either.
It seems that the metalation reaction is strongly favored when
bulky substituents are in the proximity of coordinating nitrogen
atoms; thus, imines with picolinyl and quinolinyl fragments can
be easily metalated. In the same sense, the cyclopalladated
derivative of imine 1 is easy to obtain (which presents two
methyl groups in α position relative to imine nitrogen), but
imine 4 (which presents two methyl groups in β-positions) does
not experience the metalation.
All of these results suggest that the bulkiness of the imine plays
an important role in the cyclopalladation reaction. The steric
promotion in the cyclometalation reactions of some N-donor
ligands have been reported,1 and also the beneficial effect of the
bulkiness of the phosphines in their cyclometalation processes
due to entropic factors has also been known for quite a long
time.13 Although the use of geminal substitution is an important
tool for synthetic chemists to increase the rate of formation and
yield of cyclization processes,14 it does not seem to be the main
factor in our case. When cyclometalations of imine 1 and imine 4
are compared, the steric promotion in the vicinity of the
coordinating nitrogen atoms in the cyclometalation reactions
seems to be a more important factor than the gem-disubstituent
effect.
cyclopalladated derivatives present the expected signals in the
aromatic region, but for the aliphatic chain protons only broad
signals are observed. The existence of a fluxional process
concerning the six-membered metallacycle has been confirmed
by the measurement of the same spectra at 240 K, where signals
corresponding to the nonequivalent CH2 protons and methyl
groups are observed (Figure 2). The XRD of the related
Figure 2. 1H NMR of 7mPd at 298 and 240 K.
platinum complex 7mPt (see below) confirms the lack of
planarity of the six-membered metallacycle, which adopts a half-
skew-chair conformation, agreeing with the spectrum in Figure
2.
Synthesis of Platinum Compounds. In contrast to
cyclopalladated complexes, one of the best synthetic strategies
to obtain cycloplatinated compounds is the use of cis-
[PtCl2(DMSO)2] as the starting platinum material. The best
reaction conditions involve the use of methanol as solvent and
long reaction times, in agreement with the fact that platinum
compounds are much more inert than the equivalent palladium
derivatives. Furthermore, in these processes sodium acetate was
generally added as an external base to promote C−H bond
activation by base-assisted deprotonations and avoid acidolysis
decomposition equilibria.16 Scheme 2 collects a summary of the
conditions used for the reaction of the imines indicated in Figure
1 with cis-bis(dimethyl sulfoxide)dichloridoplatinum(II). Re-
actions without an external base were conducted in order to
favor the obtention of the corresponding coordination
compound intermediates.
Imines 1, 3, 5, 9, 11, 12, and 13 afforded the expected
nonmetalated coordination complexes in good yields in the
absence of sodium acetate. It is noticeable that all of these imines
contain an unsubstituted pyridine moiety with the exception of
13, which is a picolinyl derivative with an unsubstituted imine
nitrogen α-carbon. When the same reaction was carried out with
α-substituted imines but with substituted pyridine fragments
(picolinyl or quinolinyl fragments; 2, 7, 10, and 14), the
cycloplatinated derivatives were obtained with good yield and
the corresponding coordination compounds were not detected.
All of these results are in good agreement with those described
above for cyclopalladation of the same imines, indicating that
both the presence of two methyl groups on the imine nitrogen α-
carbon and the pyridine moiety bulkiness have considerable
beneficial influences on the process.
The new compounds have been characterized by elemental
analyses, 1H and 13C{1H} NMR spectroscopy, and electrospray
mass spectrometry. The high-resolution electrospray mass
spectra of all metalated derivatives show a signal corresponding
to the [M − AcO]+ fragment (M being the molecular mass of the
corresponding metalated derivative), in agreement with the
results described for related cyclopalladated compounds.15 It is
remarkable that palladium acetato coordination complexes
undergo metalation inside the ionization chamber, with the
signal corresponding to the aforementioned [M − AcO]+
fragment being observed. It should be noted that room-
temperature 1H NMR spectra of all the six-membered
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a
Suitable crystals for X-ray diffraction of complexes 7mPt and
10mPt were obtained from solutions in mixtures of dichloro-
methane and diethyl ether. The crystal structures correspond to
discrete molecules separated by van der Waals distances.
Structures and selected bond lengths and angles are collected
in Figures 3 and 4 for 7mPt and 10mPt, respectively. Although
Scheme 2. Synthesis of Platinum Compounds
Figure 3. Molecular crystal structure of 7mPt. Selected bond lengths
(Å) and bond angles (deg): Pt(1)−N(1) = 2.0022(18), Pt(1)−C(1) =
2.0047(19), Pt(1)−N(2) = 2.1688(17), Pt(1)−Cl(1) = 2.3124(5),
N(1)−C(11) = 1.289(3), N(1)−C(8) = 1.494(3), N(2)−C(12) =
1.340(3), N(2)−C(20) = 1.375(3), N(1)−Pt(1)−C(1) = 94.62(8),
N(1)−Pt(1)−N(2) = 78.69(7), C(1)−Pt(1)−Cl(1) = 88.86(6),
N(2)−Pt(1)−Cl(1) = 99.11(5).
a
Reagents and conditions: (i) cis-[PtCl2(DMSO)2], MeOH; (ii) cis-
[PtCl2(DMSO)2], MeOH, NaOAc (temperatures and reaction times
depend on the imine).
Interestingly, the ring size of the resulting cyclometalated
compound is also a variable that has a dramatic influence on the
cycloplatination reaction. While imine 1 affords the correspond-
ing six-membered platinacycle by refluxing in methanol for 4 h,
even in the absence of an external base, the reaction of the
closely related imine 9 requires the presence of sodium acetate
to achieve the formation of the corresponding five-membered
platinacycle. It is even possible to cycloplatinate imines 5 and 6
(having one and no methyl group on the aliphatic chain,
respectively), in the presence of sodium acetate with the
formation of the six-membered platinacycles. In contrast, when
the same reaction was performed with the analogous imines 12
and 13, the formation of the corresponding five-membered
platinacycles was not observed and only coordination
compounds were obtained. In conclusion, these results indicate
that, surprisingly, the formation of six-membered platinacycles is
especially favored.
All of the new [N,N] and [C,N,N′] platinum compounds
were characterized by elemental analyses, 1H and 13C{1H} NMR
spectroscopy, and electrospray mass spectrometry. The
coupling of the imine proton to platinum is in the 88−95 Hz
range for [N,N′] coordination compounds and in the 100−110
Hz range for cycloplatinated [C,N,N′] derivatives, as for other
cycloplatinated imines. This is an effect that has been associated
with the higher electron density at the metal center in the
cyclometalated complex.17
Figure 4. Molecular crystal structure of 10mPt. Selected bond lengths
(Å) and bond angles (deg): Pt(1)−N(1) = 1.948(3), Pt(1)−C(1) =
1.975(3), Pt(1)−N(2) = 2.209(3), Pt(1)−Cl(1) = 2.3115(11), N(1)−
C(10) = 1.285(5), N(1)−C(7) = 1.506 (4), N(3)−C(15) = 1.348(4),
N(3)−C(11) = 1.373(5), N(1)−Pt(1)−C(1) = 82.92(15), N(1)−
Pt(1)−N(3) = 79.11(13), C(1)−Pt(1)−Cl(1) = 93.78(11), N(3)−
Pt(1)−Cl(1) = 104.14(8).
four different molecules (A−D) were found per unit cell for
compound 10mPt, only slight differences in bond lengths and
angles are found between them and the average values are
reported in Figure 4. Crystal and structure refinement data are
collected in Tables S1 and S2.
In the two structures, the platinum atoms have the expected
square-planar coordination with the tridentate [C,N,N′] ligand.
All bond distances are in the expected range for both
As indicated above for the cyclopalladated compounds, the
1H NMR spectra of all six-membered derivatives present broad
signals in the CH2N and methyl proton regions, suggesting the
existence of a fluxional process for the six-membered cycle; again
the 1H spectra at 240 K confirms this fact.
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complexes.18 The 2.1688(17) Å distance for Pt−N(2) is
significantly longer than that for Pt−N(1) (2.0022(18) Å) for
7mPt, while for 10mPt the same trend is true (2.209(3) versus
1.948(3) Å), consistent with the strong trans influence of the
carbon donor ligands.
The structure of 7mPt confirms the lack of planarity of the six-
membered metallacycle, which adopts a screw-boat conforma-
tion with deviations from the mean plane of −0.199(1),
0.240(2), 0.054(2), −0.436(2), 0.348(2), and −0.007(2) Å for
Pt(1), C(1), C(6), C(7), C(8), and N(1), respectively. In
contrast, the structure of 10mPt shows a planar five-membered
platinacycle, the deviations from the mean plane being
−0.0005(1), 0.0298(4), 0.0143(4), 0.0183(4) and
−0.0078(3) Å for Pt(1), C(1), C(6), C(7), and N(1),
respectively. These facts explain the observed fluxionality for
all of the six-membered metallacycles of palladium, while the
corresponding five-membered metallacycles show nondynamic
NMR spectra.
that no significant differences could be associated with the
solvent used, and thus the addition of a 5% chloroform
concentrated solution of the complexes to preheated toluene has
been used as the standard technique for the monitoring of the
reactions. The data collected for these reactions occurring on the
Pd(II) complexes indicated in Scheme 3 produced the set of
Eyring and ln k versus P plots shown in Figure 5. In this figure it
Kinetico-Mechanistic Studies on the C−H Activation
Processes. In view of the very interesting results on the
preparation of the cyclometalated compounds of Pd(II) and
Pt(II) and their relevance in some catalytic processes,1,2 we
decided to take advantage of the aforementioned uncommon
preparative isolation of the complexes with the directing groups
already coordinated.19
Given our previous knowledge of the mechanisms participat-
ing in these C−H and other C−X bond activation
reactions,19a,f,20 we have carried out an study from a kinetico-
mechanistic perspective of the proper C−H activation reaction
on these d8 metal center complexes. For this purpose, we have
selected equivalent Pd(II) and Pt(II) complexes, for which the
coordination compounds have been isolated in good yield.
Furthermore, those having two methyl groups at the imine
nitrogen α-carbon and none at the β-position and an aliphatic
chain length that allowed the formation of five- and six-
membered metalated species represent the best choice (Scheme
3). All of the processes have been monitored at variable
Figure 5. (a) Eyring and (b) ln k versus P plots for the C−H bond
activation reaction on Pd(II) compounds 9cPd (leading to a five-
membered ring) and 1cPd (leading to a six-membered ring). The
solvent is toluene unless specified otherwise; empty points indicate a
solution made by the addition of a concentrated solution in chloroform
to preheated toluene.
Scheme 3. Metalation Process Studied
is clear that the aforementioned solvent independence of the
process applies. The figure also indicates the different activation
parameter features of the reactions occurring for the n = 0 and n
= 1 coordination compounds, producing the five- and six-
membered (1mPd and 9mPd) final metallacycles (first two
entries of Table 1).
Clearly, from the data collected in the first two entries of Table
1, the electrophilic substitution reaction occurring on the
metalating phenyl ring19f,21 needs a large degree of ordering and
expansion for the formation of the five-membered 9mPd
cyclopalladated compound. For the formation of the equivalent
1mPd (six-membered metallacycle) the values of entropy are
less negative, and the activation volume falls to 0 within error. As
described in similar systems,19d,22 the transition state for
electrophilic C−H bond activations on Pd(II) is rather
advanced in the reaction coordinate. This is, the reactions are
occurring with a fairly dissociated acetate ligand on acceptance
of the proton from the C−H bond; thus, an ordered but
otherwise expanded transition state situation is expected.19b,23b
This effect is much more pronounced on the more rigid and
sterically demanding n = 1 system, as effectively observed. The
temperature and pressure in order to obtain the relevant thermal
and pressure activation parameters, which are indicative of the
mechanism occurring in the reaction.
For M = Pd(II) the C−H bond activation process of the
acetate derivatives (1cPd and 9cPd) was conducted in toluene
solution, as for the preparative procedures. Given the fact that
these complexes have a very low solubility at room temperature
in this solvent, some experiments were also carried out in
acetone or chloroform solution. The results obtained indicated
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Table 1. Thermal and Pressure Activation Parameters for the C−H Bond Activation Reactions Indicated in Scheme 3
metal, X
metalated ring (n) cyclometalated compound
ligand
ΔH⧧/kJ mol−1
ΔS⧧/J K−1 mol−1
ΔV⧧/cm3 mol−1
Pd, AcO
Pd, AcO
Pt, Cl
5-membered (n = 0) 9mPd
6-membered (n = 1) 1mPd
5-membered (n = 0) 9mPt
6-membered (n = 1) 1mPt
9
1
9
1
65
92
102
92
5
5
9
6
−112 15
−43 14
−12 30
−42 20
11
∼0
−3.7 0.2
−7.0 0.4
3
Pt, Cl
recently reported eCMD mechanistic classification can also be
applied to the processes monitored,24 as it also applies to our
previously studied systems.
The same kinetico-mechanistic study on the C−H bond
activation was conducted with the equivalent 1cPt and 9cPt
Pt(II) chloride complexes in methanol solution (again the
solvent used in the preparative procedures). In this case the
intimate mechanism of the reaction can be viewed as an
electrophilic substitution (or electrophilic concerted metal-
ation−deprotonation mechanism), liberating protons, or an
alternative oxidative addition to produce a Pt(IV) hydrido
complex, followed by a reductive elimination of HCl.19f,25 In this
respect, we have been involved for some time in the study of
such processes and the results indicated that, for non-
organometallic starting materials, the process can be more
adequately viewed as an electrophilic substitution with
liberation of H+. Nevertheless, the intimate mechanics of the
reaction is far from unambiguous, and some important literature
exists on the matter.24,26
In view of these premises, and from our previous studies on
similar {PtII[N,N′]Cl} cyclometalating units, stoichiometric
sodium acetate, as an external base, was also added to the
methanol solution (as was done in the preparative procedures
indicated above) in some experiments. UV−vis time-resolved
monitoring indicated that a neat reaction occurs even in the
absence of added sodium acetate; furthermore, the process
monitored is equivalent to that observed when 10−60-fold
excesses of acetate were added to the reaction medium (Table
S3). It is important to note that, at the 10−4 M concentration
level used in the kinetic studies even in the absence of sodium
acetate, the NMR characterization of the final product of the
reaction shows that C−H bond activation has effectively taken
place. Furthermore, the compound isolated under the same
conditions but in the presence of sodium acetate has undergone
the chloride by acetate exchange, as for other {PtII[N,N′]Cl}
units.25 It is thus clear that concentration factors are extremely
relevant in the processes studied; probably the formation of a
high concentration of acid under the standard preparative
conditions has to be prevented to avoid Pt(II)−C bond
acidolysis,21,27 while at the concentration level used for kinetic
runs this is not necessary.
Once these preliminary features were clarified, we carried out
the kinetico-mechanistic study of the cycloplatination reaction
of compounds 1cPt and 9cPt in methanol solution at variable
temperatures and pressures. The data collected for these
reactions occurring on the Pt(II) complexes (indicated in
Scheme 3) produced the set of Eyring and ln k versus P plots
shown in Figure 6. In the figure the aforementioned acetate
concentration independence of the process is indicated.
Furthermore, although the activation volumes are diverse,
extremely similar thermal activation parameters are obtained for
the two reactions producing the five- and six-membered (1mPt
and 9mPt) final metallacycles. These data are collected in the
last two entries of Table 1.
Figure 6. (a) Eyring and (b) ln k versus P plots for the C−H bond
activation reaction on Pt(II) compounds 9cPt (leading to a five-
membered ring) and 1cPt (leading to a six-membered ring). The
solvent was methanol; empty points indicate values for solutions
containing an excess of sodium acetate at the concentrations indicated.
From the data shown in Table 1 we can state that the reaction
of C−H bond activation on complexes 9cPt and 1cPt takes
place with extremely similar thermal activation parameters (see
Figure 6), a rather high enthalpy of activation, and close to 0
activation entropy, especially for the formation of the five-
membered compound. In contrast, the values of the activation
volumes indicate that the contraction observed for the transition
state in both systems doubles on going from the five-membered
to the six-membered metallacycles (−3.7 versus −7.0 cm3/mol).
As expected, the size of the ring formed produces a larger
compression for compound 1cPt due to the flexibility of the
longer metalating chain of the 1 ligand. Furthermore, this higher
compression (or lower expansion) has been also observed for
the Pd(II) systems studied in this work. Clearly, if the process
relates to an electrophilic substitution mechanism, the systems
show a much earlier transition state with respect to the Pd(II)
counterparts in the reaction coordinate. The chloride anion
seems to be still rather close to the metal center on accepting the
proton from the cyclometalating ligand, thus being contracted
by the approaching C−H bond to be activated.
Surprisingly, the noticeable differences observed in the
thermal activation parameters for the formation of the five-
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and six-membered acetato palladacycles do not transfer to the
equivalent Pt(II) systems. Clearly, the nature of the d8 metal
centers is playing a determinant role in the reactivity observed,
with the Pt(II) square-planar center being much more involved
in the energetics of the reaction. That is, the length of the
metalating arm on the ligands 1 and 9 does not seem to be too
important for the values of the enthalpies of activation; only the
value of ΔS⧧ is slightly more negative for the formation of the
six-membered ring, in line with the higher flexibility and
contraction of the system. As a whole, this effect can be related to
the continuous mechanism tuning of these types of reactions
that go from an electrophilic substitution (Scheme 4, left) to an
efficient catalytic or stoichiometric C−H activation processes. In
this sense, very preliminary results in the synthesis of 2,2-
disubstituted indolines via Pd-catalyzed C−H functionalization
with imine 2 showed yields similar to those achieved with imine
1.9 Therefore, an increase om the steric hindrance of the imine in
this reaction did not detrimentally affect the steps that follow the
C−H activation step.
EXPERIMENTAL SECTION
■
Materials and Methods. All of the operations were carried out in
air. All chemicals were obtained from commercial sources and used as
received otherwise specified. Solvents were distilled and dried before
use.
a
Proton NMR spectra were recorded at 298 and 240 K with Varian
Mercury 400 and Bruker Avance I 500 spectrometers, respectively. 13C
NMR spectra were recorded with a Varian Mercury 400 or a Bruker 400
spectrometer. The deuterated solvent is specified for each compound,
and chemical shifts are given in δ values (ppm) relative to SiMe4.
Coupling constants are given in Hz, and multiplicity is expressed as s
(singlet), d (doublet), t (triplet), and m (multiplet). High-resolution
mass spectrometry (HRMS) and low-resolution mass spectrometry
(LRMS) analyses were performed with electrospray ionization. ESI
spectra were acquired either on an LC/MSD-TOF instrument or on a
ZQ mass spectrometer, utilizing a mixture of H2O and CH3CN (1/1, v/
v) as the eluent. Elemental analyses were carried out at the Serveis
Scheme 4. Mechanisms Proposed for C−H Activation
̀
Cientifico-Tecnics (Universitat de Barcelona); although some
elemental analyses are outside the range viewed as establishing
analytical purity, they are provided to illustrate the best values obtained
to date.
X-ray Diffraction. In both cases, a prismatic crystal was selected and
used for the X-ray crystallographic analysis. The X-ray intensity data
were measured on a D8 Venture system equipped with a multilayer
monochromator and a Mo microfocus (λ = 0.71073 Å).
a
E stands for the cyclometalation directing group.
oxidative addition/reductive elimination sequence (Scheme 4,
right).26 The Pt(II) center is known to be more prone to the
existence of oxidatively added Pt(IV) hydrido complexes, which
should play a role in the abstraction by chloride of the proton
from the C−H bonds, with low discrimination in the thermal
activation parameters for ligands 1 and 9 (Scheme 4, middle).26b
The frames were integrated with the Bruker SAINT software package
using a narrow-frame algorithm. Data were corrected for absorption
effects using the multi-scan method (SADABS), and the structure was
solved and refined using the Bruker SHELXTL software package.
CCDC nos. 2038592 (7mPt) and 2038593 (10mPt) contain the
supplementary crystallographic data for this paper. These data are also
available free of charge via www.ccdc.cam.ac.uk/cgi-bin/catreqcgi or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax: +44 1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk).
Kinetics. The kinetic profiles for the reactions were followed by
UV−vis spectroscopy in the full 700−300 nm range on HP8452A and
Cary50 instruments equipped with thermostated multicell transports.
The observed rate constants were derived from absorbance versus time
traces at the wavelengths where a maximum increase and/or decrease in
absorbance were observed; alternatively, the full spectral time-resolved
changes were used. For the reactions carried out at varying pressure, the
previously described pillbox cell and pressurizing system28 were used
and the final treatment of data was the same as that described before.
The calculations of the observed rate constants from the absorbance
versus time monitoring of reactions, studied under first-order
concentration conditions, were carried out using the SPECFIT or
RecatLab software.29 The general kinetic technique is that previously
described.19g,30 Table S3 collects all of the obtained kobs values for all of
the systems studied as a function of the reaction studied, solvent,
temperature, and pressure. All postrun fittings were carried out by the
standard available commercial programs. All experiments were carried
out on solutions that were (1−4) × 10−4 M in metal complex; the low
solubility of the palladium compounds was sorted out by preparing 50-
fold more concentrated chloroform solutions and adding a small
amount of these to preheated toluene. Sodium acetate solutions in
methanol were prepared by weight in the spectrophotometric cells used
for the kinetic runs.
CONCLUSIONS
■
It has been shown that, for the cyclometalation of α- and β-
substituted imines of the ArCHNCH2(CH2)nPh (Ar = 2-
pyridinyl, 2-picolinyl, 2-quinolinyl, n = 0, 1) family, the presence
of two methyl groups at the imine nitrogen α-carbon facilities
the process. The heterocyclic Ar fragment also has been found to
have a relevant influence in the process, the trend following the
order picolinyl > quinolinyl > pyridinyl. A combination of these
two effects has been found to be determinant for both palladium
and platinum chemistry. All of these results can be explained by
the steric promotion of the metalation process: the reaction is
strongly favored when bulky substituents are located in the
proximity of the coordinating nitrogen atoms (both with
palladium and platinum). Unexpectedly, it has also been
shown that the formation of six-membered platinacycles (n =
1) is especially favored.
A kinetico-mechanistic study of the C−H activation reaction
on some equivalent Pd(II) and Pt(II) coordination complexes
has shown that the nature of the d8 metal center plays a
determinant role in the reactivity observed. In this respect, the
full process can be seen as a mechanistic continuum that goes
from an electrophilic substitution (Pd(II) centers) to an
oxidative addition/reductive elimination sequence (Pt(II)
centers).
The findings described here provide new and relevant
information about the metalation process by palladium or
platinum reagents, which can be useful in the design of new,
Synthesis of Imines. All imines were synthesized following the
general procedure already known:9 the corresponding primary amine
and 2-formylpyridine, 2-formyl-6-picoline, or 2-formylquinoline (1:1
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molar ratio) were dissolved in toluene (10 mL/mmol). The mixture
was heated to reflux overnight under nitrogen with a Dean−Stark
apparatus. After the mixture was cooled to room temperature, the
solvent was eliminated to afford the pure imine.
Phenethylamine, cumylamine, benzylamine, and (R)-1-phenylethan-
1-amine were purchased from commercial sources. 2-Methyl-1-
phenylpropan-2-amine was synthesized as in previous works.9,11c 2-
Methyl-2-phenylpropan-1-amine was prepared from 2-methyl-2-
phenylpropanenitrile by reduction.31 1-Phenylpropan-2-amine was
obtained by the oxidation of 1-phenylpropan-2-ol32 followed by
aminative reduction of the ketone.33 Imine 1 has been previously
reported.9
(E)-N-(2-Methyl-1-phenylpropan-2-yl)-1-(pyridin-2-yl)-
methanimine (1). Brown oil, 798 mg (3.35 mmol, 100% yield) from 2-
methyl-1-phenylpropan-2-amine and 2-formylpyridine. 1H NMR (400
MHz, CDCl3): δ 8.62 (ddd, J = 4.9, 1.8, 0.9 Hz, 1H), 8.13 (s, 1H), 8.07
(dd, J = 7.9, 1.0 Hz, 1H), 7.76 (td, J = 7.7, 1.8 Hz, 1H), 7.30 (ddt, J = 6.9,
4.9, 1.0 Hz, 1H), 7.22−7.12 (m, 5H), 2.92 (s, 2H), 1.28 (s, 6H). 13C
NMR (101 MHz, CDCl3): δ 157.2, 155.5, 149.4, 138.4, 136.7, 130.9,
127.8, 126.2, 124.6, 121.0, 61.1, 49.8, 27.0. IR (FTIR-ATR, ν, cm−1):
3062, 3031, 2964, 2917, 1465. HRMS (ESI+, m/z): [M + H]+ calcd for
C16H19N2, 239.1543; found 239.1549.
139.9, 136.9, 129.0, 128.5, 126.3, 124.5, 118.5, 63.1, 37.5, 24.5. IR
(FTIR-ATR, ν, cm−1): 3062, 3024, 2926, 2860, 2831, 1454. HRMS
(ESI+, m/z): [M + H]+ calcd for C15H17N2, 225.1386; found,
225.1393.
(E)-N-(2-Methyl-1-phenylpropan-2-yl)-1-(quinolin-2-yl)-
methanimine (7). Brown oil, 288 mg (1.00 mmol, 100% yield) from 2-
methyl-1-phenylpropan-2-amine and 2-formylquinoline. 1H NMR
(400 MHz, CDCl3): δ 8.34−8.29 (m, 1H), 8.28 (d, J = 8.6 Hz, 1H),
8.21 (d, J = 8.6 Hz, 1H), 8.10 (ddt, J = 8.5, 1.4, 0.8 Hz, 1H), 7.85 (dd, J =
8.1, 1.4 Hz, 1H), 7.73 (ddd, J = 8.5, 6.9, 1.3 Hz, 1H), 7.57 (ddd, J = 8.1,
6.9, 1.3 Hz, 1H), 7.23−7.15 (m, 5H), 2.96 (s, 2H), 1.33 (s, 6H). 13C
NMR (101 MHz, CDCl3): δ 157.6, 155.8, 147.9, 138.4, 136.6, 130.9,
129.8, 129.6, 128.9, 127.9, 127.8, 127.3, 126.2, 118.4, 61.4, 49.9, 27.1.
IR (FTIR-ATR, ν, cm−1): 3056, 3024, 2964, 2913, 1642, 1595, 1502.
HRMS (ESI+, m/z): [M + H]+ calcd for C20H21N2, 289.1699; found,
289.1700.
(E)-N-Phenethyl-1-(quinolin-2-yl)methanimine (8). Yellow solid,
286 mg (1.10 mmol, 100% yield) from phenethylamine and 2-
1
formylquinoline. Mp (°C): 51−52. H NMR (400 MHz, CDCl3): δ
8.48 (s, 1H), 8.23−8.08 (m, 3H), 7.84 (d, J = 8.0 Hz, 1H), 7.73 (ddd, J
= 8.4, 6.9, 1.4 Hz, 1H), 7.57 (ddd, J = 8.0, 6.9, 1.2 Hz, 1H), 7.32−7.24
(m, 4H), 7.23−7.17 (m, 1H), 4.00 (td, J = 7.5, 1.4 Hz, 2H), 3.08 (t, J =
7.5 Hz, 2H). 13C NMR (101 MHz, CDCl3): δ 163.0, 154.9, 147.9,
139.8, 136.7, 129.9, 129.8, 129.1, 128.9, 128.6, 127.8, 127.5, 126.4,
118.5, 63.2, 37.5. IR (FTIR-ATR, ν, cm−1): 3062, 302, 2955, 2917,
2863, 2825, 1498. HRMS (ESI+, m/z): [M + H]+ calcd for C18H17N2,
261.1386; found, 261.1389.
(E)-N-(2-Methyl-1-phenylpropan-2-yl)-1-(6-methylpyridin-2-yl)-
methanimine (2). Brown reddish oil, 254 mg (1.01 mmol, 100% yield)
1
from 2-methyl-1-phenylpropan-2-amine and 2-formyl-6-picoline. H
NMR (400 MHz, CDCl3): δ 8.13 (s, 1H), 7.92 (d, J = 7.8 Hz, 1H), 7.64
(t, J = 7.8 Hz, 1H), 7.23−7.12 (m, 6H), 2.91 (s, 2H), 2.57 (s, 3H), 1.27
(s, 6H). 13C NMR (101 MHz, CDCl3): δ 157.9, 157.5, 155.1, 138.5,
136.9, 130.8, 127.7, 126.2, 124.2, 117.8, 61.0, 49.8, 27.0, 24.4. IR
(FTIR-ATR, ν, cm−1): 3062, 3024, 2964, 2917, 1454. HRMS (ESI+,
m/z): [M + H]+ calcd for C17H21N2, 253.1699; found 253.1702.
(E)-N-Phenethyl-1-(pyridin-2-yl)methanimine (3). Brown oil, 420
mg (2.00 mmol, 100% yield) from phenethylamine and 2-
(E)-N-(2-Phenylpropan-2-yl)-1-(pyridin-2-yl)methanimine (9).
Brown oil, 830 mg (3.70 mmol, 100% yield) from cumylamine and
2-formylpyridine. 1H NMR (400 MHz, CDCl3): δ 8.63 (ddd, J = 4.9,
1.7, 0.8 Hz, 1H), 8.34 (d, J = 0.8 Hz, 1H), 8.13 (dt, J = 7.9, 1.2 Hz, 1H),
7.74 (tdd, J = 8.1, 1.7, 0.7 Hz, 1H), 7.44 (dt, J = 7.9, 1.2 Hz, 2H), 7.36−
7.28 (m, 3H), 7.27−7.19 (m, 1H), 1.68 (s, 6H). 13C NMR (101 MHz,
CDCl3): δ 158.4, 155.5, 149.4, 147.7, 136.7, 128.4, 126.6, 126.2, 124.7,
121.2, 63.3, 29.7. IR (FTIR-ATR, ν, cm−1): 3056, 2970, 2923, 1465.
HRMS (ESI+, m/z): [M + H]+ calcd for C15H17N2, 225.1386; found,
225.1389.
(E)-1-(6-Methylpyridin-2-yl)-N-(2-phenylpropan-2-yl)-
methanimine (10). Colorless oil, 238 mg (1.00 mmol, 100% yield)
from cumylamine and 2-formyl-6-picoline. 1H NMR (400 MHz,
CDCl3): δ 8.34 (s, 1H), 7.97 (d, J = 7.7 Hz, 1H), 7.63 (t, J = 7.7 Hz,
1H), 7.47−7.40 (m, 2H), 7.37−7.28 (m, 2H), 7.27−7.17 (m, 1H), 7.17
(d, J = 7.7 Hz, 1H), 2.59 (s, 3H), 1.66 (s, 6H). 13C NMR (101 MHz,
CDCl3): δ 158.7, 158.0, 155.1, 148.0, 136.9, 128.3, 126.5, 126.1, 124.3,
118.1, 63.2, 29.7, 24.4. IR (FTIR-ATR, ν, cm−1): 3056, 3015, 2974,
2920, 1454. HRMS (ESI+, m/z): [M + H]+ calcd for C16H19N2,
239.1543; found, 239.1547.
1
formylpyridine. H NMR (400 MHz, CDCl3): δ 8.63 (ddd, J = 4.9,
1.8, 1.1 Hz, 1H), 8.30 (td, J = 1.4, 0.7 Hz, 1H), 7.98 (dt, J = 7.9, 1.1 Hz,
1H), 7.74 (tdd, J = 7.9, 1.8, 0.7 Hz, 1H), 7.33−7.30 (m, 1H), 7.30−7.28
(m, 1H), 7.28−7.24 (m, 1H), 7.26−7.17 (m, 3H), 3.93 (td, J = 7.6, 1.4
Hz, 2H), 3.04 (t, J = 7.6 Hz, 2H). 13C NMR (101 MHz, CDCl3): δ
162.5, 154.6, 149.6, 139.8, 136.7, 129.1, 128.5, 126.3, 124.8, 121.4, 63.1,
37.5. IR (FTIR-ATR, ν, cm−1): 3060, 3029, 2880, 2836, 1650, 1434.
HRMS (ESI+, m/z): [M + H]+ calcd for C14H15N2, 211.1230; found
211.1229.
(E)-N-(2-Methyl-2-phenylpropyl)-1-(pyridin-2-yl)methanimine
(4). Brown oil, 300 mg (1.26 mmol, 100% yield) from 2-methyl-2-
1
phenylpropan-1-amine and 2-formylpyridine. H NMR (400 MHz,
CDCl3): δ 8.61 (dd, J = 4.9, 0.8 Hz, 1H), 8.26 (s, 1H), 7.98 (dt, J = 7.9,
1.2 Hz, 1H), 7.71 (td, J = 7.9, 1.7 Hz, 1H), 7.43 (dd, J = 8.4, 1.2 Hz,
2H), 7.36−7.24 (m, 3H), 7.21−7.16 (m, 1H), 3.79 (d, J = 1.4 Hz, 2H),
1.43 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 162.5, 154.8, 149.4,
148.3, 136.6, 128.2, 126.2, 126.0, 124.7, 121.2, 73.6, 39.7, 27.1. IR
(FTIR-ATR, ν, cm−1): 3056, 3024, 2965, 2917, 1644, 1585, 1465.
HRMS (ESI+, m/z): [M + H]+ calcd for C16H19N2, 239.1543; found
239.1550.
(E)-N-Benzyl-1-(pyridin-2-yl)methanimine (11). Brown oil, 385 mg
(1.96 mmol, 98%) from benzylamine and 2-formylpyridine. 1H NMR
(400 MHz, CDCl3): δ 8.65 (ddd, J = 4.8, 1.8, 1.1 Hz, 1H), 8.49 (q, J =
1.1 Hz, 1H), 8.07 (dt, J = 7.8, 1.1 Hz, 1H), 7.74 (td, J = 7.8, 1.8 Hz, 1H),
7.36 (s, 2H), 7.35 (s, 2H), 7.34−7.27 (m, 2H), 4.88 (d, J = 1.5 Hz, 2H).
13C NMR (101 MHz, CDCl3): δ 163.0, 154.7, 149.5, 138.8, 136.7,
128.7, 128.3, 127.3, 125.0, 121.5, 65.1. IR (FTIR-ATR, ν, cm−1): 3056,
3024, 2882, 2834, 1644, 1585, 1566, 1434. HRMS (ESI+, m/z): [M +
H]+ calcd for C13H13N2, 197.1073; found, 197.1074.
(E)-N-(1-Phenylpropan-2-yl)-1-(pyridin-2-yl)methanimine (5).
Brown oil, 367 mg (1.64 mmol, 92% yield) from 1-phenylpropan-2-
1
amine and 2-formylpyridine. H NMR (400 MHz, CDCl3): δ 8.61
(ddd, J = 4.8, 1.8, 1.0 Hz, 1H), 8.16 (s, 1H), 7.97 (dt, J = 8.0, 1.0 Hz,
1H), 7.73 (dddd, J = 8.0, 7.6, 1.8, 0.6 Hz, 1H), 7.29 (ddd, J = 7.6, 4.8, 1.2
Hz, 1H), 7.26−7.21 (m, 2H), 7.18−7.13 (m, 3H), 3.72−3.62 (m, 1H),
2.93 (qd, J = 13.4, 6.7 Hz, 2H), 1.32 (d, J = 6.3 Hz, 3H). 13C NMR (101
MHz, CDCl3): δ 160.2, 154.6, 149.4, 139.2, 136.5, 129.6, 128.2, 126.1,
124.6, 121.4, 67.9, 44.4, 22.0. IR (FTIR-ATR, ν, cm−1): 3056, 3018,
2967, 2923, 2853, 1644, 1586, 1467. HRMS (ESI+, m/z): [M + H]+
calcd for C15H17N2, 225.1386; found, 225.1396.
(E)-1-(6-Methylpyridin-2-yl)-N-phenethylmethanimine (6). Yel-
low oil, 224 mg (1.00 mmol, 100% yield) from phenethylamine and
2-formyl-6-picoline. 1H NMR (400 MHz, CDCl3): δ 8.29 (t, J = 0.7 Hz,
1H), 7.78 (ddd, J = 7.8, 1.2, 0.7 Hz, 1H), 7.62 (t, J = 7.8 Hz, 1H), 7.31−
7.15 (m, 6H), 3.91 (ddd, J = 8.0, 7.3, 1.4 Hz, 2H), 3.03 (t, J = 7.6 Hz,
2H), 2.58 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 162.8, 158.3, 154.0,
(R,E)-N-(1-Phenylethyl)-1-(pyridin-2-yl)methanimine (12). Yel-
lowish oil, 421 mg (2.00 mmol, 100% yield) from (R)-1-phenyl-
ethan-1-amine and 2-formylpyridine. 1H NMR (400 MHz, CDCl3): δ
8.63 (ddd, J = 4.9, 1.7, 1.1 Hz, 1H), 8.47 (s, 1H), 8.09 (dt, J = 7.9, 1.1
Hz, 1H), 7.75−7.70 (m, 1H), 7.46−7.41 (m, 2H), 7.37−7.21 (m, 4H),
4.64 (q, J = 6.6 Hz, 1H), 1.61 (d, J = 6.6 Hz, 3H). 13C NMR (101 MHz,
CDCl3): δ 160.5, 154.9, 149.4, 144.7, 136.6, 128.6, 127.1, 126.8, 124.8,
121.6, 69.7, 24.7. IR (FTIR-ATR, ν, cm−1): 3059, 2955, 2912, 2848,
1467. HRMS (ESI+, m/z): [M + H]+ calcd for C14H15N2, 211.1230;
found, 211.1228.
(E)-N-Benzyl-1-(6-methylpyridin-2-yl)methanimine (13). Yellow
oil, 294 mg (1.40 mmol, 100% yield) from benzylamine and 2-formyl-6-
picoline. 1H NMR (400 MHz, CDCl3): δ 8.47 (p, J = 0.8 Hz, 1H), 7.87
(d, J = 7.7 Hz, 1H), 7.62 (t, J = 7.7 Hz, 1H), 7.34 (d, J = 4.4 Hz, 4H),
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7.30−7.24 (m, 1H), 7.18 (d, J = 7.7 Hz, 1H), 4.87 (d, J = 1.5 Hz, 2H),
2.60 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 163.3, 158.3, 154.1,
138.9, 136.9, 128.7, 128.3, 127.3, 124.6, 118.6, 65.1, 24.5. IR (FTIR-
ATR, ν, cm−1): 3062, 3027, 2913, 2869, 2828, 1589, 1452. HRMS (ESI
+, m/z): [M + H]+ calcd for C14H15N2, 211.1230; found, 211.1232.
(E)-N-(2-Phenylpropan-2-yl)-1-(quinolin-2-yl)methanimine (14).
Yellow oil, 274 mg (1.00 mmol, 100% yield) from cumylamine and 2-
formylquinoline. 1H NMR (400 MHz, CDCl3): δ 8.54 (d, J = 0.9 Hz,
1H), 8.31 (d, J = 8.5 Hz, 1H), 8.19 (d, J = 8.5 Hz, 1H), 8.11 (dd, J = 8.5,
0.9 Hz, 1H), 7.84 (dd, J = 8.1, 1.4 Hz, 1H), 7.73 (ddd, J = 8.5, 6.9, 1.4
Hz, 1H), 7.57 (ddt, J = 8.1, 6.9, 0.7 Hz, 1H), 7.48 (dt, J = 7.8, 1.1 Hz,
2H), 7.35 (ddd, J = 7.8, 7.0, 0.7 Hz, 2H), 7.27−7.22 (m, 1H), 1.72 (s,
6H). 13C NMR (101 MHz, CDCl3): δ 158.8, 155.8, 147.9, 147.8, 136.6,
129.9, 129.6, 129.0, 128.4, 127.9, 127.4, 126.7, 126.2, 118.6, 63.5, 29.7.
IR (FTIR-ATR, ν, cm−1): 3059, 2970, 2926, 1637, 1595, 1493. HRMS
(ESI+, m/z): [M + H]+ calcd for C19H19N2, 275.1543; found,
275.1538.
(E)-N-Benzyl-1-(quinolin-2-yl)methanimine (15). Red oil, 483 mg
(1.96 mmol, 98% yield) from benzylamine and 2-formylquinoline. 1H
NMR (400 MHz, CDCl3): δ 8.66 (s, 1H), 8.24−8.16 (m, 2H), 8.13 (dt,
J = 8.4, 0.8 Hz, 1H), 7.84 (ddd, J = 8.1, 1.5, 0.8 Hz, 1H), 7.74 (ddd, J =
8.4, 6.9, 1.5 Hz, 1H), 7.58 (ddd, J = 8.1, 6.9, 1.1 Hz, 1H), 7.42−7.26 (m,
5H), 4.95 (d, J = 1.4 Hz, 2H). 13C NMR (101 MHz, CDCl3): δ 163.3,
154.8, 147.8, 138.6, 136.5, 129.8, 129.6, 128.8, 128.6, 128.2, 127.7,
127.4, 127.2, 118.5, 65.0. IR (FTIR-ATR, ν, cm−1): 3059, 3027, 2869,
2828, 1642, 1595, 1501. HRMS (ESI+, m/z): calcd for [M + H]+ calcd
for C17H15N2, 247.1230; found 247.1230.
Brown solid. Rf (DCM/MeOH 95/5) = 0.25. 1H NMR (400 MHz,
CDCl3): δ 8.16 (dd, J = 5.5, 1.4 Hz, 1H), 7.96 (td, J = 7.8, 1.5 Hz, 1H),
7.61 (dd, J = 7.3, 1.1 Hz, 1H), 7.45 (ddd, J = 7.8, 5.5, 1.4 Hz, 1H), 7.37−
7.33 (m, 2H), 7.32−7.28 (m, 2H), 7.25−7.22 (m, 1H), 7.21 (s, 1H),
3.53 (s, 2H), 2.08 (s, 3H), 2.08 (s, 3H), 1.60 (s, 6H). 13C NMR (101
MHz, CDCl3): δ 178.5, 178.1, 168.7, 154.6, 150.8, 145.1, 140.3, 128.8,
127.7, 127.1, 126.9, 126.7, 69.2, 41.6, 26.5, 23.5, 23.4. IR (FTIR-ATR,
ν, cm−1): 3069, 3034, 2961, 2929, 1710, 1590, 1368, 1315. EA (calcd
for C20H24N2O4Pd): C, 49.7 (51.90); H, 5.0 (5.23); N, 6.1 (6.05).
LRMS (ESI+, m/z): [M − OAc]+ calcd for C16H17N2Pd, 343.04;
found, 343.04.34
5cPd. A mixture of imine 5 (81 mg, 0.36 mmol) and palladium
acetate (80 mg, 0.36 mmol) in an 1/1 molar ratio was stirred at room
temperature in 10 mL of toluene for 1 h. The brown precipitate was
filtered in vacuo to obtain 5cPd (148 mg, 91%).
Brown solid. Rf (DCM/MeOH 95:5) = 0.30. 1H NMR (400 MHz,
CDCl3): δ 8.23 (s, 1H), 8.06 (tt, J = 7.7, 1.6 Hz, 1H), 7.98−7.85 (m,
2H), 7.53 (ddd, J = 7.7, 5.6, 1.5 Hz, 1H), 7.19 (dd, J = 14.3, 7.0 Hz, 5H),
4.06 (q, J = 7.0 Hz, 1H), 3.36 (dd, J = 13.4, 5.2 Hz, 1H), 2.83 (ddd, J =
13.4, 7.4, 1.8 Hz, 1H), 2.08 (s, 3H), 2.07 (s, 3H), 1.34 (dd, J = 6.6, 1.8
Hz, 3H). 13C NMR (101 MHz, CDCl3): δ 178.4, 178.3, 165.0, 155.1,
150.6, 140.4, 136.7, 129.8, 128.6, 127.8, 127.3, 126.9, 65.0, 41.8, 23.5,
18.3. IR (FTIR-ATR, ν, cm−1): 3031, 2974, 2920, 1621, 1590, 1361,
1307. EA (calcd for C19H22N2O4Pd): C, 48.8 (50.85); H, 4.9 (4.94); N,
6.0 (6.24). LRMS (ESI+, m/z): [M − OAc]+ calcd for C15H15N2Pd,
329.03; found, 329.03.34
5mPd. Coordination compound 5cPd (60 mg, 0.13 mmol) was
allowed to react in dry toluene (6 mL) at 90 °C for 2.5 h and then
filtered. The solvent was removed in a rotary evaporator and the residue
was eluted in a flash chromatography column (DCM/MeOH 97/3 to
95/5), yielding a solid which was filtered in vacuo to obtain 5mPd in 5%
yield.
Synthesis of Palladium Compounds. 1cPd and 1mPd have been
previously reported.9
2mPd. A mixture of imine 2 (110 mg, 0.44 mmol) and palladium
acetate (99 mg, 0.44 mmol) in a 1/1 molar ratio was stirred at room
temperature in 15 mL of toluene for 2 h. The brown precipitate was
filtered in vacuo to obtain 2mPd (154 mg, 85%).
A second fraction of 2mPd can be obtained from the toluene
solution. The solvent was removed in a rotary evaporator, and the
residue was recrystallized in cold dichloromethane−diethyl ether,
yielding a solid which was filtered in vacuo.
Brown solid. Rf (DCM/MeOH 95/5) = 0.65. 1H NMR (400 MHz,
CDCl3): δ 9.29 (dd, J = 5.1, 0.8 Hz, 1H), 8.61 (d, J = 1.1 Hz, 1H), 8.00
(td, J = 7.7, 1.7 Hz, 1H), 7.96 (dd, J = 7.5, 1.6 Hz, 1H), 7.73 (dt, J = 7.7,
1.1 Hz, 1H), 7.67 (ddd, J = 7.7, 5.1, 1.3 Hz, 1H), 7.03−6.90 (m, 2H),
6.87 (dd, J = 6.9, 2.1 Hz, 1H), 3.96 (dt, J = 6.7, 3.5 Hz, 1H), 3.32 (dd, J =
14.3, 2.9 Hz, 1H), 2.86 (dd, J = 14.3, 3.9 Hz, 1H), 1.56 (s, 3H), 1.02 (d,
J = 6.6 Hz, 3H). 13C NMR (101 MHz, CDCl3): δ 163.2, 152.1, 150.7,
140.3, 139.1, 138.9, 128.7, 128.0, 125.7, 125.0, 124.7, 61.0, 46.6, 29.8,
20.5. IR (FTIR-ATR, ν, cm−1): 3056, 3027, 2951, 2920, 2847, 1732,
1587, 1438. HRMS (ESI+, m/z): [M − OAc]+ calcd for C15H15N2Pd,
329.0270; found, 329.0266.
Brown solid. Rf (DCM/MeOH 90/10) = 0.28. 1H NMR (500 MHz,
CDCl3, 298 K): δ 8.37 (s, 1H), 7.84 (t, J = 7.7 Hz, 1H), 7.52 (dt, J = 7.4,
0.9 Hz, 1H), 7.44 (dd, J = 8.0, 1.3 Hz, 1H), 7.38−7.35 (m, 1H), 6.97−
6.94 (m, 2H), 6.82 (dd, J = 5.9, 3.0 Hz, 1H), 3.07 (br, 2H), 2.82 (s, 3H),
2.07 (s, 3H), 1.27 (br, 6H); 1H NMR (500 MHz, CDCl3, 240 K): δ 8.42
(s, 1H), 7.91 (t, J = 7.7 Hz, 1H), 7.61 (d, J = 7.4 Hz, 1H), 7.49 (dd, J =
8.1, 1.2 Hz, 1H), 7.36 (dd, J = 7.2, 1.8 Hz, 1H), 7.04−6.97 (m, 2H),
6.87 (dd, J = 6.6, 2.3 Hz, 1H), 3.52 (d, J = 13.7 Hz, 1H), 2.81 (s, 3H),
2.70−2.63 (m, 1H), 2.14 (s, 3H), 1.68 (s, 3H), 0.90 (s, 3H). 13C NMR
(101 MHz, CDCl3): δ 165.0, 164.0, 152.7, 139.7, 138.4, 136.6, 130.0,
128.0, 124.7, 124.6, 124.5, 60.7, 54.4, 27.8, 26.2. IR (FTIR-ATR, ν,
cm−1): 3043, 2970, 2926, 1592, 1556, 1416, 1385. Anal. Found (calcd)
for C19H22N2O2Pd): C, 53.9 (54.75); H, 5.3 (5.32); N, 6.9 (6.72).
LRMS (ESI+, m/z): [M − OAc]+ calcd for C17H19N2Pd, 357.06;
found, 357.06.
6cPd. A mixture of imine 6 (100 mg, 0.45 mmol) and palladium
acetate (100 mg, 0.45 mmol) in a 1/1 molar ratio was stirred at room
temperature in 10 mL of toluene for 1.5 h. The yellow precipitate was
filtered in vacuo to obtain 6cPd (185 mg, 93%).
Yellow solid. Rf (DCM/MeOH 97:3) = 0.28. 1H NMR (400 MHz,
CDCl3): δ 7.83 (t, J = 7.8 Hz, 1H), 7.66 (s, 1H), 7.51 (dd, J = 7.5, 1.4
Hz, 1H), 7.30 (dd, J = 8.0, 1.4 Hz, 1H), 7.29−7.23 (m, 4H), 7.21 (dt, J =
8.5, 4.1 Hz, 1H), 3.64 (t, J = 6.9 Hz, 2H), 3.13 (t, J = 7.0 Hz, 2H), 2.70
(s, 3H), 2.08 (s, 3H), 2.01 (s, 3H). 13C NMR (101 MHz, CDCl3): δ
178.8, 178.5, 169.0, 165.7, 155.2, 139.6, 137.3, 130.3, 129.3, 128.8,
127.0, 125.8, 77.4, 61.0, 36.0, 23.6, 23.2. IR (FTIR-ATR, ν, cm−1):
3072, 3002, 2974, 2923, 1591, 1366, 1311. Anal. Found (calcd) for
C19H22N2O4Pd: C, 50.2 (50.85); H, 5.1 (4.94); N, 6.1 (6.24). LRMS
(ESI+, m/z): [M − OAc]+ calcd for C15H15N2Pd, 329.03; found,
329.03.34
3cPd. A mixture of imine 3 (142 mg, 0.68 mmol) and palladium
acetate (152 mg, 0.68 mmol) in an 1/1 molar ratio was stirred at room
temperature in 15 mL of toluene for 1 h. The beige precipitate was
filtered in vacuo to obtain 3cPd (20 mg, 68%).
1
Beige solid. Rf (hexane/EtOAc 1/1) = 0.35. H NMR (400 MHz,
CDCl3): δ 8.22 (ddd, J = 5.5, 1.5, 0.7 Hz, 1H), 8.02 (td, J = 7.8, 1.5 Hz,
1H), 7.87−7.84 (m, 2H), 7.49 (ddd, J = 7.8, 5.5, 1.4 Hz, 1H), 7.28−
7.15 (m, 5H), 3.72 (td, J = 7.1, 1.2 Hz, 2H), 3.15 (t, J = 7.1 Hz, 2H),
2.11 (s, 3H), 2.08 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 178.7,
178.6, 167.5, 154.8, 150.8, 140.4, 137.2, 129.4, 128.9, 127.8, 127.5,
127.1, 61.7, 35.9, 23.5, 23.3. IR (FTIR-ATR, ν, cm−1): 3059, 3002,
2983, 1622, 1593, 1302. HRMS (ESI+, m/z): [M − AcO]+ calcd for
C14H13N2Pd, 315.0114; found, 315.0119.34
4cPd. A mixture of imine 4 (103 mg, 0.43 mmol) and palladium
acetate (96 mg, 0.43 mmol) in a 1/1 molar ratio was stirred at room
temperature in 10 mL of toluene for 1 h. The brown precipitate was
filtered in vacuo to obtain 4cPd (198 mg, 99%).
7mPd. A mixture of imine 7 (87 mg, 0.30 mmol) and palladium
acetate (67 mg, 0.30 mmol) in dry toluene (10 mL) was heated with
stirring in a bath at 90 °C for 1 h and then filtered. The solvent was
removed in a rotary evaporator, and the residue was washed with diethyl
ether, yielding a brown solid which was filtered in vacuo to obtain 7mPd
as a brown solid (109 mg, 80%).
Brown solid. Rf (DCM/MeOH 95:5) = 0.25. 1H NMR (500 MHz,
CDCl3, 298 K): δ 9.13 (d, J = 9.2 Hz, 1H), 8.62 (s, 1H), 8.48 (d, J = 8.2
Hz, 1H), 7.91−7.86 (m, 2H), 7.77 (d, J = 8.2 Hz, 1H), 7.71 (td, J = 7.3,
6.8, 1.1 Hz, 1H), 7.47−7.44 (m, 1H), 7.02−6.96 (m, 2H), 6.87−6.84
(m, 1H), 3.12 (s, 2H), 2.17 (s, 3H), 1.35 (s, 6H); 1H NMR (500 MHz,
CDCl3, 240 K): δ 9.04 (d, J = 8.8 Hz, 1H), 8.69 (s, 1H), 8.55 (d, J = 8.2
211
https://dx.doi.org/10.1021/acs.organomet.0c00703
Organometallics 2021, 40, 203−217

Organometallics
pubs.acs.org/Organometallics
Article
Hz, 1H), 7.95 (d, J = 8.2 Hz, 1H), 7.91 (ddd, J = 8.4, 6.8, 1.4 Hz, 1H),
7.86 (d, J = 8.2 Hz, 1H), 7.76 (t, J = 7.5 Hz, 1H), 7.44 (dd, J = 7.0, 2.0
Hz, 1H), 7.07−7.00 (m, 2H), 6.91 (dd, J = 6.4, 2.2 Hz, 1H), 3.59 (d, J =
14.3 Hz, 1H), 2.74 (d, J = 14.3 Hz, 1H), 2.24 (s, 3H), 1.76 (s, 3H), 1.00
(s, 3H). 13C NMR (101 MHz, CDCl3): δ 164.2, 152.5, 148.3, 140.6,
140.0, 136.9, 133.8, 132.3, 130.2, 129.5, 128.8, 127.8, 124.7, 124.6,
122.2, 61.8, 53.9, 27.8. IR (FTIR-ATR, ν, cm−1): 3043, 2964, 2926,
1588, 1556, 1366. Anal. Found (calcd) for C22H22N2O2Pd: C, 57.6
(58.35); H, 4.9 (4.90); N, 6.3 (6.19). LRMS (ESI+, m/z): [M − OAc]+
calcd for C20H19N2Pd, 393.06; found, 393.06.
9cPd. A mixture of imine 9 (215 mg, 0.96 mmol) and palladium
acetate (215 mg, 0.96 mmol) in an 1/1 molar ratio was stirred at room
temperature in 20 mL of toluene for 1 h. The yellow precipitate was
filtered in vacuo to obtain 9cPd (381 mg, 88%).
3029, 2917, 2844, 1701, 1361. LRMS (ESI+, m/z): [M − OAc]+ calcd
for C13H11N2Pd, 301.0; found, 301.00.34
12cPd. A mixture of imine 12 (110 mg, 0.52 mmol) and palladium
acetate (116 mg, 0.52 mmol) in an 1/1 molar ratio was stirred at room
temperature in 10 mL of toluene for 1 h. The brown precipitate was
filtered in vacuo to obtain 12cPd (147 mg, 65%).
Brown solid. Rf (DCM/MeOH 97/3) = 0.13. 1H NMR (400 MHz,
CDCl3): δ 8.28 (dd, J = 4.8, 2.9 Hz, 1H), 8.07 (td, J = 7.8, 1.6 Hz, 1H),
7.71 (d, J = 7.7 Hz, 1H), 7.67 (s, 1H), 7.54 (dd, J = 7.6, 5.8 Hz, 1H),
7.47−7.36 (m, 5H), 5.22 (q, J = 7.0 Hz, 1H), 2.09 (s, 3H), 2.06 (s, 3H),
1.80 (d, J = 7.0 Hz, 3H). 13C NMR (101 MHz, CDCl3): δ 178.7, 178.5,
165.0, 155.1, 151.1, 140.4, 137.2, 129.5, 129.3, 128.5, 127.95, 127.1,
65.5, 23.5, 23.4, 20.3. IR (FTIR-ATR, ν, cm−1): 3032, 2992, 2917,
1494, 1403. Anal. Found (calcd) for C18H20N2O4Pd: C, 49.4 (49.72);
H, 4.6 (4.64); N, 6.6 (6.44). LRMS (ESI+, m/z): [M − OAc]+ calcd for
C14H13N2Pd, 315.01; found, 315.01.34
Yellow solid. Rf (DCM/MeOH 97/3) = 0.25. 1H NMR (400 MHz,
CDCl3): δ 8.34 (dd, J = 5.6, 1.5 Hz, 1H), 8.04 (td, J = 7.8, 1.5 Hz, 1H),
7.68 (s, 1H), 7.65 (ddd, J = 7.8, 1.4, 0.7 Hz, 1H), 7.56 (ddd, J = 7.8, 5.5,
1.4 Hz, 1H), 7.46−7.41 (m, 2H), 7.39−7.33 (m, 3H), 2.06 (s, 3H), 1.91
(s, 6H), 1.81 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 178.2, 163.7,
155.2, 151.1, 142.1, 140.0, 129.3, 128.4, 127.8, 127.0, 126.4, 70.7, 28.2,
23.3. IR (FTIR-ATR, ν, cm−1): 3053, 3027, 2915, 2848, 1723, 1598,
1376. Anal. Found (calcd) C19H22N2O4Pd: C, 49.8 (50.85); H, 5.0
(4.94); N, 6.3 (6.24). LRMS (ESI+, m/z): [M − OAc+MeCN]+ calcd
for C19H22N3O2Pd, 430.07; found, 430.09.
9mPd. Coordination compound 9cPd (200 mg, 0.45 mmol) was
allowed to react in dry toluene (6 mL) at 90 °C for 1 h and then filtered.
The solvent was removed in a rotary evaporator and the residue was
recrystallized in cold dichloromethane-diethyl ether, yielding a brown
solid which was filtered in vacuo to obtain 9mPd (169 mg, 99%).
Brown solid. Rf (DCM/MeOH 97/3) = 0.38. 1H NMR (400 MHz,
CDCl3): δ 8.85 (d, J = 5.1 Hz, 1H), 8.48 (s, 1H), 7.96 (td, J = 7.8, 1.6
Hz, 1H), 7.68 (d, J = 7.7 Hz, 1H), 7.64 (dd, J = 7.8, 5.1 Hz, 1H), 7.26−
7.24 (m, 1H), 7.08 (td, J = 7.2, 1.2 Hz, 1H), 7.02 (td, J = 7.2, 1.1 Hz,
1H), 6.69 (dd, J = 7.6, 1.5 Hz, 1H), 2.24 (s, 3H), 1.73 (s, 6H). 13C NMR
(101 MHz, CDCl3): δ 178.2, 160.7, 158.2, 155.0, 151.9, 144.1, 139.1,
132.6, 128.7, 126.0, 125.9, 125.6, 121.6, 76.7, 30.9, 24.4. IR (FTIR-
ATR, ν, cm−1): 3069, 3034, 2977, 2932, 1591, 1375. Anal. Found
(calcd) for C17H18N2O2Pd: C, 52.4 (52.52); H, 5.1 (4.67); N, 7.2
(7.21). LRMS (ESI+, m/z): [M − OAc + MeCN]+ calcd for
C17H18N3Pd, 370.05; found, 370.05.
13cPd. A mixture of imine 13 (105 mg, 0.5 mmol) and palladium
acetate (100 mg, 0.45 mmol) in a 1/1 molar ratio was stirred at room
temperature in 10 mL of toluene for 1 h. The yellow precipitate was
filtered in vacuo to obtain 13cPd (147 mg, 68%).
Yellow solid. Rf (DCM/MeOH 97/3) = 0.30. 1H NMR (400 MHz,
CDCl3): δ 7.82 (t, J = 7.8 Hz, 1H), 7.69 (t, J = 1.9 Hz, 1H), 7.52 (d, J =
7.7 Hz, 1H), 7.47−7.41 (m, 3H), 7.36−7.30 (m, 3H), 4.83 (d, J = 1.9
Hz, 2H), 2.70 (s, 3H), 2.09 (s, 3H), 2.01 (s, 3H). 13C NMR (101 MHz,
CDCl3): δ 178.7, 167.0, 166.1, 155.4, 139.4, 132.5, 130.5, 130.5, 129.7,
129.4, 125.1, 61.4, 23.7, 23.3, 23.1. IR (FTIR-ATR, ν, cm−1): 3062,
3034, 2996, 2967, 2920, 1637, 1613, 1595, 1293. HRMS (ESI+, m/z):
[M − OAc]+ calcd for C14H13N2Pd, 315.0114; found, 315.0124.34
14mPd. A mixture of imine 14 (100 mg, 0.37 mmol) and palladium
acetate (83 mg, 0.37 mmol) in dry toluene (10 mL) was heated with
stirring in a bath at 90 °C for 1 h and then filtered. The red precipitate
was filtered in vacuo to obtain 14mPd (114 mg, 71%).
1
Red solid. Rf (DCM/MeOH 95/5) = 0.26. H NMR (400 MHz,
CDCl3): δ 8.76 (s, 1H), 8.72 (dt, J = 8.7, 0.9 Hz, 1H), 8.31 (d, J = 8.3
Hz, 1H), 7.90−7.80 (m, 2H), 7.73 (d, J = 8.4 Hz, 1H), 7.74−7.65 (m,
1H), 7.17 (dd, J = 7.6, 1.3 Hz, 1H), 7.09 (td, J = 7.4, 1.4 Hz, 1H), 7.04
(td, J = 7.4, 1.6 Hz, 1H), 6.66 (dd, J = 7.5, 1.6 Hz, 1H), 2.34 (s, 3H),
1.69 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 178.0, 161.6, 157.9,
154.7, 148.1, 143.1, 139.7, 132.8, 132.7, 130.6, 129.6, 129.3, 127.6,
126.3, 125.7, 121.9, 121.7, 76.6, 30.9, 25.1. IR (FTIR-ATR, ν, cm−1):
3065, 3034, 2967, 2955, 2920, 1610, 1591, 1371, 1323. Anal. Found
(calcd) for C21H20N2O2Pd: C, 56.4 (57.48); H, 4.6 (4.59); N, 6.3
(6.38). LRMS (ESI+, m/z): [M − OAc]+ calcd for C19H17N2Pd,
379.04; found, 379.04.
10mPd. A mixture of imine 10 (116 mg, 0.49 mmol)) and palladium
acetate (110 mg, 0.49 mmol) in a 1/1 molar ratio was stirred at room
temperature in 15 mL of toluene for 2 h. The yellow precipitate was
filtered in vacuo to obtain 10mPd (154 mg, 85%).
A second fraction of 10mPd can be obtained from the toluene
solution. The solvent was removed in a rotary evaporator, and the
residue was recrystallized in cold dichloromethane−diethyl ether,
yielding a solid which was filtered in vacuo. The overall yield of the
process was 87% (170 mg).
Synthesis of Platinum Compounds. cis-[PtCl2(DMSO)2] was
prepared as reported elsewhere.35
1mPt. A mixture of imine 1 (100 mg, 0.42 mmol) and cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol) was allowed to react in
refluxing methanol (20 mL) for 4 h. The orange precipitate was filtered
in vacuo to obtain 1mPt (81 mg, 41%).
Yellow solid. Rf (DCM/MeOH 95/5) = 0.26. 1H NMR (400 MHz,
CDCl3): δ 8.49 (s, 1H), 7.78 (t, J = 7.7 Hz, 1H), 7.52−7.43 (m, 2H),
7.11 (dd, J = 7.6, 1.4 Hz, 1H), 7.06 (td, J = 7.5, 1.5 Hz, 1H), 6.99 (td, J =
7.4, 1.6 Hz, 1H), 6.66 (dd, J = 7.5, 1.6 Hz, 1H), 2.74 (s, 3H), 2.19 (s,
3H), 1.68 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 177.8, 163.2, 161.2,
157.9, 154.7, 142.6, 138.8, 132.6, 129.6, 126.1, 125.5, 124.0, 121.5, 76.4,
30.9, 24.8, 23.5. IR (FTIR-ATR, ν, cm−1): 3031, 2964, 2923, 1612,
1593, 1315. Anal. Found (calcd) for C18H20N2O2Pd: C, 51.9 (53.68);
H, 5.0 (5.01); N, 6.7 (6.95). LRMS (ESI+, m/z): [M − OAc]+ calcd for
C16H17N2Pd, 343.04; found, 343.04.
Orange solid. Rf (DCM/MeOH 97/3) = 0.65. 1H NMR (600 MHz,
CDCl3, 298 K): δ 9.71 (d, J = 5.4 Hz, 1H), 9.20 (s, JPt−H = 107.4 Hz,
1H), 8.10 (t, J = 7.7 Hz, 1H), 7.94 (d, J = 7.6 Hz, 1H), 7.86 (d, J = 7.7
Hz, 1H), 7.81 (t, J = 6.6 Hz, 1H), 7.05 (t, J = 7.4 Hz, 1H), 7.00 (t, J = 7.2
Hz, 1H), 6.92 (d, J = 7.2 Hz, 1H); 1H NMR (600 MHz, CDCl3, 233 K):
δ 9.67 (d, J = 5.4 Hz, 1H), 9.25 (s, JPt−H = 99.7 Hz, 1H), 8.18 (t, J = 7.7
Hz, 1H), 7.95 (t, J = 8.4 Hz, 2H), 7.86 (t, J = 6.4 Hz, 1H), 7.12 (t, J = 7.4
Hz, 1H), 7.06 (t, J = 7.2 Hz, 1H), 6.99 (d, J = 7.3 Hz, 1H), 3.45 (d, J =
14.5 Hz, 1H), 2.74 (d, J = 14.5 Hz, 1H), 1.86 (s, 3H), 1.11 (s, 3H). 13C
NMR (101 MHz, DMSO-d6): δ 165.5, 155.5, 147.9, 140.0, 139.8,
137.7, 131.3, 128.5, 127.7, 127.1, 123.5, 123.2, 62.4, 53.7, 27.0. IR
(FTIR-ATR, ν, cm−1): 3053, 3037, 2964, 2926, 2891, 1425. Anal.
Found (calcd) for C16H17ClN2Pt: C, 40.2 (41.08); H, 3.7 (3.66); N, 5.8
(5.99). LRMS (ESI+, m/z): [M + H]+ calcd for C16H18ClN2Pt, 468.08;
found, 468.08.
11cPd. A mixture of imine 11 (100 mg, 0.51 mmol) and palladium
acetate (114 mg, 0.51 mmol) in a 1/1 molar ratio was stirred at room
temperature in 15 mL of toluene for 1 h. The yellow precipitate was
filtered in vacuo to obtain 11cPd (160 mg, 75%).
Yellow solid. Rf (DCM/MeOH 97/3) = 0.63. 1H NMR (400 MHz,
CDCl3): δ 8.29 (d, J = 5.5 Hz, 1H), 8.03 (t, J = 7.7 Hz, 1H), 7.75−7.66
(m, 2H), 7.54 (t, J = 6.7 Hz, 1H), 7.48−7.40 (m, 3H), 7.40−7.30 (m,
2H), 4.93 (d, J = 2.0 Hz, 2H), 2.12 (s, 3H), 2.09 (s, 3H). 13C NMR (101
MHz, CDCl3): δ 178.7, 178.5, 166.6, 155.1, 151.0, 140.3, 132.8, 130.3,
129.7, 129.4, 127.9, 127.3, 62.0, 23.5, 23.3. IR (FTIR-ATR, ν, cm−1):
1cPt. A mixture of imine 1 (100 mg, 0.42 mmol) and cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol) was stirred at room
temperature in 10 mL of methanol for 4 h. The solvent was removed
in a rotary evaporator, and the residue was washed with diethyl ether,
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Article
yielding a brown solid which was filtered in vacuo to obtain 1cPt (175
mg, 83%).
Hz, 1H), 8.05 (ddd, J = 7.7, 5.4, 1.4 Hz, 1H), 7.85 (dd, J = 7.7, 1.5 Hz,
1H), 7.18 (dd, J = 7.8, 1.5 Hz, 1H), 6.93 (ddd, J = 7.8, 7.1, 1.5 Hz, 1H),
6.80 (ddd, J = 7.7, 7.0, 1.5 Hz, 1H), 3.79 (br, 2H), 1.49 (s, 6H). 13C
NMR (101 MHz, DMSO-d6): δ 167.3, 153.8, 148.8, 148.6, 140.2,
139.4, 130.4, 128.7, 127.0, 123.4, 123.1, 121.4, 67.5, 43.6. IR (FTIR-
ATR, ν, cm−1): 3103, 3072, 3034, 2951, 2920, 2860, 1441, 1296. EA
(calcd for C16H17ClN2Pt): C, 41.3 (41.08); H, 3.6 (3.66); N, 6.0
(5.99). HRMS (ESI+, m/z): [M + H]+ calcd for C16H18ClN2Pt,
468.0800; found, 468.0795.
5cPt. A mixture of imine 5 (80 mg, 0.36 mmol), cis-
[PtCl2(DMSO)2] (152 mg, 0.36 mmol), and sodium acetate (30 mg,
0.36 mmol) was allowed to react in refluxing methanol (15 mL) for 24
h. The precipitate was filtered in vacuo to obtain 5cPt (101 mg, 62%).
Yellow solid. Rf (DCM/MeOH 97/3) = 0.55. 1H NMR (400 MHz,
DMSO-d6): δ 9.41 (ddd, J = 5.8, 1.4, 0.6 Hz, 1H), 9.12 (d, J = 1.0 Hz,
Brown solid. Rf (DCM/MeOH 97/3) = 0.57. 1H NMR (400 MHz,
CDCl3): δ 9.84 (dd, J = 5.9, 1.3 Hz, 1H), 8.35 (s, JPt−H = 92.8 Hz, 1H),
8.14 (td, J = 7.8, 1.4 Hz, 1H), 7.94−7.86 (m, 1H), 7.65 (ddd, J = 7.6,
5.9, 1.5 Hz, 1H), 7.46−7.38 (m, 2H), 7.24−7.15 (m, 3H), 3.71 (s, 2H),
1.71 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 166.3, 157.7, 150.1,
139.6, 137.0, 131.0, 128.3, 128.2, 128.1, 126.8, 72.1, 46.0, 28.5. IR
(FTIR-ATR, ν, cm−1): 3059, 3027, 2967, 2920, 2866, 1444. Anal.
Found (calcd) for C16H18Cl2N2Pt: C, 36.4 (38.11); H, 3.4 (3.60); N,
5.3 (5.55). LRMS (ESI+, m/z): [M+NH4]+ calcd for C16H22Cl2N3Pt,
521.08; found 521.08.
2mPt. A mixture of imine 2 (144 mg, 0.57 mmol) and cis-
[PtCl2(DMSO)2] (240 mg, 0.42 mmol) was allowed to react in
refluxing methanol (20 mL) for 24 h. The solvent was removed with a
rotary evaporator, and the residue was eluted in a flash chromatography
column (DCM/MeOH 98/2), yielding a solid which was filtered in
vacuo to obtain 2mPt (155 mg, 56%).
J
Pt−H = 93.9 Hz, 1H), 8.38 (td, J = 7.7, 1.5 Hz, 1H), 8.11 (ddd, J = 7.7,
1.6, 0.7 Hz, 1H), 7.91 (ddd, J = 7.6, 5.8, 1.6 Hz, 1H), 7.36−7.25 (m,
4H), 7.28−7.18 (m, 1H), 5.09−4.99 (m, 1H), 3.44 (dd, J = 13.2, 5.0
Hz, 1H), 2.88 (dd, J = 13.3, 8.5 Hz, 1H), 1.35 (d, J = 6.7 Hz, 3H). 13C
NMR (101 MHz, DMSO-d6): δ 168.8, 157.6, 148.8, 140.8, 137.4,
129.4, 129.0, 128.5, 128.4, 126.6, 41.5, 18.6. IR (FTIR-ATR, ν, cm−1):
3043, 2970, 2920, 2863, 1448, 1365. HRMS (ESI+, m/z): [M + NH4]+
calcd for C15H20Cl2N3Pt, 507.0676; found, 507.0684.
Orange solid. Rf (DCM/MeOH 98/2) = 0.82. 1H NMR (500 MHz,
acetone-d6, 298 K): δ 9.75 (s, JPt−H = 100.4 Hz, 1H), 8.16 (t, J = 7.7 Hz,
1H), 8.04 (dd, J = 7.5, 1.1 Hz, 1H), 7.78 (dd, J = 7.9, 1.4 Hz, 1H), 7.71−
7.69 (m, 1H), 6.85−6.78 (m, 3H), 3.18 (s, 3H); 1H NMR (500 MHz,
acetone-d6, 240 K): δ 9.79 (s, JPt−H = 100.3 Hz, 1H), 8.21 (t, J = 7.7 Hz,
1H), 8.07 (dd, J = 7.6, 1.3 Hz, 1H), 7.83 (dd, J = 7.9, 1.5 Hz, 1H), 7.69−
7.63 (m, 1H), 6.86−6.77 (m, 3H), 3.31−3.26 (m, 1H), 3.12 (s, 3H),
2.68 (d, J = 14.0 Hz, 1H), 1.80 (s, 3H), 0.88 (s, 3H). 13C NMR (101
MHz, DMSO-d6): δ 167.0, 164.0, 155.3, 139.4, 139.0, 137.6, 130.9,
126.6, 126.4, 125.7, 123.4, 123.0, 61.7, 53.4, 27.2, 25.8. IR (FTIR-ATR,
ν, cm−1): 3059, 3037, 2967, 2923, 1454. Anal. Found (calcd) for
C17H19ClN2Pt: C, 42.7 (42.37); H, 3.9 (3.97); N, 5.5 (5.81). LRMS
(ESI+, m/z): [M − Cl+MeCN]+ calcd for C19H22N3Pt, 487.15; found,
487.14.
5mPt. A mixture of imine 5 (100 mg, 0.42 mmol), cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol) and sodium acetate (34 mg,
0.42 mmol) was allowed to react in refluxing ethanol (15 mL) for 72 h.
The precipitate was filtered in vacuo to obtain a solid. The elution of this
solid in a flash chromatography column (DCM) permitted us to obtain
pure 5mPt (13 mg, 25%).
1
Red solid. Rf (DCM/MeOH 97/3) = 0.68. H NMR (400 MHz,
CDCl3): δ 9.62 (d, J = 5.3 Hz, 1H), 9.25 (s, JPt−H = 107.6 Hz, 1H), 8.04
(td, J = 7.7, 1.6 Hz, 1H), 7.98 (dd, J = 7.6, 1.5 Hz, 1H), 7.83−7.74 (m,
2H), 7.05 (td, J = 7.4, 1.7 Hz, 1H), 6.99 (td, J = 7.2, 1.5 Hz, 1H), 6.90
(dd, J = 7.3, 1.7 Hz, 1H), 4.06−3.98 (m, 1H), 3.28 (d, J = 14.5 Hz, 1H),
2.75 (dd, J = 14.5, 3.8 Hz, 1H), 1.10 (d, J = 6.6 Hz, 3H). 13C NMR (101
MHz, CDCl3): δ 162.8, 154.4, 149.8, 139.1, 138.4, 128.1, 125.7, 125.0,
124.4, 62.6, 46.9, 21.2. IR (FTIR-ATR, ν, cm−1): 3034, 2961, 2917,
2856, 1454. HRMS (ESI+, m/z): [M + NH4]+ calcd for C15H19ClN3Pt,
471.0909; found, 471.0900.
6mPt. A mixture of imine 6 (73 mg, 0.33 mmol), cis-
[PtCl2(DMSO)2] (140 mg, 0.33 mmol), and sodium acetate (27 mg,
0.33 mmol) was allowed to react in refluxing ethanol (10 mL) for 72 h.
The precipitate was eluted in a flash chromatography column (DCM/
MeOH 97/3) to obtain 6mPt (27 mg, 18%).
3cPt. A mixture of imine 3 (100 mg, 0.48 mmol), cis-
[PtCl2(DMSO)2] (202 mg, 0.48 mmol), and sodium acetate (40 mg,
0.48 mmol) was allowed to react in refluxing methanol (15 mL) for 24
h. The yellow precipitate was filtered in vacuo to obtain 3cPt (142 mg,
62%).
Yellow solid. Rf (hexane/EtOAc 1/1) = 0.31. 1H NMR (400 MHz,
DMSO-d6): δ 9.35 (ddd, J = 5.7, 1.4, 0.6 Hz, 1H), 8.94 (s, JPt−H = 92.5
Hz, 1H), 8.32 (td, J = 7.7, 1.4 Hz, 1H), 8.02 (ddd, J = 7.8, 1.6, 0.7 Hz,
1H), 7.87 (ddd, J = 7.8, 5.8, 1.6 Hz, 1H), 7.32−7.22 (m, 4H), 7.23−
7.14 (m, 1H), 4.18 (td, J = 7.7, 1.0 Hz, 2H), 3.12 (dd, J = 8.2, 7.0 Hz,
2H). 13C NMR (101 MHz, DMSO-d6): δ 171.0, 156.7, 149.07, 140.8,
137.7, 129.1, 128.9, 128.6, 128.3, 126.6, 60.5, 36.5. IR (FTIR-ATR, ν,
cm−1): 3065, 3024, 1690, 1494, 1475. Anal. Found (calcd) for
C14H14Cl2N2Pt: C, 35.7 (35.31); H, 3.0 (2.96); N, 5.7 (5.88). LRMS
(ESI+, m/z): [M − Cl]+ calcd for C14H14ClN2Pt, 440.05; found,
440.05.
Orange solid. Rf (DCM/MeOH 95/5) = 0.78. 1H NMR (400 MHz,
DMSO-d6): δ 9.71 (t, J = 1.5 Hz, JPt−H = 101.7 Hz, 1H), 8.17 (t, J = 7.7
Hz, 1H), 7.99 (dd, J = 7.8, 1.3 Hz, 1H), 7.81 (dd, J = 7.9, 1.4 Hz, 1H),
7.56 (dd, J = 7.0, 2.0 Hz, 1H), 6.91−6.77 (m, 3H), 3.77−3.73 (m, 2H),
3.09 (s, 3H), 2.88 (dd, J = 6.5, 3.8 Hz, 2H). 13C NMR (101 MHz,
DMSO-d6): δ 168.1, 164.4, 154.0, 141.1, 139.6, 138.5, 131.1, 125.4,
125.1, 125.0, 123.4, 123.1, 57.9, 25.7. IR (FTIR-ATR, ν, cm−1): 3056,
3037, 2999, 2913, 1593, 1463. HRMS (ESI+, m/z): [M+NH4]+ calcd
for C15H19ClN3Pt, 471.0909; found, 471.0904.
4cPt and 4mPt. A mixture of imine 4 (100 mg, 0.42 mmol), cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol), and sodium acetate (34 mg,
0.42 mmol) was allowed to react in refluxing methanol (15 mL) for 24
h. The precipitate was filtered in vacuo to obtain a mixture of 4cPt (99
mg, 47%) and 4mPt (74 mg, 37%). The elution of this mixture in a flash
chromatography column (DCM/MeOH 98/2) permitted us to obtain
small quantities of pure 4cPt and 4mPt.
4mPt. A mixture of imine 4 (100 mg, 0.42 mmol), cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol), and sodium acetate (34 mg,
0.42 mmol) was allowed to react in refluxing ethanol (15 mL) for 72 h.
The precipitate was filtered in vacuo to obtain pure 4mPt (185 mg,
97%).
7mPt. A mixture of imine 7 (170 mg, 0.56 mmol) and cis-
[PtCl2(DMSO)2] (236 mg, 0.56 mmol) was allowed to react in
refluxing methanol (25 mL) for 24 h. The precipitate was filtered in
vacuo to obtain 7mPt (131 mg, 46%).
Brown solid. Rf (DCM/MeOH 98/2) = 0.87. 1H NMR (500 MHz,
acetone-d6, 298 K): δ 10.37 (dd, J = 9.0, 0.9 Hz, 1H), 10.09 (s, JPt−H
=
103.8 Hz, 1H), 8.91 (dd, J = 8.3, 0.7 Hz, 1H), 8.23 (d, J = 8.3 Hz, 1H),
8.15 (dd, J = 8.2, 1.5 Hz, 1H), 7.97 (ddd, J = 8.8, 6.8, 1.6 Hz, 1H), 7.86
(ddd, J = 8.0, 6.8, 1.1 Hz, 1H), 7.76−7.73 (m, 1H), 6.90−6.84 (m, 3H);
1H NMR (500 MHz, acetone-d6, 240 K): δ 10.30 (dd, J = 8.9, 0.9 Hz,
1H), 10.12 (s, JPt−H = 104.5 Hz, 1H), 8.97 (d, J = 8.2 Hz, 1H), 8.27 (d, J
= 8.3 Hz, 1H), 8.20 (dd, J = 8.3, 1.5 Hz, 1H), 8.00 (ddd, J = 8.7, 6.8, 1.5
Hz, 1H), 7.89 (ddd, J = 8.1, 6.9, 1.1 Hz, 1H), 7.74−7.68 (m, 1H), 6.90−
6.84 (m, 3H), 3.37 (d, J = 15.0 Hz, 1H), 2.77 (d, J = 14.0 Hz, 1H), 1.88
(s, 3H), 0.97 (s, 3H). 13C NMR (101 MHz, DMSO-d6): δ 167.7,
156.77, 148.1, 140.9, 139.2, 137.5, 131.6, 130.8, 129.0, 128.9, 128.5,
126.8, 126.5, 123.5, 123.3, 123.0, 62.5, 53.5, 27.3. IR (FTIR-ATR, ν,
4cPt. Orange solid. Rf (DCM) = 0.10. 1H NMR (400 MHz, CDCl3):
δ 9.43 (dt, J = 5.8, 0.8 Hz, 1H), 8.01 (tdd, J = 7.7, 1.4, 0.5 Hz, 1H), 7.55
(ddd, J = 7.7, 5.8, 1.5 Hz, 1H), 7.34−7.25 (m, 6H), 7.20 (s, 1H), 4.32 (s,
2H), 1.61 (s, 6H). 13C NMR (101 MHz, CDCl3): δ 169.2, 156.9, 149.9,
145.5, 139.4, 128.9, 128.1, 127.2, 126.9, 126.7, 68.2, 42.3, 26.5. IR
(FTIR-ATR, ν, cm−1): 3046, 2964, 2913, 1470. HRMS (ESI+, m/z):
[M + NH4]+ calcd for C16H22Cl2N3Pt, 521.0833; found, 521.0837.
4mPt. Red solid. Rf (DCM) = 0.25. 1H NMR (400 MHz, DMSO-
d6): δ 9.69 (t, J = 1.5 Hz, JPt−H = 111.3 Hz, 1H), 9.34 (ddd, J = 5.3, 1.6,
0.8 Hz, 1H), 8.35 (td, J = 7.7, 1.6 Hz, 1H), 8.20 (ddd, J = 7.7, 1.4, 0.7
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cm−1): 3069, 3034, 2970, 2923, 1590, 1432. Anal. Found (calcd) for
C20H19ClN2Pt: C, 43.7 (46.38); H, 3.4 (3.70); N, 5.2 (5.41). LRMS
(ESI+, m/z): [M − Cl]+ calcd for C20H19N2Pt, 482.12; found, 482.12.
9cPt. A mixture of imine 9 (108 mg, 0.44 mmol) and cis-
[PtCl2(DMSO)2] (186 mg, 0.44 mmol) in an 1/1 molar ratio was
stirred at room temperature in 10 mL of methanol for 4 h. The yellow
precipitate was filtered in vacuo to obtain 9cPt (168 mg, 77%).
Yellow solid. Rf (DCM/MeOH 98/2) = 0.34. 1H NMR (400 MHz,
DMSO-d6): δ 9.50 (dd, J = 5.9, 1.4 Hz, 1H), 9.26 (s, JPt−H = 88.1 Hz,
1H), 8.43 (td, J = 7.7, 1.4 Hz, 1H), 8.28 (dd, J = 7.8, 1.5 Hz, 1H), 7.89
(ddd, J = 7.6, 5.8, 1.7 Hz, 1H), 7.34−7.24 (m, 4H), 7.21 (ddd, J = 7.5,
5.4, 3.5 Hz, 1H), 1.94 (s, 6H). 13C NMR (101 MHz, DMSO-d6): δ
169.4, 158.1, 148.5, 145.2, 140.3, 129.4, 128.8, 127.7, 126.2, 125.4, 72.0,
30.4. IR (FTIR-ATR, ν, cm−1): 3034, 2983, 2920, 1242. Anal. Found
(calcd) for C15H16Cl2N2Pt: C, 36.8 (36.75); H, 3.3 (3.29); N, 5.8
(5.71). LRMS (ESI+, m/z): [M+NH4]+ calcd for C15H20Cl2N3Pt,
507.07, found 507.07.
157.4, 150.4, 139.5, 138.2, 129.5, 129.3, 128.7, 128.6, 127.3, 65.1, 21.4.
IR (FTIR-ATR, ν, cm−1): 3043, 2977, 2932, 1600, 1441, 1302. HRMS
(ESI+, m/z): [M+NH4]+ calcd for C14H18Cl2N3Pt, 493.0520; found,
493.0522.
13cPt. A mixture of imine 13 (80 mg, 0.38 mmol), cis-
[PtCl2(DMSO)2] (160 mg, 0.38 mmol), and sodium acetate (32 mg,
0.38 mmol) was allowed to react in refluxing ethanol (10 mL) for 72 h.
The precipitate was eluted in a flash chromatography column (DCM/
MeOH 97/3), to obtain 13cPt (12 mg, 6%).
Brown solid. Rf (DCM/MeOH 97/3) = 0.68. 1H NMR (400 MHz,
CDCl3): δ 8.61 (t, J = 1.2 Hz, 1H), 7.85 (t, J = 7.7 Hz, 1H), 7.57 (d, J =
7.4 Hz, 1H), 7.48−7.40 (m, 2H), 7.38−7.34 (m, 4H), 5.36 (d, J = 1.1
Hz, 2H), 3.07 (s, 3H). 13C NMR (101 MHz, CDCl3): δ 138.7, 134.7,
131.4, 130.0, 129.4, 129.0, 125.6, 62.2, 28.1. IR (FTIR-ATR, ν, cm−1):
3046, 2951, 2920, 2850, 1463, 1261. HRMS (ESI+, m/z): [M + NH4]+
calcd for C14H18Cl2N3Pt, 493.0520; found, 493.0516.
14mPt. A mixture of imine 14 (104 mg, 0.38 mmol) and cis-
[PtCl2(DMSO)2] (160 mg, 0.38 mmol) was allowed to react in
refluxing methanol (15 mL) for 24 h. The brown precipitate was filtered
in vacuo to obtain 14mPt (118 mg, 62%).
9mPt. A mixture of imine 9 (100 mg, 0.45 mmol), cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol), and sodium acetate (38 mg,
0.45 mmol) was allowed to react in refluxing methanol (15 mL) for 72
h. The orange precipitate was filtered in vacuo to obtain 9cPt (170 mg,
84%).
Brown solid. Rf (DCM/MeOH 98/2) = 0.85. 1H NMR (400 MHz,
DMSO-d6): δ 10.32 (s, JPt−H = 107.6 Hz, 1H), 10.03 (dd, J = 8.8, 1.0 Hz,
1H), 8.96 (d, J = 8.3 Hz, 1H), 8.17 (dd, J = 8.3, 1.4 Hz, 1H), 8.13 (d, J =
8.3 Hz, 1H), 7.99 (ddd, J = 8.7, 6.8, 1.6 Hz, 1H), 7.87 (ddd, J = 8.1, 6.8,
1.1 Hz, 1H), 7.60 (dd, J = 7.7, 1.4 Hz, 1H), 7.05 (td, J = 7.3, 1.4 Hz,
1H), 6.97 (td, J = 7.4, 1.6 Hz, 1H), 6.87 (dd, J = 7.6, 1.6 Hz, 1H), 1.80
(s, 6H). 13C NMR (101 MHz, DMSO-d6): δ 164.1, 159.7, 159.2, 148.6,
141.4, 132.5, 132.5, 131.3, 129.1, 128.8, 128.7, 128.2, 124.8, 124.6,
122.9, 121.8, 76.2, 30.4. IR (FTIR-ATR, ν, cm−1): 3050, 3015, 2993,
2961, 2923, 1425. EA (calcd for C19H17ClN2Pt): C, 44.7 (45.29); H,
3.2 (3.40); N, 5.3 (5.56). LRMS (ESI+, m/z): [M − Cl]+ calcd for
C19H17N2Pt, 468.10; found, 468.10.
Orange solid. Rf (DCM/MeOH 98/2) = 0.65. 1H NMR (400 MHz,
DMSO-d6): δ 9.96 (s, JPt−H = 110.0 Hz, 1H), 8.92 (d, J = 5.2 Hz, 1H),
8.33 (t, J = 7.7 Hz, 1H), 8.15−8.05 (m, 2H), 7.41 (d, J = 6.7 Hz, JPt−H
=
42.7 Hz, 1H), 7.01 (t, J = 7.5 Hz, 1H), 6.91 (t, J = 7.3 Hz, 1H), 6.85 (d, J
= 7.6 Hz, 1H), 1.75 (s, 6H). 13C NMR (101 MHz, DMSO-d6): δ 162.5,
160.2, 158.8, 148.2, 140.5, 134.0, 133.6, 129.5, 127.4, 124.6, 124.4,
121.7, 76.5, 30.3. IR (FTIR-ATR, ν, cm−1): 3018, 2974, 2961, 2920,
1432, 1362. Anal. Found (calcd) for C15H15ClN2Pt: C, 39.1 (39.70); H,
3.2 (3.33); N, 6.2 (5.89). LRMS (ESI+, m/z): [M − Cl]+ calcd for
C15H15N2Pt, 418.09; found, 418.08.
10mPt. A mixture of imine 10 (76 mg, 0.32 mmol) and cis-
[PtCl2(DMSO)2] (177 mg, 0.42 mmol) was allowed to react in
refluxing methanol (15 mL) for 24 h. The red precipitate was filtered in
vacuo to obtain 10mPt (55 mg, 37%).
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00703.
1
Red solid. Rf (DCM/MeOH 98/2) = 0.69. H NMR (400 MHz,
DMSO-d6): δ 10.04 (s, JPt−H = 105.6 Hz, 1H), 8.17 (t, J = 7.7 Hz, 1H),
7.97−7.87 (m, 2H), 7.57 (dd, J = 7.7, 1.4 Hz, 1H), 6.99 (td, J = 7.4, 1.5
Hz, 1H), 6.91 (td, J = 7.5, 1.4 Hz, 1H), 6.82 (dd, J = 7.6, 1.2 Hz, 1H),
3.01 (s, 3H), 1.72 (s, 6H). 13C NMR (101 MHz, DMSO-d6): δ 163.9,
163.4, 159.3, 158.1, 140.0, 132.6, 131.1, 128.1, 125.2, 124.4, 124.4,
121.6, 75.6, 30.4, 25.5. IR (FTIR-ATR, ν, cm−1): 3037, 2977, 2923,
1454, 1429. Anal. Found (calcd) for C16H17ClN2Pt: C, 40.9 (41.08); H,
3.5 (3.66); N 6.0 (5.99). LRMS (ESI+, m/z): [M − Cl]+ calcdfor
C16H17N2Pt, 432.10; found, 432.10.
1H NMR and 13C spectra, crystal data and structure
refinement for 7mPt and 10mPt, and values of kobs for all
of the systems studied as a function of temperature and
pressure (PDF)
Accession Codes
CCDC 2038592−2038593 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: +44 1223 336033.
11cPt. A mixture of imine 11 (80 mg, 0.41 mmol), cis-
[PtCl2(DMSO)2] (173 mg, 0.41 mmol), and sodium acetate (34 mg,
0.41 mmol) was allowed to react in refluxing methanol (15 mL) for 24
h. The greenish precipitate was filtered in vacuo to obtain 11cPt (118
mg, 63%).
1
Greenish solid. Rf (DCM/MeOH 97/3) = 0.60. H NMR (400
MHz, DMSO-d6): δ 8.91 (dd, J = 5.8, 0.8 Hz, 1H), 8.86 (s, 1H), 7.92
(td, J = 7.8, 1.5 Hz, 1H), 7.71 (ddd, J = 7.8, 1.6, 0.7 Hz, 1H), 7.46 (ddd, J
= 7.6, 5.8, 1.6 Hz, 1H), 7.12−7.05 (m, 2H), 6.99−6.85 (m, 3H), 4.87 (s,
2H). 13C NMR (101 MHz, DMSO-d6): δ 172.1, 156.9, 149.0, 140.7,
136.2, 129.2, 128.9, 128.8, 128.6, 128.0, 60.7. IR (FTIR-ATR, ν, cm−1):
3157, 3024, 1555, 1406. Anal. Found (calcd) for C13H12Cl2N2Pt: C,
32.5 (33.78); H, 2.3 (2.62); N, 6.1 (6.06). LRMS (ESI+, m/z): [M
+NH4]+ calcd for C13H16Cl2N3Pt, 479.04; found, 479.04.
AUTHOR INFORMATION
■
Corresponding Authors
Xavier Ariza − Departament de Química Inorgànica i Orgànica,
Secció de Química Orgànica i Institut de Biomedicina (IBUB),
Facultat de Química, Universitat de Barcelona, 08028
Barcelona, Spain; CIBER Fisiopatología de la Obesidad y la
Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid,
Spain; orcid.org/0000-0002-1479-3668; Email: xariza@
ub.edu
Jaume Granell − Departament de Química Inorgànica i
Orgànica, Secció de Química Inorgànica, Facultat de Quimica,
Universitat de Barcelona, 08028 Barcelona, Spain;
orcid.org/0000-0001-6360-7043; Email: jaumegranell@
ub.edu
12cPt. A mixture of imine 12 (147 mg, 0.70 mmol), cis-
[PtCl2(DMSO)2] (295 mg, 0.70 mmol), and sodium acetate (57 mg,
0.70 mmol) was allowed to react in refluxing methanol (15 mL) for 24
h. The greenish precipitate was filtered in vacuo to obtain 12cPt (64 mg,
20%).
Brown solid. Rf (DCM/MeOH 98/2) = 0.50. 1H NMR (400 MHz,
CDCl3): δ 9.73 (t, J = 4.9 Hz, 1H), 8.42 (d, J = 3.7 Hz, JPt−H = 95.1 Hz,
1H), 8.09 (td, J = 7.8, 1.4 Hz, 1H), 7.71 (dd, J = 8.0, 3.9 Hz, 1H), 7.66
(ddd, J = 7.6, 5.6, 1.4 Hz, 1H), 7.50−7.37 (m, 5H), 6.41 (q, J = 6.2 Hz,
1H), 1.92 (d, J = 6.9 Hz, 3H). 13C NMR (101 MHz, CDCl3): δ 166.4,
214
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Organometallics 2021, 40, 203−217

Organometallics
Authors
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Article
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Mild metal-catalyzed C-H activation: examples and concepts. Chem.
́
Hector Torralvo − Departament de Química Inorgànica i
Orgànica, Secció de Química Orgànica i Institut de
Biomedicina (IBUB), Facultat de Química, Universitat de
Barcelona, 08028 Barcelona, Spain; orcid.org/0000-0001-
7887-9324
Joan Albert − Departament de Química Inorgànica i Orgànica,
Secció de Química Inorgànica, Facultat de Quimica,
Universitat de Barcelona, 08028 Barcelona, Spain;
orcid.org/0000-0002-8256-2650
̀
Merce Font-Bardia − Unitat de Difracció de Raigs-X., Centre
̀
Científic i Tecnològic de la Universitat de Barcelona,
Universitat de Barcelona, 08028 Barcelona, Spain;
Departament de Cristal·lografia, Mineralogia i Dipòsits
Minerals, Facultat de Geologia, 08028 Barcelona, Spain;
orcid.org/0000-0002-7892-8744
Jordi Garcia − Departament de Química Inorgànica i Orgànica,
Secció de Química Orgànica i Institut de Biomedicina (IBUB),
Facultat de Química, Universitat de Barcelona, 08028
Barcelona, Spain; CIBER Fisiopatología de la Obesidad y la
Nutrición (CIBERobn), Instituto de Salud Carlos III, Madrid,
Spain; orcid.org/0000-0001-9379-2577
Manuel Martinez − Departament de Química Inorgànica i
Orgànica, Secció de Química Inorgànica, Facultat de Quimica
and Institute of Nanoscience and Nanotechnology (IN2UB),
Universitat de Barcelona, 08028 Barcelona, Spain;
orcid.org/0000-0002-6289-4586
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.0c00703
̈
Soc. Rev. 2016, 45, 2900−2936. (j) Sambiagio, C.; Schonbauer, D.;
Blieck, R.; Dao-Huy, T.; Pototschnig, G.; Schaaf, P.; Wiesinger, T.; Zia,
̈
M. F.; Wencel-Delord, J.; Besset, T. A.; Maes, B. U. W.; Schnurch, M. A
Notes
The authors declare no competing financial interest.
comprehensive overview of directing groups applied in metal-catalysed
C-H functionalisation chemistry. Chem. Soc. Rev. 2018, 47, 6603−6743.
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ACKNOWLEDGMENTS
■
We thank the Ministerio de Economía y Competitividad: grant
numbers CTQ2015-65040-P, 2017SGR474, SAF2017-83813-
C3-1-R, PCI2018-092997, and PID2019-107006GB-C21.
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