Platinum-mediated C-H bond activation of arene solvents and subsequent C-C bond formation

Article abstract of DOI:10.1021/om100743z

The reactions of cis-[PtCl₂(SOMe₂)₂] and imines 2,6-Cl₂C₆H₃CH=NCH₂(4-XC ₆H₄) (1a, X = H; 1b, X = Cl), 2,6-Cl₂C ₆H₃CH=NCH₂(2,6-F₂C₆H ₃) (1f), and 2,6-Cl₂C₆H₃CH=N(4- ClC₆H₄) (1g) carried out in toluene at 90 °C in the presence of sodium acetate dissolved in methanol produced compounds [PtCl{(MeC₆H₃)(2-ClC₆H₃)CHNR)} SOMe₂] (R = CH₂C₆H₅ (4a), CH ₂(4-ClC₆H₄) (4b), CH₂(2,6-F ₂C₆H₃) (4f), and 4-ClC₆H₄ (4g)), containing seven-membered platinacycles via formal insertion of a toluene molecule in the metallacycle. These compounds are formed in a process involving several steps, the most relevant being intermolecular C-H activation of a solvent toluene molecule and formation of a carbon-carbon bond. The reaction of cis-[PtCl₂(SOMe₂)₂] and imine 2,6-Cl₂C₆H₃CH=NCH₂(4-ClC ₆H₄) (1b) under analogous conditions was also carried out using other arene solvents such as benzene and ortho-, meta-, and para-xylene and produced in all cases seven-membered platinacycles. DFT calculations indicate that the stability of the metallacycles increases in the order p-xylyl < m-xylyl < o-xylyl < tolyl < phenyl and have helped to suggest a possible reaction path.

Full text of DOI:10.1021/om100743z

Organometallics 2010, 29, 4619–4627 4619
DOI: 10.1021/om100743z
Platinum-Mediated C-H Bond Activation of Arene Solvents and
Subsequent C-C Bond Formation
Joan Albert, Ramon Bosque, Margarita Crespo,* Jaume Granell, Judit Rodrıguez, and
Javier Zafrilla
´
ꢀ
Departament de Quımica Inorganica, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain
Received July 28, 2010
The reactions of cis-[PtCl2(SOMe2)2] and imines 2,6-Cl2C6H3CHdNCH2(4-XC6H4) (1a, X = H; 1b,
X = Cl), 2,6-Cl2C6H3CHdNCH2(2,6-F2C6H3) (1f ), and 2,6-Cl2C6H3CHdN(4-ClC6H4) (1g) carried out
in toluene at 90 °C in the presence of sodium acetate dissolved in methanol produced compounds
[PtCl{(MeC6H3)(2-ClC6H3)CHNR)}SOMe2] (R = CH2C6H5 (4a), CH2(4-ClC6H4) (4b), CH2(2,6-
F2C6H3) (4f ), and 4-ClC6H4 (4g)), containing seven-membered platinacycles via “formal insertion” of a
toluene molecule in the metallacycle. These compounds are formed in a process involving several steps, the
most relevant being intermolecular C-H activation of a solvent toluene molecule and formation of a
carbon-carbon bond. The reaction of cis-[PtCl2(SOMe2)2] and imine 2,6-Cl2C6H3CHdNCH2(4-ClC6H4)
(1b) under analogous conditions was also carried out using other arene solvents such as benzene and ortho-,
meta-, and para-xylene and produced in all cases seven-membered platinacycles. DFT calculations indicate
that the stability of the metallacycles increases in the order p-xylyl<m-xylyl<o-xylyl<tolyl<phenyl
and have helped to suggest a possible reaction path.
Introduction
should be the direct functionalization of the ubiquitous C-H
bonds3 since, in spite of the large bond dissociation energy of
the C-H bond, the fundamental features of the C-H bond
cleavage reactions have been elucidated.4 Several groups have
developed group 10 transition metal catalyzed C-H activation/
C-C bond formation processes that use an arene C-H bond as
one of the coupling partners,5 and the great potential of catalysis
involving palladium in oxidation states higher than those of
conventional palladium(0)/palladium(II) cycles has been under-
lined.6 Intermolecular C-H activation leading to C-C coupling
has also been described in the formation of bridging biphenyl
platinum complexes.7
C-C bond formation is an important process in organic
synthesis; in particular, biaryl linkages are key features of diverse
natural products and many important organic molecules.1
The most common method for biaryl C-C bond construction
is metal-catalyzed cross-coupling between two functionalized
starting materials.2 An ideal method to construct C-C bonds
*To whom correspondence should be addressed. Phone: þ34934039132.
Fax: þ34934907725. E-mail: margarita.crespo@qi.ub.es.
(1) (a) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58,
ꢁ
9633. (b) Hassan, J.; Sevignon, M.; Gozzi, C.; Shulz, E.; Lemaire, M. Chem.
In a preliminary communication8 we have reported the first
example of a formal toluene “insertion” into a metal-carbon
bond, by means of an unprecedented process involving intra-
molecular activation of a Caryl-Cl bond of an imine, an inter-
molecular activation of a Caryl-H bond of toluene, and the
formation of a new carbon-carbon bond, between a toluene
molecule and the benzal ring of the imine. The aim of this work
is to explore the scope of this unexpected process taking place
when toluene was used as a solvent and to analyze whether it can
be extended to other arenes such as benzene or xylenes as well as
to other imines. In this case, this new process could be con-
sidered as a general procedure for C-C coupling arising from
intermolecular C-H activation of arene solvents.
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124, 1586. (d) Kakiuchi, F.; Chatani, N. Adv. Synth. Catal. 2003, 345, 1077.
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A. R. Angew. Chem., Int. Ed. 2009, 48, 9792. (k) Chen, X.; Engle, K. M.;
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~
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(8) A preliminary communication on the intermolecular activation of
toluene with imines 1a and 1b and cis [PtCl2(SOMe2)2] has been
ꢁ
published: Capape, A.; Crespo, M.; Granell, J.; Vizcarro, A.; Zafrilla,
J.; Font-Bardia, M.; Solans, X. Chem. Commun. 2006, 4128.
r
2010 American Chemical Society
Published on Web 09/24/2010
pubs.acs.org/Organometallics

4620 Organometallics, Vol. 29, No. 20, 2010
Albert et al.
Scheme 1a
Me3C6H2CHNCH2(4-ClC6H4) (1e) (Scheme 1), the “formal
insertion” of toluene was not detected and only the expected
complexes were obtained: the endo-metallacycles [PtCl{(4-
ClC6H3)CHNCH2(4-XC6H4)}{SOMe2}] (3c, X = H; 3d,
X = Cl), in the case of imines 1c and 1d, and the corre-
sponding exo-derivative [PtCl{MeC6H2CHNCH2(4-ClC6H3)}-
{SOMe2}], 2e, in the case of imine 1e.9 These results show that
the presence of C-Cl bonds in the ortho position of the imine
plays a crucial role in this process. Furthermore, compounds 4a
and 4b could also be obtained using [Pt(OAc)2(SOMe2)2] as
platinum substrate, which suggests that the chloro bound to
platinum in the final product arises from ortho C-Cl bond
activation.
In order to rule out the possibility that exo-metallacycles
could be precursors of compounds 4, an equimolar mixture of
2b and NaOAc (in a small amount of methanol) was heated at
90 °C during 48 h in toluene, after which time the exo-metalla-
cycle was recovered unchanged. In addition, when the reaction
of compound [Pt(OAc)2(SOMe2)2] and imine 1b was carried
out in d8-toluene (90 °C, 48 h), to produce d6-4b, no changes
were observed in the 1H NMR spectrum for the signals corre-
sponding to the imine protons, which indicates that H-D
exchange does not occur in the N-donor ligand.
The low yields obtained for compounds 4a and 4b (15%
and 30%, respectively) can be related to the formation of the
exo-derivative as a byproduct. For this reason and in order to
expand the process to new ligands, imines 1f and 1g were
investigated in this work. These ligands were selected because
the presence of two fluorine atoms in the ortho positions for 1f or
the unlikely formation of a four-membered cycle for 1g prevents
formation of an exo-metallacycle. Seven-membered metalla-
cycles 4f and 4g, analogous to 4a and 4b, were obtained with
these imines; however the yield of the process did not increase
significantly. The low yields are probably due to decomposition
and hydrolyses processes, as evidenced by formation of metallic
platinum and aldehyde. The reaction with imine 1h, containing
two nitrogen atoms, was also carried out under the same
conditions; however in this case the only product was coordina-
tion compound Ih, which suggests that the presence of a labile
ligand is required for further reaction to take place. NMR
spectra of compounds 4f, 4g, and Ih are consistent with the
proposed formulas. For 4f and 4g two isomers were detected in
the crude reaction mixture, but only one isomer could be isolated
and characterized in each case.
Further work was focused on imine 1b, and since accord-
ing to the stoichiometry of the reaction (see below) two
equivalents of HCl should be formed, the reaction was tested
under the same conditions as above but using two equiva-
lents of sodium acetate. Under these conditions, a higher
yield of compound 4b (45%) was obtained. Further increase
in the amount of sodium acetate did not produce an increase
in the obtained yield. On the other hand, an increase in the
reaction time produced the formation of higher amounts of
metallic platinum and lower yields for 4b.
“Formal Insertion” of Other Arenes. In order to expand the
scope of this novel process, the activation of other aromatic
solvents such as benzene and ortho-, meta-, and para-xylene
was explored in this work. Intermolecular aromatic C-H
bond activation at platinum(II) compounds containing
N-donor ligands is now well established,4,10,11 and the
factors that influence the selectivity and reactivity of activation
of benzene, toluene, or xylenes have been studied.12
a (i) þ cis-[PtCl2(dmso)2] þ NaOAc (1:1:1) in MeOH, 65 °C, 48 h.
Results and Discussion
“Formal Insertion” of Toluene. As previously reported,8 in
order to explore the synthetic ability of cis-[PtCl2(SOMe2)2] in
the preparation of exo-platinacycles, the reactions of cis-[PtCl2-
(SOMe2)2] with 2,6-Cl2C6H3CHdNCH2(4-XC6H4) (1a, X=H;
1b, X = Cl) were planned, with the aim that the chloro sub-
stituents in the ortho positions of the benzal ring would force the
formation of the less common exo-platinacycles (Scheme 1).
When the reactions of equimolar amounts of cis-[PtCl2-
(SOMe2)2], the corresponding imine, and sodium acetate
(dissolved in a small amount of methanol) were carried out
in dry toluene, heating the reaction mixture at 90 °C during 48 h,
the reactions produced the new compound 4a or 4b (Scheme 2),
in addition to the expected exo-cyclometalated platinum(II)
compounds [PtCl{(2,6-Cl2C6H3)CHNCH2(4-XC6H3)}{SO-
Me2}] (2a, X=H; 2b, X=Cl).9 Compounds 4a and 4b obtained
as white (4a) or light yellow (4b) crystals arise from a novel
process leading to seven-membered platinacycles via a “formal
insertion” of a solvent toluene molecule. Compound [PtCl{(Me-
C6H3)(2-ClC6H3)CHNCH2(4-ClC6H4)}{SOMe2}] (4b) was
crystallized in dichloromethane-methanol from the crude prod-
uct, while [PtCl{(MeC6H3)ClC6H3CHNCH2C6H5}{SOMe2}]
(4a) was crystallized after purifying the crude product by column
chromatography (silica, ethyl acetate-hexane=100:20). Com-
pounds 4a and 4b were characterized by elemental analyses,
mass spectra, and NMR spectroscopy. In the 1H NMR spectra
of both compounds in addition to the main set of signals,
resonances due to a minor isomer (abundance ca. 20% (4a0)
and 30% (4b0)) with the same spectral pattern were observed.8,9
A singlet resonance coupled to platinum at 6.63 (4a) or6.56ppm
(4b) corresponding to the major isomer is assigned to the aro-
matic proton adjacent to the Pt-C bond. On this basis, the
major isomer is assigned to that with a meta arrangement
between the Pt-C bond and the methyl substituent (as in the
crystal structure of 4a8 shown in Figure 1), and the minor isomer
corresponds to the para isomer. DFT calculations performed
on 4b and 4b0 show that the former is slightly more stable,
although the difference in energies between both isomers;only
0.40 kcal/mol;is too small to be significant.
When the same reaction was performed with the imines
4-ClC6H4CHNCH2(4-XC6H4) (1c, X = H; 1d, X = Cl) and
ꢁ
(9) Capape, A.; Crespo, M.; Granell, J.; Font-Bardia, M.; Solans, X.
Dalton Trans. 2007, 2030.
(10) Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471.

Article
Organometallics, Vol. 29, No. 20, 2010 4621
Scheme 2a
a (i): þ cis-[PtCl2(dmso)2] þ NaOAc-MeOH (1:1:1 or 1:1:2) (see text) in toluene, 90 °C, 48 h. (ii): þ cis-[PtCl2(dmso)2] þ NaOAc-MeOH (1:1:2) in
toluene, 90 °C, 72 h.
The reactions were carried out from imine 1b, cis-[PtCl2-
(SOMe2)2], and NaAcO under the same experimental con-
ditions described above, in the corresponding aromatic
solvent. The activation of the arenes used as solvents took
place in all cases, with formation of the corresponding seven-
membered metallacycles (Scheme 3). Again, formation of the
exo derivative 2b is observed in all cases, and isolation of the
desired compounds was possible by means of column chro-
matography separation.
observed. The NMR spectra show, in addition to the main
set of signals, resonances due to a minor isomer (ca. 36%). In
this case, the major isomer shows a singlet not coupled to
platinum at 6.63 ppm, and the minor isomer shows a singlet
at 6.40 ppm coupled to platinum (J(H-Pt) = 51.8 Hz). DFT
calculations performed on the 7b/7b0 couple show that the
former is 1.4 kcal/mol lower in energy. This difference in
energy is larger than in the toluene derivatives, due to the
steric hindrance in 7b0 between the methyl group from the
xylene and the iminic aromatic ring. In all other cases, only
one isomer was observed. This is the expected situation for
benzene due to the absence of substituents, leading to
compound 5b.
1H-1H COSY and NOESY NMR spectra of all these
compounds allow proposing the structures depicted in
Scheme 3 for the different isomers. In the case of meta-xylene
the formation of the two possible isomers (7b and 7b0) was

4622 Organometallics, Vol. 29, No. 20, 2010
Albert et al.
the activated sites, formation of compound 8b derived from
para-xylene was also possible.
The 195Pt NMR spectra show one signal at about -3800
ppm for compounds 5b, 6b, and 8b, while two resonances at
-3768.7 and -3782.4 ppm are observed for the product
arising from meta-xylene, in agreement with the presence of
two isomers. The resonance at lower field corresponds to the
major isomer; it has been reported that the presence of a
methyl group in an ortho position produces a downfield shift
of the 195Pt resonance.13 In agreement with this, the value
observed for 8b (-3758.7 ppm) appears at lower field than
those observed for 5b and 6b.
In order to compare the relative stability of the seven-
membered metallacycles, we have calculated, at the DFT level,
the energy increment corresponding to the following hypothet-
ical one-step processes, which correspond to the reaction in the
absence and presence of sodium acetate, respectively:
cis-½PtCl2ðSOMe2Þ2ꢀ þ L-Cl þ H-Ar-H
f ½PtClðAr-LÞðSOMe2Þꢀ þ 2HCl þ SOMe2
ð1Þ
cis-½PtCl2ðSOMe2Þ2ꢀ þ L-Cl þ H-Ar-H
þ 2AcO- f ½PtClðAr-LÞðSOMe2Þꢀ þ 2Cl-
þ SOMe2 þ 2HAcO
Figure 1. Molecular structure of compound 4a showing 50%
probability ellipsoids (ref 8).
However, for ortho-xylene three possible isomers could be
expected. The presence of a singlet coupled to platinum
assigned to H9 and showing a cross-peak with Me2 in the
NOESY NMR spectrum indicate that the obtained isomer
6b is that having the methyl groups para to platinum and to
the biaryl linkage, respectively. This isomer is the less
sterically hindered of the three possible isomers derived from
ortho-xylene. DFT calculations were carried out on the three
possible isomers, 6b, 6b0 (methyl groups ortho to the plati-
num and para to the biaryl linkage, respectively) and 6b00
(methyl groups para to the platinum and ortho to the biaryl
linkage, respectively). The optimized geometries are shown
in Figure 2. The most stable isomer is indeed 6b, while 6b0 is
2.4 kcal/mol higher in energy; this difference is larger than in
both 4b/4b0 and 7b/7b0 couples, in which both isomers are
observed. Moreover, 6b00 is 6.2 kcal/mol higher in energy
than 6b. On the other hand, in spite of the steric hindrance
due to the presence of methyl groups in adjacent positions to
ð2Þ
where L-Cl, H-Ar-H, and [PtCl(Ar-L)(SOMe2)] represent re-
spectively the imine ligand, the arene, and the seven-membered
cyclometalated compound 4 arising from formation of a bond
between the arene and the ligand fragments.
Results are shown in Table 1. In the cases where the “formal
insertion” of the aromatic hydrocarbon (toluene, ortho- and
meta-xylene) could lead to more than one isomer, only the
most stable one has been taken into account. The stability of
the metallacycles increases in the order p-xylyl < m-xylyl <
o-xylyl<tolyl<phenyl, thus suggesting that the steric hindrance
between the methyl groups and the aromatic ring that completes
the biaryl group is the most important factor that causes the
differences in the relative energies. On the other hand, we have
included the calculations for the formation of compound 4g;
the comparison with 4b can be useful to assess the importance of
the substituents of the nitrogen atom in the stability of the
metallacycles. In fact, the presence of the -CH2- moiety
between the nitrogen atom and the aromatic ring stabilizes the
metallacycle about 6 kcal/mol. As there are no appreciable
differences in steric hindrance between the nitrogen substituents
and the rest of the molecule in 4b and 4g (the optimized
geometries are shown in Figure 3), these differences are due
probably to changes in the relative basicity of the nitrogen atom.
Finally, the comparison of the energy increments corresponding
to processes 1 and 2 confirms that the addition of sodium acetate
is necessary for the reaction to take place.
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Article
Organometallics, Vol. 29, No. 20, 2010 4623
Scheme 3
between a freely rotating aryl group and a rigid aryl ring of a
metallacycle. The process here reported is more complex since it
requires both intramolecular Caryl-Cl activation of the coordi-
nated imine to produce a [C,N] metallacycle and intermolecular
Caryl-H bond activation of the aromatic solvent presumably to
form a Pt-Caryl σ-bond with elimination of HCl, as preliminary
steps to undergo the “formal insertion” of toluene in the
metallacycle with elimination of another HCl molecule.
A competition experiment was carried out for the synthesis of
8b in a mixture of para-xylene and d10-para-xylene (molar ratio
1:1). The analysis of the H/D content of the isolated product
by proton NMR spectra provides a KIE value, kH/kD=2.75.
Analogous values have been reported for activation of aromatic
C-H bonds both at platinum(IV) (kH/kD = 2.3 and 3.0 for
toluene and benzene, respectively)10,15 and at platinum(II)
species (kH/kD=2.8 for ortho-xylene).16
In order to gain some insight into the mechanistic aspects of
the formation of seven-membered cyclometalated complexes
with inserted arene systems, we have performed DFT calcula-
tions on several possible intermediate systems. With the aim of
facilitating the interpretation of the results and also of removing
the difficulty of dealing with different isomers, we have taken the
“formal insertion” of benzene as a model. We have performed
the calculations in gas phase and in benzene, and we have
calculated the energetics of the different reaction steps both in
the presence and in the absence of sodium acetate (see Table S1,
Supporting Information). The results of the calculations in
benzene and in the presence of sodium acetate are shown in
Scheme 5 and will be discussed next.
The first step consists in the dissociation of a SOMe2
ligand and the coordination of the imine to the platinum(II)
center, resulting in an energy increment of 3.69 kcal/mol. The
resulting coordination compound, B, could react in several
ways. In the absence of sodium acetate the most favored path
is the oxidative addition of a C-Cl bond to give the
endocyclic platinum(IV) compound D. In the presence of
base, the formation of the exocyclic platinum(II) derivative
(15) Shulpin, G. B.; Nizova, G. V.; Nikitaev, A. T. J. Organomet.
Chem. 1984, 276, 115.
(16) Zhang, F.; Kirby, C. W.; Hairsine, D. W.; Jennings, M. C.;
Puddephatt, R. J. J. Am. Chem. Soc. 2005, 127, 14196.

4624 Organometallics, Vol. 29, No. 20, 2010
Albert et al.
Table 1. Energy Increments (in kcal/mol) Corresponding to the
Formation of Seven-Membered Metallacycles in the Absence (A)
and in the Presence (B) of Sodium Acetate (reactions 1 and 2
described in the text, respectively)
compound
A
B
4b
4g
5b
6b
7b
8b
12.04
18.09
10.61
12.30
14.23
16.80
-38.68
-32.64
-40.11
-38.42
-36.49
-33.92
Figure 3. Optimized geometries for 4b (upper) and 4g (lower).
Figure 2. Optimized geometries for 6b (upper), 6b0 (middle),
and 6b00 (lower).
product G. An analogous process involving reductive elim-
ination from a platinum(IV) compound with formation of a
C-C bond followed by intramolecular C-H activation has
been postulated for analogous systems involving fluorinated
arenes.17 As a whole, our calculations suggest that the
preferred path to form the final compound G would feature
the intermediates B, E, F, and H.
However, although decoordination of the labile ligand
SOMe2 to yield I is an endergonic process, previous mecha-
nistic studies18 indicate that prior dissociation of a ligand to
form a five-coordinate intermediate is involved in C-C
C and the activation of a solvent C-H bond to render the
coordination compound E are more favored. The oxidative
addition of a C-Cl bond on compound E results in the
formation of the endocyclic cycloplatinated compound F;
this complex can also be formed from D via an activation of
an arene C-H bond followed by the loss of a chloride ligand.
Both reactions are exergonic in the presence of sodium
acetate.
The most energetically favored path for the formation of
the final compound G from platinum(IV) compound F
consists in (1) formation of a C-C bond, through reductive
elimination of Pt(IV) to Pt(II), yielding H, and (2) activation
of the C-H bond of the aromatic ring, leading to the final
ꢁ
(17) Calvet, T.; Crespo, M.; Font-Bardia, M.; Gomez, K.; Gonzalez,
G.; Martınez, M. Organometallics 2009, 28, 5096.
(18) (a) Crumpton, D. M.; Goldberg, K. I. J. Am. Chem. Soc. 2000,
122, 962. (b) Fekl, U.; Goldberg, K. I. J. Am. Chem. Soc. 2002, 124, 6804.
(c) Luedtke, A. T.; Goldberg, K. I. Inorg. Chem. 2007, 46, 8496.
ꢁ

Article
Organometallics, Vol. 29, No. 20, 2010 4625
Scheme 4. Formation of Seven-Membered Platinacycles from Platinum(IV) Precursors
Scheme 5. Possible Paths in the Formation of the Benzene Inserted Cyclometalated Complexa
a Energy values are expressed in kcal/mol.
reductive elimination from six-coordinate platinum(IV)
compounds. Such five-coordinate intermediates have also
being postulated in the proposed mechanisms for the forma-
tion of analogous seven-membered metallacycles14c either
through a fully concerted transition state (K) or via the inter-
mediate formation of a hydride complex (J).
In conclusion, the “formal insertion” of benzene, toluene, and
ortho-, meta-, and para-xylene, typical “innocent” solvents, into
platinum-carbon bonds is produced in the reaction of cis-[Pt-
Cl2(SOMe2)2] with different imines. Therefore, the process can
be considered a general procedure for intermolecular C-H acti-
vation leading to C-C coupling to produce metalated biaryls.

4626 Organometallics, Vol. 29, No. 20, 2010
Albert et al.
Our results suggest that both the steric hindrance arising from
the methyl substituents of the arene and the basicity of the
nitrogen atom determine the stability of the obtained seven-
membered metallacycles. On the other hand, the presence of
C-Cl bonds in the ortho positions of the imine plays a crucial
role in the process that takes place through a platinum(IV)
intermediate. This result can be related to the Shilov mechanism
for platinum(II)-mediated C-H bond activation, which re-
quires oxidation of platinum(II) to platinum(IV), and indeed
a recent review10 pointed out that cyclometalated compounds
could be promising candidates for developing intermolecular
C-H activation chemistry of platinum. Moreover, the key role
of acetate disclosed for these reactions through computational
studies is consistent with base-assisted inter- and intramolecular
C-H activation processes recently reviewed.19
produce a white solid. Yield: 0.952 g (88%). 1H NMR (300
MHz, CDCl3): δ 8.52 (t, 1H, 4J(H4-H3) = 1.2, H4), 7.17-7.39
(m, 4H, H2,5,6), 6.92 (t, 2H, 3J(H1-F) = 3J(H1-H2) = 7.5, H1),
4.97 (d, 2H, 4J(H6-H3) = 1.5, H3). 19F NMR (282 MHz,
CDCl3): δ -115.4 (t, 3J(F-H1) = 6.5). MS-CI{NH3} (m/z): 300.0
[M þ H]þ.
Imine 1g was prepared using an analogous procedure from
1.511 g (8.67 mmol) of 2,6-dichlorobenzaldehyde and 1.106 g (8.67
1
mmol) of 4-chloroaniline. Yield: 2.020 g (82%). H NMR (300
MHz, CDCl3): δ 8.65 (s, 1H, H3), 7.41 (d, 2H, 3J(H4-H5) = 7.3,
H4), 7.39 (d, 2H, 3J(H1-H2) = 8.8, H1), 7.28 (m, 1H, H5), 7.20 (d,
2H, 3J(H1-H2) = 8.9, H2). MS-CI{NH3} (m/z): 284.2 [M þ H]þ.
Preparation of Platinum Compounds. [PtCl2{(2,6-Cl2C6H3)-
CHNCH2CH2NMe2] (Ih). This was obtained from 0.208 g (0.50
mmol) of cis-[PtCl2(SOMe2)2], 0.120 g (0.50 mmol) of imine 1h,
and 82 mg (1 mmol) of sodium acetate (dissolved in 1 mL of
methanol), which were allowed to react in refluxing toluene
(30 mL) for 72 h. A white solid was filtered. Yield: 221 mg
(80%). 1H NMR (400 MHz, CDCl3): δ 9.59 (d, 1H, 3J(H-Pt) =
54.3, 4J(H-H) = 1.9, H1), 7.42 (m, 3H, H5, H6), 3.62 (td, 2H,
3J(H-H) = 5.9, 4J(H-H) = 1.7, H2), 3.12 (t, 6H, 3J(H-Pt) =
29.4, H4), 2.69 (t, 2H, 3J(H-H) = 6.1, H3). ESI-MS (m/z): 528.2
[M þ H2O]þ. Anal. Found (calcd for C11H14Cl4N2Pt): C: 25.4
(25.85); H: 2.8 (2.76); N: 5.0 (5.48).
Experimental Section
General Procedures. All reactants and arene solvents (ACS
grade) were used as received from commercial sources. Silica gel
(70-230 mesh) was used for chromatography columns.
IR spectra were recorded with a Nicolet 5700 spectrophoto-
meter, using KBr pellets.
[PtCl{(CD3C6D3)(2-ClC6H3)CHNCH2(4-ClC6H4)}{SOMe2}]
(d6-4b). This was obtained from 0.150 g (0.32 mmol) of [Pt-
(OAc)2(SOMe2)2] and 0.095 g (0.32 mmol) of imine 1b, which were
allowed to react in deuterated toluene (5 mL) at 90 °C for 48 h
under N2. The mixture was filtered, the solvent was removed under
vacuum, and the residue was eluted with silica column chromatog-
raphy using ethyl acetate-hexane (100:80) as eluent; d6-4b was
obtained from the last fraction. Yield: 42 mg (30%). 1H NMR (250
MHz, CDCl3): major isomer δ 8.59 (s, 3J(Pt-H) = 116.0, 1H, H4),
7.46-7.34 (m, 3H), {7.24 (d, 3J(H-H) = 8.0, 2H), 7.12 (d,
3J(H-H) = 8.0, 2H), H1, H2}, 5.48 (dd, 2J(H-H) = 13.0,
NMR spectra were performed at the Unitat de RMN d’Alt
Camp de la Universitat de Barcelona. 1H, 19F, and 195Pt NMR
spectra were recorded by using Bruker DRX-250 (195Pt, 54
MHz), Varian 300 (19F, 282.0 MHz), Mercury-400 (1H, 400
MHz; 1H-1H-NOESY; 195Pt, 86 MHz), and Bruker DMX-500
(1H, 500 MHz; 1H-1H-COSY) spectrometers and referenced to
SiMe4 (1H), CFCl3 (19F), and H2PtCl6 in D2O (195Pt). δ values
are given in ppm and J values in Hz. Abbreviations used: s =
singlet; d=doublet; t=triplet; m=multiplet; b=broad; NMR
labels as shown in Schemes 2 and 3.
Mass spectra were obtained by the Servei d’Espectrometria de
Masses de la Universitat de Barcelona. FAB mass spectra were
obtained with a VG-Quattro (with a 3-nitrobenzyl alcohol
matrix), MALDI mass spectra with a Voyager DE-RP (with a
dithranol matrix), electrospray ESI(þ) mass spectra with a LC/
MSD-TOF spectrometer using H2O-CH3CN (1:1) to introduce
the sample, and CI mass spectra (with NH3 as reactive gas) with
a ThermoFinnigan TRACE DSQ spectrometer.
4
2
0
J(H-H) = 1.6, 1H, H3), 4.90 (d, J(H-H) = 13.0, 1H, H3 ), 3.29
(s, 3J(Pt-H) = 21.6, 3H, SOMe), 2.82 (s, 3J(Pt-H) = 30.0, 3H,
SOMe); minor isomer δ 8.52 (s, 3J(Pt-H) = 104.0, 1H, H4), {7.24
(d, 3J(H-H) = 8.0, 2H), 7.13 (d, 3J(H-H) = 8.0, 2H), H1, H2},
5.40 (dd, 2J(H-H) = 13.6, 4J(H-H) = 1.7, 1H, H3), 5.03
2
0
(d, J(H-H) = 14.2, 1H, H3 ), 3.30 (s, 3H, SOMe), 2.85 (s,
3J(Pt-H)=30.0, 3H, SOMe). MALDI-MS, m/z: 632.0 [M - Cl]þ,
554.0 [M - Cl - SOMe2]þ, 359.0 [M - Cl - SOMe2 - Pt]þ.
[PtCl{(MeC6H3)(2-ClC6H3)CHNCH2(2,6-F2C6H3)}SOMe2]
(4f). This was obtained from 0.202 g (0.48 mmol) of cis-[PtCl2-
(SOMe2)2], 0.142 g (0.47 mmol) of imine 1f, and 76 mg (0.93
mmol) of sodium acetate (dissolved in 2 mL of methanol), which
were allowed to react in toluene at 90 °C (25 mL) for 48 h. The
mixture was filtered, the solvent was removed under vacuum,
and the residue was extracted with dichloromethane. Upon
removal of the solvent under vacuum, the oily residue was crys-
tallized in acetone at low temperature. Yield: 45 mg (14%). 1H
NMR (500 MHz, CDCl3): δ 8.69 (s, 1H, 3J(H-Pt) = 109.3, H4),
7.46 (t, 1H, 3J(H-H) = 7.8, H6), 7.41 (dd, 1H, 3J(H-H) = 8.0,
4J(H-H)=1, H5), 7.35 (dd, 1H, 3J(H-H)=7.5, 4J(H-H)=1.2,
H7), 7.30 (t, 1H, 3J(H-H)=7.4, H1), 6.82 (d, 1H, 3J(H-H)=7.7,
H8), 6.78 (t, 2H, 3J(H-H) = 8.1, H2), 6.71 (d, 1H, 3J(H-H) =
7.7, H9), 6.47 (s, 1H, 3J(H-Pt) = 51.8, H10), 5.76 (dd, 1H,
Microanalyses were performed by the Servei de Recursos
ꢀ
Cientıfics i Tecnics de la Universitat Rovira i Virgili de Tarragona
with a Carlo Erba 1106 or an Eager 1108 microanalyzer.
Preparation of the Compounds. cis-[PtCl2(SOMe2)2]20 and
imine 1h21 were prepared as reported elsewhere. [Pt(OAc)2(SO-
Me2)2] was prepared from 200 mg (0.47 mmol) of cis-[PtCl2-
(SOMe2)2] and 158 mg (0.95 mmol) of Ag(OAc), which were
allowed to react protected from the light in a mixture of dichloro-
methane (20 mL) and methanol (20 mL) with vigorous stirring
during 24 h. The AgCl was filtered off and the solvent was removed
in vacuo to yield a white solid. Yield: 180 mg (81.6%). 1H NMR
(200 MHz, CDCl3): δ 3.41 [s, 3J(Pt-H) = 15.0, 12H, SOMe2], 2.02
[s, 6H, AcO]. FAB-MS, m/z: 409.0 [M - AcO]þ, 350.0 [M -
2AcO]þ. The synthesis and characterization of compounds 2a-e,
3, 4a, and 4b have been previously reported.8,9
Preparation of Imines. Imine 1f was prepared from 1.001 g (5.7
mmol) of 2,6-dichlorobenzaldehyde and 818 mg (5.7 mmol) of
2,6-difluorobenzylamine, which were allowed to react in reflux-
ing dichloromethane (25 mL) in the presence of Na2SO4 for two
hours. The mixture was filtered, and the solvent was removed to
2
4
2
0
J(H3-H3 )=12.8, J(H3-H4)=1.5, H3), 4.86 (d, 1H, J(H3-
0
0
H3 )=12.8, H3 ), 3.35 (s 3H, SOMe), 2.90 (s, 3H, SOMe), 2.05 (s,
3H, Me). 19F NMR (282.0 MHz, CDCl3): δ -113.69 (t, J =
13.1) . ESI-MS (m/z): 627.1 [M - Cl]þ. Anal. Found (calcd for
C23H21Cl2F2NOPtS): C: 41.5 (41.64); H: 3.0 (3.19); N: 2.0
(2.11); S: 4.6 (4.83).
(19) Boutadla, Y.; Davies, D. L.; Macgregor, S. A.; Poblador-
Bahamonde, A. I. Dalton Trans. 2009, 5820–5831.
(20) (a) Price, J. H.; Williamson, A. N.; Schramm, R. F.; Wayland,
B. B. Inorg. Chem. 1972, 11 (6), 1280. (b) Kukushkin, V. Y.; Pombeiro,
A. J. L.; Ferreira, C. M. P.; Elding, L. I. Inorg. Synth. 2002, 33, 189.
(21) Anderson, C. M.; Crespo, M.; Jennings, M. C.; Lough, A. J.;
Ferguson, G.; Puddephatt, R. J. Organometallics 1991, 10, 2672.
[PtCl{(MeC6H3)(2-ClC6H3)CHN(4-ClC6H4)}SOMe2] (4g).
This was obtained under analogous conditions from 0.201 g
(0.48 mmol) of cis-[PtCl2(SOMe2)2], 0.134 g (0.47 mmol) of imine
1g, and 76 mg (0.93 mmol) of sodium acetate. Yield: 41 mg (14%).
1H NMR (300 MHz, CDCl3): δ 8.69 (s, 1H, 3J(H-Pt) = 106.7,
H4), 7.60-7.30 (m, 6H, HAr), 7.01 (d, 2H, 3J(H-H) = 7.7, H1),

Article
Organometallics, Vol. 29, No. 20, 2010 4627
3
6.92 (d, 2H, 3J(H-H) = 7.7, H2), 3.33 (s 3H, 3J(H-Pt) = 23.4,
SOMe), 2.89 (s, 3H, 3J(H-Pt) = 32.9, SOMe), 2.36 (s, 3H, Me).
195Pt NMR (86 MHz, CDCl3): δ -3802.4 (s). ESI-MS (m/z):
611.04 [M - Cl]þ. Anal. Found (calcd for C22H20Cl3NOPtS): C:
41.1 (40.78); H: 3.2 (3.11); N: 2.2 (2.16); S: 4.6 (4.95).
[PtCl{(C6H4)(2-ClC6H3)CHNCH2(40-ClC6H4)}SOMe2] (5b).
This was obtained from 0.150 g (0.36 mmol) of cis-[PtCl2(SO-
Me2)2], 0.106 g (0.36 mmol) of imine 1b, and 58 mg (0.71 mmol) of
sodium acetate (dissolved in 1 mL of methanol), which were
allowed to react in refluxing benzene (30 mL) for 48 h. The mixture
was filtered, the solvent was removed under vacuum, and the
residue was eluted in a chromatography silica column using CHCl3
as eluent. From the latest fraction collected 5b was obtained as a
brownish solid. Yield: 57 mg (25%).
3J(H-Pt)=104.7, H4), 7.45 (t, 1H, J(H-H)=7.8, H6), 7.33
3
4
(dd, 1H, J(H-H) = 7.5, J(H-H) = 1.2, H5), 7.40 (dd, 1H,
3J(H-H)=8.1, 4J(H-H)=1.3, H7), 7.21 (d, 2H, 3J(H-H)=8.5,
H1), 6.86 (d, 2H, 3J(H-H)=8.4, H2), 6.81 (d, 1H, 3J(H-H)=
7.7, H8), 6.74 (d, 1H, 3J(H-H)=7.6, H9), 5.22 (dd, 1H, 2J(H3-
4
2
0
0
H3 )=14.3, J(H3-H4)=2.0, H3), 5.03 (d, 1H, J(H3-H3 ) =
3
0
14.3, H3 ), 3.31 (s 3H, J(H-Pt) =25.6, SOMe), 2.88 (s, 3H,
3J(H-Pt)=25.8, SOMe), 2.08 (s, 3H, Me1), 2.01 (s, 3H, Me2).
195Pt NMR (54 MHz, CDCl3): δ -3758.7 (s). IR (cm-1): ν(Cd
N)=1639, ν(SdO)=1118. MALDI-MS (m/z): 639.8 [M - Cl]þ,
561.9 [M - Cl - SOMe2]þ, 365.9 [M - Cl - SOMe2 - Pt]þ.
Anal. Found (calcd for C24H24Cl3NOPtS): C: 42.6 (42.64); H:
3.9 (3.58); N: 1.9 (2.07); S: 4.3 (4.74).
Isotope Effects. The synthesis was carried out in a similar way
to that above but using equimolar amounts of para-xylene and d10-
para-xylene. The relative reactivities were determined by isolation
of the products followed by analysis using 1H NMR and MALDI
Compounds 6b, 7b/7b0, and 8b were obtained under anal-
ogous conditions from 141, 167, and 188 mg of cis-[Pt(Cl2-
(SOMe2)2], in ortho-, meta-, and para-xylene, respectively, and
using molar ratios [Pt]:[imine]:[NaAcO] = 1:1:2 and a reaction
temperature of 90 °C. For compounds 1d/1d0 and 1e, the middle
fractions contained a mixture of the expected products and
the exo-derivative; a second chromatography column using
CHCl3-MeOH (100:2) as eluent allowed the separation of these
products. Compounds 6b, 7b/7b0, and8b were obtained as off-white
solids with 25%, 22%, and 28% yields, respectively.
mass spectrometry. The integrals corresponding to H8, H9, Me1,
2
and Me were compared to those corresponding to H2, H3, and H3 ,
0
and the isotope ratio of 8b to d8-8b was determined to be 2.75. Peaks
corresponding to 8b (640.1 [M - Cl]þ; 562.0 [M - Cl - SOMe2]þ)
and d8-8b (647.9 [M - Cl]þ; 569.2 [M - Cl - SOMe2]þ) were ob-
served in the MALDI mass spectra.
Theoretical Calculations. All calculations were carried out
with the Gaussian 0322 package of programs at the B3LYP com-
putational level.23 The basis set was chosen as follows: For Pt, then
the LANL2DZ basis, where an effective core potential was used to
replace the 36 innermost electrons,24 was used. For carbon, hydro-
gen, chlorine, sulfur, and nitrogen the 6-31G(d,p) basis including
polarization functions25 was used. Geometries have been optimized
under vacuum, without including any symmetry constraints. Sol-
vent effects have been included using the CPCM (polarizable con-
ductor calculation) method on the previously optimized species.26
[PtCl{(C6H4)(2-ClC6H3)CHNCH2(40-ClC6H4)}SOMe2] (5b).
3
1H NMR (400 MHz, CDCl3): δ 8.56 (s, 1H, J(H-Pt) =111.0,
H4), 7.49 (t, 1H, 3J(H-H)=7.8, H6), 7.43 (dd, 1H, 3J(H-H)=8.0,
J(H-H)=1.4, H5), 7.37 (dd, 1H, 3J(H-H)=8.9, J(H-H)=1.3,
H7), 7.23 (d, 2H, 3J(H-H)=8.5, H1), 7.12 (d, 2H, 3J(H-H)=8.4,
2
0
H2), 7.00-6.85 (m, 4H, H8-H11), 5.43 (dd, 1H, J(H3-H3 ) =
4
2
0
0
13.5, J(H3-H4)=1.9, H3), 4.93 (d, 1H, J(H3-H3 )=13.6, H3 ),
3.31 (s 3H, 3J(H-Pt)=19.4, SOMe), 2.84 (s, 3H, 3J(H-Pt)=27.7,
SOMe). 195Pt NMR (54 MHz, CDCl3): δ -3796.2 (s). IR (cm-1):
ν(CdN) = 1635, ν(SdO) = 1127. MALDI-MS (m/z): 669.8 [M þ
Na]þ, 611.9 [M - Cl]þ, 595.9 [M þ Na - SOMe2]þ, 337.9 [M - Cl
- SOMe2 - Pt]þ. Anal. Found (calcd for C22H20Cl3NOPtS): C:
40.6 (40.78); H: 3.0 (3.11); N: 1.9 (2.16); S: 4.5 (4.95).
ꢁ
Acknowledgment. We thank the Ministerio de Educacion
y Ciencia (project CTQ2009-11501) for financial support and
for a fellowship (J.Z.).
[PtCl{(ortho-Me2C6H2)(2-ClC6H3)CHNCH2(40-ClC6H4)}-
SOMe2] (6b). 1H NMR (400 MHz, CDCl3): δ 8.56 (s, 1H,
Supporting Information Available: Table S1: Energy (in au)
corresponding to all the species shown in Scheme 5, in the
presence and absence of solvent. Table S2: Energy increments
(in kcal/mol) corresponding to the reactions shown in Scheme 5,
in the presence and absence of sodium acetate. Table S3:
Optimized atomic coordinates and energies (in the gas phase)
for all the species calculated. This material is available free of
charge via the Internet at http://pubs.acs.org.
3J(H-Pt) = 114.2, J(H3-H4) = 1.5, H4), 7.33-7.50 (m, 3H,
4
H5, H6, H7), 7.22 (d, 2H, 3J(H-H) = 8.5, H1), 7.13 (d, 2H,
3J(H-H)=8.4, H2), 6.74 (s, 1H, H8), 6.52 (s 1H, J(H-Pt)=
3
2
4
0
50.1, H9), 5.45 (dd, 1H, J(H3-H3 )=13.2, J(H3-H4)=1.9, H3),
2
3
0
0
4.94 (d, 1H, J(H3-H3 )=13.3, H3 ), 3.29 (s, 3H, J(H-Pt)= 19.8,
SOMe), 2.83 (s, 3H, 3J(H-Pt) = 32.6, SOMe), 2.14 (s, 3H, Me1),
2.10 (s, 3H, Me2). 195Pt NMR (54 MHz, CDCl3): δ -3813.3 (s).
IR (cm-1): ν(CdN) =1629, ν(SdO) =1014. MALDI-MS (m/z):
639.8 [M - Cl]þ, 561.9 [M - Cl - SOMe2]þ, 365.9 [M - Cl -
SOMe2 - Pt]þ.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev,
O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala,
P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas,
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[PtCl{(meta-Me2C6H2)(2-ClC6H3)CHNCH2(40-ClC6H4)}-
SOMe2] (7b/7b0). 1H NMR (400 MHz, CDCl3): major isomer, δ
8.50 (s, 1H, 3J(H-Pt) = 110.1, H4), 7.35-7.53 (m, 3H, H5, H6,
H7), 7.23 (d, 2H, 3J(H-H)=8.4, H1), 6.97 (d, 2H, 3J(H-H)=
8.4, H2), 6.70 (s, 1H, H9), 6.63 (s, 1H, H8), 5.31 (dd, 1H, 2J(H3-
4
2
0
0
H3 )=14.3, J(H3-H4) = 2.0, H3), 5.09 (d, 1H, J(H3-H3 )=
0
14.3, H3 ), 3.31 (br s, 3H, SOMe), 2.87 (br s, 3H, SOMe), 2.24 (s,
3H, Me1), 2.10 (s, 3H, Me2). 195Pt NMR (54 MHz, CDCl3): δ
-3768.7 (s); minor isomer, δ 8.57 (s, 1H, 3J(H-Pt)=108.2, H4),
7.35-7.53 (m, 3H, H5, H6, H7), 7.2 (m, H1 overlapped with free
meta-xylene), 7.07 (d, 2H, 3J(H-H) = 8.4, H2), 6.75 (s, 1H, H8),
3
2
0
6.40 (s, 1H, J(H-Pt) = 51.8, H9), 5.40 (dd, 1H, J(H3-H3 )=
4
2
0
0
13.2, J(H3-H4)=1.9, H3), 4.89 (d, 1H, J(H3-H3 )=13.2, H3 ),
3.27 (s, 3H, SOMe), 2.85 (s, 3H, SOMe), 2.12 (s, 3H, Me1), 1.98
(s, 3H, Me2). 195Pt NMR (54 MHz, CDCl3): δ -3782.4 (s). IR
(cm-1): ν(CdN) = 1645, ν(SdO) = 1014. MALDI-MS (m/z):
639.8 [M - Cl]þ, 561.9 [M - Cl - SOMe2]þ, 365.9 [M - Cl -
SOMe2 - Pt]þ. Anal. Found (calcd for C24H24Cl3NOPtS): C:
42.5 (42.64); H: 3.8 (3.58); N: 1.9 (2.07); S: 4.4 (4.74).
[PtCl{(para-Me2C6H2)(2-ClC6H3)CHNCH2(40-ClC6H4)}-
SOMe2] (8b). 1H NMR (400 MHz, CDCl3): δ 8.50 (s, 1H,