Kinetico-mechanistic insight into the platinum-mediated C-C coupling of fluorinated arenes

Article abstract of DOI:10.1021/om9004934

The reaction of compound cis-[Pt(C₆F₅) ₂(SEt₂)₂] with the imine ligands ArCH=NCH2CH2NMe2 (Ar = 2-BrC₆H₄ (la) or 2,6-Cl ₂C₆H₃ (1b)) in toluene produces coordination compounds cis-[Pt(C₆F₅)₂(ArCH=NCH ₂CH₂NMe₂)] (2a, 2b) containing a bidentate [N,N'] ligand. No further reactivity has been observed from this point. Compound 2b has been characterized by single-crystal XRD. Under analogous conditions, imine ligand 2-BrC₆H₄CH=NCH₂(4′-ClC ₆H₄) (1c) produced the Pt"-metalated compound [PtBr{6-(C₆F₅)(2-C)C₅H₃CHNCH ₂(4′-ClC₆H₄)SEt₂] (2c), which contains a five-membered metallacycle with a biaryl linkage involving a C ₆F₅ group. The derivative compounds [PtBr{6-(C ₆F₅)(2-C)C₅H₃CHNCH ₂(4′-ClC₆H₄)L](L = SMe₂ (3c), L = PPh₃ (4c)) were also prepared, and compound 4c has also been characterized by XRD. The kinetico-mechanistic study of the formation of compound 2c has also been pursued in view of the previously published data, leading to seven-membered metallacycles. The time monitoring via UV-vis of the full process allowed the detection and NMR characterization of two intermediate species. An initial Pt^IV complex is present in steady-state low-concentration conditions, and formation of a non-cyclometalated intermediate Pt^II compound is also detected during the process. The latter already contains the C-C coupled ligand arising from a reductive elimination of the former. Intramolecular C-H activation from the latter produces the final characterized compound 2c along with C₆F₅H. The full process has been studied as a function of temperature and pressure as well as at varying nonstoichiometric concentrations of SEt₂ and free imine ligand. The results agree with the quenching of the process at important excesses of SEt₂ (for stoichiometric reasons) or free imine (avoiding the formation of the final complex from the C-C reductively coupled intermediate). The thermal and pressure activation parameters measured indicate that the mechanism operating in this case lies out of the continuum existing for the series of C-H bond activations studied so far. The more than probable associative shift of the reactivity of the Pt^II complex containing the electron-withdrawing C₆F₅ ligands is held responsible for this fact

Full text of DOI:10.1021/om9004934

5096 Organometallics 2009, 28, 5096–5106
DOI: 10.1021/om9004934
Kinetico-Mechanistic Insight into the Platinum-Mediated C-C Coupling
of Fluorinated Arenes
†
Teresa Calvet, Margarita Crespo,* Merce Font-Bardia, Kerman Gomez,
,‡
†
§
ꢀ
Gabriel Gonzalez, and Manuel Martı
ꢁ
´
nez*,‡
§
ꢁ
†
ꢀ
´
Departament de Crystal lografia, Mineralogia i Diposits Minerals, Universitat de Barcelona, Martı i
Franques s/n, E-08028 Barcelona, Spain, Departament de Quımica Inorganica, Universitat de Barcelona,
3
‡
ꢀ
´
ꢀ
§
´ ´
ꢁ
Martı i Franques, 1-11, E-08028 Barcelona, Spain, and Institut Catala d’Investigacio Quımica, Avinguda
ꢀ
ꢀ
dels Paısos Catalans 16, E-43007 Tarragona, Spain
¨
Received June 11, 2009
The reaction of compound cis-[Pt(C6F5)2(SEt2)2] with the imine ligands ArCHdNCH2CH2NMe2
(Ar = 2-BrC6H4 (1a) or 2,6-Cl2C6H3 (1b)) in toluene produces coordination compounds cis-[Pt-
(C6F5)2(ArCHdNCH2CH2NMe2)] (2a, 2b) containing a bidentate [N,N0] ligand. No further
reactivity has been observed from this point. Compound 2b has been characterized by single-crystal
XRD. Under analogous conditions, imine ligand 2-BrC6H4CHdNCH2(40-ClC6H4) (1c) produced the
PtII-metalated compound [PtBr{6-(C6F5)(2-C)C5H3CHNCH2(40-ClC6H4)SEt2] (2c), which contains a
five-membered metallacycle with a biaryl linkage involving a C6F5 group. The derivative compounds
[PtBr{6-(C6F5)(2-C)C5H3CHNCH2(40-ClC6H4)L] (L = SMe2 (3c), L = PPh3 (4c)) were also prepared,
and compound 4c has also been characterized by XRD. The kinetico-mechanistic study of the
formation of compound 2c has also been pursued in view of the previously published data, leading
to seven-membered metallacycles. The time monitoring via UV-vis of the full process allowed the
detection and NMR characterization of two intermediate species. An initial PtIV complex is present in
steady-state low-concentration conditions, and formation of a non-cyclometalated intermediate PtII
compound is also detected during the process. The latter already contains the C-C coupled ligand
arising from a reductive elimination of the former. Intramolecular C-H activation from the latter
produces the final characterized compound 2c along with C6F5H. The full process has been studied as a
function of temperature and pressure as well as at varying nonstoichiometric concentrations of SEt2 and
free imine ligand. The results agree with the quenching of the process at important excesses of SEt2 (for
stoichiometric reasons) or free imine (avoiding the formation of the final complex from the C-C
reductively coupled intermediate). The thermal and pressure activation parameters measured indicate
that the mechanism operating in this case lies out of the continuum existing for the series of C-H bond
activations studied so far. The more than probable associative shift of the reactivity of the PtII complex
containing the electron-withdrawing C6F5 ligands is held responsible for this fact.
Introduction
activation via oxidative addition (PtII) or electrophilic
substitution (PdII).3-7 Similarly, most of the overall pro-
cesses end up with a reductive elimination reaction from
these metal centers. Nevertheless, these are very seldom C-X
reductive eliminations and much more often C-C reductive
couplings.8-13 In this respect, although both biaryl lin-
kages14 and fluorine substituents15 are entities frequently
The involvement of PtII and PdII d8 organometallic com-
plexes in the activation of organic substrates is a fairly
developed field; its implication in an important number of
value-added catalytic cycles is well known.1 Good examples
of this reactivity are the Shilov, Wacker, and Heck reac-
tions.2 The majority of these processes involve an initial
C-X (X = Cl, Br, I) oxidative addition (PtII, PdII) or a C-H
(8) Amatore, C.; Catellani, M.; Deledda, S.; Jutand, A.; Motti, E.
Organometallics 2008, 27, 4549–4554.
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3949–3952.
*Corresponding authors. E-mail: margarita.crespo@qi.ub.es; manel.
martinez@qi.ub.es.
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Published on Web 08/20/2009

Article
Organometallics, Vol. 28, No. 17, 2009 5097
incorporated in new biologically active pharmaceuticals, the
cross-coupling of aryl fluorides has received less attention
than that of other aryl halides.11 In particular, it is only
recently that the first examples of platinum-catalyzed cross-
coupling of polyfluoroarylimines have been reported,16,17
which can be associated with the challenge of activating the
strong C-F bond.18-20
aryl imines. The desired outcome is the occurrence of aryl-aryl
coupling between the Pt-bound pentafluorophenyl group and
the aryl group of the incoming imine. The process has been
found to be plausible despite the increased energetic demands
needed, which has allowed for the kinetic and spectroscopic
characterization of intermediate species not detected in similar
systems. The full characterization by XRD of the final cyclo-
metalated complex, having the C-C coupled ligand, has been
achieved and the full kinetico-mechanistic study has also been
carried out. The results obtained allow for the establishment of
a very important associative shift of the processes involving
PtII complexes with C6F5 ligands that also explains the
quenching of the reactivity when a significant excess of any
ligand is present in the reaction medium.
We have been involved for some time in developing prepara-
tive strategies for the activation of some C-X
(X = H, F, Cl, Br) bonds on PtII simple complexes,3,18,19,21-24
as well as in the kinetico-mechanistic study of the oxidative
addition process.18,23,25 From the oxidatively added PtIV com-
plexes, reductive aryl-aryl coupling has also been observed in
some cases;21,26-28 furthermore, the reductive eliminated
complexes normally underwent an oxidative addition process,
leading to the final characterized species. The kinetico-mechan-
istic details of these processes have been determined either
directly or indirectly.24,29 The presence of bulky ligand arrange-
ments around the PtII center have been shown to be crucial, as
well as the increased Lewis acidity of the metal center. In this
respect, the presence of electron-withdrawing ligands attached to
the PtIV center has allowed the observation of an interesting
unprecedented associative shift of the general reactivity of these
organometallic complexes30,31 having an important number of
Pt-C bonds, which usually lead to a dissociatively activated
general reactivity32-35 despite some differentiating cases.36
With this background in mind, in order to overcome the
difficulty associated with C-C coupling with perfluori-
nated ligands and following our recent work using diaryl-
platinum compounds as precursors for C-C coupling pro-
cesses,21,24,26-29 we present in this paper a new preparative
strategy based on the reaction of cis-[Pt(C6F5)2(SEt2)2] with
Results
Preparation of Compounds. Imines Me2N(CH2)2NCHR
(R= 2-BrC6H4 (1a); 2,6-Cl2C6H3 (1b)) and (4-ClC6H4)-
CH2NCHR (R= 2-BrC6H4 (1c); 2,6-Cl2C6H3 (1d); 4-
ClC6H4 (1e)) were obtained from the condensation reaction
between Me2N(CH2)2NH2 or 4-ClC6H4CH2NH2 and the
corresponding aldehydes following well-established proce-
dures.3,19,24 The reactions of cis-[Pt(C6F5)2(SEt2)2] with po-
tentially N-N-C terdentate (after intramolecular C-Br bond
activation) ligands 1a and 1b were initially tested in toluene
at room temperature. After 15 h, the starting materials were
recovered unchanged. When the reactions were carried out in
refluxing toluene, coordination compounds [Pt(C6F5)2-
{Me2NCH2CH2NCH(2-BrC6H4)}] (2a) and [Pt(C6F5)2-
{Me2NCH2CH2NCH(2,6-Cl2C6H3)}] (2b) were formed
within 4 h. These compounds were characterized by 1H
and 19F NMR spectra, mass spectrometry, and elemental
analyses, and the corresponding structures are shown in
Chart 1. For both compounds evidence of coordination of
the two nitrogen atoms to platinum is obtained from the fact
that both methylamino and imine protons are coupled to
195Pt. The imine adopts an E conformation according to a
cross-peak observed between the imine and the methylene
protons in a 2D-NOESY NMR carried out for 2a. In the 19F
NMR spectra, the obtained values for δ(F), J(F-F), and
J(F-Pt) are consistent with those described for analogous
cis-[Pt(C6F5)2L2] compounds.37-40 For both compounds,
the two pentafluoro groups are nonequivalent, as indicated
by the presence of two para F signals; in each case, the
presence of only two ortho F and two meta F signals is
consistent with free rotation of the C6F5 groups around the
Pt-C bond. The ortho F are downfield shifted (δ ca. -119
to -120 ppm) and coupled to 195Pt (J(F-Pt) in the range
453-476 Hz), and the higher J(F-Pt) values (458.5 Hz (2a)
and 475.6 Hz (2b)) are assigned to the C6F5 trans to the
NMe2, in agreement with the lower trans influence of the
amine moiety. Compound 2b was also characterized crystal-
lographically, and the molecular structure confirms the
geometry predicted from spectroscopic data.
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Attempts to produce intramolecular activation of C-Br
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5098 Organometallics, Vol. 28, No. 17, 2009
Calvet et al.
Chart 1
toluene solutions of compounds 2a or 2b for extended
periods (several days). Although analogous reactions have
been reported for [PtMe2L] or [PtAr2L] compounds (L = 1a
or 1b; Ar = Ph, 4-CH3C6H4),3,27,28 in this case compounds
2a and 2b were recovered unaltered. This fact can be related
to the reduced electronic density on the platinum center,
having two coordinated pentafluorophenyl groups. Further-
more, the presence of two nitrogen atoms in these ligands
may account for the formation of very stable chelate com-
plexes, which could hamper further reaction.
In order to promote intramolecular C-X bond activation
(X=Br, Cl, or H), the reactions of cis-[Pt(C6F5)2(SEt2)2] with
ligands 1c, 1d, and 1e, which contain only one nitrogen atom,
were pursued. No reaction between cis-[Pt(C6F5)2(SEt2)2]
and ligand 1c was observed in toluene at room temperature;
however, compound 2c was obtained after 4 h in refluxing
toluene. Under the same conditions, no reaction occurs with
ligands 1d and 1e. The difference is consistent with the lower
reactivity expected for C-Cl or C-H versus C-Br bonds,
although these bonds have been activated for analogous
ligands when platinum substrate [{PtMe2(μ-SMe2)}2] was
used.23 As indicated above, the presence of electron-with-
drawing C6F5 groups on the platinum center clearly reduces
its reactivity toward intramolecular C-X bond activation.
Given the fact that the necessary initial substitution of
diethylsulfide for the imine should also be affected by the
strong inductive effect of the pentafluorophenyl groups,41,42
(41) Minniti, D. J. Chem. Soc., Dalton Trans. 1993, 1343–1345.
(42) Deacon, G. B.; Nelson-Reed, K. T. J. Organomet. Chem. 1987,
322, 257–268.

Article
Organometallics, Vol. 28, No. 17, 2009 5099
to 195Pt. The large value observed for J(P-Pt) (4164 Hz) in
the 31P NMR spectrum indicates that the PPh3 is trans to the
imine.
˚
Table 1. Selected Bond Lengths (A) and Angles (deg) for Com-
pounds 2b and 4c with Estimated Standard Deviations
compound 2b
compound 4c
Crystal Structure of Compounds 2b and 4c. Suitable crys-
tals of 2b and 4c were grown by slow diffusion of a CH2Cl2
solution into MeOH. The crystal structures are composed of
discrete molecules separated by van der Waals interactions.
Selected bond lengths and angles are given in Table 1, and the
molecular views are shown in Figure 1. For 2b, square-planar
coordination of the platinum(II) is achieved with a bidentate
[N,N0] and two pentafluorophenyl ligands. While the chelate
ligand is nearly coplanar with the coordination plane, the
dihedral angle being 8.3(2)°, the two pentafluorophenyl rings
are twisted from that plane (angles of 67.4(2)° and 80.0(2)°),
as reported for similar compounds.45 The imine adopts an E
configuration, which is suitable for intramolecular activa-
tion of the C-Cl bonds; moreover, one of the ortho chloro
substituents is close enough to the platinum center as to be
Pt-C(12)
Pt-C(18)
Pt-N(1)
Pt-N(2)
2.006 (4)
2.007 (4)
2.044 (4)
2.130 (4)
1.287 (6)
Pt(1)-C(1)
Pt(1)-N
Pt(1)-P
Pt(1)-Br
C(5)-C(7)
2.072 (5)
2.098 (3)
2.2448 (15)
2.4799 (14)
1.489 (7)
N(1)-C(7)
C(12)-Pt-C(18)
C(18)-Pt-N(1)
C(12)-Pt-N(2)
N(1)-Pt-N(2)
89.16 (17)
94.53 (15)
94.15 (17)
82.01 (15)
C(1)-Pt(1)-N
C(1)-Pt(1)-P
N-Pt(1)-Br
P-Pt(1)-Br
80.74 (16)
95.74 (13)
90.99(11)
92.70(6)
reaction of 1c with cis-[Pt(C6F5)2(SMe2)2] was also tested.
The results indicate that, even with this lower basicity ligand
(SMe2), the reaction to produce compound 3c did not
proceed at room temperature and required analogous con-
ditions to those reported above for 2c.
Compounds 2c and 3c were characterized by 1H, 19F, and
195Pt 1D-NMR spectra, mass spectrometry, and elemental
analyses (2c); in addition, 2D-NMR experiments (1H-1H
COSY, 1H-1H NOESY, 1H-19F HOESY, and 1H-13C
gHSQC) were carried for 2c. In the 1H NMR spectra a signal
at 7.77-7.78 ppm coupled to 195Pt (J(H-Pt) = 121.6-125.2
Hz) is assigned to the imine resonance, and the value of the
coupling to platinum is consistent with the presence of a
bromine atom trans to the imine in a platinum(II) com-
pound. The methylene protons are also coupled to platinum,
and a cross-peak observed in the 2D-NOESY NMR spectra
between the imine and the methylene protons suggests an E
conformation about the CHdN moiety. In the 19F NMR
spectra, one set of signals for the ortho, meta, and para F is
observed; in this case, both the δ value and the lack of
coupling to 195Pt for the ortho F suggest that the C6F5 group
is uncoordinated to platinum.43 In addition, only five cross-
peaks were observed in the aromatic region for the 1H-13C
heterocorrelation spectrum, and cross-peaks between ortho
F and both the imine proton and one aromatic proton (He)
are observed in the 1H-19F HOESY spectrum. The signals
observed in the 195Pt NMR spectra are in the range expected
for a platinum(II) coordinated to a [C,N,S,X] donor atoms
set.44 All these results are consistent with the structure shown
in Chart 1 for compounds 2c and 3c, in which a five-
membered metallacycle with an “exo” Caryl-Caryl bond is
formed. This result is in contrast with those previously
reported26-29 in which seven-membered metallacycles,
which include the biaryl linkage, are formed. In order to
confirm this proposal, the reaction of 2c with triphenylpho-
sphine was studied, and the resulting compound 4c was
characterized crystallographically. The reaction of 2c with
triphenylphosphine was carried out in acetone at room
temperature and led to substitution of the coordinated
SEt2 ligand for PPh3. The obtained compound 4c was
characterized by 1H, 19F, and 31P NMR spectra, mass
spectrometry, elemental analyses, and crystal structure.
The 1H NMR spectrum shows the presence of the methylene
protons coupled to 195Pt, but the imine proton could not be
observed since it is overlapped by the PPh3 resonances. As
for 2c and 3c, one set of signals for the ortho, meta, and para F
is observed in the 19F NMR spectra, none of them coupled
activated (Cl(2) Pt=3.624 A). Therefore, the failure to
3 3 3
react could be related to disfavored electronic effects arising
from the presence of two electron-withdrawing pentafluoro-
phenyl rings. In 4c, a C6F5 group is bound to the benzal ring
of the imine ligand in an adjacent position to the imine group,
thus leading to a biphenyl system with a dihedral angle
between both aryl rings of 62.8(3)°. The ligand behaves as
[C,N,]-bidentate, and a five-membered endo metallacycle is
formed. A bromo and a triphenylphosphine ligand complete
the square-planar coordination of the platinum atom. The
metallacycle is approximately planar, as suggested by the
sum of internal angles, which is close to 540° and nearly
coplanar with the coordination plane, the dihedral angle
between the mean planes being 3.62(15)°.
In both cases, bond lengths and angles are well within the
range of values obtained for analogous compounds. Bond
angles at platinum are close to the ideal value of 90°, and the
smallest angle corresponds to the bidentate ligand, with the
“bite” angles N(1)-Pt-N(2) (2b) and C(1)-Pt-N (4c) being
82.01(15)° and 80.74(16)°, respectively. For 2b, in agreement
with the lower ligating ability of amines for platinum, the
Pt-amine distance (2.130(4) A) is longer than the Pt-imine
distance (2.044(4) A).
Kinetico-Mechanistic Study. The chemical reactivity oc-
curring during the preparation of complex 2c described
above from cis-[Pt(C6F5)2(SEt2)2] plus imine 1c is dramatically
different from that observed for the formation of similar
cyclometalated complexes from [{Pt(Me)2(μ-SMe2)}2] and
[Pt(Ph)2(SMe2)2] with the same imines.26,29 In the present case,
the reaction sequence leading to the formation of the final
cyclometalated complex, where a C-C coupling has taken
place, occurs at a much slower time scale. When a toluene
solution of cis-[Pt(C6F5)2(SEt2)2] is mixed with ligand 1c in a 1
( 30% ratio, no changes in the UV-vis spectrum are detected
at room temperature. When the temperature is raised to the
70-90 °C margin, the expected reactivity, leading to the final
highly colored compound obtained on the preparative scale,
2c, is observed. Furthermore, the presence of large excesses of
SEt2 produces a quenching of the process, leading to com-
pound 2c, despite the fact that for the formation of cyclome-
talated complexes with [{Pt(Me)2(μ-SMe2)}2] and [Pt(Ph)2-
(SMe2)2] as starting material limiting kinetics have been
observed.18,23,25 The addition of the cyclometalating imine in
ꢁ
(43) Espinet, P.; Albeniz, A. C.; Casares, J. A.; Martınez-Ilarduya,
´
J. M. Coord. Chem. Rev. 2008, 252, 2180–2208.
(44) Pregosin, P. S. Coord. Chem. Rev. 1982, 44, 247–291.
(45) Nishida, J.; Maruyama, A.; Iwata, T.; Yamashita, Y. Chem.
Lett. 2005, 34, 592–593.

5100 Organometallics, Vol. 28, No. 17, 2009
Calvet et al.
Figure 1. Molecular structure of compounds 2b (left) and 4c (right).
Figure 2. Changes with time of the ortho fluorine signals for the 19F NMR spectrum of the different complexes involved in the reaction
of 1 ꢀ 10-3 M solution of 1c and cis-[Pt(C6F5)2(SEt2)2] at 75 °C in toluene solution: (a) 19F NMR spectra; (b) changes of the relative
integral with time.
large excesses also produces the quenching of the formation of
compound 2c.
compound at -119.56 ppm decreases exponentially, the
appearance of the final 2c complex, -140.34 ppm (as well
an C6F5H group, -142.10 ppm),46 has an induction period.
Furthermore, from the data it is evident that there is an initial
formation and further depletion of a new species with signals
at -117.50 (J(Pt-F) = 470 Hz) and -142.00 ppm. These
signals are indicative of the formation of a compound having
a PtII-C6F5 group, as well as an organic pentafluorophenyl
substituent (R-C6F5).43 The presence of a very small signal at
-122.05 ppm with a steady-state intensity is associated with
With these observations in hand, the kinetico-mechanistic
study of the reactivity at high temperatures (70-90 °C) for
5-24 h and under stoichiometric conditions ([Pt] ≈ [imine] ≈
0.5 ꢀ 10-3 M) was further pursued. The monitoring of the
changes in the UV-vis spectrum of the solutions was carried
out in m-xylene to avoid solvent evaporation during the
study. The absorbance versus time profiles obtained
(Figure S1) show, at 425 nm, an induction period, indicating
the presence of a complex reaction sequence occurring under
the preparative conditions for 2c. 19F NMR time monitoring
at 75 °C of equimolar (1 ꢀ 10-3 M) toluene-d8 solutions
of platinum starting material and imine 1c proved to be an
excellent handle for the establishment of the reaction se-
quence. Figure 2 shows the changes with time of the ortho
fluorine signals of the different compounds present in
the solution. While the signal associated with the initial
the presence of a putative Pt .
IV 47,48 No other species whatso-
ever is observed in the 19F NMR spectrum of the samples
studied.
From the plots it is clear that, under these reaction
conditions, no relevant buildup of any PtII-coordinated
imine or PtIV-metalated imine complexes occurs. Conse-
quently the reaction sequence corresponds to eq 1, which
ꢁ
´
n, A.; Oliva, J.; Tomas, M. Inorg. Chim. Acta
(47) Casas, J. M.; Martı
1995, 229, 291–298.
ꢁ
ꢁ
ꢁ
(46) Donghi, D.; Maggioni, D.; Beringhelli, T.; D’Alfonso, D. Eur. J.
Inorg. Chem. 2008, 3606–3613.
(48) Menjon, B.; Gomez-Saso, M. A.; Fornies, J.; Falvello, L. R.;
Martın, A.; Tsipis, A. Chem.;Eur. J. 2009, 15, 6371–6382.
´

Article
Organometallics, Vol. 28, No. 17, 2009 5101
Figure 3. Fitting of the UV-vis spectral changes observed for the reaction of 0.48 ꢀ 10-3 M cis-[Pt(C6F5)2(SEt2)2] with 0.62 ꢀ 10-3
M
imine 1c at 97 °C in m-xylene solution: (a) absorbance versus time fitting to an {A + B f C f D} profile at 400 nm where B (1c) does not
absorb; (b) concentration versus time profiles extracted from the fitting.
Table 2. Summary of the Kinetic and Thermal Activation Parameters Obtained for the Reactions of cis-[Pt(C6F5)2(SEt2)2] with Imine 1c
in m-xylenea
process
k (T /K)
ΔHq/kJ mol-1
ΔSq/J K-1 mol-1
ΔVq(T)/cm3 mol-1(/K)
{Pt(C6F5)2} + 1c f {PtII(C6F5)}{R-C6F5}
{PtII(C6F5)}{R-C6F5} f 2c
0.038 M-1 s-1 (361)
135 ( 13
86 ( 8
100 ( 40
-85 ( 22
12 ( 2(363)
8.5 ꢀ 10-5 s-1 (361)
-34 ( 4(363)
a Stoichiometric [Pt] ≈ [imine] ≈ 5.0 ꢀ 10-4 ( 30% M.
Figure 4. (a) Eyring plots for the processes observed during the solution chemistry study of the reactions of cis-[Pt(C6F5)2(SEt2)2] with
imine 1c (see text for details). (b) ln k versus P plots for the same reactions.
has a {A + B f C f D} kinetic profile.
data the extremely different nature of the two processes
occurring under high temperatures and long time conditions,
(A+B f C) and (C f D), is evident.
fPtðC6F5Þ2g þ 1c f fPtIIðC6F5ÞgfR-C6F5g f 2c
þ C6F5H
ð1Þ
Discussion
Fitting of the UV-vis spectral changes to this reaction
sequence produced rather good results, as seen in Figure 3,
where the parallelism with the 19F NMR experiments shown
in Figure 2 is evident.
The values of the corresponding second- (A + B f C) and
first-order (C f D) rate constants, as well as the derived
activation parameters, are collected in Table 2. Figure 4
shows the Eyring and ln k versus P plots obtained for the
activation parameters for the studied processes. From these
Intermediate {PtII(C6F5)}{R-C6F5} Species Formation.
Comparison of the data obtained in the present kinetico-
mechanistic study (Table 2) with that available in the litera-
ture (Table 3) for similar systems represents the best ap-
proach to the determination of the nature of compound C
({PtII(C6F5)}{R-C6F5}) in the kinetic sequence shown in
Figures 2 and 3 and eq 1. The only reaction studied so far
on these types of complexes showing positive ΔSq and ΔVq,

5102 Organometallics, Vol. 28, No. 17, 2009
Calvet et al.
Table 3. Relevant Data for Other C-X (X = Br, H) Bond Activation, Pt-C Insertion, and C-C Coupling Processes for Similar Systems
to That Studied in This Worka
process
k/s-1
ΔHq/kJ mol-1
ΔSq/J K-1 mol-1
-125 ( 23
ΔVq/cm3 mol-1
-22 ( 1
[{PtII(Me)2(μ-SMe2)}2] + 2-BrC6H4CHNBzl
C-Br oxidative additionb
5.9 ꢀ 10-3
48 ( 7
[{PtII(Me)2(μ-SMe2)}2] + C6H5CHNBzl
C-H oxidative additionb
3.4 ꢀ 10-3
1.4 ꢀ 10-3
2.2 ꢀ 10-3
3.6 ꢀ 10-3
7.3 ꢀ 10-4
3.0 ꢀ 10-4
7.8 ꢀ 10-5
60 ( 5
87 ( 4
75 ( 3
96 ( 3
94 ( 3
91 ( 7
100 ( 4
-100 ( 10
-11 ( 13
-52 ( 12
29 ( 10
12 ( 9
-17 ( 1
-4.1 ( 0.6
-7.0 ( 0.7
13 ( 1
[PtIIPh2(SMe2)2] + 2-BrC6H4CHNCH2(40-ClC6H4)
C-Br oxidative additionc
[PtIIPh2(SMe2)2] + 2-PhC6H4CHNBzl
C-H oxidative additionc
[PtIVPh2Br(2-CC5H4CHNBzl)]
C-C reductive elimination couplingd
[PtIVPh2Br(2-CC5H4CHNCH2Me)]
C-C reductive elimination couplingd
[PtIVPh2Br(2-CC5H4CHNBzl)]
Ph insertion on the Pt-C bondd
[PtIVPh2Br(2-CC5H4CHNCH2Me)]
Ph insertion on the Pt-C bondd
10 ( 1
-9 ( 24
10 ( 12
∼0
∼0
a Unless stated [Pt] = (0.5-2.1) ꢀ 10-4 M; [imine] = (4.5-120) ꢀ 10-4 M; acetone solution; 298 K. b Limiting rate data.25 c This work; toluene
solution; limiting rate data. d Chloroform solution.29
Scheme 1
as well as fairly large ΔHq, corresponds to reductive C-C
coupling on cyclometalated PtIV compounds.29 The 19F
NMR data indicated in the previous section agree with the
reaction sequence A+B f C shown in Scheme 1. The low
stability of the PtIV oxidatively added intermediate (Figure 2
and Scheme 1) can be held responsible for its lack of
significant buildup concentration in the reaction medium
and determines the general features observed.
the larger errors involved due to the second-order conditions
that have had to be used for the study. It is clear that large
excesses of SEt2 should prevent the advance of the process
stoichiometrically competing with imine 1c in an initial
substitution reaction, as observed. Even more, the strong
electron-withdrawing features of the C6F5 groups should
drive the substitution processes on the starting compound to
be associatively activated,54 contrarily to what is expected
for the presence of two Pt-C cis bonds,32 thus favoring
reentry of the SEt2 ligand. In fact, vacuum heating of
cis-[PtII(C6F5)2(SR2)2] does not produce the expected
[{Pt(C6F5)2(μ-SR2)}2] (R = Me, Et) compounds, which is
indicative of the nonoccurrence of dissociative pathways.55
Furthermore, the low electron density on the platinum center
has to make difficult the oxidative addition reaction of the 1c
imine C-Br bond and reduce the stability of the PtIV
complex formed. As a consequence of all these facts, the
equilibrium producing this compound would be very little
displaced, as observed (Figure 2, -122.05 ppm signal).
As for the quenching of the formation of compound 2c by
large excesses of imine, there is no reason to believe that an
The positive ΔVq and ΔSq values agree with a late transi-
tion state for the reductive elimination C-C coupling, thus
involving also a fairly large activation enthalpy. Although
reductive elimination C-C coupling on PtIV complexes is
well known1 and some new interesting contributions have
been appearing in the last years,13,34,35,49 there are not many
studies involving the determination of the activation para-
meters for the process.29,50-53 In all cases the values of the
parameters found agree with those presented here, despite
(49) Pawlikowski, A. V.; Getty, A. D.; Goldberg, K. I. J. Am. Chem.
Soc. 2007, 129, 10382–10393.
(50) Felk, U.; Zahl, A.; van Eldik, R. Organometallics 1999, 18, 4156–
4164.
(51) Wik, B. J.; Ivanovic-Burmazovic, I.; Tilset, M.; van Eldik, R.
Inorg. Chem. 2006, 45, 3613–3621.
(52) Stahl, S. S.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc.
1996, 118, 5961–5976.
(53) Crumpton, D. M.; Goldberg, K. I. J. Am. Chem. Soc. 2003, 125,
9442–9456.
(54) Tobe, M. L.; Burgess, J. Inorganic Reaction Mechanisms;
Longman: White Plains, NY, 1999.
(55) Rashidi, M.; Fakhroeian, Z.; Puddephatt, R. J. J. Organomet.
Chem. 1991, 406, 261–267.

Article
Organometallics, Vol. 28, No. 17, 2009 5103
Scheme 2
increased difficulty in the oxidative addition process is
responsible for this fact, which has not been observed in
similar systems.18,19,23,25 Time 19F NMR monitoring of the
reaction of a toluene-d8 solution being [1c] = 6 ꢀ [Pt] = 1 ꢀ
10-3 M under the conditions indicated in Figure 2 proved to
be revealing. Under these concentration ratio conditions no
signal at -122.05 ppm is observed, indicating that the PtIV
compound in Scheme 1 is not present in measurable
amounts. Furthermore, a signal that agrees with the presence
of the free, C-C coupled (2-C6F5)C6H4CHNCH2(20-
ClC6H4) ligand56 emerges very slowly in the 19F NMR spec-
trum together with a complex pattern of PtII-coupled signals in
the ortho-fluorine zone of the C6F5 groups. The full disappear-
ance of the starting material occurs during these changes
(Figure S2). The important difference in bulk for imines 1c
and (2-C6F5)C6H4CHNCH2(40-ClC6H4) plus the associatively
activated characteristics of the substitution on the intermediate
PtII complex (C, Scheme 1), showing only a Pt-C bond, should
force a (2-C6F5)C6H4CHNCH2(40-ClC6H4) by 1c substitution,
thus leading to a mixture of unresolved complexes that produce
the quenching of the reaction leading to compound 2c under
excess imine conditions (see below).
[PtIIBrPh{(2-C6F5)C6H4CHNCH2(40-ClC6H4)}(SEt2)], fol-
lowed by a fast C6F5-hydride reductive elimination to
form the final complex as found for similar phenyl PtII
complexes.26,29 It is interesting to note, though, that C-H
bond activation had not been observed on trans-[PtIIBrPh-
(SMe2)2] with the 2-PhC6H4CHNBzl ligand. This fact had
been associated with the lack of preliminary coordination of
the imine (due to its low Lewis basicity and bulky character,
as well as to the associativeness of the substitution on a PtII
center having only a Pt-C bond).32,60,61 In the present study
the same factors apply, especially considering the above-
mentioned electron-withdrawing character of the C6F5
ligand. Dissociation of the already coordinated C-C
coupled imine ligand (in the absence of a better ligand, see
above) is impeded, contrarily to what has been observed
from [PtIIBrPh(2-PhC6H4CHNBzl)(SMe2)] in the presence
of large excesses of SMe2.29 As a result, C-H bond activa-
tion is made feasible under these rather comparatively strong
conditions. Table 3 collects the kinetic and activation para-
meters available in the literature for C-Br and C-H oxida-
tive addition reactions on similar PtII complexes, as well as
some new values determined in this work.62
At this point a note should be raised about the reductive
elimination C-C coupling reaction occurring on a fully
saturated PtIV 18-electron complex and not on a pentacoor-
dinated intermediate. Although the presence of a pentacoor-
dinated intermediate has been found necessary in most of the
oxidative addition/reductive elimination equilibria on
platinum complexes,16,34,51,57-59 some examples of reactions
For all the systems studied having an organometallic
cis-{PtII(R)2} (R=Me, Ph) arrangement, the reaction me-
chanism had been found equivalent.18,25 Figure 5 collects
simplified isokinetic relationships obtained. From the plots it
is clear that the substitution of two PtII-Me by PtII-Ph
bonds produces an increase of ca. 25 kJ/mol in the ΔHq
values, but this higher enthalpic demand is compensated by a
less negative ΔSq value, so producing equivalent values of k
at the isokinetic temperature (ca. 298 K).54,63 The linearity
observed for the ΔHq versus ΔVq plots also ascertains the
equivalence of the mechanism.
occurring on fully saturated octahedral 18-electron [PtIV
-
(Ph)2Br{2-CC5H4CHNBzl}(SMe2)] or [PtIV(Ph)2Br{2-CC5-
H4CHN(CH2)2N(Me)2}] complexes have already been re-
ported.9,10,27-29,35,53
Final[PtIIBr{6-C6F5,2-CC5H3CHNCH2(40-ClC6H4)}(SEt2)],
2c, Complex Formation. It is clear from the results discussed
above that the appearance of the final 2c compound from
cis-[Pt(C6F5)2(SEt2)2]+1c is related to the C f D kinetic profile
indicated (Scheme 2).
From the same plots it is clear that the C-H bond
activation process indicated in Scheme 2 produces a set of
activation parameters (Table 2, / in Figure 5) that deviate
from the relationship, indicating a discontinuity on the
(60) Romeo, R.; Plutino, M. R.; Scolaro, L. M.; Stoccoro, S.;
Minghetti, G. Inorg. Chem. 2000, 39, 4749–4755.
(61) Alibrandi, G.; Bruno, G.; Lanza, S.; Minniti, D.; Romeo, R.;
The process thus corresponds to a C-H oxidative addi-
tiontothe intermediatePtII complexC indicatedinScheme1,
Tobe, M. L. Inorg. Chem. 1987, 26, 185–190.
(56) 19F NMR signals at -140.76 (Fortho) [dd, J=29.6; 11.2]; -154.77
(Fpara) [t, J=51.7]; -162.01 (Fmeta) [m].
(62) Experiments were carried out at varying high concentration of
imine (0.018-0.025 M) with a concentration of cis-[Pt(Ph)2(SMe2)2] of
(2-4) ꢀ 10-4 M. Under these conditions, and according to the trend
observed in previous work, no significant variation of kobs with the imine
concentration was observed (Supporting Information), and these values
were used for the derivation of the thermal and pressure activation
parameters collected in Table 3.
(57) Arthur, K. L.; Wang, Q. L.; Bregel, D. M.; Smythe, N. A.;
O’Neil, B. A.; Goldberg, K. I.; Moloy, K. G. Organometallics 2005, 24,
4624–4628.
(58) Procelewska, J.; Zhal, A.; Liehr, G.; van Eldik, R.; Smythe,
N. A.; Williams, B. S.; Goldberg, K. I. Inorg. Chem. 2005, 44, 7732–7742.
(59) Wik, B. J.; Lersch, M.; Krivokapic, A.; Tilset, M. J. Am. Chem.
Soc. 2006, 128, 2682–2896.
(63) Wilkins, R. G. Kinetics and Mechanisms of Reactions of Transi-
tion Metal Complexes; VCH: Weinheim, 1991.

5104 Organometallics, Vol. 28, No. 17, 2009
Calvet et al.
Figure 5. (a) Simplified isokinetic relationship for C-X concerted oxidative addition reactions on PtII compounds of this family. (b)
Equivalent ΔHq versus ΔVq plot, except for the data indicated in the text extracted from refs 25 and 18. Arrows indicate the shift
observed on going from a cis-{PtII(Me)2} to a cis-{PtII(Ph)2} complex; / corresponds to the C-H bond activation related to the
cis-{PtII(C6F5)2} moiety complexes studied (Scheme 2).
mechanism for the process. The fact that the PtII compound
responsible for this bond activation has only a PtII-C bond
with bad donor characteristics (Scheme 2) should be held
responsible for the difference. For the compound we are
dealing with in this study the standard preliminary ligand
dissociation to produce a vacant coordination site, observed
Conclusions
The work reported here shows that compound cis-[Pt-
(C6F5)2(SEt2)2] is an efficient substrate to produce C-C
coupling between a pentafluorophenyl ligand and imine
2-BrC6H4CHdNCH2(4-ClC6H4) (1c). Although previous
work carried out for platinum substrates cis-[Pt(Ph)2-
(SMe2)2] or [{Pt(4-MeC6H4)2(μ-SEt2)}2] produced seven-
membered metallacycles containing a biaryl linkage, in this
for systems of the same family, is very much impeded.23
A
similar type of associative shift has already been established
for the substitution processes occurring on PtIV organome-
tallic complexes with ligands having a high electron-with-
drawing character.30,31 Having this in mind a possible
oxidative addition reaction occurring directly from the
square-planar 16-electron PtII complex may be possible. In
fact the relative accessibility of such 14/16-electron species
has recently been discussed for PdII compounds, a key point
being the electron-donating capabilities of the ligands
attached to the metal center.64 Thus if the process does not
require the dissociation of any ligand, the ordering/volume
collapse on going from the reactants to the transition
state has to be much more important, as seen in Figure 5.
Alternatively a putative C6F5 assistance for the hydrogen
abstraction might be also considered as part of the mechan-
istic continuum for bond activation reactions.65-67 The
process will then be a formal electrophilic substitution, as
those observed and accepted on PdII centers,68-71 which
have also been claimed for certain C-H bond activation
processes at PtII.22
case a five-membered metallacycle with an “exo Caryl-Caryl
”
bond is obtained, as for other systems where direct metala-
tion of the ((2-C6H5)C6H4)CHNCH2Ph biaryl imine has
been tried. The kinetico-mechanistic study carried out on
the system indicates the presence of very small amounts of an
initial PtIV compound arising from the C-Br bond activa-
tion of imine 1c that thus undergoes a C-C reductive
elimination to produce a ligand already having the aryl-
pentafluorophenyl coupling. Further reaction from this
point produces a C-H activation on the phenyl ring leading
to the final five-membered cyclometalated PtII compound
after elimination of C6F5H. In this respect reaction of the
same starting material with imines RCHNCH2(4-ClC6H4)
(R = 2,6-Cl2C6H3 (1d); 4-ClC6H4 (1e)) having stronger
C-Cl or C-H bonds in the positions to be initially activated
do not undergo such reaction. Quenching of the process by
excess amounts of imine or SEt2 ligands indicates that the
initial presence of the PtIV cyclometalated material and its
preservation during the time needed for the formation of the
final thermodynamically stable PtII form are crucial points
for the reactivity observed.
ꢁ
(64) Moncho, S.; Ujaque, G.; Lledos, A.; Espinet, P. Chem.;Eur. J.
2008, 14, 8986–8994.
(65) Vastine, B. A.; Hall, M. B. J. Am. Chem. Soc. 2007, 129, 12068–
12069.
(66) Oxgaard, J.; Tenn, W. J.; Nielsen, R. B.; Periana, R. A.;
Goddard, W. A. Organometallics 2007, 26, 1565–1567.
(67) Perutz, R. N.; Sabo-Etienne, S. Angew. Chem., Int. Ed. 2007, 46,
2578–2592.
Experimental Section
General Procedures. Microanalyses were performed at the
ꢀ
Serveis Cientifico-Tecnics (Universitat de Barcelona). Mass
ꢁ
ꢁ
´
a, M.; Gomez, M.;
(68) Aullon, G.; Chat, R.; Favier, I.; Font-Bardı
Granell, J.; Martınez, M.; Solans, X. Dalton Trans. 2009, DOI 10.10391/
b905134a.
(69) Favier, I.; Gomez, M.; Granell, J.; Martı
M.; Solans, X. Dalton Trans. 2005, 123–132.
spectra were performed at the Servei d’Espectrometria de
Masses (Universitat de Barcelona). Electrospray mass spectra
were carried out in a LC/MSD-TOF spectrometer using H2O-
CH3CN (1:1) to introduce the sample. NMR spectra were
obtained at the Unitat de RMN d’Alt Camp (Universitat de
´
ꢁ
´
nez, M.; Font-Bardıa,
´
ꢁ
(70) Gomez, M.; Granell, J.; Martı
´
nez, M. J. Chem. Soc., Dalton
Trans. 1998, 37–44.
(71) Gomez, M.; Granell, J.; Martı
´
ꢀ
ꢁ
Barcelona) and at the Institut Catala d’Investigacio Quı
´
mica.
ꢁ
nez, M. Organometallics 1997, 16,
1H, 19F, 31P, and 195Pt NMR spectra were recorded by using
2539–2546.

Article
Organometallics, Vol. 28, No. 17, 2009 5105
Bruker 250 (195Pt, 54 MHz), Varian Unity 300 (1H, 300 MHz;
19F, 282.2 MHz; 31P, 121.42 MHz), Varian Inova 300 (HOESY,
1H-19F), Mercury 400 (1H, 400 MHz; 19F, 376.5 MHz; 1H-1H-
COSY; 1H-1H-NOESY), Varian Inova DMX-500 (1H, 500
MHz; 1H-13C-gHSQC), or Bruker Avance 500 (19F, 470.3
MHz) spectrometers and referenced to SiMe4 (1H, internal),
H3PO4 (31P, external), CFCl3 (19F, external), and H2PtCl6 in
D2O (195Pt, external). δ values are in ppm and J values in Hz; s=
singlet; d = doublet; t=triplet; m = multiplet; NMR labeling is
as shown in Chart 1.
Table 4. Crystallographic and Refinement Data for Compounds
2b and 4c
compound 2b
compound 4c
formula
fw
C
774.35
293(2)
0.71073
monoclinic
P21/c
12.271(5)
13.321(3)
15.371(5)
90
95.64(2)
90
2500.4(14); 4
2.057
5.916
23H14Cl2F10N2Pt
C38H25BrClF5NPPt
932.01
293(2)
0.71073
triclinic
P1
12.233(7)
12.259(5)
13.842(6)
111.65(3)
98.54(3)
109.89(3)
1722.8(16); 2
1.797
temp, K
wavelength, A
cryst syst
space group
a, A
b, A
c, A
R, deg
β, deg
Preparation of Compounds. cis-[Pt(C6F5)2(SR2)2] (R = Me;
Et), cis-[Pt(Ph)2(SMe2)2], and 1a-1e and 2-PhC6H4CHNBzl
ligands were prepared as reported elsewhere.3,23,24,26,72,73
[Pt(C6F5)2{Me2NCH2CH2NCH(2-BrC6H4)] (2a) was ob-
tained from 100 mg (0.14 mmol) of cis-[Pt(C6F5)2(SEt2)2] and
36 mg (0.14 mmol) of ligand 1a, which were allowed to react in
refluxing toluene for 4 h. The solvent was removed in a rotary
evaporator, and the residue was treated with hexane. A yellow
solid was isolated by filtration in vacuo. Yield: 50 mg (45.5%).
γ, deg
V, A3; Z
d(calcd), mg/m3
abs coeff, mm-1
F(000)
5412
900
1472
25 342/6954 [R(int) = 21 069/10 973[R(int) =
3
rflns coll/unique
1H NMR (400 MHz, CDCl3): δ 2.85 [s, J(Pt-H)=21.6, 6H,
0.0483]
3829/0/221
0.0628]
10 973/0/433
Ha]; 2.90 [t, J(H-H)=5.6, 2H, Hb]; 4.26 [td, J(H-H)=5.2; 1.6,
2H, Hc]; {7.19 [td, J(H-H) = 8.0; 2.0, 1H]; 7.31[d, J(H-H)=
8.0, 1H]; 7.40-7.46 [m, 1H]; 7.91-7.93 [m, 1H], aromatic
protons}; 8.92 [s, 3J(Pt-H)=62.8, 1H, Hd]. 19F NMR (376.48
MHz, CDCl3): δ -120.09 [m, J(F-Pt)=453.3, 2F, Fortho]; -
120.17 [m, J(F-Pt) = 458.5, 2F, Fortho]; -162.50 [t, J(F-F) =
19.9, 1F, Fpara]; -164.31 [t, J(F-F)=19.9, 1F, Fpara]; -164.95
[m, 2F]; -165.61 [m, 2F]. ESI-MS, m/z: 616.99 [M - C6F5]þ.
Anal. Found (calc for C23H15BrF10N2Pt): C: 36.1 (35.22); H: 2.0
(1.93); N: 4.0 (3.57).
data/restraints/
params
GOF on F2
R1(I > 2σ(I))
wR2 (all data)
1110
0.0349
0.1034
1.054
0.0468
0.1214
0.926 and -1.135
peak and hole, e A-3 1.688 and -1.681
3
7.1, 2F, Fmeta]. 19F NMR (376.48 MHz, toluene-d8): δ -141.13
[dd, J(F-F)=23.3; 8.2, 2F, Fortho]; -153.87 [t, J(F-F)=21.0, 1F,
Fpara]; -161.38 [td, J(F-F)=21.8; 6.8, 2F, Fmeta]. 195Pt NMR (54
[Pt(C6F5)2{Me2NCH2CH2NCH(2,6-Cl2C6H3)] (2b) was ob-
tained from 50 mg (0.07 mmol) of cis-[Pt(C6F5)2(SEt2)2] and
20 mg (0.08 mmol) of ligand 1b, which were allowed to react in
refluxing toluene for 4 h. The solvent was removed in a rotary
evaporator, and the residue was treated with hexane. A light
yellow solid was isolated by filtration in vacuo and recrystallized
in dichloromethane-methanol. Yield: 25 mg (46.0%). 1H NMR
(400 MHz, CDCl3): δ 2.83 [s, 3J(Pt-H)=27.6, 6H, Ha]; 2.92 [t,
J(H-H)=5.7, 2H, Hb]; 4.32 [td, J(H-H)=6.0; 1.8, 2H, Hc]; 7.14
MHz, CDCl3):
δ
-3947.20. ESI-MS, m/z: 680.05
[M - Br]þ. Anal. Found (calc for C24H20BrClF5NPtS): C: 37.9
(37.93); H: 2.6 (2.65); N: 2.3 (1.84); S 4.0 (4.22).
[PtBr{6-(C6F5)(2-C)C5H3CHNCH2(40-ClC6H4)SMe2] (3c)
was obtained using an analogous procedure from cis-[Pt-
1
(C6F5)2(SMe2)2]. Yield: 55 mg (49.0%). H NMR (400 MHz,
CDCl3): δ 2.75 [s, J(H-Pt)=52.4, 3H, Ha]; 5.39 [s, 3J(Pt-H)=
28.0, 2H, Hc]; {7.01 [d, J(H-H) =7.6, He, 1H]; 7.29-7.33 [m,
5H], 7.71 [d, J(H-H) = 8.0, 1H], aromatic protons}; 7.78 [s,
3J(Pt-H)=121.6, 1H, Hd]. 19F NMR (376.48 MHz, CDCl3):
δ -140.88 [dd, J(F-F)=22.6; 8.3, 2F, Fortho]; -153.55 [t, J(F
-F) = 20.7, 1F, Fpara]; -161.17 [td, J(F-F) = 22.6; 8.0, 2F,
Fmeta]. 195Pt NMR (54 MHz, CDCl3): δ -3861.7. ESI-MS, m/z:
731.04 [M]; 652.02 [M - Br]þ.
[m, 3H, aromatic protons]; 8.76 [s, 3J(Pt-H)=72.0, 1H, Hd]. 19
F
NMR (376.48 MHz, CDCl3): δ -119.11 [d, J(F-F) = 31.7,
J(F-Pt) = 475.6, 2F, Fortho]; -119.77 [d, J(F-F) = 31.7, J(F-
Pt) = 459.8, 2F, Fortho]; -162.61 [t, J(F-F)=19.8, 1F, Fpara]; -
164.54 [t, J(F-F)=19.8, 1F, Fpara]; -165.00 [m, 2F]; -165.04
[m, 2F]. ESI-MS, m/z: 792.03 [MþNH4]þ. Anal. Found (calc for
C23H14Cl2F10N2Pt): C: 35.6 (35.67); H: 2.1 (1.82); N: 4.0 (3.62).
[PtBr{6-(C6F5)(2-C)C5H3CHNCH2(40-ClC6H4)PPh3] (4c)
was obtained from 20 mg (0.03 mmol) of compound 2c and 8
mg (0.03 mmol) of triphenylphosphine, which were allowed to
react in acetone at room temperature for 2 h. The solvent was
removed in a rotary evaporator, and the residue was washed
with pentane. An orange solid was isolated by filtration in vacuo.
Yield: 20 mg (81.0%). 1H NMR (400 MHz, CDCl3): δ 5.49 [s,
3J(Pt-H) = 15.3, 2H, CH2]; {6.64 [m, 2H]; 6.78 [m, 1H], 7.38-
7.41 [m, 13H], 7.73-7.77 [m, 7H], aromatic þ imine protons}.
19F NMR (282.23 MHz, CDCl3): δ -140.68 [dd, J(F-F)=21.8;
7.9, 2F, Fortho]; -153.90 [t, J(F-F)=19.8, 1F, Fpara]; -161.41
[td, J(F-F) = 21.8; 7.9, 2F, Fmeta]. 31P NMR (121.42 MHz,
CDCl3): δ 22.72 [s, J(P-Pt) = 4164]. ESI-MS, m/z: 852.09 [M -
Br]þ. Anal. Found (calc for C38H25BrClF5NPPt): C: 49.9
(48.97); H: 2.8 (2.70); N: 2.0 (1.50).
[PtBr{6-(C6F5)(2-C)C5H3CHNCH2(40-ClC6H4)SEt2]
(2c)
was obtained from 100 mg (0.14 mmol) of cis-[Pt(C6F5)2(SEt2)2]
and 43.5 mg (0.14 mmol) of ligand 1c, which were allowed to
react in refluxing toluene for 4 h. The solvent was removed in a
rotary evaporator, and the residue was treated with hexane. An
orange solid was isolated by filtration in vacuo. Yield: 55 mg
(52.0%). 1H NMR (400 MHz, CDCl3): δ 1.40 [t, J(H-H)=7.6,
6H, Ha]; 3.02 [m, 2H, Hb]; 3.40 [m, 2H, Hb]; 5.40 [s, 3J(Pt-H)=
28.8, 2H, Hc]. {6.99 [d, J(H-H)=7.6, He, 1H]; 7.29-7.33 [m,
5H], 7.78 [d, J(H-H) = 7.6, 1H], aromatic protons}; 7.77 [s,
3J(Pt-H)=125.2, 1H, Hd]. 1H NMR (400 MHz, toluene-d8): δ
1.06 [t, J(H-H)=7.6, 6H, Ha]; 2.43 [m, 2H, Hb]; 3.24 [m, 2H,
Hb]; 5.19 [s, 3J(Pt-H) = 34.0, 2H, Hc]. {6.79 [d, J(H-H) = 8.4,
1H];6.93 [m, 1H]; 7.09 [m, 4H], 7.86 [d, J(H-H)=7.2, 3J(Pt-H)=
X-ray Structure Analysis. Prismatic crystals were selected and
mounted on a MAR345 diffractometer with an image plate
detector. Intensities were collected with graphite-monochroma-
tized Mo KR radiation. The structures were solved by direct
methods using the SHELXS computer program74 and refined
by the full-matrix least-squares method, with the SHELXL97
computer program using 25 342 (2b) and 21 069 (4c) reflections
(very negative intensities were not assumed). All hydrogen
3
47.6, 1H], aromatic protons}; 7.51 [s, J(Pt-H) = 121.6, 1H,
Hd]. 13C NMR (1H-13C gHSQC, 500 MHz, CDCl3): δ 13.0 [Ca];
33.0 [Cb]; 62.5 [Cc]; {126.0 [1C], 129.0 [2C], 131.0 [2C], 132.0 [1C],
133.0 [1C], aromatic carbon}; 176.5 [Cd]. 19F NMR (376.48
MHz, CDCl3): δ -140.81 [dd, J(F-F) = 23.7; 7.9, 2F, Fortho];
-153.61 [t, J(F-F)=21, 1F, Fpara]; -161.21 [td, J(F-F)=21.0;
(72) Steele, B. R.; Vrieze, K. Transition Met. Chem. 1977, 2, 140–144.
ꢁ
ꢁ
ꢁ
(73) Uson, R.; Fornies, J.; Tomas, M.; Menjon, B.; Navarro, R.
ꢁ
€
€
(74) Sheldrick, G. M. SHELXS; Universitat of Gottingen: Germany,
1997.
Inorg. Chim. Acta 1989, 162, 33–37.

5106 Organometallics, Vol. 28, No. 17, 2009
Calvet et al.
atoms were computed and refined using a riding model, with an
isotropic temperature factor equal to 1.2 times the equivalent
temperature factor of the atom to which they are linked. Further
details are given in Table 4.
Due to the larger errors involved in the method, all experi-
ments were run at least in duplicate and special care was
taken in the global analysis results of the fitting. The general
kinetic technique is that previously described.25,26,30 Table S1
collects the obtained kobs values for all the systems studied as a
function of the starting complex, process studied, platinum and
imine concentrations, pressure, and temperature. All post-run
fittings were carried out by the standard available commercial
programs.
Kinetics. The kinetic profiles for the reactions were followed
in general by UV-vis spectroscopy in the 500-330 nm range.
Some nonkinetic, but time-dependent NMR experiments were
also conducted (Figure 2). Atmospheric pressure runs were
recorded on an HP8452A or Cary50 instrument equipped with
thermostated multicell transports. Observed rate constants were
derived from absorbance versus time traces at the wavelengths
where a maximum increase and/or decrease of absorbance was
observed. For runs at variable pressure, a previously described
pressurizing system and pill-box cell were used;71 the system was
connected to a J&M TIDAS spectrophotometer, which was used
for the absorbance measurements. The calculation of the ob-
served rateconstants from the absorbance versustime monitoring
of reactions, studied under second- or first-order concentration
conditions, was carried out using the SPECFIT software.75
Acknowledgment. We would like to thank the
ꢁ
Ministerio de Educacion y Ciencia (CTQ2006-02007/
BQU, CTQ2006-14909-C02-02) for financial support.
Supporting Information Available: Crystallographic data in
CIF format; values of kobs determined as a function of the
complex, solvent, temperature, and pressure; and observed
UV-vis and NMR spectral changes for one of the reactions
studied. This material is available free of charge via the Internet
at http://pubs.acs.org.
(75) Binstead, R. A.; Zuberbuhler, A. D.; Jung, B. SPECFIT32,
[3.0.34]; Spectrum Software Associates, 2005.