New insights in the formation of five- Versus seven-Membered platinacycles: A kinetico-Mechanistic study

Article abstract of DOI:10.1021/ic3023584

The reaction of Pt(IV) organometallic cyclometalated complexes of type [PtXAr₂(Ar′CHNCH₂CH₂NMe₂)] to produce 5- and 7-membered Pt(II) metalacycles by a formal C-C reductive elimination/C-H oxidative addition/Ar-H reductive elimination sequence has been studied from a preparative and kinetico-mechanistic perspective. The detection and characterization of key intermediates has also been achieved via the careful selection of reaction conditions, including time, extracted from the kinetic studies. From the data collected, it is clear that a fine-tuning of the reactivity is possible with respect to the formation of the alternative 5- and 7-membered cyclometalated complexes (i.e., [PtX(Ar-Ar′CH-NCH ₂CH₂NMe₂)] and [PtX(Ar-Ar′CH-NCH ₂CH₂NMe₂)]). In all cases a common reductive elimination reaction occurs to form a non cyclometalated intermediate compound of type [PtX(Ar)(Ar-Ar′CH-NCH₂CH₂NMe₂)], which leads to the selective formation of the above-mentioned complexes by the actuation of an unexpected equilibrium between its cis-(X,NMe₂) and trans-(X,NMe₂) isomers. While the cis-(X,NMe₂) isomer produces the 7-membered metallacycle, the trans-(X,NMe₂) form leads exclusively to the 5-membered analogue. The isomerization process is dominated by the steric hindrance existing between the Ar-Pt and Ar-Ar′CHN-Pt moieties in the cis-(X,NMe₂) isomer that forces a Z conformation of the imine, thus leading exclusively to the 7-membered ring formation only for the less hindered X = Cl systems.

Full text of DOI:10.1021/ic3023584

Article
pubs.acs.org/IC
New Insights in the Formation of Five- Versus Seven-Membered
Platinacycles: A Kinetico-Mechanistic Study
Paul V. Bernhardt,† Teresa Calvet,‡ Margarita Crespo,*,§ Merce Font-Bardía,‡,∥ Susanna Jansat,§
̀
and Manuel Martínez*,§
†School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
‡Departament de Mineralogia, Cristal·lografia i Dipos
Spain
§Departament de Química Inorgan
∥Unitat de Difraccio
de RX, Centres Científics i Tecnolog
̀ ̀
its Minerals, Universitat de Barcelona, Martí i Franques s/n, E-08028 Barcelona,
̀
̀
ica, Facultat de Química, Universitat de Barcelona, Martí i Franques 1-11, E0-028 Barcelona, Spain
́
̀
ics de la Universitat de Barcelona (CCiTUB), Universitat de Barcelona, Sole
̀
i Sabarís 1-3, E-08028 Barcelona, Spain
S
* Supporting Information
ABSTRACT: The reaction of Pt(IV) organometallic cyclometalated com-
plexes of type [PtXAr2(Ar′CHNCH2CH2NMe2)] to produce 5- and 7-
membered Pt(II) metalacycles by a formal C−C reductive elimination/C−H
oxidative addition/Ar−H reductive elimination sequence has been studied
from a preparative and kinetico-mechanistic perspective. The detection and
characterization of key intermediates has also been achieved via the careful
selection of reaction conditions, including time, extracted from the kinetic
studies. From the data collected, it is clear that a fine-tuning of the reactivity is
possible with respect to the formation of the alternative 5- and 7-membered
cyclometalated complexes (i.e., [PtX(Ar-Ar′CHNCH2CH2NMe2)] and
[PtX(Ar-Ar′CHNCH2CH2NMe2)]). In all cases a common reductive
elimination reaction occurs to form a non cyclometalated intermediate
compound of type [PtX(Ar)(Ar−Ar′CHNCH2CH2NMe2)], which leads to
the selective formation of the above-mentioned complexes by the actuation of an unexpected equilibrium between its cis-
(X,NMe2) and trans-(X,NMe2) isomers. While the cis-(X,NMe2) isomer produces the 7-membered metallacycle, the trans-
(X,NMe2) form leads exclusively to the 5-membered analogue. The isomerization process is dominated by the steric hindrance
existing between the Ar−Pt and Ar−Ar′CHN-Pt moieties in the cis-(X,NMe2) isomer that forces a Z conformation of the imine,
thus leading exclusively to the 7-membered ring formation only for the less hindered X = Cl systems.
(IV) cyclometalated compounds [PtXAr2(Ar′CHNCH2-
CH2NMe2)].6−11 For this process, it has been suggested that
the first step consists of a reductive elimination to give a
platinum(II) compound with a bidentate ligand containing
amine and imine functionalities in which a dangling biphenyl
moiety is already formed.12,13 However, many of these
intermediates have never been isolated despite their possible
importance in isomerism reactions. Furthermore, the nature of
the final compounds of the reaction of [PtII(Ar)2(2-XAr′CHN-
CH2CH2NMe2)] has been found to be extremely dependent on
the nature of the X ortho substituent on the metalating amino-
imino ligand,10,14 despite the homogeneity observed in the
kinetico-mechanistic studies carried out on similar sys-
tems.13,15−20 To gain insight into these reactions, a
comprehensive kinetico-mechanistic study of the reactions of
cyclometalated platinum(IV) compounds of type [PtXAr2-
(Ar′CHNCH2CH2NMe2)] in toluene solution was undertaken.
INTRODUCTION
■
C−C bond formation is one of the most important processes in
organic synthesis. Involvement of Pd(II)/Pd(IV), in addition to
Pd(0)/Pd(II) systems, plays a decisive role in catalytic
processes, and, since Pt(IV) species are more readily accessible,
parallel studies with organoplatinum compounds are often
useful in providing mechanistic information.1 In addition,
unsymmetrical bidentate ligands containing amine and imine
functionalities have been proven to be useful in catalysis.2,3 For
this type of ligand, it has been observed that geometrical
isomerism of square-planar palladium and platinum compounds
is controlled by steric effects. The trigonal planar arrangement
around the unsaturated N-atom (sp2) is supposed to be more
tolerable to the steric strain than the saturated N-atom (sp3).4
Recently, the great importance of isomerization steps, tradi-
tionally overlooked in catalytic cycles, has been shown for Stille
coupling.5
In recent years, we have been involved in studies related to
the formation of platinum(II) cyclometalated compounds
containing a biaryl moiety from the corresponding platinum-
Received: October 29, 2012
© XXXX American Chemical Society
A
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Scheme 1
Figure 1. Molecular structure of compounds (a) 5-II-Br,H, (b) E-II-Br,H, and (c) E-II′-Br,H.
As will be shown, two distinct geometrical isomers with a
dangling biphenyl moiety are formed, and these intermediates
lead to either five or seven-membered platinum(II) cyclo-
metalated compounds.
t h e m o r e i n e r t b r o m i d o an a l o g u e [ P t B r ( 4 -
MeC6H4)2(CC5H4CHNCH2CH2NMe2)] has not been
studied so far. An initial attempt to produce an analogous
seven-membered platinacycle was carried out in refluxing
toluene following the procedure reported for the chlorinated
compounds.14 In this case, though, a complex mixture of
compounds resulted in which the major component was a five-
membered platinacycle with an “exo Caryl-Caryl” bond (5-II-
Br,H). As a first glance, a general picture of the observed
processes should consist of: (i) Caryl-Caryl reductive elimination
from the platinum(IV) compounds of type 5-IV to give
platinum(II) compounds of type II containing a biphenyl; (ii)
C−H activation at either a distal or a proximal position of the
biphenyl moiety leading, respectively, to seven (7-II) or five-
membered (5-II) platinacycles with elimination of a toluene
molecule.
RESULTS AND DISCUSSION
■
Formation of Five- Versus Seven-Membered Platina-
cycles Containing Biphenyl Moieties: Characterization
of Intermediates. Previous studies indicated that the
reactions of [Pt2(4-MeC6H4)4(μ-SEt2)2] with bidentate N-
donor ligands 2,6-Cl2C6H3CHNCH2CH2NMe2 and 2-
XC6H4CHNCH2CH2NMe2 (X = Cl or Br) lead to
coordination of the ligand followed by intramolecular C-X (X
= Cl or Br) oxidative addition. The process produces the
cyclometalated platinum(IV) compounds of type 5-IV shown
in Scheme 1. Further reaction of these compounds in refluxing
toluene gives the seven-membered cyclometalated platinum(II)
c o mp o u nd s [P t C l ( 4 - M e C C 5 H 3 - 2 - C l C6 H 3 C H 
NCH2CH2NMe2)] (7-II-Cl,Cl)10 and [PtCl(4-MeCC5H3−
C6H4CHNCH2CH2NMe2)] (7-II-Cl,H)21 in a process
involving formation of a C−C bond between two aryl rings
and release of a toluene molecule. In contrast, the reactivity of
To prove the validity of this common mechanism as well as
to understand the factors governing the formation of either five
or seven-membered platinacycles, attempts to isolate and
characterize the proposed intermediates II were carried out.
Preliminary time-resolved experiments were conducted at
different temperatures to ascertain the best set of conditions
B
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Table 1. Selected Bond Lengths (Å) and Angles (deg) for the Structures Determined for Compounds 5-II-Br,H, E-II-Br,H, and
E-II′-Br,H with Estimated Standard Deviations
5-II-Br,H
E-II-Br,H
E-II′-Br,H
Pt−C(1)
Pt−N(1)
Pt−N(2)
Pt−Br
C(1)−Pt−N(2)
N(1)−Pt−N(2)
C(1)−Pt−Br
1.979(9)
2.167(7)
1.931(5)
2.438(1)
78.9(3)
85.5(2)
99.2(3)
96.3(2)
Pt−C(19)
Pt−N(1)
Pt−N(2)
Pt−Br
C(19)−Pt−N(1)
N(1)−Pt−N(2)
C(19)−Pt−Br
N(2)−Pt−Br
1.999(5)
2.065(4)
2.108(5)
2.426(9)
95.8(2)
81.6(2)
87.3(1)
95.3(1)
Pt−C(19)
Pt−N(1)
Pt−N(2)
Pt−Br
C(19)−Pt−N(2)
N(1)−Pt−N(2)
C(19)−Pt−Br
N(1)−Pt−Br
1.97(1)
2.21(1)
1.98(1)
2.417(2)
95.6(6)
81.3(5)
91.7(4)
95.3(1)
N(1)−Pt−Br
where each of the species was present in representative
amounts (see following sections). For example, the reactions of
5-IV-Cl,Cl and 5-IV-Cl,H in toluene at 70 °C were sampled
and monitored by 1H NMR spectra at different times. While for
5-IV-Cl,Cl, resonances assigned to an intermediate II-Cl,Cl
were only observed at the very beginning of the process, for 5-
IV-Cl,H, formation and build up of intermediate II-Cl,H was
clearly observed.
shorter than the distance to the carbon atoms available for
formation of seven membered platinacycles (Pt···C(15) = 4.880
Å and Pt···C(11) = 6.695 Å) which confirms the suitability of
II-Br,H as a precursor of five-membered cyclometalated
compound 5-II-Br,H. It is interesting to note that the NMR
data obtained for compound II-Br,H in solution are in good
agreement with the E-SP-4-3 arrangement determined by XRD.
In particular, the value of J(HCN−Pt) is characteristic of
both an E conformation of the imine and the presence of a C-
donor ligand trans to the same group, while the biphenyl
hydrogen closest to the platinum center (C(5)-H)) appears as a
downfield shifted doublet.24 Because of the presence of the
chelate amine-imine ligand, only isomers SP-4-3 and SP-4-2 are
possible; furthermore, a similar stability can be expected for
them based on the similar trans influence of amine and imine
ligands.4 Additionally, the imine group may adopt an E or a Z
conformation, thus producing four possible isomers, as shown
in Chart 1. Moreover, the dangling biaryl moiety may adopt
different rotational arrangements to reduce the steric hindrance
of these highly crowded complexes.
In view of the higher complexity of the behavior of species 5-
I V - B r , H ( [ P t B r ( 4 - M e C 6 H 4 ) 2 ( C C 5 H 4 C H 
NCH2CH2NMe2)]), its solution reactivity was studied more
thoroughly. The complex was dissolved in a 1:1 mixture of
toluene-methanol, and the mixture was heated at 45 °C. After
1
24 h, the H NMR spectra reveals that the solution contains
70% of compound II-Br,H and 20% of compound 5-II-Br,H,
along with other minor components; crystals of II-Br,H
suitable for X-ray analysis could be obtained directly from this
reaction mixture. In another experiment, compound 5-IV-Br,H
was dissolved in toluene and warmed at 60 °C for 36 h, under
these conditions the presence of 5-II-Br,H, along with two
isomeric forms of II-Br,H (later identified as Z- and E-SP-4-2)
were detected in solution. Orange crystals of compound 5-II-
Br,H were obtained from the mixture and crystallographically
characterized. The X-ray diffraction (XRD) studies on
compound 5-II-Br,H (Figure 1a, Table 1) show the presence
of a fused [5,5,6] tricyclic system formed by a five-membered
platinacycle, a [N,N′] chelate and a phenyl group of the biaryl
moiety. As found in related systems, the Pt-amine bond is
longer than the corresponding Pt-imine (2.167(7) Å vs
1.931(5) Å), and the smallest angles around the platinum are
those involving the chelate and the metalacycle (N(1)−Pt−
N(2) = 85.5(2) ° and N(2)−Pt−C(1) = 78.9(3) °). The results
clearly indicate that compound II-Br,H is formed from 5-IV-
Br,H in a reductive elimination process, leading to formation of
a biphenyl moiety, while compound 5-II-Br,H could be formed
in a subsequent process involving intramolecular C−H
activation, leading to a five-membered platinacycle concurrent
with toluene elimination.
From the final reaction mixture obtained in toluene at 95 °C,
the E-SP-4-2 form of the II-Br,H species (II′-Br,H) depicted in
Chart 1. Four Possible Isomers of the Compound Formed in
a
the Reductive Elimination Process from 5-IV-Br,H
As stated, complex II-Br,H formed in a reductive elimination
process from 5-IV-Br,H has been unequivocally characterized
by crystallography (Figure 1b, Table 1). As expected, a biphenyl
fragment is formed involving a para-tolyl ligand and the aryl
ring of the nitrogen ligand. The amine-imine ligand is
bidentate, and the square planar coordination around the
platinum is completed with a bromido, trans to the dimethyl-
amine moiety, and a para-tolyl ligand. The arrangement around
the imine fragment is E, which is the most favored to produce a
five-membered platinacycle through metalation at C(5). The
distance Pt···C(5) is 3.607 Å, in the range reported for
formation of this type of metalacycle22,23 and considerably
a
1H NMR data (CDCl3, δ in ppm; J(H−Pt) [in brackets] in hertz
(Hz), * not observed) for the imine, the methylene and the doublet, at
lowest field in the aromatic region, included.
C
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Scheme 2
Chart 1 could also be isolated and identified in solution given
the high value of J(HCN−Pt) = 152 Hz observed for the
imine proton, as well as for the doublet at δ = 9.15 ppm,
assigned to an aromatic proton vicinal to the platinum.
Similarly, Z-SP-4-2 form of the same species could also be
protons appear upfield because of their proximity to the biaryl
system.
From the general view of Chart 1, we can speculate that for
the isomers with a Z arrangement around the imine the distal
hydrogen atoms of the biaryl are closer to the platinum center
and, therefore, formation of a seven-membered platinacycle
should arise from these isomers. For the detection of these
proposed intermediates with a Z configuration, harsher
conditions were tested. After reacting for 2 h at 95 °C a
toluene solution of compound 5-IV-Br,H a complex mixture of
compounds was formed. The major component of the mixture
corresponds to the E-SP-4-2 form of compound II-Br,H, while
the five-membered cyclometalated compound 5-II-Br,H was
also present in significant quantities. Only small amounts of the
Z-SP-4-2 form of II-Br,H were present as well as the new
seven-membered platinacycle 7-II-Br,H. Longer reaction times
under the same conditions led to reaction mixtures with
decreasing proportions of E- and Z-SP-4-2 and increasing
amounts of both 5-II-Br,H and 7-II-Br,H. To attempt the
isolation of compound 7-II-Br,H, the reaction of [Pt2(4-
MeC6 H4 )4 (μ-SEt2 )2 ] with imine 2-BrC6 H4 CH
NCH2CH2NMe2 was carried out in refluxing toluene. After 6
h, workup of the reaction mixture gave, in addition to
compound 5-II-Br,H, a light yellow solid showing a 1H
NMR spectrum consistent with that expected for the Z-SP-4-3
isomeric form depicted in Chart 1. On increasing the reaction
time up to 16 h, a five-, 5-II-Br,H, and seven-membered
1
isolated and characterized by H NMR, with a much smaller
1
J(HCN−Pt) (80 Hz) value; the NOESY H−1H spectra
revealing cross-peaks between methylene and aromatic protons
support the Z conformation of the imine. From the solutions of
complex II′-Br,H good quality crystals could be isolated and
the corresponding XRD studies were conducted; Figure 1c and
Table 1 collect the structural data for the complex. As expected,
this compound is a geometrical isomer of compound II-Br,H
(E-SP-4-3, Chart 1) in which a para-tolyl ligand is trans to the
dimethylamine moiety, and the arrangement around the imine
fragment is E. As for isomer E-SP-4-3 discussed above, for E-
SP-4-2 the shorter distance of the platinum center to the
proximal C−H bond [Pt···C(7) = 3.500 Å] than to the distal
C−H bonds of the biphenyl [Pt···C(17) = 5.485 Å and
Pt···C(13) = 7.012 Å] indicates its suitability to act as a
precursor of five- rather than seven membered cyclometalated
compounds. While for E-SP-4-2, the Pt-imine bond length
(1.975(11) Å) is shorter than the Pt-amine distance (2.223(14)
Å) in agreement with the lower coordinating ability of amine
versus imine nitrogen atom, the reverse trend is observed for
compound E-SP-4-3, in which the Pt-imine (2.108(5) Å) is
slightly longer than the Pt-amine (2.066(5) Å) distance. This
result can be related to the larger trans influence of the para-
tolyl versus the bromido ligand. It is important to note that neat
solutions of E-SP-4-2 or Z-SP-4-2 in CDCl3 at room
temperature evolve in a few days to mixtures of both isomers,
the predominant species having a Z conformation, which
suggest a facile isomerization process favoring the less hindered
species.
1
platinacycle 7-II-Br,H mixture was detected by H NMR, the
5-II-Br,H:7-II-Br,H ratio being 4:1. Compound 7-II-Br,H
could not be isolated from these mixtures and was only
characterized in solution according to the data available for
analogous seven-membered platinacycles.10,21
Thus, the observed preparative results suggest that formation
of seven-membered platinacycles require both the SP-4-3/SP-4-
2 isomerization at the platinum center and E/Z rearrangement
to produce the required precursor. In contrast, formation of a
five-membered platinacycle can take place under milder
conditions from the E-SP-4-3 isomer formed on reductive
elimination from compounds of type 5-IV. In this respect it is
interesting to point out that a seven-membered platinacycle is
formed readily upon reaction of imine 2-BrC6H4CH
NCH2(4-ClC6H4) with [Pt2(4-MeC6H4)4(μ-SEt2)2],10 which
suggests that the required isomer is more easily formed for
imines containing just one nitrogen donor atom.
As indicated above, all the isomers shown in Chart 1 can be
1
readily identified by H NMR spectroscopy, since previous
studies carried out for compounds [PtCl2(ArCH
NCH2CH2NMe2)] or [PtPh2(ArCHNCH2CH2NMe2)] in-
dicate that larger J(HCN−Pt) values are expected for (i)
imine moieties trans to a halido ligand versus trans to a C-donor
ligand, and (ii) E versus Z conformation of the imine.17,24,25 In
addition, for these compounds, the aromatic hydrogen which is
close to the platinum atom in the E isomers appears as a
doublet shifted downfield, and for the Z isomers the methylene
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Figure 2. Eyring plots for the reactions observed by UV−vis monitoring of the two step process occurring on solution of 5-IV-Cl,H (a) and 5-IV-
Cl,Cl (b) in different solvents and temperatures.
Table 2. Kinetic and Thermal Activation Parameters for the Two Reaction Steps Observed for the Reaction of 5-IV-Cl,H, 5-IV-
Cl,Cl, and 5-IV-Br,H Leading to 7-II-Cl,H, 7-II-Cl,Cl, and 5-II-Br,H, Respectively
a
See text.
Kinetico-Mechanistic Studies on the Formation of
Seven-Membered 7-II-Cl,Cl and 7-II-Cl,H Metallacycles. It
is thus clear that a distinct reactivity is observed arising from the
Pt(IV) five-membered cyclometalated complexes [PtCl(4-
MeC6H4)2(2-ClCC5H3CHNCH2CH2NMe2)], [PtCl(4-
MeC6H4)2(CC5H4CHNCH2CH2NMe2)], and [PtBr(4-
MeC6H4)2(CC5H4CHNCH2CH2NMe2)] (Scheme 2). The
formation of these platinum(IV) compounds from the
corresponding Pt(II) [Pt(4-MeC6H4)2(2-X,YC6H3CH
NCH2CH2NMe2)] (X = Y = Cl; X = Cl, Y = H; X = Br, Y
= H) precursors has been recently studied kinetico-mechanis-
tically,15 and a detailed mechanistic study of the reactivity of the
final Pt(IV) cyclometalated complexes has been now pursued.
As indicated in the previous section, only compounds 5-IV-
Cl,Cl and 5-IV-Cl,H produced the expected seven-membered
cyclometalated complexes via the straightforward reductive
elimination/oxidative addition/reductive elimination reaction
sequence indicated in Scheme 2.8,10,21 As the reactivity of
compound 5-IV-Br,H was much more complex, initial studies
were conducted on the chloro analogues. Initial time-resolved
UV−vis spectroscopy of toluene solutions of complexes 5-IV-
Cl,Cl and 5-IV-Cl,H indicated that the process involves a
sequence with significant differences between the two
compounds. Although UV−vis spectral changes could be
associated with a two step process using SPECFIT for both
compounds,26 only for compound 5-IV-Cl,H could the build
up of an intermediate be detected spectroscopically; for
compound 5-IV-Cl,Cl only a small induction period could be
quantified. Figure 2 collects the Eyring plots derived for the
studies carried out for the two systems at different temper-
atures. In the figure the data of the reactions measured in ionic
liquid (Bmim)(NTf2) solvent is also included; the perfect
alignment with the data in toluene or xylene indicates the
expected absence of polar components in the transition states
involved in the process.27,28 Table 2 collects the relevant kinetic
and thermal activation parameters determined for the two steps
indicated.
The difference between the two systems is noticeable,
especially with reference to the slow step observed, as assigned
in Figure 2 and Table 2. If the fast reaction step corresponds to
the first reaction from the sequence indicated in Scheme 2, the
build up of the intermediate species in the 5-IV-X,Y → 7-II-
X,Y reaction should be seen which is only in agreement with
the spectroscopic data for the 5-IV-Cl,H → 7-II-Cl,H process.
For the reaction of the 5-IV-Cl,Cl the lack of an observable
intermediate indicates that a fast step is occurring after the first
slower process has started. Nevertheless, the detection of the
two processes indicates that the difference in rate constants
should not be very large, as effectively indicated in Table 2. To
confirm the above suppositions, as well as the probable II-X,Y
nature of the intermediate compound, parallel 1H NMR
monitoring of the reaction was conducted. For the 5-IV-Cl,H
→ 7-II-Cl,H process at 70 °C, sampling of the medium showed
the presence of II-Cl,H in its E form in the reaction medium
immediately after the reaction had started. On standing, species
7-II-Cl,H begins to appear in the reaction medium, and a
E
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Figure 3. Eyring plots for the reactions observed by UV−vis monitoring of the sequential process occurring on (a) solution of 5-IV-Br,H and (b)
solution of II-Br,H. Empty points toluene/xylene solutions, full points (Bmim)(NTf2) solution.
progressive disappearance of E-II-Cl,H occurs once the initial
5-IV-Cl,H complex has been totally consumed. However,
monitoring of the 5-IV-Cl,Cl → 7-II-Cl,Cl process indicates no
build up of the equivalent II-Cl,Cl complex, and the reaction
medium only ever shows the presence of the initial 5-IV-Cl,Cl
and final 7-II-Cl,Cl compounds.
thus not being rate determining in any case.2,17,32 The same
reasoning applies for the equivalent compounds where the
relative position of the X and tolyl ligands is reversed in the
square planar complex (see below).
Kinetico-Mechanistic Studies on the Spontaneous
Reaction of the Five-Membered 5-IV-Br,H Metallacycle.
As indicated in the sections above, as well as in previously
carried out studies,15 the spontaneous reaction of 5-IV-Br,H in
toluene solution, under the same conditions used for the
reaction of compounds 5-IV-Cl,Cl and 5-IV-Cl,H, showed a
rather different behavior. The UV−vis spectral monitoring of
the changes indicated a series of reaction steps that could be
properly evaluated once the correct temperature conditions had
been established. SPECFIT26 fitting of these spectral changes
to a series of three consecutive processes produced a set of
coherent spectral changes and rate constants. Figure 3a collects
the Eyring plots corresponding to the data collected in toluene
and (Bmim)(NTf2) solution. It should be noted that the initial
observation of these separate reactions steps, as well as their
optimal temperature and time conditions, have allowed the
isolation of the intermediate/dead end complexes indicated in
the above preparative section on this report. When the reaction
has been carried out using the isolated E-II-Br,H, indicated in
the previous sections (from mild reaction conditions), the
results have been very revealing as to the assignment of one of
the three steps appearing in Figure 3a. Figure 3b shows the
good agreement of the data from the spontaneous reaction of
this isolated E-II-Br,H in toluene or (Bmim)(NTf2) solution.
From the data it is clear that the reaction leading to the
reductively eliminated biphenyl ligand complex from 5-IV-Br,H
corresponds to the red squares/dashed line in Figure 3.
As for the reactions indicated in the same figure by the blue
and green line/symbols, the application of more forcing
reaction conditions on 5-IV-Br,H or E-II-Br,H showed the
presence of two compounds in all cases, even at very long
reaction times. It is thus clear that a consecutive fast+slow
reaction step sequence does not apply for the process observed.
The alternative slow+fast consecutive sequence can also be
discarded given the observation of both steps at low
temperature; the difference between the rates of the two
processes being too large for the kinetic measurement of an
induction period (1.5 × 10−5 versus 3.7 × 10−4 s−1 at 40
°C).33,34 The operation of two parallel processes is the only
possible explanation for the facts observed. A careful choice of
reaction conditions (as indicated in the first section of this
report) allowed the isolation from the reaction medium of the
new 5-membered cyclometalated Pt(II) complex, 5-II-Br,H, as
As a whole the general 5-IV-X,Y → 7-II-X,Y process seems
to occur in a rather different rate sequence despite the common
reactivity observed. For the Cl,H system the process is
triggered by a concerted reductive elimination of a biphenyl
moiety followed by a rate limiting distal C−H oxidative
addition reaction, and a fast reductive elimination of toluene
from the Pt(IV) hydride species formed.6,7 The absence of
differences in the reaction rates with the use of the
(Bmim)(NTf2) ionic liquid as the solvent confirms the
expected concerted nature of the processes occurring upon
decoordination of the -NMe2 moiety to form the 14/16
electron intermediates required by the microreversibility
principle.15,17,20 The values determined for ΔH⧧ and ΔS⧧
agree with such mechanism given the need of a Pt(IV/II)-
NMe2 bond dissociation in both steps, when compared with the
more facile loss of a SMe2 ligand.12,29,30 For the analogous
Cl,Cl complex system the initial reductive elimination of the
biphenyl moiety is the slower reaction in the process, being rate
limiting. The distal C−H oxidative addition reaction (and
consequent rapid reductive elimination of toluene from the
Pt(IV) hydride species formed) represents a faster process (see
Table 2). It is clear that the change from Y = H to Y = Cl
produces dramatic differences in the relative rates of the
processes observed, as well as in the general rate of the full
process (see Table 2). The most plausible explanation for the
facts observed are related to the already indicated intra-
molecular hydrogen bonding possibility between the -NCH-
hydrogen and the Y = Cl substituent in complex 5-IV-
Cl,Cl,15,17,31 not possible for Y = H. Thus for this species the
biphenyl reductive elimination reaction should be somehow
hampered when compared with that occurring on the 5-IV-
Cl,H compound (3.4 × 10−5 versus 9.1 × 10−5 s−1 at 67 °C,
Table 2). Furthermore, if the structure of the two possible II-
Cl,Y intermediates (E and Z) are compared, steric factors
should produce a much higher effective concentration of the
correctly positioned Z-form species indicated at the bottom of
Scheme 2 for Y = Cl with respect to that for Y = H, thus
producing a higher biphenyl C−H oxidative addition rate (29 ×
10−5 versus 0.29 × 10−5 s−1 at 67 °C, Table 2). It should also be
taken into account that the Z ⇆ E isomerization process should
be rather fast under the conditions of the reactions studied,
F
dx.doi.org/10.1021/ic3023584 | Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
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Scheme 3
well as the new E-II′-Br,H compound differing from E-II-Br,H
in Scheme 2 by the relative trans Br/tolyl position in the square
planar environment of the Pt(II) (see Chart 1). Given the fact
that compound 5-II-Br,H is a dead-end, as far as the formation
of E-II′-Br,H is concerned, the process leading to this proximal
cyclometalated derivative should correspond to the slower step
of the set observed (green circles/dotted line). The reaction
indicated by the blue triangles/solid line corresponds then to
the II-Br,H ⇆ II′-Br,H isomerization equilibrium process.
Table 2 collects the kinetic and thermal activation parameters
corresponding to the C−H bond activation related processes,
and Scheme 3 summarizes the reactivity observed for this
system (considering that the Z ⇆ E isomerization process
should be rather fast under the conditions of the reactions
studied).
It seems that under these conditions, as stated, the activation
of the proximal C−H bond of compound E-II-Br,H producing
5-II-Br,H is preferred to that of the distal activation, in the Z
form, leading to a possible 7-II-Br,H. The relatively facile II-
Br,H ⇆ II′-Br,H isomerization equilibrium process can only be
held responsible for this fact if the Z-II′-Br,H form is also less
reactive in the formation of the 7-II-Br,H species. The kinetic
and thermal activation parameters collected in Table 2 indicate
that while the values determined for the ΔH⧧ and ΔS⧧
corresponding to the reductive elimination process are in line
of those found for the other two systems in the previous
section, those for the proximal C−H bond activation to form
the new 5-II-Br,H show an activation enthalpy more favorable,
despite the higher degree of ordering needed for the process to
take place (as expected). As for the values of the activation
parameters determined for the II-Br,H ⇆ II′-Br,H isomer-
ization process, collected in Table 2, it is clear that the reaction
is not related to a rate limiting highly dissociative sequence.35
The very negative value determined for ΔS⧧, as well as the low
activation enthalpy, indicate a highly ordered transition state
that does not correlate with a limiting dissociation of the
ancillary -NMe2 group,36 followed by the reorganization of the
14 electron species formed has been established for Pd(II)
complexes.37,38 The alternative dissociation of the bromido
ligand adds up the improbable formation of ionic species in
toluene to the above-mentioned factors.
II′-Br,H isomerization process appears to be slowed down
considerably (isokinetic temperature for the 5-IV-Br,H → 5-II-
Br,H and II-Br,H ⇆ II′-Br,H being ca. 90−95 °C, Figure 3),
led us to the study of the reaction of the isolated II′-Br,H
complex under much harsher conditions. Effectively, the
previously indicated preparative procedures show that com-
pound 7-II,Br,H can be obtained from toluene solutions of 5-
IV-Br,H after 6 h in refluxing toluene.
It seems thus clear that under conditions where the back
isomerization from the SP-4-2 II′-Br,H to the SP-4-3 II-Br,H
analogue is slow enough, the seven-membered Pt(II) cyclo-
metalated 7-II-Br,H compound (Scheme 2) is formed, thus
indicating that this reaction occurs on the Z-SP-4-2 isomers of
this complex. The distinct reactivity of the family of complexes
studied (i.e., 5-IV-Cl,Cl, 5-IV-Cl,H, and 5-IV-Br,H) can then
be solely related to the feasibility of a favorable SP-4-3 to SP-4-
2 isomerization for II-Cl,Cl and II-Cl,H complexes, as already
reported for some Pd(II) complexes,5 that allows the formation
of the 7-II-X,Y compounds without the appearance of the 5-II-
Cl,H species formed from the proximal C−H bond activation,
when X = Cl and Y = H. Scheme 4 summarizes the complete
reactivity observed for the compounds studied. The distinct
isomerization reactivity from 5-IV-Cl,H and 5-IV-Br,H remains
the only point that still needs some explanation. The evaluation
of the relative trans influence of the chlorido and bromido
ligands39 indicates that the weakening of the Pt-NMe2 cannot
be held responsible for the facts. This observation is in line with
the thermal activation parameters indicated in Table 2 plus the
fact that dissociation of this ancillary group should lead to the
C−H bond activation process.13,15,20,40,41 An alternative
associative triggered isomerization mechanism would be much
more in line with the activation parameters obtained, as well as
with the fact that only a Pt−C bond exists in the complex, thus
disfavoring a dissociatively activated general substitution
reactivity of the complexes.42,43,43,44 A possible C−H···Pt
agostic interaction of a correctly positioned phenyl ring (see
Scheme 3) in the empty axial position could generate a
transient pentacoordinated species capable of undergoing a
rotation and establishing the SP-4-3 ⇆ SP4−2 equilibrium
observed under the reaction conditions.45,46 Clearly the
presence of a more sterically demanding bromido ligand should
produce a hampering of the process with respect to X = Cl,
The fact that compound II′-Br,H could be isolated from the
reaction mixtures, and that at high temperatures the II-Br,H ⇆
G
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Inorganic Chemistry
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Scheme 4
(Universitat de Barcelona) in a LC/MSD-TOF spectrometer using
H2O−CH3CN 1:1 to introduce the sample. NMR spectra were
performed at the Unitat de RMN d’Alt Camp de la Universitat de
Barcelona using a Mercury-400 spectrometer and referenced to SiMe4.
δ values are given in ppm and J values in Hz. Abbreviations used: s =
singlet; d = doublet; t = triplet; m = multiplet; br = broad. For
numbering used for NMR spectra assignments, see Chart 2.
Compounds. Compounds cis-[Pt(4-C6H4Me)2(μ-SEt2)]2,47 5-IV-
Cl,Cl, 5-IV-Cl,H, 5-IV-Br,H, 7-II-Cl,Cl, and 7-II-Cl,H were prepared
as reported elsewhere.10,15,21
thus slowing down the reaction and enabling the direct II-Br,H
→ 5-II-Br,H metalation reaction.
Finally the regioselective formation of seven-membered
metallacycles from complexes II′-X,Y also needs some
explanation, given the fact that the expected preferential
formation of five-membered compounds has been observed in
this work from II-Br,H, as well as in previous reports with
similar complexes.7 The overall results indicate that the Z-SP-4-
2 form of the series of complexes [PtX(Ar)(Ar−Ar′CH
NCH2CH2NMe2)] (Scheme 4) is the only reacting form
producing such seven-membered compounds; the much more
hindered nature of this isomeric form forces the biphenyl ligand
to adopt a Z positioning, thus facilitating the formation of 7-II
type metallacycles observed. The only five-membered biphenyl
compounds are obtained in situations where the SP-4-3
arrangement is favored.
II-Cl,Cl (E-SP-4-3-[PtCl(4-MeC6H4){2-(4-MeC6H4)6-ClC6H3CH
NCH2CH2NMe2}]). This compound was detected in solution when
the reaction of compound 5-IV-Cl,Cl to produce 7-II-Cl,Cl carried
out in toluene at 70 °C was monitored by 1H NMR. 1H NMR
(CDCl3, 400 MHz): δ = 8.75 [s, br, 1H, CHN]; 8.05 [dd, 3J(H−H) =
4
3
4
8.0, J(H−H) = 2.0, 1H]; 8.03 [dd, J(H−H) = 7.6, J(H−H) = 1.2,
3
1H]; 7.30−7.32 [m, 1H]; 7.28 [d, J(H−H) = 7.6, 2H]; 7.15 [d,
3J(H−H) = 7.2, 2H]; 2.77 [s, 6H, NMe2]; 2.39 [s, 3H, Me]; 2.25 [s,
3H, Me].
CONCLUSIONS
II-Cl,H (E-SP-4-3-[PtCl(4-MeC6H4){2-(4-MeC6H4)C6H4CH
NCH2CH2NMe2}]). A 50 mg portion of [Pt(4-MeC6H4)2(2-
ClC6H4CHNCH2CH2NMe2] were dissolved in toluene (10 mL)
and the solution was heated at 70 °C for 2 h. After this time, 20 mg of
7-II-Cl,H were filtered off, and the toluene was concentrated to half-
volume. Crystals of II-Cl,H, slightly unpurified with 7-II-Cl,H, were
■
From the data collected on the solution behavior of complexes
5-IV-X,Y (Scheme 4) it is clear that a rather fine-tuning of the
reactivity occurs with respect to the formation of the alternative
7-II,X,Y or 5-II,X,H complexes. A common reductive
elimination reaction occurs to form compounds E-II-X,Y,
which should lead to the formation of complexes 5-II-X,Y (as
observed for 5-II-Br,H), since the facile equilibration reaction
to Z-II-X,H leading directly to complexes 7-II-X,H does not
occur. Nevertheless, the actuation of a fast SP-4-3 ⇆ SP-4-2
(II-X,Y ⇆ II′-X,Y) isomerization process for X = Cl prevents
this 5-II-X,Y formation process. In this case the rapidly
equilibrated II′-X,Y compounds establish a E ⇆ Z equilibrium,
and the Z form (the major component detected in the
preparative procedures) produces exclusively the final 7-II-X,Y
compounds.
1
formed. The solution was concentrated to dryness and a H NMR in
CDCl3 was taken showing the presence of isomers E-SP-4-3, E-SP-4-2
and Z-SP-4-2. 1H NMR (CDCl3, 400 MHz): (E-SP-4-3): δ = 9.01 [d,
3
3J(H−H) = 7.2, 1H]; 8.56 [s, J(H−Pt) = 32.0, 1H, CHN]; 7.54 [t,
3J(H−H) = 8.0, 1H]; 7.52 [t, 3J(H−H) = 8.0, 1H]; 7.35 [d, 3J(H−H)
= 8.0, 4H]; 7.24 [d, 3J(H−H) = 8.0, 2H]; 7.18−7.14 [m, 1H]; 6.83 [d,
3J(H−H) = 8.0, 2H]; 3.81 [t, 2J(H−H) = 5.0, 2H]; 2.85 [s, 6H,
NMe2]; 2.70 [m, 2H]; 2.41 [s, 3H, Me]; 2.25 [s, 3H, Me]. (E-SP-4-2):
δ = 9.22 [d, J(H−H) = 8.0]; 8.33 [s, J(H−Pt) = 146]. (Z-SP-4-2): δ =
8.69 [s].
II-Br,H (E-SP-4-3-[PtBr(4-MeC6H4){2-(4-MeC6H4)C6H4CH
NCH2CH2NMe2}]). A 200 mg portion (0.31 mmol) of 5-IV-Br,H was
dissolved in 60 mL of a 1:1 mixture of toluene-methanol, and the final
solution was heated at 46 °C for 36 h. The solution was concentrated
at low pressure and the solid precipitated by adding 15 mL of ether.
Recrystallization in acetone at room temperature affords 56 mg of
compound II-Br,H. 1H NMR (CDCl3, 400 MHz): δ = 8.91 [d, 3J(H−
EXPERIMENTAL SECTION
General Information. Microanalyses were performed at the
■
Serveis Cientifico-Tec
mass spectra were performed at the Servei d’Espectrometria de Masses
̀
nics (Universitat de Barcelona). Electrospray
H
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Chart 2. Numbering Used for NMR Spectra Assignments
3
H) = 8.0, 1H, Ha]; 8.56 [s, J(H−Pt) = 32.0, 1H, CHN]; 7.53 [t,
3J(H−H) = 4.0, 2H, CH2]; 2.98 [s, 6H, NMe2]; 2.42 [s, 3H, Me]; 2.11
3J(H−H) = 8.0, 1H, Hb or c]; 7.46 [t, 3J(H−H) = 8.0, 1H, Hb or c]; 7.38
3
[t, J(H−H) = 4.0, 2H, CH2]; 1.26 [s, 3H, Me].
[d, 3J(H−H) = 8.0, 2H]; 7.36−7.25 [m, 5H]; 6.81 [d, 3J(H−H) = 8.0,
2H]; 3.83 [t, 3J(H−H) = 4.0, 2H, CH2]; 2.85 [s, 3J(H−Pt) = 24.0, 6H,
NMe2]; 2.71 [t, 3J(H−H) = 4.0, 2H, CH2]; 2.41 [s, 3H, Me]; 2.25 [s,
3H, Me]. ESI(+)-MS, m/z: 650 [M + NH4]; 541 [M + PhMe]; 460
[M − PhMe-Br].
5-II-Br,H. A solution of 5-IV-Br,H (190 mg, 0.3 mmol) in 16 mL of
toluene was heated at 60 °C for 36 h. After this time, the solution was
1
concentrated at low pressure and analyzed by H NMR showing the
presence of species 5-II-Br,H, and II′-Br,H (Z and E isomers).
1
Recrystallization allows isolation of orange crystals of 5-II-Br,H. H
II′-Br,H (Z-SP-4-2-[PtBr(4-MeC6H4){2-(4-MeC6H4)C6H4CH
NCH2CH2NMe2}]). A 50 mg portion of 5-IV-Br,H was dissolved in
toluene and heated at 95 °C for 2 h. The solvent was removed, and the
residue was crystallized in CH2Cl2-MeOH, leading to a first crop of
compound 5-II-Br,H, followed by a second crop of II′-Br,H. 1H NMR
(CDCl3, 400 MHz): δ = 8.46 [s, 3J(H−Pt) = 80.0, 1H, CHN]; 7.51 [t,
NMR (CDCl3, 400 MHz): δ = 8.37 [s, 3J(H−Pt) = 148.0, 1H, CHN];
7.92 [d, 3J(H−H) = 8.0, 3J(H−Pt) = 40.0, 1H, Ha]; 7.26 [m, 1H, Hb];
7.22 [s, 4H, Hd,e]; 6.90 [d, 3J(H−H) = 8.0, 1H, Hc]; 4.00 [t, 3J(H−H)
3
3
= 4.0, J(H−Pt) = 36, 2H, CH2]; 3.07 [t, J(H−H) = 4.0, 2H, CH2];
3
2.93 [s, J(H−Pt) = 12.0, 6H, NMe2]; 2.40 [s, 3H, Me]. ESI(+)-MS,
541.0 [M+H], 501.2 [M-Br+CH3CN], 460.0 [M-Br]. Anal. Calc. for:
C18H21BrN2Pt: C: 40.01; H: 3.92; N: 5.18%. Found: C: 39.94; H:
4.04; N: 4.87%
3J(H−H) = 8.0, 1H, Hb or c]; 7.41 [d, J(H−H) = 8.0, 1H, Ha or d];
3
7.35 [t, 3J(H−H) = 8.0, 1H, Hb or c]; 7.34 [d, 3J(H−H) = 8.0, 2H, Hf];
7.23 [d, J(H−H) = 8.0, 1H, Ha or d]; 7.09 [d, J(H−H) = 8.0, 4H,
7-II-Br,H. This compound was characterized by H NMR in the
3
3
1
Hg,e]; 6.71 [d, J(H−H) = 8.0, 2H, Hh]; 3.39 [td, J(H−H) = 12.0,
reaction mixture obtained when 5-IV-Br,H (20 mg) were heated in
3
2
3J(H−H) = 4.0, 2H, CH2]; 2.77 [s, 6H, NMe2]; 2.47 [s, 3H, Mea];
refluxing toluene for 16 h. 1H NMR (CDCl3, 400 MHz): δ = 8.74 [s, 3
3
4
2.28 [t, 3J(H−H) = 4.0, 2H, CH2]; 2.20 [s, 3H, Meb]. ESI(+)-MS, m/
z: 1282.26 [2 M + NH4]; 654.00 [M + Na]; 650.15 [M + NH4].
II′-Br,H (E-SP-4-2-[PtBr(4-MeC6H4){2-(4-MeC6H4)C6H4CH
NCH2CH2NMe2}]). A 50 mg portion of 5-IV-Br,H was dissolved in
toluene and heated at 95 °C for 2 h. The solvent was partially
removed, and the solution was cooled. Light yellow crystals of II′-
Br,H were formed. 1H NMR (CDCl3, 400 MHz): δ = 9.15 [d, 3J(H−
J(H−Pt) = 156.0, 1H, CHN]; 7.61 [td, J(H−H) = 7.6, J(H−H) =
3
1.6, 1H]; 7.55 [s, 1H]; 7.50 [d, J(H−H) = 7.6, 1H]; 6.80 [m, 2H];
4.47 [td, J(H−H) = 12; 4.0, 1H, CH2]; 3.81 [dd, 3J(H−H) = 12; 4.0,
1H, CH2]; 3.02 [s, 3H, NMe2]; 2.74 [s, 3H, NMe2]; 2.57 [dd, 3J(H−
H) = 12.0; 4.0, 2H, CH2]; 2.30 [s, 3H, Me].
Kinetics. The kinetic profiles for the reactions were followed by
UV−vis spectroscopy in the 700−300 nm range on HP8452A or
Cary50 instruments equipped with thermostatted multicell transports.
Observed rate constants were derived from absorbance versus time
traces at the wavelengths where a maximum increase and/or decrease
of absorbance were observed. The calculation of the observed rate
constants from the absorbance versus time monitoring of reactions,
studied under second or first order concentration conditions, were
carried out using the SPECFIT software.26 The general kinetic
technique is that previously described.6,15,48 Supporting Information,
Table S1 collects all the obtained kobs values for all the systems studied
as a function of the starting complex, process studied, and temperature.
All post-run fittings were carried out by the standard available
commercial programs.
X-ray Structure Analysis. Prismatic crystals were selected and
mounted on a MAR345 diffractometer with an image plate detector
(E-II-Br,H and 5-II-Br,H) or on an Oxford Diffraction Gemini CCD
diffractometer employing an Oxford Cryosystems Series 600 Cryo-
stream Cooler (E-II′-Br,H). The structures were solved by direct
methods using the SHELXS computer program and refined by the full-
matrix least-squares method, with the SHELXL97 computer
program.49,50 All hydrogen atom positional parameters were computed
and refined using a riding model, with an isotropic temperature factor
H) = 8.0, 1H, Ha]; 8.42 [s, J(H−Pt) = 152.0, 1H, CHN]; 7.33 [td,
3
3J(H−H) = 7.2, 4J(H−H) = 1.6, 1H, Hb or c]; 7.26 [d, 3J(H−H) = 8.0,
2H]; 7.18 [td, J(H−H) = 7.6, J(H−H) = 1.2, 1H, Hb or c]; 7.15 [d,
3
4
3J(H−H) = 8.0, 2H]; 7.05 [dd, J(H−H) = 7.6, J(H−H) = 1.2, 1H,
3
4
Hd]; 6.92 [d, 3J(H−H) = 8.0, 2H]; 6.34 [d, 3J(H−H) = 8.0, 2H]; 4.15
[t, 3J(H−H) = 4.0, 2H, CH2]; 2.98 [s, 6H, NMe2]; 2.62 [t, 3J(H−H) =
4.0, 2H, CH2]; 2.42 [s, 3H, Me]; 1.91 [s, 3H, Me]. ESI(+)-MS, m/z:
1282.26 [2 M + NH4]; 650.15 [M + NH4]. Anal. Calc. for:
C25H29BrN2Pt: C: 47.47; H: 4.62; N: 4.43%. Found: C: 47.24; H:
4.54; N: 4.39%.
II-Br,H (Z-SP-4-3-[PtBr(4-MeC6H4){2-(4-MeC6H4)C6H4CH
NCH2CH2NMe2}]). A 50 mg portion of 5-IV-Br,H was dissolved in
20 mL of toluene, and the solution was refluxed for 6 h. The solvent
was removed, and the residue was crystallized in CH2Cl2-MeOH,
leading to a first crop of compound 5-II-Br,H, followed by a second
1
crop of II-Br,H as pale yellow solid (15 mg). H NMR (CDCl3, 400
MHz): δ = 9.78 [s, 1H, CHN]; 7.59 [td, J(H−H) = 7.6, 4J(H−H) =
3
1.2, 1H, Hb or c]; 7.52 [d, J(H−H) = 8.0, 2H]; 7.45 [td, J(H−H) =
3
3
8.0, J(H−H) = 1.2, 1H, Hb or c]; 7.38 [d, J(H−H) = 7.2, 2H]; 7.34
[d, 3J(H−H) = 8.0, 2H]; 7.18 [d, 3J(H−H) = 8.0, 2H]; 7.09 [d, 3J(H−
4
3
H) = 8.0, 1H, Ha or d]; 6.71 [d, J(H−H) = 8.0, 1H, Ha or d]; 3.32 [t,
3
I
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Inorganic Chemistry
Article
Table 3. Crystallographic and Refinement Data for Compounds 5-II-Br,H, E-II-Br,H, and E-II′-Br,H
5-II-Br,H
E-II-Br,H
E-II′-Br,H
formula
C18H21BrN2Pt
540.37
2C25H29BrN2Pt·CH3OH
1297.05
C25H29BrN2Pt
632.50
Fw
temp, K
173(2)
293(2)
173(2)
wavelength, Å
crystal system
space group
a, Å
0.71073
0.71073
1.54180
orthorhombic
P21cn
monoclinic
C2/c
tetragonal
I 41/a
9.734(5)
14.922(6)
12.734(5)
27.778(11)
15.491(5)
13.504(3)
109.51(2)
5477(3); 4
1.573
21.655(4)
b, Å
c, Å
20.826(7)
β, deg
V, Å3 ; Z
d (calcd), Mg/m3
abs coeff, mm−1
F(000)
1850(1); 4
1.941
9767 (4); 16
1.721
9.745
6.597
12.747
1024
2520
4896
rflns coll./ unique
16733/4767
[R(int) = 0.0603]
4767/4/200
1.089
26357/7970
[R(int) = 0.0888]
7970/4/283
1.115
11220/3875
[R(int) = 0.0457]
3875/0/266
1.036
data/restraint/parameter
GOF on F2
final R [I > 2σ(I)]
R1 = 0.0495
wR2 = 0.1308
R1 = 0.0529
wR2 = 0.1357
1.521 and −3.182
904051
R1 = 0.0514
wR2 = 0.1545
R1 = 0.0591
wR2 = 0.1623
2.571 and −2.077
904052
R1 = 0.0622
wR2 = 0.1658
R1 = 0.0914
wR2 = 0.1962
2.692 and −1.361
901843
R (all data)
peak and hole, e Å−3
CCDC reference no.
equal to 1.2 times the equivalent temperature factor of the atom to
which they are linked; further details are given in Table 3.
(8) Crespo, M.; Font-Bardia, M.; Calvet, T. Dalton Trans. 2011, 40,
9431−9438.
(9) Crespo, M.; Calvet, T.; Font-Bardia, M. Dalton Trans. 2010, 39,
6936−6938.
ASSOCIATED CONTENT
* Supporting Information
■
(10) Martín, R.; Crespo, M.; Font-Bardia, M.; Calvet, T. Organo-
metallics 2009, 28, 587−597.
S
Table S1 with values of kobs for all the systems studied as a
function of temperature and solvent. This material is available
free of charge via the Internet at http://pubs.acs.org.
(11) Crespo, M.; Font-Bardia, M.; Solans, X. Organometallics 2004,
23, 1708−1713.
(12) Crespo, M.; Anderson, C. M.; Kfoury, N.; Font-Bardia, M.;
Calvet, T. Organometallics 2012, 31, 4401−4404.
AUTHOR INFORMATION
Corresponding Author
*E-mail: margarita.crespo@qi.ub.edu (M.C.), manel.martinez@
qi.ub.edu (M.M.).
́ ́
(13) Calvet, T.; Crespo, M.; Font-Bardía, M.; Gomez, K.; Gonzalez,
■
G.; Martínez, M. Organometallics 2009, 28, 5096−5106.
(14) Albert, J.; Bosque, R.; Crespo, M.; Granell, J.; Rodríguez, J.;
Zafrilla, J. Organometallics 2010, 29, 4619−4627.
(15) Calvet, T.; Crespo, M.; Font-Bardía, M.; Jansat, S.; Martínez, M.
Organometallics 2012, 31, 4367−4373.
Notes
The authors declare no competing financial interest.
(16) Granell, J.; Martínez, M. Dalton Trans. 2012, 41, 11243−11258.
(17) Crespo, M.; Font-Bardía, M.; Granell, J.; Martínez, M.; Solans,
X. Dalton Trans. 2003, 3763−3769.
ACKNOWLEDGMENTS
Financial support from projects CTQ2012-37821-C02-01 and
CTQ2009-11501 from the Spanish Ministerio de Ciencia e
■
(18) Crespo, M.; Martínez, M.; de Pablo, E. J. Chem. Soc., Dalton
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Organometallics 1992, 11, 1288−1295.
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