Cyclometallated platinum(ii) complexes: Oxidation to, and C-H activation by, platinum(iv)

Article abstract of DOI:10.1039/b705609e

A series of cyclometallated phenylpyridine platinum(ii) complexes have been synthesised with a systematic variation in both the phenylpyridine and the ancillary ligand. Oxidation of one of the cyclometallated species leads to a number of isomeric platinum(iv) complexes, all of which eventually isomerise to a single compound. The route to these new compounds has been demonstrated to involve an initial slow oxidation followed by a rapid C-H activation to give doubly cyclometallated complexes. The solid state structures of a number of both the platinum(ii) and the platinum(iv) species have been solved; many of the structures exhibited extended interactions that result in complex three dimensional packing. The Royal Society of Chemistry.

Full text of DOI:10.1039/b705609e

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PAPER
www.rsc.org/dalton | Dalton Transactions
Cyclometallated platinum(II) complexes: oxidation to, and C–H activation by,
platinum(IV)†‡
Christopher P. Newman, Katherine Casey-Green, Guy J. Clarkson, Gareth W. V. Cave, W. Errington and
Jonathan P. Rourke*
Received 13th April 2007, Accepted 17th May 2007
First published as an Advance Article on the web 15th June 2007
DOI: 10.1039/b705609e
A series of cyclometallated phenylpyridine platinum(II) complexes have been synthesised with a
systematic variation in both the phenylpyridine and the ancillary ligand. Oxidation of one of the
cyclometallated species leads to a number of isomeric platinum(IV) complexes, all of which eventually
isomerise to a single compound. The route to these new compounds has been demonstrated to involve
an initial slow oxidation followed by a rapid C–H activation to give doubly cyclometallated complexes.
The solid state structures of a number of both the platinum(II) and the platinum(IV) species have been
solved; many of the structures exhibited extended interactions that result in complex three dimensional
packing.
Introduction
Results and discussion
The study of the cyclometallation reaction is of considerable
interest from a mechanistic point of view1 because of its role
in the functionalisation of C–H bonds,2–6 and because of the
use of the derived complexes.7–9 We have recently published a
couple of papers dealing with the mono- and di-cycloplatination
of diphenylpyridines where we developed a high yielding route
to CNC triply coordinating complexes,10,11 another one that dealt
with the unusual situation that can lead to the formation of a
carbene species, rather than a cyclometallated species12 and a
comparison of the cyclometallation of pyridazine by palladium
and platinum.13 To date, the vast majority of cycloplatination reac-
tions have involved starting with, and ending up with platinum(II)
species, though other examples have platinum(IV) species being
formed by oxidative addition to these platinum(II) complexes.14–17
Such platinum(IV) species are proving to be of increasing interest,
including use as sensors18 and as models for the Fischer–Tropsch
synthesis.19
Even though the reductive elimination of hydrocarbons from
platinum(IV), which can be seen as analogous to the reverse
of a C–H activation, has been widely studied,20–25 and the
Pt(II)/Pt(IV) redox cycle has been investigated as a model for the
activation of C–H bonds,26,27 there have been few reports of C–
H activation by a platinum(IV) centre to date.28–31 Here we report
the synthesis of some cyclometallated platinum(II) compounds
derived from substituted phenylpyridines and discuss the reactivity
of these complexes with respect to oxidation. We also report the
generation of new platinum(IV) species that can only have arisen
from the cyclometallation (C–H activation) of other platinum(IV)
species.
Synthesis of the Pt(II) complexes
The reaction of 2-phenylpyridine, 1a, with platinum to give
cyclometallated products 2a and 3a, Scheme 1, has been previously
reported by Ford.32 In a 1995 paper he reported the synthesis,
structure and some spectroscopic properties of a couple of
derivatives (X = H, Me), and we have largely followed his
synthetic procedure. However, we found it easier to achieve
high yields by intentionally isolating the mixed cyclometallated-
pendant phenylpyridine complex 2, a minor by-product in Ford’s
methodology. This intermediate can conveniently be converted
to complexes 3, 4, 5 and 6 by the displacement of the pendant
phenylpyridine, Scheme 1. In order to vary the electronic proper-
ties of our complexes, we used two substituted 2-phenylpyridines
(2-(4-methoxy- and 2-(4-fluorophenyl)pyridine) in addition to
2-phenylpyridine. In each case we were able to isolate the
mixed cyclometallated-pendant phenylpyridine complex 2 in high
(>80%) yield. Spectroscopic properties were similar to Ford’s,
and additionally we isolated crystals of X-ray quality of the 2-
(4-fluorophenyl)pyridine derivative 2b. The structure of 2b, Fig. 1,
was similar to that of 2a, previously reported by Ford, and is
discussed in more detail below.
Department of Chemistry, Warwick University, Coventry, UK CV4 7AL.
E-mail: j.rourke@warwick.ac.uk
Scheme 1
† The HTML version of this article has been enhanced with colour images.
‡ CCDC reference numbers 643939–643945. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/b705609e
Displacement of the pendant phenylpyridine by other ligands
proved a convenient method for the synthesis of other derivatives.
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Fig. 3 The X-ray structure of 5b.
Fig. 1 The X-ray structure of 2b, ellipsoids at 50% probability.
In addition to the carbonyl derivatives 3 mentioned by Ford, which
are synthesised via the bubbling of CO gas through a solution of
2, we were also able to isolate the dmso derivatives 4, ammonia
derivatives 5 and pyridine derivatives 6. A high concentration of
incoming ligand is necessary, and we found it most convenient to
dissolve complexes 2 in dmso or pyridine to synthesise complexes
4 and 6. We found it difficult to isolate the ammonia derivatives 5
in high yield directly from the pendant phenylpyridine complexes
2 by bubbling ammonia gas through a solution of 2 and found
that going via the dmso derivatives gave a higher (>70%) yield.
Ford had previously reported the X-ray structure of the carbonyl
complex 3a, and we solved the crystal structures of the dmso,
ammonia and pyridine complexes 4b, Fig. 2, 5b, Fig. 3, and 6b,
Fig. 4. In all cases, the new ligand is confirmed as having directly
replaced the phenylpyridine and is found trans to the pyridine
nitrogen. The structures are discussed in more detail below.
Fig. 4 The X-ray structure of 6b, ellipsoids at 50% probability.
Spectroscopic properties of the Pt(II) complexes
One feature of note in the NMR spectra of complexes 2, 3, 4,
5 and 6 is the effect of changing the co-ligand on the chemical
shift of the hydrogen adjacent to the coordinated carbon of the
cyclometallated phenylpyridine. In the fluorinated complexes this
proton resonates at 5.70 ppm for the pendant phenylpyridine
complex 2b, 7.10 ppm for carbonyl complex 3b, 8.05 ppm for dmso
complex 4b, 6.85 ppm for ammonia complex 5b and 5.9 for the
pyridine complex 6b. In the crystal structures of 2a, 2b and 6b, this
hydrogen is seen to point directly into the centre of the adjacent
pyridine ring and this is the likely cause of its relatively high
shielding. On the other hand, it is presumably the proximity of this
hydrogen to the carbon to oxygen triple bond (in 3b) or the sulfur
to oxygen double bond (in 4b) that results in the deshielding of this
proton that is observed in these complexes. A similar variation is
seen for the non-fluorinated and methoxy substituted complexes.
3
The JPtH of this hydrogen is close to 55 Hz for all complexes,
except the carbonyl complex, where it is 77 Hz. If we consider
the well known p-acidity of the carbonyl group, we can see that
reducing electron density at the metal centre by the carbonyl could
be compensated by a strengthening of the bond from the phenyl
ring to the platinum, leading to an increased coupling constant.
4
Fig. 2 The X-ray structure of 4b, ellipsoids at 50% probability.
Interestingly, the JPtF shows the opposite effect: it is 40 Hz in
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carbonyl complex 3b, but 57 Hz for the pendant phenylpyridine
complex 2b, the ammonia complex 5b and the pyridine complex 6b
and 56 Hz for the dmso complex 4b. The lower value of the 4JPtF
coupling constant for the carbonyl complex can be rationalized
on the basis of stronger p-bonding to the carbonyl leading to a
stronger p-bonding from the F, and this resulting in a weaker
r-bond from the F to the aromatic ring (leading to a reduced
coupling constant).33
The stretch of the carbonyl group in complexes 3 is clearly
visible in their infrared spectra and this allows us to quantify
the effect of changing the substituents on the cyclometallated
phenylpyridine. The carbonyl stretch has values of 2104 cm−1,
2108 cm−1 and 2101 cm−1 for 3a, 3b and 3c respectively. This
variation is easily explained in terms of a change in electron
donating ability of the cyclometallated phenylpyridine: relative to
complex 3a, the F in complex 3b results in less electron donation
to the metal, with less back-bonding to the carbonyl, and thus a
higher stretching frequency (the opposite effect is observed with
the electron donating OMe in complex 3c). However, the observed
variation in carbonyl stretch is really quite small, suggesting that
the phenyl substituent has only a small effect on the electronic
properties of the complex at platinum.
Fig. 5 The X-ray structure of 8a, ellipsoids at 50% probability.
the appearance of a whole host of new compounds. Typically the
19F NMR showed 6 new peaks, all with platinum satellites having
4JPtF values of the order of 30 Hz, indicating Pt(IV) species. H–
Comparisons of the bond lengths measured in the X-ray
structures gives little further insight in to the structures of the
1
complexes. If we compare the Pt–N bond length of 2.114(19) A
195Pt correlation experiments on the reaction mixtures only showed
cross-peaks to platinum in the range −1800 to −1500 ppm, again
indicating Pt(IV) species. There were never any fluorine signals
without platinum coupling, indicating all of the phenylpyridine
moieties had cyclometallated.
˚
that Ford measured in 3a, we can see that it is significantly
˚
longer than the 2.002(7), 2.065(4), 2.020(8) and 2.025(5) A we
see in complexes 2b, 4b, 5b and 6b, respectively. This observation
fits with a weakening of the Pt–N bond by the strong trans-
influence carbonyl ligand. Other conclusions are harder to draw:
the platinum to cyclometallated carbon bond lengths vary by only
At early stages of the reaction (in the first half hour or so)
3 major new peaks were observed, but with time 3 other peaks
appeared and by 4 h these 3 peaks accounted for the vast majority
of the material present. Whilst the initial 3 new peaks showed
varying intensities, two of the three peaks that came to dominate
the sample with time always appeared with equal intensity, sug-
gesting they were both arising from the same compound. Though
we were unable to do a direct 19F–195Pt correlation experiment,
a sequence of 2D HETCOR NMR experiments allowed us to
establish that these particular two 19F signals did indeed come
˚
0.05 A across all complexes, and the platinum to chlorine distance
˚
varies by a similar 0.04 A.
Oxidation of the pendant phenylpyridine Pt(II) complexes
We observed that solutions of complexes 2, 3, 4, 5 and 6 were
prone to decomposition in air. After the isolation of a crystal from
a solution of 2a we were able to solve the X-ray structure and
identify one of the decomposition products as the platinum(IV)
species 8a, Fig. 5. Intrigued by this result we set about a systematic
study of the oxidation of the pendant phenylpyridine complexes
2. We concentrated on the 4-fluorophenylpyridine derivative 2b
as both the 19F shift and the coupling of this nucleus to 195Pt in
these complexes should prove to be a very useful spectroscopic
handle. Though new peaks in the NMR spectra of 2b grow
slowly at room temperature, and crystals of 8a can be formed
from the irradiation of a chloroform solution of 2a with low
intensity UV light (whereupon we would expect reaction with
photodecomposition products of the chloroform), we decided to
speed up the oxidation by using hydrogen peroxide as the oxidant.
We performed oxidation reactions on a number of occasions:
typically we took 10 mg of pendant phenylpyridine complex 2b
in 0.7 ml of d6-acetone and added excess hydrogen peroxide
(30% in H2O) at room temperature, and in the presence of air.
In addition potassium chloride (2.5 mg) was added to ensure
sufficient chloride was present to convert any potential platinum
hydroxides to chlorides. Reactions were much faster: all the initial
platinum(II) material was consumed in less than an hour, with
1
from one compound; we used a H–19F correlation to identify
which of the protons ortho to both the F and the Pt coupled to
1
which 19F, and then a H–195Pt correlation to identify which of
these protons coupled to which 195Pt. Thus we could then identify
which 19F signals corresponded to which 195Pt nuclei. Table 1 lists
the correlations we were able to make on samples at both early
and later stages of the reaction, and we were able to confirm
that the two 19F peaks that appeared to have equal intensity were
indeed attached to the same platinum. When the reactions were
left for a day or two, a precipitate would normally form (less
concentrated samples tended not to give precipitates). Collection
of this precipitate followed by dissolution in dry dmso showed
us that this material was a mixture containing only the “later” 19
F
compounds (3 signals, but only 2 compounds), and that the 2 signal
compound slowly changed into the other single signal compound
(complete in a week). We were then able to fully characterise
this new compound, including growing crystals suitable for X-ray
diffraction, and establish that it was exactly analogous to 8a (i.e.
it was 8b), Fig. 6. An elemental analysis of the initial precipitate
(containing both compounds) gave a composition identical to that
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Table 1 Selected spectroscopic data for the species in Scheme 2
Compound
dF (ppm)
4JFPt/Hz
dPt (ppm)
2ba
2bb
−109.3 (metallated ring)
−111.6
56
—
56
—
32
32
31
31
31
31
31
32
32
−3151
—
—
−113.3 (metallated ring)
−111.1
—
initial isomer 1b
initial isomer 2b
initial isomer 3b
7ba
−108.5
−1492
−1464
−1408
−1566
—
—
—
−108.1
−107.8
−107.4
−106.9
7bb
−107.3
−107.7
8ba
8bb
−105.8
−1807
−107.3
—
a d6-dmso. b d6-acetone.
of pure 8b, indicating that the 2 signal compound was simply an
isomer of 8b.
Fig. 6 The X-ray structure of 8b, ellipsoids at 50% probability.
Furthermore, we are confident that the three “early” com-
pounds are also isomers of 8b, as the only real alternative would
be for compounds that contain hydroxides rather than chlorides.
Since we would expect any hydroxide peak to rapidly exchange
H with both water and hydrogen peroxide in the acetone reaction
of doubly cyclometallated octahedral platinum(IV) indicates that
there are 5 possible compounds, Scheme 2. Our final product, 8b,
would have just a single 19F resonance, as would 3 of the other
isomers. Only one, identified as 7b in Scheme 2, would have two
19F resonances. We can thus be confident that the final products
are 7b and 8b and that 7b then isomerises to 8b, and that the three
initial products are the other possible isomers. Multiple isomers
of similar complexes observed upon hydrogen peroxide oxidation
have been seen previously,35 though they can be kinetically inert.36
The eventual outcome of our oxidation reaction is to give 8b in
very high yield: no other fluorine containing products are formed,
and no residual platinum is obvious.
1
solution, the absence of a peak in the H NMR is not, in itself,
conclusive. To try and identify such a peak, we did stop an oxida-
tion after an hour (when the 19F clearly indicated the three initial
compounds were still present) and removed all solvents under high
1
vacuum. A H NMR spectrum of this material in dry dmso did
not show any signals that might be attributed to hydroxides. A 1H–
195Pt correlation spectrum of the reaction mixture showed these
three compounds had very similar 195Pt chemical shifts to each
other, and to the known chloride compound 7b, whereas we might
expect a hydroxide compound to have a substantially different 195Pt
chemical shift, Table 1.34 Consideration of the possible isomers
We performed most of our oxidations in the presence of extra
chloride as this would allow for the formation of the products we
see (which contain two chlorides per platinum, whereas the starting
Scheme 2
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material had only one chloride per platinum), without the need for
the reactions to scavenge chloride. However, given the small scale
we were working on, there sometimes appeared to be sufficient
chloride present as an impurity in 2b or in the hydrogen peroxide
or on the glassware used for a reaction performed without added
chloride to show essentially the products, and in these cases we saw
no significant change in the relative proportions of the oxidised
products, or the final product. Having said all that, it is clear that
hydroxides are isolable: when we used different conditions (wet
dmf, high temperature, air as the oxidant) we did on one occasion
form a poorly defined mixture of compounds from which we were
able to extract a single crystal of the platinum(IV) hydroxide 9b,
Fig. 7.
Scheme 3
Scheme 4
Other groups have made use of silver salts to synthesise Pt(II)
species similar to 10.44
However the reaction conditions used by von Zelewsky are
totally unlike the conditions we used in our reactions. Indeed,
one of our original intentions with compounds 2 was to use our
synthetic procedure10,11 that led to CNC doubly cyclometallated
species to make bis(cyclometallated) species such as 10. However
we have not yet succeeded in this aim, and control experiments
whereby we treat 2b with heat and/or light in acetone or dmso in
the strict absence of air do not show anything other than starting
2b. Close examinations of the NMR spectra of our reaction
mixtures did not show any platinum(II) compounds intermediate
between the starting material and the products.
Von Zelewsky does note the ease by which compounds like
10 may be oxidised, either thermally or photochemically, to
octahedral Pt(IV) species, and some of his papers deal with this
specific reaction.45,46 In all the cases he discusses, the oxidation
occurs as part of an oxidative addition reaction of either a
dihalogen (I2 and Br2) or an alkyl halide (e.g. MeI). This type
of oxidation is well documented for platinum(II) complexes,14,47
and there are other of examples of the oxidative addition of a
C–H bond to Pt(II) to give a Pt(IV) complex.48,49 Since these types
of oxidations are not directly analogous to ours, we investigated
the oxidation of complexes 4-fluoro-10 under the conditions we
used in the oxidation of 2b. The behaviour of 4-fluoro-10 under
these conditions was quite unlike that of 2b, and did not give 8b
cleanly, strongly suggesting that 2b does not cyclometallate prior
to oxidation.
Fig. 7 The X-ray structure of 9b, ellipsoids at 50% probability.
We also investigated the oxidation of bis(cyclometallated)4-
fluorophenylpyridine platinum(II) under the conditions we used
in the oxidation of 2b (i.e. hydrogen peroxide in acetone with
added KCl). Oxidation did occur, but it was much slower: even
after several days, clear signals in the 19F NMR of the initial
cyclometallated platinum(II) species were present, alongside those
for Pt(IV) oxidation products (which included 8b and its isomers).
Oxidation: discussion
Broadly speaking, there are two possible routes by which
compounds 2a–c transform into compounds 7 and 8: either
an initial oxidation is followed by a cyclometallation, or an
initial cyclometallation is followed by an oxidation, Scheme 3.
Bis(cyclometallated) phenylpyridine complexes of platinum have
considerable precedent: in the 1980s von Zelewsky reported a route
into the synthesis of bis(cyclometallated) phenylpyridine com-
plexes such as 10, Scheme 4.37 This high yielding route relied on the
prior deprotonation of the cyclometallating species, and reaction
with a metal salt under very mild conditions, allowing the exclusive
isolation of cis isomers. A number of further examples, varying
from the simple 2-phenylpyridine, through phenylpyrazoles and
thienylpyridines,38 to compounds with two different ligands39 and
those where steric constraints induce chirality40,41 were reported.
Later work on these compounds included a number of papers
where chiral groups were appended to the cyclometallating species
in order to predetermine the chirality of the metal complex.42,43
More relevant is the use of hydrogen peroxide35,50,51 or molec-
ular oxygen52,53 to generate Pt(IV) species. In these examples of
oxidation reactions kinetics are reported to be complex and
difficult to reproduce, with radicals implicated in some instances,
though not detected in others (a comparison of some oxidants
has also been published54). However, broadly speaking conditions
used are similar to ours, and clean oxidations are observed
under similar timescales. Hence it seems entirely appropriate to
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suggest that we might be seeing an initial oxidation followed by a
cyclometallation. In addition to the work we report in this paper
with the pendant phenyl pyridine complex 2b, we have begun
studies on the oxidation of the pyridine complex 6b with hydrogen
peroxide.55 With these compounds there is no possibility of a
second cyclometallation, and yet the oxidation appears to proceed
in a very similar fashion to that of 2b.
Thus, taking in consideration all of the above observations, we
would argue that an initial oxidation of the platinum(II) centre 2b
is rapidly followed by a second cyclometallation (i.e. the upper
route in Scheme 3), eventually giving 8b. Since cyclometallation is
believed to be an electrophilic attack by the platinum1 one could
justify the spontaneous nature of this second cyclometallation
in terms of a Pt(IV) centre being more electrophilic than the
starting Pt(II) centre. Thus our second cyclometallation, or C–
H activation, is taking place at a Pt(IV) centre. To the best of our
knowledge this work represents the first documented example of
a cyclometallation reaction by a Pt(IV) complex.
Solid state structures of the complexes‡
Table 2 lists the crystal data for all the structures reported in this
paper. The solid state structure of 2b is very similar to that reported
by Ford32 for 2a; selected bond lengths and angles are reported in
Table 3. Important bond lengths (i.e. those directly involving the
central platinum) are very similar, with the Pt–Cl and Pt–N lengths
being the same (within the ESDs) and the Pt–C distance being only
˚
˚
slightly shorter at 1.941(10) A compared with 1.975(8) A. Angles
are also similar. The structure of 2a reported by Ford does not
include any secondary interactions between molecules, and this
is in contrast to the structure of 2b. Within the structure of 2b
there are several close contacts between CHs and electronegative
atoms. Many of these contacts involve a chloroform molecule of
crystallisation, though there are short contacts between hydrogens
and the fluorines. There is also a p stacking interaction between the
cyclometallated pyridine and a symmetry related cyclometallated
pyridine, Fig. 8; the distance between the mean planes through
˚
each p stacking unit is 3.35 A.
The solid state structure of 4b contains essentially flat molecules
(only the Me groups of the dmso are out of a plane); selected bond
lengths and angles are reported in Table 4. The structure was
solved in the Pnma space group which, in this case, requires that the
molecule has exact mirror symmetry. The packing of the individual
molecules is of interest: they exist in a hexagonal honeycomb type
˚
of array in flat sheets, Fig. 9. Adjacent sheets are spaced at 3.531 A,
though there are no Pt–Pt interactions between them, presumably
because the methyls of the dmsos interfere with the close approach
of the platinums, leading to a dislocation between adjacent sheets.
The solid state structure of 5b consists of flat units; selected
bond lengths and angles are reported in Table 5. The molecules
within the structure interact to form chains giving a continuous ar-
˚
rangement of molecules, separated by Pt–Pt distances 3.3634(3) A,
extended throughout the crystal. The Pt–Pt chain is almost linear
with Pt–Pt–Pt angles of 176.68◦. The interaction of two molecules
is shown in Fig. 3, and it is clear that, in addition to the Pt–
Pt interaction, hydrogen bonds exist between the chlorides on
one molecule and the ammonias on the next; further stabilisation
comes from p-stacking of the aromatic rings. The infinite nature
of the chain that forms is shown in Fig. 10, and it is apparent that
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˚
Fig. 8 The stacking arrangement present in the X-ray structure of 2b; the centroid to centroid distance of the two pyridine rings is 3.687 A, with the
˚
closest atomic contact being 3.364 A.
◦
˚
Table 3 Selected bond lengths [A] and angles [ ] for 2b
Pt1–C212
Pt1–N21
Pt1–N11
Pt1–Cl1
1.941(10)
2.002(7)
2.023(8)
2.412(3)
C212–Pt1–N21
C212–Pt1–N11
N21–Pt1–N11
C212–Pt1–Cl1
N21–Pt1–Cl1
N11–Pt1–Cl1
C26–N21–C22
C26–N21–Pt1
C22–N21–Pt1
C211–C212–C27
C211–C212–Pt1
C27–C212–Pt1
82.1(4)
92.6(4)
174.3(3)
175.8(3)
97.0(3)
88.2(2)
118.2(9)
117.3(7)
124.5(7)
114.7(9)
132.2(9)
113.1(8)
◦
˚
Table 4 Selected bond lengths [A] and angles [ ] for 4b
Pt1–C8
Pt1-N1
Pt1–S1
Pt1–Cl1
1.998(5)
2.065(4)
2.2161(16)
2.3962(17)
C8–Pt1–N1
C8–Pt1–S1
N1–Pt1–S1
C8–Pt1–Cl1
N1–Pt1–Cl1
S1–Pt1–Cl1
C2–N1–C6
C2–N1–Pt1
C6–N1–Pt1
C9–C8–C7
C9–C8–Pt1
C7–C8–Pt1
81.00(18)
98.46(14)
179.46(11)
173.38(15)
92.38(12)
88.16(6)
119.9(5)
125.6(4)
114.5(3)
117.0(5)
129.0(4)
114.0(4)
Fig. 9 The planar hexagonal honeycomb arrangement present in the
X-ray structure of 4b.
Pt–Pt interactions in the solid state have considerable precedent:
a search of the Cambridge Crystallographic Database56 currently
reveals 36 structures of organometallic compounds that have a
Pt–Pt interaction unsupported by chelating ligands, with the mean
˚
value of the Pt–Pt distance being 3.249 A. We ourselves have pub-
lished a paper where we reported a dimetallated diphenylpyridine
each subsequent molecule in the chain is rotated by 180◦, with
respect to its neighbours, about an axis that bisects the Cl–Pt–
NH3 angle in the plane of the aromatic residue. This leads to the
alternating pattern of chloride and amine fragments lying above
each other in neighbouring units.
that existed as dimers with a Pt–Pt “bond” of 3.243(1) A.57 In our
˚
previously reported structure the platinums◦in adjacent dimers
˚
were separated by 6.17 A at an angle of 53.5 to the Pt–Pt bond
in the dimer, giving rise to a zigzag along the extended platinum
chain. This type of alternating short–long Pt–Pt distance is much
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◦
◦
˚
˚
Table 6 Selected bond lengths [A] and angles [ ] for 6b
Table 5 Selected bond lengths [A] and angles [ ] for 5b
Pt1–C8
Pt1–N1
Pt1–N01
Pt1–Cl1
1.990(9)
2.020(8)
2.022(9)
2.431(3)
Pt1–C112
Pt1–N201
Pt1–N101
Pt1–Cl1
1.977(6)
2.022(5)
2.025(5)
2.397(2)
C8–Pt1–N1
C8–Pt1–N01
N1–Pt1–N01
C8–Pt1–Cl1
N1–Pt1–Cl1
N01–Pt1–Cl1
C6–N1–C2
C6–N1–Pt1
C2–N1–Pt1
C7–C8–Pt1
C9–C8–Pt1
80.5(3)
96.3(4)
176.7(4)
177.4(3)
96.9(2)
C112–Pt1–N201
C112–Pt1–N101
N201–Pt1–N101
C112–Pt1–Cl1
N201–Pt1–Cl1
N101–Pt1–Cl1
C102–N101–C106
C102–N101–Pt1
C106–N101–Pt1
94.0(2)
81.1(2)
174.7(2)
178.22(18)
87.30(15)
97.66(17)
119.4(6)
125.4(5)
115.1(5)
86.3(3)
120.2(8)
115.8(6)
124.0(7)
115.5(6)
127.6(7)
Fig. 11 The planar hexagonal honeycomb arrangement present in the
X-ray structure of 5b.
Fig. 10 The infinite chains of molecules that exist in the X-ray structure
of 5b; the Pt–Pt distance is 3.3634(3) A.
The structures of 8a and 8b are very similar: each compound has
trans nitrogens and cis chlorides, and bond lengths and angles are
practically identical, Tables 7 and 8; note that the platinum in 8b
sits on a two fold axis, hence bond lengths to both phenylpyridines
and chlorines are identical. Hydrogen bonds exist to many of the
halogen atoms and p-stacking occurs between some of the rings
in the structure of 8a, this is illustrated in Fig. 12.
˚
the most common form of Pt–Pt interaction: 33 of the 36 structures
from the Cambridge Database have this type of structure, and
only 3 have a near identical repeat like that which we observe in
the structure of 5b.58 The bonding between two platinums can be
2
rationalised in part as arising from the overlap of 5dz and 6pz
orbitals,59 though presumably the hydrogen bonding we observe
between ammonia and chloride supplements the intermolecular
interactions significantly, resulting in the identical repeat that we
observe. Interestingly, whilst a red colour has long been recognised
as indicative of strong Pt–Pt interactions in the solid state,60,61
crystals of 5b are a dark green with hints of blue–black. As well as
the interactions described above, molecules of 5b hydrogen bond
sideways to form a honeycomb structure similar to that seen with
4b, Fig. 11. Unlike the arrays formed by molecules of 4b, which are
perfectly flat, those formed by 5b have alternate molecules slightly
raised or lowered from the mean plane.
The structure of 9b is different from those of 8a and 8b in
that both the nitrogens and the two anionic ligands are mutually
cis, though bond lengths and angles are similar, Table 9. Quite
why the two nitrogens are now cis is unclear, though it might
have something to do with keeping the oxygen from being trans
to carbon, an example of the so-called “transphobia”.62–64 The
hydrogen bonds between the hydroxyl and chloride ligands of an
inversion related second molecule result in dimeric units in the
solid state, this is illustrated in Fig. 13.
Conclusions
The asymmetric unit of the solid state structure of 6b contains
just the complex with no additional weak interactions or molecules
of solvent; selected bond lengths and angles are listed in Table 6.
A number of platinum(II) cyclometallated phenylpyridine com-
plexes have been synthesised. Variation of the phenylpyridine
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˚
˚
Fig. 12 The stacking in the structure of 8a: the rings are parallel with a centroid–centroid distance of 3.770 A, and the closest atomic contact is 3.465 A.
◦
◦
˚
˚
Table 9 Selected bond lengths [A] and angles [ ] for 9b
Table 7 Selected bond lengths [A] and angles [ ] for 8a
Pt1–C11
Pt1–N2
Pt1–C22
Pt1–N1
Pt1–Cl2
Pt1–Cl1
2.007(6)
2.020(4)
2.030(5)
2.033(4)
2.4386(13)
2.4435(14)
Pt1–C212
Pt1–N101
Pt1–C112
Pt1–O1
Pt1–N201
Pt1–Cl1
1.968(19)
1.981(17)
1.99(2)
2.034(11)
2.147(15)
2.420(5)
0.84(2)
O1–H1
C11–Pt1–N2
C11–Pt1–C22
N2–Pt1–C22
C11–Pt1–N1
N2–Pt1–N1
C22–Pt1–N1
C11–Pt1–Cl2
N2–Pt1–Cl2
C22–Pt1–Cl2
N1–Pt1–Cl2
C11–Pt1–Cl1
N2–Pt1–Cl1
C22–Pt1–Cl1
N1–Pt1–Cl1
Cl2–Pt1–Cl1
95.1(2)
87.8(2)
81.3(2)
C212–Pt1–N101
C212–Pt1–C112
N101–Pt1–C112
C212–Pt1–O1
N101–Pt1–O1
C112–Pt1–O1
C212–Pt1–N201
N101–Pt1–N201
C112–Pt1–N201
O1–Pt1–N201
C212–Pt1–Cl1
N101–Pt1–Cl1
C112–Pt1–Cl1
O1–Pt1–Cl1
90.6(6)
94.5(8)
81.1(9)
88.9(6)
174.6(6)
93.6(7)
80.6(7)
97.8(7)
174.9(7)
87.5(5)
174.7(6)
88.8(4)
90.6(5)
92.2(3)
94.3(4)
120(10)
81.8(2)
174.73(18)
94.29(19)
89.51(14)
95.69(13)
175.81(14)
88.55(12)
177.28(15)
87.09(13)
90.85(15)
95.92(14)
91.92(5)
N201–Pt1–Cl1
Pt1–O1–H1
◦
˚
Table 8 Selected bond lengths [A] and angles [ ] for 8b
Oxidation of these Pt(II) species is facile and oxidation of the
pendant phenylpyridine complex results in doubly cyclometallated
Pt(IV) complexes. A number of isomers form and eventually a
single complex results. The route to these complexes involves two
steps and the evidence indicates that an initial oxidation gives rise
to Pt(IV) species that rapidly undergoes a C–H activation to give a
doubly cyclometallated complex.
Pt1–C108
Pt1–N101
Pt1–Cl1
2.022(7)
2.042(6)
2.4403(19)
C10H–Pt1–C108
C108–Pt1–N10A
C108–Pt1–N101
N10A–Pt1–N101
C108–Pt1–Cl1A
C108–Pt1–Cl1
N10A–Pt1–Cl1
N101–Pt1–Cl1
Cl1A–Pt1–Cl1
89.5(4)
93.9(3)
81.2(3)
173.2(3)
90.90(18)
177.7(2)
88.37(17)
96.50(18)
88.77(10)
Experimental
General
(changing the substitution of the 4ꢀ position from H to OMe and
F) has little effect on the electronic properties of the central Pt
(as evidenced from the CO stretch of the carbonyl complexes).
Variation of the co-ligand has an effect on the bonding of the Pt to
the phenylpyridine though, whilst NMR coupling constants reflect
changes in the ligands, the bond lengths (as measured by X-ray
structures) show little variation. The three dimensional structures
of all of the complexes reported here contain one or more of
platinum–platinum, hydrogen bonding or p-stacking interactions,
resulting in extended arrays.
All chemicals were used as supplied, unless noted otherwise. All
NMR spectra were obtained on a Bruker Avance 400 or 500 MHz
spectrometers and are referenced to external TMS, assignments
being made with the use of decoupling, NOE and DEPT and
COSY pulse sequences. H–19F and H–195Pt correlation spectra
were recorded using a variant of the HMBC pulse sequence.
19F chemical shifts are quoted from the directly observed signals
(referenced to external CFCl3) whereas the 195Pt chemical shifts
quoted are taken from the 2D HETCOR spectra (referenced to
external Na2PtCl6). All elemental analyses were performed by
1
1
3178 | Dalton Trans., 2007, 3170–3182
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Compound 2b
2-(4-Fluorophenyl)pyridine (89 mg, 5.13 × 10−4 mol) reacted to
give 2b in 86% yield. Crystals suitable for X-ray diffraction were
grown by the slow evaporation of solvent from a chloroform
solution.
dH (CDCl3): 9.5 (d, 1H, 3JHH 6 Hz, 3JPtH 37 Hz); 9.1 (d, 1H, 3JHH
6 Hz, 3JPtH 40 Hz); 8.0 (m, 2H); 7.9 (dt, 1H, 3JHH 8 Hz, 4JHH 2 Hz);
3
3
3
7.7 (t, 1H, JHH 8 Hz); 7.55 (d, 1H, JHH 8 Hz); 7.4 (d, 1H, JHH
3
4
3
8 Hz); 7.35 (dt, 1H, JHH 6 Hz, JHH 2 Hz); 7.25 (dd, 1H, JHH
9 Hz, 4JHF 6 Hz); 7.0 (t, 1H, 3JHH 6 Hz); 6.95 (t, 2H, 3JHH 8.5 Hz);
6.6 (dt, 1H, 3JHH 9 Hz, 4JHH 3 Hz); 5.7 (dd, 1H, 3JHF 10 Hz, 4JHH
3 Hz, 3JPtH 53 Hz). dC (CDCl3): 166.2; 163.2 (1JCF 262 Hz); 161.3;
154.4; 151.2; 138.7; 138.1; 131.5 (3JCF 10 Hz); 127.3; 124.9 (3JCF
10 Hz); 124.1; 121.6; 118.1; 116.9 (2JCF 20 Hz); 115.0 (2JCF 20 Hz).
dF (CDCl3): −110.6 (4JFPt 57 Hz); −112.2. MS (LSIMS): m/z 575
(M+); 540 (M+ − Cl); 367 (M+ − Cl − FPhPy). Anal. calcd for
C22H15ClF2N2Pt: C, 45.9; H, 2.6; N 4.9; Found: C, 45.4; H, 2.6; N,
4.4.
Compound 2c
Fig. 13 Hydrogen bonded dimer formation between two molecules of 9b
related by an inversion centre; the O1 · · · Cl1A distance is 3.225(12) A.
2-(4-Methoxyphenyl)pyridine (97 mg, 2.62 × 10−4 mol) reacted to
give 2c in 81% yield.
˚
dH (CDCl3): 9.4 (d, 1H, 3JHH 6 Hz, 3JHH 38 Hz); 9.1 (d, 1H, 3JHH
6 Hz, 3JHPt 40 Hz); 8.0 (d, 2H, 3JHH 8 Hz, ); 7.8 (t, 1H, 3JHH 6 Hz,
); 7.5 (m, 2H); 7.25 (m, 2H); 7.1 (d, 1H, 3JHH 8 Hz, ); 6.85 (t, 1H,
3JHH 6 Hz); 6.75 (d, 2H, 3JHH 8 Hz); 6.4 (d, 1H, 3JHH 8 Hz); 5.6 (s,
1H, 3JHPt 47 Hz); 3.6 (s, 3H); 3.5 (s, 3H).
dC (CDCl3): 167.3; 162.3; 160.9; 160.6; 154.7; 151.2; 143.1; 138.7;
138.1; 137.7; 132.8; 131.3; 127.5; 125.1; 123.7; 120.9; 117.9; 116.7;
113.8; 108.4; 55.5; 55.3. MS (LSIMS): m/z 599 (M+). Anal. calcd
for C24H21ClN2O2Pt: C, 48.0; H, 3.5; N 4.7; Found: C, 47.8; H,
3.1; N, 4.7.
Warwick Analytical Service. All X-ray crystal structures were
collected on a Siemens Smart 1K, individual details are given
in Table 2. K2PtCl4 was purchased from Strem, 2-phenylpyridine
was purchased from Aldrich, and 2-(4-fluorophenyl)pyridine was
made via the Suzuki coupling of 4-fluorobenzeneboronic acid with
2-bromopyridine using tetrakistriphenylphosphine palladium as
catalyst.65
Synthesis of pendant phenylpyridine complexes 2
Synthesis of dmso complexes 4
The appropriate phenylpyridine (two equivalents) and potassium
tetrachloroplatinate(II) (50 mg) were suspended in pure ethanoic
acid (25 ml) and heated at 75◦ C for 15 h. The solution was
allowed to cool to room temperature and the solvent was removed.
The residue was dissolved in dichloromethane and washed with
hydrochloric acid (2.5 M, 20 ml) and water (20 ml); it was then
dried over MgSO4 and the solution was concentrated. Addition of
diethyl ether yielded a pale yellow precipitate, which was collected
by filtration.
The appropriate (phpy)platinum(Hphpy)chloride complex
(50 mg) was dissolved in DMSO (10 ml). A few drops of water
were added to the solution and the mixture was heated at 40 ◦C for
15 h. The solution was allowed to cool to room temperature and
water was added until a yellow precipitate formed; the precipitate
was collected by filtration and washed with water and hexane.
Compound 4a
2a (63 mg, 1.17 × 10−4 mol) reacted to give 4a in 91% yield.
dH (DMSO-d6): 9.55 (d, 1H, 3JHH 5 Hz, 3JHPt 36 Hz); 8.25 (dd,
1H, 3JHH 8 Hz, 4JHH 2 Hz, 3JHPt 45 Hz); 7.75 (t, 1H, 3JHH 8 Hz); 7.65
(d, 1H, 3JHH 8 Hz); 7.45 (dd, 1H, 3JHH 7 Hz, 4JHH 2 Hz); 7.2 (m, 1H);
7.15 (m, 1H); 7.1 (m, 1H); 3.55 (s, 6H, 3JHPt 24 Hz). dC (DMSO-d6):
165.6; 163.7; 150.1; 146.2; 141.2; 137.9; 126.4; 123.4; 122.3; 121.8;
119.0; 48.2. MS (EI): m/z 463 (M+); 385 (M+ − OSC2H6); 350
(M+ − OSC2H6 − Cl). Anal. calcd for C13H14ClNOPtS: C, 33.7;
H, 3.1; N 3.0; Found: C, 34.3; H, 3.0; N, 3.4.
Compound 2a
2-Phenylpyridine (46 mg, 2.96 × 10−4 mol) reacted to give 2a in
82% yield.
3
4
3
dH (CDCl3): 9.5 (dd, 1H, JHH 6 Hz, JHH 1 Hz, JHPt 35 Hz);
9.15 (dd, 1H, JHH 6 Hz, JHH 1 Hz, JHPt 42 Hz); 8.0 (m, 2H);
3
4
3
3
4
3
7.85 (dt, 1H, JHH 8 Hz, JHH 2 Hz); 7.6 (t, 1H, JHH 8 Hz); 7.5
(d, 1H, 3JHH 8 Hz); 7.4 (d, 1H, 3JHH 8 Hz); 7.3 (t, 1H, 3JHH 7 Hz);
7.2 (m, 4H); 6.95 (t, 1H, 3JHH 6 Hz); 6.9 (t, 1H, 3JHH 8 Hz); 6.8 (t,
3
1H, JHH 7 Hz); 6.1 (d, 1H, 3JHH 8 Hz, 3JHPt 46 Hz). dC (CDCl3):
Compound 4b
172.8; 162.3; 154.3; 151.2; 146.1; 141.0; 139.8; 138.4; 137.7; 130.8;
129.8; 129.6; 129.3; 127.8; 127.3; 123.9; 123.2; 123.1; 121.7. MS
(LSIMS): m/z 540 (M+). Anal. calcd for C22H17ClN2Pt: C, 48.9;
H, 3.2; N 5.2; Found: C, 49.2; H, 3.0; N, 5.0.
2b (76 mg, 1.32 × 10−4 mol) reacted to give 4b in 93% yield. Crystals
suitable for X-ray diffraction were grown by the slow evaporation
of solvent from a chloroform solution.
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3
3
3
3
dH (CDCl3): 9.5 (d, 1H, JHH 6 Hz, JPtH 36 Hz); 8.05 (dd, 1H,
dH (CDCl3): 9.3 (d, 1H, JHH 6 Hz, JHPt 33 Hz); 7.8 (dt, 1H,
3JHF 11 Hz, JHH 3 Hz, JPtH 54 Hz); 7.8 (t, 1H, JHH 8 Hz); 7.6
(d, 1H, JHH 8 Hz); 7.4 (dd, 1H, JHH 9 Hz, JHF 6 Hz); 7.1 (m,
3JHH 8 Hz, JHH 2 Hz); 7.6 (d, 1H, JHH 8 Hz); 7.45 (d, 1H, JHH
8 Hz); 7.2 (m, 1H); 6.95 (d, 1H, 4JHH 3 Hz, 3JHPt 75 Hz); 6.7 (dd,
1H, 3JHH 8 Hz, 4JHH 2 Hz). dC (CDCl3): 149.6; 140.0; 125.6; 120.7;
118.3; 117.9; 115.1; 56.7; MS (LSIMS): m/z 442 (M+). Anal. calcd
for C13H10ClNO2Pt: C, 35.3; H, 2.3; N 3.2; Found: C, 34.8; H, 1.9;
N, 3.0. IR (CHCl3 solution): 2101 cm−1 (C≡O stretch).
4
3
3
4
3
3
3
3
4
3
3
4
1H); 6.8 (dt, 1H, JHH 8 Hz, JHF 8 Hz, JHH 3 Hz); 3.6 (s, 6H,
3JHPt 23 Hz). dC (CDCl3): 165.0; 163.9 (1JCF 286 Hz); 150.3 (2JCPt
24 Hz); 143.3; 141.0; 140.8; 125.7 (3JCF 7 Hz, JCPt 54 Hz); 122.4
3
(2JCF 23 Hz); 122.0 (3JCPt 31 Hz); 121.1 (2JCF 22 Hz, 2JCPt 74 Hz);
118.9 (3JCPt 39 Hz); 47.5 (2JCPt 58 Hz). dF (CDCl3): −107.0 (4JFPt
56 Hz). MS (LSIMS): m/z 481 (M+); 445 (M+ − Cl); 367 (M+ −
Cl − OSC2H6). Anal. calcd for C13H13ClNFOPtS: C, 32.5; H, 2.7;
N 2.9; Found: C, 32.8; H, 2.9; N, 2.9.
Synthesis of ammonia complexes 5
The relevant (phpy)platinum(DMSO)chloride complex 4 (50 mg)
was dissolved in dichloromethane and gaseous ammonia was
bubbled through the solution for 2 h. The precipitate that formed
was collected by filtration and washed with dichloromethane.
Compound 4c
2c (57 mg, 9.5 × 10−5 mol) reacted to give 4c in 82% yield.
dH (CDCl3): 9.4 (d, 1H, 3JHH 6 Hz, 3JHPt 33 Hz); 7.9 (d, 1H, 4JHH
Compound 5a
3
3
4
3 Hz, JHPt 46 Hz); 7.65 (dt, 1H, JHH 8 Hz, JHH 2 Hz); 7.45 (d,
3
3
3
1H, JHH 8 Hz); 7.3 (d, 1H, JHH 8 Hz); 7.0 (dt, 1H, JHH 6 Hz,
4JHH 2 Hz); 6.6 (dd, 1H, 3JHH 8 Hz, 4JHH 2 Hz); 3.75 (s, 3H); 3.55
(s, 6H, 3JHPt 28 Hz). dC (CDCl3): 166.1; 161.5; 150.0; 142.6; 140.6;
137.3; 125.6; 120.9; 118.5; 118.3; 112.3; 55.8; 47.5 (2JCPt 59 Hz).
MS (LSIMS): m/z 493 (M+); 307 (M+ − MeOPhPy). Anal. calcd
for C14H16ClNO2PtS: C, 34.1; H, 3.3; N 2.8; Found: C, 34.2; H,
3.3; N, 2.9.
4a (65 mg, 1.45 × 10−4 mol) reacted to give 5a in 64% yield.
3
3
dH (acetone-d6): 9.45 (d, 1H, JHH 6 Hz, JHPt 39 Hz); 7.85 (dt,
1H, 3JHH 8 Hz, 4JHH 2 Hz); 7.7 (d, 1H, 3JHH 8 Hz); 7.45 (m, 1H); 7.1
(m, 2H, 3JHPt 47 Hz); 6.9 (m, 2H); 4.05 (br, 3H). dC (acetone-d6):
164.9; 163.3; 150.0; 144.5; 136.2; 130.6; 126.4; 124.1; 121.4; 120.8;
118.2. MS (LSIMS): m/z 402 (M+); 367 (M+ − Cl); 349 (M+ −
Cl − NH3). Anal. calcd for C11H11ClN2Pt: C, 32.9; H, 2.8; N 7.0;
Found: C, 33.3; H, 3.2; N, 6.6.
Synthesis of carbonyl complexes 3
Compound 5b
The relevant (phpy)platinum(DMSO)chloride complex 4 (50 mg)
was dissolved in dichloromethane. Gaseous carbon monoxide
was bubbled through the solution for approximately 5 h. Fine
yellow needles normally crystallised out of the solution, and were
collected by filtration and washed with ethyl acetate and diethyl
ether.
4b (83 mg, 1.78 × 10−4 mol) reacted to give 5b in 70% yield. Crystals
suitable for X-ray diffraction were grown by the slow evaporation
of solvent from an acetone solution.
3
3
dH (acetone-d6): 9.42 (d, 1H, JHH 8 Hz, JHPt 39 Hz); 7.85 (dt,
3
4
3
1H, JHH 8 Hz, JHH 2 Hz); 7.7 (d, 1H, JHH 8 Hz); 7.5 (dd, 1H,
3JHH 9 Hz, 4JHF 6 Hz); 7.1 (dt, 1H, 3JHH 8 Hz, 4JHH 2 Hz); 6.85 (dd,
3
4
3
3
Compound 3a
1H, JHH 10 Hz, JHH 3 Hz, JHPt 56 Hz); 6.7 (dt, 1H, JHH 9 Hz,
4JHH 3 Hz, 3JHF 9 Hz); 4.15 (br, 3H). dC (acetone-d6): 149.8; 140.6;
124.3 (3JCF 5 Hz); 122.7 (2JCF 22 Hz); 122.4; 120.9 (2JCF 22 Hz);
118.3. dF (acetone-d6): −111.4 (4JFPt 57 Hz). MS (LSIMS): m/z
384 (M+ − Cl). Anal. calcd for C11H10ClFNPt: C, 31.5; H, 2.4; N
6.7; Found: C, 31.6; H, 2.6; N, 6.4.
4a (51 mg, 1.14 × 10−4 mol) gave 3a in 78% yield.
dH (CDCl3): 9.4 (d, 1H, 3JHH 6 Hz, 3JHPt 31 Hz); 7.9 (d, 1H, 3JHH
8 Hz); 7.7 (d, 1H, 3JHH 8 Hz); 7.5 (d, 1H, 3JHH 8 Hz); 7.4 (d, 1H,
3
3
3JHH 8 Hz); 7.3 (t, 1H, JHH 7 Hz); 7.2 (m, 1H); 7.1 (t, 1H, JHH
7 Hz). dC (CDCl3): 165.7; 164.1; 150.6; 146.8; 140.0; 138.3; 127.1;
124.6; 123.8; 121.6; 118.9. MS (LSIMS): m/z 412 (M+). Anal.
calcd for C12H8ClNOPt: C, 34.9; H, 2.0; N 3.4; Found: C, 34.7; H,
1.7; N, 3.1. IR (CHCl3 solution): 2104 cm−1 (C≡O stretch).
Compound 5c
4c (48 mg, 1.00 × 10−4 mol) reacted to give 5c in 70% yield.
dH (acetone-d6): 9.5 (d, 1H, 3JHH 6 Hz, 3JHPt 34 Hz); 7.9 (dt, 1H,
Compound 3b
4
3
3
3JHH 8 Hz, JHH 2 Hz); 7.8 (d, 1H, JHH 8 Hz); 7.5 (d, 1H, JHH
8 Hz); 7.2 (t, 1H, 3JHH 6 Hz); 6.85 (d, 1H, 4JHH 2 Hz, 3JHPt 55 Hz);
4b (66 mg, 1.41 × 10−4 mol) gave 3b in 81% yield.
3
4
3
3
6.65 (dd, 1H, JHH 8 Hz, JHH 2 Hz); 4.2 (br, 3H); 3.8 (s, 3H). dC
(acetone-d6): 150.6; 141.9; 124.6; 122.4; 119.1; 118.6; 116.5; 53.2.
MS (LSIMS): m/z 432 (M+). Anal. calcd for C12H13ClN2OPt: C,
33.4; H, 3.0; N 6.5; Found: C, 33.1; H, 2.7; N, 6.1.
dH (CDCl3): 9.4 (d, 1H, JHH 6 Hz, JHPt 32 Hz); 7.9 (t, 1H,
3JHH 8 Hz); 7.65 (d, 1H, 3JHH 8 Hz); 7.55 (dd, 1H, 3JHH 9 Hz, 4JHF
3
3
5 Hz); 7.3 (t, 1H, JHH 6 Hz); 7.1 (dd, 1H, JHF 9 Hz, 4JHH 3 Hz,
3JHPt 77 Hz); 6.9 (dt, 1H, JHH 9 Hz, JHF 9 Hz, JHH 2 Hz). dC
(CDCl3): 151.2; 140.2; 126.3 (3JCF 6 Hz); 123.5 (2JCF 25 Hz); 122.8
(2JCF 24 Hz); 122.6; 118.4. dF (CDCl3): −106.9 (4JFPt 40 Hz). MS
(LSIMS): m/z 431 (M+). Anal. calcd for C12H7ClFNOPt: C, 33.5;
H, 1.6; N 3.3; Found: C, 32.9; H, 1.2; N, 3.2. IR (CHCl3 solution):
2108 cm−1 (C≡O stretch).
3
3
4
Synthesis of pyridine complex 6b
2b (104 mg, 1.93 × 10−4 mol) was dissolved in pyridine (5 ml) and
stirred under ambient conditions for 6 h. The solution was flooded
with water and filtered. The precipitate collected was washed
with water and diethyl ether and dried in vacuo. The product
was recrystallised from chloroform–diethyl ether to give crystals
suitable for X-ray diffraction. Yield: 91 mg, 85%
Compound 3c
4c (61 mg, 1.27 × 10−4 mol) gave 3c in 75% yield.
3180 | Dalton Trans., 2007, 3170–3182
This journal is
The Royal Society of Chemistry 2007
©

View Online
dH (CDCl3): 9.6 (dd, 1H, 3JHH 6 Hz, 4JHH 1 Hz, 3JHPt 38 Hz); 8.9
15 M. Crespo, C. Grande and A. Klein, J. Chem. Soc., Dalton Trans., 1999,
1629–1637.
16 K. Osakada, in Comprehensive Organometallic Chemistry III, ed.
A. J. Canty, Elsevier, Oxford, 2006, vol. 8, pp. 445–610.
17 S. W. Zhang and S. Takahashi, Organometallics, 1998, 17, 4757–
4759.
3
3
3
(d, 2H, JHH 6 Hz, JHPt 44 Hz); 7.85 (t, 1H, JHH 8 Hz); 7.75 (t,
1H, 3JHH 8 Hz); 7.5 (d, 1H, 3JHH 8 Hz); 7.4 (m, 3H); 7.05 (t, 1H,
3
3
3JHH 6 Hz); 6.7 (dt, 1H, JHF 9 Hz, 4JHH 3 Hz); 5.9 (dd, 1H, JHF
4
3
10 Hz, JHH 3 Hz, JHPt 55 Hz). dC NMR (CDCl3): 166.3; 163.4
(1JCF 254 Hz); 153.9; 151.3; 144.6 (4JCF 6 Hz); 141.0; 139.0; 138.1;
126.3; 125.4 (3JCF 9 Hz); 121.7; 118.2; 117.2 (2JCF 19 Hz); 110.5
(2JCF 23 Hz). dF (CDCl3): −109.4 (4JFPt 57 Hz). MS (EI): m/z 481
(M+), 446 (M+ − Cl). Anal. calcd for C16H12ClFN2Pt: C, 39.9; H,
2.5; N 5.8; Found: C, 39.8; H, 2.4; N, 5.7.
18 S. W. Thomas, K. Venkatesan, P. Muller and T. M. Swager, J. Am.
Chem. Soc., 2006, 128, 16641–16648.
19 S. Reinartz, M. Brookhart and J. L. Templeton, Organometallics, 2002,
21, 247–249.
20 U. Fekl, A. Zahl and R. van Eldik, Organometallics, 1999, 18, 4156–
4164.
21 L. Johansson, M. Tilset, J. A. Labinger and J. E. Bercaw, J. Am. Chem.
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22 L. Johansson and M. Tilset, J. Am. Chem. Soc., 2001, 123, 739–740.
23 M. P. Jensen, D. D. Wick, S. Reinartz, P. S. White, J. L. Templeton and
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24 D. M. Crumpton-Bregel and K. I. Goldberg, J. Am. Chem. Soc., 2003,
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Synthesis of complex 8a
A solution of 2a (95 mg, 0.176 mmol) in chloroform (10 ml) was
irradiated with a tungsten lamp, until the solution was colourless
and a precipitate had formed (1 d). The solvent was removed
and the red crystals washed with hexane (5 cm3). The complex
as isolated analyses as a chloroform solvate. Yield: 77.7 mg
(0.112 mmol), 64%. MS (MALDI TOF): m/z 574 (M+ ). Anal.
calcd for C23H17Cl5N2Pt: C, 39.8; H, 2.5; N 4.0; Found: C, 40.2;
H, 2.9; N, 4.4.
25 C. Gallego, M. Martinez and V. S. Safont, Organometallics, 2007, 26,
527–537.
26 A. R. Dick, J. W. Kampf and M. S. Sanford, Organometallics, 2005, 24,
482–485.
•
27 K. L. Hull, E. L. Lanni and M. S. Sanford, J. Am. Chem. Soc., 2006,
128, 14047–14049.
28 G. B. Shulpin, A. E. Shilov, A. N. Kitaigorodskii and J. V. Z. Krevor,
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30 G. B. Shulpin and A. N. Kitaigorodskii, J. Organomet. Chem., 1981,
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Synthesis of complex 8b
31 G. B. Shulpin, G. V. Nizova and A. E. Shilov, J. Chem. Soc., Chem.
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32 M. M. Mdleleni, J. S. Bridgewater, R. J. Watts and P. C. Ford, Inorg.
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A solution of 2b (60 mg, 0.104 mmol) in acetone (10 ml) was treated
with 30% H2O2 (0.1 ml) and potassium chloride (15 mg) and the
mixture stirred (1 d). A precipitate formed and this was collected
and redissolved in dmso (0.5ml) and left to stand for a week.
Water (10 ml) was then added and the pale yellow precipitate was
collected and washed with acetone (2 × 0.5 ml). Yield: 52 mg
(0.086 mmol), 82%.
dH (dmso): 5.71 (1H, dd, 3JHF 8.5 Hz, 4JHH 2.5 Hz, 3JHPt 29 Hz);
7.17 (1H, dt, 3JHF 9 Hz, 3JHH 9 Hz, 4JHH 2 Hz); 7.89 (1H, dt, 3JHH
6.5 Hz, 4JHH 1 Hz); 8.20 (1H, dd, 3JHH 8.5 Hz, 4JHF 5.5 Hz); 8.48
(1H, dt, 3JHH 8 Hz, 4JHH 1.5 Hz); 8.55 (1H, t, 3JHH 8.5 Hz); 9.73 (1H,
36 C. M. Ciandomenico, M. J. Abrams, B. A. Murrer, J. F. Vollano, M. I.
Rheinheimer, S. B. Wyer, G. E. Bossard and J. D. Higgins, Inorg. Chem.,
1995, 34, 1015–1021.
37 L. Chassot, E. Muller and A. von Zelewsky, Inorg. Chem., 1984, 23,
4249–4253.
3
4
3
dd, JHH 6 Hz, JHH 1 Hz, JHPt 21 Hz). dF (dmso): −105.8 (4JFPt
32 Hz). dPt(dmso): −1807. MS (EI): m/z 610 (M+), 575 (M+ − Cl),
540 (M+ − 2Cl). Anal. calcd for C22H14Cl2N2F2Pt: C, 43.3; H, 2.3;
N 4.6; Found: C, 44.4; H, 2.6; N, 4.2.
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42 P. Hayoz, A. von Zelewsky and H. Stoeckli-Evans, J. Am. Chem. Soc.,
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