Control of the coordination geometry around platinum by a supramolecular capsule

Article abstract of DOI:10.1002/ejic.201100809

The coordination geometry around a platinum atom can be controlled by a diphosphane capsule composed of a tetracationic xantphos-type ligand and a tetraanionic calix[4]arene. Reaction of the diphosphane capsule with the platinum precursor [PtCl₂(MeCN)₂] yields the bisligated biscalix[4]arene trans-platinum capsule, whereas the same diphosphane in the absence of calix[4]arene prefers the formation of the monoligated cis-platinum complex, as indicated by ³¹P{¹H} NMR and ESI-MS. The two calix[4]arenes stabilize the kinetic product (trans-Pt), and slow the formation of the thermodynamic product (cis-Pt). Metal in the box! A new supramolecular strategy for controlling the coordination chemistry of transition metal complexes is reported, which involves the encapsulation of metal complexes by mixing functionalized calixarenes and bisphosphane ligated complexes.

Full text of DOI:10.1002/ejic.201100809

FULL PAPER
DOI: 10.1002/ejic.201100809
Control of the Coordination Geometry Around Platinum by a Supramolecular
Capsule
Tehila S. Koblenz,[a] Henk L. Dekker,[b] Chris G. de Koster,[b] Piet W. N. M. van Leeuwen,[a]
and Joost N. H. Reek*[a]
Keywords: Supramolecular chemistry / Supramolecular capsules / Platinum / Calixarenes / Ionic interactions / Phosphane
ligands
The coordination geometry around a platinum atom can be
controlled by a diphosphane capsule composed of a tetracat-
ionic xantphos-type ligand and a tetraanionic calix[4]arene.
Reaction of the diphosphane capsule with the platinum pre-
cursor [PtCl2(MeCN)2] yields the bisligated biscalix[4]arene
trans-platinum capsule, whereas the same diphosphane in
the absence of calix[4]arene prefers the formation of the
monoligated cis-platinum complex, as indicated by 31P{1H}
NMR and ESI-MS. The two calix[4]arenes stabilize the ki-
netic product (trans-Pt), and slow the formation of the
thermodynamic product (cis-Pt).
tion of the encapsulated trans-Pt complex trans-[Pt{(Zn)3·
PA}2Cl2].[2d] This cis-to-trans isomerism is induced by the
second coordination sphere around the transition metal.
Introduction
The catalytic properties of transition metal complexes de-
pend on ligand parameters such as steric and electronic
properties, bite angle and chirality. Supramolecular chemis-
try provides new strategies for influencing ligand param-
eters and consequently the properties of their transition
metal complexes.[1] We have encapsulated transition metals
by applying pyridylphosphane ligands, which coordinate
the transition metal through the phosphorus atom, and at
the same time, the nitrogen atoms of the pyridyl groups
selectively coordinate to ZnII–porphyrins or ZnII–salphens,
resulting in a hemispherical ligand–template capsule around
the transition metal (Figure 1, a).[2] When tris(m-pyridyl)-
phosphane is applied, the steric hindrance created around
the metal results in the decoordination of one of the two
pyridylphosphane ligands. These encapsulated rhodium
complexes were shown to have unusual reactivity and selec-
tivity in the hydroformylation of terminal and internal al-
kenes. Interestingly, the tris(m-pyridyl)phosphane and
tris(p-pyridyl)phosphane give rise to very different com-
plexes. For example, addition of 6 equiv. of ZnII–salphen to
cis-[Pt(PA)2Cl2] [PA = tris(p-pyridyl)phosphane] did not lead
to ligand dissociation but gave rise to the exclusive forma-
[a] Homogeneous and Supramolecular Catalysis, Van’t Hoff
Institute for Molecular Sciences, University of Amsterdam,
Postbox 94720, 1090 GS Amsterdam, The Netherlands
Fax: +31-20-5255604
Figure 1. Hemispherical ligand–template capsule (a) and templated
chelating bidentate ligand (b).
E-mail: J.N.H.Reek@uva.nl
[b] Mass Spectrometry of Biomacromolecules, Swammerdam
Institute for Life Sciences, University of Amsterdam,
Postbox 94720, 1090 GS Amsterdam, The Netherlands
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100809.
Chelating (hetero)bidentate ligands can be assembled
from two monodentate ligands by equipping them with
complementary binding motifs or by applying a template
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J. N. H. Reek et al.
FULL PAPER
that contains two binding sites for the two monodentate
Xantphos ligands have large natural bite angles, typically
ligands.[3] We have previously studied the template-induced between 100 and 120° (P–M–P angle), which can act as
formation of chelating bidentate ligands by the selective both a cis and trans chelating ligand in square planar palla-
self-assembly of two monodentate pyridylphosphane li- dium(II) and platinum(II) complexes, as shown by van
gands (PB) on a rigid biszinc(II) salphen template with two Leeuwen and coworkers.[6] Kollar and coworkers have syn-
identical binding sites (Figure 1, b).[3b] Addition of the tem- thesized the cis-[Pt(xantphos)Cl2] complex by heating
plate to cis-[Pt(PB)2Cl2] resulted in a mixture of the tem- [PtCl2(PhCN)2] and xantphos in a 1:1 ratio in benzene
plated cis-Pt complex (15%) and templated trans-Pt com- (Scheme 2).[7] Addition of a second equivalent of xantphos
plex (85%). The templated trans-Pt complex is the thermo- to the cis-Pt complex at room temperature resulted in a cis-
dynamic product and is stabilized by the formation of a to-trans rearrangement, to give the ionic trans-
bidentate chelating ligand.
[Pt(xantphos)(η1-xantphos)Cl]Cl complex with the second
We report here a supramolecular diphosphane capsule, xantphos ligand coordinating in a monodentate fashion.
which controls the coordination geometry around a plati- The platinum–xantphos–tin(II) chloride system, which is a
num atom. Supramolecular capsules are composed of two mixture of cis- and trans complexes, has been applied as a
or more, not necessarily identical, building blocks pro- hydroformylation catalyst.[6h,7,8] Van Leeuwen and cowork-
grammed to self-assemble in solution into the desired struc- ers, Matt and coworkers and den Heeten have reported
ture.[1b,1c,4] We have previously reported capsule A·C, which trans-[PtCl2(diphosphane)] complexes using the trans-span-
is formed by ionic interactions and composed of a tetracat- ning diphosphane ligand SPANphos, trans-spanning di-
ionic xantphos-type diphosphane A and the complemen- phosphanes based on a cyclodextrin cavity and a cyclic
tary tetraanionic calix[4]arene C (Scheme 1).[5] The free and bisxantphos ligand, respectively.[9] To the best of our knowl-
bound building blocks of A·C undergo a fast exchange on edge, a platinum dichloride complex containing only one
the NMR time scale. Encapsulation of a transition metal trans-coordinating xantphos-type ligand, i.e. trans-
within this framework is achieved by using the metal com- [Pt(xantphos)Cl2], has not been reported.
plex of the tetracationic diphosphane ligand for the as-
sembly process. The encapsulated metal is still available for
catalytic transformations as it is not involved in the as-
sembly process.[5a–5b] We have recently demonstrated that
encapsulation of a rhodium hydroformylation catalyst in
this diphosphane-based capsule results in new product re-
gioselectivities, high product chemoselectivity and substrate
selectivity.[5d]
Scheme 2. Synthesis of cis- and trans-platinum(II) xantphos com-
plexes.[7]
Results and Discussion
1. Platinum Complexes
We compared the reaction between the tetracationic
xantphos-type ligand A-HOTs (A) and [PtCl2(MeCN)2]
with the reaction between the diphosphane capsule A·C and
[PtCl2(MeCN)2]. The products were characterized by
31P{1H} NMR spectroscopy and ESI-MS, see Exp. Sect.
and Supporting Information. The molecular structure of A-
HOTs (A) is given in Figure 2. Depending on the conditions
used, the reaction of [PtCl2(MeCN)2] with A in methanol
led to the formation of cis-[Pt(A)Cl2] (B1) and/or trans-
[Pt(A)(η1-A)Cl]Cl (B2), vide infra, as indicated by in situ
31P{1H} NMR spectroscopy and ESI-MS (Scheme 3 and
Table 2, Entries 1 and 3). The 31P{1H} NMR spectrum of
cis-B1 shows a characteristic 1/4/1 pattern consisting of a
singlet at 6.2 ppm, flanked by 195Pt satellites with a cou-
pling constant JPt–P of 3728 Hz (Table 1 and Figure 4, b).
This coupling constant indicates that a chloride ligand is
present trans to the phosphorus donor, in line with the cis-
chelation of A.[7,8,10] The 31P{1H} NMR spectrum of trans-
B2 shows the presence of three different phosphorus atoms
Scheme 1. Self-assembly of A·C composed of diphosphane A and
calixarene C.
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Coordination of Pt by a Supramolecular Capsule
(Table 1, Figures 3 and 4, c): a triplet signal for PX at Table 1. 31P{1H} NMR spectroscopic data of the diphosphanes,
platinum complexes and capsules.[a]
15.9 ppm (1 P) flanked by 195Pt satellites with JPt–P of
4074 Hz, a doublet signal for PY at 15.0 ppm (2 P) flanked
by 195Pt satellites with JPt–P of 2679 Hz, indicating that the
two phosphorus atoms are trans to one another, and a sing-
[b]
[b]
δPX
δPY
δPZ
[ppm]
1JPt–P 1JPt–P 2JP
X–PY
X Y
[ppm]
[ppm]
[Hz]
[Hz]
[Hz]
A
–16.9 (s)
–17.5 (s)
–
–
–
–
–
–
–
–
–
–
let signal at –22.6 ppm (1 P) assigned to PZ, the noncoordi- A·C
nating phosphorus atom of the monodentate ligand.[7,10]
The triplet and doublet signals have a cis coupling constant
JP–P of 18.1 Hz.
cis-B1
(cis-B1)·C
6.2 (s)
6.6 (s)
–
–
–
–
3728
3727
–
–
–
–
trans-B2
(trans-B2)·(C)2
15.9 (t)
15.0 (d)
–22.6 (s) 4074
2679
2652
18.1
–
[c]
15.2 (br. s) 15.2 (br. s) –24.1 (s) 4091
[a] Spectra were measured in CD3OD. [b] Multiplicities are given
for the central lines. [c] The triplet and doublet resonances of PX
and PY coalesce as one broad central line.
Figure 2. Molecular structure of A.
Figure 3. Phosphorus numbering in trans-B2.
Reaction of [PtCl2(MeCN)2] with 1 equiv. of A in
CD3OD at 20 °C resulted in the disappearance of A and
the formation of cis-B1 (79%) and trans-B2 (21%) after two
hours (Scheme 3 and Figure 4, a). At 20 °C a slow transfor-
mation of trans-B2 to cis-B1 was observed; after three hours
at 20 °C their ratio changed to cis-B1 (81%) and trans-B2
(19%). Upon heating the NMR tube to 60 °C, trans-B2
transformed immediately and quantitatively into cis-B1
(Scheme 3 and Figure 4, b).
Subsequently, we added an excess of ligand to the metal
precursor in order study the effect on the product distribu-
tion. Reaction of [PtCl2(MeCN)2] with 2 equiv. of A in
CD3OD at 20 °C resulted in the consumption of 53% of A
and in the formation of a larger amount of trans-B2, i.e. cis-
Scheme 3. Reaction of [PtCl2(MeCN)2] with A to give cis-B1 and
trans-B2.
Figure 4. In situ 31P{1H} NMR experiments in CD3OD of [PtCl2(MeCN)2] and A to give cis-B1 and trans-B2.
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B1 (9%) and trans-B2 (91%) after two hours (Scheme 3 and
The ESI-MS of (cis-B1)·C and (trans-B2)·(C)2 confirmed
Figure 4, c). A very slow transformation of cis-B1 to trans- their formation and stabilities in the gas phase (Figure 5, a,
B2 at 20 °C was observed; after one night at 20 °C their
ratio changed to cis-B1 (7%) and trans-B2 (93%). Upon
heating the NMR tube to 60 °C for five hours, a large
amount of trans-B2 transformed into cis-B1, i.e. cis-B1
(51%) and trans-B2 (49%), which was accompanied by an
increase of the amount of A (Scheme 3).
In summary, upon reaction of A with the Pt precursor,
cis-B1 is formed as the major product at lower and higher
temperatures (20 °C and 60 °C), and trans-B2 is formed as
the major product only when 2 equiv. of ligand are applied
at lower temperatures (20 °C). These results imply that, un-
der the given conditions, cis-B1 is the thermodynamic prod-
uct and trans-B2 is the kinetic product (at a Pt/PP ratio of
1:1).
2. Platinum Capsules
Pt Capsules by Self-Assembly of Preformed Metal
Complexes
Platinum encapsulation can be achieved by self-assembly
of a platinum complex containing A and C or by the reac-
tion between a platinum precursor and a diphosphane cap-
sule. Self-assembly of the platinum capsules from preformed
metal complexes was carried out by mixing methanol solu-
tions of the precharged platinum complex (cis-B1 or trans-
B2) and the tetrasulfonatocalix[4]arene tetrasodium salt C-
SO3Na (Scheme 4). The platinum capsules (cis-B1)·C and
(trans-B2)·(C)2 formed instantaneously with NaOTs formed
as a sideproduct. The platinum complexes cis-B1 and trans-
B2 contain 1 and 2 equiv. of the tetracationic diphosphane
ligand A, respectively. Hence, capsule (cis-B1)·C contains
(a) and (trans-B2)·(C)2 [Pt + A·C Ǟ (trans-B2)·(C)2] (b) in CH3OH
one unit of C, whereas capsule (trans-B2)·(C)2 contains two. (inset: measured isotope patterns, see Supporting Information).
Figure 5. ESI-MS spectra of (cis-B1)·C (cis-B1 + C Ǟ (cis-B1)·C)
Scheme 4. Platinum encapsulation: self-assembly of (cis-B1)·C (a) and (trans-B2)·(C)2 (b).
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Coordination of Pt by a Supramolecular Capsule
and Table 2, Entries 2 and 4). Prominent ion peaks were
observed for the platinum capsules in CH3OH. The charge
on the capsules is created by loss of chloride ions from the
platinum complex and/or by addition of protons or sodium
cations from the solution. The ESI-MS of (cis-B1)·C and
(trans-B2)·(C)2 confirm that cis-B1 and trans-B2 remain in-
tact upon capsule formation. (cis-B1)·C and (trans-B2)·(C)2
1
gave very broad proton resonances in their H NMR spec-
1
tra and therefore could not be characterized by H NMR
spectroscopy.[5c,7]
Table 2. ESI-MS data[a,b] of cis-B1, trans-B2, (cis-B1)·C and (trans-
B2)·(C)2.
Entry Compound
(formation) [c]
Assignment [d]
(Elemental composition)
Found Calcd.
m/z m/z
1
2
3
4
5
6
cis-B1
[B1-2OTs]2+
765.25 765.25
1091.36 1091.36
977.06 977.05
(C73H94Cl2N4O7P2PtS2)
[B1·C – Cl + H]2+
Scheme 5. Self-assembly of A·C from neutral building blocks.
(cis-B1)·C
(B1 + C Ǟ)
trans-B2
(C103H133ClN4O21P2PtS4)
[B2 – Cl – H– 3OTs]3+
(C153H194ClN8O17S5P4Pt)
ure 6, a). As a result of signal broadening, the resonances
of PX and PY coalesce into one broad singlet. Still, the Pt
satellites of (trans-B2)·(C)2 are visible (PX: JP–Pt = 4091 Hz
and PY: JP–Pt = 2652 Hz) confirming that trans-B2 has the
same structure in its encapsulated form.
(trans-B2)·(C)2
(B2 + 2C Ǟ)
(trans-B2)·(C)2
(Pt + A·C Ǟ)
(trans-B2)·(C)2
(Pt + A·C Ǟ)
[B2·(C)2 – Cl + 2H + Na]4+ 1039.87 1039.87
(C206H266ClN8O42P4PtS8Na)
[B2·(C)2 – Cl + 2H]3+
1378.83 1378.83
776.07 776.07
(C206H266ClN8O42P4PtS8)
[B2·(C)2 – C – Cl – H]4+
(C162H211ClN8O22P4PtS4)
[e]
[a] The ESI-MS were measured in CH3OH. [b] See the Exp. Section
and Supporting Information for more ion peaks and the measured
and calculated isotope patterns. [c] The reaction equations given in
the brackets describe the way the Pt capsules were formed. [d] OTs
= C7H7SO3. [e] The same ion peaks of (trans-B2)·C were observed
in the ESI-MS of (trans-B2)·(C)2 formed by self-assembly, i.e. trans-
B2 + 2C.
Pt Capsules by Coordination to Preformed Ligand Capsule
Platinum encapsulation can also be achieved by the reac-
tion of a platinum precursor and the preformed diphos-
phane capsule A·C. The ionic-based diphosphane capsule
A·C consists of the tetracationic diphosphane A and C
Scheme 6. Platinum encapsulation by reaction of [PtCl2(MeCN)2]
with A·C to give (cis-B1)·C and (trans-B2)·(C)2.
The ESI-MS of (trans-B2)·(C)2 formed by the reaction of
(Scheme 5).[5b–5c] Mixing methanol solutions of the neutral [PtCl2(MeCN)2] with A·C supports the presence of two C
building blocks a and C-SO3H resulted in quantitative pro- units around trans-B2 (Figure 5, b and Table 2, Entry 5).
tonation of a by C-SO3H, which led to capsule A·C without Interestingly, in the ESI-MS of (trans-B2)·(C)2 we also ob-
salt formation.[11]
served ion peaks corresponding to [B2·C]4+, i.e. [B2·(C)2 –
Depending on the conditions used, reaction of C – Cl – H]4+ (Figure 5, b and Table 2, Entry 6). We assume
[PtCl2(MeCN)2] with A·C in methanol led to the formation that [B2·C]4+ is formed by abstraction of one C unit from
of the platinum capsules (cis-B1)·C and (trans-B2)·(C)2, vide (trans-B2)·(C)2 during the ionization process.
infra, as indicated by in situ 31P{1H} NMR spectroscopy
Reaction of [PtCl2(MeCN)2] with 1 equiv. of A·C in
and ESI-MS (Scheme 6, Figure 5, b and Table 2, Entry 5). methanol at 20 °C resulted in the disappearance of A·C and
The chemical shifts of the Pt capsules in the 31P{1H} NMR the formation of (cis-B1)·C (2%) and (trans-B2)·(C)2 (98%)
spectra are comparable to those of their corresponding Pt after three hours (Scheme 6 and Figure 6, a). We observed
complexes but the signals of the capsules are broad.[5c] The a slow transformation of (trans-B2)·(C)2 to (cis-B1)·C at
phosphorus resonances of (cis-B1)·C show a characteristic 20 °C; after one night at 20 °C their ratio changed to (cis-
1/4/1 pattern consisting of a singlet at 6.6 ppm, flanked by B1)·C (9%) and (trans-B2)·(C)2 (91%). Upon heating the
195Pt satellites with a coupling constant JPt–P of 3727 Hz NMR tube to 60 °C, (trans-B2)·(C)2 continued to transform
(Table 1 and Figure 6, b). The 31P{1H} NMR spectrum of into (cis-B1)·C up to (cis-B1)·C (82%) and (trans-B2)·(C)2
(trans-B2)·(C)2 consists of one singlet at –24.1 ppm (1 P) (18%) (Scheme 6 and Figure 6, b). This ratio was reached
assigned to the noncoordinating PZ, and one singlet at after seven hours at 60 °C and did not change even after
15.2 ppm (3 P) assigned to PX and PY (Table 1 and Fig- eight more hours.
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Figure 6. In situ 31P{1H} NMR experiments in CD3OD of [PtCl2(MeCN)2] and A·C to give (cis-B1)·C and (trans-B2)·(C)2 at 20 °C (a)
and at 60 °C (b).
In summary, at lower temperatures (20 °C) the reaction
of [PtCl2(MeCN)2] with A·C results in (trans-B2)·(C)2 as the
major product (98%), whereas the same reaction with A
results in cis-B1 as the major product (79%). At higher tem-
peratures (60 °C) both A·C and A have a preference towards
the cis species, i.e. (cis-B1)·C (82%) and cis-B1 (100%),
respectively. The difference in product selectivity between
A·C and A at low temperatures shows that the presence of
two calix[4]arenes around the platinum complex stabilizes
the kinetic product, i.e. the trans-B2 species. This stabiliza-
tion is supported by the incomplete transformation to the
cis-Pt complex (82%) at high temperatures.
3. Molecular Modelling Study
The modelled structures of the platinum complexes cis-
B1 and trans-B2 were first calculated using DFT, and the
optimized structures were subsequently used as input for
PM3 calculations. In order to calculate the structures of
capsules (cis-B1)·C and (trans-B2)·(C)2, the structures of cis-
B1 and trans-B2 were frozen, except for the diethylammoni-
ummethyl substituents, and C molecules were added (mod-
elled at the PM3 level). These structures were used as input
Figure 7. Modelled structures and schematic pictures of (cis-B1)·C
(a), trans-B2 (with xantphos ligands) (b) and (trans-B2)·(C)2 (c).
for molecular mechanics calculations (MMFF), and sub-
sequently the structure of (cis-B1)·C was also subjected to
PM3 calculation [PM3 calculation of (trans-B2)·(C)2 failed
because it is too large]. The modelled structure of cis-B1 b). The monodentate ligand is situated partly between the
(with a xantphos ligand) illustrates the square planar geom- two P(Ar)2 groups of the bidentate ligand. Consequently, C
etry around platinum. The modelled structure of capsule cannot interact solely with the bidentate ligand or solely
(cis-B1)·C illustrates that cis-B1 and C are complementary, with the monodentate ligand. The modelled structure of
facing one another, as a result of interaction between the (trans-B2)·(C)2 illustrates that two molecules of the rigid,
ammonium and sulfonato groups. In addition, the platinum concave calix[4]arene interact with trans-B2 (Figure 7, c).
ion is located inside the capsule (Figure 7, a).
One of the two tetraanionic calix[4]arenes interacts with
The modelled structure of the bisligated complex trans- four cationic groups of trans-B2 bound to four different
B2 (with two xantphos ligands) shows that the ionic Pt com- phosphorus atoms and the other calix[4]arene interacts with
plex adopts a distorted square planar geometry with the three cationic groups of trans-B2 situated at three different
first diphosphane ligand coordinating to platinum in a trans phosphorus atoms. Hence, each calix[4]arene interacts
fashion and the second in a monodentate fashion (Figure 7, simultaneously with both ligands. Consequently, (trans-B2)·
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Coordination of Pt by a Supramolecular Capsule
(C)2 is composed of two semicapsules with an undefined phane in the absence of calix[4]arene prefers the formation
structure. The platinum atom is situated between (not of the monoligated cis-Pt complex, indicated by 31P{1H}
within) the two semicapsules, i.e. the platinum atom is not NMR and ESI-MS. The two calix[4]arenes stabilize the ki-
directly encapsulated. Interestingly, (trans-B2)·(C)2 has a netic product, the trans-Pt species, and slow the formation
sandwich-like structure with the two calix[4]arenes pointing of the thermodynamic product, the cis-Pt species. This new
towards one another and the platinum complex is situated supramolecular strategy for controlling the coordination
in between. The modelled structure of (trans-B2)·(C)2 dis- chemistry of transition metal complexes reveals new oppor-
plays only one of the possible conformations and therefore tunities to control the activity, stability and selectivity of
it is likely that the two calix[4]arenes interact with trans-B2 the potential homogeneous catalysts.
in more ways than we have presented here.
Experimental Section
Kinetic Product Stabilization
General Remarks: All reactions were carried out under a dry, inert
atmosphere of purified nitrogen or argon using standard Schlenk
techniques, unless stated otherwise. Solvents were dried and dis-
tilled under nitrogen prior to use. Diethyl ether was distilled with
sodium/benzophenone. Methanol was distilled with CaH2. Deuter-
We know that upon reaction of [PtCl2(MeCN)2] with A
or A·C, the kinetic products trans-B2 and (trans-B2)·(C)2 are
the first products that are formed. Subsequently, upon co-
ordination of the Pt precursor to the noncoordinating phos-
phorus atom of trans-B2, the kinetic products transform ated solvents were distilled with the appropriate drying agents. Un-
less stated otherwise, all chemicals were obtained from commercial
suppliers and used as received. 4,5-Bis(bis{p-[(diethylamino)-
methyl]phenyl}phosphanyl)-9,9-dimethylxanthene (a),[5b] 4,5-bis-
(bis{p-[(diethylammonium tosylate)methyl]phenyl}phosphanyl)-
9,9-dimethylxanthene A-HOTs (A),[5d] 5,11,17,23-tetrakis(sulfon-
ato)-25,26,27,28-tetrakis(2-ethoxyethoxy)calix[4]arene tetrasodium
salt (C-SO3Na)[5b,12] and 25,26,27,28-tetrakis(2-ethoxyethoxy)ca-
lix[4]arene-5,11,17,23-tetrasulfonic acid (C-SO3H)[5c] were synthe-
sized according to reported procedures. NMR spectra were re-
corded with Varian Inova 500, Bruker Avance DRX 300 and Var-
into the thermodynamic products cis-B1 and (cis-B1)·C,
respectively. The low solubility of [PtCl2(MeCN)2] in meth-
anol results initially in an excess of A and A·C with respect
to the metal, which enhances the formation of the kinetic
product (as observed by in situ 31P{1H} NMR). The kinetic
product, (trans-B2)·(C)2, is stabilized by the two calix[4]ar-
ene units, and therefore the formation of the corresponding
thermodynamic product, (cis-B1)·C, is inhibited [at 20 °C,
Pt/PP = 1, (cis-B1)·C 2% and (trans-B2)·(C)2 98%]. In con-
trast, the kinetic product trans-B2 is not stabilized by its ian Mercury 300 NMR spectrometers. Chemical shifts are given in
ppm relative to TMS (1H and 13C NMR) and 85% H3PO4
eight tosylate counterions and therefore it transforms im-
mediately to the corresponding thermodynamic product cis-
B1 (at 20 °C, Pt/PP = 1, cis-B1 79% and trans-B2 21%).
Steric congestion is created around trans-B2 in (trans-B2)·
(C)2 by the two calix[4]arenes. This inhibits the access of
the Pt precursor to the noncoordinating phosphorus atom
of trans-B2 and consequently the formation of the thermo-
dynamic product, (cis-B1)·C, is also inhibited. The modelled
structure of (trans-B2)·(C)2 implies that each tetraanionic
(31P{1H} NMR). HRMS (FAB) measurements were carried out
with a JEOL JMS SX/SX 102A at the Department of Mass Spec-
trometry at the University of Amsterdam. ESI-MS measurements
were carried out with a Q-TOF (Micromass, Waters, Whyttensh-
awe, UK) mass spectrometer equipped with a Z-spray orthogonal
nanoelectrospray source, using Econo Tips (New Objective, Wob-
urn, MA) to create an off line nanospray, at the Department of
Mass Spectrometry of Biomacromolecules at the University of Am-
sterdam. The MS spectra were processed with software tools em-
calix[4]arene interacts with the cationic groups of the two bedded in Masslynx software (Micromass, Waters, Whyttenshawe,
UK), additional isotopic pattern analysis was performed with the
use of the Bruker Daltonics Isotope Pattern software program
(Bruker Daltonik, Bremen, Germany, version 1.0.125.0), and the
calculated isotope patterns shown in the Supporting Information
were calculated using the IsoPro 3.1 software program. Molecular
modelling calculations were performed using Spartan Ј08 V1.0.3
software (B3LYP LACVP basis set).
different ligands of trans-B2 and consequently fix the spatial
orientation of the two ligands relative to each other, which
results in the stabilization of the kinetic product. This stabi-
lization of (trans-B2)·(C)2 compared to trans-B2, leads to a
higher energy barrier for transformation of the kinetic
product, (trans-B2)·(C)2, into the thermodynamic product,
(cis-B1)·C and a relative shift in equilibrium to the trans-Pt
species.
cis-[Pt(A)Cl2] (cis-B1): A-HOTs (97.4 mg, 60.57 μmol) was added
to a fine suspension of [PtCl2(MeCN)2] (21.08 mg, 60.57 μmol) in
methanol (8 mL). After stirring for 1 h at room temperature, the
clear reaction mixture was heated to reflux overnight. The solvent
was evaporated, and the yellow solid was washed three times with
diethyl ether. cis-B1 was obtained as a pale yellow microcrystalline
powder. 31P{1H} NMR (121.5 MHz, CD3OD, 293 K): δ = 6.2 (s,
Conclusions
We have demonstrated that the coordination geometry
around a platinum atom can be influenced by supramolec-
ular capsules. The capsule used in this study is formed by
ionic interactions and is composed of a tetracationic
xantphos-type diphosphane ligand and a complementary
tetraanionic calix[4]arene. Reaction of the diphosphane
capsule with a platinum precursor yields the bisligated bi-
1
JPt–P = 3728 Hz) ppm. H NMR (300 MHz, CD3OD, 293 K): δ =
7.87 (d, J = 7.5 Hz, 2 H), 7.70 (d, J = 8.1 Hz, 8 H, OTs–), 7.61–
7.14 (m, 20 H), 7.25 (d, J = 8.4 Hz, 8 H, OTs–), 4.31 (s, 8 H,
CH2N), 3.04 (m, 16 H, NCH2CH3), 2.34 (s, 12 H, OTs–), 1.87 [s, 6
H, C(CH3)2], 1.22 (t, J = 7.8 Hz, 24 H, NCH2CH3) ppm. cis-B1
gave broad carbon resonances in its 13C{1H} NMR spectrum and
scalix[4]arene trans-Pt capsule, whereas the same diphos- therefore could not be characterized by 13C NMR spectroscopy.
Eur. J. Inorg. Chem. 2011, 4837–4845
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4843

J. N. H. Reek et al.
FULL PAPER
Self-Assembly of A·C: A methanol solution of C-SO3H (1 equiv.) 805.04 [B2 – Cl – 4H – 6OTs]3+, 690.03 [B2 – Cl – H – 4OTs]4+
,
was slowly added to a methanol solution of a (1 equiv.). The solu-
tion was stirred for 30 min at room temperature before the solvent
was evaporated, which left A·C. Observed upfield shifts of the pro-
ton resonances (ΔδH) of the CH2NH+(CH2CH3)2 protons of A·C,
with respect to those of the corresponding free A-HOTs in
CD3OD: Δδ(CH2CH3) = 0.37, Δδ(CH2CH3) = 0.34 and Δδ(NCH2)
= 0.25 ppm (A/C = 1:1). ESI-MS (CH3OH): m/z = 977.06 [A·C +
594.79 [B2-2Cl – 4H – 6OTs]4+
.
(cis-B1)·C: ESI-MS (CH3OH): m/z = 1109.86 [B1·C + 2H]2+
,
1091.36 [B1·C – Cl + H]2+, 715.93 [B1·C – 2Cl + H]3+, 723.23
[B1·C – 2Cl + Na]3+, 727.91 [B1·C – Cl + 2H]3+, 735.24 [B1·C – Cl
+ Na + H]3+, 742.55 [B1·C – Cl + 2Na]3+
.
Self-assembly of (trans-B2)·(C)2 from trans-B2 + C: ESI-MS
(CH3OH): m/z = 1393.48 [B2·(C)2 – Cl + 2Na]3+, 1378.83 [B2·
(C)2 – Cl + 2H]3+, 1034.39 [B2·(C)2 – Cl + 3H]4+, 1039.87 [B2·
2H]2+, 651.74 [A·C + 3H]3+
.
Self-Assembly of (cis-B1)·C: Equimolar methanol solutions of cis-
B1 and C-SO3Na were mixed at room temperature, which resulted
in the immediate formation of (cis-B1)·C together with 4 equiv. of
NaOTs.
(C)2 – Cl + 2H + Na]4+, 1045.35 [B2·(C)2 – Cl + H + 2Na]4+
,
,
1050.86 [B2·(C)2 – Cl + 3Na]4+, 776.07 [B2·(C)2 – C – Cl – H]4+
767.08 [B2·(C)2 – C – 2Cl – 2H]4+
.
Reaction of [PtCl2(MeCN)2] and A·C to give (trans-B2)·(C)2: ESI-
MS (CH3OH): m/z = 1378.83 [B2·(C)2 – Cl + 2H]3+, 1034.39 [B2·
(C)2 – Cl + 3H]4+, 767.08 [B2·(C)2 – C – 2Cl – 2H]4+, 776.07 [B2·
Self-Assembly of (trans-B2)·(C)2: Methanol solutions of trans-B2
(synthesized in situ) (1 equiv.) and C-SO3Na (2 equiv.) were mixed
at room temperature, which resulted in the immediate formation of
(trans-B2)·(C)2 together with 8 equiv. of NaOTs.
(C)2 – C – Cl – H]4+
.
In situ VT 31P{1H} NMR Studies
Supporting Information (see footnote on the first page of this arti-
cle): ESI-MS, measured and calculated isotope patterns of the com-
pounds.
cis-B1: A solution of [PtCl2(MeCN)2] (2.611 mg, 7.5 μmol, 1 equiv.)
and A-HOTs (12.060 mg, 7.5 μmol, 1 equiv.) in CD3OD (0.5 mL)
was vigorously stirred for 2 h at room temperature to ensure that
all the reactants dissolved. The reaction mixture was transferred
into a NMR tube and the reaction was followed by 31P{1H} NMR
over time, i.e. 3 h at 20 °C and 3 h at 60 °C.
[1] a) P. W. N. M. Van Leeuwen (Ed.), Supramolecular catalysis,
Wiley-VCH, Weinheim, Germany, 2008; b) T. S. Koblenz, J.
Wassenaar, J. N. H. Reek, Chem. Soc. Rev. 2008, 37, 247–262;
c) J. I. Van der Vlugt, T. S. Koblenz, J. Wassenaar, J. N. H.
Reek, Chemistry in Self-Assembled Nanoreactors, in: Molecular
Encapsulation: Organic Reactions in Constrained Systems (Eds.:
U. H. Brinker, J.-L. Mieusset), p. 145–174, John Wiley & Sons,
Chichester, UK, 2010; d) D. M. Vriezema, M. C. Aragones,
J. A. A. W. Elemans, J. J. L. M. Cornelissen, A. E. Rowan,
R. J. M. Nolte, Chem. Rev. 2005, 105, 1445–1489; e) D. Fiedler,
D. H. Leung, R. G. Bergman, K. N. Raymond, Acc. Chem.
Res. 2005, 38, 349–358; f) D. H. Leung, R. G. Bergman, K. N.
Raymond, J. Am. Chem. Soc. 2006, 128, 9781–9797; g) D. H.
Leung, R. G. Bergman, K. N. Raymond, J. Am. Chem. Soc.
2007, 129, 2746–2747.
[2] a) V. F. Slagt, J. N. H. Reek, P. C. J. Kamer, P. W. N. M.
van Leeuwen, Angew. Chem. 2001, 113, 4401; Angew. Chem.
Int. Ed. 2001, 40, 4271–4274; b) V. F. Slagt, P. W. N. M.
van Leeuwen, J. N. H. Reek, Angew. Chem. 2003, 115, 5777;
Angew. Chem. Int. Ed. 2003, 42, 5619–5623; c) V. F. Slagt,
P. C. J. Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek, J. Am.
Chem. Soc. 2004, 126, 1526–1536; d) A. W. Kleij, M. Lutz,
A. L. Spek, P. W. N. M. van Leeuwen, J. N. H. Reek, Chem.
Commun. 2005, 29, 3661–3663; e) A. W. Kleij, J. N. H. Reek,
Chem. Eur. J. 2006, 12, 4218–4227; f) A. W. Kleij, M. Kuil,
D. M. Tooke, A. L. Spek, J. N. H. Reek, Inorg. Chem. 2005, 44,
7696–7698; g) M. Kuil, T. Soltner, P. W. N. M. van Leeuwen,
J. N. H. Reek, J. Am. Chem. Soc. 2006, 128, 11344–11345; h) J.
Flapper, J. N. H. Reek, Angew. Chem. 2007, 119, 8744; Angew.
Chem. Int. Ed. 2007, 46, 8590–8592.
[3] a) M. J. Wilkinson, P. W. N. M. van Leeuwen, J. N. H. Reek,
Org. Biomol. Chem. 2005, 3, 2371–2383; b) M. Kuil, P. E. Gou-
driaan, A. W. Kleij, D. M. Tooke, A. L. Spek, P. W. N. M.
van Leeuwen, J. N. H. Reek, Dalton Trans. 2007, 22, 2311–
2320; c) P. E. Goudriaan, M. Kuil, X.-B. Jiang, P. W. N. M.
van Leeuwen, J. N. H. Reek, Dalton Trans. 2009, 10, 1801–
1805; d) L. K. Knight, Z. Freixa, P. W. N. M. van Leeuwen,
J. N. H. Reek, Organometallics 2006, 25, 954–960; e) A. J.
Sandee, A. M. van der Burg, J. N. H. Reek, Chem. Commun.
2007, 8, 864–866; f) D. Rivillo, H. Gulyas, J. Benet-Buchholz,
E. C. Escudero-Adan, Z. Freixa, P. W. N. M. van Leeuwen, An-
gew. Chem. 2007, 119, 7385; Angew. Chem. Int. Ed. 2007, 46,
7247–7250; g) H. Gulyas, J. Benet-Buchholz, E. C. Escudero-
Adan, Z. Freixa, P. W. N. M. van Leeuwen, Chem. Eur. J. 2007,
13, 3424–3430; h) B. Breit, Angew. Chem. 2005, 117, 6976; An-
gew. Chem. Int. Ed. 2005, 44, 6816–6825; i) W. Seiche, B. Breit,
trans-B2: A solution of [PtCl2(MeCN)2] (2.611 mg, 7.5 μmol,
1 equiv.) and A-HOTs (24.120 mg, 15.0 μmol, 2 equiv.) in CD3OD
(0.5 mL) was vigorously stirred for 2 h at room temperature to en-
sure that all the reactants dissolved. The reaction mixture was
transferred into a NMR tube and the reaction was followed by
31P{1H} NMR over time, i.e. 16 h at 20 °C and 5 h at 60 °C. (cis-
B1)·C and (trans-B2)·(C)2: A solution of [PtCl2(MeCN)2] (2.611 mg,
7.5 μmol, 1 equiv.) and A·C (14.643 mg, 7.5 μmol, 1 equiv.) in
CD3OD (0.5 mL) was vigorously stirred for 3 h at room tempera-
ture to ensure that all the reactants dissolved. The reaction mixture
was transferred into a NMR tube and the reaction was followed
by 31P{1H} NMR over time, i.e. 16 h at 20 °C and 20 h at 60 °C.
ESI-MS: Samples of the complexes and capsules with initial con-
centrations of 100–250 μm were diluted in MeOH to a final concen-
tration of 1%. ESI-MS analysis of cis-B1 was carried out with an
isolated sample of cis-B1. ESI-MS analysis of trans-B2 was carried
out with an in situ generated sample of trans-B2, which was pre-
pared by stirring a methanol solution of [PtCl2(MeCN)2] and A (2
equiv.) overnight at 20 °C. ESI-MS analysis of (cis-B1)·C was car-
ried out by mixing methanol solutions of cis-B1 and C, i.e. self-
assembly. ESI-MS analysis of (trans-B2)·(C)2 was performed in two
ways: (1) by mixing methanol solutions of trans-B2 and C, i.e. self-
assembly and (2) by using an in situ generated sample of (trans-
B2)·(C)2, which was prepared by stirring a methanol solution of
[PtCl2(MeCN)2] and A·C overnight at 20 °C. No ion peaks for
higher aggregates than 1:1 for (cis-B1)·C and 1:2 for (trans-B2)·
(C)2 were detected. Comparison of the measured isotope patterns
of the Pt complexes and capsules with those calculated confirms
the elemental composition and charge state (see Supporting Infor-
mation). The reported m/z values correspond to the 100% ion peak
(isotope with the highest intensity).
cis-B1: ESI-MS (CH3OH): m/z = 765.25 [B1 – 2OTs]2+, 661.26 [B1 –
Cl – 2H – 3OTs]2+, 575.25 [B1 – Cl – 3H – 4OTs]2+, 453.17 [B1-
3OTs]3+, 441.18 [B1 – Cl – H – 3OTs]3+, 395.84 [B1 – H – 4OTs]3+
,
383.82 [B1 – Cl – 2H – 4OTs]3+
.
trans-B2: ESI-MS (CH3OH): m/z = 977.06 [B2 – Cl – H – 3OTs]3+
919.71 [B2 – Cl – 2H – 4OTs]3+, 862.37 [B2 – Cl –3H – 5OTs]3+
,
,
4844
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Eur. J. Inorg. Chem. 2011, 4837–4845

Coordination of Pt by a Supramolecular Capsule
Phosphorus Ligands Asymmetric Catal. 2008, 2, 848–885; j)
S. A. Moteki, J. M. Takacs, Angew. Chem. 2008, 120, 908; An-
gew. Chem. Int. Ed. 2008, 47, 894–897.
Buchwald, J. Am. Chem. Soc. 2002, 124, 6043–6048; h) L. A.
Van der Veen, P. K. Keeven, P. C. J. Kamer, P. W. N. M.
van Leeuwen, J. Chem. Soc., Dalton Trans. 2000, 13, 2105–
2112; i) M. Kranenburg, P. C. J. Kamer, P. W. N. M.
van Leeuwen, Eur. J. Inorg. Chem. 1998, 2, 155–157; j) R. J.
Van Haaren, K. Goubitz, J. Fraanje, G. P. F. van Strijdonck, H.
Oevering, B. Coussens, J. N. H. Reek, P. C. J. Kamer,
P. W. N. M. van Leeuwen, Inorg. Chem. 2001, 40, 3363–3372.
[7] G. Petocz, Z. Berente, T. Kegl, L. Kollar, J. Organomet. Chem.
2004, 689, 1188–1193.
[4] a) M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusu-
kawa, K. Biradha, Chem. Commun. 2001, 6, 509–518; b) J. Re-
bek Jr., Angew. Chem. 2005, 117, 2104; Angew. Chem. Int. Ed.
2005, 44, 2068–2078; c) F. Hof, S. L. Craig, C. Nuckolls, J.
Rebek Jr., Angew. Chem. 2002, 114, 1556; Angew. Chem. Int.
Ed. 2002, 41, 1488–1508; d) M. M. Conn, J. Rebek Jr, Chem.
Rev. 1997, 97, 1647–1668.
[5] a) T. S. Koblenz, H. L. Dekker, C. G. De Koster, P. W. N. M.
van Leeuwen, J. N. H. Reek, Chem. Commun. 2006, 16, 1700–
[8] R. Van Duren, J. I. van der Vlugt, H. Kooijman, A. L. Spek,
D. Vogt, Dalton Trans. 2007, 10, 1053–1059.
1702; b) T. S. Koblenz, H. L. Dekker, C. G. De Koster, [9] a) Z. Freixa, M. S. Beentjes, G. D. Batema, C. B. Dieleman,
P. W. N. M. van Leeuwen, J. N. H. Reek, Chem. Asian J. 2011,
6, 2431; c) T. S. Koblenz, H. L. Dekker, C. G. De Koster,
P. W. N. M. van Leeuwen, J. N. H. Reek, Chem. Asian J. 2011,
6, 2444; d) T. S. Koblenz, M. Kuil, V. Bocokic, P. W. N. M.
van Leeuwen, J. N. H. Reek, manuscript in preparation.
G. P. F. van Strijdonck, J. N. H. Reek, P. C. J. Kamer, J.
Fraanje, K. Goubitz, P. W. N. M. van Leeuwen, Angew. Chem.
2003, 115, 1322; Angew. Chem. Int. Ed. 2003, 42, 1284–1287;
b) L. Poorters, D. Armspach, D. Matt, L. Toupet, S. Choua,
P. Turek, Chem. Eur. J. 2007, 13, 9448–9461; c) R. Den Heeten,
PhD Thesis, University of Amsterdam, The Netherlands, 2009;
d) Z. Freixa, P. W. N. M. van Leeuwen, Coord. Chem. Rev.
2008, 252, 1755–1786.
[6] a) M. Kranenburg, Y. E. M. van der Burgt, P. C. J. Kamer,
P. W. N. M. van Leeuwen, K. Goubitz, J. Fraanje, Organome-
tallics 1995, 14, 3081–3089; b) P. W. N. M. van Leeuwen,
P. C. J. Kamer, J. N. H. Reek, Pure Appl. Chem. 1999, 71, 1443–
1452; c) P. W. N. M. Van Leeuwen, P. C. J. Kamer, J. N. H.
Reek, P. Dierkes, Chem. Rev. 2000, 100, 2741–2769; d) P. C. J.
Kamer, P. W. N. M. van Leeuwen, J. N. H. Reek, Acc. Chem.
Res. 2001, 34, 895–904; e) Z. Freixa, P. W. N. M. van Leeuwen,
[10] L. Kollar, G. Szalontai, J. Organomet. Chem. 1991, 421, 341–
345.
[11] a) R. Zadmard, T. Schrader, T. Grawe, A. Kraft, Org. Lett.
2002, 4, 1687–1690; b) B. Kuberski, A. Szumna, Chem. Com-
mun. 2009, 15, 1959–1961.
Dalton Trans. 2003, 10, 1890–1901; f) M. A. Zuideveld, [12] R. Fiammengo, P. Timmerman, J. Huskens, K. Versluis,
B. H. G. Swennenhuis, M. D. K. Boele, Y. Guari, G. P. F.
van Strijdonck, J. N. H. Reek, P. C. J. Kamer, K. Goubitz, J.
Fraanje, M. Lutz, A. L. Spek, P. W. N. M. van Leeuwen, J.
Chem. Soc., Dalton Trans. 2002, 11, 2308–2317; g) J. Yin, S. L.
A. J. R. Heck, D. N. Reinhoudt, Tetrahedron 2002, 58, 757–
764.
Received: August 1, 2011
Published Online: September 16, 2011
Eur. J. Inorg. Chem. 2011, 4837–4845
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4845