Coulombic inter-ligand repulsion effects on the Pt(ii) coordination chemistry of oligocationic, ammonium-functionalized triarylphosphines

Article abstract of DOI:10.1039/c0dt01105c

The Pt(ii) coordination chemistry of oligocationic ammoniomethyl- and neutral aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX₂(L)₂ (X = Cl, I) have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1] ⁶⁺ and [2]⁶⁺, two ligands always occupy a trans-configuration with respect to each other in complexes of the type PtX ₂(L)₂, while for the tri-para-ammoniomethyl-substituted ligand [7]³⁺, the trans/cis ratio is dependent on the ionic strength of the solution. This behaviour was not observed for the neutral aminomethyl-substituted ligands. In the crystal structure of trans-[PtI ₂(1)₂]I₁₂, the geometrical parameters of the phosphine ligand [1]⁶⁺ are very similar to those found in the analogous complex of the benchmark ligand PPh₃, i.e. trans-PtI ₂(PPh₃)₂, indicating that no significant increase in the steric congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine ligands is dominated by repulsive Coulombic inter-ligand interactions.

Full text of DOI:10.1039/c0dt01105c

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PAPER
Coulombic inter-ligand repulsion effects on the Pt(II) coordination chemistry
of oligocationic, ammonium-functionalized triarylphosphines†
Dennis J. M. Snelders,a Maxime A. Siegler,b Lars S. von Chrzanowski,b Anthony L. Spek,b Gerard van Kotena
and Robertus J. M. Klein Gebbink*a
Received 26th August 2010, Accepted 26th November 2010
DOI: 10.1039/c0dt01105c
The Pt(II) coordination chemistry of oligocationic ammoniomethyl- and neutral
aminomethyl-substituted triarylphosphines (L) is described. Complexes of the type PtX2(L)2 (X = Cl, I)
have been isolated and characterized. For the hexa-meta-ammoniomethyl-substituted ligands [1]6+ and
[2]6+, two ligands always occupy a trans-configuration with respect to each other in complexes of the
type PtX2(L)2, while for the tri-para-ammoniomethyl-substituted ligand [7]3+, the trans/cis ratio is
dependent on the ionic strength of the solution. This behaviour was not observed for the neutral
aminomethyl-substituted ligands. In the crystal structure of trans-[PtI2(1)2]I12, the geometrical
parameters of the phosphine ligand [1]6+ are very similar to those found in the analogous complex of
the benchmark ligand PPh3, i.e. trans-PtI2(PPh3)2, indicating that no significant increase in the steric
congestion is present in the complex. Instead, the coordination chemistry of this class of phosphine
ligands is dominated by repulsive Coulombic inter-ligand interactions.
the phosphine ligands. Although several examples of phosphine
1
Introduction
ligands bearing anionic6 as well as cationic7 (Fig. 1) substituents
exist, the number of ionic groups per phosphine functionality is
usually limited to one, two or three. Ligands of this type have
mainly been investigated to enhance the solubility of catalysts in
polar or unconventional media and to enable their recycling, e.g.
through an aqueous/organic biphasic setup.8 Perhaps for these
reasons, repulsive Coulombic interactions between phosphine
ligands have only scarcely been described in the literature.1a
The use of additional supramolecular interactions between phos-
phine ligands coordinated to a metal centre is emerging as an
important tool in the design of new ligand systems.1 In particular,
the construction of bidentate phosphine ligands, which self-
assemble from monodentate phosphines via attractive noncovalent
interactions, is a powerful concept.2,3 Of special interest is the
design of bidentate phosphine ligands that are exclusively trans-
chelating.4 The supramolecular interactions involved are in most
cases hydrogen bonding or metal–ligand interactions.
Van Leeuwen et al.5 reported on the use of Coulombic inter-
actions to assemble triphenylphosphine derivatives. It was shown
that the cationic and anionic moieties of two different phosphine
ligands form ion pairs and that the resulting diphosphine ligand
acts as a bidentate, cis- or trans-chelating ligand in various
transition-metal complexes.
Hydrogen bonding, metal–ligand interactions or Coulombic
attractive forces between opposite charges, as supramolecular
interactions are all attractive in nature. However, in the case of
Coulombic interactions, the combination of functional groups of
the same charge should give rise to repulsive interactions between
aOrganic Chemistry & Catalysis, Debye Institute for Nanomaterials Science,
Faculty of Science, Utrecht University, Padualaan 8, 3584 CH Utrecht, The
Netherlands. E-mail: r.j.m.kleingebbink@uu.nl; Fax: (+31)30-252-3615
Fig. 1 Some known examples of cationic phosphine ligands.
The hexa-ammoniomethyl-functionalized Dendriphos ligands
[1]6+ and [2]6+ (Fig. 2) were recently reported by us9a and the appli-
cation of [2]Br6, as well as the higher generations of this class of lig-
ands in the Pd-catalyzed Suzuki-Miyaura cross-coupling reaction,
has been investigated.9b–d The high activity in the Suzuki-Miyaura
bCrystal and Structural Chemistry, Bijvoet Center for Biomolecular Re-
search, Faculty of Science, Utrecht University, Padualaan 8, 3584 CH
Utrecht, The Netherlands
† CCDC reference numbers 791148 and 791149. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0dt01105c
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2
Results
2.1 The reaction of hexacationic and neutral ligands with
PtCl2(cod).
Two equiv. of either the hexa-ammonium chloride ligand [1]Cl6 or
[2]Cl6 were added to PtCl2(cod) in MeOH–CH2Cl2 and stirred for
1 h at reflux temperature. Analysis of the products by 31P-NMR in
CD3OD showed one singlet resonance in each case, at 24.5 ppm
and 24.8 ppm, respectively, with 31P–195Pt coupling constants of
2655 and 2663 Hz (Table 1, entries 1 and 7). The magnitudes of
these coupling constants are characteristic for trans-PtCl2L2 (L =
tertiary phosphine) complexes.10 No other peaks were observed,
indicating that the complexes trans-[PtCl2L2]Cl12 (8a: L = 1; 8b: L =
2) were the only products of these reactions (Scheme 1). The
complexes were isolated and fully characterized. ESI-MS spectra
n+
showed peaks corresponding to the ions [PtL2]Cl(14-n) (L = 1,
2; n = 3, 4. Table 2, entries 1, 2), which is consistent with the
coordination of two phosphine ligands to the Pt centre. Ionization
by the loss of multiple halide ions is generally observed for this
type of oligocationic compound.9a,11
Fig. 2 The oligocationic ammoniomethyl- and neutral aminomethyl-sub-
stituted ligands considered in the present study.
After the addition of 0.2 equiv. of free [1]Cl6 or [2]Cl6 to
a solution in CD3OD of trans-8a or trans-8b, respectively and
heating to 65 ◦C, or after standing for 1 week in solution at room
temperature, the only species observed by 31P-NMR were trans-
8a–b, indicating that these complexes do not undergo trans–cis
isomerization, even in the presence of excess phosphine.12 In order
to investigate whether the trans-isomers are the kinetic products,
or whether they are formed via thermal isomerization of the cis-
isomers, the reactions of [1]Cl6 and [2]Cl6 with PtCl2(cod) were
performed at room temperature. The 31P-NMR spectra of the
products in CD3OD now showed trans-8a–b, along with a second
minor peak at 28.3 ppm (1JP,Pt = 4436, in the case of [1]Cl6) and
28.2 ppm (1JP,Pt = 4430, in the case of [2]Cl6). Upon heating the
solutions to 65 ◦C, this peak completely disappeared and did
reaction of catalytic systems employing these ligands is ascribed to
a Coulombic repulsive interaction between neighbouring ligands,
leading to a preferential formation of coordinatively unsaturated
complexes. Next to the hexacationic Dendriphos ligands, di-, tri
and tetra-ammoniomethyl functionialized [5]4+, [6]2+ and [7]3+ have
been developed.9d Hexa-aminomethyl functionalized 314 and 49d
were designed as neutral, sterically similar analogues of [1]6+
and [2]6+. Here, we turn our attention to the reactivity of this
series of oligocationic ligands, as well as their neutral analogues
3 and 4, with respect to Pt(II) ions and present investigations
concerning the role that repulsive Coulombic interactions play
in their coordination behaviour.
Table 1 31P-NMR spectral data for the products of the respective reactions of 1–4, PPh3 and P(4-CF3C6H4)3 with PtCl2(cod)
31P-NMR
Entry
L
L/Pt
Solvent
Product(s)
d (ppm)
1JP,Pt (Hz)
% obs.a
1
2
3
4
5
6
7
8
[1]Cl6
[1]Cl6
[1]Cl6
[1]Cl6
[1][BF4]6
[1][BF4]6
[2]Cl6
[2]Cl6
[2]Cl6
[2][BF4]6
[2][BF4]6
3
2
2
1
2
1
2
2
1
2
1
2
2
2
CD3OD
D2O
trans-[PtCl2(1)2]Cl12 (8a)
trans-[PtCl2(1)2]Cl12 (8a)
[PtCl3(1)]Cl5
trans-[PtCl2(1)2]Cl12 (8a)
cis-[PtCl2(DMSO)(1)][BF4]6
trans-[PtCl2(1)2][BF4]12
trans-[PtCl2(2)2]Cl12 (8b)
[PtCl3(2)]Cl5
trans-[PtCl2(2)2]Cl12 (8b)
cis-[PtCl2(DMSO)(2)][BF4]6
trans-[PtCl2(2)2][BF4]12
cis-PtCl2(3)2 (9a)
cis-PtCl2(4)2 (9b)
trans-PtCl2(4)2 (9b)
cis-PtCl2(PPh3)2
trans-PtCl2(PPh3)2
cis-PtCl2(DMSO)(PPh3)
[NBu4][PtCl3PPh3]
cis-PtCl2(PPh3)2
cis-PtCl2(P(4-CF3C6H4)3)2
24.5
23.9
9.0
23.5
16.9
23.7
24.8
8.2
23.0
16.3
24.6
14.7
15.4
21.0
14.9
21.7
17.6
7.2
2655
2652
3946
2627
3828
2682
2663
3960
2642
3818
not obs.
3641
3649
2615
3681
2626
3798
3945
3681
3655
100
100
100
100
100
100
100
100
100
100
100
100
70
30
25
5
35
35
100
100
DMSO-d6
DMSO-d6
DMSO-d6
DMSO-d6
CD3OD
DMSO-d6
DMSO-d6
DMSO-d6
DMSO-d6
C6D6
9
10
11
12b
13
4
DMSO-d6
14c
PPh3
1
DMSO-d6
15
16
PPh3
P(4-CF3C6H4)3
2
2
DMSO-d6
DMSO-d6
14.9
14.9
a Relative percentages. b Ref. 14 c Reaction performed in the presence of NBu4Cl (6 equiv. with respect to PPh3).
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Table 2 The major ions observed by ESI-MS analysis of the selected complexes
Entry
1a
Structure
Major ions observed
Calcd (m/z)
Found (m/z)
3+
[PtCl2(1)2]Cl12 (8a)
[PtCl2(2)2]Cl12 (8b)
[Pt(1)2]Cl11
658.59
484.70
962.390
713.046
551.18
779.27
507.86
696.24
435.16
924.38
587.58
812.36
587.52
825.49
508.03
349.30
658.62
484.72
962.385
713.050
551.22
779.31
508.26
696.38
435.24
924.47
587.31
812.39
587.53
825.58
508.07
349.32
4+
[Pt(1)2]Cl10
∑
b
3+
2a
[Pt(2)2]Cl11
4+
[Pt(2)2]Cl10
3c
4c
[PtCl3(1)]Cl5
[PtCl3(2)]Cl5
[Pt(1)]Cl6
2+
2+
[Pt(2)]Cl6
3+
[Pt(2)]Cl5
5c
6c
7d
8c
[PtCl2(DMSO)(1)][BF4]6
[PtCl2(DMSO)(2)][BF4]6
[PtCl2(1)2][BF4]12
[PtCl2(DMSO)(1)][BF4]4
[PtCl2(DMSO)(1)][BF4]3
[PtCl2(DMSO)(2)][BF4]4
[PtCl2(DMSO)(2)][BF4]3
2+
3+
2+
3+
3+
[PtCl2(1)2][BF4]9
4+
[PtCl2(1)2][BF4]8
2+
[PtI3(1)]I5
[Pt(1)]I6
[Pt(1)]I5
3+
4+
[Pt(1)]I4
a Prepared by the reaction of PtCl2(cod) with two equiv. of [1]Cl6 or [2]Cl6, respectively, in MeOH–CH2Cl2. b High resolution measurement. c Prepared by
the reaction of PtX2(cod) with one equiv. [1]Cl6, [2]Cl6, [1][BF4]6, [2][BF4]6 (X = Cl) or [1]I6 (X = I), respectively, in DMSO-d6. d Prepared by the reaction
of [PtCl2(DMSO)(1)][BF4]6 with [1][BF4]6 in DMSO-d6.
Scheme 1 The reaction of hexacationic and neutral ligands with PtCl2(cod).
not return after cooling to room temperature.13 Due to its labile
nature, this species could not be identified, but the magnitude of
the observed 31P–195Pt coupling constant rules out the possibility
that it corresponds to a complex of the type cis-[PtCl2L2]Cl12 (L =
1, 2).10
2.2 Investigations into the mechanism of the reaction of [1]6+ or
[2]6+ with PtCl2(cod)
In order to investigate the mechanism of formation of the
complexes trans-[PtCl2L2]12+ (L = 1, 2), the reaction of one and
subsequently two equiv. of [1]6+ or [2]6+ with PtCl2(cod) was
studied. These reactions were carried out in an NMR tube, by
mixing the reactants in DMSO-d6 for 1 min at room temperature,
followed by heating at 65◦ for 15–30 min. The products were not
isolated but were directly characterized by 31P-NMR and ESI-
MS. Using one equiv. of [1]Cl6 or [2]Cl6, the observation of a
sharp singlet by 31P-NMR indicated the formation of a single
species in both cases (Table 1, entries 3 and 8). ESI-MS analysis of
the reaction mixtures showed fragments containing one phosphine
The neutral ligand 3, which is sterically similar to [1]6+ and
bears six aminomethyl groups instead of ammoniomethyl groups,
has previously been reported to form the complex cis-PtCl2(3)2
(9a) upon reaction with PtCl2(cod) in C6D6 (Scheme 1).14 The
reaction of two equiv. of its larger benzylamine analogue 4, which
is sterically similar to [2]6+,9d with PtCl2(cod) gave a mixture of
cis- and trans-PtCl2(4)2 (9b), in a ratio of 70 : 30 in DMSO-d6
and 85 : 15 in toluene-d8 (Table 1, entries 12, 13).15 The analo-
gous reaction of benchmark ligand PPh3 exclusively yielded cis-
PtCl2(PPh3)2 in DMSO-d6 (entry 15). The commercially available
ligand P(4-CF3C6H4)3 is a significantly less strongly s-donating
ligand than PPh3. Its s-donating strength is comparable to those of
both [1]6+ and [2]6+.9d The reaction of two equiv. of P(4-CF3C6H4)3
with PtCl2(cod) in DMSO-d6 yielded exclusively cis-PtCl2(P(4-
CF3C6H4)3)2 (entry 16).
n+
per Pt centre, i.e. [PtL]Cl(8-n) (L = 1, 2; n = 2, 3. Table 2, entries 3
and 4). The analogous reaction of PPh3 yielded a mixture of cis-
and trans-PtCl2(PPh3)2, cis-PtCl2(DMSO)(PPh3) and unreacted
PtCl2(cod).16,17 When this reaction was performed in the presence
of 6 equiv. of NBu4Cl, a fourth signal was observed, corresponding
to the anion [PtCl3PPh3]- (Table 1, entry 14).18 In view of the
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Scheme 2 Effect of the presence of free chloride on the coordination chemistry of [1]6+ and [2]6+ with Pt(II) in DMSO-d6.
similarity of the 31P-NMR spectra of the products obtained for
the reactions of [1]Cl6 and [2]Cl6 to that of [PtCl3PPh3]- (Table 1,
entries 3, 8 and 14), the observed products were assigned the
structures [PtCl3(1)]Cl5 and [PtCl3(2)]Cl5 (Scheme 2). The ESI-MS
measurements are consistent with these structures. The reaction of
one equiv. of 4 with PtCl2(cod) in DMSO-d6 resulted in a mixture
of cis- and trans-9b, a third, unidentified product (d 19 ppm,
presumably PtCl2(DMSO)(4)) and unreacted PtCl2(cod).
Upon addition of a second equiv. of [1]Cl6 or [2]Cl6, respectively,
to a solution of [PtCl3L]Cl5 (L = 1, 2), the immediate and
quantitative formation of trans-[PtCl2L2]Cl12 (L = 1, 2) (i.e. 8a,b)
was observed by 31P-NMR. In contrast, when a second equiv.
of [1][BF4]6 or [2][BF4]6, respectively, was added to a solution of
[PtCl2(DMSO)(L)][BF4]6 (L = 1, 2), initially no further reaction
occurred and the added free ligand remained uncoordinated in
solution, as observed by 31P-NMR. When the solutions were
stirred for a prolonged period, eventually quantitative formation
of trans-[PtCl2L2][BF4]12 (L = 1, 2) was observed (Scheme 2). In
the case of the reaction between [PtCl2(DMSO)(1)][BF4]6 and
[1][BF4]6, the reaction took 3 h at room temperature to go to
completion. The identity of the product trans-[PtCl2(1)2][BF4]12
was confirmed by 31P-NMR (Table 1, entry 6) and ESI-MS
(Table 2, entry 7). When the reaction was performed at 65 ◦C,
complete conversion was obtained after 5 min. The reaction of
[PtCl2(DMSO)(2)][BF4]6 with [2][BF4]6 was much slower: stirring
at 65 ◦C for 24 h was required for complete conversion to the
product trans-[PtCl2(2)2][BF4]12.
The analogous reaction of one equiv. of the chloride-free ligands
[1][BF4]6 or [2][BF4]6 also led to the formation of one major species
in both cases, but the 31P-NMR spectra of the products were clearly
different from those obtained with [1]Cl6 and [2]Cl6 (Table 1,
entries 3 and 8 vs. entries 5 and 10). The 31P-NMR data found
for these species closely match those for cis-PtCl2(DMSO)(PPh3)
(entry 14). Analysis by ESI-MS showed signals corresponding to
n+
the ions [PtCl2(DMSO)(L)][BF4](6-n) (L = 1, 2; n = 2, 3. Table 2,
entries 5 and 6). The major products were therefore assigned the
structures cis-[PtCl2(DMSO)(L)][BF4]6 (L = 1, 2).
The 31P-NMR spectrum of the solution obtained after mixing
one equiv. of [1][BF4]6 with PtCl2(cod), apart from the intense
sharp singlet attributed to [PtCl2(DMSO)(1)][BF4]6, showed a
minor, broad signal at 9.1 ppm, which corresponds to the chemical
shift observed for [PtCl3(1)]Cl5.19 Therefore, we propose that
[PtCl2(DMSO)(1)][BF4]6 in DMSO solution exists in equilibrium
with [PtCl3(1)][BF4]5 and, presumably, [PtCl(DMSO)2(1)][BF4]7.
Added amounts of the free chloride should diminish the con-
centrations of [PtCl2(DMSO)(1)]X6 and [PtCl(DMSO)2(1)][X]7 in
favour of [PtCl3(1)]X5 (X = Cl, BF4). Indeed, when increasing
amounts (0.4–2.0 equiv. with respect to Pt) of NBu4Cl were added
to a solution of [PtCl2(DMSO)(1)][BF4]6, the signal for the latter
species gradually disappeared, while that for [PtCl3(1)]X5 gained
intensity. When an excess of NBu4Cl was added, only the signal
for [PtCl3(1)]X5 was observed.
2.3 The reactions of [1]I6, [5]I4, [6]I2 and [7]I3 with PtI2(cod)
The reaction of two equiv. of [1]I6 with PtI2(cod), in either refluxing
MeOH–CH2Cl2 or in H2O at room temperature, resulted in the
exclusive formation of trans-[PtI2(1)2]I12 (10a) (Scheme 3). The
31P-NMR spectrum measured in D2O showed one singlet at d
16.2 ppm with Pt satellites (1JP,Pt = 2583 Hz). No isomerization
to the cis isomer was observed, not even at higher temperatures
and in the presence of free hexacationic ligand. For tetra-
meta-ammoniomethyl substituted [5]I4, di-meta-ammoniomethyl
substituted [6]I2 and tri-para-ammoniomethyl substituted [7]I3, the
reaction with PtI2(cod) in MeOH–CH2Cl2 yielded mixtures of cis-
and trans-isomers of the complexes [PtI2(5)2]I8 (10b), [PtI2(6)2]I4
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Table 3 31P-NMR data for the products of the respective reactions of [1]I6, [5]I4, [6]I2 and [7]I3 with PtI2(cod)
31P-NMR
Entry
L
L/Pt
Solvent
Product(s)
d (ppm)
1JP,Pt (Hz)
% obs.
1
2
[1]I6
[1]I6
2
2
D2O
DMSO-d6
trans-[PtI2(1)2]I12 (10a)
trans-[PtI2(1)2]I12 (10a)
[PtI3(1)]I5
16.4
13.8
11.4
-3.3
11.4
12.7
11.6
12.6
13.2
12.4
11.8
12.0
11.3
13.1
12.4
2583
2520
3596
100
80
20
[1]I6
3
4
[1]I6
[5]I4
[5]I4
[6]I2
1
2
2
2
DMSO-d6
D2O
DMSO-d6
D2O
[PtI3(1)]I5
3596
2498
2488
2478
3479
2478
3471
2467
3491
2491
3455
100
100
90
25
75
80
20
55
45
80
20
trans-[PtI2(5)2]I8 (10b)
trans-[PtI2(5)2]I8 (10b)
trans-[PtI2(6)2]I4 (10c)
cis-[PtI2(6)2]I4 (10c)
trans-[PtI2(6)2]I4 (10c)
cis-[PtI2(6)2]I4 (10c)
trans-[PtI2(7)2]I6 (11)
cis-[PtI2(7)2]I6 (11)
trans-PtI2(PPh3)2
cis-PtI2(PPh3)2
5
6a
7
8
9
[6]I2
[7]I3
PPh3
2
2
2
DMSO-d6
D2O
CDCl3
a Measured at 45 ◦C.
Scheme 3 The reactions of di- tri- tetra- and hexacationic ligands with PtI2(cod).
(10c) and [PtI2(7)2]I6 (11) (Scheme 3), as indicated by their 31P-
NMR spectra, measured in either D2O or DMSO-d6 (Table 3). In
the 13C-NMR spectra of 10a–c and 11, the ipso- and ortho-carbons
of the aryl rings were observed as pseudo triplets, indicating the
presence of an AA¢X system (A = P, X = C),20 which is consistent
with the coordination of two phosphine ligands to the Pt centre.
In the case of 10b, only the trans-isomer was observed in D2O,
while a small amount of the cis-isomer was observed in DMSO-d6
(10%). For 10c, the cis-isomer was favoured in D2O (75 : 25), while
in DMSO-d6 the trans-isomer was favoured (20 : 80).21 Trans-10b
and trans-10c have very similar chemical shifts and 1JP,Pt coupling
constants in 31P-NMR (with a difference of 0.1 ppm and 20 Hz,
respectively, in D2O), while trans-10a has a chemical shift that is
3.7 ppm higher and a 1JP,Pt coupling constant that is 85 Hz higher
than that of trans-10b (Table 3). The origin of this difference is
unclear.
31
13
Fig. 3 The dependence of the trans/cis equilibrium position of [PtI2(7)2]I6
(11) on the concentration of added NaI, at 65 ◦C.
For [PtI2(7)2]I6 (11), a small excess of the trans isomer was
present in D2O at room temperature (55 : 45). Complex 11 readily
isomerized upon increasing the temperature,22 leading to a shift of
the equilibrium to the side of the trans isomer. Upon cooling down,
the original distribution was restored. Furthermore, the position
of this equilibrium was found to be dependent on the ionic strength
of the solution (Fig. 3). The addition of NaI up to a concentration
of 0.2 M led to a shift to the side of the cis-isomer. Increasing
the temperature, both in the absence and in the presence of 0.2 M
NaI, allowed the calculation of the thermodynamic parameters
(Table 4) for trans- to cis-isomerization in both cases, using Van ’t
Hoff plots (Fig. 4). These values show that trans- to cis-conversion
results in a significantly larger negative enthalpy change in the
presence of 0.2 M NaI, confirming the stabilization of the cis-
isomer by the added NaI.
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Table 4 Enthalpy and entropy changes for trans- to cis-isomerization of
[PtI2(7)2]I6 (11)
Table 5 Selected bond lengths and angles of trans-[PtI2(1)2]I12 (10a)
Angle (◦) Angle (◦)
˚
Bond length (A)
[NaI] (mol L-1)
DH (kJ mol-1)
DS (J mol-1 K-1)
Pt1-P1 2.3163 (10)
I1-Pt1-P1 91.15(3) C11-P1-C21 107.41(18)
P1-Pt1-I1a 88.84(3) C11-P1-C31 98.86(19)
Pt1-P1-C11 115.46(14) C21-P1-C31 103.44(18)
Pt1-P1-C21 112.07(13)
0.0
0.2
-22.0
-32.3
-73.1
-95.0
Pt1-I1 2.6136(3)
P1-C11 1.831(4)
P1-C21 1.828(4)
P1-C31 1.833(4)
Pt1-P1-C31 118.06(13)
inclination angles found between the planes of the three aryl
rings with respect to the P–Pt axis of direction are 5.88(17)◦,
9.60(17)◦ and 63.22(16)◦ and show a significant deviation from a
C3-symmetrical propeller-shape. Thus, the P–Pt axis of direction
is roughly parallel to the mean molecular planes of two of the
three independent aryl rings. Two of the six free iodide anions
per phosphine ligand (I2 and I3, Fig. 5) are embedded in cationic
pockets formed by several of the ammonium groups, while the
other anions (i.e. I4–I8) are located in between adjacent molecules
in the crystal lattice. Iodides I6 (I6A/I6B) and I8 (I8A/I8B) are
disordered and are split over two positions. Iodides I7 and I8A/B
both have a population occupancy of 0.5 (further details about
the refinement can be found in the experimental section). Finally,
based on the crystal structure of trans-10a, a Tolman cone angle31
of 195◦ can be estimated for [1]I6 using the method of Mu¨ller
and Mingos.23 However, this value seems to be overestimated (see
Discussion).
◦
Fig. 4 Van ’t Hoff plots for trans- to cis-isomerization of [PtI2(7)2]I6 (11),
Trans-[PtI2(1)2]I12 (10a) is stable up to a temperature of 85 C
at 0.0 M NaI (25–85 ◦C) and at 0.2 M NaI (65–85 ◦C).
in D2O. In contrast, upon dissolving trans-10a in DMSO-d6, a
ligand exchange of [1]I6 for iodide occurred, forming [PtI3(1)]I5
1
(d = 11.4 ppm, JP,Pt = 3596 Hz, Scheme 4) and uncoordinated
2.4 Structure and reactivity of trans-[PtI2(1)2]I12 (10a)
[1]I6. Such reactivity was not observed for complexes 10b and 10c,
not even at high temperatures. When PtI2(cod) was reacted with 1
equiv. of [1]I6 in DMSO-d6, [PtI3(1)]I5 was formed quantitatively.
An ESI-MS spectrum of this solution showed the fragments
Crystals of trans-[PtI2(1)2]I12 (10a), suitable for single-crystal X-ray
structure determination, were grown from a concentrated solution
of 10a in hot H2O, which was allowed to cool down to room
temperature. The molecular structure of trans-10a is depicted in
Fig. 5 and selected bond lengths and angles are given in Table 5.
In the cation of trans-10a, the Pt(II) centre, which is found at a
site of inversion symmetry, is bonded to two iodide ligands and
two phosphine ligands in a trans square planar geometry. The
n+
[Pt(1)]I(8-n) (n = 2, 3, 4) (Table 2, entry 8). Upon increasing
the temperature, the ratio [PtI3(1)]I5 + [1]I6 : trans-[PtI2(1)2]I12
◦
increased from 0.25 at room temperature, to 1.0 at 85 C. After
cooling down, the initial product distribution was restored.
Addition of one equiv. of molecular iodine to a solution of 10a
Fig. 5 Displacement ellipsoid plots (50% probability level) of trans-[PtI2(1)2]I12 (10a) given at 150(2) K. Left: hydrogen atoms and lattice iodide counter
anions have been omitted for clarity. One half of the molecule is generated by inversion symmetry. Right: the crystallographically independent phosphine
ligand and lattice iodide counter anions viewed down the direction of the P–Pt–P axis. Hydrogen atoms have been omitted for clarity.
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Scheme 4 The two ways of formation of [PtI31]I5 from trans-10a.
Table 6 Selected bond lengths and angles of [PtI3(1)]I5
in THF–H2O also led to the formation of [PtI3(1)]I5 (d 13.8 ppm,
1JP,Pt = 3620 Hz, D2O) (Scheme 4).24 In this reaction, one equiv.
of the phosphine oxide of [1]I6 was formed as a coproduct and
identical reactivity was observed for 10b and 10c. No Pt(IV)
species were observed by 31P-NMR. When I2 was added to a
solution of PtI2(PPh3)2 in CHCl3–THF, no reaction occurred, but
when the reaction was carried out in the presence of NBu4I and
H2O, a reactivity similar to that of 10a–c was observed, forming
[NBu4][PtI3PPh3] (d 12.1 ppm, 1JP,Pt = 3631 Hz, CDCl3).25
˚
Bond length (A)
Angle (◦)
Angle (◦)
Pt1-P1 2.2196 (18)
I1-Pt1-I2 88.620(17) Pt1-P1-C1 105.7 (2)
I1-Pt1-I3 176.95(2) Pt1-P1-C15 120.7(3)
Pt1-I1 2.5824(5)
Pt1-I2 2.6460(5)
Pt1-I3 2.6207(7)
P1-C1 1.811(7)
P1-C15 1.807(7)
P1-C29 1.830(7)
I1-Pt1-P1 92.83(5)
Pt1-P1-C29 117.6(2)
I2-Pt1-I3 89.822(17) C1-P1-C15 106.8(3)
I2-Pt1-P1 170.23(5) C1-P1-C29 106.2(3)
I3-Pt1-P1 89.15(5)
C15-P1-C29 98.3(3)
Crystals were grown from a concentrated solution of [PtI3(1)]I5
in D2O. The molecular structure of [PtI3(1)]I5 is depicted in
Fig. 6 and selected bond lengths and angles are given in Table 6.
The crystal structure shows that the Pt(II) ion is bonded to
one phosphine ligand and three iodide ligands and is found
in a distorted square planar geometry. The Pt centre bears a
formal negative charge, leaving five remaining lattice counterions,
found near the hexacationic phosphine ligand, for charge balance.
The sum of occupancy factors for all lattice iodides (i.e. I4-
I9) is 5 (further details about the refinement can be found in
the experimental section). Two of these iodides (I6 and I8) are
embedded in cationic pockets formed by the ammonium groups.
Table 7 Selected bond lengths and angles in the crystal structures of
complexes of the type trans-PtI2L2 (L = monodentate phosphine) and the
Tolman cone angles of the corresponding phosphines
P-Ligand CPC (◦)
Cone Angle (◦)
145a
˚ ˚
P–Pt (A) P–C (A) Ref.
PPh3
P(Cy)3
[1]6+
107.6(3)
103.2(3)
101.7(3)
104.96
2.318(2)
2.371(2)
1.826(4) 26a
1.844(8) 26c
1.861(10)
170a
108.33
102.19
1.891(9)
107.41(18) 2.3165(10) 1.830(4) this work 195b, 150c
98.86(19)
103.44(18)
a Tolman cone angle, determined from CPK molecular models, see ref.
31 b Estimated from the X-ray crystal structure of trans-[PtI2(1)2]I12
(10a). c Estimated from the 31P-NMR chemical shift of the complex
[PdCl2(1)2]Cl12.
3
Discussion
3.1 Crystal structures of trans-[PtI2(1)2]I12 (10a) and [PtI3(1)]I5.
In complexes of the type trans-PtI2L2 (L = monodentate phosphine
ligand), the Pt-P bond length, as well as the C-P-C angles and the
C-P bond lengths in the phosphine, are known to increase with
an increasing steric demand of the phosphine ligand.26 For trans-
[PtI2(1)2]I12 (10a), these geometrical parameters are very similar
to those found in trans-PtI2(PPh3)2 (Table 7), indicating that no
significant increase in the steric congestion is present in trans-10a.
In the structure of [PtI3(1)]I5, the bond length between the Pt
˚
centre and the I atom trans to the phosphine is about 0.016 A
shorter than in [NBu4][PtI3(PPh3)].25 This suggests a weaker trans-
Fig. 6 Displacement ellipsoid plot (50% probability level) of [PtI3(1)]I5
given at 110(2) K. Hydrogen atoms have been omitted for clarity.
influence of [1]6+ compared to PPh3. This is consistent with the
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weaker s-donating strength of [1]6+, which we have previously
demonstrated by evaluation of the 1JP,Se coupling constants in 31P-
NMR of the corresponding phosphine selenides.9d
31P-NMR chemical shifts of the corresponding complexes trans-
PdCl2L2 (L = [2]6+, 4),9d have earlier pointed out that the neutral
ligand 4 is sterically similar to [2]6+. This observation suggests that
steric factors do not play an important role in the behaviour of
[1]6+ and [2]6+. The electron donating ability of a phosphine ligand
may, through its trans-influence, also influence the preference for
the cis- or trans-isomers. By measuring the coupling constant
1JP,Se in the 31P-NMR spectrum of the corresponding phosphine
selenides, we have previously established that the s-donating
ability of both [1]6+ and [2]6+ is significantly less strong than that
of PPh3 and is comparable to that of P(4-CF3C6H4)3.9d The latter
ligand forms the complex cis-PtCl2(P(4-CF3C6H4)3)2 exclusively,
indicating that the reduced s-donating strength, and thus the
weaker trans-influence of these phosphines, probably does not
play an important role either in their preference for the formation
of trans-complexes. Importantly, the 31P-NMR measurements for
each of these complexes (see Table 1) were performed in the same
solvent, i.e. DMSO-d6, thus eliminating the influence of the solvent
in these comparisons. Instead, repulsive Coulombic forces between
the coordinated ligands in complexes of the type PtCl2L2 (L = [1]6+,
[2]6+) seem to be the dominating factor in their exclusive formation
of the trans-isomers. Such repulsive forces are stronger in the cis-
complexes due to the closer proximity of the ligands, explaining
the higher thermodynamic stability of the trans-isomers.
More evidence for the importance of the Coulombic inter-
ligand repulsion forces in this type of complex is provided
by the observation that the cis-trans-equilibrium position of
[PtI2(7)2]I6 (11) is dependent on the ionic strength of the solution.
Increasing the NaI concentration leads to a shift in the equilibrium
to the side of the cis-isomer. Therefore, we propose that the
repulsive Coulombic interaction, which disfavours the cis-isomer,
is attenuated at higher ionic strengths due to the shielding of
the charges. Furthermore, the increased polarity of the medium
upon increasing the ionic strength33 may favour the cis-isomer
due to its large dipole moment. No further shift was observed
at concentrations higher than 0.15 M. It is likely that at this
concentration, other factors begin to dominate, such as steric
factors as well as the respective trans-influences of the ligands.
Several examples are found in the literature where related repulsive
Coulombic interactions have been put forward as the driving force
for the formation of square planar trans-complexes; yet, in none of
these cases has this explanation been substantiated. Hexa-anionic
tris-para-phosphonated triphenylphosphine (p-TPPTP) forms the
trans-isomer of the complex PtCl2(p-TPPTP)2 exclusively (in
D2O).34 The palladium(II) complex cis-PdCl2[P(CH2)2NMe2)3]2
was shown to undergo quantitative cis- to trans-isomerization
upon protonation of the dimethylamino groups.35 Yet, trianionic
tris-meta-sulfonated triphenylphosphine (TPPTS) forms predom-
inantly the cis-isomer of the complex PtCl2(TPPTS)2 (cis : trans =
80 : 20 at RT in DMSO-d6).36 It is likely that similar repulsive
Coulombic forces exist in this complex, although in this case they
apparently do not outweigh the contributions of other factors.
As mentioned above, the repulsive Coulombic forces between
the ligands coordinated to Pt(II) have for a long time been known
to contribute to the total of factors governing cis-trans-equilibria
and can be rationalized by a release of inter-ligand repulsive forces
in the trans-isomers with respect to the cis-isomers. This effect has
previously been described to originate from the partial negative
charges on the halide ligands and the partial positive charges
Even though the geometrical parameters for trans-10a given in
Table 7 do not indicate an increased steric congestion compared
to trans-PtI2(PPh3)2, the bulky character of [1]6+ as a ligand is
evident from the overall shape of the phosphine in the structure
of trans-10a (Fig. 5). Based on this structure, a cone angle of
195◦ can be estimated for [1]6+.23 The structures of trans-10a,
[PtI3(1)]I5 and previously reported [1(S)]I69d show clear differences
in the positioning of the cations and anions, as well as in the
conformations of the aryl rings and ammoniomethyl substituents.
This indicates that these structures are relatively flexible and
adopt different conformations upon crystallizing, which leads
to significant differences in the cone angles obtained from each
of the three structures. In all cases, the sterically demanding
conformation in the solid state, i.e. the coplanarity of the aryl
rings with respect to the P–Pt axis of direction, is adopted in order
to accommodate the large iodide ions in the cationic pockets. In
polar solvents, this conformation is probably not retained due
to solvent separated ion pairing,27 leading to an overall smaller
effective cone angle in solution. Indeed, when the cone angles of
[1]6+ and [2]6+, respectively, were estimated by measuring the 31P-
NMR chemical shifts of the complexes trans-[PdCl2L2]Cl12 (L = 1,
2),9d a much smaller value of approximately 150◦ was found in both
cases, which seems to be in better agreement with the geometrical
parameters in Table 7. These NMR spectra were measured in
CD3OD, ensuring minimal ion pairing and the value can thus be
attributed to the cone angle of the ‘naked’ cations [1]6+ and [2]6+.
3.2 Effects of Coulombic inter-ligand repulsion forces
Differences in the thermodynamic stabilities of cis- and trans-
isomers of species of the type PtX2L2 (L = tertiary phosphine,
X = halide) have been described in detail in the literature and are
ascribed to a complex combination of factors.28,29 The differences
in bond energies between the cis- and trans-isomers originate
mainly from the differences in the respective trans-influences of the
tertiary phosphine ligand L and the halide ligand X and favour the
cis-isomers.30 Coulombic interactions between the partial negative
charges on X and the partial positive charges on Pt and L
favour the trans-isomers. Due to the large difference in the dipole
moments of the isomers, the solvation effects favour the cis-isomers
in polar solvents and the trans-isomers in apolar solvents. Finally,
when bulky phosphine ligands are used, the steric repulsion
favours the trans-isomers.31,32 Each of these factors has its own
effect on the thermodynamic stability of the respective isomers
and these are often finely balanced. The cis-trans isomerization of
these complexes is in most cases catalyzed by free phosphine, free
halide or a solvent molecule.29
The complete selectivity of the hexacationic ligands [1]6+ and
[2]6+ towards the formation of the trans-isomers of the com-
plexes [PtCl2L2]Cl12 (L = 1, 2), without subsequent trans- to cis-
isomerization, indicates that a large energetic difference exists
between the trans- and cis-isomers of these complexes. In contrast,
the neutral ligands 3 and 4 form the corresponding cis-isomers ei-
ther exclusively or predominantly. For PtCl2(4)2 (9b), cis- to trans-
isomerization was observed upon heating in the presence of free
4, indicating that the cis-isomer is thermodynamically favoured.
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on the phosphine ligands.28 The phosphine ligands considered in
the present study carry permanent ionic groups. Based upon our
own observations as well as those of others,34,35 we believe that
the commonly accepted principle of repulsive Coulombic inter-
ligand interaction can be invoked to describe the behaviour of
these oligocationic phosphine ligands.
substitution of the DMSO ligand by the incoming phosphine to
form trans-[PtCl2(1)2]12+ thus has to occur in two steps. Assuming
that a pathway via the hypothetical cis-[PtCl2(1)2]12+ is energetically
unfavourable due to the cis-configuration of the two hexacationic
phosphine ligands, it is plausible that the actual substitution
step occurs after disproportionation of [PtCl2(DMSO)(1)]6+ into
[PtCl(DMSO)2(1)]7+ and [PtCl3(1)]5+ (Scheme 5). The latter species
may react with [1]6+, leading to trans-[PtCl2(1)2]12+. The occurrence
of such disproportionation in DMSO solution is indicated by
the 31P-NMR spectrum of [PtCl2(DMSO)(1)]6+, in which a minor
signal attributed to [PtCl3(1)]5+ is observed.
Trans-[PtI2(1)2]I12 (10a) partially dissociates in DMSO-d6 solu-
tion, establishing an equilibrium with [PtI31]I5 and uncoordinated
[1]I6. In contrast, such dynamic behaviour was not observed for
[PtI2(5)2]I8 (10b), [PtI2(6)2]I4 (10c) or trans-[PtCl2(1)2]Cl12 (8a), not
even at elevated temperatures. This suggests that the increase
in steric and Coulombic repulsion forces going from 10c and
10b to 10a destabilizes the complex. In the crystal structure
of trans-10a, values found for the Pt–P and C–P bond lengths
and the C–P–C angles are very similar to those found in trans-
PtI2(PPh3)2 (vide supra).26a As these parameters are known to be
sensitive to the steric bulk of the phosphine, this indicates that the
steric demand of [1]I6 is most likely not the main reason for the
observed lability of trans-10a and suggests an important role for
the repulsive Coulombic forces. The difference in stability upon
dissolution in DMSO-d6, between trans-[PtCl2(1)2]Cl12 (8a) and
trans-[PtI2(1)2]I12 (10a) indicates that the anion plays an important
role as well and could originate from a higher thermodynamic
stability of the product [PtX3(1)]X5 for X = I compared to X =
Cl. Thus, the nature of the phosphine ligand, the anion and the
solvent each contribute to the dynamic behaviour observed for
10a.
Scheme 5 Proposed mechanism of formation of trans-[PtCl2(1)2]12+
.
4
Conclusions
Upon combination with a Pt(II) salt, the hexacationic meta-
ammoniomethyl-substituted ligands [1]6+ and [2]6+ lead to the ex-
clusive formation of monophosphine-Pt(II) or trans-bisphosphine
Pt(II) complexes. This behaviour is not matched by either neutral
meta-aminomethyl-substituted analogues of these ligands or by
triphenylphosphine and is attributed to repulsive Coulombic inter-
ligand interactions. Such interactions have been put forward as
the driving force for this type of coordination behaviour in some
earlier cases of ionic phosphine ligands; yet, this is the first time
that this explanation has been substantiated. These insights are
in line with our previous studies, in which we attributed the high
activity of the catalytic systems employing this class of ligands in
the Pd-catalyzed Suzuki-Miyaura reaction9b–d to their Coulombic
repulsive inter-ligand interactions.
3.3 Mechanism of formation of trans-[PtCl2L2]12+ (L = 1, 2).
In the reaction of one equiv. of the phosphines [1]Cl6 or [2]Cl6
with PtCl2(cod) in DMSO-d6, a complete selectivity towards the
formation of the complexes [PtCl3L]Cl5 (L = 1, 2) was observed.
In contrast, the analogous reaction of neutral 4 and that of
PPh3, even when carried out in the presence of NBu4Cl (6 equiv.
with respect to PPh3) yielded a mixture of products, including a
significant amount of cis-PtCl2L2 (L = 4, PPh3). This suggests
that the reaction of the free phosphines [1]Cl6 or [2]Cl6 with
PtCl2(cod) proceeds much faster than the subsequent reaction
with [PtCl3L]Cl5 (L = 1, 2) to form trans-[PtCl2L2]Cl12 (8a,b).
Based on our considerations outlined above, we attribute this
observation to repulsive Coulombic interactions between the free
cationic phosphines [1]6+ or [2]6+ and the corresponding cationic
monophosphine complexes [PtCl3L]5+ (L = 1, 2). The complexes
[PtCl3L]Cl5 (L = 1, 2) can thus be regarded as intermediates in the
reaction of [1]Cl6 and [2]Cl6, respectively, with PtCl2(cod) to form
trans-8a–b.
The reaction of [1][BF4]6 with cis-[PtCl2(DMSO)(1)][BF4]6 re-
quired stirring for 3 h at RT to go to completion, while the
reaction of [1]Cl6 with [PtCl3(1)]Cl5 was complete within 1 min
(Scheme 2). The attack of [1]6+ on [PtCl2(DMSO)(1)]6+ to give
trans-[PtCl2(1)2]12+ thus appears to be kinetically inhibited. Substi-
tutions at Pt(II) occur with retention of the stereochemistry.29,37
Formation of trans-[PtCl2(1)2]12+ starting from [PtCl3(1)]5+ can
thus occur in one step, i.e. by substitution of the chloride trans
to the phosphine in [PtCl3(1)]5+, which is favoured by the high
trans-effect37 of the coordinated phosphine ligand. In contrast,
in [PtCl2(DMSO)(1)]6+, the phosphine and the DMSO ligands
have a cis-configuration with respect to each other38 and the
5
Experimental
General remarks
Experiments involving free phosphines were performed using
deoxygenated solvents and under an inert N2 atmosphere using
standard Schlenk techniques. Amberlite IRA-900 was purchased
from Acros Chimica. PtCl2(cod),39 PtI2(cod),40 [1]I6,9a [2]Br6,9a
[5]I4,9d [6]I2,9d [7]I3,9d [1][BF4]6 and [2][BF4]6 were synthesized
9e
9e
according to reported literature procedures. NMR spectra were
recorded on a Varian Inova 300 or a Varian AS 400 spectrometer
◦
1
1
at 25 C unless stated otherwise. H and 13C { H} spectra were
referenced to residual solvent signals. MALDI-TOF MS spectra
were recorded with an Applied Biosystems Voyager System mass
spectrometer using 9-nitroanthracene as the matrix. Elemental
analyses were carried out by Dornis & Kolbe, Mikroanalytisches
Laboratorium, Mu¨llheim a/d Ruhr, Germany. Time-of-flight
electrospray ionization mass spectra (ESI-MS) were measured
by the Biomolecular Mass Spectrometry and Proteomics Group,
Utrecht University, on a Micromass LC-T mass spectrometer
(Waters, Manchester, UK), operating in positive ion mode. The
samples were introduced at concentrations of 20–50 mM. The
nanospray needle potential was typically set to 1300 V and the
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cone voltage to 20–60 V. The source block temperature was set to
80 ◦C.
found: C 48.36, H 7.30, Cl 23.46, N 8.04, P 2.89%. Calc. for
C84H150Cl14N12P2Pt (2081.56): C 48.47, H 7.26, Cl 23.85, N 8.07, P
2.98%.
Synthesis of [1]Cl6 and [2]Cl6.
[PtCl2(2)2]Cl12 (8b)
Hexacationic phosphines [1]I6 and [2]Br6 were subjected to anion
exchange using an Amberlite IRA-900 (Cl) resin. Before use, the
resin (70 mL, wet) was rinsed with a solution of LiCl in MeOH
(0.3 M, 250 mL), until the eluate was colourless, followed by H2O
(200 mL) and MeOH (100 mL). The ion exchange was performed
under a N2 atmosphere using MeOH as the eluent (200 mL),
followed by the evaporation of the solvent in vacuo. A column
with dimensions 20–25 cm (length) and 2 cm (width) was used.
Starting from PtCl2(cod) (14 mg, 0.037 mmol) and [2]Cl6 (0.10 g,
0.075 mmol), 8b was obtained as a yellow powder. Yield: 0.12 g
1
(quant.). H-NMR (300 MHz, CD3OD): d (ppm) = 8.69 (br. s,
12H, o-Ar), 8.03 (s, 6H, p-Ar), 7.72 (d, 3JH,H = 7.8 Hz, 24H, o-Ph),
7.47 (m, 36H, m- and p-Ph), 4.93 (br. s, 24H, Ph-CH2N), 4.75
(br. s, 24H, Bn-NCH2), 2.96 (s, 72H, N(CH3)2). 13C{ H}-NMR
1
(100 MHz, CD3OD): d (ppm) = 143.0 (br. s, Ar), 142.4 (s, Ar),
134.6 (s, Ph), 132.0 (s, Ph), 130.8 (br. s, Ar), 130.3 (s, Ph), 129.5
(s, Ar), 129.0 (s, Ph), 67.0 (s, NCH2), 66.6 (s, NCH2), 49.7 (s,
[1]Cl6
1
N(CH3)2). 31P{ H}-NMR (122 MHz, CD3OD): d (ppm) = 24.8
Starting from 0.540 g of [1]I6, the product was obtained as an
(s, 1JP,Pt = 2663 Hz). HR-ESI MS: (m/z) 962.390 {[M-3Cl]3+, calc.
962.385}, 713.046 {[M-4Cl]4+, calc. 713.050}. Elem. anal. found:
C 61.51, H 6.41, N 5.55, P 2.16%. Calc. for C156H198Cl14N12P2Pt
(2994.73): C 62.57, H 6.66, N 5.61, P 2.07%.
1
off-white powder. Yield: 0.347 g (quant.). H-NMR (400 MHz,
3
CD3OD): d (ppm) = 8.13 (d, JP,H = 7.2 Hz, 6H, o-Ar), 7.89 (s,
1
3H, p-Ar), 4.71 (s, 12H, NCH2), 3.21 (s, 54H, N(CH3)3). 13C{ H}-
2
NMR (100 MHz, CD3OD): d (ppm) = 141.8 (d, JP,C = 20.7 Hz,
1
o-Ar), 141.5 (d, JP,C = 15.3 Hz, i-Ar), 139.7 (s, p-Ar), 131.3 (d,
1
3JP,C = 7.0 Hz, m-Ar), 68.8 (s, NCH2), 53.4 (s, N(CH3)3). 31P{ H}-
PtCl2(4)2 (9b)
NMR (162 MHz, CD3OD): d (ppm) = -2.9. HR-ESI MS: (m/z)
417.230 {[M-2Cl]2+, calc. 417.227}.
A solution of PtCl2(cod) (33 mg, 0.089 mmol) in CH2Cl2 (3 mL)
was added to a solution of 4 (189 mg, 0.178 mmol, 2.0 equiv.) in
CH2Cl2 (10 mL). The mixture was heated at reflux temperature
for 1 h and subsequently dried in vacuo, yielding 9b as a viscous
yellow oil (226 mg, quant.). 1H-NMR (400 MHz, C6D6): d (ppm) =
(signals attributed to the cis-isomer) 7.80 (d, 3JH,P = 10.4 Hz, 12H,
o-Ar), 7.67 (s, 6H, p-Ar), 7.32 (d, 3JH,H = 7.2 Hz, 12H, o-Ph), 7.20
(t, 3JH,H = 7.6 Hz, 12H, m-Ph), 7.08 (t, 3JH,H = 7.2 Hz, 6H, p-Ph),
3.27 (s, 12H, NCH2), 3.23 (s, 12H, NCH2), 1.96 (s, 18H, NCH3).
13C-NMR (100 MHz, C6D6): d (ppm) = (signals attributed to the
cis-isomer) 139.7 (br. s, Ar), 134.9 (br. s, Ar), 131.6 (s, Ar), 130.9
(s, Ar), 129.2 (s, Ph), 128.7 (s, Ph), 128.5 (s, Ph), 127.3 (s, Ph),
[2]Cl6
Starting from 0.500 g of [2]Br6, the product was obtained as an
1
off-white powder. Yield: 0.405 g (quant.). H-NMR (300 MHz,
CD3OD): d (ppm) = 8.30 (d, 3JP,H = 7.2 Hz, 6H, o-Ar), 7.84 (s, 3H,
3
p-Ar), 7.62 (d, JH,H = 6.6 Hz, 12H, o-Ph), 7.53 (m, 18H, m- and
p-Ph), 4.73 (s, 12H, Ph-CH2N), 4.70 (s, 12H, Bn-NCH2), 3.04 (s,
1
36H, N(CH3)2). 13C{ H}-NMR (100 MHz, CD3OD): d (ppm) =
2
1
142.2 (d, JP,C = 19.9 Hz, o-Ar), 141.7 (d, JP,C = 15.0 Hz, i-Ar),
140.0 (s, p-Ar), 134.6 (s, Ph), 131.9 (s, Ph), 131.0 (d, 3JP,C = 7.0 Hz,
m-Ar), 130.2 (s, Ph), 129.0 (s, Ph), 68.7 (s, NCH2), 68.5 (s, NCH2),
62.0 (s, NCH2), 61.6 (s, NCH2), 42.4 (s, NCH3). 31P{ H}-NMR
1
1
49.5 (s, N(CH3)2). 31P{ H}-NMR (121 MHz, CD3OD): d (ppm) =
(162 MHz, Toluene-d8): d (ppm) = 21.0 (s, 1JP,Pt = 2653 Hz, trans-
isomer), 16.6 (s, 1JP,Pt = 3610 Hz, cis-isomer). MALDI-TOF MS:
(m/z) 2350.9 {[M-Cl]+, calc. 2351.2}. Elem. anal. found: C 72.49,
H 6.90, N 6.95, P 2.54%. Calc. for C144H162Cl2N12P2Pt (2388.88):
C 72.40, H 6.84, N 7.04, P 2.59%.
-2.4. ESI MS: (m/z) 645.31 {[M-2Cl]2+, calc. 645.32}, 418.53 {[M-
3Cl]3+, calc. 418.56}. Elem. anal. found: C 68.58, H 7.35, Cl 15.53,
N 6.08, P 2.31%. Calc. for C78H99Cl6N6P (1364.37): C 68.67, H
7.31, Cl 15.59, N 6.16, P 2.27%.
Synthesis of PtCl2L2 complexes 8a–b
[PtI2(1)2]I12 (10a)
A solution of PtCl2(cod) in CH2Cl2 (2 mL) was added to a solution
of [1]Cl6 or [2]Cl6 (2.0 equiv.) in MeOH (10 mL). The mixtures
were heated at reflux temperature for 1 h and subsequently dried
in vacuo.
A solution of PtI2(cod) (37 mg, 0.066 mmol) in CH2Cl2 (10 mL)
was added at 60 ◦C to a solution of [1]I6 (193 mg, 0.133 mmol, 2.0
equiv.) in MeOH (50 mL), upon which a precipitate formed. The
mixture was heated at reflux temperature for 1 h and subsequently
centrifuged. The precipitate was dried in vacuo, affording 10a as
a light yellow powder (179 mg, 81%). 1H-NMR (400 MHz, D2O):
d (ppm) = 8.53 (br. s, 12H, o-Ar), 7.99 (s, 6H, p-Ar), 4.89 (s, 24H,
[PtCl2(1)2]Cl12 (8a)
Starting from PtCl2(cod) (8.5 mg, 0.023 mmol) and [1]Cl6 (41 mg,
0.045 mmol), 8a was obtained as a yellow powder. Yield: 50 mg
1
NCH2), 3.24 (s, 108H, N(CH3)3). 13C{ H}-NMR (75 MHz, D2O):
1
(quant.). H-NMR (400 MHz, CD3OD): d (ppm) = 8.52 (br. s,
d (ppm) = 142.0 (br. s, m-Ar), 141.2 (s, p-Ar), 134.1 (pseudo t,
JC,P = 29.6 Hz, i-Ar), 129.5 (pseudo t, JC,P = 5.6 Hz, o-Ar), 67.5
12H, o-Ar), 8.07 (s, 6H, p-Ar), 4.88 (s, 24H, NCH2), 3.18 (s, 108H,
1
1
N(CH3)3). 13C{ H}-NMR (75 MHz, CD3OD): d (ppm) = 143.0
(s, NCH2), 53.4 (s, N(CH3)3). 31P{ H}-NMR (162 MHz, D2O): d
(s, Ar), 142.1 (s, Ar), 131.1 (m, overlapping i- and o-Ar), 68.4 (s,
(ppm) = 16.4 (s, 1JP,Pt = 2583 Hz). ESI MS: (m/z) 993.46 {[M-3I]3+,
calc. 993.36}, 825.34 {[M-[1]I6-2I]2+, calc. 825.48}, 713.40 {[M-
4I]4+, calc. 713.29}, 545.43 {[M-5I]5+, calc. 545.25}, 433.22 {[M-
6I]6+, calc. 433.23}. Elem. anal. found: C 29.76, H 4.78, I 52.39,
1
NCH2), 53.6 (s, N(CH3)3). 31P{ H}-NMR (162 MHz, CD3OD):
1
d (ppm) = 24.5 (s, JP,Pt = 2655 Hz). ESI MS: (m/z) 658.62 {[M-
3Cl]3+, calc. 658.59}, 484.72 {[M-4Cl]4+, calc. 484.70}. Elem. anal.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 2588–2600 | 2597
©

View Article Online
◦
1
trans isomers). 13C{ H}-NMR (100 MHz, D2O, 65 C): d (ppm) =
136.5 (pseudo t, JC,P = 6.0 Hz, m-Ar, trans-isomer), 136.2 (pseudo
t, JC,P = 5.4 Hz, m-Ar, cis-isomer), 134.4 (pseudo t, JC,P = 29.5 Hz,
i-Ar, trans-isomer), 133.4 (pseudo t, JC,P = 5.6 Hz, o-Ar, cis-isomer),
133.2 (pseudo t, JC,P = 5.6 Hz, o-Ar, trans-isomer), 131.7 (s, p-Ar,
cis-isomer), 131.2 (s, p-Ar, trans-isomer), 69.6 (s, NCH2, trans-
isomer), 69.3 (s, NCH2, cis-isomer), 53.8 (s, N(CH3)3, cis-isomer),
53.7 (s, N(CH3)3, trans-isomer). The signal for i-Ar, cis-isomer
N 4.72, P 1.65, Pt 5.90%. Calc. for C84H150I14N12P2Pt (3361.89): C
30.01, H 4.50, I 52.85, N 5.00, P 1.84, Pt 5.80%.
[PtI2(5)2]I8 (10b)
A solution of PtI2(cod) (29 mg, 0.052 mmol) in CH2Cl2 (1 mL)
was added at 60 ◦C to a solution of [5]I4 (110 mg, 0.10 mmol,
2.0 equiv.) in MeOH (10 mL). The mixture was heated at reflux
temperature for 1 h and subsequently dried in vacuo, affording
10b as an orange powder (128 mg, quant.). 1H-NMR (400 MHz,
D2O): d (ppm) = 8.30 (t, JH,P = 5.0 Hz, o-Ar), 8.20 (m, 4H, o-Ph),
7.87 (s, 4H, p-Ar), 7.71 (m, 6H, m- and p-Ph), 4.75 (s, 16H, NCH2),
was not resolved. 31P{ H}-NMR (162 MHz, D2O): d (ppm) =
1
1
1
12.0 (s, JP,Pt = 2467 Hz, trans-isomer), 11.2 (s, JP,Pt = 3491 Hz,
cis-isomer). ESI MS: (m/z) 527.01 {[M-[7]I3-2I]2+, calc. 527.01},
306.47 {[M-5I]5+, calc. 306.47}, 234.38 {[M-6I]6+, calc. 234.24}.
Elem. anal. found: C 33.11, H 4.25, N 3.73, P 2.92, Pt 9.08%.
Calc. for C60H90I8N6P2Pt (2167.68): C 33.25, H 4.18, N 3.88, P
2.86, Pt 9.00%.
1
3.15 (s, 72H, N(CH3)3). 13C{ H}-NMR (75 MHz, DMSO-d6): d
(ppm) = (signals attributed to the trans-isomer) 139.9 (br. s, m-Ar),
139.1 (br. s, p-Ar), 137.6 (br. s, Ph), 135.7 (br. s, Ph), 134.3 (pseudo
t, JC,P = 29.1 Hz, i-Ar), 131.4 (br. s, Ph), 129.7 (m, i-Ph), 128.5
1
(s, o-Ar), 65.8 (br. s, NCH2), 51.8 (s, N(CH3)3). 31P{ H}-NMR
1
X-Ray crystallography
(162 MHz, D2O): d (ppm) = 12.2 (s, JP,Pt = 2498 Hz). ESI MS:
(m/z) 1379.6 {[M-[5]I4–I]+, calc. 1379.9}, 1155.3 {[M-2I]2+, calc.
1155.5}, 728.26 {[M-3I]3+, calc. 728.38}, 626.33 {[M-[5]I4-2I]2+,
calc. 626.50}. Elem. anal. found: C 31.73, H 4.38, I 49.40, N 4.32,
P 2.38, Pt 7.45%. Calc. for C68H110I10N8P2Pt (2565.75): C 31.83, H
4.32, I 49.46, N 4.37, P 2.41, Pt 7.60%.
All reflection intensities were measured using a Nonius Kap-
paCCD diffractometer (equipped with a rotating anode) with
graphite-monochromated Mo-Ka radiation (l = 0.71073 A)
˚
under the program COLLECT.41 The program PEAKREF42 was
used to refine the cell dimensions. Data reduction was done
using EVALCCD.43 The structures of trans-10a and [PtI3(1)]I5
were, respectively, solved with the programs SHELXS-9744 and
DIRDIF0845 and were both refined on F2 with SHELXL-
97.44 Multi-scan semi-empirical absorption corrections (based on
symmetry-related measurements) were applied to all data using
the program SADABS.46 The temperature of the data collection
was controlled using the system OXFORD CRYOSTREAM 600
(manufactured by OXFORD CRYOSYSTEMS). H-atoms (except
when specified) were placed at calculated positions and refined
with a riding model (instructions AFIX 23, AFIX 43 and AFIX
137) with isotropic displacement parameters having values 1.2 or
1.5 times Ueq of the attached C atom. In the structure of [PtI31]I5,
the D-atoms (treated as hydrogen atoms in the model since the
elements H and D have the same number of electrons and since
no interpretable difference between H and D can be derived from
X-ray diffraction measurements) of the two crystallographically
independent lattice water molecules were located in difference
Fourier maps and restrained using the DFIX instructions such that
the O–H distances and H–O–H angles have reasonable values [i.◦e.,
[PtI2(6)2]I4 (10c)
A solution of PtI2(cod) (35 mg, 0.062 mmol) in CH2Cl2 (1 mL) was
added at 60 ◦C to a solution of [6]I2 (82 mg, 0.12 mmol, 2.0 equiv.)
in MeOH (10 mL). The mixture was heated at reflux temperature
for 1 h and subsequently dried in vacuo, affording 10c as an orange
powder (112 mg, quant.). 1H-NMR (400 MHz, DMSO-d6): d
(ppm) = (signals attributed to the trans-isomer) 7.88 (br. s, 8H,
o-Ph), 7.74 (m, 6H, o- and p-Ar), 7.54 (s, 12H, m- and p-Ph), 4.67
(s, 8H, NCH2), 3.00 (s, 36H, N(CH3)3). Minor signals attributed
to the cis-isomer were observed at 4.44 (s, NCH2) and 2.92 ppm (s,
1
N(CH3)3); the aromatic signals were not resolved. 13C{ H}-NMR
(100 MHz, DMSO-d6): d (ppm) = (signals attributed to the trans-
isomer) 139.6 (s, Ar), 138.4 (s, Ar), 136.0 (pseudo t, JC,P = 29.1 Hz,
i-Ar), 135.3 (s, Ph), 131.6 (s, Ar), 131.1 (s, Ph), 130.4 (pseudo t, JC,P
=
29.9 Hz, i-Ph), 128.3 (s, Ph), 66.4 (s, NCH2), 51.7 (s, N(CH3)3).
1
1
31P{ H}-NMR (121 MHz, DMSO-d6): d (ppm) = 12.4 (s, JP,Pt
=
2478 Hz, trans-isomer), 11.8 (s, 1JP,Pt = 3471 Hz, cis-isomer). ESI
MS: (m/z) 1642.2 {[M-I]+, calc. 1642.0}, 981.60 {[M-[6]I2–I]+,
calc. 981.93}, 756.82 {[M-2I]2+, calc. 757.04}, 462.65 {[M-3I]3+,
calc. 462.73}. Elem. anal. found: C 35.12, H 3.92, I 43.11, N 3.22,
P 3.45, Pt 11.10%. Calc. for C52H70I6N4P2Pt (1769.61): C 35.29, H
3.99, I 43.03, N 3.17, P 3.50, Pt 11.02%.
˚
˚
d(O–H) ª 0.84 A, d(H ◊ ◊ ◊ H) ª 1.33 A so that H–O–H ª 104.5 ].
Geometry calculations and graphical illustrations (displacement
ellipsoid plots) were made with the PLATON program.47
Refinement details for trans-10a. The asymmetric unit of
trans-10a contains one half of the trans-10a complex [the Pt(II)
centre is found at sites of inversion symmetry, the other half of
trans-10a complex is symmetry generated], four ordered lattice
iodides with full occupancy (I2, I3, I4, I5), one ordered lattice
iodide with a population factor of 0.5 (I7), one fully-occupied
lattice iodide ion disordered over two positions [I6A/I6B, major
occupancy factor = 0.534(2)], one half-occupied lattice iodide
ion disordered over two positions [I8A/I8B, major occupancy
factor = 0.327(3) ¥ 0.5] and some unresolved chemical species
(probably some disordered solvent molecules). The contribution
of these species was subsequently taken out for the final stage of
the refinement using the program SQUEEZE (see details below).48
[PtI2(7)2]I6 (11)
A solution of PtI2(cod) (23 mg, 0.041 mmol) in CH2Cl2 (1 mL)
was added at 60 ◦C to a solution of [7]I3 (72 mg, 0.084 mmol, 2.0
equiv.) in MeOH (5 mL), upon which a precipitate formed. The
mixture was heated at reflux temperature for 1 h. The precipitate
was washed once with hot MeOH (5 mL) and subsequently dried
in vacuo, affording 11 as a light orange powder (64 mg, 71%).
1H-NMR (400 MHz, D2O): d (ppm) = 8.02 (m, o-Ar, cis-isomer),
7.81 (m, o-Ar, trans-isomer), 7.75 (d, JH,H = 8.4 Hz, m-Ar, cis-
isomer), 7.59 (d, JH,H = 8.0 Hz, m-Ar, trans-isomer), 4.63, 4.62
(s, NCH2, cis and trans isomers), 3.16, 3.15 (s, N(CH3)3, cis and
3
3
2598 | Dalton Trans., 2011, 40, 2588–2600
This journal is
The Royal Society of Chemistry 2011
©

View Article Online
Crystallographic data for trans-10a. C84H150I14N12P2Pt + sol-
vent, FW = 3361.79,‡ needle, 0.48 ¥ 0.15 ¥ 0.12 mm3, triclinic,
Chem., Int. Ed., 2005, 44, 6816–6825; (c) A. J. Sandee and J. N. H.
Reek, Dalton Trans., 2006, 3385–3391.
3 Some recent examples: (a) C. Machut, J. Patrigeon, S. Tilloy, H. Bricout,
F. Hapiot and E. Monflier, Angew. Chem., Int. Ed., 2007, 46, 3040–3042;
(b) A. C. Laungani, J. M. Slattery, I. Krossing and B. Breit, Chem.–
Eur. J., 2008, 14, 4488–4502; (c) F. W. Patureau, M. Kuil, A. J. Sandee
and J. N. H. Reek, Angew. Chem., Int. Ed., 2008, 47, 3180–3183 and
references therein; (d) C. G. Oliveri, P. A. Ulmann, M. J. Wiester and
C. A. Mirkin, Acc. Chem. Res., 2008, 41, 1618–1629; (e) S. A. Moteki
and J. M. Takacs, Angew. Chem., Int. Ed., 2008, 47, 894–897.
4 (a) P. A. Duckmanton, A. J. Blake and J. B. Love, Inorg. Chem., 2005,
44, 7708–7710; (b) L. A. Knight, Z. Freixa, P. W. N. M. Van Leeuwen
and J. N. J. Reek, Organometallics, 2006, 25, 954–960; (c) Z. Freixa and
P. W. N. M. Van Leeuwen, Coord. Chem. Rev., 2008, 252, 1755–1786.
5 H. Gulya´s, J. Benet-Buchholz, E. C. Escudero-Adan, Z. Freixa and
P. W. N. M. Van Leeuwen, Chem.–Eur. J., 2007, 13, 3424–3430.
6 (a) B. Cornils and E. G. Kuntz, J. Organomet. Chem., 1995, 502, 177–
186; (b) O. Herd, D. Hoff, K. W. Kottsieper, C. Liek, K. Wenz, O. Stelzer
and W. S. Sheldrick, Inorg. Chem., 2002, 41, 5034–5042; (c) E. Genin,
R. Amengual, V. Michelet, M. Savignac, A. Jutand, L. Neuville and
J. P. Geneˆt, Adv. Synth. Catal., 2004, 346, 1733–1741; (d) L. R. Moore,
E. C. Western, R. Craciun, J. M. Spruell, D. A. Dixon, K. P. O’Halloran
and K. H. Shaughnessy, Organometallics, 2008, 27, 576–593.
7 (a) R. T. Smith and M. C. Baird, Inorg. Chim. Acta, 1982, 62, 135–139;
(b) E. Renaud, R. B. Russell, S. Fortier, S. J. Brown and M. C. Baird,
J. Organomet. Chem., 1991, 419, 403–415; (c) T. Okano, N. Harada and
J. Kiji, Chem. Lett., 1994, 1057–1060; (d) B. Mohr, D. M. Lynn and
R. H. Grubbs, Organometallics, 1996, 15, 4317–4325; (e) A. Hessler and
O. Stelzer, J. Org. Chem., 1997, 62, 2362–2369; (f) F. P. Pruchnik and
P. Smolenski, Appl. Organomet. Chem., 1999, 13, 829–836; (g) C. C.
Brasse, U. Englert and A. Salzer, Organometallics, 2000, 19, 3818–
3823; (h) R. B. DeVasher, L. R. Moore and K. H. Shaughnessy, J. Org.
Chem., 2004, 69, 7919–7927; (i) M. P. Coles and P. B. Hitchcock, Chem.
Commun., 2007, 5229–5231.
¯
˚
P1(no. 2), a = 14.5266(2), b = 16.8586(1), c = 17.1335(2) A, a =
◦
3
˚
101.202(1), b = 103.197(1), g = 113.487(1) , V = 3550.37(8) A ,
Z = 1, Dx = 1.57 g cm-3,‡ m = 4.09 mm-1.‡ 52744 reflections
were measured up to a resolution of (sin q/l)max = 0.65 A .
-1
˚
16172 reflections were unique (Rint = 0.030), of which 13846 were
observed [I > 2s(I)]. 558 parameters were refined. R1/wR2 [I
> 2s(I)]: 0.0394/0.1132. R1/wR2 [all refl.]: 0.0466/0.1172. S =
1.104. Residual electron density found between -1.93 and 2.77
-3
3
˚
˚
eA . SQUEEZE details: one void of 284 A filled with 94 electrons
3
˚
and two voids of 215 A filled with 72 electrons (all numbers are
given per unit cell).
Refinement details for [PtI3(1)]I5. The asymmetric unit of
[PtI3(1)]I5 contains one [PtI3(1)]5+ complex, two lattice deuterated
water molecules and five lattice iodide counter anions. The lattice
water molecules and some lattice iodide ions (I4, I5 and I8) form
˚
weak hydrogen bond O–H ◊ ◊ ◊ I interactions (O ◊ ◊ ◊ I ª 3.49–3.55 A).
The lattice iodide I7 is found at sites of twofold axial symmetry and
the SHELX population was constrained to be 0.5. The occupancy
factors of the remaining iodides I4, I5, I6, I8 and I9 were refined
using the FVAR (free variable) instructions. The sum of these
occupancy factors were constrained to be 4.5 using the SUMP
instruction as a requirement for charge balance. The free variables
for the occupancy factors of I4, I5, I6, I8 and I9 refined to 0.998(2),
0.997(2), 0.991(2), 0.972(2) and 0.541(2), respectively. The final
difference Fourier map is relatively flat except for some peaks
8 (a) Reviews: W. A. Herrmann and C. W. Kohlpaintner, Angew. Chem.,
Int. Ed. Engl., 1993, 32, 1524–1544; (b) O. Stelzer, S. Rossenbach, D.
Hoff, M. Schreuder-Goedheijt, P. C. J. Kamer, J. N. H. Reek and
P. W. N. M. Van Leeuwen, Multiphase homogeneous catalysis, Wiley-
VCH, 2005, 1, 66-82; (c) K. H. Shaughnessy, Eur. J. Org. Chem., 2006,
1827–1835; (d) D. M. Chisholm and J. S. McIndoe, Dalton Trans., 2008,
3933–3945; (e) K. H. Shaughnessy, Chem. Rev., 2009, 109, 643–710.
9 (a) R. Kreiter, R. J. M. Klein Gebbink and G. van Koten, Tetrahedron,
2003, 59, 3989–3997; (b) D. J. M. Snelders, R. Kreiter, J. J. Firet, G. van
Koten and R. J. M. Klein Gebbink, Adv. Synth. Catal., 2008, 350, 262–
266; (c) D. J. M. Snelders, G. van Koten and R. J. M. Klein Gebbink,
J. Am. Chem. Soc., 2009, 131, 11407–11416; (d) D. J. M. Snelders, C.
Van Der Burg, M. Lutz, A. L. Spek, G. van Koten and R. J. M. Klein
Gebbink, ChemCatChem, 2010, 2, 1425–1437; (e) D. J. M. Snelders, K.
Kunna, C. Mu¨ller, D. Vogt, G. van Koten and R. J. M. Klein Gebbink,
Tetrahedron: Asymmetry, 2010, 21, 1411–1420.
-3
˚
˚
found near I9 (2.2–3.6 A), which are as large as 3.3–4.1 e A . Such
large peaks may result from disorder of the iodide I9 although
there is no sign of disorder in its atomic displacement parameters,
or may result from very disordered solvent molecules which may
be partially contained in one void [(0.5, 0.171, 0.25)] found near
I9.
Crystallographic data for [PtI3(1)]I5. C42H79I8N6O2PPt, FW =
1941.37, plate, 0.24 ¥ 0.18 ¥ 0.06 mm3, monoclinic, C2/c (no. 15),
˚
a = 17.2539(5), b = 17.4111(5), c = 41.5254(9) A, b = 90.2090(10),
3
-3
-1
˚
V = 12474.5(6) A , Z = 8, Dx = 2.07 g cm , m = 6.27 mm . 67316
reflections were measured up to a resolution of (sin q/l)max
=
-1
˚
0.59 A . 10730 reflections were unique (Rint = 0.044), of which 9090
were observed [I > 2s(I)]. 581 parameters were refined. R1/wR2
[I > 2s(I)]: 0.0369/0.0813. R1/wR2 [all refl.]: 0.0499/0.0862.
10 I. M. Al-najjar, Inorg. Chim. Acta, 1987, 128, 93–104.
11 (a) A. W. Kleij, R. van de Coevering, R. J. M. Klein Gebbink, A.
Noordman, A. L. Spek and G. van Koten, Chem.–Eur. J., 2001, 7, 181–
191; (b) R. van de Coevering, P. C. A. Bruijnincx, M. Lutz, A. L. Spek,
G. van Koten and R. J. M. Klein Gebbink, New J. Chem., 2007, 31,
1337–1348.
S = 1.085. Residual electron density found between -1.15 and
-3
˚
4.07 eA .
12 Isomerization of square planar Pt(II) complexes is catalyzed by free
phosphine: see ref. 29.
13 No other peak appeared, indicating that these species had irreversibly
converted to trans-8a and trans-8b, respectively. When trans-8a was
synthesized starting from PtCl2(DMSO)2 as the Pt precursor, this minor
product did not form, indicating that it is a thermally labile intermediate
species in the reactions of these phosphines with PtCl2(cod).
14 R. Kreiter, J. J. Firet, M. J. J. Ruts, M. Lutz, A. L. Spek, R. J. M. Klein
Gebbink and G. van Koten, J. Organomet. Chem., 2006, 691, 422–432.
15 When a solution of 9b in toluene-d8 was heated in the presence of a
small quantity of free 4, the cis-trans equilibrium shifted in favour
of the trans-isomer. Isomerization occurred at temperatures higher
than 65 ◦C. At 105 ◦C, the cis : trans ratio had shifted from 85 : 15
to 55 : 45. After cooling, the original product distribution was restored.
No isomerization occurred in the absence of free 4.
16 The reaction of PtCl2(DMSO)2 with one equiv. of PPh3 in CDCl3
was also performed; a mixture of cis- and trans-PtCl2(PPh3)2 and cis-
PtCl2(DMSO)(PPh3) was obtained (approximate ratio: 3 : 4 : 3). The
complex cis-PtCl2(DMSO)(PPh3) was identified by a characteristic
Acknowledgements
The authors thank Cees Versluis and Ronald van Ooijen (Bijvoet
Institute, Biomolecular Mass Spectrometry, Utrecht University)
for the ESI-MS analyses.
Notes and references
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Dalton Trans., 2011, 40, 2588–2600 | 2599
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2600 | Dalton Trans., 2011, 40, 2588–2600
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