Self-assembly of isomeric clamshell dimers of platinum(ii)

Article abstract of DOI:10.1039/c2dt31584j

The controlled synthesis of isomeric organoplatinum clamshell dimers [Pt₂Me₂(μ₂-κ³-6-dppd) ₂]²⁺, 6-dppd = 1,4-di-2-pyridyl-5,6,7,8,9,10- hexahydrocycloocta[d]pyridazine, is reported. The new complexes are formed selectively by self-assembly from mononuclear precursors, taking advantage of the slow cis-trans isomerization at platinum(ii). Thus reaction of endo-[PtClMe(κ²-6-dppd)] with AgOTf gave endo,endo-[Pt ₂Me₂(μ₂-κ³-6-dppd) ₂]²⁺, while the reaction of [PtMe₂(κ ²-6-dppd)] with HOTf in solvent S = Me₂CO or MeCN gave first a mixture of exo- and endo-[PtMe(S)(κ²-6-dppd)] ⁺ and then, by loss of solvent, a mixture of exo,exo- and endo,endo-[Pt₂Me₂(μ₂-κ³-6- dppd)₂]²⁺. The endo,endo isomer slowly isomerized to the more stable exo,exo isomer in solution. Reaction of PPh₃ with endo-[PtClMe(κ²-6-dppd)] gave a mixture of endo- and exo-[PtMe(PPh₃)(κ²-6-dppd)]⁺ but reaction with exo,exo-[Pt₂Me₂(μ₂- κ³-6-dppd)₂]²⁺ gave exo-[PtMe(PPh ₃)(κ²-6-dppd)]⁺ selectively, with retention of stereochemistry. The structures of the clamshell dimers and of key precursors are reported and equilibria are studied both experimentally and by DFT calculations.

Full text of DOI:10.1039/c2dt31584j

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PAPER
Self-assembly of isomeric clamshell dimers of platinum(II)†
Matthew S. McCready and Richard J. Puddephatt*
Received 17th July 2012, Accepted 15th August 2012
DOI: 10.1039/c2dt31584j
The controlled synthesis of isomeric organoplatinum clamshell dimers [Pt2Me2(μ2-κ3-6-dppd)2]2+,
6-dppd = 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocycloocta[d]pyridazine, is reported. The new complexes
are formed selectively by self-assembly from mononuclear precursors, taking advantage of the slow
cis–trans isomerization at platinum(II). Thus reaction of endo-[PtClMe(κ2-6-dppd)] with AgOTf gave
endo,endo-[Pt2Me2(μ2-κ3-6-dppd)2]2+, while the reaction of [PtMe2(κ2-6-dppd)] with HOTf in solvent
S = Me2CvO or MeCN gave first a mixture of exo- and endo-[PtMe(S)(κ2-6-dppd)]+ and then, by loss of
solvent, a mixture of exo,exo- and endo,endo-[Pt2Me2(μ2-κ3-6-dppd)2]2+. The endo,endo isomer slowly
isomerized to the more stable exo,exo isomer in solution. Reaction of PPh3 with endo-[PtClMe-
(κ2-6-dppd)] gave a mixture of endo- and exo-[PtMe(PPh3)(κ2-6-dppd)]+ but reaction with exo,exo-
[Pt2Me2(μ2-κ3-6-dppd)2]2+ gave exo-[PtMe(PPh3)(κ2-6-dppd)]+ selectively, with retention of
stereochemistry. The structures of the clamshell dimers and of key precursors are reported and
equilibria are studied both experimentally and by DFT calculations.
Introduction
The use of self-assembly techniques for the synthesis of
complex structures continues to be an active field of research.1 In
self-association of coordination complexes, the method typically
relies on reversible formation and cleavage of labile metal–
ligand bonds, which allows self-sorting and error correction, so
that the thermodynamically favored isomer may be formed selec-
tively.1,2 For example, the monomer fragment A shown in
Scheme 1 selectively forms a macrocyclic tetramer B.2
There are few examples where less stable isomers (kinetic
mistakes) can be isolated, though intermediates can be detected
more often.1,3 For example, the reaction of dithiols with AsCl3
occurs through intermediate steps to give macrocycles such as
the mixture of syn- and anti-C (Chart 1), of which the syn
isomer was structurally characterized. However, the isomers
cannot be formed selectively.3
Scheme 1 Selective formation of a macrocycle.
Square planar platinum(II) complexes have long been known
to undergo ligand substitution with retention of stereochemistry,
with selectivity often determined by the trans-effect, and it has
been possible to synthesize many simple isomeric complexes by
applying these principles.4 The products are often inert to cis–
trans isomerization, as is important for applications in medi-
cine.5 Chart 2 gives examples D and E of binuclear platinum(II)
complexes which exhibit isomerism.6
This synthetic methodology based on cis–trans isomerism at
platinum(II) should be applicable in the field of self-assembly,
Chart 1 Isomers formed by self-assembly.
Department of Chemistry, University of Western Ontario, London,
Canada N6A 5B7. E-mail: pudd@uwo.ca; Fax: +519-661-3022;
Tel: +519-661-2111
†CCDC 869542–869547 and 892425. For crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2dt31584j
but we are not aware of any examples of complex isomeric struc-
tures being obtained in this way.1,2,6 This article reports
the isolation and structural characterization of an isomeric pair
of binuclear organoplatinum “clamshell” complexes. These
12378 | Dalton Trans., 2012, 41, 12378–12385
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Scheme 2
Chart 2 Isomeric diplatinum(II) complexes.
complexes are prepared in a logical way and so establish a useful
synthetic protocol for self-assembly of isomeric self-assembled
molecular materials.
Results and discussion
Some of the synthetic chemistry is described in Scheme 2. The
ligand 6-dppd = 1,4-di-2-pyridyl-5,6,7,8,9,10-hexahydrocyclo-
octa[d]pyridazine was used in this work.7 Platinum(II) complexes
of the parent ligand 1,4-di-2-pyridyl-pyridazine have been
studied earlier and it has been shown that only one platinum(II)
centre can be accommodated,8 thus leaving a free 2-pyridyl
group, which might then be used in self-assembly. We used the
cyclo-C6H12 substituent of 6-dppd to improve the solubility of
the complexes, but the substituent is thought to play only a
minor role in the coordination chemistry. The structure of the
ligand was determined and is shown in Fig. 1. The 2-pyridyl
rings are twisted out of the plane of the pyridazine ring by 53°
(N1 ring) and 55° (N4 ring), in order to minimize steric effects.
Fig. 1 Structure of the ligand 6-dppd. Bond distance N(2)–N(3)
1.355(1) Å.
to N2), with the assignment confirmed by 1H–1H NOESY
NMR analysis, since only the exo-Me group has a through space
interaction with the ortho-hydrogen of the coordinated pyridyl
group [δ(H6) = 9.48, 3J(PtH6) = 18 Hz]. Complex 1 gave a
2
single methylplatinum resonance at δ = 1.36, J(PtH) = 80 Hz
and the NOESY NMR showed no interaction with the
ortho-hydrogen of the coordinated pyridyl group at δ = 9.77,
3J(PtH6) = 21 Hz. This confirms that the structure with the endo
methylplatinum group and exo chloride (Fig. 2) is formed selec-
tively. The preference for the endo isomer 1 probably arises from
a favorable intramolecular CH⋯Cl interaction. In the structures
of 1 and 2 the coordinated 2-pyridyl group is twisted out of the
plane of the pyridazine ring by 21° and 15° respectively, repres-
enting a balance between the ideal planar chelate conformation
and the steric effects. The free 2-pyridyl ring is twisted out of
the plane of the pyridazine ring by 55 and 41° in 1 and 2
respectively.
Synthesis of precursor complexes
The ligand 6-dppd7 coordinates easily to methylplatinum(II)
centres by displacement of Me2S from trans-[PtClMe(SMe2)2]
or [Pt2Me4(μ-SMe2)2]9 to form simple chelate complexes
[PtClMe(6-dppd)], 1, or [PtMe2(6-dppd)], 2 (Fig. 2), but the
second potential nitrogen-donor of the pyridazine group is steri-
cally blocked, so the ligand acts only as a mono(chelate).8 The
structures of 1 and 2 are shown in Fig. 2, and the complexes
were also characterized spectroscopically. For complex 2, the
methylplatinum resonances appeared at δ = 1.26, 2J(PtH) = 84 Hz
2
(endo, trans to N1) and δ = 1.46, J(PtH) = 88 Hz (exo, trans
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The structures of both isomers 3 and 4 (in three solvated
crystal forms, noting that the solvent molecules are not chemi-
cally bonded to the platinum complexes) were determined and
are shown in Fig. 3. Complex 3 (Fig. 3a) has crystallographically
imposed C2 symmetry and complex 4 (Fig. 3b) has approximate
C2 symmetry. The degree of strain in 3 and 4 is indicated by the
distortions from “normal” geometry. In complexes 1, 2, 3 and 4
the angles between the pyridyl and pyridazine rings of the
chelate unit are 21, 15, 32 and 12° respectively, indicating great-
est strain in 3 (some distortion from planarity is necessary to
avoid steric interaction with the cyclo-octyl substituent). The
angles between trans donor atoms have average values of 168°
and 175° in 3 and 4 respectively, again indicating greater strain
Fig. 2 Structures of (a) complex 1 and (b) complex 2. Selected bond
parameters: 1, Pt(1)–N(1) 2.095(5), Pt(1)–N(2) 1.988(5), Pt(1)–C(21)
2.062(5), Pt(1)–Cl(1) 2.310(2), N(2)–N(3) 1.329(6) Å, N(1)–Pt(1)–N(2)
79.0(1), C(21)–Pt(1)–Cl(1) = 89.9(1)°; 2, Pt(1)–N(1) 2.105(5), Pt(1)–N(2)
2.060(5), Pt(1)–C(22) = 2.037(5), Pt(1)–C(21) 2.082(5), N(2)–N(3)
1.332(6) Å, N(1)–Pt(1)–N(2) = 76.6(2), C(22)–Pt(1)–C(21) = 84.9(2)°.
Synthesis of the clamshell dimers
The synthesis of binuclear complexes was carried out by generat-
ing a vacant site at platinum(II) leading to self-association
through coordination of the free pyridyl group (N4 in Fig. 2), as
shown in Scheme 2. The first clamshell dimer endo,endo-
[Pt2Me2(μ2-κ3-6-dppd)2](OTf)2, 3, was prepared by reaction of
complex 1 with silver triflate in acetone solution, the vacant site
being generated by chloride abstraction from complex 1. The
1H NMR spectrum of 3 contained a single methylplatinum reso-
nance at δ = 1.54, 2J(PtH) = 75 Hz, and the endo stereochemistry
was confirmed by the NOESY NMR. The coordination of the
second pyridyl group was confirmed by the presence of 195Pt sat-
ellites for both ortho hydrogen resonances at δ = 9.05, 3J(PtH) =
34 Hz (trans to N) and δ = 8.59, 3J(PtH) = 20 Hz (trans to Me).
The second clamshell dimer exo,exo-[Pt2Me2(μ2-κ3-6-dppd)2]-
(OTf)2, 4, was prepared by reaction of complex 2 with triflic
acid in acetone solution, the vacant site being generated by pro-
tonolysis of a methylplatinum bond of complex 2. The 1H NMR
spectrum of complex 4 contained a single methylplatinum reso-
Fig. 3 Structures of clamshell dimers (a) complex 3 (symmetry code
for A: 1/2 − x, y, 1/2 − z); (b) complex 4 as 4.2Me2CO·H2O. Selected
bond parameters: 3, Pt(1)–N(1) 2.102(9), Pt(1)–N(2) 2.005(9), Pt(1)–
N(4) 2.028(9), Pt(1)–C(21) 2.02(1), N(2)–N(3A) 1.35(1) Å, N(1)–
Pt(1)–N(2) 78.4(4), N(1)–Pt(1)–N(4) 102.5(4), N(2)–Pt(1)–C(21) 96.1(4),
N(4)–Pt(1)–C(21)
= 85.3(4)°; 4, Pt(1)–N(5) 2.021(1), Pt(1)–N(4)
2
nance at δ = 1.20, J(PtH) = 74 Hz, and the exo stereochemistry
2.039(1), Pt(1)–N(6) 2.090(1), Pt(1)–C(21) 2.091(9), Pt(2)–N(1) =
1.996(1), Pt(2)–N(2) = 2.102(1), Pt(2)–N(8) = 2.027(1), Pt(2)–C(42)
2.078(9) Å, N(5)–Pt(1)–N(6) 78.2(6), N(4)–Pt(1)–N(6) = 97.7(6), N(5)–
Pt(1)–C(21) 96.7(3), N(4)–Pt(1)–C(21) 87.4(3), N(1)–Pt(2)–N(2)
77.9(3), N(2)–Pt(2)–N(8) 99.0(3), N(1)–Pt(2)–C(42) 96.1(3), N(8)–
Pt(2)–C(42) = 87.1(3)°.
was confirmed by the NOESY NMR. The coordination of the
second pyridyl group was again confirmed by the presence of
195Pt satellites for both ortho hydrogen resonances at δ = 9.06,
3
3J(PtH) = 34 Hz (trans to N) and δ = 8.88, J(PtH) = 21 Hz
(trans to Me).
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in 3. Another significant difference between isomers 3 and 4 is
the degree of opening of the “clamshell” structure. If the hinge
angle α is defined as the angle between the central pyridazine
rings, then α = 32° in 3 and α = 50–57° in the different crystal-
line forms of 4, indicating a more open shell, and hence a larger
cavity, in complex 4. There is no solvent occlusion in complex 3
but the more open clamshell structure of complex 4 accommo-
dates a molecule of solvent acetone or dichloromethane, as
shown in Fig. 4.
Studies of the mechanism and selectivity
In order to probe the mechanism of formation of complexes 3
and 4, the reaction of 2 with triflic acid in acetone-d6 or CD3CN
was monitored by NMR spectroscopy. In acetone-d6 two inter-
mediates were detected in a 3 : 1 ratio having methylplatinum
resonances at δ = 0.99, 2J(PtH) = 75 Hz, and δ = 1.04, 2J(PtH) =
80 Hz. These are assigned to complexes 6a and 5a respectively,
noting that weakly bonding ligands acetone or triflate are
expected to be in rapid equilibrium.10 After 30 min, these reson-
ances had decayed and resonances due to 3 and 4 were observed
in about a 1 : 1 ratio. After 6 days, the resonances for 3 had
decayed and only the resonances of complex 4 were present. The
intermediates were more stable in the stronger donor solvent
CD3CN, and the intermediates 6b and 5b were identified by the
methylplatinum resonances in a 2 : 1 intensity ratio at δ = 1.01,
2
2J(PtH) = 75 Hz, and δ = 1.13, J(PtH) = 75 Hz. The coordi-
nation of acetonitrile in 5b and 6b was confirmed by carrying
out the reaction in acetone-d6 containing a small excess of
MeCN. Now coordinated MeCN resonances were also observed
in a 2 : 1 ratio at δ = 2.77, 4J(PtH) = 8 Hz, and δ = 2.89, 4J(PtH)
= 15 Hz. After 2 days, peaks due to 4, 6b and 5b were present in
a ratio of 12 : 3 : 1. These observations show that the protonolysis
of a methylplatinum group from complex 2 is not highly selec-
tive and gives a mixture of isomers 5a and 6a in acetone-d6 or
5b and 6b in CD3CN solution. The endo monomer 5a can
dimerize to form the endo,endo dimer 3, but it can also equili-
brate slowly with the exo monomer 6a, which can then dimerize
to form the more stable exo,exo dimer 4. We note that open
dimers with one solvent molecule and one free pyridine group
[Pt2Me2(μ2-κ3-6-dppd)(κ2-6-dppd)(S)](OTf)2, an unsymmetrical
dimer endo,exo-[Pt2Me2(μ2-κ3-6-dppd)2](OTf)2 and higher oli-
gomers (compare Scheme 1) are possible products, but they were
never formed in detectable quantities.2
The reversibility of formation of complex 4 was tested by car-
rying out reactions with donor ligands (Scheme 2). Complex 4
did not react with pyridine even on reflux, but it did react easily
with triphenylphosphine to give the complex [PtMe(6-dppd)-
(PPh3)]OTf, 6c. The 1H NMR spectrum of 6c contained a
methylplatinum resonance at δ = 0.85, which appeared as a
3
2
doublet with J(PH) = 3 Hz, with 195Pt satellites with J(PtH) =
71 Hz. The ortho proton resonance of the coordinated pyridyl
group gave a resonance at δ = 9.35 which also gave coupling to
Fig. 4 Side views of the structures of (a) complex 3, α = 32° and (b)
complex 4, α = 57°, with occluded acetone molecule (c) complex 4, α =
57°, with occluded dichloromethane molecule.
both 195Pt and 31P, with J(PtH) = 33 Hz and J(PH) = 4 Hz,
suggesting the stereochemistry with phosphorus trans to pyri-
dine. The methylplatinum and pyridyl groups were shown to be
3
4
The exo stereochemistry of 6c was finally confirmed by a struc-
ture determination (Fig. 5). No evidence for the formation of the
alternative endo isomer 5c, with the methyl group and PPh3
mutually cis by H–1H NOESY NMR analysis. The 31P NMR
1
1
spectrum contained a singlet at δ = 19.37, J(PtP) = 4360 Hz.
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Fig. 5 The structure of complex 6c. Selected bond parameters: Pt(1)–
N(1) 2.090(2), Pt(1)–N(2) 2.093(2), Pt(1)–P(1) 2.234(1), Pt(1)–C(21) =
2.047(2) Å, N(1)–Pt(1)–N(2) 77.9(2), N(1)–Pt(1)–C(21) 92.8(1), N(2)–
Pt(1)–P(1) 97.0(1), P(1)–Pt(1)–C(21) 92.3(1)°.
groups directed inward and outward respectively, was observed
in this reaction. However, the complex [PtMe(6-dppd)(PPh3)]Cl
could be prepared in situ by the direct reaction of complex 1
with triphenylphosphine and, in this case, an equilibrium
between 6c and a second complex, tentatively identified as 5c,
Scheme 2, was present in solution. Complex 5c was character-
ized in the 31P NMR spectrum by a singlet resonance at δ =
18.45, 1J(PtP) = 4920 Hz and in the 1H NMR spectrum (at
−20 °C) by a methylplatinum resonance at δ = 0.32, which
Fig. 6 Calculated structures and relative energies for the isomers of
model complexes [PtClMe(dppd)], [PtMe(NCMe)(dppd)]+ and [PtMe-
(PPh3)(dppd)]+.
3
appeared as a doublet with J(PH) = 3 Hz, with 195Pt satellites
2
with J(PtH) = 70 Hz. At room temperature, the two complexes
were present in about equal amounts but the ratio was tempera-
ture dependent with 6c/5c = 3.0, 3.9 and 8.7 at 273, 263 and
253 K respectively. From these equilibrium constants, the ther-
modynamic parameters can be calculated as ΔH = −6.5(2) kJ mol−1
and ΔS = −17.6(2) J K−1 mol−1. It was not possible to
isolate 5c in pure form so the structural assignment is tentative.
It is evidently the presence of the chloride counterion which
leads to the easy isomerisation in this case.
Computational studies
DFT calculations were carried out for the isomers of the com-
plexes, using the parent ligand dppd as a model for 6-dppd, and
results are summarised in Fig. 6 and 7. The theory predicts that
endo-[PtClMe(dppd)] is more stable than the exo-isomer by
19 kJ mol−1, Fig. 6a, consistent with the selective formation of
endo-1. However, the endo and exo isomers of [PtMe(CNMe)-
(dppd)]+ are calculated to have almost equal energies and this is
also consistent with the observation that the compounds exist in
equilibrium. For [PtMe(PPh3)(dppd)]+ the exo isomer is calcu-
Fig. 7 Calculated structures and relative energies of the dimers 3 and 4.
Fig. 6c, which is in remarkably close agreement with the exper-
imental value of ΔH = −6.5 kJ mol−1 determined for the chlor-
ide salt.
DFT calculations for the dimers (Fig. 7) lead to the prediction
that exo,exo-[Pt2Me2(μ2-κ3-dppd)2]2+ is more stable than
lated to be more stable than the endo isomer by 7 kJ mol−1
,
12382 | Dalton Trans., 2012, 41, 12378–12385
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endo,endo-[Pt2Me2(μ2-κ3-dppd)2] by 43 kJ mol−1. This is fully
consistent with the observation that 4 is more stable than 3, and
is the only isomer present under equilibrium conditions.
change was observed and a bright orange precipitate formed in
the reaction flask. After letting the reaction stir for 30 min, the
solvent was decanted, the product washed with ether (3 × 5 mL)
and then dried under high vacuum. Yield 82%. Crystals of the
product were grown by dissolving the orange powdered solid in
dichloromethane and allowing vapour diffusion of pentane into
the vial. Anal. Calcd for C21H23N4ClPt·0.25CH2Cl2: C, 43.76;
H, 4.06; N, 9.61. Found: C, 43.75; H, 3.97; N, 9.57%. NMR in
CD2Cl2: δ(1H) = 1.36 [s, 3H, 2J(PtH) = 80 Hz, PtMe]; 1.56
[m, 2H, CH2]; 1.70 [m, 2H, CH2]; 2.07 [m, 4H, 2 × CH2]; 3.00
[t, 2H, CH2]; 3.33 [t, 2H, CH2]; 7.46 [m, 1H, H5′]; 7.75 [t, 1H,
H5]; 7.96 [t, 1H, H4′]; 8.08 [t, 1H, H4]; 8.20 [d, 1H, H3];
8.23 [d, 1H, H3′]; 8.73 [d, 1H, H6′]; 9.77 [d, 1H, H6]. δ(13C) =
−11.15 [s, Pt-CH3]; 26.09, 26.74, 28.01, 28.12, 29.83, 30.70
(CH2); 124.29, 125.89, 125.94, 127.32, 131.67, 136.51, 137.19,
137.36, 137.77, 146.28, 146.79, 148.54, 150.89, 154.64 (aromatic).
Conclusions
It is shown that clamshell dimers of platinum(II) can be formed
selectively by self-assembly from mononuclear precursors. The
method relies on differing relative stabilities of isomeric mono-
nuclear precursors [PtClMe(κ2-6-dppd)] or [PtMeL(κ2-6-dppd)]+
and on the slow equilibration between the isomers in the absence
of a good nucleophile. In particular, the complex [PtClMe(κ2-6-
dppd)], 1, is most stable as the endo isomer, and the intermediate
endo-5a is generated selectively from 1 by reaction with silver
triflate. In turn, endo-5a dimerises to give the endo,endo dimer
3, which crystallises from solution faster than it isomerises to
exo-6a (Scheme 1). On the other hand, the reaction of complex 2
with triflic acid gives the intermediates as a mixture of the
exo (6a or 6b) and endo (5a or 5b) isomers. These intermediates
can dimerise, with loss of coordinated solvent, only by self-
recognition1,2 to give the exo,exo dimer 4 or the endo,endo
dimer 3 respectively. Molecular models show that the endo,exo
dimer is highly strained so that no assembly by self-discrimi-
nation can occur.1,2 The less stable dimer 3 slowly converts to 4
in solution, presumably by reversible dissociation to 5a, isomeri-
sation to 6a and dimerization, so the self-sorting process even-
tually yields complex 4 selectively (Scheme 2). Thus, the self-
assembly with complexes that are relatively inert towards cis–
trans isomerisation can occur selectively to yield isomeric pro-
ducts. The method clearly has potential in forming more
complex structures.
[PtMe2(6-dppd)], 2. [Pt2Me4(μ-SMe2)2] (0.5 g, 0.869 mmol)
dissolved in toluene was added to a stirring solution of 6-dppd
(0.55 g, 1.74 mmol) in ether. Upon mixing an immediate colour
change was observed and the product began to precipitate as a
deep red solid. The reaction mixture was cooled to 5 °C for 16 h,
the solvent was decanted off and the red product was washed
with ether (3 × 5 mL) and pentane (3 × 5 mL) and dried under
high vacuum. Yield: 84%. Red needle-shaped crystals were
grown from acetone–pentane by slow diffusion. Anal. Calcd for
C22H26N4Pt·0.25C3H6O: C, 49.14; H, 4.98; N, 10.08. Found:
C, 49.43; H, 4.58; N, 10.33%. NMR in CDCl3: δ(1H) = 1.26 [s,
2
2
3H, J(PtH) = 84 Hz, PtMe]; 1.46 [s, 3H, J(Pt-H) = 88 Hz,
PtMe]; 1.54 [m, 2H, CH2D]; 1.69 [m, 2H, CH2C]; 2.06 [m, 4H,
2 × CH2B,E]; 2.99 [t, 2H, CH2A]; 3.27 [t, 2H, CH2 ]; 7.41 [m, 1H,
F
H5′]; 7.60 [t, 1H, H5]; 7.93 [t, 1H, H4′]; 8.15 [t, 1H, H4]; 8.18
[d, 1H, H3]; 8.24 [d, 1H, H3′]; 8.71 [d, 1H, H6′]; 9.48 [d, 1H, H6].
Experimental
endo,endo-[Pt2Me2(6-dppd)2][OSO2CF3]2, 3. To a solution of
[PtMeCl(6-dppd)], 1 (0.010 g, 0.01781 mmol), in acetone-d6
(1 mL) was added silver trifluoromethanesulfonate (0.005 g,
0.01959 mmol) at room temperature. The mixture was stirred for
15 min, then the precipitate of AgCl was removed by filtration,
the resultant yellow solution was studied by NMR spectroscopy.
Anal. Calcd for C44H46F6N8O6S2Pt2·2CH2Cl2: C, 36.32; H,
3.31; N, 7.37; S, 4.22. Found: C, 36.36; H, 3.56; N, 7.55; S,
4.74%. NMR in acetone-d6: δ(1H) = 1.52 [m, 1H, CH2C]; 1.54
[s, 3H, CH3, 2J(Pt-H) = 75 Hz]; 1.68 [m, 1H, CH2E]; 1.90
Reagents and general procedures
All reactions were carried out in an inert atmosphere of dry
nitrogen using standard Schlenk techniques, unless otherwise
specified. All solvents used for air and moisture sensitive
materials were purified using an Innovative Technology Inc.
PURE SOLV solvent purification system (SPS). NMR spectra
were recorded at ambient temperature, unless otherwise noted
(ca. 25 °C), on Varian Mercury 400 or Varian Inova 400 or 600
spectrometers. Chemical shifts are reported relative to TMS
(1H), 85% H3PO4 (31P), and trifluorotoluene (19F). Complete
F
[m, 4H, CH2D, CH2D, CH2B, CH2C]; 2.14 [m, 1H, CH2 ]; 2.71
F
[td, 1H, CH2B]; 2.91 [m, 1H, CH2 ]; 2.98 [dt, 1H, CH2E]; 7.85
assignment of each compound was aided by the use of H–1H
1
[m, 1H, H5′]; 8.04 [m, 1H, H5]; 8.28 [d, 1H, H3′]; 8.43 [t, 1H,
NOESY, 1H–13C{1H}-HSQC and 1H–1H gCOSY experiments.
Commonly practiced labeling schemes for pyridyl rings are uti-
lized when labeling signals in NMR analysis. Mass spectro-
metric analysis was carried out using a PE-Sciex Mass
Spectrometer (ESI-MS) coupled with a TOF detector. DFT cal-
culations were carried out by using the 2011 Amsterdam Density
Functional program based on the BLYP functional, with frozen
core potential, first-order scalar relativistic corrections (ZORA,
SAPA) and the double zeta (DZP) basis set.
3
H4′]; 8.50 [d, 1H, H3]; 8.59 [t, 1H, H4]; 8.59 [d, 1H, J(PtH6′) =
3
20 Hz, H6′]; 9.05 [d, 1H, J(PtH6) = 34 Hz, H6]. δ(13C) = −4.41
[s, PtMe]; 25.43, 25.69, 27.34, 29.03, 30.06, 30.16 [CH2];
127.40, 128.18, 128.46, 128.87, 139.37, 139.76, 140.88, 141.72,
143.07, 147.15, 148.48, 153.64, 154.94, 161.67 (aromatic).
δ(19F) = −78.80 (s, free trifluoromethanesulfonate). ESI-MS:
Calc. for [C42H46N8Pt2]2+: m/z = 526.16; Found m/z = 526.20;
z = 2.
exo,exo-[Pt2Me2(6-dppd)2][OSO2CF3]2, 4. To a solution of
[PtMe2(6-dppd)], 2 (0.010 g, 0.01848 mmol), in acetone (2 mL)
was added trifluoromethanesulfonic acid (1.9 μL, 0.0215 mmol)
at 0 °C. After 2 h the volume of the yellow solution was reduced
[PtMeCl(6-dppd)], 1. A solution of [PtMeCl(SMe2)2] in ether
(0.010 g, 0.027 mmol) was added with stirring to a solution of
6-dppd in ether (0.008 g, 0.027 mmol). An immediate colour
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under vacuum, and pentane (1 mL) was added to give the
product as a yellow solid, which was isolated by filtration,
washed with pentane, and dried under vacuum. Yield: 92%
(0.0121 g). Anal. Calcd for C44H46F6N8O6S2Pt2·CH2Cl2 (%): C,
37.64; H, 3.37; N, 7.94; S, 4.47. Found: C, 37.85; H, 3.76; N,
7.54; S, 4.28. NMR in acetone-d6: δ(1H) = 1.00 [m, 1H, CH2C];
E
2
1.12 [m, 1H, CH2 ]; 1.20 [s, 3H, CH3, J(Pt-H) = 74 Hz]; 1.56
[m, 4H, CH2D, CH2D, CH2B, CH2C]; 1.78 [m, 1H, CH2 ]; 2.26
F
[m, 1H, CH2B]; 2.73 [dt, 1H, CH2 ]; 2.98 [td, 1H, CH2E]; 3.11
F
[t, 1H, CH2A]; 3.52 [d, 1H, CH2A]; 7.45 [d, 1H, H3′]; 7.65 [m,
1H, H5′]; 7.68 [m, 1H, H5]; 8.11 [m, 1H, H4′]; 8.32 [t, 1H, H4];
8.38 [d, 1H, H3]; 8.88 [d, 1H, J(PtH6′) = 21 Hz, H6′]; 9.06 [d,
3
1H, J(PtH6) = 34 Hz, H6]. δ(13C) = −6.22 [s, CH3, Pt-CH3];
3
25.63, 26.47, 28.07, 28.25, 29.63, 29.82 [CH2]; 127.19, 128.19,
128.26, 129.10, 139.95, 141.02, 146.12, 146.54, 151.00, 154.30,
155.86, 156.48 (aromatic). δ(19F) = −78.82 [s, free trifluoro-
methanesulfonate]. ESI-MS: Calc. for [C42H46N8Pt2]2+: m/z =
526.16; Found m/z = 526.20, z = 2.
[PtMe(PPh3)(6-dppd)][OSO2CF3], 6c. To
a
solution of
[PtMe2(6-dppd)], 2 (10 mg, 0.01848 mmol), in MeCN (1 mL)
was added a solution of CF3SO3H in MeCN at 0 °C. After stir-
ring for 10 min at 0 °C, a solution of Ph3P (4.84 mg,
0.01848 mmol) in MeCN (1 mL) was added, and the reaction
mixture was allowed to warm to room temperature. After 3 h, the
solvent was evaporated under vacuum to afford a red-orange
solid, which was washed with ether (3 × 2 mL) and dried under
vacuum. Crystals were grown from acetone–pentane by slow
diffusion. Yield: 73%. Anal. Calcd for C41H38F3N4O3-
PSPt·1.5C3H6O: C, 52.14; H, 4.62; N, 5.47. Found: C, 52.60; H,
4.98; N, 6.02%. NMR in acetone-d6: δ(1H) = 0.85 [d, 3H, CH3,
2J(Pt-H) = 71 Hz, J(P-H) = 3 Hz]; 1.43 [m, 2H, CH2D]; 1.68
3
[m, 2H, CH2C]; 1.73 [m, 2H, CH2B]; 2.18 [m, 2H, CH2E]; 3.14
F
[t, 2H, CH2A]; 3.47 [t, 2H, CH2 ]; 6.24 [d, 1H, H3′]; 7.37 [m,
6H, Hm]; 7.43 [m, 1H, H5′]; 7.49 [m, 3H, Hp]; 7.54 [t, 1H, H4′];
7.68 [m, 6H, Ho]; 8.17 [m, 1H, H5]; 8.60 [d, 1H, H6′]; 8.69 [m,
3
1H, H4]; 8.21 [d, 1H, H3]; 9.35 [m, 1H, J(PtH6) = 33 Hz, H6].
δ(13C) = −5.27 [s, CH3, Pt-CH3]; 22.03, 25.15, 26.38, 28.03,
29.49, 30.25 [CH2]; 124.07, 124.64, 128.27, 128.27, 128.96,
129.72, 130.88, 132.57, 134.23, 134.28, 136.54, 141.37, 144.58,
146.46, 148.51, 149.10, 151.75, 153.55 (aromatic). δ(19F) =
−78.82 [s, free trifluoromethanesulfonate). δ(31P) = 19.37 [s,
1J(Pt-P) = 4360 Hz]. ESI-MS: Calc. for [C39H38N4PPt]+: m/z =
788.250. Found: m/z = 788.248.
X-ray crystallography. In a typical case, a crystal was coated
in Paratone oil and mounted on a glass fiber loop. X-ray data
were collected at 150 K with ω and φ scans on a Bruker Smart
Apex II diffractometer using graphite-monochromated MoΚα
radiation (λ = 0.71073 Å) and Bruker SMART software. Unit
cell parameters were calculated and refined from the full data set.
Cell refinement and data reduction were performed using the
Bruker APEX2 and SAINT programs respectively. Reflections
were scaled and corrected for absorption effects using SADABS.
Crystal data are summarized in Table 1. The unit cell of com-
pound 4a contained a disordered trifluoromethanesulfonate
molecule, which was refined isotropically along with the MePt
carbon atom. The unit cell of compound 4b·2(C3H6O)·(H2O)
contains a water molecule, which was modeled as an isolated
12384 | Dalton Trans., 2012, 41, 12378–12385
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E. Dalcanale, Proc. Natl. Acad. Sci. U. S. A., 2002, 99, 4911; Z. Qin,
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The unit cell of 4c·(CH2Cl2) contained a disordered solvent
molecule, for which no suitable model could be found. The elec-
tron density related to this molecule was removed from the
reflection data using SQUEEZE (PLATON), leaving a void of
about 214 Å3.
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This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 12378–12385 | 12385