Self-assembly of flexible supramolecular metallacyclic ensembles: Structures and adsorption properties of their nanoporous crystalline frameworks

Article abstract of DOI:10.1021/ja0388919

The syntheses, structures, and N₂ adsorption properties of six new supramolecular metallacycles are reported. Flexible ditopic linkers, 1-4, with systematically varied lengths and conformational degrees of freedom were synthesized utilizing ester linkages. They were used in combination with (dppp)M(OTf)₂, where M = PT(II) and Pd(II), and cis-(Me ₃P)₂Pt(OTf)₂ to form flexible supramolecular metallacycles 5-10 in 88-98% isolated yields. Their structures were characterized via multinuclear NMR and X-ray crystallography. The metallacycles stack to form porous structures in the crystalline state. The pore dimensions depend on both the phosphorus ligands attached to the metals and the flexible linkers. Adsorption studies on the porous materials show that 5a, 6, 8, and 9 held 11.7, 16.5, 5.7, and 6.8 cm³/g STP of N₂ at 77 K, respectively. A guest-exchange study with nitromethane and toluene reveals that the nanopore in 5 is flexible, a property which was transferred from the linker to the supramolecular structure in the solid state.

Full text of DOI:10.1021/ja0388919

Published on Web 08/10/2004
Self-Assembly of Flexible Supramolecular Metallacyclic
Ensembles: Structures and Adsorption Properties of Their
Nanoporous Crystalline Frameworks
Biswaroop Chatterjee,† Juan C. Noveron,*,‡ Marino J. E. Resendiz,† Jie Liu,†
Takuya Yamamoto,† Daniel Parker,† Martin Cinke,§ Cattien V. Nguyen,§
Atta M. Arif,† and Peter J. Stang*,†
Contribution from the Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112,
Department of Chemistry, UniVersity of Texas at El Paso, El Paso, Texas 79968, and
Eloret Corporation, NASA Ames Research Center, Moffett Field, California 94035
Received October 6, 2003; E-mail: jcnoveron@utep.edu; stang@chem.utah.edu
Abstract: The syntheses, structures, and N2 adsorption properties of six new supramolecular metallacycles
are reported. Flexible ditopic linkers, 1-4, with systematically varied lengths and conformational degrees
of freedom were synthesized utilizing ester linkages. They were used in combination with (dppp)M(OTf)2,
where M ) Pt(II) and Pd(II), and cis-(Me3P)2Pt(OTf)2 to form flexible supramolecular metallacycles 5-10
in 88-98% isolated yields. Their structures were characterized via multinuclear NMR and X-ray
crystallography. The metallacycles stack to form porous structures in the crystalline state. The pore
dimensions depend on both the phosphorus ligands attached to the metals and the flexible linkers. Adsorption
studies on the porous materials show that 5a, 6, 8, and 9 held 11.7, 16.5, 5.7, and 6.8 cm3/g STP of N2 at
77 K, respectively. A guest-exchange study with nitromethane and toluene reveals that the nanopore in 5
is flexible, a property which was transferred from the linker to the supramolecular structure in the solid
state.
nanostructures. For example, substrate binding sites,10 porphyrin
units,11 Lewis base receptor sites,12 and shape-selective cavities8e,9b
have been incorporated within coordination-directed supra-
Introduction
The use of coordination-directed self-assembly is now an
established methodology for the synthesis of discrete molecular
species.1 This approach offers a variety of opportunities for the
preparation of nanoscopic supramolecular ensembles of pre-
determined shape, size, and symmetry. For example, numerous
triangular2 and quadrangular3 two-dimensional assemblies as
well as three-dimensional ensembles including Platonic4 and
Archimedean5 polyhedra, adamantanoids,6 boxes,7 prisms,8 and
tetragonal architectures9 have been reported. The ability to
modify the organic components of frameworks also offers
unlimited possibilities for the introduction of functionality into
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† University of Utah.
‡ University of Texas at El Paso.
§ Eloret Corp.
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J. AM. CHEM. SOC. 2004, 126, 10645-10656
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A R T I C L E S
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molecular ensembles. Furthermore, when considering that metal-
containing structures often possess magnetic, photophysical, and
redox properties not accessible from purely organic systems,
supramolecular metal-organic assemblies that couple both the
functionality of the organic frames and the properties of the
inorganic components could have a significant impact in the
areas of molecular sensing, catalysis, molecular electronics, and
new hydrogen fuel technologies.13
Current research directions that apply the edge-directed1b,c
and the face-directed1d strategies for self-assembly have focused
on the design and synthesis of rigid molecular components
which control the geometry and symmetry of the final en-
sembles. The use of flexible donor components is less common
in self-assembly, and only a handful of examples exist that
employ flexible organic linkers to generate discrete structures.14
Flexible organic components are generally less predictable
during self-assembly and have a tendency to generate [2]-
catenanes15 or oligomers16 upon reaction with metals. They often
need guest molecules acting as templates in order to form
discrete structures.14b,15a
Figure 1. Flexible linkers 1-4 used in this study (left) with the number
of atoms (n) present in the spacer group between the pyridyl moieties (right).
lacycles stack together in the crystalline state, generating
nanopores that run along one or two directions of the crystals.
Solvent-exchange and N2 adsorption studies on the porous nature
of these materials are reported.
Incorporating flexible linkers into supramolecular systems has
several potential advantages. They can generate ensembles in
which the flexible nature of the units is reflected in the
supramolecule, thus affording nanostructures that can “breathe”
in the solid state and exhibit dynamic properties. This is
particularly interesting if the flexible groups contain dynamic
modes that generate predictable conformational changes in the
solid state. Flexible components in self-assembly could poten-
tially “find” conformations that are thermodynamically favorable
for host-guest interactions, thus allowing for chemosensing
activity in the solid state. These properties are yet to be realized
in supramolecular systems; hence, studies that incorporate
flexible units in supramolecular ensembles are desirable.
Results
Syntheses of Ditopic Flexible Linkers 1-4. The linkers
shown in Figure 1 were prepared according to eqs 1 and 2.
Herein, we report on the self-assembly of six metallacycles
from flexible linkers and cis-square-planar metal units. The
linkers used are ditopic pyridyl molecules that are systematically
varied in length and conformational degrees of freedom: 1,2-
ethanediyl di-4-pyridinecarboxylate (1), 1,3-propanediyl di-4-
pyridinecarboxylate (2), 2-butyne-1,4-diyl di-4-pyridinecarbox-
ylate (3), and bis(4-pyridylmethyl) pyridine-2,6-dicarboxylate
(4) (Figure 1). Upon self-assembly with (dppp)Pt(OTf)2, (dppp)-
Pd(OTf)2 (where (dppp) ) 1,3-bis(diphenylphosphino)propane),
and cis-(Me3P)2Pt(OTf)2, large dimeric metallacycles were
formed from 1-3. In the case of 4, an equilibrium of dimeric
and trimeric structures was observed. They were then crystal-
lized and characterized by X-ray crystallography. The metal-
Reaction of 2 equiv of isonicotinoyl chloride with the corre-
sponding diol in anhydrous dichloromethane and triethylamine
under reflux generated the corresponding products 1-3 in good
yields (eq 1). Similarly, a 2:1 mixture of 4-pyridinemethanol
and 2,6-pyridinedicarboxylic acid chloride generated the ditopic
flexible linker 4 with an inverted ester group (eq 2).
Syntheses of Metallacycles 5-10. The discrete metallacyclic
complexes 5-9 (Figure 2) were prepared when stoichiometric
mixtures of the cis-square-planar metal units and the corre-
sponding flexible linkers 1-3 were reacted in nitromethane-
d3.
(11) (a) Stang, P. J.; Fan, J.; Olenyuk, B. Chem. Commun. 1997, 1453-1454.
(b) Drain, C. M.; Lehn, J.-M. J. Chem. Soc., Chem. Commun. 1994, 2313-
2315. (c) Fan, J.; Whiteford, J. A.; Olenyuk, B.; Levin, M. D.; Stang, P.
J.; Fleischer, E. B. J. Am. Chem. Soc. 1999, 121, 2741-2752.
(12) (a) Schnebeck, R.-D.; Randaccio, L.; Zangrando, E.; Lippert, B. Angew.
Chem., Int. Ed. 1998, 37, 119-121. (b) Whiteford, J. A.; Lu, C. V.; Stang,
P. J. J. Am. Chem. Soc. 1997, 119, 2524-2533. (c) Whiteford, J. A.; Stang,
P. J.; Huang, S. D. Inorg. Chem. 1998, 37, 5595-5601.
(13) Berry, G. D.; Aceves, S. M. Energy Fuels 1998, 12, 49-55.
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Soc. 2001, 123, 7740-7741. (b) Tabellion, F. M.; Seidel, S. R.; Arif, A.
M.; Stang, P. J. J. Am. Chem. Soc. 2001, 123, 11982-11990.
(15) (a) Fujita, M.; Ibukuro, F.; Ogura, K.; Seki, H.; Kamo, O.; Imanari, M. J.
Am. Chem. Soc. 1996, 118, 899-900. (b) Fujita, M.; Aoyagi, M.; Ibukuro,
F.; Ogura, K.; Yamaguchi, K. J. Am. Chem. Soc. 1998, 120, 611-612. (c)
Fujita, M.; Ibukuro, F.; Yamaguchi, K.; Ogura, K. J. Am. Chem. Soc. 1995,
117, 4175-4176.
For example, when (dppp)Pt(OTf)2 was combined with an
equimolar amount of 1 at room temperature, it resulted in the
spontaneous formation of the metallacyclic assembly [(dppp)-
Pt(1)]2(OTf)4 (5). The self-assemblies of 6-9 were carried out
in the same manner. The chemical shift changes of the
phosphorus atoms attached to the metals and the R- and
â-pyridyl protons of the flexible ligands are indicative of the
formation of the self-assemblies. The highly symmetrical nature
(16) (a) Hiraoka, S.; Fujita, M. J. Am. Chem. Soc. 1999, 121, 10239-10240.
(b) Fujita, M.; Kwon, Y. J.; Sasaki, O.; Yamaguchi, K.; Ogura, K. J. Am.
Chem. Soc. 1995, 117, 7287-7288.
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Flexible Supramolecular Metallacyclic Ensembles
A R T I C L E S
Figure 2. Chemical structures of metallacycles 5-10.
of 5-9 in solution is shown by sharp singlet peaks in the 31P-
{1H} NMR spectra at δ -13.1, 9.5-9.3, and -27.9 ppm for
the metallacycles consisting of (dppp)Pt, (dppp)Pd, and (Me3P)2-
Pt, respectively. The difference in the 195Pt satellite coupling
constants of the two types of phosphorus ligands was relatively
small: JP-Pt ) 3015 Hz for (dppp)Pt, 3150 and 3147 Hz for
1600.3 for {[(dppp)Pd(4)]2(OTf)3}+ and {[(dppp)Pd(4)]3-
(OTf)4}2+, respectively. The 31P{1H} NMR spectrum of the
reaction mixture was indicative of two highly symmetrical
species, as shown by two sharp singlet peaks at δ 10.8 and 9.3
1
ppm. Similarly, two sets of signals were observed in the H
NMR spectrum, whereas only one singlet appeared at δ -78.6
ppm in the 19F NMR spectrum. However, upon crystallization,
only the dimeric structure [(dppp)Pd(4)]2(OTf)4 (10) was
obtained (Figure 2).
1
(Me3P)2Pt. Well-defined peaks in the H NMR spectra were
observed for 5-9. The chemical shifts of the R-pyridyl protons
(δ 8.88-8.75 ppm) were similar to those of the free linkers,
whereas the â-pyridyl protons shifted upfield to δ 7.65-7.54
ppm for the complexes consisting of (dppp)M units. In the case
of the reactions with (Me3P)2Pt(OTf)2, downfield shifts were
observed for both R- and â-pyridyl protons (δ 9.11-9.04 and
8.15-8.09 ppm, respectively). This indicates that the chemical
shifts of the R- and â-pyridyl protons depend largely on the
phosphorus ligands and less on the metals. The uncoordinated
triflate counterions of 5-9 exhibit singlet peaks between δ
-78.5 and -78.7 ppm in the 19F NMR spectra.
In contrast to the single species formation in the self-assembly
of 5-9, equimolar reaction of (dppp)Pd(OTf)2 with ligand 4 in
nitromethane-d3 at room temperature generated an equilibrium
of two structures. ESI-MS indicates that the two species were
dimeric [(dppp)Pd(4)]2(OTf)4 and trimeric [(dppp)Pd(4)]3(OTf)6.
Isotopically resolved peaks were found at m/z ) 2183.0 and
Crystal Structures of Metallacycles 5a, 5b, and 6-10.
X-ray-quality crystals of 5a, 7, 8, and 10 were obtained by
diethyl ether diffusion into solutions of the corresponding
compounds in nitromethane. When 5a was recrystallized from
a mixture of dichloromethane and toluene (90:10), a new host-
guest complex of 5 + toluene (5b) was obtained. Metallacycles
6 and 9 were crystallized by diethyl ether diffusion into methanol
solution of the assemblies. The crystal structures of 5a, 5b, and
6-10 are shown in Figures 3-9. Their crystallographic
parameters are shown in Table 1, and relevant bond lengths
and bond angles are summarized in Table 2.
The crystal structures of the metallacycles 5a, 5b, and 6-10
reveal interesting trends depending on the metal (Pt or Pd), P
ligand, (dppp) or (Me3P)2, and N linker (flexible linkers, 1-4)
used (Table 2). As expected, the metal-to-metal distance (M-
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Figure 3. Crystal structure of 5a. Hydrogen atoms, solvent molecules, and counterions are omitted for clarity. Metallacycle 5, [(dppp)Pt(1)]2(OTf)4, incorporated
six nitromethane molecules (omitted) to form 5a; π-π stacking interactions are observed between the pyridyl groups of the linker and the two phenyl groups
of the (dppp) moiety.
Figure 4. Crystal structure of 5b incorporating a toluene guest. Hydrogen atoms and counterions are omitted for clarity. In the solid state, π-π stacking
interactions are observed between the pyridyl groups of the linker and the two phenyl groups of the (dppp) moiety as well as between the pyridyl group and
the incorporated toluene molecule.
Figure 5. Crystal structure of 6. Hydrogen atoms, solvent molecules, and counterions are omitted for clarity. In the solid state, π-π stacking interactions
are observed between the pyridyl groups of the linker and the two phenyl groups of the (dppp) moiety.
M) in each metallacycle increases as the length of the N linker
increases within the same P ligand series except for 10; i.e.,
M-M increases as 5a ) 12.3 Å, 5b ) 12.7 Å, 6 ) 15.0 Å, 9
) 15.4 Å, and for 7 ) 14.2 Å, 8 ) 14.7 Å. However, ensemble
10, with the longest linker, has a constricted cavity in the solid
state (M-M ) 8.8 Å). The ethanediyl groups in the crystal
structures of 5a, 5b, and 7 can adopt two possible conformations,
trans (T) and gauche (G), for O(2)-C(7)-C(8)-O(3). This can
also be applied to O(2)-C(7)-C(10)-O(3) in the crystal
structure of 9 by considering that the four-carbon unit C(7)-
9
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Flexible Supramolecular Metallacyclic Ensembles
A R T I C L E S
Figure 6. Crystal structure of 7. Hydrogen atoms, solvent molecules, and counterions are omitted for clarity.
Figure 7. Crystal structure of 8. Hydrogen atoms, solvent molecules, and counterions are omitted for clarity.
Figure 8. Crystal structure of 9. Hydrogen atoms, solvent molecules, and counterions are omitted for clarity. In the solid state, π-π stacking interactions
are observed between the pyridyl groups of the linker and the two phenyl groups of the (dppp) moiety.
C(8)-C(9)-C(10) is almost straight. In the case of 6 and 8,
the propanediyl group has four possible conformations, TT, GT,
GG, and GG′,17 for O(2)-C(7)-C(8)-C(9) and C(7)-C(8)-
C(9)-O(3). All the N linkers in 5a, 5b, and 7-9 are in the
gauche conformation. Interestingly, the conformations in 6 are
gauche and trans (GT), whereas the (Me3P)2Pt counterpart 8
has two gauche conformations (GG).
The geometries at the square-planar metals are also notable.
Although all the metallacycles have identical bond lengths of
M-P (2.3 Å) and M-N (2.1 Å), the angles in the square-planar
Pt and Pd are quite different. The (dppp)Pt of 5a and 5b and
the (dppp)Pd of 9 and 10 have similar angular distributions.
For these species the angles of P(1)-M-P(2) and N(1)-M-
N(2) range from 91.3 to 92.7° and from 85.6 to 86.3°
respectively. On the other hand, the complexes 7 and 8 have
larger P(1)-M-P(2) (96.1°) but smaller N(1)-M-N(2) (81.1-
(17) Carlucci, L.; Ciani, G.; v. Gundenberg, D. W.; Proserpio, D. M. Inorg.
Chem. 1997, 36, 3812-3813.
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Chatterjee et al.
Figure 9. Crystal structure of 10. Hydrogen atoms, solvent molecules, and counterions are omitted for clarity. A constricted cavity is observed. In the solid
state, π-π stacking interactions are observed between the pyridyl groups of the linker and the two phenyl groups of the (dppp) moiety.
Table 1. Crystal Data for 5a, 5b, and 6-10
5a
5b
6
7
8
9
10
empirical formula
C92 H94 F12 N10 C97 H89 F12 N4 C90 H92 F12 N4 C45 H63 F12 N5 C50 H74 F12 N4 C91 H80 F12 N4 C98 H88 F12 N8
O32 P4 Pt2 S4 O20 P4 Pt2 S4 O24 P4 Pd2 S4 O22 P4 Pt2 S4 O21 P4 Pt2 S4 O21 P4 Pd2 S4 O24 P4 Pd2 S4
2722.07 2501.02 2306.60 1896.30 1937.43 2258.51 2454.68
formula weight
space group
unit cell dimensions
a, Å
b, Å
c, Å
P21/n
P21/n
P1h
P1h
P1h
P21/n
P1h
13.6056(3)
23.3073(4)
19.1246(4)
90
105.4608(10)
90
13.2388(3)
24.2168(5)
19.0150(4)
90
106.8891(11)
90
10.5043(2)
12.0394(3)
20.2334(6)
91.9466(10)
104.8438(12)
90.2628(20)
2471.77(11)
9915
8.81510(10)
9.03470(10)
22.8904(4)
90.8881(6)
91.5730(6)
99.6842(6)
1796.00(4)
8054
8.8035(2)
9.1015(2)
23.3350(7)
89.8587(7)
88.1624(8)
80.5377(16)
1843.32(8)
8082
12.8418(3)
28.6558(7)
14.1269(4)
90
105.4719(10)
90
11.7834(2)
15.3708(3)
15.4053(3)
88.4998(8)
81.9321(8)
70.4728(13)
2603.06(8)
11 811
R, °
â, °
γ, °
volume, Å3
independent reflctns
goodness-of-fit on F2
final R indices
5845.1(2)
10 604
5833.3(2)
13 219
5010.2(2)
11 291
1.116
1.086
1.016
1.187
1.054
1.033
1.027
[I > 2σ(I)]: R1,a wR2b 0.0652, 0.1650
0.0812, 0.1872
0.0551, 0.1242
0.0510, 0.1217
0.0429, 0.0938
0.0690, 0.1619
0.0615, 0.1384
2
2
2
a R1 ) ∑(||Fo| - |Fc||)/∑|Fo|. b wR2 ) [∑(w(Fo - Fc )2)/∑(Fo )2]1/2
.
81.4°) angles. This is likely caused by the π-π staking
interaction of the phenyl groups of the (dppp) ligands and the
pyridyl groups of the N linkers (Figures 3, 4, 8, and 9). This
interaction “pulls” the pyridyl groups outward, resulting in the
larger N(1)-M-N(2) angle in 5a, 5b, 9, and 10 compared to
those of the (Me3P)2Pt systems (7 and 8). Consequently,
relatively small angles of P(1)-M-P(2) for 5a, 5b, 9, and 10
are observed compared to those in 7 and 8. The P-M-N angles
are also similar throughout these complexes 5a, 5b, and 7-10.
The square-planar geometry at the Pd center in 6 is different
from that in the others, although it has a similar π-π stacking
interaction (Figure 5). Both P(1)-M-P(2) (89.0°) and N(1)-
M-N(2) (83.3°) angles are noticeably smaller than in the other
(dppp)M complexes.
counterion is located on each side of the coordination plane
(axial position) of the square-planar metal centers. For the
(dppp)M complexes, the closest oxygen atom is found ap-
proximately 3 Å away from the metal center on one side of the
(dppp)M coordination plane, while on the other side the nearest
oxygen atom is significantly farther away (3.9-4.3 Å) (Table
2). In contrast, the closest triflate oxygen atoms are ap-
proximately equidistant to the metal centers (3.6-3.9 Å) on
either side of the (Me3P)2Pt coordination plane in complexes 7
and 8.
Adsorption Isotherms of Crystals 5a, 6, 8, and 9. Adsorp-
tion isotherms with N2 were measured on desolvated polycrys-
talline samples 5a, 6, 8, and 9. The N2 adsorption experiments
were carried out by introducing high-purity grade N2 gas at 77
K. Isotherm plots and maximum volumes adsorbed for 5a, 6,
8, and 9 are shown in Figure 10 and Table 2, respectively.
Desolvated crystals of 6 exhibit the greatest adsorption; 16.5
cm3 STP of N2 was adsorbed per gram of 6 at 750 Torr. A
Another interesting differentiation between the (dppp)M and
(Me3P)2Pt systems is the position of the triflate counterions in
the crystal structures of 5a, 5b, and 6-10. The counterions were
found nearby the positively charged metal centers. One triflate
9
10650 J. AM. CHEM. SOC. VOL. 126, NO. 34, 2004

Flexible Supramolecular Metallacyclic Ensembles
A R T I C L E S
Table 2. Metallacycle and Pore Crystallographic Data for 5a, 5b, and 6-10 and N2 Adsorption Data for 5a, 6, 8, and 9
5a
5b
6
7
8
9
10
Metallacycle Crystallographic Data
M
Pt
Pt
Pd
Pt
Pt
Pd
Pd
P ligand
N linker
dppp
1
dppp
1
dppp
2
(Me3P)2
1
(Me3P)2
2
dppp
3
dppp
4
M-M (Å)
12.3
12.3
G
12.7
11.9
G
15.0
10.4
GT
61.2
0.8
2.3
2.3
2.1
2.1
89.0
83.3
93.3
94.5
6.4
5.4
4.1
5.1
4.8
14.2
9.9
G
14.7
10.6
GG
63.5
67.7
2.3
2.3
2.1
2.1
96.1
81.4
90.9
91.5
4.6
3.6
3.8
4.1
5.3
15.4
11.1
G
8.8
12.9
N linker-N linker (Å)a
N linker conformationb
N linker dihedral angle (°)b
73.3
75.6
90.7
84.7
M-P(1) (Å)
2.3
2.3
2.1
2.1
92.7
86.1
89.5
91.7
6.4
4.3
5.1
5.2
3.2
2.3
2.3
2.1
2.1
92.6
85.6
91.6
90.3
4.9
5.4
3.1
5.2
4.2
2.3
2.3
2.1
2.1
96.1
81.1
91.3
91.4
3.9
5.1
4.0
3.6
3.9
2.3
2.3
2.1
2.1
91.7
86.3
91.9
90.1
3.9
6.1
6.1
3.0
5.1
2.3
2.3
2.1
2.1
91.3
85.7
91.4
91.9
5.5
6.6
4.3
5.2
3.2
M-P(2) (Å)
M-N(1) (Å)
M-N(2) (Å)c
P(1)-M-P(2) (°)
N(1)-M-N(2) (°)
P(1)-M-N (°)d
P(2)-M-N (°)d
M-OTf (Å)e
M-O(5)
M-O(6)
M-O(7)
M-O(8)
M-O(9)
M-O(10)
5.4
6.5
2.9
4.5
3.7
4.9
4.4
Pore Crystallographic Data
pore direction by crystallographic axis
metallacycle stacking distance (Å)
estimated pore dimension, M-M (Å)
estimated pore dimension,
c
c
a
a, b
a, b
a
a
19.1
10.8
8.5
19.0
11.1
7.9
10.5
8.9
6.0
8.8, 9.0
12.6, 12.7
3.4, 2.6
8.8, 9.1
13.0, 13.1
3.0, 3.7
12.8
9.1
6.7
11.8
6.9
6.9
N linker-N linker (Å)
N2 Adsorption Data
16.5
maximum volume adsorbed (cm3/g STP)
corresponding pressure (Torr)
11.7
757
40
5.7
755
18
6.8
762
36
750
107
Langmuir surface area (m2/g)
a N linker-N linker is the distance of C(7)-C(8′) for 5a, 5b, and 7, C(8)-C(8′) for 6 and 8, C(8)-C(9′) for 9, and N(2)-N(2′) for 10. b N linker
conformation and dihedral angle are O(2)-C(7)-C(8)-O(3) for 5a, 5b, and 7, O(2)-C(7)-C(8)-C(9) and C(7)-C(8)-C(9)-O(3) for 6 and 8, and O(2)-
C(7)-C(10)-O(3) for 9. c Pd(1)-N(3′) for 10. d Angle specified by P(1)-M-N, where N is a nitrogen atom that is located at the cis-position relative to
P(1), and so forth. e The oxygen atoms O(5), O(6), and O(7) belong to one triflate counterion and O(8), O(9), and O(10) to another.
as well. Polycrystalline samples of 8 and 9 adsorbed 5.7 and
6.8 cm3/g STP of N2 at 755 and 762 Torr, respectively,
significantly less than 5a and 6; however, both 8 and 9 also
exhibit hysteresis.
Discussion
The flexible linkers (1-4) in this study have different lengths
and conformational degrees of freedom. They provided an
opportunity to examine the effects of flexibility in coordination-
directed self-assembly. We utilized the ester moiety to link a
variety of spacer units with pyridyl groups that can bind to metal
units. The use of ester linkages provided several advantages,
such as stability, ease of synthesis, and a simple but useful
functional group. Esters also have the added advantage of being
hydrogen bond acceptors. Assemblies containing such groups
could exhibit host-guest properties based on hydrogen bonding.
Incorporating flexible linkers in porous molecular materials
could generate ensembles where the flexibility of the linkers
might be transferred to the supramolecular structure. Hence, we
studied the structural changes that complex 5a undergoes upon
exchange with other solvents. When the nitromethane-containing
crystal structure 5a was recrystallized from a dichloromethane-
toluene mixture, a new structure 5b was obtained that incor-
porated toluene molecules instead of nitromethane molecules
in the pore. X-ray analysis of structure 5b reveals that the
flexible framework undergoes a slight conformational change
in the C(6)-O(2)-C(7)-C(8) dihedral angle from 154.5° in
Figure 10. Adsorption isotherms for N2 on desolvated polycrystalline
compounds of 5a, 6, 8, and 9 at 77 K. Filled and unfilled data points indicate
adsorption and desorption, respectively.
rapid adsorption of N2 was observed with pronounced hysteresis
upon desorption. A polycrystalline sample of 5a showed the
second highest adsorption (11.7 cm3/g STP of N2 at 757 Torr)
and exhibited hysteresis between its adsorption and desorption
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A R T I C L E S
Chatterjee et al.
layers of the metallacycles are parallel to the ab-plane. Two
adjacent layers are shifted by half of the dimensions of the ab-
plane of the unit cell (Figure 12). Thus, in this alternating
stacking manner, the pores in the crystals of 5a and 5b are
formed by every second layer of the metallacycles, resulting in
significantly larger stacking distances between metallacycles
forming a given channel (19.1 Å for 5a and 19.0 Å for 5b).
The actual pore size is effectively reduced from the estimated
values (10.8 Å × 8.5 Å for 5a) because the two adjacent layers
of metallacycles partially block each other’s pore. The crystal
of 5a contains six nitromethane molecules per metallacycle; five
were found inside the pore, and one was found outside. The
crystal of 5b contains three toluene molecules with 50%
occupancy per metallacycle. One toluene molecule is present
within each metallacycle, while the other two are between
adjacent metallacycles. In contrast to the stacking of alternating
layers in 5a and 5b, 6 has the layers of metallacycles aligned;
i.e., the cavities are right on top of each other (Figure 13). As
a result, the pore dimensions of 6 remain reasonably large
without a significant reduction from the estimated values (8.9
Å × 6.0 Å). The crystal of 6 contains two water and two
methanol molecules per metallacycle; the water molecules are
found inside the pore, whereas the methanol molecules are
located outside. The complexes 7 and 8 have nanopores along
the crystallographic axes a and b (Figure 14). However, this
requires approximately a 45° tilt from the two axes, thus
resulting in very narrow pores in the N linker-N linker direction
(for 7, 3.4, 2.6 Å; for 8, 3.0, 3.7 Å). The cavities of 7 and 8 are
filled with one nitromethane and one diethyl ether molecule,
respectively. The estimated pore dimensions of 9 are fairly large
(9.1 Å × 6.7 Å), and the metallacyclic layers are aligned, but
the phenyl groups of the (dppp) moieties block a large proportion
of the pore and this reduces the overall porosity of the crystal
(Figure 15). One methanol molecule per metallacycle is found
inside the pore of 9. The crystal structure of 10 indicates two
nitromethane molecules per metallacycle are located outside of
the pore.
Figure 11. (a) Enclathrated toluene molecule in 5b is held via π-π stacking
interactions. (b) The flexible linker framework in 5b underwent confor-
mational change from 5a.
5a to 160.2° in 5b, to form strong π-π stacking interactions
(3.6 Å) between the pyridyl groups and the toluene molecules
(Figure 11). This suggests that the flexibility of the linker 1
was transferred to the solid-state structures of 5a and 5b. Similar
behavior has been observed with other flexible spacer units in
coordination networks.14b
Analyses of the X-ray crystal structures of 5a, 5b, and 6-10
reveal that the metallacycles stack along one or two of the
crystallographic axes, forming nanopore channels. The shape
and topology of the nanopores are largely determined by the
flexible linkers, the metal units with phosphorus ligands, and
the stacking of the metallacycles. To determine the pore
dimensions, the factors that need to be considered are the tilting
of the metallacycles with respect to their stacking axes and the
ionic and van der Waals radii. The pore dimensions are
estimated by projecting the cavity of the metallacycles to the
plane perpendicular to the stacking axes and then subtracting
the ionic and van der Waals radii from the distances of M-M
and N linker-N linker, respectively, in the projected images
(Table 2). The pores of 5a and 5b are along the c-axis, and the
To assess the porous properties of the crystalline materials,
we carried out N2 adsorption studies at 77 K. Prior to the
experiments, the samples were placed under vacuum until no
Figure 12. Packing diagram of 5a. The red arrow indicates the direction of the pores (c-axis). (a) Viewed along the a-axis. The two adjacent layers of
metallcycles 5 are shifted by half of the dimensions of the ab-plane of the unit cell. (b) Viewed along the c-axis. The partially blocked pore caused by the
alternating positions of the layers can be observed (center of the picture).
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10652 J. AM. CHEM. SOC. VOL. 126, NO. 34, 2004

Flexible Supramolecular Metallacyclic Ensembles
A R T I C L E S
Figure 13. Packing diagram of 6. The red arrow indicates the direction of the pores (a-axis). (a) Viewed along the a-axis. (b) Viewed along the b-axis. The
layers of the metallacycles 6 are aligned; as a result, the cavities are right on top of each other.
Figure 14. Packing diagram of 8. The directions of the pores are indicated in red. This crystal forms pores that can be seen from two directions (a- and
b-axes). However, in both directions, the pores are quite narrow, and the dimensions in the N linker-N linker directions are short. (a) Viewed along the
a-axis. (b) Viewed along the b-axis.
further weight loss from solvent evaporation was observed. The
experiment was repeated several times for each sample to
reproduce the isotherm. As shown in Figure 10, complexes 5a,
6, 8, and 9 exhibit N2 adsorption with pronounced hysteresis
upon desorption. The rapid rise followed by a monotonically
increasing curve at low pressure is indicative of uniform pore
size distribution and is characteristic of other nanoporous
materials.18,19 The pronounced hysteresis may have arisen from
capillary condensation within the crystals.18 Moreover, the
desorption in these crystals is unusual since it releases the
absorbed N2 quite rapidly as pressure decreases. This behavior
might arise from structural strain built up during the adsorption,
possibly due to the flexibility of the linker frameworks. For
this reason, no isotherm plots from the crystals fit any IUPAC
classifications.20
Sample 6 exhibits the greatest N2 adsorption with 16.5 cm3/g
STP (750 Torr), and the Langmuir surface area for 6 was
calculated to be 107 m2/g.21 Clearly this is due to the effective
stacking of the aligned layers of the metallacycles (Figure 13)
(19) (a) Fletcher, A. J.; Cussen, E. J.; Prior, T. J.; Rosseinsky, M. J.; Kepert, C.
J.; Thomas, K. M. J. Am. Chem. Soc. 2001, 123, 10001-10011. (b) Kepert,
C. J.; Prior, T. J.; Rosseinsky, M. J. J. Am. Chem Soc. 2000, 122, 5158-
5168. (c) Rujiwatra, A.; Kepert, C. J.; Claridge, J. B.; Rosseinsky, M. J.;
Kumagai, H.; Kurmoo, M. J. Am. Chem. Soc. 2001, 123, 10584-10594.
(d) Li, H.; Eddaoudi, M.; Groy, T. L.; Yaghi, O. M. J. Am. Chem. Soc.
1998, 120, 8571-8572. (e) Reineke, T. M.; Eddaoudi, M.; O’Keeffe, M.;
Yaghi, O. M. Angew. Chem., Int. Ed. 1999, 38, 2590-2594. (f) Eddaoudi,
M.; Li, H.; Yaghi, O. M. J. Am. Chem. Soc. 2000, 122, 1391-1397. (g)
Chen, B.; Eddaoudi, M.; Hyde, S. T.; O’Keeffe, M.; Yaghi, O. M. Science
2001, 291, 1021-1023.
(18) Sigmoidal isotherms are observed when guest-inclusion is accompanied
by phase changes. For complete discussion see: (a) Dewa, T.; Endo, K.;
Aoyama, Y. J. Am. Chem. Soc. 1998, 120, 8933-8940. (b) Dewa, T.;
Aoyama, Y. Chem. Lett. 2000, 854-855. (c) Ariga, K.; Endo, K.; Aoyama,
Y.; Okahata, Y. Colloids Surf., A 2000, 169, 177-186. (d) Matsuura, K.;
Ariga, K.; Endo, K.; Aoyama, Y.; Okahata, Y. Chem.-Eur. J. 2000, 6,
1750-1756. (e) Dewa, T.; Saiki, T.; Imai, Y.; Endo, K.; Aoyama, Y. Bull.
Chem. Soc. Jpn. 2000, 73, 2123-2127. (f) Naito, M.; Sasaki, Y.; Dewa,
T.; Aoyama, Y.; Okahata, Y. J. Am. Chem. Soc. 2001, 123, 11037-11041.
(20) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R.
A.; Rouque´rol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 603-
619.
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A R T I C L E S
Chatterjee et al.
Figure 15. (a) Packing diagram of 9 viewed along the a-axis. The directions of the pores are indicated in red. Although this crystal forms pores along the
a-axis, the phenyl groups of dppp block a large proportion of the pores (shown in red ovals). (b) Viewed along the c-axis. (c) CPK representation of the
packing diagram of 9 viewed along the a-axis. This view illustrates the pore blockage by the phenyl groups. (d) CPK respresentation of 6 showing the
unblocked pores resulting in the highest N2 adsorption.
and the reasonably large pore dimensions (8.9 Å × 6.0 Å, Table
2). Crystals of 5a had the second highest N2 adsorption of 11.7
cm3/g STP (757 Torr) with 40 m2/g of Langmuir surface area.
Although this complex has fairly large estimated pore dimen-
sions (10.8 Å × 8.5 Å), the alternating layers of the metalla-
cycles in 5a are not as effective at adsorbing N2 as the aligned
layer crystals of 6 are (Figure 12). Assemblies 8 and 9 adsorbed
significantly less N2 than 5a and 6. Although the pores in 8
can be seen along the a- and b-axes, they are very narrow (13.0
Å × 3.0 Å along the a-axis and 13.1 Å × 3.7 Å along the
b-axis) (Figure 14). Considering the dimensions of an N2
molecule, this material was expected to be inefficient at N2
adsorption. Indeed, 8 adsorbed only 5.7 cm3/g STP (755 Torr)
with an 18 m2/g Langmuir surface area. The estimated pore
dimensions of 9 are relatively large (9.1 Å × 6.7 Å), but its N2
adsorption was only 6.8 cm3/g STP (762 Torr). In the packing
of 9, the phenyl groups of the (dppp) moieties block a large
proportion of the pores in the crystal (Figure 15). Although N2
is restricted from going into these pores, the surface area should
be available because the pores are partially blocked but not
completely filled. Thus, a Langmuir surface area of 36 m2/g
for 9 was calculated, which is twice as large as that of 8.
Conclusion
A family of discrete metallacycles that comprise flexible
organic components of various lengths and conformational
degrees of freedom were synthesized via self-assembly. The
flexible ditopic linkers used (1-4) contain ester linkages that
join two pyridyl groups at each end of a spacer unit. Upon
reaction with ditopic cis-square-planar metal units, supramo-
lecular metallacycle structures (5-10) formed and were fully
characterized in both solution and the solid states. The crystal
structures reveal that the metallacycles are stacked along one
or two of the crystallographic axes, forming nanoscopic pores.
Polycrystalline samples of 5a, 6, 8, and 9 exhibit nanoporous
properties and adsorbed 11.7, 16.5, 5.7, and 6.8 cm3/g STP of
(21) Gregg, S. J.; Sing, K. S. W. Adsorption, Surface Area and Porosity, 2nd
ed.; Academic Press: London, UK, 1982.
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A R T I C L E S
2-Butyne-1,4-diyl Di-4-pyridinecarboxylate (3). Compound 3 was
prepared in a manner similar to that used for 1, except that 2-butyne-
1,4-diol (103 mg, 1.20 mmol) was used. Yield: 300 mg (85%). H
NMR (CDCl3): δ (ppm) 8.82 (bd, J ) 5.6 Hz, 4H, PyHR), 7.89 (bd,
J ) 5.9 Hz, 4H, PyHâ), 5.03 (s, 4H, CH2). 13C{1H} NMR (CDCl3): δ
(ppm) 164.6 (CdO), 150.9 (PyCR), 136.7 (PyCγ), 123.1 (PyCâ), 81.1
(CtC), 53.4 (CH2). Anal. Calcd for C16H12N2O4: C, 64.86; H, 4.08;
N, 9.45. Found: C, 64.40; H, 4.07; N, 9.18.
N2, respectively. The trend of N2 adsorption can be explained
by the estimated pore sizes and packing of the metallacycles.
X-ray studies on the exchange of nitromethane solvent molecules
for toluene reveals that the flexible framework of 5 can undergo
a conformational change to maximize interactions with the
newly introduced guest. Our work demonstrates that metalla-
cycles with ditopic flexible linkers allow the formation of
zeolite-like frameworks with custom-designed pore sizes and
molecular topologies.
1
Bis(4-pyridylmethyl) Pyridine-2,6-dicarboxylate (4). To a stirred
mixture of 2,6-pyridinedicarboxylic acid chloride (510 mg, 2.50 mmol)
in anhydrous dichloromethane (50 mL) and triethylamine (0.72 mL,
5.2 mmol) was added 2 equiv of 4-pyridinemethanol (560 mg, 5.13
mmol), and the mixture was refluxed for 12 h. Following a workup
Experimental Section
General. Isonicotinoyl chloride hydrochloride, ethylene glycol, 1,3-
propanediol, 2-butyne-1,4-diol, 2,6-pyridinedicarboxylic acid chloride,
and 4-pyridinemethanol were used as received from commercial sources
(Sigma-Aldrich or Lancaster). All solvents were distilled using standard
methods prior to use. NMR spectra were obtained at room temperature
with a Varian XL-300 spectrometer. The 1H NMR spectra were recorded
at 300 MHz, and the chemical shifts were reported relative to those of
the residual protons in the deuterated solvents, δ 7.27 and 4.33 ppm in
CDCl3 and CD3NO2, respectively. The 13C{1H} NMR spectra were
recorded at 75 MHz, and the chemical shifts were reported relative to
that of the 13C in CDCl3 (δ 77.2 ppm). The 19F and 31P{1H} NMR
spectra were recorded at 282 and 121 MHz, respectively, and the
chemical shifts were reported relative to those of external standards of
CFCl3 and H3PO4, respectively (δ 0.0 ppm in each case). Elemental
analysis was performed by Atlantic Microlab Inc. (Norcross, GA).
Single-crystal X-ray diffraction data for all compounds were collected
on a Nonius KappaCCD diffractometer equipped with Mo KR radiation
(λ ) 0.71073 Å) at 150(1) K. The structures were solved by a
combination of direct and heavy-atom methods using SIR 97. SHELXL97
was used for the final structural refinement. ESI-MS spectra were
recorded on a Micromass Quattro II triple-quadrupole mass spectrometer
with Micromass MassLynx software. Adsorption isotherms were
measured with a Micromeritics ASAP 2010 surface area and porosim-
etry analyzer. The polycrystalline samples were degassed overnight and
then loaded onto the instrument. N2 (99.9995%) was incrementally
dosed into the sample tubes to provide the adsorption measurements.
The experiment was carried out at 77 K. Calculation of surface area
was carried out according to the literature.22
1
similar to that used for 1, 4 was obtained. Yield: 786 mg (90%). H
NMR (CDCl3): δ (ppm) 8.64 (bd, J ) 5.9 Hz, 4H, PyHR), 8.36 (d, J
) 7.6 Hz, 2H, pyridyleneHâ), 8.08 (t, J ) 7.8 Hz, 1H, pyridyleneHγ),
7.40 (bd, J ) 5.6 Hz, 4H, PyHâ), 5.49 (s, 4H, CH2). 13C{1H} NMR
(CDCl3): δ (ppm) 164.3 (CdO), 150.4 (PyCR), 148.2 (pyridyleneCR),
144.5 (PyCγ), 138.8 (pyridyleneCγ), 128.6 (pyridyleneCâ), 122.2 (PyCâ),
65.9 (CH2). Anal. Calcd for C19H15N3O4: C, 65.32; H, 4.33; N, 12.03.
Found: C, 64.92; H, 4.35; N, 11.93.
[(dppp)Pt(1)]2(OTf)4 (5). A 1.0 mL nitromethane-d3 solution of
(dppp)Pt(OTf)2 (3.57 mg, 3.94 µmol) was added to 1 (1.08 mg, 3.97
µmol) and stirred for 10 min at ambient temperature. The solvent
volume was reduced, and 5 was precipitated by addition of diethyl
ether. The resulting white solid was dried under vacuum. Yield: 4.45
1
mg (90%). H NMR (CD3NO2): δ (ppm) 8.88 (bd, J ) 6.1 Hz, 8H,
PyHR), 7.74-7.42 (m, 40H, PhH), 7.65 (bd, J ) 6.6 Hz, 8H, PyHâ),
4.55 (s, 8H, OCH2), 3.33 (m, 8H, PCH2), 2.41 (m, 4H, PCH2CH2).
31P{1H} NMR (CD3NO2): δ (ppm) -13.1 (s, JP-Pt ) 3015 Hz). 19F
NMR (CD3NO2): δ (ppm) -78.5. Anal. Calcd for C86H76F12N4O20P4-
Pt2S4‚2(CH3CH2)2O: C, 45.09; H, 3.86; N, 2.24; S, 5.12. Found: C,
45.34; H, 3.98; N, 2.45; S, 5.10.
[(dppp)Pt(1)]2(OTf)4‚6Nitromethane (5a). Compound 5 was dis-
solved in nitromethane (ca. 1 mM), and diethyl ether was diffused into
the solution for 2 days, affording 5a as X-ray quality crystals.
[(dppp)Pt(1)]2(OTf)4‚1.5Toluene (5b). Compound 5a was redis-
solved in a mixture of dichloromethane-toluene (90:10), and the
solution was allowed to slowly evaporate at room temperature. After
24 h, X-ray quality crystals of 5b were obtained.
1,2-Ethanediyl Di-4-pyridinecarboxylate (1). To a stirred mixture
of isonicotinoyl chloride hydrochloride (513 mg, 2.88 mmol) in
anhydrous dichloromethane (50 mL) at room temperature was added
triethylamine (0.82 mL, 5.9 mmol). Subsequently, ethylene glycol (85.0
mg, 1.37 mmol) was added to the reaction, and the mixture was refluxed
for 12 h. After the mixture was washed with saturated aqueous sodium
bicarbonate solution (20 mL), the organic phase was dried over
anhydrous potassium carbonate and filtered. Removal of the solvent
[(dppp)Pd(2)]2(OTf)4 (6). A 1.0 mL nitromethane-d3 solution of
(dppp)Pd(OTf)2 (2.94 mg, 3.60 µmol) was added to 2 (1.03 mg, 3.60
µmol) and stirred for 10 min at ambient temperature. The solvent
volume was reduced, and 6 was precipitated by addition of diethyl
ether. The resulting white solid was dried under vacuum. Yield: 3.94
mg (98%). Compound 6 was then redissolved in methanol (ca. 1 mM),
and diethyl ether was diffused into the solution for 2 days, affording
X-ray quality crystals. 1H NMR (CD3NO2): δ (ppm) 8.75 (bd, J ) 5.1
Hz, 8H, PyHR), 7.70-7.35 (m, 40H, PhH), 7.54 (bd, J ) 6.4 Hz, 8H,
PyHâ), 4.31 (t, J ) 5.3 Hz, 8H, OCH2), 3.25 (m, 8H, PCH2), 2.43 (m,
4H, PCH2CH2), 2.14 (quintet, J ) 5.3 Hz, 4H, OCH2CH2). 31P{1H}
NMR (CD3NO2): δ (ppm) 9.5 (s). 19F NMR (CD3NO2): δ (ppm)
-78.7. Anal. Calcd for C88H80F12N4O20P4Pd2S4‚2H2O: C, 47.13; H,
3.78; N, 2.50; S, 5.72. Found: C, 46.96; H, 3.83; N, 2.57; S, 5.65.
1
gave 1. Yield: 305 mg (82%). H NMR (CDCl3): δ (ppm) 8.79 (dd,
J ) 4.4, 1.7 Hz, 4H, PyHR), 7.85 (dd, J ) 4.4, 1.5 Hz, 4H, PyHâ),
4.72 (s, 4H, CH2). 13C{1H} NMR (CDCl3): δ (ppm) 165.1 (CdO),
150.9 (PyCR), 137.0 (PyCγ), 123.0 (PyCâ), 63.4 (CH2). Anal. Calcd
for C14H12N2O4: C, 61.76; H, 4.44; N, 10.29. Found: C, 61.40; H,
4.40; N, 10.08.
1,3-Propanediyl Di-4-pyridinecarboxylate (2). Compound 2 was
prepared in a manner similar to that used for 1, except that 1,3-
propanediol (107 mg, 1.41 mmol) was used in the reaction. Yield: 350
mg (87%). 1H NMR (CDCl3): δ (ppm) 8.79 (dd, J ) 4.4, 1.6 Hz, 4H,
PyHR), 7.84 (dd, J ) 4.4, 1.7 Hz, 4H, PyHâ), 4.55 (t, J ) 6.3 Hz, 4H,
OCH2), 2.31 (quintet, J ) 6.2 Hz, 2H, OCH2CH2). 13C{1H} NMR
(CDCl3): 165.1 (CdO), 150.8 (PyCR), 137.2 (PyCγ), 122.9 (PyCâ),
62.5 (OCH2), 28.1 (OCH2CH2). Anal. Calcd for C15H14N2O4: C, 62.93;
H, 4.93; N, 9.79. Found: C, 62.83; H, 4.81; N, 9.57.
[(Me3P)2Pt(1)]2(OTf)4 (7). A 2.0 mL nitromethane-d3 solution of
cis-(Me3P)2Pt(OTf)2 (4.75 mg, 7.36 µmol) was added to 1 (1.98 mg,
7.27 µmol) and stirred for 10 min at ambient temperature. The solvent
volume was reduced, and 7 was precipitated by addition of diethyl
ether. The resulting white solid was dried under vacuum. Yield: 6.40
mg (96%). Compound 7 was then redissolved in nitromethane (ca. 1
mM), and diethyl ether was diffused into the solution for 7 days,
1
affording X-ray quality crystals. H NMR (CD3NO2): δ (ppm) 9.11
(bd, J ) 4.4 Hz, 8H, PyHR), 8.15 (bd, J ) 5.9 Hz, 8H, PyHâ), 4.71 (s,
8H, OCH2), 1.65 (d, JH-P ) 11.2 Hz, 36H, P(CH3)3). 31P{1H} NMR
(CD3NO2): δ (ppm) -27.9 (s, JP-Pt ) 3150 Hz). 19F NMR (CD3NO2):
(22) Webb, P. A.; Orr, C. Analytical Methods in Fine Particle Technology;
Micromeritics: Norcross, GA, 1997.
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A R T I C L E S
Chatterjee et al.
δ (ppm) -78.7. Anal. Calcd for C44H60F12N4O20P4Pt2S4: C, 28.80; H,
3.30; N, 3.05; S, 6.99. Found: C, 29.02; H, 3.72; N, 3.29; S, 6.89.
[(Me3P)2Pt(2)]2(OTf)4 (8). A 2.0 mL nitromethane-d3 solution of
cis-(Me3P)2Pt(OTf)2 (4.61 mg, 7.14 µmol) was added to 2 (2.04 mg,
7.13 µmol) and stirred for 10 min at ambient temperature. The solvent
volume was reduced, and 8 was precipitated by addition of diethyl
ether. The resulting white solid was dried under vacuum. Yield: 6.31
mg (88%). Compound 8 was then redissolved in nitromethane (ca. 1
mM), and diethyl ether was diffused into the solution for 7 days,
was reduced, and 10 was precipitated by addition of diethyl ether. The
resulting white solid was dried under vacuum. Yield: 13.0 mg (91%).
Compound 10 was then redissolved in nitromethane (ca. 1 mM), and
diethyl ether was diffused into the solution for 2 days, affording X-ray
quality crystals. Although two species were observed in solution, only
1
the dimeric species crystallized. H NMR (CD3NO2): δ (ppm) 8.65
(bd, J ) 5.1 Hz, PyHR), 8.57 (bd, J ) 4.9 Hz, PyHR), 8.36-8.09 (m,
pyridyleneHâ,γ), 8.36-8.09 (m, pyridyleneHâ,γ), 7.82-7.38 (m, PhH),
7.71-7.38 (m, PhH), 7.29 (bd, J ) 6.2 Hz, PyHâ), 7.19 (bd, J ) 5.9
Hz, PyHâ), 5.29 (s, OCH2), 5.01 (s, OCH2), 3.25 (m, PCH2), 3.25 (m,
PCH2), 2.47 (m, PCH2CH2), 2.39 (m, PCH2CH2). 31P{1H} NMR (CD3-
NO2): δ (ppm) 10.8 (s), 9.3 (s). 19F NMR (CD3NO2): δ (ppm) -78.6.
ESI-MS: m/z 2183.0 (calcd for {[(dppp)Pd(4)]2(OTf)3}+ 2183.2),
1600.3 (calcd for {[(dppp)Pd(4)]3(OTf)4}2+ 1600.1). Anal. Calcd for
C96H82F12N6O20P4Pd2S4‚CH3NO2‚(CH3CH2)2O: C, 49.16; H, 3.88; N,
3.97; S, 5.20. Found: C, 49.53; H, 3.86; N, 3.61; S, 5.38.
1
affording X-ray quality crystals. H NMR (CD3NO2): δ (ppm) 9.04
(bd, J ) 4.4 Hz, 8H, PyHR), 8.09 (bd, J ) 6.1 Hz, 8H, PyHâ), 4.49 (t,
J ) 5.5 Hz, 8H, OCH2), 2.29 (quintet, J ) 5.2 Hz, 4H, OCH2CH2),
1.67 (d, JH-P ) 11.2 Hz, 36H, P(CH3)3). 31P{1H} NMR (CD3NO2): δ
(ppm) -27.9 (s, JP-Pt ) 3147 Hz). 19F NMR (CD3NO2): δ (ppm)
-78.7. Anal. Calcd for C46H64F12N4O20P4Pt2S4‚CH3NO2‚(CH3CH2)2O‚
H2O: C, 30.38; H, 3.95; N, 3.47; S, 6.36. Found: C, 30.13; H, 3.80;
N, 3.19; S, 6.66.
[(dppp)Pd(3)]2(OTf)4 (9). A 2.5 mL nitromethane-d3 solution of
(dppp)Pd(OTf)2 (24.05 mg, 29.44 µmol) was added to 3 (8.72 mg, 29.4
µmol) and stirred for 10 min at ambient temperature. The assembly 9
was precipitated by addition of diethyl ether. The resulting white solid
was dried under vacuum. Yield: 30.77 mg (94%). Compound 9 was
then redissolved in methanol (ca. 1 mM), and diethyl ether was diffused
into the solution for 2 days, affording X-ray quality crystals. 1H NMR
(CD3NO2): δ (ppm) 8.87 (bd, J ) 5.4 Hz, 8H, PyHR), 7.73-7.39 (m,
40H, PhH), 7.60 (bd, J ) 5.4 Hz, 8H, PyHâ), 4.90 (s, 8H, OCH2), 3.27
(m, 8H, PCH2), 2.46 (m, 4H, PCH2CH2). 31P{1H} NMR (CD3NO2): δ
(ppm) 9.3 (s). 19F NMR (CD3NO2): δ (ppm) -78.5. Anal. Calcd for
C90H76F12N4O20P4Pd2S4: C, 48.55; H, 3.44; N, 2.52; S, 5.76. Found:
C, 48.42; H, 3.73; N, 2.62; S, 5.48.
Acknowledgment. Financial support by the National Science
Foundation (CHE-0306720), the National Institutes of Health
(GM-57052), and an NIH Postdoctoral Fellowship (Grant
GM66504-01) for J.C.N. is gratefully acknowledged. Work by
the ELORET authors is supported by a NASA contract. We
thank Dr. C. Addicott and Dr. E. Rachlin for assistance with
mass spectrometry.
Supporting Information Available: Crystallographic data for
5a, 5b, and 6-10 (CIF); NMR spectra (1H and 13C{1H} for
1-4; 1H and 31P{1H} for 5-10) and ESI-MS spectra for
{[(dppp)Pd(4)]2(OTf)3}+ and {[(dppp)Pd(4)]3(OTf)4}2+ (PDF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
[(dppp)Pd(4)]2(OTf)4 (10). A 4.0 mL nitromethane-d3 solution of
(dppp)Pd(OTf)2 (9.83 mg, 12.0 µmol) was added to 4 (4.05 mg, 11.6
µmol) and stirred for 10 min at ambient temperature. NMR spectra
showed two distinguishable species in equilibrium. The solvent volume
JA0388919
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10656 J. AM. CHEM. SOC. VOL. 126, NO. 34, 2004