Geometry directed self-selection in the coordination-driven self-assembly of irregular supramolecular polygons

Article abstract of DOI:10.1021/jo9002932

The self-assembly of irregular metallo-supramolecular hexagons and parallelograms has been achieved in a self-selective manner upon mixing 120° unsymmetrical dipyridyl ligands with 60° or 120° organoplatinum acceptors in a 1:1 ratio. The polygons have bee

Full text of DOI:10.1021/jo9002932

tors and electron rich ligandssthat takes advantage of the
directional bonding approach has enabled the development of
coordination-driven self-assembly, as witnessed by the myriad
metallo-supramolecular polygons and polyhedra synthesized to
date.3 Generally, complementary subunits utilized in this ap-
proach exhibit high symmetry and contain equivalent binding
sites. Much more complicated systems and situations arise when
unsymmetrical building blocks bearing different binding sites
are employed. In accord with the second Law of Thermodynam-
ics, a self-assembly involving unsymmetrical subunits will likely
produce a statistical mixture of various supramolecular isomers
provided that no driving bias exists in the system.4
Geometry Directed Self-Selection in the
Coordination-Driven Self-Assembly of Irregular
Supramolecular Polygons
Yao-Rong Zheng,† Brian H Northrop,† Hai-Bo Yang,‡
Liang Zhao,† and Peter J. Stang*,†
Department of Chemistry, UniVersity of Utah, 315 South
1400 East, RM, 2020, Salt Lake City, Utah, 84112, and
Shanghai Key Laboratory of Green Chemistry and Chemical
Processes, Department of Chemistry, East China Normal
UniVersity, Shanghai, China 200062
The selective self-assembly of one discrete structure from
within a complex mixture that has the potential of producing
multiple isomeric supramolecules can be achieved via a self-
selection process provided that there exists some form(s) of
molecular information encoded within complementary subunits
that biases the formation of one isomer over the other(s).5 We
have previously shown that self-selection can occur during the
self-assembly of unsymmetrical ambidentate pyridylcarboxylate
ligands with ditopic organoplatinum acceptors, wherein the
driving force for self-selection rests in the preference for
maximum charge separation in the supramolecular rhomboidal
isomers.5a Recently, a thorough study of the self-selection of
supramolecular squares clearly indicates that steric features
encoded within unsymmetrical subunits can also control the
fidelity of self-selection.5d
Controlling the geometric features of molecular subunits is
an alternative approach for influencing self-selection during self-
assembly. In accordance with the directional bonding approach
to coordination-driven self-assembly, small changes in the
geometry of individual molecular subunits can be used to drive
self-organization phenomena.6 In recent reports, we have
demonstrated that manipulation of the geometric factors (e.g.,
size, directionality) of rigid symmetric molecular subunits allows
for the selective self-assembly of multiple discrete supramo-
lecular polygons and polyhedra from within multicomponent
supramolecular systems,6c,e,f and this approach has been gen-
stang@chem.utah.edu
ReceiVed February 10, 2009
The self-assembly of irregular metallo-supramolecular hexa-
gons and parallelograms has been achieved in a self-selective
manner upon mixing 120° unsymmetrical dipyridyl ligands
with 60° or 120° organoplatinum acceptors in a 1:1 ratio.
The polygons have been characterized using 31P and H
1
multinuclear NMR spectroscopy and electrospray ionization
mass spectrometry (ESI-MS) as well as X-ray crystal-
lography. Geometric features of the molecular subunits direct
the self-selection process, which is supported by molecular
force field computations.
Coordination-driven, transition metal-mediated self-assembly
has become a well-established methodology in supramolecular
chemistry for constructing ensembles exhibiting wide structural
diversity1 and functionality.2 The rational design of rigid
complementary molecular subunitsselectron poor metal accep-
(3) (a) Stang, P. J.; Olenyuk, B. Acc. Chem. Res. 1997, 30, 502. (b) Leininger,
S.; Olenyuk, B.; Stang, P. J. Chem. ReV. 2000, 100, 853. (c) Seidel, S. R.; Stang,
P. J. Acc. Chem. Res. 2002, 35, 972. (d) Northrop, B. H.; Chercka, D.; Stang,
P. J. Tetrahedron 2008, 64, 11495.
(4) (a) Barboiu, M.; Petit, E.; van der Lee, A.; Vaughan, G. Inorg. Chem.
2006, 45, 484. (b) Legrand, Y.-M.; van der Lee, A.; Barboiu, M. Inorg. Chem.
2007, 46, 9540. (c) Hutin, M.; Cramer, C. J.; Gagliardi, L.; Shahi, A. R. M.;
Bernardinelli, G.; Cerny, R.; Nitschke, J. R. J. Am. Chem. Soc. 2007, 129, 8774.
(d) Langner, A.; Tait, S. L.; Lin, N.; Rajadurai, C.; Ruben, M.; Kern, K. Proc.
Natl. Acad. Sci. U.S.A. 2007, 104, 17927. (e) Rang, A.; Engeser, M.; Maier,
N. M.; Nieger, M.; Lindner, W.; Schalley, C. A. Chem.-Eur. J. 2008, 14, 3855.
(5) (a) Chi, K.-W.; Addicott, C.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc.
2004, 126, 16569. (b) Chi, K.-W.; Addicott, C.; Moon, M.-E.; Lee, H. J.; Yoon,
S. C.; Stang, P. J. J. Org. Chem. 2006, 71, 6662. (c) Ghosh, S.; Turner, D. R.;
Batten, S. R.; Mukherjee, P. S. Dalton Trans. 2007, 1869. (d) Zhao, L.; Northrop,
B. H.; Zheng, Y.-R.; Yang, H.-B.; Lee, H. J.; Lee, Y. M.; Park, J. Y.; Chi,
K.-W.; Stang, P. J. J. Org. Chem. 2008, 73, 6580.
(6) (a) Kra¨mer, R.; Lehn, J.-M.; Marquis-Rigault, A. Proc. Natl. Acad. Sci.
U.S.A. 1993, 90, 5394. (b) Caulder, D. L.; Raymond, K. N. Angew. Chem., Int.
Ed. Engl. 1997, 36, 1440. (c) Addicott, C.; Das, N.; Stang, P. J. Inorg. Chem.
2004, 43, 5335. (d) Kamada, T.; Aratani, N.; Ikeda, T.; Shibata, N.; Higuchi,
Y.; Wakamiya, A.; Yamaguchi, S.; Kim, K. S.; Yoon, Z. S.; Kim, D.; Osuka,
A. J. Am. Chem. Soc. 2006, 128, 7670. (e) Yang, H.-B.; Ghosh, K.; Northrop,
B. H.; Stang, P. J. Org. Lett. 2007, 9, 1561. (f) Zheng, Y.-R.; Yang, H.-B.;
Northrop, B. H.; Ghosh, K.; Stang, P. J. Inorg. Chem. 2008, 47, 4706. (g) Zheng,
Y.-R.; Yang, H.-B.; Ghosh, K.; Zhao, L.; Stang, P. J. Chem.-Eur. J., accepted.
† University of Utah.
‡ East China Normal University.
(1) (a) Lehn, J.-M.; Rigault, A.; Siegel, J.; Harrowfield, J.; Chevrier, B.;
Moras, D Proc. Natl. Acad. Sci. U.S.A. 1987, 84, 2565. (b) Holliday, B. J.; Mirkin,
C. A. Angew. Chem., Int. Ed. 2001, 40, 2022. (c) Fujita, M.; Umemoto, K.;
Yoshizawa, M.; Fujita, N.; Kusukawa, T.; Biradha, K. Chem. Commun. 2001,
509. (d) Ruben, M.; Rojo, J.; Romero-Salguero, F. J.; Uppadine, L. H.; Lehn,
J.-M. Angew. Chem., Int. Ed. 2004, 43, 3644. (e) Fiedler, D.; Leung, D. H.;
Bergman, R. G.; Raymond, K. N. Acc. Chem. Res. 2005, 38, 351. (f) Fujita, M.;
Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res. 2005, 38, 369. (g) Lukin,
O.; Voegtle, F. Angew. Chem., Int. Ed. 2005, 44, 1456. (h) Severin, K. Chem.
Commun. 2006, 3859. (i) Nitschke, J. R. Acc. Chem. Res. 2007, 40, 103. (j)
Pitt, M. A.; Johnson, D. W. Chem. Soc. ReV. 2007, 36, 1441. (k) Schmittel, M.;
Mahata, K. Angew. Chem., Int. Ed. 2008, 47, 5284.
(2) (a) Yoshizawa, M.; Takeyama, Y.; Kusukawa, T.; Fujita, M. Angew.
Chem., Int. Ed. 2002, 41, 1347. (b) Wu¨rthner, F.; You, C. C.; Saha-Mo¨ller, C. R.
Chem. Soc. ReV. 2004, 33, 133. (c) Murase, T.; Sato, S.; Fujita, M. Angew.
Chem., Int. Ed. 2007, 46, 1083. (d) Balzani, V.; Bergamini, G.; Campagna, S.;
Puntoriero, F. Top. Curr. Chem. 2007, 280, 1. (e) Northrop, B. H.; Yang, H.-B.;
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3554 J. Org. Chem. 2009, 74, 3554–3557
10.1021/jo9002932 CCC: $40.75 2009 American Chemical Society
Published on Web 04/06/2009

FIGURE 1. (a) ORTEP drawing (30% probability ellipsoids) of 4a; (b) 31P{1H} (top) and 1H NMR (bottom) spectra recorded for 4a; (c) calculated
(red, upper) and experimental (blue, bottom) ESI mass spectra recorded for 4a.
SCHEME 1. Graphical Representation of the Self-Selection
of (a) Supramolecular Parallelograms 4a,b and (b) Irregular
Hexagons 6a,b from the Self-Assembly of Unsymmetrical
Ligands 1a,b with 60° and 120° Organoplatinum Acceptors 2
or 3
1
FIGURE 2. (a) 31P{1H} and (b) H NMR spectra recorded for 6a.
followed by KPF6 anion exchange. The resulting self-selection
systems have been characterized using 31P and 1H multinuclear
NMR spectroscopy, ESI mass spectrometry, and in the case of
4a X-ray crystallography (Figure 1a). The experimental results
of each self-assembly indicate only one isomeric speciess
supramolecular parallelogram 4 or irregular hexagon 6sis
selectively generated, rather than a statistical mixture with 5 or
7.
The 31P{1H} NMR spectra (Figure 1b, Figure 2a, and Figures
S4-S5 in Supporting Information) recorded for each mixture
eralized to include many Pt-N coordination-driven self-
assembling systems.6g Herein, we present an investigation of
the use of unsymmetrical bipyridyl ligands to direct the self-
selection of two irregular polygons.
shows two singlet signals of approximately equal intensity with
concomitant 195Pt satellites (δ ) 12.69 ppm and 12.56 ppm for
4a; δ ) 15.18 ppm and 15.35 ppm for 4b; δ ) 13.81 ppm and
13.90 ppm for 6a; δ ) 14.72 ppm and 14.77 ppm for 6b). The
31P NMR spectra clearly indicate that only one single isomeric
structure is formed in each self-assembly and that the Pt metal
centers equally coordinate the two different pyridyl binding sites
of 1, as evidenced by the two different 31P NMR signals of
equal intensity. Similarly, sharp identifiable proton signals
attributable to the formation of highly ordered supramolecular
Rigid unsymmetrical bidentate ligands 1a,b contain two
geometrically different pyridyl binding sites (meta and para)
as shown in Scheme 1. According to the directional bonding
model,3b unsymmetrical 120° donor ligands 1a,b can undergo
a [2 + 2] and [3 + 3] self-assembly with 60° and 120°
organoplatinum acceptors 2 and 3, respectively. The dissym-
metry of 1, however, allows for the possibility of two isomeric
assemblies to be generated for each of the self-assembly as
shown in Scheme 1. The self-assembly of unsymmetrical ligands
1a,b with rigid organoplatinum acceptors 2 or 3 was carried
out by mixing the donors and acceptors in a 1:1 ratio and heating
at 60-65 °C for 6 h in an aqueous acetone solution (v/v 3:2),
1
structures are found in the H NMR spectra of each mixture
(Figure 1b, Figure 2b, and Figures S4-S5). Identification of
irregular hexagons 6a,b as the selected supramolecular isomers
can be further confirmed based on the symmetry of the 31P{1H}
NMR spectra because four different phosphorus peaks would
be expected given the varying connectivity between 1 and 3 in
J. Org. Chem. Vol. 74, No. 9, 2009 3555

FIGURE 3. Structures and relative energies of supramolecules 4-7 as obtained from MMFF force field modeling. The lowest energy supramolecule
is taken as 0.0 kcal/mol for each pair of related supramolecular isomers.
SCHEME 2. Graphical Representation of Geometrical
Match and Mismatch during Self-Assembly of
Organoplatinum Acceptor 2 with Unsymmetrical Ligand 1a
in Head-to-Tail (Top, 4a) and Head-to-Head (Bottom, 5a)
Orientations
In the systems described above, the geometric information
encoded within unsymmetrical ligands 1a,b and organoplatinum
acceptors 2 and 3 represent the major factor directing the
selective self-assembly. For example, upon forming directional
Pt-N coordination bonding interactions between subunits 1 and
2, [2 + 2] self-assembly of 4 in a head-to-tail orientation
represents a geometric match, according to the directionality
and rigidity of the subunits. However, the same molecular
subunits have to undergo energetically unfavorable structural
distortions in order to self-assemble in the head-to-head orienta-
tion of structure 5 because of the geometrical mismatch between
the subunits (Scheme 2). Structural distortions result in an
enthalpy increase for the formation of 5 as compared with 4.
Thus, a thermodynamic bias between 4 and 5 is established that
relies primarily on the geometric features of the molecular
subunits. This same analysis holds for supramolecules 6 and 7
as well. The thermodynamic bias between these isomers is able
to induce self-selection during self-assembly under thermody-
namic control.7
A computational study has also been carried out to investigate
this postulation via direct determination of the thermodynamic
energy difference between these isomers. Each individual isomer
of 4-7 was built8 within the input mode of the program Maestro
v9.51.09 and subjected to a 1 ns molecular dynamics simulation
(MMFF force field, gas phase, 300 K) to equilibrate the
structures. The output of each simulation was then minimized
to full convergence. The MMFF computational results are given
in Figure 3 and show that in each case the relative energies of
the unselected species 5 and 7 are significantly greater than those
isomer 7. For self-assembly between 1 and 2, however, NMR
spectral results are insufficient to distinguish between isomers
4 and 5.
An X-ray crystallographic study has been carried out for
further identification of 4a. Diffraction-quality single crystals
of 4a were grown by slow vapor diffusion of pentane into a
dichloromethane solution of the irregular polygon. Crystal-
lographic data and refinement parameters are listed in Table
S1 (see Supporting Information). The unambiguously established
structure of isomer 4a (Figure 1a) shows that the unsymmetrical
donor ligands coordinate with the 60° acceptors in their head-
to-tail orientation, as opposed to the head-to-head orientation
in isomer 5a (Scheme 2).
of selected isomers 4 and 6 (E5a-4a ) 2.8 kcal/mol; E5b-4b
)
17.8 kcal/mol; E7a-6a ) 27.6 kcal/mol; E7b-6b ) 5.3 kcal/mol).
While these calculations are performed at the MMFF molecular
force field level, on account of the size of 4-7, the computa-
tional results are strongly supportive in favor of the selective
self-assembly of 4 rather than 5 and 6 rather than 7.
Formation of [2 + 2] supramolecular parallelograms 4 and
[3 + 3] hexagons 6 is further supported by ESI mass
spectrometry as shown in Figure 1c and Figure S6 in the
Supporting Information. The ESI mass peaks corresponding to
the consecutive loss of nitrate anions from the supramolecular
parallelograms 4a: m/z ) 1280.6 [M - 2NO3]2+ and m/z )
833.2 [M - 3NO3]3+, and 4b: m/z ) 1380.6 [M - 2NO3]2+and
m/z ) 899.8 [M - 3NO3]3+ are observed, as are those
corresponding to the formation of the irregular hexagons: 6a at
(7) (a) Hiraoka, S.; Fujita, M. J. Am. Chem. Soc. 1999, 121, 10239. (b)
Hiraoka, S.; Kubota, Y.; Fujita, M. Chem. Commun. 2000, 1509. (c) Lehn, J.-
M. Science 2002, 295, 2400. (d) Lehn, J.-M. Proc. Natl. Acad. Sci. U.S.A. 2002,
99, 4763. (e) Yamamoto, T.; Arif, A. M.; Stang, P. J. J. Am. Chem. Soc. 2003,
125, 12309. (f) Zheng, Y.-R.; Stang, P. J. J. Am. Chem. Soc. 2009, 131, 3487.
(8) The MMFF force field employed lacks quantitative parameters for square
planar platinum structures. Therefore, a generic “dummy atom” was used in
place of platinum and all bond lengths and angles involving the platinum dummy
were constrained to fit X-ray data of analogous platinum-based supramolecular
polyhedra.
m/z ) 1598.3 [M - 2NO3]2+ and m/z ) 948.1 [M - 4NO3]4+
,
and 6b at m/z ) 2108.1 [M - 2NO3]2+ and m/z ) 1023.1 [M
- 4NO3]4+. All of these peaks are isotopically resolved and
agree with their theoretical distribution.
3556 J. Org. Chem. Vol. 74, No. 9, 2009

833.2. For 4a·4PF6 Anal. Calcd C100H152F24N4P12Pt4: C, 39.79; H,
5.08; N, 1.86. Found: C, 40.14; H, 5.07; N, 1.94.
In conclusion, the self-selection of irregular supramolecular
parallelograms and hexagons has been achieved during the self-
assembly of unsymmetrical ligands 1a,b and organoplatinum
acceptors 2 and 3. Self-selection is strongly supported by
Self-Assembly of Supramolecular Parallelogram 4b. Reaction
scale: Unsymmetrical ligand 1b (1.92 mg, 6.85 µmol) and 60°
organoplatinum acceptor 2 (7.97 mg, 6.85 µmol). 1H NMR
(Acetone-d6/D2O 1:1, 300 MHz) δ 8.94 (m, 8H, H2,6-3-Pyr, HR-4-
Pyr), 8.56 (s, 4H, H4,5), 8.22 (d, 2H, J ) 7.1 Hz, H4-3-Pyr), 7.80
(m, 6H, Hꢀ-4-Pyr, H5-3-Pyr), 7.70 (d, 8H, J ) 3.6 Hz, Hphenylene),
7.65 (d, 4H, J ) 7.1 Hz, H2,7), 7.55 (m, 8H, H1,8,9,10), 1.31 (m,
48H, PCH2CH3), 1.06 (m, 72H, PCH2CH3). 31P{1H} NMR (Acetone-
1
characterization from 31P and H multinuclear NMR spectros-
copy, ESI mass spectrometry and, in one case, X-ray crystal-
lography. The selective self-assembly of these supramolecular
polygons is directed by a thermodynamic preference for closed,
discrete structures that minimize distortion of the Pt-N
coordination bonds in the supramolecular systems. The ther-
modynamic preference between these isomers has been further
investigated using molecular modeling based on the MMFF
force field, and the computational results support the observed
experimental selectivity between each set of polygons: irregular
polygons 4 and 6 are thermodynamically favored over 5 and 7.
1
d6 /D2O: 1/1, 121.4 MHz) δ 15.35 (195Pt satellites, JPt-P ) 2690
Hz), 15.18 (195Pt satellites, 1JPt-P ) 2705 Hz). MS (ESI) calcd for
[M - 2NO3]2+ m/z 1380.4, found 1380.6; calcd for [M - 3NO3]3+
m/z 899.6, found 899.8. For 4b · 4PF6 Anal. Calcd
C
116H160F24N4P12Pt4: C, 43.29; H, 5.01; N, 1.74. Found: C, 43.58;
H, 5.02; N, 1.82.
Self-Assembly of Supramolecular Irregular Hexagon 6a.
Reaction scale: Unsymmetrical ligand 1a (1.43 mg, 7.94 µmol) and
120° organoplatinum acceptor 3 (9.26 mg, 7.94 µmol). MS (ESI)
calcd for [M - 2NO3]2+ m/z 1958.1, found 1958.3; calcd for [M
- 4NO3]4+ m/z 948.1, found 948.1. For 6a·6PF6 1H NMR
(Acetone-d6/D2O 8:1, 300 MHz) δ 9.24 (s, 3H, H2-3-Pyr), 9.02
(m, 9H, H6-3-Pyr, HR-4-Pyr), 8.39 (d, 3H, J ) 7.8 Hz, H4-3-Pyr),
7.92 (m, 9H, H5-3-Pyr, Hꢀ-4-Pyr), 7.64 (m, 12H, PhH), 7.50 (d,
12H, J ) 7.2 Hz, PhH), 1.42 (m, 72H, PCH2CH3), 1.10 (m, 108H,
PCH2CH3). 31P{1H} NMR (Acetone-d6 /D2O: 8/1, 121.4 MHz) δ
Experimental Section
Methods and Materials. The rigid and directional organoplati-
num acceptor 29 and 310 were prepared as the reported procedure.
Deuterated solvents were purchased from Cambridge Isotope
Laboratory (Andover, MA). NMR spectra were recorded on a
1
Varian Unity 300 spectrometer. The H NMR chemical shifts are
reported relative to residual solvent signals, and 31P NMR reso-
nances are referenced to an external unlocked sample of 85% H3PO4
(δ 0.0). Mass spectra for 4a, 4b, 6a, and 6b were recorded on a
Micromass Quattro II triple-quadrupole mass spectrometer using
electrospray ionization with a MassLynx operating system.
General Procedure for the Self-Assembly. Unsymmetrical
ligand 1 (1 equiv) and organoplatinum acceptor 2 or 3 (1 equiv)
were added to one glass vial. To the vial containing donors and
acceptors was added 1 mL acetone aqueous solution (v/v 3:2) and
the resulting suspension was stirred at 60-65 °C for 6 h, after which
the clear solution had formed. The clear solution was characterized
1
14.77 (195Pt satellites, JPt-P ) 2668 Hz), 14.72 (195Pt satellites,
1JPt-P ) 2650 Hz). Anal. Calcd C147H228F36N6O3P18Pt6: C, 38.89;
H, 5.06; N, 1.85. Found: C, 39.63; H, 5.09; N, 1.94.
Self-Assembly of Supramolecular Irregular Hexagon 6b.
Reaction scale: Unsymmetrical ligand 1b (1.95 mg, 6.96 µmol)
and 120° organoplatinum acceptor 3 (8.15 mg, 6.98 µmol). MS
(ESI) calcd for [M - 2NO3]2+ m/z 2108.2, found 2108.1; calcd for
[M - 4NO3]4+ m/z 1023.1, found 1023.1. For 6b·6PF6 1H NMR
(Acetone-d6/D2O 8:1, 300 MHz) δ 9.23 (s, 3H, H2-3-Pyr), 9.07 (d,
9H, J ) 5.7 Hz, H6-3-Pyr, HR-4-Pyr), 8.36 (d, 3H, J ) 7.8 Hz,
H4-3-Pyr), 7.93 (d, 9H, J ) 5.7 Hz H5-3-Pyr, Hꢀ-4-Pyr), 7.77 (d,
12H, J ) 6.0 Hz, Hphenylene), 7.69 (m, 12H, PhH), 7.57 (d, 12H, J
) 7.2 Hz, PhH), 1.51 (m, 72H, PCH2CH3), 1.18 (m, 108H,
PCH2CH3). 31P{1H} NMR (Acetone-d6 /D2O: 8/1, 121.4 MHz) δ
-
by NMR spectroscopy and ESI mass spectrometry. The NO3
counterions were exchanged for PF6- using a H2O solution of KPF6.
The product was washed several times with excess H2O and the
resulting solid collected for elemental analysis.
Self-Assembly of Supramolecular Parallelogram 4a. Reaction
scale: Unsymmetrical ligand 1a (1.50 mg, 8.32 µmol) and 60°
organoplatinum acceptor 2 (9.68 mg, 8.32 µmol). 1H NMR
(Acetone-d6/D2O 1:1, 300 MHz) δ 9.28 (s, 2H, H2-3-Pyr), 9.09 (d,
2H, H6-3-Pyr), 8.97 (t, 4H, J ) 6.3 Hz, HR-4-Pyr), 8.64 (s, 4H,
1
14.77 (195Pt satellites, JPt-P ) 2659 Hz), 14.72 (195Pt satellites,
1JPt-P ) 2659 Hz). Anal. Calcd C171H240F36N6O3P18Pt6: C, 42.44;
H, 5.00; N, 1.74. Found: C, 43.12; H, 5.04; N, 1.81.
H4,5), 8.35 (d, 2H, J ) 7.8 Hz, H4-3-Pyr), 7.94 (dd, 4H, J ) 38.1,
Acknowledgment. P.J.S. thanks the NIH (GM-057052) for
financial support. B.H.N. thanks the NIH (GM-080820) for
financial support. We thank Dr. Atta M. Arif for technical
assistance with X-ray crystallographic study.
5.4 Hz, Hꢀ-4-Pyr), 7.86 (t, 2H, J ) 7.8 Hz, H5-3-Pyr), 7.65 (d, 4H,
J ) 7.1 Hz, H2,7), 7.56 (m, 8H, H1,8,9,10), 1.33 (m, 48H, PCH2CH3),
1.08 (m, 72H, PCH2CH3). 31P{1H} NMR (Acetone-d6 /D2O: 1/1,
121.4 MHz) δ 12.69 (195Pt satellites, 1JPt-P ) 2709 Hz), 12.56 (195Pt
1
satellites, JPt-P ) 2700 Hz). MS (ESI) calcd for [M - 2NO3]2+
Supporting Information Available: Synthesis and analytical
data of 1a and 1b, NMR and ESI-MS spectra of self-selection
of 4b, 6a, and 6b, and X-ray crystal data of 4a. This material
is available free of charge via the Internet at http://pubs.acs.org.
m/z 1280.4, found 1280.6; calcd for [M - 3NO3]3+ m/z 832.9, found
(9) Kryschenko, Y. K.; Seidel, S. R.; Arif, A. M.; Stang, P. J. J. Am. Chem.
Soc. 2003, 125, 5193.
(10) Yang, H.-B.; Das, N.; Huang, F.; Hawkridge, A. M.; Muddiman, D. C.;
Stang, P. J. J. Am. Chem. Soc. 2006, 128, 10014.
JO9002932
J. Org. Chem. Vol. 74, No. 9, 2009 3557