Nanoscale tectonics: Self-assembly, characterization, and chemistry of a novel class of organoplatinum square macrocycles

Article abstract of DOI:10.1021/ja972668s

Six nanoscale molecular squares are reported. They are prepared in essentially quantitative yields via spontaneous self-assembly of preprogrammed 90°angular units with diverse bimetallic linear linkers. Characterization was accomplished with multinuclear NMR and, in two cases, via ESI-FTICR mass spectral data. The size of these novel metallomacrocycles range from 3.6 nm (diagonal) and 2.6 nm (side) for the smallest to 4.7 nm (diagonal) and 3.4 nm (side) for the largest as estimated by extensible systematic force field calculations. The molecular squares incorporating alkynyl units as corners are able to complex four Ag⁺ ions via the π-tweezer effect.

Full text of DOI:10.1021/ja972668s

J. Am. Chem. Soc. 1997, 119, 11611-11619
11611
Nanoscale Tectonics: Self-Assembly, Characterization, and
Chemistry of a Novel Class of Organoplatinum Square
Macrocycles
Joseph Manna, Christopher J. Kuehl, Jeffery A. Whiteford, Peter J. Stang,*
David C. Muddiman, Steven A. Hofstadler, and Richard D. Smith
Contribution from the Department of Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112,
and Molecular Sciences Research Center and Chemical Sciences Department, Pacific Northwest
Laboratory, Richland, Washington 99352
ReceiVed August 4, 1997X
Abstract: Six nanoscale molecular squares are reported. They are prepared in essentially quantitative yields via
spontaneous self-assembly of preprogrammed 90° angular units with diverse bimetallic linear linkers. Characterization
was accomplished with multinuclear NMR and, in two cases, via ESI-FTICR mass spectral data. The size of these
novel metallomacrocycles range from 3.6 nm (diagonal) and 2.6 nm (side) for the smallest to 4.7 nm (diagonal) and
3.4 nm (side) for the largest as estimated by extensible systematic force field calculations. The molecular squares
incorporating alkynyl units as corners are able to complex four Ag+ ions via the π-tweezer effect.
Introduction
have used coordination as the motif for the construction of
diverse molecular squares6 and, most recently, the assembly of
molecular hexagons7 and achiral8 as well as chiral9 octahedrons.
However, with few exceptions, all of these assemblies are
generally smaller than 1 nm in size.
The use of transition metals in conjunction with multidentate
ligands and the concomitant dative bonding as a means to drive
and direct the self-assembly of abiotic supramolecular species
represents a different and interesting alternative to the bio-
mimetic weak interaction (hydrogen bonding, π-π-stacking,
van der Waals interactions, etc.) controlled processes.1 This
methodology has been successfully and reasonably extensively
employed in the formation of metal helicates2 and other two-
and three-dimensional metallomacrocycles of diverse shapes and
sizes.3,4 In the last few years we,5 as well as Fujita and Ogura,4
The ultimate goal of much of this research, in common with
most of contemporary abiotic supramolecular chemistry, is the
design of methodologies and development of technology for
the assembly and manufacturing of nanoscale molecular devices
and machinery.10 This of course requires the ability to readily
construct nanoscale supramolecular species from simple, easily
available precursors. Herein, we report the formation and
characterization of nanoscale supramolecular assemblies in the
form of nanoscopic, metallocyclic molecular squares using
coordination as the motif to drive and direct their prepro-
grammed self-assembly. We also present electrospray ionization
Fourier transform ion cyclotron resonance mass spectrometry
(ESI-FTICR) data for the characterization of selected, repre-
sentative members of these novel nanoscale metallomacrocycles
along with their metal complexation with Ag+.
X Abstract published in AdVance ACS Abstracts, November 15, 1997.
(1) For key recent reviews, see: (a) ComprehensiVe Supramolecular
Chemistry; Lehn, J.-M., Atwood, J. L., Davies, J. E. D., MacNicol, D. D.,
Vogtle, F. Eds.; Pergamon Press: Oxford, 1996; Vols. 1-11. (b) Lehn,
J.-M. Supramolecular Chemistry: Concepts and PerspectiVes; VCH
Publishers: Weinheim, 1995. (c) Philip, D.; Stoddart, J. F. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 1154-1196. (d) Lawrence, D. S.; Jiang, T.; Levett,
M. Chem. ReV. 1995, 95, 2229-2260.
(2) For reviews, see: (a) Williams, A. Chem. Eur. J. 1997, 3, 15. (b)
Constable, E. C. Polynuclear Transition Metal Helicates in ComprehensiVe
Supramolecular Chemistry; Lehn, J.-M., Sauvage, J. P., Hosseini, M. W.,
Eds.; Pergamon Press: Oxford, 1996; Vol. 9, Chapter 6, p 213. (c)
Constable, E. C. Tetrahedron 1992, 48, 10013-10059.
Results and Discussion
(3) Baxter, P. N. W. Metal Ion Directed Assembly of Complex Molecular
Architectures and Nanostructures in ComprehensiVe Supramolecular
Chemistry; Lehn, J. -M., Sauvage, J. P., Hosseini, M. W., Eds.; Pergamon
Press: Oxford, 1996; Vol. 9, Chapter 5, p 165.
The rational, efficient design of nanoscale molecular squares
requires readily available “preprogrammed” building units.
Specifically, the assembly of any square requires11 shape-
defining and -directing 90° angular units A in combination with
(4) For reviews, see: (a) Fujita, M. Coord. Chem. ReV. 1996, 148, 249-
264. (b) Fujita, M. J. Synth. Org. Chem. Jpn. 1996, 54, 953-963.
(5) (a) Stang, P. J.; Fan, J.; Olenyuk, B. J. Chem. Soc., Chem. Commun.
1997, 1453-1454. (b) Stang, P. J.; Cao, D, H.; Chen, K. C.; Gray, G. M.;
Muddiman, D. C.; Smith, R. D. J. Am. Chem. Soc. 1997, 119, 5163-5168.
(c) Whiteford, J. A.; Lu, C. V.; Stang, P. J. J. Am. Chem. Soc. 1997, 119,
2524-2533. (d) Stang, P. J.; Persky, N. E. J. Chem. Soc., Chem. Commun.
1997, 77-78. (e) Manna, J.; Whiteford, J. A.; Stang, P. J. J. Am. Chem.
Soc. 1996, 118, 8731-8732. (f) Whiteford, J. A.; Rachlin, E.; Stang, P. J.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2524-2529. (g) Stang, P. J.;
Whiteford, J. A.; Olenyuk, B. J. Am. Chem. Soc. 1996, 118, 8221-8230.
(h) Stang, P. J.; Whiteford, J. A. Res. Chem. Intermed. 1996, 22, 659-
665. (i) Stang, P. J.; Olenyuk, B.; Fan, J.; Arif, A. M. Organometallics
1996, 15, 904-908. (j) Stang, P. J.; Olenyuk, B. Angew. Chem., Int. Ed.
Engl. 1996, 35, 732-736. (k) Stang, P. J.; Chen, K.; Arif, A. M. J. Am.
Chem. Soc. 1995, 117, 8793-8797. (l) Stang, P. J.; Cao, D. H.; Saito, S.;
Arif, A. M. J. Am. Chem. Soc. 1995, 117, 6273-6283. (m) Stang, P. J.;
Chen, K. J. Am. Chem. Soc. 1995, 117, 1667-1668. (n) Stang, P. J.;
Whiteford, J. A. Organometallics 1994, 13, 3776-3777. (o) Stang, P. J.;
Cao, D. H. J. Am. Chem. Soc. 1994, 116, 4981-4982.
(6) See also: (a) Slone, R. V.; Hupp, J. T.; Stern, C. L.; Albrecht-Schmitt,
T. E. Inorg. Chem. 1996, 35, 4096-4097. (b) Slone, R. V.; Yoon, D. I.;
Calhoun, R. M.; Hupp, J. T. J. Am. Chem. Soc. 1995, 117, 11813-11814.
(c) Rauter, H.; Hillgeris, E. C.; Erxleben, A.; Lippert, B. J. Am. Chem.
Soc. 1994, 116, 616-624. (d) Stricklen, P. M.; Volcko, E. J.; Verkade, J.
G. J. Am. Chem. Soc. 1983, 105, 2494-2495. (e) Drain, C. M.; Lehn, J.-
M. J. Chem. Soc., Chem. Commun. 1994, 2313-2313.
(7) Stang, P. J.; Persky, N. E.; Manna, J. J. Am. Chem. Soc. 1997, 119,
4777-4778.
(8) Fujita, M.; Oguro, D.; Miyazawa, M.; Oka, H.; Yamaguchi, K.;
Ogura, K. Nature 1995, 378, 469-471.
(9) Stang, P. J.; Olenyuk, B.; Muddiman, D. C.; Wunschel, D. S.; Smith,
R. D. Organometallics 1997, 16, 3094-3096.
(10) (a) Ball, P. Designing the Molecular World; Princeton University
Press: Princeton, NJ, 1994. (b) Drexler, K. E. Nanosystems: Molecular
Machinery, Manufacturing, and Computation; Wiley: New York, 1992.
(11) Stang, P. J.; Olenyuk, B. Acc. Chem. Res. 1997, 30. In press.
S0002-7863(97)02668-1 CCC: $14.00 © 1997 American Chemical Society

11612 J. Am. Chem. Soc., Vol. 119, No. 48, 1997
Manna et al.
Scheme 1
distinguished from the meta hydrogen signals, 7.18 (6) and 5.96
ppm (7), by the accompanying platinum satellites (3JHPt) for
the former signals of 76 and 60 Hz, respectively. Finally, the
hydrogens of the 4,4′′-ter-phenyl moiety of 8 are characterized
by three unique signals. The interior hydrogen (Hγ) is observed
as a singlet at 7.20 ppm in CD2Cl2. The ortho and meta
hydrogen signals of 8 mirror those observed for 7, with chemical
shifts of 6.55 and 6.29 ppm, respectively. The chemical shifts
of the ancillary PEt3 and PPh3 hydrogens are unexceptional and
are listed in the Experimental Section.
The corner subunits 9 and 10 (Schemes 3 and 4) have been
described previously5c and have been utilized in the construction
of smaller self-assembled cationic molecular squares.5c,k
linear linker units L as illustrated in Scheme 1. Such a design
allows for ready variation of size by (a) different types and sizes
of corner units and (b) differing lengths of linker units L. The
desired linear linkers consist of readily available bimetallic units
as described below and summarized in Scheme 2.
Preparation of Bimetallic Linear Linker Units L. Reaction
of the previously reported12 bis(trans-Pt(PR3)2I)aryl complexes
1-4 with a slight stoichiometric excess (2.1 equiv) of silver
triflate at 0 °C in a methylene chloride solution yielded the trans
bistriflate complexes 5-8 in good yield (Scheme 2), following
the workup described in the Experimental Section. The off-
white 4,4′-biphenyl- and 4,4′′-ter-phenyl-substituted complexes,
with PPh3 ancillary ligands coordinated to platinum, are soluble
and partially soluble, respectively, in CHCl3 and CH2Cl2.
Whereas, the white 1,4-benzene and 4,4′-biphenyl derivatives,
with PEt3 ancillary ligands coordinated to platinum, are soluble
in CHCl3 and CH2Cl2, insoluble in hexanes, and partially soluble
in diethyl ether and acetone. Complexes 5-8 were fully
characterized by FT-IR spectrometry, NMR spectroscopy (1H,
13C{1H}, 19F{1H}, and 31P{1H}), FAB mass spectrometry,
elemental analysis, and physical means. These complexes are
oxygen stable for short periods of time; however, they are
hygroscopic. The all-trans nature of the phosphine ligands at
the metal center is unambiguously proven by our observation
of a singlet, with concomitant platinum satellites, in the 31P
NMR spectra. We do not observe any trans to cis rearrange-
ment for these complexes, even after prolonged time in solution.
A cis geometry would be evident by observation of two sets of
doublets in the 31P{1H} NMR spectra.
Spontaneous Self-Assembly of Nanoscale Molecular
Squares. The preparation of several discrete nanoscale platinum
macrocyclic complexes can be achieved with surprising simplic-
ity and, when the proper conditions are employed, in essentially
quantitative yield in all cases. Due to the highly ionic, charged,
nature of the macrocycles studied, all manipulations were
undertaken in an inert atmosphere drybox.
Addition of a CD2Cl2 solution of the neutral cis-Pt(dppp)-
(CtCPy)2 10 to the solid bistriflate monomer 5 results in the
quantitative formation of the smallest macrocycle of the type
described in this paper, structural motif 11. In a similar manner,
addition of a solution of the corner 10 to pure linear monomers
6, 7, and 8 yielded the nanoscale macrocycles 12, 13, and 14,
respectively, (Scheme 3) of differing topology and dimensions.
Interestingly, we found that the self-assembly of macrocycle
13 was concentration dependent. If a 2.0 × 10-2 M CD2Cl2
solution of corner 10 was added to a 2.0 × 10-2 M solution of
linear linkage 7 in CD2Cl2, a mixture of two products form;
however, neither product is oligomeric in nature. One of the
products is indeed macrocycle 13 (70%); whereas the other
product is as yet a structurally unidentifiable macrocycle (30%).
If the tectonics is performed by the addition of a concentrated
solution of 10 (4.0 × 10-2 M) to solid 7, then only one product
is obtained, macrocycle 13.
It has been demonstrated that in certain systems the formation
of macrocycle versus polymer is, as might be expected,
concentration dependent. For example, Hunter and co-workers13
showed that, at low concentration, monomer is prevalent in
solution, while at higher concentration tetramer formation is
preferred. At even greater concentration, polymer formation
is expected. In contrast, our results for 13 indicate that at higher
concentration the simplest macrocycle expected is formed while
in a dilute solution the product distribution includes a higher
order more complex system. These results indicate that at the
present time we lack a correct model that fully describes the
self-assembly process for our nanoscale macrocycles.
The 31P{1H} NMR chemical shifts for the PEt3 derivatives 5
and 6 differ significantly from those of the PPh3 derivatives 7
and 8. The latter complexes are observed as singlets, coinci-
dentally identical, at 29.3 ppm (1JPPt ) 3219 Hz (7), 3198 Hz
(8)); whereas the PEt3 complexes are observed at 21.58 (5) and
1
24.97 ppm (6) with JPPt of 2882 and 2838 Hz, respectively.
The 31P{1H} NMR chemical shift and single-bond platinum-
phosphorus nuclei spin-spin coupling constant are two of
several critical parameters examined for the characterization of
the novel, self-assembled architectures to be presented. As was
expected, the bistriflate complexes 5-8 exhibit singlet signals
between -76 and -78 ppm in the 19F{1H} NMR, referenced
to external CFCl3.
The proton NMR signals of complexes 5-8 are also
diagnostic of the trans-Pt(PR3)2-substituted nature of the 1,4-
benzene, 4,4′-biphenyl, and 4,4′′-ter-phenyl moieties. The
aromatic hydrogen of complex 5 dissolved in CD2Cl2 is
1
observed as a pseudosinglet at 6.79 ppm in the H NMR with
coupling to platinum across three bonds. The hydrogens of the
biphenyl linkage of complexes 6 and 7 are observed as two
sets of doublets in the NMR. The ortho and meta hydrogens
are magnetically coupled to each other over three bonds with a
spin-spin coupling constant of 8.2-8.4 Hz. The ortho
hydrogens signals, 7.29 (6) and 6.40 ppm (7), are easily
Addition of a acetone/CH2Cl2 solution of iodonium subunit
9 to CH2Cl2 solutions of the trans bistriflate linkers 5 and 7
results in ready assembly of the macrocycles 15 and 16,
(12) Manna, J.; Kuehl, C. J.; Whiteford, J. A.; Stang, P. J. Organo-
metallics 1997, 16, 1897-1905.
(13) Chi, X.; Guerin, A. J.; Haykock, R. A.; Hunter, C. A.; Sarson, L.
D. J. Chem. Soc., Chem. Commun. 1995, 2563-2565.

Nanoscale Tectonics
J. Am. Chem. Soc., Vol. 119, No. 48, 1997 11613
Scheme 2
Scheme 3
NMR spectra. For example, the 31P{1H} NMR of macrocycle
11 exhibits two sharp singlets with a 2:1 intensity ratio at 14.33
ppm (1JPPt ) 2722 Hz) and -5.83 ppm (1JPPt ) 2172 Hz) that
are assignable to the cis-dppp and trans-Pt(PEt3)2 units,
respectively. These values are shifted considerably from those
1
of the pure precursors 5 (21.58 ppm, JPPt ) 2882 Hz) and 10
1
(-3.1 ppm, JPPt ) 2185 Hz). Comparable upfield shifts in
the 31P{1H} NMR spectra of the cis and trans phosphorus
signals are observed for 12-14. For the macrocycles incor-
porating the iodonium modules, as expected, only a singlet is
observed due to the trans phosphorus ancillary ligands. The
31P{1H} NMR spectrum of molecular squares 15 and 16 display
a singlets at 14.2 ppm (1JPPt ) 2720 Hz) and 22.5 ppm (1JPPt
)
3076 Hz). The former values are akin to those for the trans-
Pt(PEt3)2 moiety of macrocycle 11.
1
Examination of the H NMR spectra of these macrocycles
reveals significant spectroscopic differences from their pure
monomeric subunits. While the chemical shifts of the hydrogens
of the ancillary ligands (dppp, PEt3, and PPh3) differ only
slightly from those of the precursor building blocks, the chemical
shifts of the macrocyclic framework 4-(4-bromophenyl)pyridine,
4-alkynylpyridine, 1,4-benzene, 4,4′-biphenyl, and 4,4′′-ter-
phenyl) hydrogens are in most cases significantly shifted. For
macrocycle 11, the R and â hydrogens of the pyridyl fragment
3
are observed at 8.20 and 6.87 ppm, respectively, with a JHH
coupling of 6.0 Hz, in contrast to chemical shifts of 8.20 and
6.62 ppm, respectively, observed for the free corner 10. The
hydrogen of the benzene linker for 11 is observed at 6.96 ppm,
shifted downfield by 0.17 ppm from free 5. Similar chemical
shifts for the R and â hydrogens of the orthogonal directing
corner are observed for system 12. Unfortunately, the hydrogens
of the biphenyl unit of 12 are partially obscured by the dppp
aryl hydrogens. For squares 13 and 14, the R and â hydrogens
of the pyridyl unit are translated 0.67-0.63 and 0.74-0.72 ppm
upfield, respectively, from the free ligand 10. While it might
be reasoned that these large shifts are a consequence of the
anisotropic ring current of the PPh3 group versus that of PEt3,
an equally plausible explanation of the greater pyridyl hydrogen
shifts might be the increased electrophilicity of monomer 7 and
8 versus that of 5 and 6, as a consequence of the greater s-donor
ability of PEt3 over PPh3. The ortho and meta hydrogens of
macrocycles 13 and 14, are translated down field by 0.27 (13)
or 0.23 (14) and 0.34 (13) or 0.28 (14) ppm, respectively,
relative to the free linear linkers.
respectively. These self-assemblies proved to be concentration
independent, yielding only a single desired product in both cases.
The new macrocycles prepared were characterized by FT-IR
spectroscopy, NMR spectroscopy (1H, 13C{1H}, 19F{1H}, and
31P{1H}), elemental analysis, and physical means as described
in the Experimental Section. For macrocycles 13 and 16, these
systems were additionally probed by ESI-FTICR mass spec-
trometry (Vide infra). The formation of these macrocycles was
The 13C{1H} NMR data for these macrocycles are consistent
with our structural formulation. The resonances assigned to
iodonium corner 9 and the cis-Pt(dppp)(4-CtCPyr) 10 parallel
the values observed for other previously reported5c,k molecular
1
most easily monitored by examination of the H and 31P{1H}

11614 J. Am. Chem. Soc., Vol. 119, No. 48, 1997
Manna et al.
Scheme 4
Figure 1. Space-filling model of cationic portion of macrocycle 11,
obtained from ESFF simulations. The view is along the main axis of
the molecule.
sions between each diagonal cis-Pt center is ∼36 Å, while the
distance from cis-Pt to cis-Pt along the sides of the system is
∼26 Å. As expected, the smallest macrocycle of this class is
considerably larger than any of the previously reported systems.
Our estimate of the dimensions of 14 are 5 nm diagonally and
3.4 nm along the edge.
ESI-FTICR-MS of Selected Nanoscale Systems. Struc-
tural elucidation of the macrocyclic architectures presented in
this study was firmly achieved by mass spectrometry. Elec-
trospray ionization (ESI), a gentle ionization technique, coupled
with Fourier transform ion cyclotron resonance (FTICR)
provides charge state and isotopic resolution which allows direct
charge state determination.15
squares incorporating fragments 9 and 10. Furthermore, the
resonances of the linear linkers for these macrocycles are clearly
distinct from those of the monomer bistriflate complexes.
Moreover, the 13C{1H} NMR data of the 4,4′-bis(trans-
Pt(PPh3)2)biphenyl subunit of 13 is nearly identical to the data
reported for the pyridine adduct 4,4′-bis(trans-Pt(PPh3)2-
(pyridine))biphenyl. Finally, the triflate resonance in the
19F{1H} NMR is observed as a singlet between -76 and -79
ppm, respectively, referenced to external CFCl3.
These nanoscale macrocycles were found to vary in color
from light-yellow for the systems with corner 9 to orange-yellow
for the structures incorporating the alkynyl corner 10. The
macrocycles with the iodonium subunits were found to be
soluble in acetone and insoluble in ether, methylene chloride,
and chloroform. The macrocycles with the alkynyl pyridyl units
10 were found to be soluble in methylene chloride and insoluble
in chloroform, hexanes, and diethyl ether.
In order to get a rough idea of the expected dimension of
these new macrocycles, the simplest macrocycle prepared, 11,
was structurally minimized by employing the computer model-
ing program Biosym.14 Admittedly, the computer model is not
as informative as an accurate X-ray crystal structure in regard
to the evaluation of subtle electronic and steric effects.
However, the model should give reasonably accurate dimensions
for the system. Figure 1 displays the minimized van der Waals
space-filling model for macrocycle 11. The calculated dimen-
The upper mass spectrum of Figure 2 shows the isotopically
resolved ESI-FTICR mass spectrum obtained from macrocycle
13 using the selected ion accumulation method16-18 clearly
defining the tetrameric nature of the macrocycle. The isotopi-
cally resolved signal centered at m/z 2012 corresponds to the
[M - 5 OTf]5+ charge state species. The charge state was
determined by examining the isotopic distribution and the
relationship: charge state ) 1/(m/z) spacing. The mass of the
5+ ion was determined to be 10 060.15 Da (i.e., discrete
macrocycle and three triflates minus five of the triflate counter
anions) which is in good agreement with the theoretical mass
of 10 060.03 Da with a mass error of ∼12 ppm.
The lower spectrum of Figure 2 shows the tandem-MS
obtained after a sustained off-resonance irradiation (SORI)
dissociation event was introduced to fragment the 5+ charge
(15) Vorm, O.; Roepstorff, P.; Mann, M. Anal. Chem. 1994, 66, 3281-
3287.
(16) Winger, B. E.; Hofstadler, S. A.; Bruce, J. E.; Udseth, H. R.; Smith,
R. D. J. Am. Mass Spectrom. 1993, 4, 566-577.
(17) Gale, D. C.; Smith, R. D. Rapid Commun. Mass Spectrom. 1993,
7, 1017.
(18) Bruce, J. E.; Vanorden, S. L.; Anderson, G. A.; Hofstadler, S. A.;
Sherman, M. G.; Rockwood, A. L.; Smith, R. D. J. Mass Spectrom. 1995,
30, 124-133.
(14) (a) Dinur, U.; Hagler, A. T. Approaches to Empirical Force Fields.
In ReView of Computational Chemistry; Lipkowitz, K. B., Boyd, D. B.,
Eds.; VCH: New York, 1991; Vol. 2, Chapter 4. (b) Maple, J. R.; Thacher,
T. S.; Dinur, U.; Hagler, A. T. Chem. Des. Automat. News 1990, 5, 5. (c)
Ermer, O. Struct. Bonding 1976, 27, 161.

Nanoscale Tectonics
J. Am. Chem. Soc., Vol. 119, No. 48, 1997 11615
Figure 3. ESI-FTICR mass spectrum of 16.
Figure 2. (A) Isotopically resolved ESI-FTICR mass spectrum of
macrocycle 13. (B) Tandem-MS obtained after a sustained off-resonance
irradiation (SORI) dissociation event.
state. Since each charge corresponds to the loss of a single
triflate ion group, a charge of 6+ is expected to correspond to
the intact macrocycle minus six triflates. The expected mo-
lecular weight of the intact macrocycle minus the six triflates
is 9001.02 (most abundant isotope) and the experimental
molecular weight was determined to be 9000.98 (error ) 4.4
ppm). As shown in Figure 3, the mass measurement is in
excellent agreement with the predicted mass which allows
assignment to the product molecule.
Lewis Acid-Base Coordination Chemistry of Nanoscale
Macrocycles 11 and 13. It has recently been demonstrated
that self-assembled molecular squares employing the bis alkynyl
corner 10 are useful Lewis bases for binding electropositive
metal guests such as silver triflate (Lewis acid).5c For example,
it was proven by a full range of spectroscopic methods, as well
as mass spectrometry, that a mixed, neutral-charged Pt-Pt or
Pt-Pd macrocycles incorporating two corners of type 10 can
bind a single Ag cation at each corner by the “π-tweezer effect”.
This concept has been fully explored by the studies of Lang
and co-workers.19 In a similar manner, we investigated the
possibility of observing analogous π-alkynyl silver coordination
for macrocycles 11 and 13.
Table 1. Structural Assignments from (ESI-FTICR)2 Mass
Spectrum of Macrocycle 13
peak
label
mass
mass
error
m/z
z
assignmenta
(obsd)b (calcd)b (ppm)
a
b
c
d
e
f
g
h
i
1201.245
1607.406
1651.684
1720.280
1876.788
1922.445
2079.838
2146.355
2
2
3
1
4
3
4
2
1
2
1C + 1L
2C + 1L
2402.49 2402.54
3214.81 3214.74
21
22
2
17
52
19
46
23
2C + 2L + 1T 4955.05 4955.04
1L + 1T
1740.28 1740.31
3C + 3L + 2T 7507.15 7507.54
3C + 2L + 1T 5767.34 5767.23
4C + 3L + 2T 8319.35 8319.73
1C + 2L + 2T 4292.71 4292.81
∼2552c
1C + 1L + 1T
2C + 2L + 2T
2551.50
5103.99
i
∼2552c
a C ) corner 10; L ) linker 7; T ) triflate ion. b Based on most
abundant isotope. c Nominal m/z; mixture of two (or more) fragment
ions.
state of the macrocycle.17 The structure was elucidated by mass
transformation of the ion fragments (i.e., converting m/z to the
molecular weight domain) utilizing the above relationship and
is labeled in the figure. For each ion fragment, charge balance
was consistent with the proposed structure. For example, the
ion fragment centered around m/z 1877 was determined to be a
4+ charge state ion which clearly indicated this fragment
contained three corners (10), three linkers (7-2OTf), and two
triflate counteranions. Since each linker contains two trans
platinum centers, the neutral molecule should have six triflates.
However, since this is the 4+ charge state, there should be a
mass deficit corresponding to two triflates, which is indeed the
case. This confirms the proposed charging mechanism in the
electrospray ionization process that the loss of each triflate
contributes to a single charge on the molecule. Thus, for each
charge observed, there is a loss of 149 Da for the charging
mechanism. Table 1 lists the structural assignments, with
observed and calculated masses, from the tandem mass spec-
trum. The fragment ions that were not isotopically resolved
were not assigned. Moreover, it is important to note that on
the basis of our structure assignment we would not expect to
observe any identifiable fragments of the of the type (a) three
linkers and one corner or (b) three corners and one linker. One
might only expect to see these masses if “aggregation” occurred.
Examination of the tandem mass spectrum of 13 revealed no
assignable features that could be accountable to such fragments.
Figure 3 displays the ESI-FTICR mass spectrum of 16. The
peak at m/z ) 1500 is isotopically resolved (m/z spacing of
1/6) allowing direct charge state assignment as the 6+ charge
Addition of slightly more than 4 equiv of silver triflate to
the nanoscale systems 11 and 13 resulted in the quantitative
formation of silver adducts 17 and 18 (Scheme 5). These
complexes were also characterized by spectroscopic, analytical,
and physical means. Several spectroscopic parameters undergo
considerable modulation due to the coordination of the alkynyl
moiety to the silver cation. For example, ν(CtC) for 17 is
observed as a broad singlet at 2086 cm-1 in the FT-IR spectrum
versus 2119 cm-1 observed for macrocycle 13. Furthermore,
significant shifts, relative to 13, are observed in the 31P{1H}
NMR spectrum of 18 for the cis-Pt(dppp) resonance. This signal
is translated upfield to -9.0 ppm (1JPPt ) 2359 Hz), while that
of the trans-Pt(PPh3)2 signal is nearly unchanged at 20.5 ppm
(1JPPt ) 3048 Hz). The decrease in ν(CtC) and large increase
1
in JPPt (cis-Pt(dppp) of 18, versus that of 13, is primarily
accountable to the decrease in electron density of the alkynyl
unit on coordination to silver and, hence, the weakened trans
influencing ability of CtCPy on the dppp phosphorus-platinum
bond. The 13C{1H} NMR data of the silver-bound corner 10
incorporated into square 18 are akin to the values reported for
the mixed, neutral-charged Pt-Pt-Ag macrocycles.5c
(19) (a) Janssen, M. D.; Herres, M.; Zsolnai, L.; Spek, A. L.; Grove, D.
M.; Lang, H.; van Koten, G. Inorg. Chem. 1996, 35, 2476-2483. (b) Lang,
H.; Weinmann, M. Synlett 1996, 1-10. (c) Janssen, M. D. Structural Aspects
and ReactiVity of Self-Assembling Organocopper and Copper Arenethiolate
Aggregates; Thesis Universiteit Utrecht, 1996; p 152. (d) Lang, H.; Blau,
S.; Pritzkow, H.; Zsolnai, L. Organometallics 1995, 14, 1850-1854.

11616 J. Am. Chem. Soc., Vol. 119, No. 48, 1997
Manna et al.
Scheme 5
metal, methylene chloride was distilled from calcium hydride, and
acetone was distilled from potassium permanganate. All NMR solvents
(CD2Cl2, CDCl3, and acetone-d6) were stored over 4 Å molecular sieves
in a drybox prior to use.
Platinum tetrakis(triphenylphosphine), silver trifluoromethane-
sulfonate (AgOTf), and bis[4-(4′-pyridyl)phenyl]iodonium trifluoro-
methanesulfonate were prepared by the standard literature procedures.
4,4′-Diiodobiphenyl was purchased from Aldrich and purified by
recrystallization from chloroform.
Competition Experiment. Insight into the nature of the self-
assembly process and stability of these macrocycles can be
obtained by performing a simple experiment. We were
interested in determining whether there is any preferential
selectivity for formation of one macrcocycle over another.
Specifically, we monitored the reaction between a solid mixture
of 0.5 equiv of each of both linear linkers 6 and 7 with 1.0
equiv of the corner 10, dissolved in CD2Cl2 with dropwise
addition. Statistically, there are six possible macrocycles that
could form. Two of the products should be the pure squares
12 and 13. While the other four possible systems would have
a mixture of linkers 6 and 7 with corner 10. Indeed, the
observed product distribution, as best we can determine, is a
mixture of the six possible squares, as indicated by the complex
All NMR spectra were obtained at room temperature with a Varian
XL-300 or VXR-500 spectrometer employing a deuterium sample as
an internal lock unless noted otherwise. The operating frequencies of
the former spectrometer for the 1H, 13C{1H}, 31P{1H}, and 19F{1H}
NMR spectra were 300.0, 75.4, 121.4, and 282.3 MHz, respectively.
1
For the latter spectrometer, the operating frequencies of the H and
13C{1H} NMR spectra were 499.8 and 125.7 MHz, respectively. The
1H chemical shifts are reported relative to the residual nondeuterated
solvent of CD2Cl2 (5.32 ppm), CDCl3 (7.27 ppm), or acetone-d6 (2.05
ppm). The 13C{1H} chemical shifts are reported relative to CDCl3 (77.0
ppm), CD2Cl2 (53.8 ppm), or acetone-d6 (29.9 ppm). In contrast to
the 1H and 13C{1H} NMR spectra, the 31P{1H} and 19F{1H} NMR
spectra were referenced to sealed external standards of 85% phosphoric
acid and fluorotrichloromethane, respectively.
1
31P{1H} and H NMR data. We would have only expected to
observe pure macrocycles 12 and 13 if the phosphine ligands
(PEt3 versus PPh3) would manifest some enhanced electronic
and/or steric stability to the pure macrocycles over the linker
mixed macrocycles. It is interesting that we observe no
oligomer formation. This suggests that the nature of the
phosphine is not a critical parameter for macrocycle formation.
Elemental analyses were performed by Oneida Research Service,
Whitesboro, NY, or Atlantic Microlab Inc., Norcross, GA. IR spectra
were obtained with a Mattson Polaris FT-IR spectrometer at 2 cm-1
resolution. Melting points were obtained with a Mel-Temp capillary
apparatus and are uncorrected.
Mass spectra of 5-8 were obtained with a Finnigan MAT 95 mass
spectrometer employing a Finnigan MAT ICIS II operating system
under positive ion fast atom bombardment (FAB) conditions at 8 keV.
3-Nitrobenzyl alcohol was used as a matrix in CH2Cl2 or CHCl3 as
solvent, and polypropylene glycol and cesium iodide were used as a
reference for peak matching.
Conclusion
Two types of nanoscale metallocyclic molecular squares are
reported. The first kind employs alkynylpyridine-containing
angular building blocks as shape defining and -directing units.
The second type uses bis(heteroaryliodonium) salts as corner
units. These novel supramolecular species are formed in
quantitative yields as assessed by NMR via spontaneous self-
assembly of these angular corner units with diverse bimetallic
linear linkers via dative bonding and the coordination motif.
ESI-FTICR mass spectral data unambiguously establish the
tetrameric nature of these molecules and, in conjunction with
multinuclear NMR and physical data, their exact structure. Force
field calculations and modeling establish the size of these species
as ranging from approximately 3.6 to 4.7 nm (diagonally) and
2.6 to 3.4 nm (side) and, hence, the structures as true nanoscale
supramolecular species.
1,4-Bis(trans-Pt(PEt3)2(OSO2CF3))benzene (5). To a stirred solu-
tion of 4,4′-bis(trans-Pt(PEt3)2I)benzene (0.211 g, 0.177 mmol) in
CH2Cl2 (10 mL) at 0 °C was added, AgOTf (0.049 g, 0.19 mmol) in
the dark and under a nitrogen atmosphere; a light-yellow suspension
immediately formed. After ∼2 h of stirring, the room-temperature
suspension was cannula filtered to remove the AgI, and to the filtrate
was added an equal volume of dry diethyl ether. The resulting solution
was subsequently placed in the freezer for 1-2 days. The white,
crystalline solid that formed was then filtered under nitrogen and dried
in Vacuo with slight heating (40 °C): yield 0.195 g (89%); mp 247-
250 °C (dec.); IR (thin film, CD2Cl2, cm-1) 2910, 2878 (C-H), 1436,
1418, 1383, 1094 (OTf); 1H NMR (CD2Cl2) δ 6.79 (s, 4H, 3JHPt ) 70
Hz), 1.63 (m, 24H, PCH2CH3), 1.12 (m, 36H, PCH2CH3); 13C{1H}
Experimental Section
General Methods. All experiments were performed under an inert
atmosphere of nitrogen utilizing standard Schlenk and glovebox
techniques. Solvents used in the reactions were reagent or HPLC grade
and purified in the following manner: toluene was distilled from sodium
1
NMR δ 136.1 (s, Co-Pt), 120.2 (q, JCF ) 319 Hz, OTf), 116.1 (s,

Nanoscale Tectonics
J. Am. Chem. Soc., Vol. 119, No. 48, 1997 11617
Ci-Pt), 14.0 (m, PCH2CH3), 8.0 (m, PCH2CH3); 31P{1H} NMR
(CD2Cl2) δ 21.6 (s, 1JPPt ) 2884 Hz); 19F{1H} NMR (CD2Cl2) δ -77.7
(s). Anal. Calcd for C32H64F6O6P4Pt2S2: C, 31.07; H, 5.21; S, 5.18.
Found: C, 31.16; H, 5.18; S, 5.10.
(diphenylphosphino)propane (0.0131 g, 0.0162 mmol) was added
dropwise to solid 4,4′-bis(trans-Pt(PEt3)2(OSO2CF3))biphenyl (0.0200
g, 0.0162 mmol) with stirring in the drybox. The self-assembly was
1
monitored by H and 31P{1H} NMR spectroscopy and determined to
be complete, and the yield of the macrocycle was quantitative, after 1
h. The light-orange solution was then dried in Vacuo yielding an
orange-colored solid: yield 0.0311 g (94%); mp 302-304 °C (dec.);
IR (thin film, CD2Cl2, cm-1) 3340, 3123 (C-H), 2116 (CtC), 1603,
1487, 1437 (Ar), 1271, 1158, 1104, 1032 (OTf); 1H NMR (300 MHz,
CD2Cl2) δ 8.20 (d, 3JHH ) 5.7 Hz, 16H, HR-Py), 7.68, 7.43 (m, 80H,
4,4′-Bis(trans-Pt(PEt3)2(OSO2CF3))biphenyl (6). To a stirred
solution of 4,4′-bis(trans-Pt(PEt3)2I)biphenyl (0.166 g, 0.09 mmol) in
CH2Cl2 (10 mL) at 0 °C was added AgOTf (0.049 g, 0.19 mmol) in
the dark and under a nitrogen atmosphere; a light-yellow suspension
immediately formed. After ∼2 h of stirring, the room-temperature
suspension was cannula filtered to remove the AgI, and to the filtrate
was added an equal volume of dry diethyl ether. The resulting solution
was subsequently placed in the freezer for 1-2 days. The white,
crystalline solid that formed was then filtered under nitrogen and dried
in Vacuo with slight heating (40 °C): yield 0.137 g (80%); mp 247-
250 °C (dec.); IR (thin film, CD2Cl2, cm-1) 2960, 2964 (C-H), 1309,
1232, 1170, 1037 (OTf); 1H NMR (CD2Cl2) δ 7.29 (d, 4H, 3JHH ) 8.4
Hz, 3JHPt ) 76 Hz, Ho-Pt), 7.18 (d, 4H, 3JHH ) 8.4 Hz, Hm-Pt), 1.65
(m, 24H, PCH2CH3), 1.13 (m, 36H, PCH2CH3); 13C{1H} NMR δ 136.6
(br s, Co-Pt), 135.4 (s, Cp-Pt), 125.8 (s, 3JCPt ) 80 Hz, Cm-Pt), 122.7
3
HP), 6.96 (s, 16H, Ho-Pt), 6.88 (d, 16H, JHH ) 6.3 Hz, Hâ-Py),
2.65 (br s, 16H, CH2CH2P-dppp), 2.08 (br s, 8H, CH2CH2P-dppp), 1.26
(m, 96H, PCH2CH3), 1.08 (m, 144H, PCH2CH3); 13C{1H} NMR (125.7
MHz, CD2Cl2) δ 150.8 (s, CR-Py), 138.9 (s, Cγ-Py), 137.1 (s, Co-
Pt), 133.9 (br s, Co-PPh2), 131.5 (s, Cp-PPh2), 130.7 (m, Ci-PPh2),
129.2 (s, Câ-Py), 129.1 (s, Cm-PPh2), 125.5 (br s, CtCR-Pt), 121.6
(q, 1JCF ) 314 Hz, OTf), (Pt-Ci not observed), 107.4 (m, CtCâ-Pt),
25.5 (m, CH2CH2P-dppp), 20.0 (br s, CH2CH2P-dppp), 12.9 (t, JCP
)
20 Hz, PCH2CH3), 7.9 (s, PCH2CH3); 31P{1H} NMR (CD2Cl2) δ 14.3
1
1
2
1
(s, 16P, JPPt ) 2722 Hz, PEt3), -5.8 (s, 8P, JPPt ) 2171 Hz, PPh2);
19F{1H} NMR (CD2Cl2)
-77.9 (s). Anal. Calcd for
(t, JCP ) 10 Hz, Ci-Pt), 120.2 (q, JCF ) 319 Hz, OTf), 14.1 (m,
PCH2CH3), 8.0 (m, PCH2CH3); 31P{1H} NMR (CD2Cl2) δ 25.0 (s, 1JPPt
) 2841 Hz); 19F{1H} NMR (CD2Cl2) δ -75.8 (s). Anal. Calcd for
C38H68F6O6P4Pt2S2: C, 34.76; H, 5.22; S, 4.88. Found: C, 34.58; H,
5.18; S, 4.82.
δ
C292H392F24N8O24P24Pt12S8: C, 42.81; H, 4.82; N, 1.37; S, 3.13.
Found: C, 42.68; H, 4.91; N, 1.34; S, 3.10.
Cyclotetrakis[[cis-Pt(dppp)(4-ethynylpyridine)2][4,4′-bis(trans-
Pt(PEt3)2(OTf))biphenyl]] (12). A room temperature methylene
chloride solution (0.7 mL) of (bis(4-ethynylpyridyl)platinum)-1,3-bis-
(diphenylphosphino)propane (0.0131 g, 0.0162 mmol) was added
dropwise to solid 4,4′-bis(trans-Pt(PEt3)2(OSO2CF3))biphenyl (0.0212
g, 0.0162 mmol) with stirring in the drybox. The self-assembly was
4,4′-Bis(trans-Pt(PPh3)2(OSO2CF3))biphenyl (7). To a stirred
solution of 4,4′-bis(trans-Pt(PPh3)2I)biphenyl (0.166 g, 0.09 mmol) in
CH2Cl2 (13 mL) at -5 °C was added AgOTf (0.049 g, 0.19 mmol) in
the dark and under a nitrogen atmosphere; a light-yellow suspension
immediately formed. After ∼6 h of stirring, the room-temperature
suspension was cannula filtered to remove the AgI, and the filtrate
was obtained as a solid by evaporation of the colorless solution
employing a flow of nitrogen. The white solid was then dried in Vacuo
with slight heating (40 °C). The crystalline product was obtained by
slow evaporation of a concentrated chloroform solution at room
temperature: yield 0.137 g (80%); mp 228-232 °C (dec.); IR (thin
film, CD2Cl2, cm-1) 3061 (C-H), 1434, 1470 (Ar), 1282, 1263, 1181,
1077 (OTf); 1H NMR (CD2Cl2) δ 7.51 (m, 24H, Ho-P), 7.40 (t, 12H,
3JHH ) 7.2 Hz, Hp-P), 7.30 (m, 24H, Hm-P), 6.40 (d, 4H, 3JHH ) 8.2
1
monitored by H and 31P{1H} NMR spectroscopy and determined to
be complete, and the yield of the macrocycle was quantitative, after 1
h. The light-orange solution was then dried in Vacuo yielding a light-
yellow solid: yield 0.0333 g (97%); mp 255-260 °C (dec.); IR (thin
film, CD2Cl2, cm-1) 3055, 2967 (C-H), 2118 (CtC), 1603, 1486, 1436
1
(Ar), 1268, 1151, 1102, 1031 (OTf); H NMR (300 MHz, CD2Cl2) δ
8.23 (d, 3JHH ) 6.4 Hz, 16H, HR-Py), 7.69, 7.43, 7.34 (m, 112H, HP,
3
Ho-Pt, Hm-Pt), 6.90 (d, 16H, JHH ) 6.4 Hz, Hâ-Py), 2.66 (br s,
16H, CH2P-dppp), 2.11 (br s, 8H, CH2CH2P-dppp), 1.28 (m, 96H, PCH2-
CH3), 1.07 (m, 144H, PCH2CH3); 13C{1H} NMR (125.7 MHz; CD2-
Cl2) δ 150.8 (s, CR-Py), 139.04 (s, Cγ-Py), 136.7 (s, Co-Pt), 136.1
(s, Cp-Pt), 133.9 (br s, Co-PPh2), 131.5 (s, Cp-PPh2), 131.0 (m, Ci-
PPh2), 129.3 (s, Câ-Py), 129.10 (s, Cm-PPh2), 126.3 (s, Cm-Pt), 121.6
3
3
Hz, JHPt ) 60 Hz, Ho-Pt), 5.96 (d, 4H, JHH ) 8.2 Hz, Hm-Pt);
13C{1H} NMR δ 135.6 (br s, Co-Pt), 134.9 (t, 2JCP ) 6.3 Hz, Co-P),
1
130.6 (s, Cp-P), 128.9 (t, JCP ) 28.1 Hz, Ci-P), 128.8 (s, Cp-Pt),
128.2 (t, 3JCP ) 5.9 Hz, Cm-P), 125.9 (s, Cm-Pt), 122.4 (t, 2JCP ) 8.1
Hz, Ci-Pt), 118.9 (q, 1JCF ) 319 Hz, OTf); 31P{1H} NMR (CDCl3) δ
1
(q, JCF ) 322 Hz, OTf), (CtCR-Pt and Pt-Ci not observed), 107.4
29.3 (s, JPPt ) 3219 Hz); 19F{1H} NMR (CDCl3) δ -77.9 (s); FAB-
1
(m, CtCâ-Pt), 25.5 (m, CH2CH2P-dppp), 20.0 (br s, CH2CH2P-dppp),
MS m/z (rel intensity) 1740 (M - OTf+, 100), 1478 (M - OTf -
PPh3+, 68).
12.8 (t, JCP ) 20 Hz, PCH2CH3), 7.9 (s, PCH2CH3); 31P{1H} NMR
1
1
(CD2Cl2) δ 16.45 (s, 16P, JPPt ) 2699 Hz, PEt3), -4.47 (s, 8P, JPPt
) 2185 Hz, PPh2); 19F{1H} NMR (CD2Cl2) δ -76.5 (s). Anal. Calcd
for C316H408F24N8O24P24Pt12S8: C, 44.66; H, 4.84; N, 1.32; S, 3.02.
Found: C, 43.61; H, 4.79; N, 1.33; S, 3.01.
4,4′′-Bis(trans-Pt(PPh3)2(OSO2CF3))-p-terphenyl (8). To a stirred
suspension of 4,4′-bis(trans-Pt(PPh3)2I)-p-terphenyl (0.251 g, 0.13
mmol) in cooled CH2Cl2 (5 °C, 18 mL) was added AgOTf (0.71 g,
0.27 mmol) in the dark and under a nitrogen atmosphere. Immediately
after addition of AgOTf, the ice bath was removed, and the reaction
was allowed to warm to room temperature. After ∼2.5 h of stirring,
light-yellow suspension was cannula filtered to remove the AgI, and
the filtrate was obtained as a solid by evaporation of the colorless
solution employing a flow of nitrogen. The solid was dried in Vacuo
at ∼40 °C for 4 h (Yield 0.202 g, 79%). The white solid was found
to be only partially soluble in chloroform or methylene chloride.
Microcrystalline product could be obtained, with considerable difficulty,
by first dissolving the solid into methylene chloride (∼20 mL) followed
by addition of dry toluene (∼8 mL). Nitrogen gas was subsequently
passed over the solution at room temperature; after slow evaporation
of the liquid phase to half volume, pure microcrystals were obtained:
Cyclotetrakis[[cis-Pt(dppp)(4-ethynylpyridine)2][4,4′-bis(trans-
Pt(PPh3)2(OTf))biphenyl]] (13). A room temperature methylene
chloride solution (0.7 mL) of (bis(4-ethynylpyridyl)platinum)-1,3-bis-
(diphenylphosphino)propane (0.0180 g, 0.0220 mmol) was added
dropwise to solid 4,4′-bis(trans-Pt(PPh3)2(OSO2CF3))biphenyl (0.0411
g, 0.0218 mmol) with stirring in the drybox. The self-assembly was
1
monitored by H and 31P{1H} NMR spectroscopy and determined to
be complete, and the yield of the macrocycle was quantitative, after 1
h. The light-orange solution was then dried in Vacuo yielding a light-
yellow solid: yield 0.035 g (58%); mp 215-220 °C (dec.); IR (thin
film, CD2Cl2, cm-1) 3076, 3054 (C-H), 2119 (CtC), 1605, 1587,
1482, 1435 (Ar), 1265, 1150, 1100, 1030 (OTf); 1H NMR (300 MHz,
3
CD2Cl2) δ 7.65 (m, 32H, HP), 7.53 (d, JHH ) 6.5 Hz, 16H, HR-Py),
yield 0.129 g (50%); mp 230-232 °C (dec.); IR (mull, fluorolube, cm-1
)
7.39, 7.28, 7.18 (m, 288H, HP), 6.67 (d, 16H, 3JHH ) 8.1 Hz, Ho-Pt),
3051 (C-H); 1H NMR (CD2Cl2) δ 7.50 (m, 24H, Ho-P), 7.43 (t, 12H,
3
3
6.30 (d, 16H, JHH ) 8.1 Hz, Hm-Pt), 5.87 (d, 16H, JHH ) 6.4 Hz,
Hâ-Py), 2.53 (br s, 16H, PCH2CH3), 2.04 (br s, 8H, PCH2CH3);
13C{1H} NMR (125.7 MHz, CD2Cl2) δ 150.5 (s, CR-Py), 137.9 (s,
3JHH ) 7.3 Hz, Hp-P), 7.33 (m, 24H, Hm-P), 7.20 (s, 4H, Hγ), 6.55
3
3
(d, 4H, JHH ) 8.4 Hz, Ho-Pt), 6.29 (d, 4H, JHH ) 8.4 Hz, Hm-Pt);
31P{1H} NMR (CDCl3) δ 29.3 (s, JPPt ) 3198 Hz); 19F{1H} NMR
1
2
Co-Pt), 137.4 (br s, Cγ-Py), 136.5 (s, Cp-Pt), 134.5 (t, JCP ) 5.8
(CDCl3) δ -78.0 (s); FAB-MS m/z (ion, rel intensity) 1817.6 (M -
Hz, Co-PPh3), 133.9 (br s, Co-PPh2), 131.7 (s, Cp-PPh2), 131.4 (s,
OTf+, 100), 1555.3 (M - OTf - PPh3+, 30).
Cp-PPh3), 131.0 (m, Ci-PPh2), 129.1 (t, 3JCP ) 5.2 Hz, Cm-PPh3 and
1
Cyclotetrakis[[cis-Pt(dppp)(4-ethynylpyridine)2][1,4-bis(trans-
Pt(PEt3)2(OTf))benzene]] (11). A room temperature methylene
chloride solution (0.7 mL) of bis(4-ethynylpyridyl)platinum)-1,3-bis-
PPh2), 128.0 (t, JCP ) 25.4 Hz, Ci-PPh3), 127.8 (s, Câ-Py), ∼128
1
(obscured, Ci-Pt), 126.4 (s, Cm-Pt), 121.8 (q, JCF ) 321 Hz, OTf),
122.0 (m, CtCR-Pt), 107.1 (m, CtCâ-Pt), 26.1 (m, CH2CH2P-dppp),

11618 J. Am. Chem. Soc., Vol. 119, No. 48, 1997
Manna et al.
20.3 (br s, CH2CH2P-dppp); 31P{1H} NMR (CD2Cl2) δ 21.4 (s, 16P,
) 6.0 Hz, Co-P), 131.8 (s, Cp-P), 131.6 (s, Câ-PhI), 129.6 (t, 3JCP
)
1
1JPPt ) 3060 Hz, PPh3), -5.5 (s, 8P, JPPt ) 2198 Hz, PPh2); 19F{1H}
5.2 Hz, Cm-P), 128.6 (t, 1JCP ) 28.2 Hz, Ci-P), (Ci-Pt not observed),
1
NMR (CDCl3) δ -78 (s). Anal. Calcd for C508H408F24N8O24P24-
Pt12S8: C, 56.47; H, 3.81; N, 1.04. Found: C, 55.32; H, 3.89; N, 1.04.
126.3 (s, Cm-Pt), 124.9 (s, Câ-Py), 122.4 (q, JCF ) 314 Hz, OTf),
116.7 (s, Ci-PhI), 12.9 (s, PCH2CH3), 7.8 (s, PCH2CH3); 31P{1H} NMR
1
(acetone-d6) δ 22.5 (s, JPPt ) 3076 Hz); 19F{1H} NMR (CDCl3) δ
Cyclotetrakis[[cis-Pt(dppp)(4-ethynylpyridine)2][4,4′′-bis(trans-
Pt(PPh3)2(OTf))-p-terphenyl]] (14). A 0.6 mL methylene chloride-
d2 solution of light-yellow (bis(4-ethynylpyridyl)platinum)-1,3-bis-
(diphenylphosphino)propane (0.0062 g, 0.0076 mmol) was added
dropwise to solid, colorless 4,4′′-bis(trans-Pt(PPh3)2(OSO2CF3))-p-
terphenyl (0.0150 g, 0.0076 mmol) with stirring in the drybox. The
-75.2 (s); MALDI-MS m/z (rel intensity) 1500 (M - 6OTf+); ESI-
FTICR m/z (acetone) 1500.163 amu [M - 6OTf-] (mass ) 9000.98
obsd; mass ) 9001.02 calcd).
Cyclotetrakis[[cis-Pt(dppp)(4-ethynylpyridine)2][1,4-bis(trans-
Pt(PEt3)2(OTf))benzene]]‚4AgOTf (17). A methylene chloride-d2
solution (0.8 mL) of macrocycle 11 (0.0331 g, 0.0041 mmol) at room
temperature was added dropwise to a vial containing solid AgOTf
(0.0042 g, 0.0162 mmol) in the drybox. The resulting orange-yellow
solution was filtered through a short plug of glass wool after for 15
min of stirring. The reaction was found to be quantitative and yield
the single desired silver adduct, as determined by NMR spectroscopy.
For 17: yield 0.0347 g (93%); mp 214-220 °C (dec.); IR (thin film,
CD2Cl2, cm-1) 3055, 2925 (C-H), 2086 (CtC), 1606, 1587, 1481,
1
self-assembly was monitored by H and 31P{1H} NMR spectroscopy
and determined to be complete, and the yield of the macrocycle was
quantitative, after 1.25 h. The light-orange product solution was then
dried in Vacuo yielding a yellow solid: yield 0.0182 g (86%); mp 230-
234 °C (dec.); IR (thin film, CD2Cl2, cm-1) 3057 (C-H), 2117 (CtC),
1605, 1483, 1434 (Ar), 1266, 1150, 1100, 1030 (OTf); 1H NMR (300
3
MHz, CD2Cl2) δ 7.65 (m, 32H, HP), 7.57 (d, JHH ) 6.2 Hz, 16H,
HR-Py), 7.40, 7.32, 7.25 (m, 288H, HP), ∼7.23 (obscured Hγ), 6.78
1
3
3
1436 (Ar), 1266, 1205, 1100, 1030 (OTf); H NMR (500 MHz, CD2-
(d, 16H, JHH ) 8.2 Hz, Ho-Pt), 6.57 (d, 16H, JHH ) 8.2 Hz, Hm-
Pt), 5.90 (d, 16H, 3JHH ) 6.2 Hz, Hâ-Py), 2.52 (br s, 16H, CH2CH2P-
dppp), 2.05 (br s, 8H, CH2CH2P-dppp); 13C{1H} NMR (125.7 MHz,
CD2Cl2) δ 150.5 (s, CR-Py), 140.1 (s, p-C6H4-Ci), 138.2 (s, Co-Pt),
3
Cl2) δ 8.23 (d, JHH ) 3.9 Hz, 16H, HR-Py), 7.69 (m, 32H, PPh2),
3
7.44 (m, 48H, PPh2), 6.97 (s, 16H, Ho-Pt), 6.94 (d, 16H, JHH ) 3.3
Hz, Hâ-Py), 2.73 (br s, 16H, CH2CH2P-dppp), 2.13 (br s, 8H, CH2-
CH2P-dppp), 1.25 (m, 96H, PCH2CH3), 1.04 (m, 144H, PCH2CH3);
13C{1H} NMR (125.7 MHz, CD2Cl2) δ 150.9 (s, CR-Py), 137.0 (s,
Co-Pt), 135.5 (s, Cγ-Py), 134.0 (br s, Co-PPh2), 131.9 (s, Cp-PPh2),
130.1 (s, Câ-Py), 129.4 (s, Cm-PPh2), 129.0 (m, Ci-PPh2), 125.4 (br
2
137.4 (br s, Cγ-Py), 135.5 (s, Cp-Pt), 134.5 (t, JCP ) 5.5 Hz, Co-
PPh3), 134.0 (br s, Co-PPh2), 131.7 (s, Cp-PPh2), 131.5 (s, Cp-PPh3),
3
130.8 (m, Ci-PPh2), 129.3 (t, JCP ) 5.2 Hz, Cm-PPh3 and PPh2),
127.9 (t, 1JCP ) 28.2 Hz, Ci-PPh3), 127.9 (s, Câ-Py), ∼128 (obscured,
Ci-Pt), 127.0 (s, p-C6H4-Co), 126.5 (s, Cm-Pt), 121.8 (q, 1JCF ) 321
Hz, OTf), 122.0 (m, CtCR-Pt), 107.1 (m, CtCâ-Pt), 26.2 (m,
CH2CH2P-dppp), 20.4 (br s, CH2CH2P-dppp); 31P{1H} NMR (CD2Cl2)
1
s, CtCR-Pt), 121.3 (q, JCF ) 322 Hz, OTf), (Pt-Ci not observed),
109.0 (m, CtCâ-Pt), 24.9 (m, CH2CH2P-dppp), 19.8 (br s, CH2CH2P-
dppp), 12.9 (t, JCP) 20 Hz, PCH2CH3), 7.9 (s, PCH2CH3); 31P{1H}
1
1
1
NMR (CD2Cl2) δ 13.3 (s, 16P, JPPt ) 2723 Hz, PEt3), -9.2 (s, 8P,
δ 21.3 (s, 16P, JPPt ) 3049 Hz, PPh3), -5.7 (s, 8P, JPPt ) 2197 Hz,
1JPPt ) 2338 Hz, PPh2); 19F{1H} NMR (CDCl3) δ -75.4 (s). Anal.
Calcd for C220H320F36I4N8O36P16Pt8S12: C, 38.55; H, 4.28; N, 1.21; S,
4.17. Found: C, 38.65; H, 4.31; N, 1.19; S, 4.10.
PPh2); 19F{1H} NMR (CD2Cl2) δ -78 (s). Anal. Calcd for
532H424F24N8O24P24Pt12S8: C, 57.51; H, 3.85; N, 1.01. Found: C,
C
57.12; H, 3.93; N, 1.00.
Cyclotetrakis[[cis-Pt(dppp)(4-ethynylpyridine)2][4,4′-bis(trans-
Pt(PPh3)2(OTf))biphenyl]]‚4AgOTf (18). A methylene chloride-d2
solution (0.8 mL) of macrocylce 13 (0.0472 g, 0.0037 mmol) at room
temperature was added dropwise to a vial containing solid AgOTf
(0.0046 g, 0.0180 mmol) in the glovebox. The slightly darkened,
orange-yellow solution was filtered through a short plug of glass wool
after for 15 min of stirring. The reaction was found to be quantitative
and yield the single desired silver adduct, as determined by NMR
spectroscopy. The solid was dried in Vacuo and stored under vacuum
in the dark: yield 0.0471 g (91%); mp 214-220 °C (dec.); IR (thin
film, CD2Cl2, cm-1) 3055, 2925 (C-H), 2086 (CtC), 1606, 1587,
1481, 1436 (Ar), 1266, 1205, 1100, 1030 (OTf); 1H NMR (300 MHz,
Cyclotetrakis[[bis(4-(4′-pyridyl)phenyl)iodonium(OTf)][1,4-bis-
(trans-Pt(PEt3)2(OTf))benzene]] (15). To a room temperature acetone/
methylene chloride (4:3 mL) solution of 4,4′-bis(trans-Pt(PEt3)2(OSO2-
CF3))benzene (0.020 g, 0.0162 mmol) was added dropwise, with
stirring, a suspension of bis[4-(4′-pyridyl)phenyl]iodonium triflate
(0.094 g, 0.0162 mmol) in acetone/methylene chloride (3:2 mL). After
for 6 h of stirring in the drybox, the light-orange solution was filtered
and then dried in Vacuo yielding a light-orange solid. When monitored
1
by H and 31P{1H} NMR spectroscopy, the reaction is determined to
be quantitative. For 15: yield: 0.050 g (81%); mp 202-205 °C (dec.);
IR (thin film, acetone-d6, cm-1) 3058 (C-H), 1393, 1435, 1480 (Ar),
1
1276, 1260, 1155, 1098 (OTf); H NMR (499.8 MHz, acetone-d6) δ
3
3
3
CD2Cl2) δ 7.65 (m, 32H, HP), 7.52 (d, JHH ) 5.8 Hz, 16H, HR-Py),
8.98 (d, 16H, JHH ) 5.7 Hz, HR-Py), 8.54 (d, 16H, JHH ) 8.4 Hz,
HR-PhI), 8.10 (m, 32H, Hâ-PhI and Hâ-Py), 7.13 (s, Ho-Pt), 1.42
(m, 96H, PCH2CH3), 1.12 (m, 144H, PCH2CH3); 13C{1H} NMR (125.7
MHz, acetone-d6) δ 153.5 (s, CR-Py), 149.0 (s, Cγ-Py), 140.5 (s, Cγ-
PhI), 137.4 (s, CR-PhI), 137.1 (s, Co-Pt), 131.6 (s, Câ-PhI), 128.1
7.42, 7.29, 7.25 (m, 288H, HP), 6.70 (d, 16H, 3JHH ) 7.9 Hz, Ho-Pt),
3
3
6.31 (d, 16H, JHH ) 7.9 Hz, Hm-Pt), 5.83 (d, 16H, JHH ) 6.4 Hz,
Hâ-Py), 2.60 (br s, 16H, CH2CH2P-dppp), 2.07 (br s, 8H, CH2CH2P-
dppp); 13C{1H} NMR (125.7 MHz, CD2Cl2) δ 150.6 (s, CR-Py), 137.9
(s, Co-Pt), 136.5 (s, Cp-Pt), 134.4 (br s, Co-PPh3), 133.94 (br s, Co-
PPh2), ∼133.6 (partially obscured, Cγ-Py), 132.2 (s, Cp-PPh2), 131.5
(s, Cp-PPh3), 129.6 (s, Cm-PPh2), 129.2 (br s, Cm-PPh3), ∼129-130
(Ci-PPh2 obscured), 128.6 (s, Câ-Py), 127.9 (t, 1JCP ) 28.2 Hz, Ci-
PPh3), ∼128-131 (obscured, Ci-Pt), 126.4 (s, Cm-Pt), 121.54 (q, 1JCF
) 321 Hz, OTf), (not observed, CtCR-Pt), 108.7 (m, CtCâ-Pt), 25.4
(m, CH2CH2P-dppp), 19.9 (br s, CH2CH2P-dppp); 31P{1H} NMR (CD2-
Cl2) δ 20.5 (s, 16P, 1JPPt ) 3048 Hz, PPh3), -9.0 (s, 8P, 1JPPt ) 2359
Hz, PPh2); 19F{1H} NMR (CDCl3) δ -76.3 (s). Anal. Calcd for
2
1
(t, JCP ) 9 Hz, Ci-Pt), 126.0 (s, Câ-Py), 121.7 (q, JCF ) 322 Hz,
OTf), 116.4 (s, Ci-PhI); 31P{1H} NMR (acetone-d6) δ 14.2 (s, 1JPPt
2720 Hz); 19F{1H} NMR (CDCl3) δ -77 (s).
)
Cyclotetrakis[[bis(4-(4′-pyridyl)phenyl)iodonium(OTf)][4,4′-bis-
(trans-Pt(PPh3)2(OTf))biphenyl]] (16). To a room temperature acetone/
methylene chloride (4:3 mL) solution of 4,4′-bis(trans-Pt(PPh3)2(OSO2-
CF3))biphenyl (0.0500 g, 0.025 mmol) was added dropwise, with
stirring, a suspension of bis[4-(4′-pyridyl)phenyl]iodonium triflate
(0.0145 g, 0.025 mmol) in acetone/methylene chloride (3:2 mL). After
6 h of stirring in the drybox, the light-orange solution was filtered and
then dried in Vacuo yielding a light-orange solid. When monitored by
1H and 31P{1H} NMR spectroscopy, the reaction is determined to be
quantitative. For 16: yield 0.050 g (81%); mp 202-205 °C (dec.); IR
(thin film, acetone-d6, cm-1) 3058 (C-H), 1393, 1435, 1480 (Ar), 1276,
1260, 1155, 1098 (OTf); 1H NMR (499.8 MHz, acetone-d6) δ 8.52 (d,
C512H408Ag4F36N8O36P24Pt12S12: C, 51.97; H, 3.48; N, 0.95. Found:
C, 51.37; H, 3.65; N, 0.92.
Electrospray Ionization Fourier Transform (ESI-FTICR) Mass
Spectrometry of Macrocycles 13 and 16. The electrospray ionization
(ESI) Fourier transform ion cyclotron resonance (FTICR) mass
spectrometer used for the present study is based on data collected with
an Oxford 7 T superconducting magnet. A full description of this
instrumental technique has been provided in detail elsewhere.14-17
Macrocycle 13 (ca. 1 mg/mL in CH2Cl2) was electrosprayed at a
flow rate of 0.3 µL/min with a source potential of ca. 3 kV to produce
a stable positive ion current. The resistively heated desolvation capillary
temperature was reduced to 35 °C, and the capillary-skimmer potential
was reduced to 30 V; both parameters were decreased to avoid thermal
3
16H, partially obscured, HR-Py), 8.49 (d, 16H, JHH ) 8.5 Hz, HR-
3
PhI), 7.69 (d, 16H, JHH ) 8.5 Hz, Hâ-PhI), 7.50 (m, 96H, Ho-P),
3
7.40 (t, 48H, JHH ) 7.2 Hz, Hp-P), 7.32 (m, 96H, Hm-P), 7.18 (d,
3
3
16H, JHH ) 6.5 Hz, Hâ-Py), 6.82 (d, 16H, JHH ) 8.0 Hz, Ho-Pt),
6.35 (d, 16H, JHH ) 8.0 Hz, Hm-Pt); 13C{1H} NMR (125.7 MHz,
acetone-d6) δ 153.6 (s, CR-Py), 148.3 (s, Cγ-Py), 141.3 (s, Cγ-PhI),
138.6 (s, CR-PhI), 137.7 (s, Co-Pt), 136.8 (s, Cp-Pt), 135.2 (t, JCP
3
2

Nanoscale Tectonics
J. Am. Chem. Soc., Vol. 119, No. 48, 1997 11619
or collisional dissociation, respectively, and correspond to very gentle
source conditions. To enhance the signal-to-noise and dynamic range,
selected ion accumulation (i.e., quadrupolar excitation at a single
frequency) was employed for ion accumulation during the ion injection
event. Specifically, to enhance the signal of the 5+ charge state of
macrocycle 13, a wave form was applied at m/z ) 2012 at 0.7 V peak-
to-peak. The selected ion accumulation of only the 5+ charge states
results from the magnetron ejection of other species in the ICR cell
during the relatively high pressure (∼10-4 Torr) associated with the
accumulation/pulsed valve event. The determined mass of the 5+ ion
was 10 060.15 Da (theoretical mass of 10 060.03 Da; error ) 12 ppm).
A sample of 16 was prepared by dissolving it in acetone just prior
to analysis. The sample (ca. 1 mg/mL) was then loaded into a 10 mL
Hamilton syringe, placed into a Harvard syringe pump, and introduced
into the mass spectrometer at a flow rate of 0.3 mL/min.3 The
resistively heated desolvation capillary was reduced to 2 A, and the
capillary-skimmer potential was reduced to 20 V; both parameters were
decreased to avoid thermal or collisional dissociation and correspond
to very gentle conditions. A source potential of ca. 2.5 kV was applied
to produce a stable positive ion current. A quadruple excitation wave
form was applied for selected ion accumulation at m/z 1500. The ESI-
FTICR-MS spectrum of 16 was obtained with an injection/accumula-
tion time of 10 s. The determined mass of the 6+ ion was 9000.98
Da (theoretical mass of 16, 9001.02 Da; error ) 4.4 ppm).
Tandem Mass Spectrometry of 13. The selected 5+ charge state
of macrocycle 13 was subsequently collisionally activated inside the
ICR using a sustained off-resonance irradiation (SORI) event in the
presence of a buffer gas (e.g., N2). The SORI event was applied -500
Hz off-resonance at 25 dB for a duration of 0.25 s. The total experiment
time including the ion injection and pump down sequences lasted 17
s. The fragment ions of the intact macrocycle were then identified
which was facilitated by the direct charge state determination approach
based upon the ability of the FTICR to resolve the isotopic envelope.
General Procedure for Exchange Experiments. Each macrocycle
that was studied was prepared in the drybox in the appropriate solvent
according to the given procedure (Vide supra). After reaction comple-
tion, the preformed square was added as a solution to a 4-fold excess
of the solid competitor moiety. The progress of the exchange was
1
monitored periodically by H and 31P NMR spectroscopies.
Acknowledgment. Dedicated to Professor Albert I. Meyers
on the occasion of his 65th birthday. Financial support by the
NSF (CHE-9529093), NIH (2ROCA16903), and the University
of Utah Institutional Funds Committee as well as the generous
loan of platinum(II) dichloride from Johnson-Matthey are
gratefully acknowledged.
JA972668S