Molecular architecture via coordination: Self-assembly, characterization, and host-guest chemistry of mixed, neutral-charged, Pt-Pt and Pt-Pd macrocyclic tetranuclear complexes. X-ray crystal structure of cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2</s

Article abstract of DOI:10.1021/ja9635286

Interaction of cis-Ptdppp(p-C₆H₄CN)₂ or cis-Ptdppp(p-C₂C₆H₄N)₂ with cis-ML₂(OSO₂CF₃)₂ (M = Pt or Pd; L = PEt₃ or L₂

Full text of DOI:10.1021/ja9635286

2524
J. Am. Chem. Soc. 1997, 119, 2524-2533
Molecular Architecture Via Coordination: Self-Assembly,
Characterization, and Host-Guest Chemistry of Mixed,
Neutral-Charged, Pt-Pt and Pt-Pd Macrocyclic Tetranuclear
Complexes. X-ray Crystal Structure of Cyclobis[[cis-
Pt(dppp)(4-ethynylpyridine)2][cis-Pd2+(PEt3)22-OSO2CF3]]
Jeffery A. Whiteford, Cuong V. Lu, and Peter J. Stang*
Contribution from the Department of Chemistry, The UniVersity of Utah,
Salt Lake City, Utah 84112
ReceiVed October 8, 1996X
Abstract: Interaction of cis-Ptdppp(p-C6H4CN)2 or cis-Ptdppp(p-C2C6H4N)2 with cis-ML2(OSO2CF3)2 (M ) Pt or
Pd; L ) PEt3 or L2 ) dppp), in CH2Cl2 or acetone, at room temperature, results in mixed, neutral-charged cyclic
tetranuclear, Pt-Pt or Pt-Pd macrocyclic complexes in 90-99% yields Via self-assembly. All tetramers are
microcrystalline air- and water-stable solids with decomposition points > 170 °C. The benzonitrile based macrocycles
can be disassembled in solution with 4,4′-bipyridine, while the 4-ethynylpyridine systems are more stable toward a
variety of guests. The 4-ethynylpyridine tetramers display host-guest chemistry with silver triflate Via the “π -tweezer
effect”. The X-ray crystal structure as well as FABMS, including isotope patterns, are reported for the tetranuclear
macrocycle cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pd2+(PEt3)22-OSO2CF3]] (14).
Introduction
ligands available as building blocks; (b) bond energies in
between the range of the strong covalent bonding in classical
macrocycles and the weak interactions (hydrogen bonding,
π-π-stacking, hydrophobic and hydrophilic forces, electrostatic
interactions, etc.) of systems patterned after biological models;4,6
(c) excellent product yields, due to self-assembly; (d) ready
adaptability to diverse supramolecular species including 3-D
structures; (e) enormous design variations by virtue of the
permutation of linkers and corners; (f) etc.
Self-assembly is the most efficient means for the synthesis
of a variety of discrete supramolecular species.1-3 Recently
transition metal directed self-assembly Via coordination has
emerged as a new and major motif in supramolecular architec-
ture.4,5 This motif offers a variety of design features, such as
(a) tremendous versatility due to the potentially large and diverse
number of suitable transition metal complexes and multidentate
To date, chelation and coordination have primarily been
employed in the formation of hitherto unknown molecular
squares,5,7 with unique, well defined shapes and geometries.
However, currently only all cationic,5,7 anionic,8c or neutral8a,b,d
molecular squares are known. Likewise, only homonuclear or
hybrid transition metal-iodonium molecular squares have been
prepared with no examples of heteronuclear tetramers. One of
X Abstract published in AdVance ACS Abstracts, March 1, 1997.
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Ed. Engl. 1996, 35, 1154-1196. (b) Tour, J. M. Chem. ReV. 1996, 96,
537-553. (c) Lehn, J.-M. Supramolecular Chemistry: Concepts and
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Gordon, D. M. Acc. Chem. Res. 1995, 28, 37-44. (h) Cram, D. J.; Cram,
J. M. Container Molecules and Their Guests; The Royal Society of
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(2) (a) Monographs in Supramolecular Chemistry 1-5; Stoddart, J. F.,
Ed.; Royal Society of Chemistry: Cambridge, 1989; 1991; and 1994-1995.
(b) Supramolecular Chemistry; Balzzani, V., DeCola, L., Eds.; Kluwer
Academic Publishers: The Netherlands, 1992. (c) Inclusion Phenomena
and Molecular Recognition; Atwood, J. L., Ed.; Plenum: New York, 1990.
(d) Molecular Inclusion and Molecular Recognition-Clathrates II (Topics
in Current Chemistry, Vol. 149); Weber, E., Ed.; Springer-Verlag: New
York, 1987. (e) Host-Guest Complex Chemistry/Macrocycles; Vogtle, F.,
Weber, E., Eds.; Springer-Verlag: Berlin, 1985.
(5) (a) Manna, J.; Whiteford, J. A.; Stang, P. J. J. Am. Chem. Soc. 1996,
118, 8731-8732. (b) Stang, P. J.; Whiteford, J. A. Res. Chem. Intermed.
1996, 22, 659-665. (c) Olenyuk, B.; Whiteford, J. A.; Stang, P. J. J. Am.
Chem. Soc. 1996, 118, 35, 8221-8230. (d) Stang, P. J.; Olenyuk, B. Angew.
Chem., Int. Ed. Engl. 1996, 35, 732-736. (e) Stang, P. J.; Chen, K.; Arif,
A. M. J. Am. Chem. Soc. 1995, 117, 8793-8797. (f) Stang, P. J.; Cao, D.
H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc. 1995, 117, 6273-6283. (g)
Stang, P. J.; Chen, K. J. Am. Chem. Soc. 1995, 117, 1667-1668. (h) Stang,
P. J.; Whiteford, J. A. Organometallics 1994, 13, 3776-3777. (i) Stang, P.
J.; Cao, D. H. J. Am. Chem. Soc. 1994, 116, 4981-4982. (j) Stang, P. J.;
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1036-1039.
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and Computation; Wiley; New York, 1992.
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C. O.; Sauvage, J.-P. J. Am. Chem. Soc. 1996, 118, 3285-3286. (b) Fujita,
M.; Oguro, D.; Miyazawa, M.; Oka, H.; Yamaguchi, K.; Ogura, K. Nature
1995, 378, 469-471. (c) Ashton, P. R.; Ballardini, R.; Balzani, V.; Credi,
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117, 11171-11197. (d) Bedard, T. C.; Moore, J. S. J. Am. Chem. Soc.
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S0002-7863(96)03528-7 CCC: $14.00 © 1997 American Chemical Society

Pt-Pt and Pt-Pd Macrocyclic Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 119, No. 10, 1997 2525
Scheme 1
the major design advantages of coordination is the ability to
vary the charge density (Via different metals and/or different
oxidation states) as well as the cavity size and shape (Via the
connector ligands) and thereby fine tune the potential host-
guest and molecular recognition properties of the resultant
supramolecular species.
In this paper we wish to report (1) the rational design and
characterization of the first examples of mixed neutral-charged
molecular squares; (2) the first examples of heteronuclear
molecular squares; (3) the single crystal X-ray structure of a
unique mixed neutral-charged heterobimetallic Pt-Pd molecular
square; (4) incorporation of CC triple bonds (acetylenic units)
as part of the connectors, and (5) studies on the host-guest
properties, including π-coordination of Ag+, Via the π-tweezer
effect, of these unique molecular squares.
4-Ethynylpyridine was synthesized by a modified Castro-
Stevens coupling9b of 4-bromopyridine with trimethylsilylacety-
lene followed by treatment with TBAF in THF at 0 °C.
Deprotonation of 2 equiv of 4-ethynylpyridine with tert-
butyllithium at -78 °C in THF, followed by immediate addition
of 1 equiv of 1,3-bis(diphenylphosphino)propane chelated Pt(II)-
Cl2 afforded, after workup, the desired dppp chelated monomer
6, in 68% isolated yield.
Reaction of 5 with an equimolar amount of 1 and 2,
respectively, in CH2Cl2 at room temperature results in the
formation of neutral-charged tetranuclear complexes 7 and 8,
while reaction of 5 with 3 and 4, respectively, in acetone at
room temperature, resulted in the formation of neutral-charged
tetranuclear complexes 9 and 10 (Scheme 2). In a similar
fashion, reaction of 6 with an equimolar amount of 1 and 2,
respectively, in CH2Cl2 at room temperature, resulted in the
formation of neutral-charged tetranuclear complexes 11 and 12,
while interaction of monomer 6 with 3 and 4, respectively, in
acetone at room temperature resulted in the formation of neutral-
charged tetranuclear complexes 13 and 14 all in excellent
isolated yields (Scheme 3). Although complexes 7, 8, 10, 12,
and 14 form within a matter of minutes Via self-assembly,
complexes 9, 11, and 13 required 4 h for complete conversion
to the respective tetranuclear macrocycles.
All eight tetranuclear complexes are stable microcrystalline
solids with different coloration. Homonuclear complex 7 is light
pink, whereas the homonuclear complexes 9, 11, and 13 are
white. Heteronuclear complex 8 is reddish-brown, whereas the
heteronuclear complexes 10, 12, and 14 are yellow. Mixed
neutral-charged tetranuclear macrocycles 7, 8, 11, and 12 are
soluble in organic solvents such as CH2Cl2 and CHCl3, while
macrocycles 9, 10, 13, and 14 are soluble in acetone and
nitromethane.
These macrocyclic, tetranuclear triflate complexes have been
fully characterized by analytical and spectral means as outlined
in the Experimental Section. In particular, all new compounds
have elemental analyses consistent with their respective com-
positions. The 31P{1H} spectra of 7-10 each show two singlets
Results and Discussion
The rational design of mixed neutral-charged and hetero-
bimetallic molecular squares requires a modular self-assembly
approach of appropriate subunits as complete self-assembly of
the constituent parts would result in mixtures of products (i.e.,
all neutral, all charged, mixed neutral-charged, homonuclear,
heteronuclear, etc.). The simplest approach would involve use
of the already available square planar Pt and Pd bistriflate
complexes (1-4) for the charged portion in combination with
“preconstructed” neutral monomeric units with built in connec-
tors for the uncharged corners. This approach provides the
added synergistic benefit of heteronuclear systems by simple
variation of the metals in the two different subunits. The
construction of the desired neutral connectors should be simple,
preferably a single step process from readily available precursors
(Scheme 1).
Indeed, the synthesis of neutral monomeric subunits 5 and 6
was easily accomplished using classical organic and organo-
metallic techniques and commercially or well established easily
available precursors. Lithium-halogen exchange of 4 equiv
of 4-iodobenzonitrile at -78 °C with n-butyllithium in diethyl
ether followed by immediate addition of 1 equiv of 1,3-bis-
(diphenylphosphino)propane (dppp) chelated Pt(II)Cl2 gave, after
workup, monomer 5 in 83% isolated yield (Scheme 2).
Platinum monomer 6 was prepared similarly to monomer 5.
(9) (a) Ciana, L.-D.; Haim, A. J. Heterocycl. Chem. 1984, 607-608.
(b) Takahashi, S.; Kuroyama, Y.; Sonogahira, K.; Hagihara, N. Synthesis
1980, 627-630.

2526 J. Am. Chem. Soc., Vol. 119, No. 10, 1997
Whiteford et al.
Scheme 2
Scheme 3
with a shift of 1.0-2.0 ppm for the P on the neutral Pt (P-Pt);
5.2 ppm for the P attached to the charged Pt (P-Pt2+) for 7
and 4.8 ppm for the P-Pt2+ of 9; 6.4 ppm for the P-Pd2+ of
8 and 4.8 ppm for the P-Pd2+ of 10, respectively, relative to
the precursors 1-5. Diagnostic for the tetranuclear complexes
the precursors 6 and 1-4. Also diagnostic for the tetranuclear
1
complexes 11-14 are the respective H and 13C{1H} NMR
spectra. Similar to 7 and 8, the 1H NMR signals for the
methylenes of 11 and 12 for the charged metal chelating dppp
units are shifted downfield, relative to the precursors 1, 2, and
6, while the methylenes of the neutral metal chelating dppp units
remain essentially unchanged. Also observed were complex
overlapping aromatic resonances for the two sets of phenyl
groups of the dppp ligand for 11 and 12, while squares 13 and
14 have signals for the methyl and methylene groups of the
triethylphoshine ligands. The two sets of aromatic resonances
for the 4-ethynylpyridine unit (R and â to the pyridyl nitrogen)
are virtually identical. Integration of the proton signals is in
accord with the requirements for 11-14. The 19F spectra
1
7-10 are the respective H and 13C{1H} NMR spectra. The
1H NMR signals for the methylenes of 7 and 8 for the charged
metal chelating dppp units are shifted downfield, relative to the
precursors 1, 2, and 5, while the methylenes of the neutral metal
chelating dppp units remain essentially unchanged. Also
observed were overlapping aromatic resonances for the two sets
of phenyl groups of the dppp ligand for 7 and 8, while squares
9 and 10 have signals for the methyl and methylene groups of
the triethylphosphine ligands. The two sets of aromatic
resonances for the cyanobenzene unit (R and â to the CN) are
virtually identical. Integration of the proton signals is in accord
with the requirements for 7-10. The 19F spectra display singlets
at -79 ppm for 7 and 8, while 9 and 10 display singlets at -75
ppm, characteristic for ionic CF3SO3-. The 31P{1H} spectra
of 11-14 each show two singlets with a shift of 0.1-1.0 ppm
for the P on the neutral Pt and 4.0 ppm for the P-Pt2+ of 11;
9.3 ppm for the P-Pt2+ of 13; 9.7 ppm for the P-Pd2+ of 12;
and 24.4 ppm for the P-Pd2+ of 14, respectively, relative to
display singlets at -79 ppm for 11 and 12, while 13 and 14
-
display singlets at -75 ppm, characteristic for ionic CF3SO3
.
Fast atom bombardment mass spectrometry (FABMS) analy-
sis of macrocycles 9, 11, and 14 gave a M - 2OTf peak for 11
(1569.3 amu) with a +2 charge state (i.e., separation of peaks
by 0.5 m/z) and the M - OTf peaks at 2933.0 amu for 9 and
2756.2 amu for 14, each with a +1 charge state (i.e., separation
of peaks by 1.0 m/z). Equally important were the isotopic
distribution patterns which were consistent with the respective

Pt-Pt and Pt-Pd Macrocyclic Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 119, No. 10, 1997 2527
Table 1. Crystal Data and Structure Refinement
compound
color/shape
empirical formula
formula weight
T, K
crystal system
space group
unit cell dimensions
a, Å
molecular square 14.5C3H6O
colorless/plate
C
125H158F12N4O17P8Pd2Pt2
3195.53
173(2)
triclinic
P-1
10.6859(2)
b, Å
17.4520(3)
c, Å
18.8824(1)
R, deg
85.750(1)
88.401(1)
89.969(1)
3510.33(9)
â, deg
γ, deg
V, Å3
Z
1
F (calcd), Mg/m3
1.512
µ, cm-1
12.465 mm-1
diffractometer/scan
radiation/wavelength, Å
Siemens SMART/CCD area detector
Mo KR (graphite monochrom)/
0.71073
F(000)
1612
crystal size, mm
θ range for data collection, deg
index ranges
0.10 × 0.20 × 0.20
1.08-27.91
-9 e h e 14, -22 e k e 21,
-24 e l e 24
22347
reflcns collected
independent/observed reflcns
15760(Rint )
0.0499)/12009([I > 2σ(I)])
semiempirical from psi-scans
0.9878 and 0.6913
absorption correction
range of relat. transm. factors
refinement method
computing
data/restraints/parameters
goodness-of-fit on F2
SHELX-93 weight parameters
final R indices [I > 2σ(I)]
R (all data)
full-matrix-block least-squares on F2
SHELXTL, Ver. 51
15752/0/833
1.247
0.0000, 46.1157
R1 ) 0.0752, wR2 ) 0.1375
R1 ) 0.1146, wR2 ) 0.1672
0.00095(10)
Figure 1. Calculated (top) and experimental (bottom) isotopic distribu-
tion pattern of M - OTf for 14.
calculated compositions of these species.10 The calculated and
experimental M - OTf peak for square 14 is shown in Figure
1. The structure of 14 was unambiguously confirmed by single-
crystal X-ray diffraction resulting in ipso facto evidence for the
exact structure of these unique macrocycles and thereby also
confirming the utility of FABMS for the observation of mixed
neutral-charged molecular squares formed by self-assembly in
solution.
extinction coefficient
largest diff. peak and hole,
eÅ-3
1.898 and -1.926
P-Pt-P angle is 92.6° whereas the C-Pt-C angle is somewhat
smaller at 88.0°. Comparison of the bond angles of coordina-
tively bonded macrocycles reported earlier5e,f reveal that the
mixed organometallic-coordination complex 14 has slightly
larger bond angles than the 4,4′-bipyridine Pt(II) dppp chelated
macrocycle and the hybrid iodonium-Pd(II) bistriethyl phosphine
macrocycle with respect to the metal corners and connecting
ligands. The N-Pt-N bond angle of the 4,4′-bipyridine
macrocycle is 83.9°, and the hybrid iodonium square N-Pd-N
bond angle is 83.5°, whereas the N-Pd-N bond angle for
macrocycle 14 is 85°. The edge-to-edge Pt-Pd distance is 9.5
Å, the diagonal Pt-Pt distance is 13.0 Å, and the diagonal Pd-
Pd distance is 14.0 Å. Examination of the space filling model
of 14, which is based upon the X-ray data and shown in Figure
3, reveals a smaller cavity than one would anticipate by simply
using the diagonal distances between metal corners. Consider-
ing that the van der Waals radius of Pt is ca. 1.75 Å and that of
Pd is ca. 1.6 Å, the effective diagonal Pt-Pt distance is 9.5 Å,
and the diagonal Pd-Pd distance is 10.8 Å. Alternatively, the
approximate effective cross sectional area of the cavity of 14 is
ca. 6.5 Å × 6.5 Å. The comparable cross sectional area of the
all 4,4′-bipyridine Pt square is ca. 7.7 Å × 7.7 Å. The 4-ethynyl
pyridine ligands of 14 are bent slightly inwards toward the center
of the square. The pyridyl ligands are nearly orthogonal to the
plane defined by the dppp ligand and do not display π-π
interaction with the phenyl rings of the dppp subunit as seen
with the cationic square crystal structures previously reported.5e,f
This can be attributed to the alkyne spacer unit in 14 which
separates the dppp ligand phenyl rings from the pyridyl ring
resulting in a distance too large between the two moieties to
Single-Crystal X-ray Molecular Structure Determinations
The geometrical features of molecular squares is of consider-
able interest since they represent a new and unique species of
macrocycles. Continued progress in design variation of these
macrocycles will prove useful for the determination of host-
guest interactions and specific binding characteristics. Bond
angles and cavity size are important features for the determi-
nation of potential guest size and dimension. Therefore, we
attempted to obtain X-ray quality crystals of all macrocyclic
squares. However, the crystals of all macrocycles described
are solvent dependent, due to extensive solvent occlusion in
their cavities, and collapse into amorphous material upon
removal from the mother liquor. To date only macrocycle 14
gave single crystals suitable for X-ray determination; the
crystallographic data for 14 is summarized in Table 1. The
numbering diagram, ORTEP representation, and significant
geometric features are shown in Figure 2. Selected key bond
distances and angles are given in Table 2. A space filling model
based on the X-ray data for square 14 using Chem3-D Plus is
shown in Figure 3.
There are several interesting structural features observed for
square 14. The overall geometry of macrocycle 14 is nearly
planar with minor deviations from a perfect square. The
bonding geometry for the Pt(II) and Pd(II) centers are square
planar but deviate slightly from the ideal 90° angles. The
(10) Whiteford, J. A.; Rachlin, E. M.; Stang, P. J. Angew. Chem., Int.
Ed. Engl. 1996, 35, 2524-2529.

2528 J. Am. Chem. Soc., Vol. 119, No. 10, 1997
Whiteford et al.
Figure 2. ORTEP representation and summary of the significant geometric features of molecular square 14.
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Molecular Square 14
Pt-C(1)
1.972(8)
2.014(9)
2.295(2)
2.297(2)
2.100(7)
2.106(7)
2.298(2)
2.299(2)
N(1)-Pd-P(3)
N(2)A-Pd-P(3)
N(1)-Pd-P(4)
N(2)A-Pd-P(4)
P(3)-Pd-P(4)
C(6)-N(1)-C(5)
C(6)-N(1)-Pd
C(5)-N(1)-Pd
88.8(2)
173.8(2)
174.1(2)
89.1(2)
Pt-C(8)
Pt-P(2)
Pt-P(1)
Pd-N(1)
97.05(9)
117.4(8)
121.9(7)
119.5(7)
119.2(8)
120.2(6)
120.4(6)
172.7(10)
174.0(11)
117.0(9)
122.4(10)
120.6(10)
119.6(10)
123.4(10)
122.8(10)
119.7(10)
179.3(9)
174.4(12)
Pd-N(2)A
Pd-P(3)
Pd-P(4)
N(1)-C(6)
N(1)-C(5)
N(2)-C(13)
N(2)-C(12)
N(2)-PdA
C(1)-C(2)
C(2)-C(3)
C(3)-C(4)
C(3)-C(7)
C(4)-C(5)
C(6)-C(7)
C(8)-C(9)
C(9)-C(10)
C(10)-C(11)
C(10)-C(14)
C(11)-C(12)
C(13)-C(14)
C(1)-Pt-C(8)
1.335(13) C(13)-N(2)-C(12)
1.337(13) C(13)-N(2)-PdA
1.326(12) C(12)-N(2)-PdA
1.331(13) C(2)-C(1)-Pt
2.106(7)
C(1)-C(2)-C(3)
1.223(12) C(4)-C(3)-C(7)
1.430(13) C(4)-C(3)-C(2)
1.39(2)
1.39(2)
C(7)-C(3)-C(2)
C(5)-C(4)-C(3)
1.375(12) N(1)-C(5)-C(4)
1.384(14) N(1)-C(6)-C(7)
1.193(13) C(6)-C(7)-C(3)
1.435(13) C(9)-C(8)-Pt
1.384(14) C(8)-C(9)-C(10)
1.396(14) C(11)-C(10)-C(14) 118.2(9)
1.419(12) C(11)-C(10)-C(9)
1.391(12) C(14)-C(10)-C(9)
122.7(10)
119.1(10)
88.0(4)
C(10)-C(11)-C(12) 119.4(10)
C(1)-Pt-P(2) 174.7(3)
N(2)-C(12)-C(11)
N(2)-C(13)-C(14)
P(2)-Pt-P(1)
121.2(9)
123.4(9)
92.59(8)
85.0(3)
C(8)-Pt-P(2)
C(1)-Pt-P(1)
91.0(3)
88.7(3)
Figure 3. Space-filling model for 14 based on X-ray data.
C(8)-Pt-P(1) 175.1(3)
N(1)-Pd-N(2)A
(9) Å] which is remarkably similar to the average bond length
distribution for organic alkynes (d(C-C)mean ) 1.435(9) Å for
55 distances with esd e 0.010 Å).11a Importantly, very few σ
bonded Pt-alkynyl crystal structures have been reported with
low esd values such as seen in square 14.11a,b
allow π-π interaction. The M-P distances (2.30 Å) are normal
and similar to distances obtained earlier on other macrocyclic
squares. Likewise the M-N distances (2.10 Å) are normal and
similar to distances on macrocyclic squares previously reported.
The M-alkyne bond lengths are 1.972(8) and 2.014(9) Å, and
the CC alkyne bond lengths are 1.193(13) and 1.223(12) Å for
macrocycle 14. For comparison, the previously reported average
M-alkyne length of cis-Pt(CCO2Me)(CO2Et)(PPh3)2 is 1.991-
(8) Å, and the CC alkyne bond length is 1.180(11) Å.11c The
average M-C bond length for bis(diphenylmethylphosphine)-
dimethylplatinum is 2.120(4) Å.11a The alkyne-pyridyl-ipso
carbon bond lengths are 1.435(13) and 1.430(13) Å which are
very close to all other metal-alkyne complexes spanning a range
of only 0.041 Å [1.421(8)-1.462(8) Å; d(C-C)mean ) 1.439-
The stacking pattern of macrocycle 14 in the solid state is
shown in Figure 4. The cationic squares are stacked along the
A-axis, resulting in long channel-like cavities similar to other
members of the molecular square family.5e,f The repeating unit
distance between each stacked cationic square is 10.7 Å which
is larger than the hybrid-iodonium-transition metal square
distance at 9.5 Å but smaller than the non-planar all transition
metal 4,4′-bipyridine square distance at 15.9 Å. The one triflate
counterion which is above and below the plane of the square
(but outside of the square framework) was disordered and
modeled by refining the triflate in two positions, each with 50%
occupancy. The other triflate is between the positively charged
Pd(II) center and the neutral Pt(II) center and is ordered.
Acetone molecules, from the solvent, reside within square
channels which propagate along the A-axis. There appear to
be multiple orientations fractionally disordered for each of the
(11) (a) Manna, J.; John, K. D.; Hopkins, M. D. AdV. Organomet. Chem.
1995, 38, 79-154, and references therein. (b) Berenguer, J. R.; Fornie´s, J.;
Lalinde, E.; Mart´ınez, F. J. Organomet. Chem. 1994, 470, C15-C18. (c)
Wisner, J. M.; Bartczak, T. J.; Ibers, J. A.; Low, J. J.; Goddard III, W. A.
J. Am. Chem. Soc. 1986, 108, 347-348.

Pt-Pt and Pt-Pd Macrocyclic Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 119, No. 10, 1997 2529
Scheme 4
Titration Experiments. Since the gross cavity size of both
the benzonitrile and 4-ethynylpyridine mixed neutral-charged
macrocycles is approximately 10.8 Å × 9.5 Å diagonally and
6.5 Å × 6.5 Å from side to side (based on molecular modeling
and the crystal structure for 14), electron rich 1,4-dihydroxy-
benzene and 1,5-dihydroxynapthalene were chosen to test for
host-guest interactions. First, a titration experiment was
conducted using 1,4-dihydroxybenzene (DHB) dissolved in
acetone-d6. Square 10 was added to a solution of DHB starting
with an initial ratio of 1.0:0.5 (DHB:10) and increasing the
concentration of square 10 by increments of 0.5 equiv. The
solubility of 10 only allowed for a ratio of 1.0:2.0 before the
solution became saturated and square 10 began to precipitate
out of solution. Neither 10 or DHB displayed a significant shift
Figure 4. Stacking diagram of square 14.
2.5 unique acetone solvent molecules per asymmetric unit (five
molecules overall in the unit cell) resulting in large thermal
parameters for the disordered atoms.
Chemistry of Mixed Neutral-Charged Molecular Squares
All mixed neutral-charged molecular squares synthesized to
date have a C2 axis featuring two positively charged metal
centers and two neutral metal centers. It is conceivable that
this type of molecular square will be suitable for binding
electron-rich guests; the squares can be considered electron
deficient since the datively bound metal centers each have a
formal charge of +2.
1
in the H-NMR; DHB showed no change in these solutions
compared with free DHB and the benzonitrile R and â protons
(with respect to the Pt metal center) of 10 shifted < 0.04 ppm.
A second titration experiment was conducted using 1,5-
dihydroxynapthalene (DHN) dissolved in acetone-d6 and square
10 starting with an initial ratio of 1.0:0.5 (DHN:10) and
increasing the concentration of square 10 by increments of 0.5
equiv. This system was considerably more soluble than the
previous system, and a ratio of 1.0:7.0 (DHN:10) was reached
prior to solution saturation. A similar relationship was observed
at a ratio of 1.0:2.0 where the DHN ortho, meta, and para
protons did not change while 10 R protons shifted < 0.04 ppm.
However, continued addition of 10 resulted in no shift for the
DHN protons, while the R protons of 10 shifted 0.09 ppm at a
ratio of 1.0:7.0 (DHN:10) relative to the pure square 10.
Since DHB and DHN showed little interaction with the
representative benzonitrile square 10, square 13 was also tested
with 1,5-dihydroxynapthalene to determine whether the 4-eth-
ynylpyridine squares are suitable hosts for organic electron-
rich guests. Again, little or no interaction was observed and
nearly identical data to square 10 were obtained for square 13
utilizing the same titration experiments for this combination of
potential host and guest.
Competition Experiments. It is known that nitrile groups
form considerably weaker complexes with Pt and Pd than
pyridine.5f,12 In fact, mixing of 4,4′-bipyridine with a platinum-
nitrile dimer resulted in exclusively the 4,4′-bipyridine tetrameric
dppp complex.5f A similar situation was expected to exist in
the case of the neutral-charged molecular squares of Pt and Pd.
To test this assumption, 1 equiv of 4,4′-bipyridine was added
to a representative of the mixed neutral-charged benzonitrile
squares; tetramer 8. Within 15 min of addition of 4,4′-bipyridine
to square 8 in CD2Cl2, none of the original neutral-charged
benzonitrile square 8 remained. The 31P signal for the free
benzonitrile dppp chelated monomer 5 was observed along with
the formation of the fully charged datively bound Pd(II) 4,4′-
bipyridine square reported earlier5f (Scheme 4). Continued
interaction for about 1 h resulted in the slow precipitation of
the Pd(II) 4,4′-bipyridine square while the benzonitrile monomer
5 remained in solution. These data confirm that pyridyl based
squares are more stable toward electron-rich guests than nitrile
based mixed neutral-charged transition metal based molecular
squares and therefore likely to be more amenable to host-guest
chemistry.
(13) (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.
(12) (a) Johnson, A.; Taube, H. J. Ind. Chem. Soc. 1989, 66, 503-511.
(b) Purcell, K. F.; Drago, R. S. J. Am. Chem. Soc. 1966, 88, 919-924.

2530 J. Am. Chem. Soc., Vol. 119, No. 10, 1997
Whiteford et al.
Scheme 5
π-Coordination with AgOTf: The “π-Tweezer Effect”.
After considering the binding characteristics of acetylene groups
to metals such as silver, copper, and gold Via π-interaction of
the acetylene to the open coordination sites of the metal guest,
as most recently demonstrated by Lang et al.;13a-d it seemed
probable that 4-ethynylpyridine transition metal squares should
be well suited to binding guests of this type. The bond angle
between the two acetylenes on the aceylene equipped titanium
example was between 87° and 91° upon interaction with the
given metal guest.13d Since the crystal structure of molecular
square 14 revealed a bond angle of 88° between the two
acetylenes, it should function effectively as a host for silver
Via the π-tweezer effect. Furthermore, the molecular squares
are particularly interesting since they have two of these binding
units per square (i.e. two neutral dpppPt-bis-ethynylpyridine
centers) and should be able to complex 2 equiv of a silver
complex (Scheme 5). Attempts to bind one equiv of silver
triflate to 11 or 14 failed, resulting only in a mixture of several
products which rapidly formed an insoluble precipitate after
about 20 min. Interaction of square 14 with 2 equiv of silver
triflate in acetone-d6 did indeed show significant shift differences
in the 31P, 13C, 1H NMR, and IR spectra. Particularly diagnostic
for the formation of complex 15 was the shift in the 31P NMR
singlet where the neutral Pt corner containing the acetylene
ligands shifted ∼2.6 ppm upfield with a coupling constant
increase of 167 Hz. This upfield shift and coupling constant
increase can be attributed to the change of the angle beween
the two acetylene ligands upon complexation, thus affecting the
angle of the two phosphines of the dppp ligand with respect to
the metal center.14 As expected the Pd center phosphines are
less affected by the Ag complexation, and, therefore, the 31P
shift was not as significant (0.03 ppm downfield). The R and
â protons of the pyridyl (with respect to the pyridine nitrogen)
resulted in further downfield shifts of 0.15 and 0.11 ppm,
respectively, upon complexation with AgOTf. The 13C data
show significant shifts particularly with respect to the ipso
carbon on the pyridyl (3.5 ppm upfield) and the â alkyne carbon
which shifted 2.4 ppm downfield with respect to the pure square
14. The IR spectrum also confirmed AgOTf complexation, thus,
the alkyne CC stretch shifted to smaller wavenumbers (2091
cm-1, δ ) 34 cm-1). This is caused by two electron backdo-
nation of each alkyne to the silver.13a Square 11 showed similar
shifts in the 31P NMR upon complexation of 2 equiv of AgOTf
(Pt-Pt 4-ethynylpyridine square-silver triflate complex 16)
where the neutral Pt corner containing the acetylene ligands
shifted 3.2 ppm upfield with a coupling constant increase of
151 Hz. The charged Pt center phosphines are also less affected
by the Ag complexation, and, therefore, the 31P shift was not
as significant (0.14 ppm downfield, coupling constant increase
of 22 Hz). The R and â protons of the pyridyl (with respect to
the pyridine nitrogen) shift 0.06 downfield and 0.01 ppm upfield,
respectively, upon Ag+ complexation. The IR spectrum ex-
hibited a single alkyne stretch shifted to smaller wavenumbers
(2081 cm-1, δ ) 33 cm-1). Both squares 11 and 14 displayed
an absorption band in the UV-vis spectra at λmax ) 324 nm. A
small blue shift was observed for the respective silver complexes
16 and 15 (λmax ) 314 and 318 nm, respectively). The most
compelling evidence for the coordination of AgOTf is the
observation by FABMS of the M - OTf base peak at 3799.9
amu (Figure 5) and the M - 2OTf peak (+2 charge state) at
1824.0 amu with isotopic distributions essentially equiv to the
calculated patterns confirming the 2:1 stoichiometry of the silver
guest to the square 11. The M - OTf peak for 16 was separated
by 1 m/z unit, as expected, indicating the +1 charge state of
this macrocyclic fragment resulting from the loss of one triflate
counterion out of a total of six. The M - 2OTf peak charge
state of +2 was indicated by the 0.5 m/z separation of the peaks
of the isotopic distribution pattern of the fragment observed.
FABMS studies of the more labile Pt-Pd 4-ethynylpyridine
square-silver triflate complex 15 resulted in a homolytic cleavage
of the host-guest complex into two equal halves and loss of
one triflate per half as indicated by the +1 charge state and the
m/z value observed (1559.3 amu).
(14) (a) Wrackmeyer, B.; Horchler, K. In Progress in NMR Spectros-
copy: NMR Parameters of Alkynes; Pergamon Press: Great Britain, 1990;
pp 209-253. (b) Morris, D. G. In The Chemistry of Functional Groups,
Supplement C: NMR Spectra of Acetylenes; Patai, S., Rappoport, Z.; Eds.;
John Wiley & Sons Ltd.: New York, 1983; pp 1035-1056.
Figure 5. Calculated (top) and experimental (bottom) isotopic distribu-
tion pattern of M - OTf for 16.

Pt-Pt and Pt-Pd Macrocyclic Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 119, No. 10, 1997 2531
groups are functionally and geometrically well suited to binding
simple silver guests such as silver triflate. Thus, addition of 2
equiv of silver triflate to the 4-ethynylpyridine based Pt-Pt and
Pt-Pd squares clearly shows host-guest interaction presumably
Via the π-tweezer effect. The 88° angle between the acetylene
moieties in the free Pt-Pd square, as determined by X-ray
crystallography, allow for the inclusion of two silver atoms (one
per neutral corner) to the 4-ethynylpyridine based molecular
squares. Significant shift values in the 31P, 1H, 13C NMR, and
IR support the proposed inclusion phenomenon for the 4-eth-
ynylpyridine based Pt-Pt and Pt-Pd organometallic squares.
FABMS studies confirmed the 1:2 host:guest stoichiometry for
the Pt-Pt host:silver triflate guest complex 16 by observation
of the M - OTf species with a +1 charge state and the M -
2OTf species with a +2 charge state for complex 16. It is
known that silver, coordinated to acetylenes, can also bind to
other species such as alkynyl and aryl moieties.13a Thus it is
likely that these molecular squares containing silver guests may
be further elaborated by the addition of other ligands to Ag+.
These studies are under active investigation.
Figure 6. Metal-to-ligand (back-) donation.
Figure 7. Energy levels for square planar platinum(II) complexes.
Experimental Section
As discussed by Lang et al.,13b the alkyne-metal interaction
can arise from a σ donation of electron density from a filled π
orbital on the alkyne to the empty sp hybrid on Ag and a back-
donating component resulting from the donation of electon
density from filled d orbitals on the metal to empty π* orbitals
on the alkyne as shown in Figure 6. EHT (Extended Hu¨ckel
Theory) analysis by van Koten13a,c et al. of the Cp2Ti-
(CCH)2CuCH3 model system indicated that the back bonding
component in the alkyne-to-MR interaction is more important.
They found that two combinations of π* alkyne orbitals possess
both suitable symmetry and energy to provide efficient interac-
tions with a filled CuI (AgI) orbital (ds mixture). The first
interaction (Figure 6a) takes place in the plane of the Ti-
(CCH)2Cu-R, while the second interaction (Figure 6b) occurs
perpendicular to this plane. The typical crystal field model for
a square planar metal system (Figure 7) shows the dxy component
at a higher energy level through π interaction with both
acetylene π* orbitals than the degenerate dxz and dyz orbitals
which are capable of interacting with only one ligand per d
orbital since the ligands of a square planar complex lie along
General Methods. Melting points (uncorrected) were obtained with
a Mel-Temp capillary melting point apparatus. Infrared spectra were
recorded as CCl4 mulls on a Mattson FT-IR spectrometer. All NMR
spectra were recorded on a Varian XL 300, Varian Unity 300, or a
1
Varian VXR 500 spectrometer. The H NMR spectra were recorded
at 300 MHz, and chemical shifts are reported relative to the residual
protonated solvent peaks of CD2Cl2 δ 5.32, and acetone-d6 δ 2.05. The
13C NMR spectra were recorded at 75 or 125 MHz, 1H decoupled, and
reported relative to CD
2Cl2 δ 54.0 or acetone-d6 δ 29.93. The 19F NMR
spectra were recorded at 282 MHz, and chemical shifts were reported
relative to external CFCl3 δ 0.0 (sealed capillary) in the appropriate
deuterated solvent. The 31P NMR spectra were recorded at 121 MHz,
1H decoupled, and reported relative to external 85% H3PO4 (sealed
capillary) in the appropriate deuterated solvent.
Mass spectra were obtained with a Finnigan MAT 95 mass
spectrometer with a Finnigan MAT ICIS II operating system under
positive fast atom bombardment (FAB) conditions at 8 keV. 3-Ni-
trobenzyl alcohol was used as a matrix in CH2Cl2 or acetone as solvent,
polypropylene glycol, and cesium iodide were used as a references for
peak matching. Microanalyses were performed by Atlantic Microlabs,
Atlanta, GA.
Materials. All commercial reagents were ACS reagent grade and
used without further purification or after sublimation. Reagent grade
methylene chloride was dried by distillation over CaH2. Diethyl ether
and THF were distilled from Na/benzophenone. Acetone was refluxed
over KMnO4, distilled, and handled under nitrogen. HPLC grade
benzene, toluene, and pentane were dried over molecular sieves and
used without further purification. Reaction flasks were flame-dried
and flushed with argon prior to use with schlenk techniques unless
otherwise noted. Trimethylsilyl acetylene, diphenylphosphinopropane,
silver triflate, 2.5 M n-butyllithium in hexanes, and 1.7 M tert-
butyllithium in pentane were purchased from Aldrich. Pd(II)dichloride
was purchased from Lancaster. The free 4-bromopyridine was obtained
by deprotonation of the hydrochloride salt with triethylamine in diethyl
ether at rt overnight in the absence of light. It is unstable and so was
generated immediately before use.
4-Ethynylpyridine. 4-Ethynylpyridine was synthesized by a modi-
fied Castro-Stevens coupling.9b To a solution of trimethylsilyl
acetylene (3.28 g, 33.4 mmol) in 60 mL of THF under argon, was
added triethylamine (3.63 g, 35.9 mmol), 4-bromopyridine (5.27g, 33.4
mmol), copper iodide (508 mg, 2.67 mmol), and palladium tetrakis-
(triphenylphosphine) (2.90 g, 2.5 mmol), and the reaction mixture
subsequently stirred overnight in the absence of light. The solvent was
removed Via rotary evaporation, and then the residue was extracted
with diethyl ether (4 × 50 mL). The ether extracts were washed with
saturated NaCl, dried over MgSO4, and filtered, and the solvent was
removed Via rotary evaporation to afford the crude trimethylsilyl-4-
2
2
the x and y axis (point directly at the dx -y orbitals). It can
also be reasoned that the effect on the the Pt system is less
than the Ti system since Pt σ bonded ligands are more covalently
bonded when compared to the Ti σ bonded ligands which are
considered to have more ionic character.15
Conclusions
A total of eight novel homo and heteronuclear mixed neutral-
charged organometallic macrocyclic squares have been synthe-
sized Via modular self-assembly featuring benzonitrile ligands
or 4-ethynylpyridine ligands with two types of Pt and Pd
phoshine ligands (dppp and triethylphoshine). The X-ray crystal
structure of 14 revealed a planar slightly rhomboid geometry
and bond angles that are <90°. As expected the benzonitrile
based squares are more labile than the 4-ethynylpyridine based
squares as determined by the addition of 1 equiv of 4,4′-
bipyridine. Neither the benzonitrile or the 4-ethynylpyridine
based squares showed a strong affinity for neutral electron-rich
aromatics such as 1,4-dihydroxybenzene or 1,5-dihydroxynaph-
thalene. The organometallic squares incorporating acetylene
(15) Waters, J. A.; Mortimer, G. A. J. Organomet. Chem. 1970, 22, 417-
424.

2532 J. Am. Chem. Soc., Vol. 119, No. 10, 1997
Whiteford et al.
3
alkynylpyridine. Desilylation of this material was achieved by treatment
with 1.0 M 40 mL of THF with TBAF (35 mL, 35.0 mmol), in THF
(40 mL) at 0 °C for 6 h. Removal of the solvent Via rotary evaporation
and sublimation of the residue (80 °C, 1 mmHg) resulted in transparent
colorless crystals (1.75 g, 50% overall yield). Physical characteristics
were consistent with previously reported data.9a
o), 7.35 (m, 32H, m, p, R), 6.99 (m, 8H, JHH ) 4.8 Hz, â), 2.33 (m,
24H), 1.90 (m, 4H), 1.31 (m, 36H); 13C{1H} NMR (acetone-d6) δ 134.1
(Pt-P-Co), 132.3 (Pt-P-Cipso), 131.1 (Pt-P-Cp), 129.2 (Pt-P-Cm),
137.2 (Pt-Câ), 129.8 (Pt-CR), 124.9 (m, Cipso), 122.3 (q, JC-F ) 322
Hz, OTf), 98.7 (m, CN), 26.1 (Pt-P-CH2), 21.8 (Pd-P-CH2), 19.5
(CH2), 18.8 (CH′2); 31P{1H} NMR (acetone-d6) δ 11.8 (s, JPt-P ) 3404
Hz), 2.7 (s, JPt-P ) 1774 Hz); 19F NMR (acetone-d6) δ -75. Anal.
Calcd for Pt2Pd2C140H116P8S4N4O12F12: C, 42.86; H, 4.19; N, 1.82; S,
4.16. Found: C, 42.95; H, 4.46; N, 1.78; S, 3.96; FAB LRMS, m/z
2933.0 (M - OTf)
cis-Pt(dppp)(4-benzonitrile)2 (5). A solution of n-BuLi (2.5 M,
hexanes, 1.77 mmol) was added Via syringe to a solution of 4-iodo-
benzonitrile (4.05 mg, 1.77 mmol) in 10 mL of Et2O at -78 °C under
argon. Platinum(II) dichloride (dppp) (300 mg, 0.44 mmol) was
immediately added in one portion at -78 °C. The cold bath was
removed, and the reaction mixture was allowed to warm to 25 ˚C on
its own and allowed to stir for 5 h at 25 °C followed by solvent removal
Via rotary evaporation at ambient temperature. The residue was
extracted with toluene (3 × 25 mL). The extracts were combined,
and the solvent was removed Via rotary evaporation. The residue was
dissolved in 4 mL of CH2Cl2. Crystallization was induced by addition
of diethyl ether and pentane resulting in yellow crystals (350 mg,
83%): mp 196-199 °C dec; IR (CCl4) 3077, 3061 (Ar), 2939 (CH2),
2212 (CN) cm-1; 1H NMR (CD2Cl2) δ 7.50-7.26 (m, 20H), 7.14 (m,
4H), 6.74 (m, 4H), 2.67 (bs, 4H), 1.88 (m, 2H); 13C{1H} NMR (CH2-
Cl2) δ 133.3 (Co), 130.5 (Cp), 128.5 (Cm), 131.7 (Pt-P-Cipso), 129.5
Cyclobis[[cis-Pt(dppp)(4-benzonitrile)2][cis-Pd2+(PEt3)22--
OSO2CF3]] (10). To a solution of monomer 5 (153 mg, 0.189 mmol)
in 8.6 mL acetone was added Pd(PEt3)2(OTf)2 4 (121 mg, 0.189 mmol)-
all at once at 25 °C and stirred for 1 h. The solvent volume was
decreased to 4 mL Via rotary evaporation. Crystallization was induced
by addition of diethyl ether and pentane, resulting in yellow crystals
(258 mg, 94%): mp 137-139 °C dec; IR (CCl4) 3057 (Ar), 2976,
2941 (CH2CH3), 2255 (CN), 1256, 1150, 1101, 1029 (OTf) cm-1; H
1
NMR (acetone-d6) δ 7.57-7.52 (m, 16H, o), 7.38-7.32 (m, 24H, m,
p), 7.21 (m, 8H, â), 6.77 (m, 8H, R) 2.91 (bs, 8H), 2.31-2.20 (m,
24H), 1.88 (m, 4H), 1.40-1.29 (m, 36H); 13C{1H} NMR (acetone-d6)
δ 134.1 (Pt-P-Co), 132.6 (Pt-P-Cipso), 131.1 (Pt-P-Cp), 129.1 (Pt-
2
(CR), 136.9 (Câ), 120.8 (Cipso), 172.4 ((Pt-Cipso′), JP-C ) 96.0 Hz),
P-Cm), 138.0 (Pt-Câ), 130.0 (Pt-CR), 122.7 (Cipso), 121.9 (q, JC-F )
104.1 (CN), 26.3 (Pt-P-CH2), 19.5 (CH2); 31P{1H} NMR (CD2Cl2) δ
0.69 (JPt-P ) 1740 Hz).
321 Hz, OTf), 102.6 (m, CN), 26.2 (m, Pt-P-CH2), 19.9 (bs, CH2),
17.3 (m, Pd-P-CH2CH3), 8.8 (bs, Pd-P-CH2CH3); 31P{1H} NMR
(acetone-d6) δ 51.8 (s), 2.9 (s, JPt-P ) 1763 Hz); 19F NMR (acetone-
d6) δ -75. Anal. Calcd for Pt2Pd2C110H128P8S4N4O12F12: C, 45.48;
H, 4.44; N, 1.93; S, 4.41. Found: C, 45.19; H, 4.45; N, 1.90; S, 4.25.
cis-Pt(dppp)(4-ethynylpyridine)2 (6). A solution of t-BuLi (1.7
M, hexanes, 1.97 mmol) was added Via syringe to a solution of
4-alkynylpyridine (202 mg, 1.97 mmol) in 80 mL of THF at -78 °C
under argon. Platinum(II) dichloride (dppp) (666 mg, 0.98 mmol) was
immediately added all at once at -78 °C. The cold bath was removed,
and the reaction mixture was allowed to warm to 25 °C on its own and
stirred for 5 h without light followed by solvent removal Via rotary
evaporation at ambient temperature. The residue was extracted with
benzene (4 × 40 mL). The extracts were combined, and the solvent
was removed Via rotary evaporation. The residue was dissolved in 4
mL of CH2Cl2. Crystallization was induced by addition of diethyl ether
and pentane resulting in white crystals (544 mg, 68%): mp 221-223
Cyclobis[[cis-Pt(dppp)(4-benzonitrile)2][cis-Pt2+(dppp)2--
OSO2CF3]] (7). To a solution of monomer 5 (0.0370 mmol) in 10
mL of CH2Cl2 was added Pt(dppp)(OTf)2 1 (33.5 mg, 0.0370 mmol)
all at once at 25 °C and stirred for 15 min. The solvent volume was
decreased to 1 mL Via rotary evaporation. Crystallization was induced
by addition of diethyl ether and pentane, resulting in light pink crystals
(57.2 mg, 90%): mp 210-213 °C dec; IR (CCl4) 3055 (Ar), 2976,
2928, 2865 (CH2), 2256 (CN), 1224, 1150, 1102, 1029 (OTf) cm-1
;
1H NMR (CD2Cl2) δ 7.30-7.18 (m, 80H), 7.00 (m, 8H), 6.25 (m, 8H),
2.97 (bs, 8H), 2.63 (m, 8H), 2.24 (m, 4H), 1.87 (m, 4H); 13C{1H} NMR
(CH2Cl2) δ 133.4 (Pt-P-Co), 131.2 (Pt-P-Cipso), 130.7 (Pt-P-Cp),
128.5 (Pt-P-Cm), 133.2 (Pt′-P-Cï), 133.1 (Pt′-P-Cp), 129.9 (Pt′-
2
P-Cm), 124.5 (Pt′-P-Cipso), 180.4 ((Pt′-Cipso′), JP-C ) 92.7 Hz),
137.3 (Pt-Câ), 129.8 (Pt-CR), 123.9 (Pt-Cipso), 121.4 (q, JC-F ) 321
Hz, OTf), 97.5 (CN), 26.1 (Pt-P-CH2), 21.7 (Pt′-P-CH2), 19.6
(CH2), 18.6 (CH′2); 31P{1H} NMR (CD2Cl2) δ -0.21 (s, JPt-P ) 1773
Hz), -12.2 (s, JPt-P ) 3349 Hz); 19F NMR (CD2Cl2) δ -79. Anal.
Calcd for Pt4C140H116P8S4N4O12F12‚CH2Cl2: C, 48.12; H, 3.49; N, 1.59;
S, 3.64. Found: C, 47.93; H, 3.61; N, 1.55; S, 3.75.
°C dec; IR (CCl4) 3057, 3037 (Ar), 2944, 2929 (CH2), 2121 (CC) cm-1
;
1H NMR (CD2Cl2) δ 8.20 (d, 4H, 3JHH ) 6.1 Hz), 7.75-7.68 (m, 8H),
7.43-7.36 (m, 12H), 6.62 (d, 4H, 3JHH ) 6.1 Hz), 2.56 (m, 4H), 2.04
(m, 2H); 13C{1H} NMR (CH2Cl2) δ 134.0 (Co), 131.4 (Cp), 129.0 (Cm),
131.2 (Pt-P-Cipso), 149.4 (CRpyr), 125.8 (Câpyr), 135.7 (Cipsopyr), 114.4
(q, CC-PtR, 2JP-C(cis) ) 21.1 Hz, 2JP-C(trans) ) 124 Hz), 104.1 (t, CC-
Cyclobis[[cis-Pt(dppp)(4-benzonitrile)2][cis-Pd2+(dppp)2--
OSO2CF3]] (8). To a solution of monomer 5 (44.0 mg 0.054 mmol)
in 10 mL of CH2Cl2 was added Pd(dppp)(OTf)2 2 (44.3 mg, 0.054
mmol) all at once at 25 °C, and the solution was stirred for 15 min.
The solvent volume was decreased to 3 mL Via rotary evaporation.
Crystallization was induced by addition of diethyl ether and pentane,
resulting in reddish brown crystals (85.0 mg, 96%): mp 169-173 °C
dec; IR (CCl4) 3057 (Ar), 2918 (CH2), 2249 (CN), 1276, 1152, 1101,
1029 (OTf) cm-1; 1H NMR (CD2Cl2) δ 7.64-7.25 (m, 80H), 7.20 (m,
8H), 6.42 (m, 8H), 2.88 (bs, 8H), 2.68 (bs, 8H), 2.30 (m, 4H), 1.90
(m, 4H); 13C{1H} NMR (CD2Cl2) δ 133.3 (Pt-P-Co), 131.1 (Pt-P-
Ptâ, JP-C ) 17.4 Hz) 26.3 (Pt-P-CH2), 19.5 (CH2); 31P{1H} NMR
2
(CD2Cl2) δ -3.1 (s, JPt-P ) 2185 Hz); FAB LRMS, m/z 812.2 (M +
H).10
Cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pt2+(dppp)2--
OSO2CF3]] (11). To a solution of monomer 6 (70.0 mg, .086 mmol)
in 7.2 mL of CH2Cl2 was added Pt(dppp)(OTf)2 1 (78.1 mg, 0.012
mmol) all at once at 25 °C, and the solution was stirred for 4 h. The
solvent volume was decreased to 4 mL Via rotary evaporation.
Crystallization was induced by addition of diethyl ether and pentane,
resulting in white crystals (141 mg, 95%): mp 211-213 °C dec; IR
(CCl4) 3051 (Ar), 2991, 2927, 2855 (CH2), 2114 (CC), 1224, 1156,
1103, 1029 (OTf) cm-1; UV-vis (CH2Cl2) λmax ) 318 nm, ꢀ ) 9.9 ×
Cipso), 130.6 (Pt-P-Cp), 128.5 (Pt-P-Cm), 133.2 (Pd-P-Cï), 133.1
(Pd-P-Cp), 129.9 (Pd-P-Cm), 125.2 (Pd-P-Cipso), 124.2 (m, Cipso),
137.2 (Pt-Câ), 129.8 (Pt-CR), 178.6 (q, Pt-Cipso, (2JP-C ) 99.4Hz)),
121.3 (q, JC-F ) 321 Hz, OTf), 98.9 (m, CN), 26.1 (Pt-P-CH2), 21.8
(Pd-P-CH2), 19.5 (CH2), 18.8 (CH′2); 31P{1H} NMR (CD2Cl2) δ 13.6-
(s), -0.29 (s, JPt-P ) 1765 Hz); 19F NMR (CD2Cl2) δ -79. Anal.
Calcd for Pt2Pd2C140H116P8S4N4O12F12: C, 51.62; H, 3.71; N, 1.72; S,
3.94. Found: C, 51.33; H, 3.85; N, 1.68; S, 3.94.
104 L cm-1 mol-1; H NMR (CD2Cl2) δ 8.20 (d, 8H, JHH ) 5.4 Hz),
1
3
3
7.70-7.20 (m, 80H), 6.28 (d, 8H, JHH ) 6.4 Hz), 3.2 (bs, 8H), 2.5
(bs, 8H), 2.10 (m, 8H); 13C{1H} NMR (CH2Cl2) δ 133.9 (Pt-P-Co),
131.0 (Pt-P-Cipso), 131.7 (Pt-P-Cp), 129.1 (Pt-P-Cm), 133.5 (Pt′-
P-Cï), 132.5 (Pt′-P-Cp), 129.7 (Pt′-P-Cm), 125.3 (Pt′-P-Cipso),
148.9 (CRpyr), 128.5 (Câpyr), 139.2 (Cipsopyr), 124.0 (q, JPt-C ) 122 Hz,
CC-PtR), 106.8 (t, 2JPt-C ) 16.7 Hz, (CC-Ptâ)), 121.8 (q, JC-F ) 321
Hz, OTf), 26.0 (Pt-P-CH2), 21.8 (Pt′-P-CH2), 20.6 (CH2), 18.2
(CH′2); 31P{1H} NMR (CD2Cl2) δ -3.0 (s, JPt-P ) 2204 Hz), -11.0
(s, JPt-P ) 3035 Hz); 19F NMR (CD2Cl2) δ -76. Anal. Calcd for
Pt4C140H120P8S4N4O12F12: C, 48.96; H, 3.52; N, 1.63. Found: C, 49.03;
H, 3.60; N, 1.65; FAB LRMS, m/z 1569.2 (M - 2OTf).10
Cyclobis[[cis-Pt(dppp)(4-benzonitrile)2][cis-Pt2+(PEt3)22--
OSO2CF3]] (9). To a solution of monomer 5 (151 mg, 0.186 mmol)
in 8.6 mL of acetone was added Pt(PEt3)2(OTf)2 3 (136 mg, 0.186
mmol) all at once at 25 °C, and the solution was stirred for 4 h. The
solvent volume was decreased to 4 mL Via rotary evaporation.
Crystallization was induced by addition of diethyl ether and pentane,
resulting in white crystals (262 mg, 91%): mp 195-197 °C dec; IR
(CCl4) 3044 (Ar), 2974, 2937 (CH2, CH3), 2259 (CN), 1260, 1146,
1101, 1029 (OTf) cm-1; 1H NMR (acetone-d6) δ 7.61-7.50 (m, 16H,
Cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pd2+(dppp)2--
OSO2CF3]] (12). To a solution of monomer 6 (78.2 mg, 0.096 mmol)

Pt-Pt and Pt-Pd Macrocyclic Tetranuclear Complexes
J. Am. Chem. Soc., Vol. 119, No. 10, 1997 2533
in 6.7 mL of CH2Cl2 was added Pd(dppp)(OTf)2 2 (78.7 mg, .014 mmol)
all at once at 25 °C, and the solution was stirred for 1 h. The solvent
volume was decreased to 4 mL Via rotary evaporation. Crystallization
was induced by addition of diethyl ether and pentane, resulting in yellow
crystals (156 mg, 99%): mp 260-263 °C dec; IR (CCl4) 3061 (Ar),
2958, 2928, 2921 (CH2), 2113 (CC), 1223, 1154, 1101, 1028 (OTf)
Cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pd2+(PEt3)22--
OSO2CF3]]‚2 AgOTf Complex (15). To a solution square 14 (39.4
mg, 0.014 mmol) dissolved in 750 µL of acetone-d6 in a 7 mm NMR
tube at 25 °C was added 2 equiv (7.0 mg, 0.028 mmol) of AgOTf in
one portion, and then the reaction mixture was shaken. The solvent
was removed under a stream of nitrogen at room temperature followed
by solvent removal in vacuo (46.0 mg, 99%): mp 179-182 °C dec;
IR (CCl4) 3059 (Ar), 2966, 2939 (CH2, CH3), 2091 (CC), 1257, 1151,
1027 (OTf) cm-1; UV-vis (CH2Cl2) λmax ) 318 nm, ꢀ ) 8.7 × 104 L
1
3
cm-1; H NMR (CD2Cl2) δ 8.19 (d, 8H, JHH ) 6.3 Hz), 7.70-7.20
3
(m, 80H), 6.25 (d, 8H, JHH ) 5.9 Hz), 3.08 (bs, 8H), 2.51 (bs, 8H),
2.05 (m, 8H); 13C{1H} NMR (CH2Cl2) δ 133.9 (Pt-P-Co), 131.1 (Pt-
P-Cipso), 131.7 (Pt-P-Cp), 129.0 (Pt-P-Cm), 133.4 (Pd-P-Cï),
132.5 (Pd-P-Cp) ,129.8 (Pd-P-Cm), 126.0 (Pd-P-Cipso), 148.9
(CRpyr), 128.1 (Câpyr), 138.7 (Cipsopyr), 122.6 (q, CC-PtR, JP-C ) 124
1
3
cm-1 mol-1; H NMR (acetone-d6) δ 8.79 (d, 8H, JHH ) 4.7 Hz),
3
7.80-7.66 (o, m, 16H), 7.49-7.38 (m, p, m, 24H), 6.82 (d, 8H, JHH
) 6.0 Hz), 3.03 (bs, 8H), 2.20-2.10 (obscured, 8H), 2.00-1.90 (m,
24H), 1.40-1.27 (m, 36H); 13C{1H} NMR (acetone-d6) δ 134.3 (Pt-
P-Co), 129.8 (Pt-P-Cipso), 132.4 (Pt-P-Cp), 129.7 (Pt-P-Cm),
150.4 (CRpyr), 129.4 (Câpyr), 137.0 (Cipsopyr), 110.1 (m, CC-Ptâ), 122.1
(q, JC-F ) 320 Hz, OTf), 23.9 (m, Pt-P-CH2), 19.7 (bs, CH2), 16.6
(m, Pd-P-CH2CH3), 8.4 (bs, Pd-P-CH2CH3); 31P{1H} NMR (acetone-
d6) δ 31.8 (s), -4.6 (s, JPt-P ) 2341 Hz); 19F NMR (acetone-d6) δ
-75.
2
Hz), 106.8 (t, CC-Ptâ, JP-C ) 15.9 Hz), 121.7 (q, JC-F ) 321 Hz,
OTf), 25.6 (m, Pt-P-CH2), 19.7 (bs, CH2), 16.8 (m, Pt-P-CH2CH3),
8.6 (bs, Pt-P-CH2CH3); 31P{1H} NMR (CD2Cl2) δ -3.1 (s, JPt-P
)
2202 Hz), 10.3 (s); 19F NMR (CD2Cl2) δ -76. Anal. Calcd for
Pt2Pd2C140H120P8S4N4O12F12‚CH2Cl2: C, 50.67; H, 3.68; N, 1.68; S,
3.84. Found: C, 50.84; H, 3.81; N, 1.80; S, 3.96.
Cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pt2+(PEt3)22--
OSO2CF3]] (13). To a solution of monomer 6 (40.3 mg, 0.050 mmol)
in 2.7 mL of acetone was added Pt(PEt3)2(OTf)2 3 (36.2 mg, 0.050
mmol) all at once at 25 °C, and the solution was stirred for 4 h .
Crystallization was induced by addition of diethyl ether and pentane,
resulting in white crystals (72 mg, 94%): mp 321-324 °C dec; IR
(CCl4) 3056 (Ar), 2971, 2937 (CH2CH3) 2944, 2929 (CH2, CH3), 2116
Cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pt2+(dppp)2--
OSO2CF3]]‚2AgOTf Complex (16). To a solution of square 11 in
750 µL CD2Cl2 in a 7 mm NMR tube (32.0 mg, 0.014 mmol) was
added 2 equiv (4.8 mg, 0.028 mmol) of AgOTf in one portion at 25
°C, and then the reaction mixture was shaken. The solvent was
removed under a stream of nitrogen at room temperature followed by
solvent removal in vacuo (36.3 mg, 99%): mp 188-191 °C dec; IR
(CCl4) 3057, 3096 (Ar), 2926 (CH2), 2081 (CC), 1256, 1156, 1103,
1027 (OTf) cm-1; UV-vis (CH2Cl2) λmax ) 314 nm, ꢀ ) 8.4 × 104 L
cm-1 mol-1; 1H NMR (CD2Cl2) δ 8.26 (d, 8H, 3JHH ) 5.1 Hz), 7.70-
1
(CC), 1223, 1161, 1106, 1029 (OTf) cm-1; H NMR (acetone-d6) δ
3
8.66 (d, 8H, JHH ) 5.6 Hz), 7.70-7.63 (m, 16H, o),7.43-7.37 (m,
3
24H, m, p), 6.75 (d, 8H, JHH ) 6.0 Hz), 2.91 (bs, 8H), 2.10-2.00
(obscured, m, 8H), 2.00-1.85 (m, 24H), 1.40-1.24 (m, 36H); 13C-
{1H} NMR (acetone-d6) δ 134.4 (Pt-P-Co), 131.3 (Pt-P-Cipso), 131.9
(Pt-P-Cp), 129.3 (Pt-P-Cm), 150.0 (CRpyr), 129.2 (Câpyr), 141.0
3
7.20 (m, 80H), 6.27 (d, 8H, JHH ) 6.0 Hz), 3.19 (bs, 8H), 2.64 (bs,
8H), 2.12 (m, 8H); 13C{1H} NMR (CD2Cl2) δ 133.5 (Pt-P-Co),
129.0-130.0 (Pt-P-Cipso), 132.4 (Pt-P-Cp), 129.6 (Pt-P-Cm), 133.7
(Pt′-P-Cï), 132.8 (Pt′-P-Cp), 129.8 (Pt′-P-Cm), 125.0 (Pt′-P-
2
(Cipsopyr), 131.8-131.2 (obscured, q, JP-C(cis) ) 20.5 Hz, CC-PtR),
2
108.0 (t, JP-C ) 17.6 Hz, CC-Ptâ), 121.8 (q, JC-F ) 322 Hz, OTf),
24.8 (m, Pt-P-CH2), 20.1 (bs, CH2), 15.6 (m, Pt-P-CH2CH3), 8.2
(bs, Pt-P-CH2CH3); 31P{1H} NMR (acetone-d6) δ 3.8 (s, JPt-P ) 3067
Hz), -2.3 (s, JPt-P ) 2174 Hz); 19F NMR (acetone-d6) δ -75. Anal.
Calcd for Pt4C110H128P8S4N4O12F12‚2OC(CH3)2: C, 43.56; H, 4.30; N,
1.78; S, 4.01. Found: C, 43.64; H, 4.27; N, 1.87; S, 4.17.
Cipso), 149.4 (CRpyr), 129.3 (Câpyr), 135.4 (Cipsopyr), 125.7-124.6
(obscured, q, CC-PtR), 121.4 (q, JC-F ) 318 Hz, OTf), 26.3 (Pt-P-
CH2), 21.8 (Pt′-P-CH2), 20.6 (CH2), 18.2 (CH′2); 31P{1H} NMR (CD2-
Cl2) δ -6.2 (s, JPt-P ) 2355 Hz), -11.1 (s, JPt-P ) 3057 Hz); 19F
NMR (CD2Cl2) δ -75; FAB LRMS, m/z 3799.9 (M - OTf), m/z 1824.0
(M - 2OTf).
Cyclobis[[cis-Pt(dppp)(4-ethynylpyridine)2][cis-Pd2+(PEt3)22--
OSO2CF3]] (14). To a solution of monomer 6 (40.3 mg, 0.050 mmol)
in 3.0 mL acetone was added Pd(PEt3)2(OTf)2 4 (31.8 mg, 0.050 mmol)-
all at once at 25 °C, and the solution was stirred for 1 h. Crystallization
was induced by addition of pentane, resulting in yellow crystals (70
mg, 97%): mp 208-211 °C dec; IR (CCl4) 3054 (Ar), 2976, 2937
(CH2, CH3), 2124 (CC), 1223, 1149, 1105, 1028 (OTf) cm-1; UV-vis
Acknowledgment. Dedicated to Professor G. J. Karabatsos
on the occasion of his 65th birthday. Financial support by the
NSF (CHE-9529093, CHE-9002690), University of Utah In-
stitutional Funds Committee and the generous loan of platinum-
(II) dichloride from Johnson-Matthey are gratefully acknowl-
edged as is the A. von Humboldt Foundation and the hospitality
of Professor M. Regitz during the summer of 1996. The authors
also thank Professor Robin D. Rogers at the University of
Alabama for X-ray structure determination.
(CH2Cl2) λmax ) 324 nm, ꢀ ) 9.0 × 104 L cm-1 mol-1
;
1H NMR
3
(acetone-d6) δ 8.65 (d, 8H, JHH ) 4.7 Hz), 7.70-7.63 (o, m, 16H),
7.44-7.37 (m, p, m, 24H), 6.70 (c, d, 8H, 3JHH ) 6.2 Hz), 2.87 (c, bs,
8H), 2.10-2.00 (obscured, 8H), 2.00-1.85 (m, 24H), 1.40-1.27 (m,
36H); 13C{1H} NMR (acetone-d6) δ 134.4 (Pt-P-Co), 131.4 (Pt-P-
Supporting Information Available: Tables of positional
parameters and esds, anistropic displacement parameters, and
an extended list of bond lengths and bond angles for compound
14 (11 pages). See any current masthead page for ordering and
internet access instructions.
C
ipso), 131.8 (Pt-P-Cp), 129.3 (Pt-P-Cm), 149.9 (CRpyr), 128.8 (Câpyr),
140.5 (Cipsopyr), 107.7 (t, 2JP-C ) 16.9 Hz, CC-Ptâ), 122.4 (q, JC-F
)
322 Hz, OTf), 24.8 (m, Pt-P-CH2), 20.1 (bs, CH2), 16.4 (m, Pd-
P-CH2CH3), 8.4 (bs, Pd-P-CH2CH3); 31P{1H} NMR (acetone-d6) δ
31.6 (s), -1.9 (s, JPt-P ) 2175 Hz); 19F NMR (acetone-d6) δ -75.
Anal. Calcd for Pt2Pd2C110H128P8S4N4O12F12: C, 45.48; H, 4.44; N,
1.93; S, 4.41. Found: C, 45.59; H, 4.53; N, 1.91; S, 4.28.
JA9635286