Selective metallacyclization and crystallographic characterization of structurally related platina-annulenes

Article abstract of DOI:10.1021/om0490987

The synthesis and characterization of seven platina-annulenes and their dehydrobenzo-annulene (DBA) analogues are reported. Assembly of these macrocycles is accomplished via Sn transmetalation or amine-mediated oxidative addition with stoichiometric PtCl₂(PR₃)₂, containing different phosphine ligands, and CuI. In contrast to previously reported DBA cyclization methodology, incorporation of a doubly σ-bonded Pt complex into the annulene backbone resulted in selective metallacyclization dependent on competing factors of ligand identity, PtCl₂(PR ₃)₂ isomer, and reaction conditions. Sn transmetalation conditions provided the most selective metallacyclization control and prevented PtCl₂(PR₃)₂ isomerization during cyclization.

Full text of DOI:10.1021/om0490987

Organometallics 2005, 24, 1161-1172
1161
Selective Metallacyclization and Crystallographic
Characterization of Structurally Related
Platina-annulenes
Charles A. Johnson, II and Michael M. Haley*
Department of Chemistry and Materials Science Institute, University of Oregon,
Eugene, Oregon 97403-1253
Elisabeth Rather, Fusen Han, and Timothy J. R. Weakley
X-ray Crystallography Laboratory, Department of Chemistry, University of Oregon,
Eugene, Oregon 97403-1253
Received November 20, 2004
The synthesis and characterization of seven platina-annulenes and their dehydrobenzo-
annulene (DBA) analogues are reported. Assembly of these macrocycles is accomplished via
Sn transmetalation or amine-mediated oxidative addition with stoichiometric PtCl2(PR3)2,
containing different phosphine ligands, and CuI. In contrast to previously reported DBA
cyclization methodology, incorporation of a doubly σ-bonded Pt complex into the annulene
backbone resulted in selective metallacyclization dependent on competing factors of ligand
identity, PtCl2(PR3)2 isomer, and reaction conditions. Sn transmetalation conditions provided
the most selective metallacyclization control and prevented PtCl2(PR3)2 isomerization during
cyclization.
Introduction
to be only slightly less efficient than a benzene moiety,7
which bodes well for materials applications for this class
of metallamacromolecules.
Highly conjugated, organometallic “rigid-rod” oligo-
mers and polymers continue to be investigated for
potential use as advanced materials with desirable
electronic and optical properties.1 In particular, Pt
σ-acetylide oligomers and polymers have received con-
siderable attention recently in this regard from both
applied and fundamental standpoints. Introduction of
Pt into a conjugated system allows triplet-state emis-
sion,2 and as a result, Pt-alkynyl oligomers and poly-
mers are ideal for use in organic photocells,3 light-
emitting diodes,2 and models for triplet manifold studies
of conjugated polymers.4 From a more fundamental
view, the delocalization through the Pt center in such
mixed metal-organic hybrids has been studied by a
number of groups.5,6 This was very recently quantified
in a Pt-alkynyl charge-transfer system by Marder et al.
As part of our continuing efforts to explore and
expand the potential materials uses of dehydrobenzo-
annulenes (DBAs),8 we have manipulated the optoelec-
tronic properties of the macrocycles by inclusion of
electron donor and/or acceptor groups9 as well as by
incorporation of transition metals into the π-conjugated
systems.6b The potential for induced polarization of the
conjugated network via π-back-bonding as well as a
(5) Pt-acetylide oligomers/polymers, inter alia: (a) Sonogashira, K.;
Fujikura, Y.; Yatake, T.; Toyoshima, N.; Takahashi, S.; Hagihara, N.
J. Organomet. Chem. 1978, 145, 101-108. (b) Furlani, A.; Licoccia,
S.; Russo, M. V.; Chiesi Villa, A.; Guastini, C. J. Chem. Soc., Dalton
Trans. 1984, 2197-2206. (c) Harriman, A.; Hissler, M.; Ziessel, R.;
De Cian, A.; Fisher, J. J. Chem. Soc., Dalton Trans. 1995, 4067-4080.
(d) Onitsuka, K.; Fujimoto, M.; Ohshiro, N.; Takahashi, S. Angew.
Chem., Int. Ed. 1999, 38, 689-692. (e) Back, S.; Albrecht, M.; Spek,
A. L.; Rheinwald, G.; Land, H.; van Koten, G. Organometallics 2001,
20, 1024-1027. (f) Wong, W.; Lu, G.; Choi, K.; Shi, J. Macromolecules
2002, 35, 3506-3516. (g) Onitsuka, K.; Yabe, K.; Ohshiro, N.; Shimizu,
A.; Okumura, R.; Takei, F.; Takahashi, S. Macromolecules 2004, 37,
8204-8211.
(6) Pt-acetylide macrocycles, inter alia: (a) Faust, R.; Diederich, F.;
Gramlich, V.; Seiler, P. Chem. Eur. J. 1995, 1, 111-117. (b) Pak, J.
J.; Weakley, T. J. R.; Haley, M. M. Organometallics 1997, 16, 4505-
4507. (c) Al Quaisi, S. M.; Galat, K. J.; Chai, M.; Ray, D. G., III; Rinaldi,
P. L.; Tessier, C. A.; Youngs, W. J. J. Am. Chem. Soc. 1998, 120,
12149-12150. (d) Bosch, E.; Barnes, C. L. Organometallics 2000, 19,
5522-5524. (e) Leininger, S.; Olenyuk, B.; Stang, P. J. Chem. Rev.
2000, 100, 853-908. (f) Siemsen, P.; Gubler, U.; Bosshard, C.; Gu¨nter,
P.; Diederich, F. Chem. Eur. J. 2001, 7, 1333-1341. (g) Campbell, K.;
McDonald, R.; Ferguson, M. J.; Tykwinski, R. R. Organometallics 2003,
22, 1353-1355. (h) Kryschenko, Y. K.; Seidel, S. R.; Arif, A. M.; Stang,
P. J. J. Am. Chem. Soc. 2003, 125, 5193-5198.
* To whom correspondence should be addressed. E-mail: haley@
uoregon.edu.
(1) (a) Nguyen, P.; Gomez-Elipe, P.; Manners, I. Chem. Rev. 1999,
99, 1515-1548. (b) Cooper, T. M. In Encyclopedia of Nanoscience and
Nanotechnology; Nalwa, H. S., Ed.; American Scientific Publishers:
Stevenson Ranch, CA, 2004; Vol. 10.
(2) (a) Wilson, J. S.; Dhoot, A. S.; Seeley, A. J. A. B.; Khan, M. S.;
Ko¨hler, A.; Friend, R. H. Nature 2001, 413, 828-831. (b) Ko¨hler, A.;
Wilson, J. S.; Friend, R. H. Adv. Mater. 2002, 14, 701-707.
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10.1021/om0490987 CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/11/2005

1162 Organometallics, Vol. 24, No. 6, 2005
Johnson et al.
Scheme 1
Scheme 2
defined directionality usually absent in most organic
DBAs are benefits of metal complex inclusion. Addition-
ally, the metal center can serve as an efficient means
to introduce stereochemistry via ligand exchange as
shown by Tykwinski et al.10
We recently reported selectivity for DBA ring forma-
tion based on reaction conditions.11 The geometry of the
organometallic intermediate in the final homocoupling
reaction was shown to directly affect macrocycle con-
figuration (Scheme 1). Cu-mediated cyclization condi-
tions, which favor a more trans-like intermediate,
provided excellent selectivity for polyyne cyclization
across the meta-fused alkynes to produce a bis[15]-
annulene. Conversely, the bis[14]annulene was selec-
tively obtained via the cyclization of the ortho-fused
alkynes of the same precursor using a cis-bidendate-
ligated Pd catalyst.
The previous results suggest a unique opportunity to
generate novel organometallic structures and explore
the extent of selectivity via incorporation of oriented
metal complexes into the annulene backbone (Scheme
2). Replacement of the cyclization (homocoupling) cata-
lyst with several isomeric Pt metal complexes should
favor incorporation of a specific Pt complex isomer into
a structure with a similar transition state. Specifically,
trans-metal complex incorporation should occur with
meta-substituted R,ω-polyynes and cis-metal complex
insertion would be favored for ortho-substituted R,ω-
polyynes. We report herein the synthesis and charac-
terization of seven new platina-annulenes along with
their purely hydrocarbon DBA analogues. In addition,
we discuss the electronic delocalization in both sets of
macrocycles by comparison of their UV-vis spectra.
Results and Discussion
Synthesis of Platina-annulenes. Unlike the chem-
istry depicted in Scheme 2, we began the synthetic
investigation of Pt complex incorporation with R,ω-
polyynes that would furnish a single metalla-annulene
to confirm feasibility of selective metallacyclization.
Production of all seven platina-annulenes originated
with known iodoarene 1.12 Sonogashira cross-coupling13
of 1 with trimethylsilylacetylene (TMSA) afforded the
differentially silylated diethynylarene 2 in 88% yield
(Scheme 3). Treatment of 2 with mild base selectively
removed the more labile trimethylsilyl (TMS) group in
the presence of the triisopropylsilyl (TIPS) protecting
group to afford the free acetylene intermediate.14 With-
out further purification, the diyne was cross-coupled
with 1,3-diiodobenzene to produce the TIPS-protected
R,ω-polyyne 3 in 56% yield. Treatment of 3 with excess
Bu4NF was followed by reaction with Me3SnNMe2,
replacing the ethynyl hydrogens with more reactive Me3-
Sn groups.15 Addition of stoichiometric trans-PtCl2-
(PEt3)3 in the presence of catalytic CuI16 resulted in
transmetalation to form platina-annulene 4 as a yellow
solid in 37% yield. [15]Annulene 5 was obtained in 76%
yield using Glaser homocoupling conditions17 after
treatment of 3 with Bu4NF.
1
Both 4 and 5 are easily distinguished by H NMR
spectroscopy due to the enhanced downfield shift of the
intraannular benzene proton from 7.74 ppm to 8.70 and
8.69 ppm, respectively.11 An increased anisotropic
(12) Wan, W. B.; Haley, M. M. J. Org. Chem. 2001, 66, 3893-3901.
(13) (a) Marsden, J. A.; Haley, M. M. In Metal-Catalyzed Cross-
Coupling Reactions, 2nd ed.; de Meijere, A., Diederich, F., Eds.; Wiley-
VCH: Weinheim, 2004; pp 317-394. (b) Sonogashira, K. In Metal-
Catalyzed Cross-Coupling Reactions; Stang, P. J., Diederich, F., Eds.;
VCH: Weinheim, 1997; pp 203-229.
(9) (a) Pak, J. J.; Weakley, T. J. R.; Haley, M. M. J. Am. Chem. Soc.
1999, 121, 8182-8192. (b) Sarkar, A.; Pak, J. J.; Rayfield, G. W.; Haley,
M. M. J. Mater. Chem. 2001, 11, 2943-2945. (c) Marsden, J. A.; Miller,
J. J.; Shirtcliff, L. D.; Haley, M. M. J. Am. Chem. Soc. 2005, 127, 2464-
2476.
(10) (a) Campbell, K.; McDonald, R.; Ferguson, M. J.; Tykwinski,
R. R. J. Organomet. Chem. 2003, 683, 379-387. (b) Campbell, K.;
Johnson, C. A.; McDonald, R.; Ferguson, M. J.; Haley, M. M.;
Tykwinski, R. R. Angew. Chem., Int. Ed. 2004, 43, 5967-5971.
(11) Marsden, J. A.; Miller, J. J.; Haley, M. M. Angew. Chem., Int.
Ed. 2004, 43, 1694-1697.
(14) Protecting Groups in Organic Synthesis, 3rd ed.; Greene, T. W.,
Wuts, P. G. M., Eds.; Wiley-VCH: New York, 1999; pp 654-657.
(15) (a) Jones, K.; Lappert, M. F. J. Chem. Soc. 1965, 1944-1951.
(b) Jones, K.; Lappert, M. F. J. Organomet. Chem. 1965, 3, 295-307.
(c) Nast, R.; Grouhi, H. J. Organomet. Chem. 1980, 186, 207-212.
(16) Khan, M. S.; Davies, S. J.; Kakkar, A. K.; Schwartz, D.; Lin,
B.; Johnson, B. F. G.; Lewis, J. J. Organomet. Chem. 1992, 424, 87-
97.
(17) Siemsen, P.; Livingston, R. C.; Diederich, F. Angew. Chem., Int.
Ed. 2000, 39, 2632-2657, and references therein.

Structurally Related Platina-annulenes
Organometallics, Vol. 24, No. 6, 2005 1163
Figure 1. (a) ORTEP of platina-annulene 4; ellipsoids drawn at the 50% probability level. Selected bond lengths (Å) and
angles (deg): Pt-P1 2.291(5), Pt-C1 2.001(15), C1-C2 1.188(19), C9-C10 1.136(18), P1-Pt-P2 172.4(3), C1′-Pt-C1
170.7(8), Pt-C1-C2 169.8(14), C1-C2-C3 168.8(16), C8-C9-C10 173.0(2), C9-C10-C11 178.1(18). (b) View of 4 down
[1 0 0] showing nonplanarity and phenyl ring twisting.
Scheme 3
deshielding effect of the ethynyl groups σ-bonded to the
Pt complex is responsible for the significant downfield
shift. The 31P NMR coupling constant (JP-Pt) of 4 (2328
Hz) is consistent with trans-Pt-bis(σ-acetylide) com-
plexes containing PEt3 ligands.5f,g,6a,f,18a
To generate platina-annulene 7 and parent [14]-
annulene 11, an ortho-substituted isomer of 3 was
required. Cross-coupling of diyne 2 to 1,2-diiodobenzene
via Sonogashira conditions afforded R,ω-polyyne 6 in
95% yield (Scheme 4). Initial attempts at obtaining 7
containing a cis-Pt complex with PEt3 ligands produced
two surprising yet undesirable results. The Sn trans-
metalation conditions successfully used to generate 4
gave a single discreet product in low yield along with
copious amounts of oligomeric material. The NMR
spectrum of the product gave a 2:1 phosphine ligand to
tert-butyl proton integration, which was confirmed by
single-crystal X-ray diffraction to be bis-Pt-polyyne 8
(Figure 2). In place of the desired second σ-acetylide
ligand, both Pt centers of 8 contain iodine, which most
certainly originated from the slight excess of CuI.
Interestingly, the phosphines on the Pt center have
isomerized from cis to trans, likely so as to incorporate
the large iodine atom.
Equally frustrating, the amine-mediated conditions
successfully used to generate similar platina-acetylides
afforded bis-Pt dimer 9 only.18 Although the 1:1 phos-
phine ligand to tert-butyl proton ratio in the NMR
spectrum was suggestive of monocycle 7, mass spec-
trometry and X-ray diffraction correctly elucidated the
dimeric structure of 9. The X-ray structure displayed
again an unexpected trans-phosphine geometry about
the Pt center, as well as an anti-relationship between
the two central phenyl rings that likely originated from
Crystals of platina-annulene 4 suitable for X-ray
diffraction were obtained by slow diffusion of hexanes
into a concentrated THF solution. The ORTEP plot
confirms retention of trans-geometry for the square
planar Pt complex that is doubly σ-bonded to the
polyyne backbone (Figure 1). Incorporation of the Pt
complex into the annulene backbone results in a distor-
tion from linearity of the σ-bonded ethynyl linkages to
the Pt (C1 10.2°, C2 11.2°). The increased strain is also
reflected around the Pt center (C1-Pt-C1i 170.7°).
Smaller degrees of distortion (C9 7.0°, C10 1.9°) are also
observed on the monoyne sides. Despite bond angle
distortion, Pt-C and Pt-P bond lengths are consistent
with other observed Pt-σ-acetylides.5,6,8,9,16 Similar to
our previously synthesized metalla-annulenes,6b,19
a
distinct nonplanarity of the hydrocarbon ligand is
observed. The planes of all three phenyl rings are bent
with respect to each other as well as twisted.
(18) (a) Cross, R. J.; Davison, M. F. J. Chem. Soc., Dalton Trans.
1986, 1987-1992. (b) Sonogashira, K.; Yatake, T.; Tohda, Y.; Taka-
hashi, S.; Hagihara, N. J. Chem. Soc., Chem. Commun. 1977, 291-
292.
(19) Pak, J. J.; Darwish, O. S.; Weakley, T. J. R.; Haley, M. M. J.
Organomet. Chem. 2003, 683, 430-434.

1164 Organometallics, Vol. 24, No. 6, 2005
Johnson et al.
Scheme 4
sterics (Figure 3). Analysis of the sp-carbon bond angles
showed decreased distortion (0.7-4.6°) in the ethynyl
groups compared to 4 and indicated a potential ther-
modynamic preference over similarly strained 7. Even
with high dilution, the required reaction temperature
of 50 °C provided sufficient thermal energy for inter-
molecular cyclization to effectively compete and produce
a structure with less acetylide linkage distortion and
thus substantially reduced ring strain.
Although intriguing, the cis to trans isomerization of
the Pt fragments in 8 and 9 is not surprising, as trans
bis-acetylides have been shown to be thermodynamically
favored over cis. CuI has also been suggested to facili-
tate isomerization via a reversible ethynyl transfer
between Pt and Cu.18 Dimerization or substitution of
both ethynyl groups with different Pt complexes is likely
favored thermodynamically over cyclization of the
strained polyyne 6 due to acetylide linkage distortion
and unfavorable entropy associated with steric and
torsional interactions from the close proximity of ortho-
substituted acetylide linkages required for cyclization.
To limit the extent of phosphine isomerization and
produce the desired cis-platina[15]annulene, we ex-
plored use of bulkier ligands, such as PPh3, as well as
bidentate phosphine ligands, such as dppe. Scheme 5
delineates the successful production of platina-annulene
10 with a cis-Pt dppe-complex via Sn transmetalation
conditions in 52% yield. Synthesis of 10 required several
attempts due to the poor solubility of PtCl2(dppe).20
Optimized conditions for 10 required use of a 1:1 THF/
CH2Cl2 solvent system and increased reaction time from
Figure 3. ORTEP of bis-Pt dimer 9; ellipsoids drawn at
the 50% probability level. The phosphine Et groups have
been removed for clarity. Selected bond lengths (Å) and
angles (deg): Pt-P1 2.280(2), Pt-C1 1.988(8), C1-C2
1.213(9), C9-C10 1.177(9), P1-Pt-P2 176.8(11), C26-Pt-
C1 176.5(3), Pt-C1-C2 174.5(7), C1-C2-C3 175.4(8), C8-
C9-C10 179.3(9), C9-C10-C11 177.6(8).
Figure 2. ORTEP of bis-Pt polyyne 8; ellipsoids drawn
at the 50% probability level. Selected bond lengths (Å) and
angles (deg): Pt-I 2.655(2), Pt-P1 2.310(8), Pt-C1 1. 88-
(2), C1-C2 1.31(3), C9-C10 1.170(3), P1-Pt-P2 175.4-
(3), I-Pt-C1 177.0(7), Pt-C1-C2 177.0(2), C1-C2-C3
177.0(3), C8-C9-C10 177.0(3), C9-C10-C11 177.0(3).

Structurally Related Platina-annulenes
Organometallics, Vol. 24, No. 6, 2005 1165
Scheme 5
12 to 72 h. Complex 10, isolated as a fine, colorless solid,
displayed a characteristic cis JP-Pt value of 2265 Hz.10,18
Application of Glaser homocoupling conditions to 6 after
removal of the TIPS groups afforded [14]annulene 11
as an orange solid in 86% yield.
which results from differential anisotropy due to phenyl
ring orientation, as well as the presumed trans-orienta-
tion of the Pt center based on the large JP-Pt value (2617
Hz). Semiempirical geometry optimization displays a
near planar structure for 13 with maximum acetylide
ligand distortion of 10° for the ethynyl groups bonded
to the Pt and 8° for the all-carbon ethynyl side.22
Synthesis of Bisplatina-annulenes. Successful
synthesis of 4, 10, 12, and 13 allowed application of the
experimentally determined selectivity principles to an
R,ω-polyyne precursor with the potential to form two
cis- or trans-Pt-acetylide complexes based on differential
acetylide ligand fusion (Scheme 2). The resultant com-
pound, a bisplatina-annulene, consists of two Pt com-
plexes with phenyl-acetylide ligands in either an ortho-
or meta-relationship on a central benzene ring. Synthe-
sis began with deprotection of diethynyl arene 2 and
subsequent Pd cross-coupling to 1,2,4,5-tetraiodoben-
zene to afford 14 (78%) (Scheme 6). Bisplatina-annulene
15 (21%), containing two trans-Pt complexes with PEt3
ligands, was successfully produced via Bu4NF depro-
tection and amine-mediated metallacyclization of 14.
Compared to monocycle 4, the intraannular protons of
In contrast to the Pt(PEt3)2-containing complexes, use
of PPh3 as ligand resulted in Pt complex isomerization
as well as retention (Scheme 5). Application of Sn
transmetalation conditions to 6 afforded the cis-platina-
annulene 12 in 11% yield. Unexpectedly, amine-medi-
ated metallacyclization produced the trans isomer 13
in slightly better yield (21%). In addition to differences
in the aromatic region of the 1H NMR spectra, the JP-Pt
value was the most distinguishing analytical difference
between 12 and 13. Cycle 13 displayed a large JP-Pt
value of 2617 Hz, indicative of trans-Pt acetylide
complexes with PPh3 ligands, while 12 showed a char-
acteristic cis-value of 2333 Hz.10,18 Temperature and
ligand identity appear to be key factors in isolation of
stereoisomers 12 and 13. In contrast to PEt3, the steric
bulk of PPh3 likely limits access for Cu-mediated
isomerization. Likewise, elevated temperature provides
increased thermal energy that favors rearrangement to
the more stable trans-Pt configuration. The dimerization
of 6 to 9 is also supported by these conclusions.
In contrast to the planar 11,21 the crystal structures
of 10 (Figure 4) and 12 (Figure 5) show that metalla-
cyclization results in a nonplanar, saddle-shaped struc-
ture, which is the result of the cis-orientation of
acetylide ligands and ortho-substitution of the central
benzene ring. The distortions of ethynyl groups σ-bond-
ed to the Pt center (10: C1 7.0°, C2 7.2°; 12: C1 4.7°,
C2 5.1°) are reduced compared to 4.
Attempts to date have not yielded crystals of 13
suitable for X-ray diffraction; however, spectroscopic
data highly suggest a planar trans-platina-annulene
monocycle similar to 4. This interpretation is supported
by marked 1H NMR differences from saddle-like 12,
(20) PtCl2(dppe) was synthesized in 2 steps from PtCl4. See: (a)
Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-428.
(b) Anderson, G. K.; Clark, H. C.; Davies, J. A. Inorg. Chem. 1981, 20,
3607-3611.
(21) The planarity of 5 and 11 is assumed based on X-ray crystal
structures of two closely related annulenes; see: (a) Baldwin, K. P.;
Matzger, A. J.; Scheiman, D. A.; Tessier, C. A.; Vollhardt, K. P. C.;
Youngs, W. J. Synlett 1995, 1215-1218. (b) Tobe, Y.; Kishi, J.; Ohki,
I.; Sonoda, M. J. Org. Chem. 2003, 68, 3330-3332.
(22) Modeled with Spartan Version 5.1.3 (MM3 or AM1 calculations)
on a Silicon Graphics Octane workstation.
Figure 4. ORTEP of platina-annulene 10; ellipsoids
drawn at the 50% probability level. Selected bond lengths
(Å) and angles (deg): Pt-P1 2.270(4), Pt-C1 1.938(14),
C1-C2 1.262(17), C9-C10 1.153(18), P1-Pt-P2 85.8(15),
C26-Pt-C1 87.6(6), Pt-C1-C2 173.0(14), C1-C2-C3
172.8(17), C8-C9-C10 177.4(19), C9-C10-C11 176.7(19).

1166 Organometallics, Vol. 24, No. 6, 2005
Johnson et al.
dimerization or extended linear structures, as the less
strained trans-bisplatina-annulene can originate from
the same precursor. On the basis of successful synthesis
of 10, PtCl2(dppe) was substituted for cis-PtCl2(PEt3)2
in an attempt to isolate bisplatina-annulene 17, con-
taining a cis-Pt center with ortho-fused acetylide ligands
(Scheme 7). Application of both metallacyclization meth-
ods surprisingly provided bisplatina-annulene 18, con-
taining two cis-Pt complexes, as the major product in
20% and 13% yields. Cycle 18 displayed the most
significant intraannular proton downfield shift (9.19
ppm) of all meta-fused platina-annulenes. The cis-metal
complex resulted in closer proximity of acetylide ligands
to the intraannular proton and increased anisotropic
deshielding. Similar to 10, 18 displayed a characteristic
cis JP-Pt value (2230 Hz) in the 31P NMR spectrum.10,18
Application of Glaser coupling conditions to 14 afforded
the parent bis-DBA 19 (39%).
Consistent with 1H NMR spectroscopy, single-crystal
X-ray diffraction of 18 (Figure 7) showed meta-fusion
of ethynyl substituents and retention of cis-Pt orienta-
tion. The largest acetylide ligand distortion of all the
platina-annulenes is displayed in the monoyne sides of
18 (C9 5.6°, C10, 11.1°) and is the result of meta-
substitution of the central benzene ring. Contrary to the
planar 15, cis-bisplatina-annulenes can display a syn-
or anti-relationship between Pt complexes. The anti-
relationship, slightly favored by 1 kJ mol-1 from mo-
lecular mechanics modeling, was isolated as the only
cyclized product (Figure 7b).22
Complex 18 appeared to directly conflict with our
previous assertion of selectivity based on transition-
state geometry.11 Detailed comparison of platina-annu-
lenes and bis-DBAs in Scheme 1 elucidated two key
concepts that rationalize 18. First, DBA cyclization
occurs with mix-matched substrate and catalyst geom-
etry but in significantly lower yields.11 Therefore, a cis-
Pt complex could be inserted into a meta-substituted
polyyne, a trans-favored substrate for DBA cyclization.
Second, the inclusion of an additional atom into the
annulene backbone appears to induce significant struc-
tural alterations compared to the annulene system
depicted in Scheme 1a. Previously synthesized [14]-
Figure 5. ORTEP of platina-annulene 12; ellipsoids
drawn at the 50% probability level. Selected bond lengths
(Å) and angles (deg): Pt-P1 2.313(18), Pt-C1 1.964(7),
C1-C2 1.220(9), C9-C10 1.197(9), P1-Pt-P2 100.2(6),
C26-Pt-C1 86.0(3), Pt-C1-C2 175.3(6), C1-C2-C3 174.9-
(7), C8-C9-C10 174.9(7), C9-C10-C11 171.6(8).
15 (8.58 ppm) were shifted slightly upfield (0.13 ppm)
and indicative of decreased phenyl ring anisotropy. The
JP-Pt value (2325 Hz) was consistent with 4 and previ-
ously published trans-PtCl2(PEt3)2 complexes.5f,g,6a,f,18a
The X-ray crystal structure of 15 (Figure 6) showed
bond angle lengths and distortions comparable to 4. In
contrast to 4, however, 15 did not display phenyl ring
twisting but instead showed a nonplanar bending
similar to a banana (Figure 6b). Single-crystal X-ray
diffraction also showed two distinctive stacking patterns
of 15 in the same crystal: face to face and edge to face,
resultant of favorable ligand-ligand and tert-butyl-
ligand interactions (Figure 6c).
As with failure to produce 7, reaction of 14 with cis-
PtCl2(PEt3)2 under amine-mediated metallacyclization
conditions resulted in isolation of 15 instead of 16. In
contrast to 8 and 9, isomerization of the Pt complex and
formation of the more stable 15 is the likely result over
Scheme 6

Structurally Related Platina-annulenes
Organometallics, Vol. 24, No. 6, 2005 1167
Figure 6. (a) ORTEP of bisplatina-annulene 15; ellipsoids drawn at the 50% probability level. Selected bond lengths (Å)
and angles (deg): Pt-P1 2.289(12), Pt-C1 2.004(4), C1-C2 1.202(5), C9-C10 1.201(5), P1-Pt-P2 174.4(4), C26-Pt-C1
170.9(17), Pt-C1-C2 170.9(4), C1-C2-C3 170.9(4), C8-C9-C10 177.8(5), C9-C10-C11 177.2(5). (b) View of 15 down
the [1 1 1] plane showing nonplanarity of the metallamacrocycle but lack of phenyl ring twisting. (c) Molecular stacking
of 15 down the [-1 1 0] plane.
annulenes with different alkyl substituents are highly
planar,8,21a whereas platinacycle variants such as 10
and 12 are bent. Subsequent molecular mechanics
geometry optimization illustrates that cis-18 is ther-
Spectroscopic and Physical Properties. The ma-
terials properties of the platina-annulenes were explored
to elucidate possible enhanced optical properties beyond
those of the parent DBAs. The key issue we sought to
discover was the result of transition metal complex
incorporation on conjugation and electron delocalization.
The amount of delocalization can be qualitatively ob-
served by comparing the electronic absorption spectra
of similar substructures. The mono-Pt-annulenes (4, 10,
12, and 13) exhibited hypsochromic shifts and λmax
decreases compared to their respective DBA analogues
(Figure 8). Cycles 10 and 12 (80 nm) showed a more
significant λmax decrease compared to 5 (15 nm), which
likely resulted from the increased nonplanarity and ring
strain of the platina-annulenes. The hypsochromic shift,
indicative of decreased electron delocalization, coincides
with previously reported platina-acetylide oligomers and
small molecules.6f The platina-annulenes also displayed
a significant decrease in charge-transfer absorptions
compared to parent annulenes.
modynamically favored over cis-17 by 36 kJ mol-1 22
.
Platinum Complex Geometry. Comparison of Pt-P
and Pt-C bond angles with JP-Pt values shows a
correlation between nonplanarity and decreased JP-Pt
(Table 1). cis-Pt complexes characteristically display
lower JP-Pt values than trans-complexes with the mag-
nitude dependent on ligand identity (PEt3 or PPh3).5,6,10,18
Compounds 4 and 15, which displayed the largest
acetylide ligand distortion for trans-bisethynyl Pt com-
plexes with PEt3 ligands, were associated with smaller
JP-Pt values than the less strained dimer 9. The lower
JP-Pt values of 4 and 15 can therefore be linked to a
syn-like ligand distortion resulting from ring strain.
This assertion is confirmed by our previously synthe-
sized trans-platina-annulene (JP-Pt ) 2344 Hz) that
displayed less ring strain and thus smaller ethynyl
distortion.6b For the cis-platina-annulenes, nonbidentate
complex 12 displayed the largest characteristically cis-
JP-Pt value resultant from significant PPh3 ligand and
ring strain induced distortion (5-10°). As expected, 10
and 18 showed the lowest cis-JP-Pt value due to the
bidentate dppe ligand.
Bisplatina-annulenes 15 and 18, however, both ex-
hibited bathochromic shifts compared to 19 (Figure 8).
Cycle 15 displayed the most significant bathochromic
shift (23 nm), and 18 showed the largest λmax value (ca.
105 000 L mol-1 cm-1). Additionally, 15 and 18 showed
enhanced absorption in the charge-transfer region

1168 Organometallics, Vol. 24, No. 6, 2005
Johnson et al.
Scheme 7
°C). For the bisplatina-annulenes, 15 exhibited a greater
exotherm than 18, which provides additional insight
into the thermodynamic stability of the mismatched cis-
bisplatina-annulene. The exothermic trends described
above and the stability of the platina-annulenes above
200 °C could potentially support a materials application
which requires either a specific or tailored energy
release.
Conclusions
In summary, we have demonstrated the selective
synthesis of seven new platinacycles via Sn transmeta-
lation and amine-mediated oxidative addition. Selectiv-
ity hypotheses based on DBA synthesis did not accu-
rately account for the experimentally determined
competing factors of ligand identity, Pt complex geom-
etry, reaction conditions, and incorporation of an ad-
ditional atom into the annulene skeleton. Bulky ligands,
such as PPh3, appeared to limit isomerization, and
bidentate phosphine ligands prevented isomerization
altogether. The more selective Sn transmetalation
conditions limited Pt complex isomerization over the
required temperature of the amine-mediated oxidative
insertion conditions. For highly strained systems, such
as the platina-annulenes 10 and 13, nonbidentate cis-
Pt complexes tended to isomerize to the more stable
trans. Based on experimental results, the most selective
metallacyclization method included use of Sn trans-
metalation conditions and a bidentate Pt complex for
cis-platina-acetylides, as ligand identity was shown to
be less important for trans-platina-acetylides. Future
studies in this area will focus on heterocyclic and tris-
ligated platina-annulenes.
compared to DBA 19. Diederich et al. have shown that
despite efficient metal to ligand charge transfer exhib-
ited by some highly conjugated platina-acetylides, elec-
tronic conjugation is localized in the acetylide ligands
due to the insulating nature of the Pt atom.6a,f A key
structural difference of the most red-shifted platina-
annulene (15) was its planarity. In contrast to hypso-
chromically shifted monocycle 4, 15 lacked any signifi-
cant phenyl ring twisting, as shown by X-ray diffraction.
Highly planar annulenes display increased electronic
properties in relation to distorted ones.8,21
All platina-annulenes exhibited a significant qualita-
tive loss in fluorescence compared to their free acetylene
precursors and parent DBAs when visualized in solution
or via TLC. Studies on monocycle 4 and bis-Pt-annulene
15 provided fluorescence quantum yield values less than
1%; thus, analysis of the remaining structures was not
attempted. Although practically advantageous for de-
termination of starting material consumption, the loss
in fluorescence could be attributed to less efficient
π-electron delocalization due to the insulating nature
of the Pt atom.6f
Comparison of platina-annulenes and DBA analogues
via DSC indicated a noticeable difference in phase
change and associated exotherm. DBAs 5 and 11
exhibited a sharp (2-4 °C) exotherm at ∼250 °C that
released 0.22 and 0.44 kJ mol-1, respectively. In con-
trast, the platina-annulenes displayed broad, multistage
decomposition above 200 °C. The more strained 15-
membered cycles 10, 12, and 13 displayed larger
exothermic release compared to 16-membered 4. Met-
allacycles 10 and 13 displayed the most significant
exotherms (7.1 kJ/mol at 417 °C and 10.3 kJ/mol at 413
Experimental Section
General Procedures. 1H, 13C, and 31P NMR spectra were
recorded using a Varian Inova 300 (1H 299.95 MHz, 13C 75.43
MHz, 31P 121.42 MHz) or Inova 500 (1H 500.10 MHz, 13C
125.75 MHz, 31P 202.44 MHz) spectrometer. Chemical shifts
(δ) are expressed in ppm downfield from tetramethylsilane
using the residual nondeuterated solvent as internal standard
(CDCl3: 1H 7.26 ppm, 13C 77.0 ppm; THF-d8: 1H 3.58 ppm,
13C 67.57 ppm; o-C6D4Cl2: 1H 7.19 ppm). Coupling constants
are expressed in hertz. IR spectra were recorded using a
Nicolet Magan-FTIR 550 spectrometer. UV-vis were recorded
using a Hewlett-Packard 8453 spectrophotometer. Mass spec-
tra were recorded using an Agilent 1100 Series LC/MSD.
Elemental analyses were performed by Robertson Microlit
Laboratories. Melting points were determined on a Meltemp
II apparatus or using a TA Instruments DSC 2920 Modulated
DSC and are uncorrected. CH2Cl2 was distilled from CaH2
under a N2 atmosphere prior to use. THF was purified using
an Innovative Technologies solvent system. Et2NH was dis-
tilled prior to use. All other chemicals were of reagent grade
and used as obtained from manufacturers. Reactions were
carried out in an inert atmosphere (dry N2 or Ar) when
necessary. Column chromatography was performed on What-
man reagent grade silica gel (230-400 mesh). Rotary chro-
matography was performed on a Harrison Research Chroma-
totron model 7924T with EM-Science 60PF254 silica gel.
Precoated silica gel plates (Sorbent Technology, UV254, 200 µm,
5 × 20 cm) were used for analytical thin-layer chromatography.
General Metallacyclization Procedure A. A solution of
R,ω-polyyne (1 equiv), Bu4NF (3-5 equiv), and 2-3 drops
MeOH in THF (10 mL per 0.1 mmol polyyne) was stirred at
room temperature and monitored by TLC until completion

Structurally Related Platina-annulenes
Organometallics, Vol. 24, No. 6, 2005 1169
Figure 7. (a) ORTEP of bisplatina-annulene 18; ellipsoids drawn at the 50% probability level. Selected bond lengths (Å)
and angles (deg): Pt-P1 2.284(2), Pt-C1 2.025(9), C1-C2 1.196(11), C9-C10 1.201(11), P1-Pt-P2 86.8(8), C26-Pt-C1
95.8(3), Pt-C1-C2 172.5(7), C1-C2-C3 176.6(9), C8-C9-C10 174.4(9), C9-C10-C11 168.9(8). (b) Side view of ORTEP
showing anti-orientation of the Pt metal centers.
Table 1. Comparison of Phosphine Ligand, Pt Isomer, 31P NMR Chemical Shift, JP-Pt Value, and Selected
Bond Angles for Platinum Complexes 4, 8-10, 12, 13, 15, and 18
31P NMR (δ)
(JP-Pt, (Hz))
P1-Pt-P2
X-Pt-C1
(deg)
Pt-C1-C2
compd
ligand
Pt isomer
(deg)
(deg)
4
8
PEt3
PEt3
PEt3
dppe
PPh3
PPh3
PEt3
dppe
trans
trans
trans
cis
10.49 (2328)
9.66 (2311)
12.09 (2360)
41.52 (2265)
17.80 (2333)
19.43 (2617)
10.63 (2325)
42.43 (2230)
172.4
175.4
176.8
85.8
170.7a
177.0b
176.5c
87.6d
86.0d
NAf
169.8
177.0
174.5
173.0
175.3
NAf
9
10
12
13
15
18
cis
100.2
transe
trans
cis
NAf
174.4
86.8
170.9c
95.8c
170.9
172.5
a X ) C1′. b X ) I. c X ) C26; centrosymmetric plane bisects central phenyl ring. d X ) C26; molecule is not centrosymmetric. e Assignment
based on NMR and MS. f Unable to obtain crystal structure.
(15-30 min). The solution was diluted with Et2O and washed
with water and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. Without further purification, the
residue was dissolved in THF (20 mL per 0.1 mmol polyyne),
and Me3SnNMe2 (1 equiv per polyyne free acetylene function-
ality) was added. The solution was stirred at room temperature
for 2 h and then concentrated in vacuo. Without further
purification, the resultant brown oil was combined with PtCl2-
(PR3)2 (1 equiv) and CuI (10 mol %) and placed under Ar.
Deoxygenated solvent (toluene, THF, or CH2Cl2; 25 mL per
0.1 mmol polyyne) was delivered via cannula, and the suspen-
sion was stirred under N2 for 12 h at room temperature. The
reaction mixture was concentrated by rotary evaporation, and
the desired product was purified by column chromatography
on silica gel or by Chromatotron.
General Metallacyclization Procedure B. A solution of
R,ω-polyyne (1 equiv), Bu4NF (3-5 equiv), and 2-3 drops
MeOH in THF (10 mL per 0.1 mmol polyyne) was stirred at
room temperature and monitored with TLC until completion
(15-30 min). The solution was diluted with Et2O and washed
with water and brine. The organic layer was dried over MgSO4
and concentrated in vacuo. Without further purification, the
residue was combined with PtCl2(PR3)2 (1 equiv) and CuI (10
mol %) and placed under an Ar environment. Deoxygenated
Et2NH (200 mL per 0.1 mmol polyyne) was delivered via
cannula, and the suspension was stirred under N2 for 12 h at
50 °C. The reaction mixture was diluted with CH2Cl2 and
washed with saturated NH4Cl solution until neutral pH. The
organic layer was dried over MgSO4 and concentrated by
rotary evaporation. The desired product was purified by
column chromatography on silica gel or by Chromatotron.
1-tert-Butyl-3-(2-triisopropylsilylethynyl)-4-(2-trime-
thylsilylethynyl)benzene (12). Iodoarene 19 (9.00 g, 20.4
mmol), CuI (388 mg, 2.04 mmol), and PdCl2(PPh3)2 (717 mg,
1.02 mmol) were combined in THF (100 mL) and i-Pr2NH (100
mL). The suspension was deoxygenated by bubbling with Ar,
and TMSA (5.65 mL, 40.8 mmol) was added via syringe. The
suspension was stirred for 12 h at room temperature under
N2. The solvent was removed by rotary evaporation, and the
residue was redissolved in Et2O. The organic layer was washed
with 10% HCl solution and then neutralized with saturated
NaHCO3 and NaCl solution until neutral pH. The organic layer
was dried with MgSO4 and concentrated in vacuo. Chroma-
tography on silica gel (3:1 hexanes/CH2Cl2) afforded 2 (7.36 g,
88%) as a highly viscous orange oil. 1H NMR (300 MHz,
CDCl3): δ 7.44 (d, J ) 1.7 Hz, 1H), 7.39 (d, J ) 8.3 Hz, 1H),
7.25 (dd, J ) 8.3, 1.7 Hz, 1H), 1.29 (s, 9H), 1.16 (s, 21H), 0.23
(s, 9H). 13C NMR (75 MHz, CDCl3): δ 151.39, 132.72, 129.65,
125.43, 125.33, 122.85, 105.86, 103.67, 97.27, 93.95, 34.68,
31.03, 18.84, 11.37, 0.02. IR (CCl4): ν 2962, 2866, 2155, 1251
cm-1. MS (CI pos) m/z (%): 481 (M+ + THF, 100), 410 (M+,
10), 409 (20), 245 (22); C26H42Si2 (410.78). Anal. Calcd for
C26H42Si2: C, 76.02, H, 10.31. Found: C, 75.88, H, 10.26.
r,ω-Polyyne 3. Ethynylarene 2 (1.19 g, 2.9 mmol) was
dissolved in Et2O (10 mL) and MeOH (20 mL). K2CO3 (1.20 g,
8.7 mmol) was added, and the suspension was stirred at room
temperature for 2 h. The suspension was diluted with Et2O
and washed thrice with water and once with brine. The organic
layer was dried over MgSO4 and concentrated in vacuo.
Without further purification, a syringe pump was used to
deliver a deoxygenated solution of the free acetylene in THF
(10 mL) over 12 h to a stirred, deoxygenated suspension of

1170 Organometallics, Vol. 24, No. 6, 2005
Johnson et al.
7.36 (m, 6H), 7.26 (t, J ) 7.7 Hz, 1H), 7.13 (dd, J ) 8.4, 2.1
Hz, 2H), 2.17-2.07 (m, 12H), 1.32 (s, 18 H), 1.18-1.07 (m,
18H). 13C NMR (75 MHz, CDCl3): δ 150.96, 137.77, 131.78,
130.45, 129.82, 127.96, 125.63, 124.67, 122.92, 121.66, 116.05
(t, J ) 14.5 Hz), 109.12, 91.73, 91.12, 34.76, 31.18, 16.30 (t, J
) 17.6 Hz), 7.94 (t, J ) 11.0 Hz). 31P NMR (121 MHz, CDCl3):
δ 10.49 (pseudo-t, J ) 2328 Hz). IR (KBr): ν 2962, 2865, 2087,
1384, 1034 cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 226 (15 000), 275
(58 000), 357 (5000) nm. MS (CI pos) m/z (%): 869 (MH+, 100),
868 (M+, 65), 531.5 (90); C46H58P2Pt (867.98). Anal. Calcd for
C46H58P2Pt: C, 63.65, H, 6.74. Found: C, 63.49, H, 6.86.
Dehydrobenzo[15]annulene 5. Polyyne 3 (100 mg, 0.13
mmol) was dissolved in THF (10 mL) and treated with MeOH
(3 drops) and Bu4NF (0.5 mL, 1 M THF solution). The solution
was stirred for 30 min at room temperature and monitored
by TLC. When complete, the reaction mixture was diluted with
Et2O and washed thrice with water and once with brine. The
organic layer was then dried with MgSO4 and concentrated
in vacuo. Without further purification, the deprotected polyyne
was dissolved in THF (10 mL) and added via syringe pump
over 24 h to a solution of CuCl (1.31 g, 13.3 mmol) in pyridine
(200 mL) and MeOH (50 mL) at 50 °C. The suspension was
stirred for an additional 12 h, then the pyridine was removed
via rotary evaporation. The resultant thick, green oil was
filtered through silica gel (1:1 hexanes/CH2Cl2) to remove Cu
salts. The filtrate was concentrated in vacuo and recrystallized
with THF/hexanes to yield 5 (44 mg, 76%) as a pale yellow
solid. Mp: 252.6 °C (dec). 1H NMR (300 MHz, CDCl3): δ 8.69
(br s, 1H), 7.58 (br s, 2H), 7.41-7.34 (m, 5H), 7.29 (d, J ) 1.2
Hz, 2H), 1.33 (s, 18H). 13C NMR (75 MHz, CDCl3): δ 151.60,
144.87, 129.69 (2C), 129.50, 128.61, 127.04, 126.58, 126.00,
124.17, 95.14, 92.29, 82.68, 77.82, 34.84, 30.96. IR (CCl4): ν
2963, 2867, 2196, 1490 cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 229
(39 000), 290 (85 000), 341 (10 000) nm. MS (CI pos) m/z (%):
579 (M+ + 2THF, 100), 507 (M+ + THF, 74), 296 (32); C34H28
(436.58). Anal. Calcd for C34H28‚C4H8O: C, 90.44, H, 6.39.
Found: C, 90.80, H, 5.98.
Figure 8. (a) Electronic absorption spectra of platina-
annulenes 5, 9, 10, and 12 and DBAs 4 and 11. (b)
Electronic absorption spectra of bisplatina-annulenes 15
and 18 and DBA 19.
r,ω-Polyyne 6. Ethynylarene 2 (1.60 g, 4.05 mmol) was
deprotected with K2CO3 (1.60 g, 12 mmol) in Et2O (10 mL)
and MeOH (20 mL). K2CO3 (1.60 g, 12 mmol) was added, and
the suspension was stirred at room temperature for 2 h. The
suspension was diluted with Et2O and washed thrice with
water and once with brine. The organic layer was dried over
MgSO4 and concentrated in vacuo. Without further purifica-
tion, a syringe pump was used to deliver a deoxygenated
solution of the free acetylene in THF (10 mL) over 12 h to a
stirred, deoxygenated suspension of 1,2-diiodobenzene (500 mg,
1.50 mmol), Pd(PPh3)4 (233 mg, 0.22 mmol), and CuI (76 mg,
0.40 mmol) in THF (150 mL) and i-Pr2NH (100 mL). The
reaction was stirred an additional 12 h at room temperature
under N2, then the solvent was removed by rotary evaporation.
The residue was redissolved in Et2O, and the organic layer
was washed with 10% HCl solution and then with saturated
NaHCO3 and NaCl solution until neutral pH. The organic layer
was dried with MgSO4 and concentrated in vacuo. Chroma-
tography of the residue on silica gel (hexanes) yielded 6 (1.08
g, 95%) as an orange, spongy solid. Mp: 121.5 °C. 1H NMR
(300 MHz, CDCl3): δ 7.61 (AA′m, 2H), 7.57 (d, J ) 1.8 Hz,
2H), 7.54 (d, J ) 8.4 Hz, 2H), 7.32 (BB′m, 2H), 7.30 (dd, J )
8.4, 1.8 Hz, 2H), 1.38 (s, 18H), 1.20 (s, 42H). 13C NMR (75 MHz,
CDCl3): δ 151.15, 132.40, 131.79, 129.43, 127.58, 126.27,
125.41, 125.24, 123.32, 105.98, 94.09, 92.59, 91.48, 34.66,
1,3-diiodobenzene (415 mg, 1.26 mmol), Pd(PPh3)4 (120 mg,
0.15 mmol), and CuI (55 mg, 0.29 mmol) in THF (100 mL) and
i-Pr2NH (50 mL). The reaction was stirred an additional 12 h
at room temperature under N2, then the solvent was removed
by rotary evaporation. The residue was redissolved in Et2O,
and the organic layer was washed successively with 10% HCl
solution and saturated NaCl and NaHCO3 solution until
neutral pH. The organic layer was dried with MgSO4 and
concentrated in vacuo. Chromatography of the residue on silica
gel (hexanes) afforded 3 (533 mg, 56%) as an orange, spongy
solid. Mp: 63 °C. 1H NMR (300 MHz, CDCl3): δ 7.74 (br s,
1H), 7.53 (d, J ) 1.8 Hz, 2H), 7.50-7.45 (m, 4H), 7.34 (dd, J
) 8.3, 1.8, Hz, 2H), 7.29 (t, J ) 7.8 Hz, 1H), 1.34 (s, 18H),
1.16 (s, 42H). 13C NMR (75 MHz, CDCl3): δ 151.32, 135.03,
131.86, 131.17, 129.53, 127.99, 125.49 (2C), 123.68, 122.90,
105.81, 94.24, 91.56, 88.80, 34.69, 31.02, 18.72, 11.36. IR (CCl4)
ν 2962, 2865, 2150, 1495 cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 225
(42 000), 248 (61 000), 260 (74 000), 304 (33 000), 325 (23 000)
nm. MS (CI pos) m/z (%): 821 (M+ + THF, 100), 751 (M+,
29), 585 (18), 515 (23); C52H70Si2 (751.28). Anal. Calcd for
C52H70Si2: C, 83.13, H, 9.39. Found: C, 82.98, H, 9.47.
trans-Platina-annulene 4. Polyyne 3 (113 mg, 0.15 mmol)
was reacted with Me3SnNMe2 (63 mg, 0.30 mmol) and then
trans-PtCl2(PEt3)2 (63 mg, 0.13 mmol) and CuI (10 mg, 0.05
mmol) in a 1:1 solution of deoxygenated THF/toluene as
described in general procedure A. Chromatography on silica
gel (2:1 hexanes/CH2Cl2) yielded 4 (46.4 mg, 37%) as a light
yellow solid. Recrystallization by vapor diffusion with THF/
hexanes yielded light, yellow-brown plate crystals. Mp: 284.5
°C (dec). 1H NMR (300 MHz, CDCl3): δ 8.70 (br s, 1H), 7.40-
31.04, 18.74, 11.41. IR (CCl4): ν 2959, 2864, 2155, 1462 cm-1
.
UV/vis (CH2Cl2): λmax (ꢀ) 242 (58 100), 249 (60 000), 257
(56 000), 296 (22 000), 315 (17 000) nm. MS (CI pos) m/z (%):
821 (M+ + THF, 22), 751 (M+, 100), 585.3 (17), 515 (20);
C52H70Si2 (751.28). Anal. Calcd for C52H70Si2: C, 83.13, H, 9.39.
Found: C, 82.91, H, 9.50.
Bis-Pt-polyyne 8. Polyyne 6 (75 mg, 0.10 mmol) was
reacted with Me3SnNMe2 (41 mg, 0.2 mmol) and subsequently
cis-PtCl2(PEt3)2 (68 mg, 0.14 mmol) and CuI (10 mg, 0.05

Structurally Related Platina-annulenes
Organometallics, Vol. 24, No. 6, 2005 1171
mmol) in deoxygenated toluene as described in general pro-
cedure A. Chromatography on silica gel (2:1 hexanes/CH2Cl2)
afforded 8 (9.5 mg, 11%) as a dark yellow solid. Recrystalli-
zation by vapor diffusion with THF/hexanes yielded light,
yellow-brown needles. Mp: 214.9 °C (dec). 1H NMR (300 MHz,
CDCl3): δ 7.51 (AA′m, 2H), 7.39 (d, J ) 8.3 Hz, 2H), 7.35 (d,
J ) 1.8 Hz, 2H), 7.22 (BB′m, 2H), 7.08 (dd, J ) 8.3, 1.8 Hz,
2H), 2.24-2.16 (m, 24H), 1.30 (s, 18H), 1.16-1.05 (m, 36H).
13C NMR (75 MHz, CDCl3): δ 150.87, 132.41, 131.77, 130.12,
128.28, 127.34, 126.61, 122.41, 121.23, 99.99, 94.61, 94.52 (t,
J ) 14.2 Hz), 89.97, 34.58, 31.10, 16.64 (t, J ) 10.7 Hz), 8.29.
31P NMR (121 MHz, CDCl3): δ 9.66 (pseudo-t, J ) 2311 Hz).
IR (CCl4): ν 2962, 2873, 2105, 1384 cm-1. MS (CI pos) m/z
(%): 1623 (M+ + THF, 15), 1554 (MH+, 82), 1553 (M+, 100);
C58H88I2P4Pt2 (1553.18). Anal. Calcd for C58H88I2P4Pt2: C,
44.85, H, 5.71. Found: C 45.07, H 5.54.
ant thick, green oil was filtered through silica gel (1:1 hexanes/
CH2Cl2) to remove Cu salts, and the filtrate was concentrated
by rotary evaporation. Chromatography on silica gel (1:1
hexanes/CH2Cl2) afforded 11 (40 mg, 86%) as a pale yellow
solid. Mp: 252.3 °C (dec). 1H NMR (300 MHz, CDCl3): δ 7.91
(AA′m, 2H), 7.81 (d, J ) 8.5 Hz, 2H), 7.63 (d, J ) 1.8 Hz, 2H),
7.52 (dd, J ) 8.5, 1.8 Hz, 2H), 7.43 (BB′m, 2H), 1.37 (s, 18H).
13C NMR (75 MHz, CDCl3): δ 151.39, 135.86, 132.79, 127.74,
126.56, 126.12, 126.04, 123.37, 122.39, 93.13, 93.09, 86.07,
79.68, 34.90, 31.06. IR (CCl4): ν 2963, 2867, 2150, 1485 cm-1
.
UV/vis (CH2Cl2): λmax (ꢀ) 231 (52 000), 271 (39 000), 295
(64 000), 302 (65 000), 313 (93 000) nm. MS (CI pos) m/z (%):
509 (M+ + THF, 100), 438 (MH+, 10); C34H28 (436.58).
cis-Platina-annulene 12. Polyyne 6 (100 mg, 0.133 mmol)
was reacted with Me3SnNMe2 (55 mg, 0.27 mmol) and subse-
quently cis-PtCl2(PPh3)2 (105 mg, 0.133 mmol) and CuI (5 mg,
0.03 mmol) in a solution of deoxygenated THF as described in
general procedure A. Purification on a Chromatotron plate (1
mm, 1:1 hexanes/CH2Cl2) yielded 12 (17 mg, 11%) as a pale
white solid. Recrystallization by vapor diffusion with C6H4Cl2/
hexanes yielded colorless crystals. Mp: 187.9 °C (dec). 1H NMR
(300 MHz, CDCl3): δ 7.66 (AA′m, 2H), 7.51-7.45 (m, 12H),
7.35 (BB′m, 2H), 7.24 (d, J ) 8.1 Hz, 2H), 7.23-7.17 (m, 6H),
7.11-7.04 (m, 12H), 6.91 (dd, J ) 8.1, 1.8 Hz, 2H), 6.57 (d, J
) 1.8 Hz, 2H), 1.13 (s, 18H). 13C NMR (75 MHz, CDCl3): δ
149.67, 134.84, 132.10, 131.91, 131.10, 129.81, 128.54, 128.44,
127.81, 127.58, 127.02, 126.43, 122.42, 121.31, 96.11, 93.27,
89.09, 34.32, 31.05. 31P NMR (121 MHz, CDCl3): δ 17.80
(pseudo-t, J ) 2333 Hz). IR (KBr): ν 2960, 2115, 1631.16, 1096
cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 231 (69 000), 258 (57 000), 305
(29 000) nm. MS (CI pos) m/z (%): 1159 (M+ + 3, 90), 1157
(MH+, 80), 1021 (100); C70H58P2Pt (1156.24). Anal. Calcd for
C70H58P2Pt‚0.5C6H4Cl2: C, 71.30, H, 4.92. Found: C, 71.43,
H, 4.83.
trans-Platina-annulene Dimer 9. Polyyne 6 (150 mg, 0.2
mmol) was reacted with cis-PtCl2(PEt3)2 (100 mg, 0.2 mmol)
and CuI (10 mg, 0.04 mmol) as described in general procedure
B. Chromatography on silica gel (2:1 hexanes/CH2Cl2) and
subsequent precipitation with CHCl3 yielded 9 (63 mg, 36%)
as a pale yellow solid. Recrystallization by vapor diffusion with
THF/hexanes afforded light yellow crystals. Mp: 315.1 °C
(dec). 1H NMR (300 MHz, CDCl3): δ 7.50 (AA′m, 2H), 7.35 (d,
J ) 8.3 Hz, 2H), 7.31 (d, J ) 1.8 Hz, 2H), 7.21 (BB′m, 2H),
7.06 (dd, J ) 8.3, 1.8 Hz, 2H), 2.07-2.05 (m, 12H), 1.26 (s,
18H), 1.09-1.03 (m, 18H). 13C NMR (75 MHz, CDCl3):
δ
150.48, 132.61, 132.27, 130.48, 128.82, 127.32, 126.42, 121.81,
121.11, 113.27 (t, J ) 15.5 Hz), 109.01, 94.31, 89.10, 34.48,
31.08, 16.41 (t, J ) 17.6 Hz), 8.50 (t, J ) 11.0 Hz),. 31P NMR
(121 MHz, CDCl3): δ 12.09 (pseudo-t, J ) 2360 Hz). IR (KBr):
ν 2962, 2091, 1384 cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 234
(104 000), 250 (99 000), 331 (43 000) nm. MS (CI pos) m/z (%):
1736 (MH+, 25), 1735 (M+, 100), 1617 (13); C92H116P4Pt2
(1735.96). Anal. Calcd for C92H116P4Pt2: C, 63.65, H, 6.74.
Found: C, 63.61, H, 6.69.
cis-Platina-annulene 10. Polyyne 6 (100 mg, 0.133 mmol)
was reacted with Me3SnNMe2 (55 mg, 0.27 mmol) and subse-
quently PtCl2(dppe) (73 mg, 0.11 mmol) and CuI (5 mg, 0.03
mmol) in a 1:1 solution of deoxygenated THF/CH2Cl2 as
described in general procedure A. Chromatography on silica
gel (1:1 hexanes/CH2Cl2) yielded 10 (70 mg, 52%) as a fine
white solid. Recrystallization by vapor diffusion with C6H4Cl2/
hexanes yielded colorless crystals. Mp: 229 °C (dec). 1H NMR
(300 MHz, THF-d8): δ 8.14-8.05 (m, 8H), 7.56 (AA′m, 2H),
7.41-7.35 (m, 12H), 7.29 (d, J ) 8.0 Hz, 2H), 7.24 (BB′m, 2H),
7.06 (d, J ) 1.9 Hz, 2H), 7.02 (dd, J ) 8.0, 1.9 Hz, 2H), 2.56-
2.42 (m, 4H), 1.21 (s, 18H). 13C NMR (125 MHz, THF-d8): δ
151.02, 134.77 (m), 134.02, 132.62, 132.32, 131.90, 131.75,
129.48 (m), 128.87, 128.03, 127.351, 122.98, 122.30, 113.30 (dd,
J ) 147.5, 14.3 Hz), 110.95 (d, J ) 34.0 Hz), 94.60, 90.49,
55.054, 35.22, 31.66. 31P NMR (121 MHz, THF-d8): δ 41.52
(pseudo-t, J ) 2265 Hz). IR (KBr): ν 3054, 2961, 2110, 1436
cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 231 (62 000), 261 (54 000), 296
(27 000), 305 (25 000) nm. MS (CI pos) m/z (%): 1031 (MH+,
65), 1030.2 (M+, 53), 531 (100); C60H52P2Pt (1030.08). Anal.
Calcd for C60H52P2Pt‚C6H4Cl2: C, 67.35, H, 4.80. Found: C,
67.55, H, 4.66.
Dehydrobenzo[14]annulene 11. Polyyne 6 (80 mg, 0.11
mmol) was dissolved in THF (10 mL) and treated with MeOH
(3 drops) and Bu4NF (0.5 mL, 1 M THF solution). The solution
was stirred for 30 min at room temperature and monitored
by TLC. Upon completion, the reaction mixture was diluted
with Et2O (20 mL) and washed thrice with water and once
with brine. The organic layer was dried with MgSO4 and
concentrated in vacuo. Without further purification, the depro-
tected polyyne was dissolved in THF (10 mL) and added via
syringe pump over 24 h to a solution of CuCl (1.03 g, 10.4
mmol) in pyridine (200 mL) and MeOH (50 mL). The suspen-
sion was stirred at 50 °C under N2 for an additional 12 h, then
the pyridine was removed via rotary evaporation. The result-
trans-Platina-annulene 13. Polyyne 6 (153 mg, 0.2 mmol)
was reacted with cis-PtCl2(PPh3)2 (160 mg, 0.2 mmol) and CuI
(14 mg, 0.08 mmol) as described in general procedure B.
Purification on a Chromatotron plate (1 mm, 2:1 hexanes/
CH2Cl2) and subsequent precipitation with hexanes yielded
1
13 (50 mg, 21%) as a white powder. Mp: 241.4 °C (dec). H
NMR (300 MHz, CDCl3): δ 8.00-7.97 (m, 12H), 7.48 (d, J )
8.1 Hz, 2H), 7.31-7.22 (m, 20H), 7.03 (dd, J ) 8.1, 1.8 Hz,
2H), 6.47 (d, J ) 1.8 Hz, 2H), 6.35 (BB′m, 2H), 1.21 (s, 18H).
13C NMR (75 MHz, CDCl3): δ 150.12, 135.39 (t, J ) 6.0 Hz),
131.50, 131.12, 130.98, 130.73, 130.12, 127.68 (t, J ) 5.0 Hz),
127.52, 127.14, 126.29, 121.39, 120.98, 117.79 (t, J ) 15.6 Hz),
114.46, 95.31, 89.27, 34.42, 31.07. 31P NMR (121 MHz,
CDCl3): δ 19.43 (pseudo-t, J ) 2617 Hz). IR (KBr): ν 2960,
2924, 2854, 2100, 1384, 1110 cm-1. UV/vis (CH2Cl2): λmax (ꢀ)
232 (50 200), 262 (42 600), 328 (13 200), 353 (12 900), 364
(12 700), 379 (12 600) nm. MS (CI pos) m/z (%): 1195 (M+
+
CH3CN, 77), 1157 (MH+, 15), 558 (100); C70H58P2Pt (1156.24).
Anal. Calcd for C70H58P2Pt: C, 72.71, H, 5.06. Found: C, 71.94,
H, 5.28.
r,ω-Polyyne 14. Ethynylarene 2 (2.3 g, 5.67 mmol) was
dissolved in Et2O (10 mL) and MeOH (20 mL). K2CO3 (2.0 g,
15 mmol) was added, and the suspension was stirred at room
temperature for 2 h. The suspension was diluted with Et2O
and washed thrice with water and once with brine. The organic
layer was dried over MgSO4 and concentrated in vacuo.
Without further purification, a syringe pump was used to
deliver a deoxygenated solution of the free acetylene in THF
(10 mL) over 24 h to a stirred, deoxygenated suspension of
1,2,4,5-tetraiodobenzene (550 mg, 0.95 mmol), Pd(PPh3)4 (231
mg, 0.20 mmol), and CuI (76 mg, 0.40 mmol) in THF (200 mL)
and i-Pr2NH (100 mL). The reaction was stirred an additional
24 h at room temperature under N2, then the solvent was
removed by rotary evaporation. The residue was redissolved
in Et2O, and the organic layer was washed with 10% HCl
solution and then with saturated NaCl and NaHCO3 solution
until neutral pH. The organic layer was dried with MgSO4 and

1172 Organometallics, Vol. 24, No. 6, 2005
Johnson et al.
concentrated in vacuo. Chromatography of the residue on silica
gel (5:1 hexanes/CH2Cl2) afforded 14 (1.04 g, 78%) as a light
yellow, fine powder. Mp: 219-221 °C. 1H NMR (300 MHz,
CDCl3): δ 7.72 (s, 2H), 7.50 (d, J ) 1.8 Hz, 4H), 7.46 (d, J )
8.1 Hz, 4H), 7.27 (dd, J ) 8.1, 1.8 Hz, 4H), 1.33 (s, 36H), 1.10
(s, 84H). 13C NMR (75 MHz, CDCl3): δ 151.29, 135.42, 132.32,
129.35, 125.43, 125.36, 125.29, 123.04, 105.69, 94.43, 94.02,
90.45, 34.70, 31.04, 18.69, 11.37. IR (CCl4): ν 2959, 2865, 2154,
1463, 1384 cm-1. UV/vis (CH2Cl2): λmax (ꢀ) 240 (62 000), 256
(48 000), 269 (50 000), 327 (24 000), 364 (17 500) nm. MS (CI
pos) m/z (%): 1495 (M+ + THF, 10), 1425 (MH+, 100), 1424
(M+, 93); C98H134Si4 (1424.45). Anal. Calcd for C98H134Si4‚0.5CH2-
Cl2: C, 80.65, H, 9.28. Found: C, 80.97, H, 9.05.
trans-Bisplatina-annulene 15. Polyyne 14 (150 mg, 0.11
mmol) was reacted with trans-PtCl2(PEt3)2 (106 mg, 0.21
mmol) and CuI (10 mg, 0.04 mmol) as described in general
procedure B. Purification on a Chromatotron plate (1 mm, 1:1
hexanes/CH2Cl2) provided 15 (32 mg, 0.02 mmol, 21%) as a
pale yellow solid. Recrystallization by vapor diffusion with
THF/hexanes afforded light yellow crystals. Mp: 341.4 °C
(dec). 1H NMR (300 MHz, CDCl3): δ 8.58 (s, 2H), 7.52 (d, J )
8.2 Hz, 4H), 7.35 (d, J ) 1.5 Hz, 4H), 7.21 (dd, J ) 8.2, 1.5 Hz,
4H), 2.15-2.11 (m, 24H), 1.34 (s, 36H), 1.18-1.08 (m, 36H).
13C NMR (75 MHz, CDCl3): δ 151.18, 137.61, 131.79, 130.73,
125.52, 124.77, 123.17, 121.87, 116.39 (t, J ) 15.0 Hz), 109.29,
96.78, 90.57, 34.84, 31.20, 16.34 (t, J ) 17.2 Hz), 7.99. 31P NMR
(121 MHz, CDCl3): δ 10.63 (pseudo-t, J ) 2325 Hz). IR
(CCl4): ν 2962, 2090, 1498, 1035 cm-1. UV/vis (CH2Cl2): λmax
(ꢀ) 228 (37 000), 286 (90 000), 436 (35 000) nm. MS (CI pos)
m/z (%): 1658 (MH+, 8), 1657 (M+, 6), 585 (35), 531 (100);
C86H110P4Pt2 (1657.84). Anal. Calcd for C86H110P4Pt2: C, 62.31,
H, 6.69. Found: C, 62.56, H, 6.50.
diluted with Et2O and washed thrice with water and once with
brine. The organic layer was dried with MgSO4 and concen-
trated in vacuo. Without further purification, the deprotected
polyyne was dissolved in THF (10 mL) and added via syringe
pump over 24 h to a solution of CuCl (514 mg, 5.2 mmol) in
pyridine (200 mL) and MeOH (50 mL). The suspension was
stirred at 50 °C for an additional 12 h, then the pyridine was
removed via rotary evaporation. The resultant thick, green oil
was filtered through silica gel (1:1 hexanes/CH2Cl2) to remove
Cu salts, and the filtrate was concentrated by rotary evapora-
tion. Chromatography on silica gel (2:1 hexanes/CH2Cl2)
afforded 19 (16 mg, 39%) as a yellow solid. Mp: 249.1 °C (dec).
1H NMR (300 MHz, CDCl3): δ 8.43 (s, 2H), 7.92 (d, J ) 8.6
Hz, 4H), 7.64 (d, J ) 1.9 Hz, 4H), 7.56 (dd, J ) 8.6, 1.9 Hz,
4H), 1.38 (s, 36H). 13C NMR (75 MHz, CDCl3): δ 151.95,
143.06, 133.04, 126.27 (3C), 122.76, 122.65, 95.03, 92.32, 86.05,
79.83, 35.04, 31.11. IR (CCl4): ν 2957, 2924, 2854 cm-1. UV/
vis (CH2Cl2): λmax (ꢀ) 230 (73 900), 300 (60 000), 342 (74 600),
356 (66 000) nm. MS (CI pos) m/z (%): 867 (M+ + THF, 100),
796 (MH+, 19), 372 (50); C62H50 (795.06).
Crystallographic Data. Intensity data for 9 were collected
at 293 K and for 10, 12, 15, and 18 at 153 K on a Bruker
SMART-APEX diffractometer using Mo ΚR radiation (λ )
0.7107 Å). Lorentz and polarization corrections were applied
and diffracted data were also corrected for absorption using
the SADABS program. Structures were solved by direct
methods and Fourier techniques. Structure solution and
2
refinement were based on |F| . All non-hydrogen atoms were
refined with anisotropic displacement parameters except for
the carbon, oxygen, and chlorine atoms of the solvent molecules
in 9, 10, and 18. In 9, the THF solvent molecule was highly
disordered and solved as a group of five carbon atoms. The H
atoms of the C-H groups were fixed in calculated positions.
In 15, three of the six Et-groups attached to the phosphorus
atoms were disordered and refined with two equally occupied
sets of coordinates. Intensity data for 4 and 8 were collected
at 293 K on a Nonius CAD-4 serial diffractometer. In 4 the
tert-butyl and ethyl moieties were disordered and left isotropic.
The tert-butyl moiety was observed to be disordered over two
positions, and the corresponding carbon atoms were refined
with occupancies of 0.5.
cis-Bisplatina-annulene 18. Polyyne 14 (75 mg, 0.05
mmol) was reacted with PtCl2(dppe) (69 mg, 0.10 mmol) and
CuI (5 mg, 0.03 mmol) as described in general procedure B.
Purification on a Chromatotron plate (1 mm, 1:1 hexanes/
CH2Cl2) provided 18 (20 mg, 19%) as a yellow solid. Recrys-
tallization by vapor diffusion with o-C6H4Cl2/hexanes afforded
light yellow crystals. Mp: 351.7 °C (dec). 1H NMR (300 MHz,
o-C6D4Cl2): δ 9.19 (s, 2H), 7.94-7.88 (m, 16H), 7.34-7.24 (m,
28H), 7.02-6.94 (m, 8H), 2.30-2.24 (m, 8H), 1.14 (s, 36H). 13
C
NMR: insufficient solubility to obtain spectrum. 31P NMR (121
MHz, CDCl3): δ 42.43 (pseudo-t, J ) 2230 Hz). IR (CCl4): ν
2958, 2924, 2091.27, 1384, 1108 cm-1. UV/vis (CH2Cl2): λmax
(ꢀ) 231 (103 000), 257 (84 000), 275 (80 500), 409 (36 000) nm.
MS (CI pos) m/z (%): 1983 (M+, 31), 1981 (23), 1426 (70), 1028
(100); C114H99P4Pt2 (1983.06). Anal. Calcd for C114H99P4-
Pt2‚2C6H4Cl2: C, 66.49, H, 4.69. Found: C, 66.29, H, 4.31.
Bisdehydrobenzo[15]annulene 19. Polyyne 14 (75 mg,
0.05 mmol) was dissolved in THF (10 mL) and treated with
MeOH (3 drops) and Bu4NF (0.5 mL, 1 M THF solution). The
solution was stirred for 30 min at room temperature and
monitored by TLC. Upon completion, the reaction mixture was
Acknowledgment. This research has been sup-
ported by the National Science Foundation (CHE-
0414175). C.A.J. acknowledges the NSF for an IGERT
fellowship. The CCD diffractometer was purchased with
funds provided by the NSF (CHE-0234965).
Supporting Information Available: X-ray structures for
4, 8-10, 12, 15, and 18. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM0490987