Supramolecular allosteric cofacial porphyrin complexes

Article abstract of DOI:10.1021/ja0661010

Nature routinely uses cooperative interactions to regulate cellular activity. For years, chemists have designed synthetic systems that aim toward harnessing the reactivity common to natural biological systems. By learning how to control these interactions in situ, one begins to allow for the preparation of man-made biomimetic systems that can efficiently mimic the interactions found in Nature. To this end, we have designed a synthetic protocol for the preparation of flexible metal-directed supramolecular cofacial porphyrin complexes which are readily obtained in greater than 90% yield through the use of new hemilabile porphyrin ligands with bifunctional ether-phosphine orthioether-phosphine substituents at the 5 and 15 positions on the porphyrin ring. The resulting architectures contain two hemilabile ligand-metal domains (Rh^I or Cu^I sites) and two cofacially aligned porphyrins (Zn^II sites), offering orthogonal functionalities and allowing these multimetallic complexes to exist in two states, "condensed" or "open". Combining the ether-phosphine ligand with the appropriate Rh^I or Cu^I transition-metal precursors results in "open" macrocyclic products. In contrast, reacting the thioether-phosphine ligand with Rh^I or Cu^I precursors yields condensed structures that can be converted into their "open" macrocyclic forms via introduction of additional ancillary ligands. The change in cavity size that occurs allows these structures to function as allosteric catalysts for the acyl transfer reaction between X-pyridylcarbinol (where X = 2, 3, or 4) and 1-acetylimidazole. For 3- and 4-pyridylcarbinol, the "open" macrocycle accelerates the acyl transfer reaction more than the condensed analogue and significantly more than the porphyrin monomer. In contrast, an allosteric effect was not observed for 2-pyridylcarbinol, which is expected to be a weaker binder and is unfavorably constrained inside the macrocyclic cavity.

Full text of DOI:10.1021/ja0661010

Published on Web 11/22/2006
Supramolecular Allosteric Cofacial Porphyrin Complexes
Christopher G. Oliveri,† Nathan C. Gianneschi,† SonBinh T. Nguyen,*,†
Chad A. Mirkin,*,† Charlotte L. Stern,† Zdzislaw Wawrzak,‡ and Maren Pink§
Contribution from the Department of Chemistry and the International Institute for
Nanotechnology, Northwestern UniVersity, 2145 Sheridan Road, EVanston, Illinois, 60208-3113,
Department of Biochemistry, Molecular Biology and Cell Biology, Northwestern UniVersity,
2205 Tech DriVe, EVanston, Illinois 60208-3500, and Department of Chemistry, Indiana
UniVersity, Bloomington, Indiana 47405
Received August 22, 2006; E-mail: stn@northwestern.edu; chadnano@northwestern.edu
Abstract: Nature routinely uses cooperative interactions to regulate cellular activity. For years, chemists
have designed synthetic systems that aim toward harnessing the reactivity common to natural biological
systems. By learning how to control these interactions in situ, one begins to allow for the preparation of
man-made biomimetic systems that can efficiently mimic the interactions found in Nature. To this end, we
have designed a synthetic protocol for the preparation of flexible metal-directed supramolecular cofacial
porphyrin complexes which are readily obtained in greater than 90% yield through the use of new hemilabile
porphyrin ligands with bifunctional ether-phosphine or thioether-phosphine substituents at the 5 and 15
positions on the porphyrin ring. The resulting architectures contain two hemilabile ligand-metal domains
(RhI or CuI sites) and two cofacially aligned porphyrins (ZnII sites), offering orthogonal functionalities and
allowing these multimetallic complexes to exist in two states, “condensed” or “open”. Combining the ether-
phosphine ligand with the appropriate RhI or CuI transition-metal precursors results in “open” macrocyclic
products. In contrast, reacting the thioether-phosphine ligand with RhI or CuI precursors yields condensed
structures that can be converted into their “open” macrocyclic forms via introduction of additional ancillary
ligands. The change in cavity size that occurs allows these structures to function as allosteric catalysts for
the acyl transfer reaction between X-pyridylcarbinol (where X ) 2, 3, or 4) and 1-acetylimidazole. For 3-
and 4-pyridylcarbinol, the “open” macrocycle accelerates the acyl transfer reaction more than the condensed
analogue and significantly more than the porphyrin monomer. In contrast, an allosteric effect was not
observed for 2-pyridylcarbinol, which is expected to be a weaker binder and is unfavorably constrained
inside the macrocyclic cavity.
photophysical properties,11-15 their ability to catalyze small
molecule transformations,16-20 and their use in molecular
recognition.21,22 Among these, cofacial porphyrin compounds
exhibit unique properties attributed to their spatial arrangement
with respect to each other, and therefore, the ability to control
that arrangement via incorporation of multiple pophyrins in
supramolecular arrays offers a potentially facile route to
Introduction
Over the past two decades, chemists have been designing
synthetic systems that incorporate cofacial porphyrin entities.1-10
These systems are of particular interest owing to their unique
† Department of Chemistry and the International Institute for Nanotech-
nology, Northwestern University.
‡ Department of Biochemistry, Molecular Biology and Cell Biology,
Northwestern University.
(11) Faure, S.; Stern, C.; Guilard, R.; Harvey, P. D. J. Am. Chem. Soc. 2004,
126, 1253-1261.
§ Indiana University.
(12) Splan, K. E.; Stern, C. L.; Hupp, J. T. Inorg. Chim. Acta. 2004, 357, 4005-
(1) Cowan, J. A.; Sanders, J. K. M. J. Chem. Soc., Chem. Commun. 1985,
1213-14.
4014.
(13) Hajjaj, F.; Yoon, Z. S.; Yoon, M. C.; Park, J.; Satake, A.; Kim, D.; Kobuke,
Y. J. Am. Chem. Soc. 2006, 128, 4612-4623.
(2) Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 2000, 122, 12393-12394.
(3) Collman, J. P.; Bencosme, C. S.; Durand, R. R., Jr.; Kreh, R. P.; Anson,
F. C. J. Am. Chem. Soc. 1983, 105, 2699-703.
(4) Feiters, M. C.; Fyfe, M. C. T.; Martinez-Diaz, M. V.; Menzer, S.; Nolte,
R. J. M.; Stoddart, J. F.; van Kan, P. J. M.; Williams, D. J. J. Am. Chem.
Soc. 1997, 119, 8119-8120.
(14) Fletcher, J. T.; Therien, M. J. J. Am. Chem. Soc. 2002, 124, 4298-4311.
(15) Kobuke, Y. Struct. Bonding 2006, 121, 145-165.
(16) Collman, J. P.; Fu, L.; Herrmann, P. C.; Zhang, X. Science. 1997, 275,
949-951.
(17) Chang, C. J.; Loh, Z.-H.; Shi, C.; Anson, F. C.; Nocera, D. G. J. Am. Chem.
Soc. 2004, 126, 10013-10020.
(5) Yagi, S.; Yonekura, I.; Awakura, M.; Ezoe, M.; Takagishi, T. Chem.
Commun. 2001, 557-558.
(18) Rosenthal, J.; Pistorio, B. J.; Chng, L. L.; Nocera, D. G. J. Org. Chem.
2005, 70, 1885-1888.
(6) Chang, C. J.; Yeh, C.-Y.; Nocera, D. G. J. Org. Chem. 2002, 67, 1403-
1406.
(19) Collman, J. P.; Wagenknecht, P. S.; Hutchison, J. E. Angew. Chem., Int.
Ed. Engl. 1994, 106, 1620-39.
(7) Jokic, D.; Asfari, Z.; Weiss, J. Org. Lett. 2002, 4, 2129-2132.
(8) Chng, L. L.; Chang, C. J.; Nocera, D. G. J. Org. Chem. 2003, 68, 4075-
4078.
(20) Rosenthal, J.; Luckett, T. D.; Hodgkiss, J. M.; Nocera, D. G. J. Am. Chem.
Soc. 2006, 128, 6546-6547.
(9) Collman, J. P.; Tyvoll, D. A.; Chng, L. L.; Fish, H. T. J. Org. Chem. 1995,
60, 1926-31.
(10) Chen, W.-H.; Yan, J.-M.; Tagashira, Y.; Yamaguchi, M.; Fujita, K.
Tetrahedron Lett. 1999, 40, 891-894.
(21) Brettar, J.; Gisselbrecht, J.-P.; Gross, M.; Solladie, N. Chem. Commun.
2001, 733-734.
(22) Jokic, D.; Boudon, C.; Pognon, G.; Bonin, M.; Schenk, K. J.; Gross, M.;
Weiss, J. Chem.-Eur. J. 2005, 11, 4199-4209.
9
16286
J. AM. CHEM. SOC. 2006, 128, 16286-16296
10.1021/ja0661010 CCC: $33.50 © 2006 American Chemical Society

Supramolecular Allosteric Cofacial Porphyrin Complexes
A R T I C L E S
Scheme 1. Design of Allosteric Porphyrin-Based Supramolecules Whose Cavity Sizes Can Be Modified by the Binding of a Ligand La
a I: Condensed Macrocycle, II: Open Macrocycle. PPh2 ) diphenylphosphine and MES ) 1,3,5-trimethylbenzene.
biomimetic structures with novel physicochemical properties.23,24
Taking inspiration from nature, a primary goal of our research
has been to prepare supramolecular structures that exhibit
allosteric behavior in the context of catalysis and small-
molecule/ion sensing analgous to that displayed ubiquitously
in natural enzymatic regulation.25-28 In this context, we reasoned
that the ability to manipulate the distance between porphyrins
by altering the shape and size of supramolecular cavities in
which they reside, via external stimuli, may provide a means
for designing abiotic allosteric mimics of biological systems.
Indeed, a clear inspiration for this kind of allosteric control over
the function of multi-porphyrin assemblies comes from perhaps
the most famous example of allosteric control in biology, the
cooperative homoallosteric protein hemoglobin, in which O2
binding at one subunit initiates conformational changes that
facilitate subsequent O2 binding at other porphyrin domains.29
To design synthetic allosteric porphyrin-based structures, an
attractive strategy entails the preparation of structures that
provide facile control over both the orientation and distance of
both porphyrins in the context of a small molecule-mediated
reaction. To date, most approaches for the synthesis of cofacial
porphyrins rely on the use of covalently attached organic
molecules as spacers between the porphyrin units.6,9,21,30-32 As
cofacial porphyrins have been prepared predominantly through
synthetic organic approaches, only a few examples exist in
which transition metals have been incorporated to facilitate the
formation of cofacial porphyrins.24,33-36 Additionally, the
backbones used to couple these cofacial porphyrins are often
based upon rigid linker molecules, which restrict the overall
flexibility of the molecule and make the incorporation of
different substrates with varying size and shape challenging.
To address this issue, several cofacial porphyrin structures have
been designed which incorporate flexible linkages.22,37-40
However, few are able to specifically access a particular
conformation via the introduction or removal of small-molecule
effectors at a distal site (i.e., in an allosteric fashion). To this
end, we hypothesized that coordination complexes of type I and
II (Scheme 1), whose cavity size can be modified in situ with
small molecules to form II would be very useful for designing
stimulant-responsive porphyrin-based biomimetic systems.
Herein, we present a general, high-yielding synthetic meth-
odology for the synthesis of cofacial porphyrin complexes that
utilizes flexible porphyrin-based hemilabile ligands and MI
precursors (where MI ) RhI or CuI) to form macrocyclic
products that can be chemically stimulated to change shape.
Our strategy, based upon the Weak-Link Approach (WLA),41-43
provides rapid and convergent access to unique cofacial
porphyrin systems because it relies on the use of metal-
heteroatom interactions to facilitate the formation of the desired
macrocyclic structures, thus allowing for the controlled and
selective modification of the resulting structures in situ via
introduction of specific external stimuli. Such stimulation can
be used to tune the efficiency of a distance-dependent bimo-
lecular acyl transfer reaction and discriminate geometric isomers
of substituted pyridylcarbinol substrates.
General Methods and Instrument Details
All reactions were carried out under an inert atmosphere of nitrogen
using standard Schlenk techniques or an inert atmosphere glovebox
unless otherwise noted. Tetrahydrofuran (THF), diethyl ether (Et2O),
dichloromethane (CH2Cl2), acetonitrile (CH3CN), and hexanes were
purified according to published methods.44 All solvents were deoxy-
genated with nitrogen or argon prior to use. 1-Chloro-2-diphenylphos-
phinoethane (Organometallics Inc.), deuterated solvents (Cambridge
Isotope Laboratories Inc.), [Rh(NBD)Cl]2 (NBD ) norbornadiene,
Strem Chemicals), and 4-bromothiophenol (Alfa Aesar) were obtained
from commercial sources and used as received. 4-(2-Chloroethoxy)-
(23) Merlau, M.; Grande, W. J.; Nguyen, S. T.; Hupp, J. T. J. Mol. Cat. A:
Chem. 2000, 156, 79-84.
(24) Merlau, M. L.; del Pilar Mejia, M.; Nguyen, S. T.; Hupp, J. T. Angew.
Chem., Int. Ed. 2001, 40, 4239-4242.
(25) Heo, J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2006, 45, 941-944.
(26) Gianneschi, N. C.; Bertin, P. A.; Nguyen, S. T.; Mirkin, C. A.; Zakharov,
L. N.; Rheingold, A. L. J. Am. Chem. Soc. 2003, 125, 10508-10509.
(27) Gianneschi, N. C.; Cho, S.-H.; Nguyen, S. T.; Mirkin, C. A. Angew. Chem.,
Int. Ed. 2004, 43, 5503-5507.
(28) Gianneschi, N. C.; Nguyen, S. T.; Mirkin, C. A. J. Am. Chem. Soc. 2005,
127, 1644-1645.
(29) Stryer, L. Biochemistry, 4th ed.; W.H. Freeman and Company: New York,
1995.
(30) Brothers, P. J.; Collman, J. P. Acc. Chem. Res. 1986, 19, 209-15.
(31) Chng, L. L.; Chang, C. J.; Nocera, D. G. J. Org. Chem. 2003, 68, 4075-
4078.
(32) Guilard, R.; Burdet, F.; Barbe, J.-M.; Gros, C. P.; Espinosa, E.; Shao, J.;
Ou, Z.; Zhan, R.; Kadish, K. M. Inorg. Chem. 2005, 44, 3972-3983.
(33) Slone, R. V.; Hupp, J. T. Inorg. Chem. 1997, 36, 5422-5423.
(34) Dinolfo, P. H.; Hupp, J. T. Chem. Mater. 2001, 13, 3113-3125.
(35) Dinolfo, P. H.; Lee, S. J.; Coropceanu, V.; Bredas, J. L.; Hupp, J. T. Inorg.
Chem. 2005, 44, 5789-5797.
(36) Benkstein, K. D.; Stern, C. L.; Splan, K. E.; Johnson, R. C.; Walters, K.
A.; Vanhelmont, F. W. M.; Hupp, J. T. Eur. J. Inorg. Chem. 2002, 2818-
2822.
(37) Ohsaki, K.; Konishi, K.; Aida, T. Chem. Commun. 2002, 1690-1691.
(38) Tomohiro, Y.; Satake, A.; Kobuke, Y. J. Org. Chem. 2001, 66, 8442-
8446.
(39) Sanders, J. K. M. Chem. Eur. J. 1998, 4, 1378-1383.
(40) Pognon, G.; Boudon, C.; Schenk, K. J.; Bonin, M.; Bach, B.; Weiss, J. J.
Am. Chem. Soc. 2006, 128, 3488-3489.
(41) Gianneschi, N. C.; Masar III, M. S.; Mirkin, C. A. Acc. Chem. Res. 2005,
38, 825-837.
(42) Farrell, J. R.; Mirkin, C. A.; Guzei, I. A.; Liable-Sands, L. M.; Rheingold,
A. L. Angew. Chem., Int. Ed. 1998, 37, 465-467.
(43) Holliday, B. J.; Mirkin, C. A. Angew. Chem., Int. Ed. 2001, 40, 2022-
2043.
(44) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.; Timmers,
F. J. Organometallics. 1996, 15, 1518-20.
9
J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006 16287

A R T I C L E S
Oliveri et al.
benzaldehyde,45 2-(4-bromophenylsulfanyl)ethyldiphenylphosphane,46
5-mesityldipyrromethane,47 and (2-(mesitylthio)ethyl)diphenylphos-
phine48 were prepared according to literature procedures. The synthesis
of [5,10,15,20-tetraphenylporphyrinato]zincII (Zn(TPP))49 was adapted
from a literature synthetic procedure. All other chemicals were used
NMR (CD2Cl2): δ 25.3 (CH2-CH2-CH2), 28.3 (CH2-CH2-CH2),
28.5 (CH2-CH2-CH2), 32.3 (CH2P), 50.8 (S-CH-S), 65.5, 65.8,
114.8 (ArC), 128.7 (ArC), 128.8 (ArC), 129.0 (ArC), 129.0 (ArC), 131.9
(ArC), 132.7 (ArC), 133.0 (ArC), 138.3 (ArC), 138.4 (CHCipso), 158.7
(OCipso). 31P{1H} NMR (CD2Cl2): δ -21.6 (s). EIMS (m/z): Calcd.
421.11 [M]+. Found: 421.10. Elemental analysis for C24H25OPS2:
Calcd. C, 67.90; H, 5.94. Found: C, 67.02; H, 5.86.
1
as received from Aldrich Chemical Co. H NMR (300.22 MHz) and
13C{1H} NMR (75.50 MHz) spectra were recorded on a Varian Mercury
300 MHz FT-NMR spectrometer and referenced relative residual proton
resonances. 31P{1H} NMR (121.53 MHz) spectra were recorded on a
Varian Mercury 300 MHz FT-NMR spectrometer and referenced
relative to an external 85% H3PO4 standard. All chemical shifts are
reported in ppm. Electrospray ionization mass spectra (ESIMS) were
recorded on a Micromass Quatro II triple quadrapole mass spectrometer
or a Micromass Q-Tof Ultima mass spectrometer. Electron impact mass
spectra (EIMS) were recorded on a Fisions VG 70-250 SE mass
spectrometer. Elemental analyses were performed by Quantitative
Technologies Inc., Whitehouse, NJ. Gas chromatography (GC) analyses
of reaction mixtures were carried out on a computer-interfaced Agilent
Technologies 6890 Network instrument equipped with a flame ioniza-
tion detector (FID). The column used was a 30-m HP-5 capillary column
with a 0.32-mm inner diameter and a 0.25-µm film thickness. GC yields
were determined through integration of the product peak against
biphenyl (internal standard) using pre-established response factors. GC
retention times of products were confirmed with analytically pure
samples.
2-{4-[2-(Diphenylphosphinothioyl)ethoxy]phenyl}-(1,3)dithiane
(3). In a 100-mL Schlenk round-bottom flask, 2 (1.18 g, 2.76 mmol)
and elemental sulfur (88.5 mg, 2.76 mmol) were stirred in THF (50
mL) for 4 h at which point the solvent was removed in Vacuo and
recrystallized from CH2Cl2/hexanes to yield 3 as a light-yellow
microcrystalline solid (1.23 g, 97% yield). 1H NMR (CD2Cl2): δ 1.83
(m, 1H, CH2-CHAHB-CH2), 2.11 (m, 1H, CH2-CHAHB-CH2), 2.84
(m, 6H, (SCH2)2 and CH2P), 4.35 (m, 2H, OCH2), 5.11 (s, 1H, S-CH-
S), 6.62 (d, 2H, JH-H ) 8.7 Hz, ArH), 7.27 (d, 2H, JH-H ) 8.4 Hz,
ArH), 7.46-7.91 (br m, 10H, P(ArH)). 13C{1H} NMR (CDCl3): δ 25.2
(CH2-CH2-CH2), 32.4 (CH2-CH2-CH2), 33.0 (CH2-CH2-CH2),
50.9 (CH2PdS), 53.6 (S-CH-S), 62.5 (OCH2), 114.8 (ArC), 128.8
(ArC), 129.0 (ArC), 129.1 (ArC), 131.1 (ArC), 131.3 (ArC), 131.8
(ArC), 131.9 (ArC), 132.2 (ArC), 133.3 (ArC), 158.1 (OCipso). 31P-
{1H} NMR (CD2Cl2): δ 39.3 (s). EIMS (m/z): Calcd. 456.08 [M+].
Found. 456.07. Elemental analysis for C24H25OPS3: Calcd. C, 68.84;
H, 5.23. Found: C, 67.43; H, 4.90.
4-[2-(Diphenylphosphinothioyl)ethoxy]benzaldehyde (4). Under
ambient conditions, NaNO2 (226 mg, 3.27 mmol) and acetyl chloride
(0.233 mL, 3.27 mmol) were stirred in in CH2Cl2 (10 mL) a 100-mL
round-bottom flask at 0 °C for 10 min. A solution of 3 (500 mg, 1.09
mmol) in CH2Cl2 was added and stirred for an additional 5 min at 0
°C. At this point, H2O (5 mL) was added and the reaction was brought
to room temperature and allowed to stir for an hour. The reaction was
neutralized with a saturated aqueous solution of NaHCO3 and was
extracted with CH2Cl2 (50 mL). The organic layer was washed with
H2O (2 × 10 mL) and dried over MgSO4. After removing the solvent
in Vacuo, the crude product was purified via column chromatography
(1:1 v/v, ethyl acetate/hexanes as eluent) yielding 4 as a light-yellow
microcrystalline solid (352 mg, 88% yield). 1H NMR (CD2Cl2): δ 2.98
(m, 2H, CH2P), 4.46 (m, 2H, OCH2), 6.78 (d, 2H, JH-H ) 9 Hz, ArH),
7.48-7.91 (br m, 12H, P(ArH)), 9.84 (s, 1H, CHO). 13C{1H} NMR
(CD2Cl2): δ 32.1 (d, JC-P ) 56 Hz, CH2PdS), 63.0 (OCH2), 114.8
(ArC), 128.8 (CipsoCHO), 128.9 (ArC), 130.4 (ArC), 131.1 (ArC), 131.2
(ArC), 131.9 (ArC), 132.4 (ArC), 133.5 (ArC), 163.2 (CipsoO), 190.7
(CHO). 31P{1H} NMR (CD2Cl2): δ 39.2 (s). EIMS (m/z): Calcd. 366.08
[M+]. Found. 366.08. Elemental analysis for C21H19O2PS: Calcd. C,
63.13; H, 5.52. Found: C, 62.68; H, 5.22.
2-[4-(2-Chloroethoxy)-phenyl]-[1,3]dithiane (1). Under ambient
conditions, 4-(2-chloroethoxy)benzaldehyde (3.00 g, 16.3 mmol) and
1,3-propanedithiol (1.95 mL, 19.2 mmol) were combined with CH3-
CN (100 mL) in a 250-mL round-bottom flask and allowed to stir at
room temperature for 5 min at which point Y(OTf)3 (437 mg, 5 mol
%) was added. The resulting solution was stirred for another 30 min
when it gradually became turbid due to product precipitation. The
mixture was dried on a rotary evaporator to give an oily residue which
was then dissolved in CH2Cl2 (100 mL), washed with H2O (2 × 25
mL), dried over MgSO4, and concentrated in Vacuo. The crude product
was purified via column chromatography (1:1 v/v, CH2Cl2/hexanes as
1
an eluent) to yield 1 as a white solid (3.38 g, 75% yield). H NMR
(CD2Cl2): δ 1.80 (m, 1H, CH2-CHAHB-CH2), 2.14 (m, 1H, CH2-
CHAHB-CH2), 2.86 (m, 2H, SCH2), 2.92 (m, 2H, SCH2), 3.81 (t, 2H,
CH2Cl), 4.21 (t, 2H, OCH2), 5.15 (s, 1H, S-CH-S), 6.87 (d, 2H, JH-H
) 8.4 Hz, ArH), 7.37 (d, 2H, JH-H ) 8.7 Hz, ArH). 13C{1H} NMR
(CDCl3): δ 25.2 (CH2-CH2-CH2), 32.4 (CH2-CH2-CH2), 42.0
(ClCH2), 50.8 (S-CH-S), 68.2 (OCH2), 115.0 (ArC), 129.3 (ArC),
132.3 (CHCipso), 158.3 (OCipso). EIMS (m/z): Calcd. 274.03 [M]+.
Found: 274.02. Elemental analysis for C12H15ClOS2: Calcd. C, 52.44;
H, 5.50. Found: C, 52.35; H, 5.44.
[2-(4-[1,3]Dithian-2-yl-phenoxy)ethyl]diphenylphosphane (2). In
a 100-mL Schlenk round-bottom flask, 1 (1.00 g, 3.64 mmol) was
dissolved in THF (50 mL). To this solution, KPPh2 (7.28 mL of a 0.5
M solution in THF, 3.64 mmol) was added over 10 min and allowed
to stir for an additional 30 min. The solvent was removed, and the
residue was extracted with degassed CH2Cl2/H2O. The solvent was
removed from the organic fraction, yielding 2 as an off-white solid,
which was recrystallized from CH2Cl2/hexanes (1.37 g, 86% yield).
1H NMR (CD2Cl2): δ 1.83 (m, 1H, CH2-CHAHB-CH2), 2.11 (m, 1H,
CH2-CHAHB-CH2), 2.54 (t, 2H, CH2P), 2.84 (m, 2H, SCH2), 3.01
(m, 2H, SCH2), 4.07 (q, 2H, OCH2), 5.12 (s, 1H, S-CH-S), 6.73 (d,
2H, JH-H ) 8.7 Hz, ArH), 7.31-7.50 (br m, 12H, P(Ar-H)). 13C{1H}
5,15-Bis-{4-[2-(diphenylphosphinothioyl)ethoxy]phenyl}-10,20-
bis-(mesityl)porphyrin (5). In an aluminum-foil-wrapped 1000-mL
Schlenk round-bottom flask, 4 (1.47 g, 4 mmol), 5-mesityldipyr-
romethane (1.06 g, 4 mmol), and activated molecular sieves (4 Å) were
stirred in CHCl3 (600 mL) and degassed under a stream of N2 for 15
min. BF3•OEt2 (0.420 mL) was added dropwise to this solution, and
the resulting mixture was allowed to stir for 3 h under N2. DDQ (1.09
g, 4.8 mmol) was then added as a solid under a stream of N2, and the
reaction was allowed to stir for an additional 30 min at which point
NEt3 (4 mL) was added. The reaction mixture was stirred for 1 min
before being filtered through a pad of Celite to remove the sieves. The
solution was concentrated in Vacuo and the resulting residue was
dissolved in a minimum amount CH2Cl2 and poured on top of a silica
gel column and purified via flash chromatography (eluent CH2Cl2) to
yield 5 as a purple microcrystalline solid (1.01 g, 41% yield). 1H NMR
(CD2Cl2): δ -2.69 (s, 2H, NH), 1.82 (s, 12H, CH3), 2.66 (s, 6H, CH3),
3.16 (m, 4H, CH2PdS), 4.66 (m, 4H, OCH2), 7.07 (d, 4H, JH-H ) 7.8
Hz, ArH), 7.30 (s, 4H), 7.59 (br s, 12H, ArH), 7.96 (m, 12H, ArH),
8.65 (d, 4H, JH-H ) 5.1 Hz, ArH), 8.79 (d, 4H, JH-H ) 4.5 Hz, ArH).
31P{1H} NMR (CD2Cl2): δ 39.5 (s). ESIMS (m/z): Calcd. 1219.4 [M+].
(45) Mao, P. C.-M.; Mouscadet, J.-F.; Leh, H.; Auclair, C.; Hsu, L.-Y. Chem.
Pharm. Bull. 2002, 50, 1634-1637.
(46) Brown, A. M.; Ovchinnikov, M. V.; Stern, C. L.; Mirkin, C. A. J. Am.
Chem. Soc. 2004, 126, 14316-14317.
(47) Laha, J. K.; Dhanalekshmi, S.; Taniguchi, M.; Ambroise, A.; Lindsey, J.
S. Org. Process Res. DeV. 2003, 7, 799-812.
(48) Brown, A. M.; Ovchinnikov, M. V.; Mirkin, C. A. Angew. Chem., Int. Ed.
2005, 44, 4207-4209.
(49) Tomizaki, K.-y.; Yu, L.; Wei, L.; Bocian, D. F.; Lindsey, J. S. J. Org.
Chem. 2003, 68, 8199-8207.
9
16288 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Supramolecular Allosteric Cofacial Porphyrin Complexes
A R T I C L E S
Found: 1219.3. Elemental analysis for C78H68N4O2P2S2: Calcd. C,
76.82; H, 5.62; N, 4.59. Found: C, 76.04; H, 5.18; N, 4.65.
Compound 9 was isolated as an off-white microcrystalline solid (3.02
g, 92% yield). 1H NMR (CD2Cl2): δ 2.68 (m, 2H, CH2PdS), 3.10 (m,
2H, SCH2), 7.12 (d, 2H, JH-H ) 8.7 Hz, ArH), 7.39 (d, 2H, JH-H
)
[5,15-Bis-{4-[2-(diphenylphosphinothioyl)ethoxy]phenyl}-10,20-
bis-(mesityl)porphyrinato]zinc (II) (6). Under ambient conditions, 5
(500 mg, 0.399 mmol) and Zn(OAc)2•2H2O (700 mg, 3.19 mmol) were
combined in a 500-mL round-bottom flask and stirred under reflux for
4 h in a CHCl3/CH3OH (4:1 v/v, 350 mL) solution. The solution was
then washed with H2O (100 mL) and extracted with CHCl3 (2 × 100
mL). The organic layer was further washed with H2O (100 mL), dried
over Na2SO4, and concentrated to give 6 as a purple microcrystalline
solid (507 mg, 96% yield). 1H NMR (THF-d8): δ 1.83 (s, 12H, CH3),
2.60 (m, 6H, CH3), 2.79 (m, 4H, CH2PdS), 4.36 (m, 4H, OCH2), 7.16
(br m, 28H, ArH), 8.09 (d, 4H, JH-H ) 8.4 Hz, ArH), 8.61 (d, 4H,
JH-H ) 4.5 Hz, ArH), 8.77 (d, 4H, JH-H ) 4.5 Hz, ArH). 31P{1H}
NMR (THF-d8): δ 39.2 (s). ESIMS (m/z): Calcd. 1282.8 [M+].
Found: 1282.2. Elemental analysis for C78H66N4O2P2S2Zn: Calcd. C,
73.03; H, 5.19 H; N, 4.37. Found: C, 72.89; H, 5.23; N, 4.17.
[5,15-Bis-[4-(2-diphenylphosphanylethoxy)phenyl]-10,20-bis-
(mesityl)porphyrinato]zinc(II) (7). In a 50-mL Schlenk round-bottom
flask, 6 (300 mg, 0.234 mmol) and Cp2ZrHCl (392 mg, 1.52 mmol)
were stirred in THF under N2 (40 mL) at 60 °C for 4 h. The solvent
was removed and the reaction was purified via column chromatography
(silica gel, THF) in a glove box under an atmosphere of N2. The solvent
was removed in Vacuo to yield 7 as a purple microcrystalline solid
8.7 Hz, ArH), 7.48 - 7.79 (m, 10H, P(ArH)). 13C{1H} NMR (CDCl3):
δ 26.9 (SCH2), 32.3 (d, CH2PdS, JC-P ) 51.3 Hz), 128.9 (ArC), 129.1
(ArC), 131.0 (ArC), 131.1 (ArC), 131.2 (ArC), 131.6 (ArC), 132.0
(ArC), 132.3 (ArC). 31P{1H} NMR (CD2Cl2): δ 41.4 (s). EIMS (m/z):
Calcd. 431.97 [M+]. Found: 431.97. Elemental analysis for C20H18-
BrPS2: Calcd. C, 55.43; H, 4.19. Found: C, 55.59, H, 4.07.
4-[2-(Diphenylphosphinothioyl)ethylsulfanyl]benzaldehyde (10).
Compound 9 (3.00 g, 6.90 mmol) was dissolved in THF (60 mL) in a
100-mL Schlenk round-bottom flask and was cooled to -78 °C. n-BuLi
(2.76 mL, 6.90 mmol, 2.5 M in hexanes) was added dropwise to the
solution over 5 min and the mixture was allowed to stir for 30 min,
before DMF (0.802 mL, 10.35 mmol) was added to the flask. This
solution was cooled to -78 °C and allowed to stir for an additional 30
min before the temperature was allowed to rise back to room
temperature. The mixture was quenched with H2O followed by
extraction with CH2Cl2. The organic layer was dried over MgSO4,
filtered, and concentrated in Vacuo to give a yellow crude product which
was then recrystallized (CH2Cl2/pentane) to yield 10 as a light-yellow
microcrystalline solid (2.35 g, 88% yield). 1H NMR (CD2Cl2): δ 2.76
(m, 2H, CH2PdS), 3.23 (m, 2H, SCH2), 7.29 (d, 2H, JH-H ) 6.6 Hz,
ArH) 7.47 (m, 6H, P(ArH)), 7.73 (d, 2H, JH-H ) 8.7 Hz, ArH), 7.79
(m, 4H, P(ArH)), 9.92 (s, 1H, CHO). 13C{1H} NMR (CDCl3): δ 25.0
(SCH2), 32.0 (d, CH2PdS, JC-P ) 51.3 Hz), 126.8 (ArC), 129.0 (ArC),
129.1 (ArC), 130.4 (ArC), 131.1 (ArC), 131.3 (ArC), 132.1 (ArC), 132.5
(ArC), 191.4 (CHO). 31P{1H} NMR (CD2Cl2): δ 41.5 (s). EIMS (m/
z): Calcd. 382.01 [M+]. Found. 382.06. Elemental analysis for C21H19-
OPS2: Calcd. C, 65.94; H, 5.01. Found: C, 65.23; H, 4.71.
1
(254 mg, 89% yield). H NMR (THF-d8): δ 1.83 (s, 12H, CH3), 2.60
(s, 6H, CH3), 2.77 (m, 4H, CH2P), 4.36 (m, 4H, CH2O), 7.17 (d, 4H,
JH-H ) 6.6 Hz, ArH), 7.30 - 7.61 (bm, 24H, ArH), 8.01 (d, 4H, JH-H
) 8.7 Hz, ArH), 8.64 (d, 4H, JH-H ) 4.5 Hz, ArH), 8.78 (d, 4H, JH-H
) 4.5 Hz, ArH). 31P{1H} NMR (THF-d8): δ -21.2 (s). ESIMS (m/z):
Calcd. 1218.74 [M+]. Found: 1217.4. Elemental analysis for
C78H66N4O2P2Zn: Calcd. C, 76.87; H, 5.46; N, 4.60. Found: C, 76.37;
H, 5.18; N, 4.45.
[5,15-Bis-[4-(2-diphenylphosphinothioylethylsulfanyl)phenyl]-10,-
20-bis-(mesityl)porphyrin (11). In an aluminum-foil-wrapped 1000-
mL Schlenk flask, compound 10 (1.23 g, 3.20 mmol), 5-mesityldipyr-
romethane (848 mg, 3.20 mmol), and activated molecular sieves (4 Å)
were stirred in CHCl3 (600 mL) and degassed under a stream of N2 for
15 min. BF3•OEt2 (0.350 mL) was added dropwise to this solution,
and the resulting mixture was allowed to stir for 3 h under N2. DDQ
(862 mg, 3.8 mmol) was then added as a solid under a stream of N2,
and the reaction was allowed to stir for an additional 30 min at which
point NEt3 (4 mL) was added. The reaction mixture was stirred for 1
min before being filtered through a pad of Celite to remove the sieves.
The solution was concentrated in Vacuo and the resulting residue was
dissolved in CH2Cl2 and poured on top of a silica gel column (eluent
CH2Cl2). Subsequent chromatography yielded 11 as a purple microc-
rystalline solid (879 mg, 44% yield). 1H NMR (CD2Cl2): δ -2.67 (s,
2H, NH), 1.84 (s, 12H, CH3), 2.63 (s, 6H, CH3), 3.03 (m, 4H, CH2Pd
S), 3.42 (m, 4H, SCH2), 7.31 (s, 4H, mesityl H), 7.55 (m, 16H, ArH),
7.89 (m, 8H, ArH), 8.13 (d, 4H, JH-H ) 8.1 Hz, ArH), 8.69 (d, 4H,
JH-H ) 5.1 Hz, ArH), 8.82 (d, 4H, JH-H ) 4.8 Hz, ArH). 31P{1H}
NMR (CD2Cl2): δ 41.6 (s). ESIMS (m/z): Calcd. 1251.6 [M+].
Found: 1251.3. Elemental analysis for C78H68N4P2S4: Calcd. C, 74.85;
H, 5.48; N, 4.48. Found: C, 74.35; H, 4.98; N, 4.43.
[(7)RhCl(CO)]2 Macrocycle (8a). A small vial was charged with
[Rh(CO)2(Cl)]2 (4.80 mg, 0.0123 mmol) and CH2Cl2 (2 mL). The
resulting solution was stirred for 1 min, at which point a solution of 7
(30.0 mg, 0.0246 mmol) in THF (5 mL) was added dropwise over 1
min. The resulting solution was stirred for 3 h. The solvent was removed
and the product was recrystallized from CH2Cl2/pentane (32.1 mg, 94%
1
yield). H NMR (CD2Cl2): δ 1.54 (s, 24H, CH3), 2.56 (s, 12H, CH3),
3.34 (br m, 8H, CH2P), 4.81 (br m, 8H, CH2O), 7.10 (br m, 22H, ArH),
7.47 (m, 22H, ArH), 7.90 (br m, 20H, ArH), 8.79 (br m, 16H, ArH).
31P{1H} NMR (CD2Cl2): δ 21.6 (d, JRh-P ) 124 Hz). ESIMS (m/z)
for [C156H132N8O4P4Rh2Zn2(CO)2]2+: Calcd. 1349.6. Found: 1349.3.
Elemental analysis for C158H132Cl2N8O6P4Rh2Zn2: Calcd. C, 68.51; H,
4.80 H; N, 4.04. Found: C, 68.38; H, 4.91; N, 3.52.
[(7)Cu(CH3CN)2(PF6)]2 Macrocycle (8b). A 50-mL Schlenk flask
was charged with [Cu(CH3CN)4]PF6 (29.8 mg, 0.0799 mmol) and CH2-
Cl2 (5 mL). A THF solution of 7 (100 mg, 0.0799 mmol, 20 mL) was
added to the “Cu” solution dropwise over 5 min at room temperature
to give a red/purple solution, which was then allowed to stir for 3 h.
The solvent was removed to yield a purple microcrystalline solid which
was recrystallized from CH2Cl2/pentane (107 mg, 92% yield). 1H NMR
(CD2Cl2): δ 1.66 (s, 24H, CH3), 2.07 (s, 12H, CH3CN), 2.43 (s, 12H,
CH3), 2.95 (br m, 8H, CH2P), 4.46 (br m, 8H, CH2O), 7.10 (s, 22H,
ArH), 7.50 (s, 22H, ArH), 7.62 (12H, ArH), 8.00 (d, 8H, JH-H ) 7.8
Hz, ArH), 8.64 (d, 8H, JH-H ) 4.2 Hz, ArH), 8.78 (d, 8H, JH-H ) 4.2
Hz, ArH). 31P{1H} NMR (CD2Cl2): δ -11.5 (s). ESIMS (m/z) for
[C156H132N8S4P4Cu2Zn2]2+: Calcd. 1282.2. Found: 1282.4. Elemental
analysis for [C164H144N12O4P6F12Zn2Cu2]: Calcd. C, 65.25; H, 4.81;
N, 5.57. Found: C, 65.32; H, 4.56; N, 6.35.
[5,15-Bis-[4-(2-diphenylphosphinothioylethylsulfanyl)phenyl]-10,-
20-bis(mesityl)porphyrinato] zinc(II) (12). In a 250-mL round-bottom
flask, 11 (400 mg, 0.319 mmol) and Zn(OAc)2•2H2O (700 mg, 3.19
mmol) were refluxed for 3 h in a CHCl3/CH3OH (4:1 v/v, 200 mL)
solution. The solution was washed with H2O (100 mL) and extracted
with CHCl3 (2 × 50 mL). The organic layer was washed again with
H
2O (50 mL), dried over Na2SO4, and concentrated to give 12 as a
1
purple microcrystalline solid (412 mg, 98% yield). H NMR (CD2-
Cl2): δ 1.82 (s, 12H, CH3), 2.63 (s, 6H, CH3), 3.03 (m, 4H, CH2PdS),
3.41 (m, 4H, SCH2), 7.31 (s, 4H, ArH), 7.54 (m, 12H, ArH), 7.89 (m,
1-Bromo-4-[2-(diphenylphosphinothioyl)ethylsulfanyl]-benzene
(9). In a 100-mL Schlenk round-bottom flask, 2-(4-bromo-phenylsul-
fanyl)-ethyldiphenylphosphane (3.00 g, 7.48 mmol), and elemental
sulfur (264 mg, 8.22 mmol) were stirred in THF (150 mL) under N2
for 3 h. The reaction mixture was concentrated in Vacuo, and the product
was purified via column chromatography (1:1 v/v, CH2Cl2/hexanes).
12H, ArH), 8.12 (d, 4H, JH-H ) 8.4 Hz, ArH), 8.76 (d, 4H, JH-H
)
5.1 Hz, ArH), 8.89 (d, 4H, JH-H ) 4.8 Hz, ArH). 31P{1H} NMR (CD2-
Cl2): δ 41.6 (s). ESIMS (m/z): Calcd. 1314.9 [M+]. Found: 1314.1.
9
J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006 16289

A R T I C L E S
Oliveri et al.
Elemental analysis for C78H66N4P2S4Zn: Calcd. C, 71.24; H, 5.06; N,
4.26. Found: C, 70.69; H, 4.97; N, 3.94.
CH2S), 7.17 - 7.55 (br m, 56H, ArH), 8.04 (d, 8H, JH-H ) 7.8 Hz,
ArH), 8.64 (d, 8H, JH-H ) 4.5 Hz, ArH), 8.70 (d, 8H, JH-H ) 4.8 Hz,
ArH). 31P{1H} NMR (CD2Cl2): δ -8.0 (s). ESIMS (m/z) for
[C156H132N8S4P4Cu2Zn2]2+: Calcd. 1314.4. Found: 1314.9.
[5,15-Bis-[4-(2-diphenylphosphanylethylsulfanyl)phenyl]-10,20-
bis(mesityl)porphyrinato]zinc(II) (13). In a 50-mL Schlenk flask, 12
(300 mg, 0.228 mmol) and Cp2ZrHCl (382 mg, 1.48 mmol) were stirred
in THF (40 mL) at 60 °C for 3 h. The solvent was removed, and the
product was purified via column chromatography (THF, silica gel) in
a glove box under an atmosphere of N2. The solvent was removed in
Vacuo to yield 13 as a purple microcrystalline solid (251 mg, 88%
yield). 1H NMR (THF-d8): δ 1.84 (s, 12H, CH3), 2.47 (m, 4H, CH2P),
2.61 (s, 6H, CH3), 3.23 (m, 4H, SCH2), 7.29 (br m, 28H, ArH), 8.09
(d, 4H, JH-H ) 7.8 Hz, ArH), 8.64 (d, 4H, JH-H ) 4.8 Hz, ArH), 8.79
(d, 4H, JH-H ) 4.2 Hz, ArH). 31P{1H} NMR (THF-d8): δ -15.2 (s).
ESIMS (m/z): Calcd. 1250.8 [M+]. Found: 1249.4. Elemental analysis
for C78H66N4P2S2Zn: Calcd. C, 74.90; H, 5.32; N, 4.48. Found: C,
73.15; H, 4.94; N, 4.16.
[(Ph2PCH2CH2S-C6H2(CH3)3)2Rh]BF4 Condensed Tweezer-Type
Complex (16a). A 20-mL vial was charged with [Rh(NBD)Cl]2 (63.2
mg, 0.137 mmol), AgBF4 (53.4 mg, 0.274 mmol), and CH2Cl2 (4 mL).
This solution was stirred for 1 h and then filtered dropwise through
Celite into a Schlenk flask. The orange solution was then diluted with
CH2Cl2 (20 mL) to give a clear yellow solution. A solution of
(2-(mesitylthio)ethyl)diphenylphosphine (200 mg, 0.549 mmol) in CH2-
Cl2 (20 mL) was added to the “Rh” solution dropwise over 5 min at
room temperature to give a clear yellow solution, which was then stirred
for an additional 3 h. The solvent was removed to yield 16a as a yellow
microcrystalline solid which was recrystallized from CH2Cl2/pentane
(113 mg, 90% yield). 1H NMR (CD2Cl2): δ 2.22 (d, 12H, CH3), 2.51
(br s, 10H, CH3 and SCH2CH2P), 2.83 (br m, 4H, CH2P), 6.71 (s, 4H,
ArH), 7.23 - 7.34 (br m, P(Ar-H)2, 20H). 31P{1H} NMR (CD2Cl2):
δ 63.0 (d, JRh-P ) 163 Hz). ESIMS (m/z) for [C46H50N8S2P2Rh]+:
Calcd. 831.8. Found: 831.6.
(Ph2PCH2CH2S-C6H2(CH3)3)2RhCl(CO) Open Tweezer-Type
Complex (16b). Compound 16a (15.0 mg, 0.0163 mmol) was dissolved
in CD2Cl2 (1 g) and placed in an air-free NMR tube. PPNCl
(bis(triphenylphosphoranylidene)ammonium chloride, 9.38 mg, 0.0163
mmol) was added as a solid and the NMR tube was then pressurized
with CO (1 atm) for 30 s. Compound 16a was quantitatively converted
to 16b as determined by 31P{1H} NMR spectroscopy. 1H NMR (CD2-
Cl2): δ 2.25 (s, 6H, CH3), 2.37 (s, 12H, CH3), 2.67 (br m, 4H, CH2P),
2.82 (br m, 4H, CH2S), 6.90 (s, 4H, ArH), 7.34 - 7.65 (br m, 50H,
(C6H5)3PPN, P(Ar-H)2). 31P{1H} NMR (CD2Cl2): δ 22.1 (s, PPNCl),
δ 23.5 (d, JRh-P ) 123 Hz). ESIMS (m/z) for [C46H50N8S2P2Rh]+ (M
- (Cl-/CO)): Calcd. 831.8. Found: 831.2.
[(13)Rh(BF4)]2 Condensed Macrocycle (14a). A small vial was
charged with [Rh(NBD)Cl]2 (31.0 mg, 0.068 mmol), AgBF4 (26.0 mg,
0.135 mmol), and CH2Cl2 (4 mL). This solution was stirred for 1 h
and then filtered dropwise through Celite into a Schlenk flask. The red
solution was then diluted with CH2Cl2 (20 mL) to give a clear yellow/
orange solution. A solution of ligand 13 (170 mg, 0.135 mmol) in THF
(20 mL) was added to the “Rh” solution dropwise over 5 min at room
temperature to give a dark-purple solution, which was then stirred for
an additional 3 h. The solvent was removed to yield 14a as a purple
microcrystalline solid which was recrystallized from CH2Cl2/pentane
1
(176 mg, 90% yield). H NMR (CD2Cl2): δ 1.48 (br s, 24H, CH3),
2.44 (br s, 12H, CH3), 2.76 (br m, 8H, CH2P), 3.20 (br m, 8H, CH2S),
6.98 (br m, 8H, ArH), 7.37 - 7.59 (br m, 40H, ArH), 8.02 (br m,
16H, ArH), 8.50 (br m, 16H, ArH). 31P{1H} NMR (CD2Cl2): δ 64.1
(d, JRh-P ) 162 Hz). ESIMS (m/z) for [C156H132N8S4P4Rh2Zn2]2+
:
Calcd.1353.7.Found: 1354.1.Elementalanalysisfor[C156H132B2F8N8S4P4-
Rh2Zn2]: Calcd. C, 65.03; H, 4.62; N, 3.89. Found: C, 65.56; H, 4.11;
N, 3.46.
General Procedure for Catalysis Experiments. The formation of
2-, 3-, and 4-acetoxymethylpyridine were monitored by GC relative to
an internal standard (biphenyl) and quantified using a previously
established calibration curve. Experiments containing 14a, 15a, or a
mixture of an analogous monomeric RhI complex (16a or 16b) and
Zn(TPP) (as the control), respectively, were run concurrently in
separate vials at room temperature in CH2Cl2 under an atmosphere of
N2 inside a glove box.
[(13)Cu(PF6)]2 Condensed Macrocycle (14b). A 50-mL Schlenk
flask was charged with [Cu(CH3CN)4]PF6 (29.8 g, 0.0799mmol). The
CuI precursor was dissolved in CH2Cl2 (5 mL), and a THF solution of
ligand 13 (100 mg, 0.0799 mmol, 20 mL) was added to the “Cu”
solution dropwise over 5 min at room temperature to give a red/purple
solution. The solution was then allowed to stir for 3 h. The solvent
was removed to yield 14b as a purple microcrystalline solid which
was recrystallized from CH2Cl2/pentane (105 mg, 90% yield). 1H NMR
(CD2Cl2): δ 1.75 (br s, 24H, CH3), 2.55 (br s, 12H, CH3), 3.00 (br m,
8H, CH2P), 3.65 (br m, 8H, CH2S), 7.24 - 7.82 (br m, 56H, ArH),
8.16 (br m, 8H, ArH), 8.76 (br s, 16H, ArH). 31P{1H} NMR (CD2Cl2):
δ 1.0 (s). ESIMS (m/z) for [C156H132N8S4P4Cu2Zn2]2+: Calcd. 1314.4.
Found: 1314.5. Elemental analysis for [C156H132N8S4P6F12Cu2Zn2]CH2-
Cl2: Calcd. C, 62.78; H, 4.50; N, 3.73. Found: C, 61.95;H, 4.18; N,
3.31.
GC Experiments for the Closed Macrocycle (14a). Inside a glove
box, CH2Cl2 stock solutions of complex 14a (0.58 mL of a 2.6 mM
solution), biphenyl (0.5 mL of a 25 mM solution), and pyridylcarbinol
(0.5 mL of a 90 mM solution) were added to a 20-mL vial. Fresh CH2-
Cl2 was added to the vial bringing the total reaction volume up to 4.5
mL. After stirring for 5 min, 1-acetylimidazole (0.5 mL of a 60 mM
solution) was added to the vial (t ) 0). At various times, an aliquot
(100 µL) was taken from the solution and added to diethyl ether (2
mL). This was then passed down a plug of Celite (3 cm × 0.5 cm) to
remove the catalyst. The plug was further treated with fresh diethyl
ether (5 mL). The combined organics were used for GC analysis.
GC Experiments for the Open Macrocycle (15a). Inside a glove box,
complex 14a (0.58 mL of a 2.6 mM solution) and benzyltriethylam-
monium chloride (0.5 mL of a 6.4 mM solution) were added to a 10-
mL Schlenk flask. The flask was removed from the glove box and
placed on a Schlenk line where CO (1 atm) was bubbled through the
solution for 30 s resulting in the formation of 15a. The flask was brought
back into the glove box and the contents were transferred into a vial.
Fresh CH2Cl2 was added to the flask and transferred into the vial
bringing the total reaction volume up to approximately 4 mL.
Pyridylcarbinol (0.5 mL of a 90 mM solution) and biphenyl (0.5 mL
of a 25 mM solution) were added to the vial and after stirring for 5
min, 1-acetylimidazole (0.5 mL of a 60 mM solution) was added to
the flask (t ) 0). At various times, an aliquot (100 µL) was taken from
the solution and added to diethyl ether (2 mL). This was then passed
down a plug of Celite (3 cm × 0.5 cm) to remove the catalyst. The
[(13)RhCl(CO)]2 Macrocycle (15a). Compound 14a (20.0 mg,
0.00694 mmol) was dissolved in CD2Cl2 (1 g) and placed in an air-
free NMR tube. PPNCl (Bis(triphenylphosphoranylidene) ammonium
chloride, 2 equiv) was added and the NMR tube was then pressurized
with CO (1 atm) for 30 s. Compound 14a was quantitatively converted
1
to 15a as determined by 31P NMR spectroscopy. H NMR (CD2Cl2):
δ 1.77 (br s, 24H, CH3), 2.54 (br s, 12H, CH3), 3.14 (br m, 8H, CH2P),
3.48 (br m, 8H, CH2S), 7.26 - 8.01 (br m, 124H, (C6H5)3PPN, P(C6H5)2,
ArH), 8.65 - 8.80 (br m, 16H, ArH). 31P{1H} NMR (CD2Cl2): δ 22.1
(s, PPNCl), δ 25.1 (d, JRh-P ) 123 Hz). ESIMS (m/z) for [C156H132N8S4P4-
Rh2Zn2]2+ (M - 2(Cl-/CO)): Calcd. 1353.7. Found: 1353.7
[(13)Cu(pyridine-d5)2(PF6)]2 Macrocycle (15b). Compound 14b
(20.0 mg, 0.00640 mmol) was dissolved in CD2Cl2 (1 g) and placed in
an air-free NMR tube. C5D5N (4 equiv.) was added to this solution
and the conversion of 15b was quantitative as determined by 1H NMR
1
and 31P NMR spectroscopy. H NMR (CD2Cl2): δ 1.72 (br s, 24H,
CH3), 2.45 (br s, 12H, CH3), 2.82 (br m, 8H, CH2P), 3.38 (br m, 8H,
9
16290 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Supramolecular Allosteric Cofacial Porphyrin Complexes
A R T I C L E S
Scheme 2. Synthesis of Ether-Based Ligand 7 and Macrocycles 8a and 8ba
a (i) 1-bromo-2-chloroethane, K2CO3, Acetone, Reflux; (ii) 1,3-propanedithiol, Y(OTf)3 (5 mol %), CH3CN; (iii) KPPh2, THF; (iv) S8, THF;( v) NaNO2,
AcCl/H2O, CH2Cl2, 0 °C f rt; (vi) 5-mesityldipyrromethane, BF3•OEt2, DDQ, NEt3, CHCl3, 4 Å Molecular Sieves; (vii) Zn(OAc)2•2H2O, 4:1 CHCl3/
MeOH, Reflux; (viii) Cp2ZrHCl, THF, 60 °C; (ix) [Rh(CO)2(Cl)]2, CH2Cl2/THF; (x) [Cu(CH3CN)4]PF6, CH2Cl2/THF.
plug was further treated with fresh diethyl ether (5 mL). The resulting
samples were used for GC analysis.
vial bringing the total reaction volume up to approximately 4 mL.
Pyridylcarbinol (0.5 mL of a 90 mM solution) and biphenyl (0.5 mL
of a 25 mM solution) were added to the vial and after stirring for 5
min, 1-acetylimidazole (0.5 mL of a 60 mM solution) was added to
the flask (t ) 0). At various times, an aliquot (100 µL) was taken from
the solution and added to diethyl ether (2 mL). This was then passed
down a plug of Celite (3 cm × 0.5 cm) to remove the catalyst. The
plug was further treated with fresh diethyl ether (5 mL). The combined
organics were used for GC analysis.
GC Control Experiments for RhI-Monomer (16a) and Porphyrin
Monomer (Zn(TPP)). Inside a glove box, CH2Cl2 stock solutions of
complex 16a (0.892 mL of a 8.0 mM solution), biphenyl (0.5 mL of a
25 mM solution), Zn(TPP) (0.20 mL of a 15 mM solution), and
pyridylcarbinol (0.5 mL of a 90 mM solution) were added to a 20-mL
vial. Fresh CH2Cl2 was added to the vial bringing the total reaction
volume up to 4.5 mL. After stirring for 5 min, 1-acetylimidazole (0.5
mL of a 60 mM solution) was added to the vial (t ) 0). At various
times, an aliquot (100 µL) was taken from the solution and added to
diethyl ether (2 mL). This was then passed down a plug of Celite (3
cm × 0.5 cm) to remove the catalyst. The plug was further treated
with fresh diethyl ether (5 mL). The combined organics were used for
GC analysis.
Results and Discussion
The Design of Ether-Phosphine Hemilabile Ligand 7. To
design porphyrin-based supramolecular systems capable of in
situ allosteric activity, flexibility must be engineered into the
backbone of the framework as well as “weak” and “strong”
binding structural domains. To this end, we synthesized two
new hemilabile porphyrin ligands which incorporate “weak”
ether or thioether functionalities in addition to “strong” phos-
phine binding sites. Ether-based ligand 7 was obtained in eight
steps from 4-hydroxybenzaldehyde (Scheme 2). 4-Hydroxy-
benzaldehyde was alkylated with excess 1-bromo-2-chloroethane
to yield 4-(2-chloroethoxy)benzaldehyde, which was trans-
formed into 3 after a dithiane protection of the aldehyde,
GC Control Experiments for RhI-Monomer (16b) and Porphyrin
Monomer . Inside a glove box, complex 16a (0.892 mL of a 8.0 mM
solution), Zn(TPP) (0.20 mL of a 15 mM solution), and benzyltriethy-
lammonium chloride (1.0 mL of a 6.4 mM solution) were added to a
10-mL Schlenk flask. The flask was removed from the glove box and
placed on a Schlenk line where CO (1 atm) was bubbled through the
solution for 30 s resulting in the formation of 16b. The flask was
brought back into the glove box and the contents were transferred into
a vial. Fresh CH2Cl2 was added to the flask and transferred into the
9
J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006 16291

A R T I C L E S
Oliveri et al.
conversion of the chloride to the corresponding phosphine, and
reaction with elemental sulfur. Deprotection of the dithiane
moiety in 3, followed by condensation of the resulting aldehyde
with 5-mesityldipyrromethane affords the freebase porphyrin 5
in gram quantities after column chromatography. Metalation
with Zn(OAc)2•2H2O gave compound 6, and desulfurization
with Schwartz’s reagent gave ligand 7 in 12% overall yield.
The use of a sulfide as the protecting group for the phosphine
moiety not only allowed for a convenient nonaqueous protection/
deprotection sequence, but also significantly increased the
scalability and the yield of the porphyrin synthesis while
simplifying the complicated purification and isolation process
that often accompanies porphyrin syntheses. Indeed, if one uses
an oxide protecting group as opposed to the sulfide, the ligand
adheres to the silica column used for chromatography and makes
the isolation of the pure product difficult.
Reactivity of Ligand 7 with RhI and CuI. Initially, our
attention was focused on the design, synthesis, and isolation of
RhI and CuI condensed intermediates of type I using ligand 7.
Unfortunately, isolation of these products proved impossible
under the conditions explored. However, we discovered that the
“open” macrocyclic structure 8a can be obtained directly in
quantitative yield upon reaction of ligand 7 with [Rh(CO)2(Cl)]2.
The 31P{1H} NMR spectrum of 8a exhibits a single resonance
at δ 21.6 (d, JRh-P ) 124 Hz), diagnostic of a highly
symmetrical porphyrin complex with trans-phosphines and is
consistent with the proposed structural formulation for 8a.50
ESIMS analysis of 8a shows a parent ion at m/z 1349.3,
indicating the loss of each Cl- ligand bound to the RhI centers.
RhI complexes with analogous coordination environments often
lose these ligands during ESIMS.50
Similar to the reactivity exhibited with RhI, ligand 7 forms
the analogous “open” macrocyclic product 8b when reacted with
[Cu(CH3CN)4]PF6. The 31P{1H} NMR spectrum of 8b exhibits
a singlet at δ -11.5 consistent with a tetrahedral CuI-P
environment.51 The resonance is substantially shifted downfield
from the one observed for free ligand at δ -21.2. Characteriza-
tion of this product via ESIMS leads to the observation of a
parent ion at m/z 1282.4 which corresponds to the loss of two
CH3CN molecules from each CuI metal center. This is consistent
with the known lability of the bound CH3CN molecules, which
has been observed in analogous systems.51
X-ray Structure Determination of 8a⊂DABCO and
8c⊂DABCO. Initial attempts to grow crystals of 8a in a variety
of solvent mixtures proved unsuccessful, presumably due to the
large free volume and flexibility of the cavity. We hypothesized
that crystals of 8a could be obtained in the presence of a ligand
that can span and coordinate to the two Zn-centers within the
macrocycle, filling the free volume and rigidifying the overall
structure. Indeed, X-ray quality crystals were obtained from
vapor diffusion of pentane/diethyl ether (1:1 v/v) into a THF/
CH2Cl2 (1:1 v/v) solution of 8a containing DABCO which was
layered with acetonitrile. The 56-membered macrocyclic product
8a⊂DABCO contains two porphyrin moieties aligned and
locked into a cofacial arrangement in the solid-state by a
DABCO ligand (Figure 1). The Zn-Zn distance of 7.09 Å is
significantly longer than the P-Rh-P distance of 4.64 which
Figure 1. Graphical representations of the X-ray crystal structure of
8a⊂DABCO as viewed (A) from the side and (B) from the top containing
a molecule of DABCO bridging both Zn atoms. Hydrogen atoms, disordered
DABCO carbon atoms, and solvent molecules have been omitted for clarity.
Pink ) Rh, Red ) O, Yellow ) Cl, Green ) P, Blue ) N, Light Blue )
Zn.
is made possible by the flexible (CH2)2O linkages between the
porphyrin moieties and the RhI hinges. This large porphyrin-
porphyrin distance allows for the mesityl arms of the porphyrin
moieties to align in a near superimposable fashion.
Attempts to crystallize 8b in a similar manner led to an
unexpected reaction with the halogenated solvent. Because the
solubility of 8b in pure THF is poor, a mixture of solvents
proved to be the most effective for crystallization. Analytically
pure samples of 8b were dissolved in a THF/CH2Cl2 solution
containing DABCO which was first layered with acetonitrile
following by a slow second layer of a solution of pentane/diethyl
ether (1:1 v/v). X-ray quality crystals were obtained from this
mixture after 1 day and subjected to single-crystal diffraction
analysis at the Advanced Photon Source (APS, Argonne
National Laboratory). Although 8b has been shown to contain
four molecules of CH3CN and two PF6- counterions according
to elemental analysis, the diffraction experiment yielded a
structure with DABCO bridging both Zn-atoms and two Cl-
anions bound to each tetrahedral Cu metal center, indicating
an oxidation of the original CuI center to CuII forming
8c⊂DABCO (see Supporting Information). Such a compound
could be formed from the dehalogenation of alkyl halide solvents
(i.e., CH2Cl2 and CHCl3) by the CuI center in 8b, similar to
that observed by Karlin et al. for (TMPA)CuI (TMPA ) (tris-
(2-pyridylmethyl)amine)) in CH2Cl2.52-54 That 8c⊂DABCO
possesses the framework expected for 8b supports our assign-
ment of an open macrocyclic structure for the product isolated
from the reaction of 7 and [Cu(CH3CN)4]PF6.
(52) Lucchese, B.; Humphreys, K. J.; Lee, D. H.; Incarvito, C. D.; Sommer, R.
D.; Rheingold, A. L.; Karlin, K. D. Inorg. Chem. 2004, 43, 5987-5998.
(53) Tyeklar, Z.; Richard, R. R.; Wei, N.; Murthy, N. N.; Zubieta, J.; Karlin,
K. D. J. Am. Chem. Soc. 1994, 43, 5987-5988.
(54) Wei, N.; Murthy, N. N.; Tyeklar, Z.; Karlin, K. D. Inorg. Chem. 1994, 33,
1177-1183.
(50) Dixon, F. M.; Eisenberg, A. E.; Farrell, J. R.; Mirkin, C. A.; Liable-Sands,
L. M.; Rheingold, A. L. Inorg. Chem. 2000, 39, 3432-3433.
(51) Masar III, M. S.; Mirkin, C. A.; Stern, C. L.; Zakharov, L. N.; Rheingold,
A. L. Inorg. Chem. 2004, 43, 4693-4701.
9
16292 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Supramolecular Allosteric Cofacial Porphyrin Complexes
A R T I C L E S
Scheme 3. Synthesis of Thioether-Based Ligand 13 and Macrocycles 14a-b, 15a-ba
a (i) ClCH2CH2PPh2, Cs2CO3, CH3CN, Reflux; (ii) S8, THF; (iii) n-BuLi, DMF, THF, -78 °C; (iv) 5-mesityldipyrromethane, BF3•OEt2, DDQ, NEt3,
CHCl3, 4 Å Molecular Sieves; (v) Zn(OAc)2•2H2O, 4:1 CHCl3/MeOH, Reflux; (vi) Cp2ZrHCl, THF, 60 °C; (vii) for 14a: [Rh(NBD)Cl]2, AgBF4, CH2Cl2/
THF; (viii) for 14b: [Cu(CH3CN)4]PF6, CH2Cl2/THF; (ix) for 15a: PPNCl/CO (1 atm); (x) for 15b: C5D5N.
Synthesis of Thioether-Phosphine Hemilabile Ligand 13.
Because type I structures are difficult to access from the ether-
phosphine ligand 7, we hypothesized that isostructural ligands
containing thioether linkages would be more effective at forming
condensed structures as has been observed previously with
analogous smaller molecules.50 To this end, we modified the
synthesis of 7 to obtain the thioether-based porphyrin ligand
13 in six steps (Scheme 3). First, 4-bromothiophenol was
stoichiometrically alkylated with 1-chloro-2-diphenylphosphi-
noethane to yield 2-(4-bromophenylsulfanyl)ethyldiphenyl phos-
phine. To protect the phosphine moiety from oxidation during
the porphyrin synthesis, reaction with elemental sulfur yields
phosphine sulfide 9, which was then formylated with n-BuLi
and DMF. The resulting aldehyde 10 was subsequently con-
densed with 5-mesityldipyrromethane in the presence of BF3•OEt2
to yield porphyrin 11 in 44% yield after a very simple
chromatographic separation. Freebase porphyrin 11 was met-
allated with Zn(OAc)2•2H2O to give 12 and followed by
deprotection of the phosphine with Schwartz’s reagent to yield
the phosphine derivative 13 in 33% overall yield.
Reactivity of Hemilabile Ligand 13 with RhI and CuI. In
contrast to the results obtained from ether ligand 7, thioether
ligand 13 reacts cleanly with “Rh(NBD)BF4”55 to form the
condensed intermediate 14a. The 31P{1H} NMR spectrum of
14a exhibits a doublet at δ 64.5 (JRh-P ) 162 Hz) which is
highly diagnostic of its symmetrical structure and cis-Rh-P
coordination centers.50 Additionally, ESIMS analysis shows a
peak corresponding to the M2+ ion at 1354.1 m/z, indicating
the formation of the desired condensed structure. Significantly,
compound 14a can be opened into macrocycle 15a by introduc-
tion of benzyltriethyl ammonium chloride or by PPNCl (where
PPNCl ) bis(triphenylphosphoranylidene)ammonium chloride)
and CO. This transformation can be followed by 31P{1H} NMR
through the appearance of a doublet at δ 25.1 (d, JP-Rh ) 123
Hz), significantly upfield from the resonance for 14a. This
resonance is characteristic of a trans-phosphine environment
about the RhI metal center and indicates a conversion from a
condensed macrocyclic intermediate to the “open” macrocycle
(55) Formed by the reaction between [Rh(NBD)Cl2 and AgBF4 (NBD )
norbornadiene).
9
J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006 16293

A R T I C L E S
Oliveri et al.
Table 1. X-ray Crystallographic Data for 8a⊂DABCO and 15a⊂DABCO
8a⊂DABCO
15a⊂DABCO
empirical formula
formula weight
C181H166Cl4N12O8P4Rh2Zn2
3239.5
C172H142Cl2N10O4P4Rh2S4Zn2
3072.54
temperature
153(2) K
100(2) K
wavelength
0.71073 Å
0.48595 Å
crystal system, space group
unit cell dimensions
triclinic, P1h
monoclinic, C2/c
a ) 17.0086(10) Å
a ) 13.9395(13) Å R ) 83.044(2)°
b ) 17.1623(17) Å â ) 73.368(2)°
c ) 20.894(2) Å γ ) 74.250(2)°
4604.5(8) Å3
b ) 44.661(3) Å â ) 104.252(2)°
c ) 23.0053(13) Å
16937.3(17) Å3
volume
Z, calculated density
absorption coefficient
F(000)
1, 1.168 Mg/m3
4, 1.205 Mg/m3
0.581 mm-1
0.342 mm-1
1678
6336
crystal size
0.170 × 0.170 × 0.50 mm
0.150 × 0.025 × 0.010 mm
theta range for data collection
reflections collected/unique
absorption correction
max. and min. transmission
refinement method
data/restraints/parameters
goodness-of-fit on F∧2
final R indices [I > 2sigma(I)]
R indices (all data)
1.02 to 28.83°
0.90 to 15.70°
42335/21291 [R(int) ) 0.0712]
integration
0.9695 and 0.8265
full-matrix least-squares on F2
21291/0/915
123297/12229 [R(int) ) 0.0780]
empirical
1.000000 and 0.649500
full-matrix least-squares on F2
12229/0/921
0.912
1.063
R1 ) 0.0910, wR2 ) 0.2301
R1 ) 0.1924, wR2 ) 0.2591
1.378 and -0.747 e-/Å-3
R1 ) 0.0937, wR2 ) 0.2816
R1 ) 0.1199, wR2 ) 0.3081
2.236 and -0.800 e-/Å-3
largest diff. peak and hole
Table 2. Selected Distances for 8a⊂DABCO and 15a⊂DABCO
selected distance
8a
⊂DABCO (Å)
15a⊂DABCO (Å)
Rh-Rh
Rh-P
Zn-Zn
24.8
2.32, 2.31
7.09
22.5
2.30
7.02
m/z, indicating formation of the desired condensed structure.
Notably, compound 14b can be converted into macrocycle 15b
upon the addition of stoichiometric quantities of pyridine. Once
again, the 31P{1H} NMR spectrum allows us to monitor this
transformation through the appearance of a singlet at δ -8.0,
which has shifted upfield from the resonance observed for 14b.
The ESIMS analysis of 15b yields a peak at 1314.9 m/z which
corresponds to the pyridine-free molecular ion.
X-ray Structure Determination of 15a⊂DABCO and
15c⊂DABCO. Similar to the problems encountered in crystal-
lizing 8a, our attempts to isolate X-ray quality single crystals
of 14a and 15a proved unfruitful. Based upon the more
promising strategy of adding DABCO to pure samples of 8a,
we hypothesized that crystals of 15a⊂DABCO could be
obtained in a similar fashion. X-ray quality crystals were
obtained from vapor diffusion of pentane/diethyl ether (1:1 v/v)
into a THF/CH2Cl2 solution of 15a containing DABCO, which
was initially layered with acetonitrile. Similar to the analogous
structure 8a⊂DABCO, the 56-membered macrocyclic product
15a⊂DABCO represents one of the largest macrocycles ever
prepared via the Weak-Link Approach. In this structure, the
Zn atoms are separated by a distance of distance of 7.02 Å and
are bridged by a DABCO ligand (Figure 2). The structure of
15a⊂DABCO is slightly puckered toward the Zn(porphyrin)
centers, leading to a slightly staggered porphyrin-porphyrin
geometry. As expected, the Rh-P and Zn-Zn distance in
8a⊂DABCO are comparable to those found for 15a⊂DABCO
while the Rh-Rh distance differs significantly, presumably due
to the presence of the four S atoms which have been incorpo-
rated in 15a⊂DABCO (Table 2).
Figure 2. Graphical representations of the X-ray crystal structure of
15a⊂DABCO as viewed (A) from the side and (B) from the top containing
a molecule of DABCO bridging both Zn atoms. Hydrogen atoms, disordered
DABCO carbon atoms and solvent molecules have been omitted for clarity.
Gray ) Carbon, Pink ) Rh, Red ) O, Orange ) S, Yellow ) Cl, Green
) P, Dark Blue ) N, Light Blue ) Zn.
15a.50 The ESIMS spectrum of 15a exhibits a peak at 1353.7
m/z, corresponding to the M2+ ion without the Cl- and CO
ligands and is consistent with ESIMS data for analogous
structures.26
We observed condensed intermediate 14b as the sole product
from the reaction between thioether-based ligand 13 and [Cu-
(CH3CN)4]PF6. The 31P{1H} NMR spectrum of 14b exhibits a
singlet at δ 1.0 which is highly diagnostic of a tetrahedral
environment at the CuI metal center.51 Additionally, ESIMS
analysis yields a peak corresponding to the M2+ ion at 1314.5
Contrary to 8b, 15b was quite soluble in pure THF; however,
our efforts to crystallize 15b from THF only yielded micro-
9
16294 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006

Supramolecular Allosteric Cofacial Porphyrin Complexes
A R T I C L E S
Figure 3. Acyl transfer reactions catalyzed by (left) a closed macrocycle vs (right) the corresponding open macrocycle. The open macrocycle can preorganize
the substrates within the cavity, thereby increasing the rate of the reaction (k2) in comparison to that (k1) observed in the presence of the closed macrocycle.
Figure 4. Formation of the three X-(acetoxymethyl)pyridine (X ) 2, 3, or 4) isomers by an acyl transfer reaction between 1-acetylimidazole and
X-pyridylcarbinol, as catalyzed by Zn-porphyrin complexes 14a and 15a. Concentration vs time plots are shown for the formation of 4-(acetoxymethyl)-
pyridine (A, 4-AMP), 3-(acetoxymethyl)pyridine (B, 3-AMP), and 2-(acetoxymethyl)pyridine (C, 2-AMP). All data were corrected for background reactions
(see Supporting Information). Conditions: CH2Cl2, rt, 9 mM X-pyridylcarbinol, 6 mM 1-acetylimidazole, 2.5 mM biphenyl (GC reference standard), and 0.3
mM supramolecular catalyst (14a and 15a). CO (1 atm) and appropriate amounts of benzyltriethylammonium chloride when indicated.
crystalline powder. Attempts to crystallize 15b using the same
conditions as used for 8b led to the formation of magenta single
crystals of 15c⊂DABCO, which were confirmed by X-ray
diffraction analysis at APS (see Supporting Information).
Macrocycle 15c⊂DABCO encapsulates a bridging DABCO
ligand between two Zn porphyrins, flanked by tetrahedral CuCl2
centers, again indicating the oxidation of CuI to CuII via solvent
dehalogenation as has been observed previously. As for
8c⊂DABCO, isolation of 15c⊂DABCO strongly suggests an
open macrocyclic structure for 15b as shown in Scheme 3.
Acyl Transfer Catalytic Experiments. To demonstrate the
ability of the ZnII-porphyrin moieties in 14a and 15a to act
cooperatively in an allosterically controlled fashion, we em-
ployed a catalytic acyl transfer reaction that has been shown
by Sanders and co-workers to accelerate in the presence of
trimetallic Lewis acidic porphyrin assemblies.56 We hypoth-
esized that the pyridylcarbinol and acetylimidazole substrates
could be brought together within the cavity of 15a by cofacial
ZnII metal centers and converted to the products in a catalytic
fashion by virtue of their proximity (Figure 3). Furthermore,
reactions involving 1-acetylimidazole and differentially substi-
tuted X-pyridylcarbinol (where X ) 2, 3, or 4) can be used to
evaluate the ability of 15a to act allosterically: only the
combination of substrates with the right distance can span the
cavity and react at an accelerated rate.
The efficiency of both the “closed” (14a) and “open” (15a)
supramolecular catalysts in the acyl transfer reaction were
evaluated against a control reaction consisting of the monomer
Zn(TPP) and analogous monomeric RhI complexes 16a and
16b (see Supporting Information). For 4-pyridylcarbinol (4-PC),
both 14a and 15a significantly accelerate the reaction rate, with
the open macrocycle 15a being almost 14 times more active
than the monomers and twice as fast as the closed macrocycle
14a (Figure 4a). While 14a is depicted as a rigid entity in Figure
3, its structure is probably dynamic when in solution and the
observed catalytic activity may originate from the conforma-
9
J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006 16295

A R T I C L E S
Oliveri et al.
tional flexibility around the S atoms and the low rotational
barrier of the porphyrin ligand about the carbon-sulfur bond in
the backbone of the ligand. For 3-pyridylcarbinol (3-PC), the
background-corrected ratemacrocycle/ratemonomers ratio (ratemonomers
) rate of the reaction in the presence of the [RhI monomer +
Importantly, these architectures possess cavities whose sizes can
be directly controlled in situ via the introduction of simple,
cooperative ancillary ligands that bond to the structure control
domains. This capability enables the cofacial porphyrin struc-
tures to act as allosteric catalysts capable of discriminating
different substrate combinations and selectively transforming
them into the desired products, two key steps in developing
new biomimetic supramolecular systems. Most notably, our
synthetic approach should allow for facile access to a range of
systems with tunable cofacial porphyrin-porphyrin distances
that are useful in studying distance-dependent electron-transfer
phenomena, molecular switches, host-guest interactions, and
catalysis. Efforts toward elaboration of these areas are currently
underway.
Zn(TPP)] mixture) and the observed allosteric effect (rate15a
/
rate14a) only drops slightly (Figure 4b), suggesting that the
cavities of 14a and 15a are still flexible enough to accommodate
the change in transition state distance for acyl transfer from
acetylimidazole upon binding. For 2-pyridylcarbinol (2-PC),
both the ratemacrocycle/ratemonomers ratio and the observed allosteric
effect (rate15a/rate14a) drop significantly with respect to 3- and
4-pyridylcarbinol and are similar to those observed for the
monomers (Figure 4c). This may be explained by a simple
geometry argument: if 2-pyridylcarbinol is bound to one of the
Zn centers, the carbinol group will be pointed away from the
imidazole N-acetyl group bound to the other side, resulting in
an unfavorable transition state (in comparison to those for 4-
and 3-pyridylcarbinol) for productive acyl transfer.
Our catalytic data offers strong evidence that Cl-/CO can
act as positive allosteric effectors in a RhI-based hemilabile
supramolecular catalyst system, enhancing the efficiency of
bimolecular acyl transfer reactions when the geometry is
optimized. Significantly, these effectors operate cooperatively
with each other and are incapable of effecting shape change if
added independently to the RhI species. That 2-pyridylcarbinol
can be selectively discriminated against 3- and 4-pyridylcarbinol
provides an impetus for employing these supramolecular as-
semblies for chemical sensing and shape-selective recognition
when coupled to catalytic processes that provide signal ampli-
fication.
Acknowledgment. C.A.M acknowledges the NSF and ARO
for support of this research and is grateful for a NIH Director’s
Pioneer Award. This work was also supported, in part, by the
NSF-NSEC program under NSF Award Number EEC-0118025.
Portions of this work were performed at the DuPont-North-
western-Dow Collaborative Access Team (DND-CAT) Syn-
chrotron Research Center located at Sector 5 of the Advanced
Photon Source. DND-CAT is supported by the E.I. DuPont de
Nemours & Co., the Dow Chemical Company, the U.S. National
Science Foundation through Grant DMR-9304725 and the State
of Illinois through the Department of Commerce and the Board
of Higher Education Grant IBHE HECA NWU 96. ChemMat-
CARS Sector 15 is principally supported by the National Science
Foundation/DepartmentofEnergyundergrantnumberCHE0087817
and by the Illinois Board of Higher Education. The Advanced
Photon Source is supported by the U.S. Department of Energy,
Basic Energy Sciences, Office of Science, under Contract No.
W-31-109-Eng-38.
Conclusion
In conclusion, we have developed a coordination chemistry-
based synthetic approach for the quantitative preparation of
flexible cofacial porphyrin assemblies in which the porphyrins
act as functional sites within an allosteric framework that is
tunable via modulation of peripheral structure control domains.
Supporting Information Available: Crystallographic data,
X-ray crystal structures of 8c⊂DABCO and 15c⊂DABCO, and
uncorrected and background reactions for 2-PC, 3-PC, and 4-PC.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(56) Mackay, L. G.; Wylie, R. S.; Sanders, J. K. M. J. Am. Chem. Soc. 1994,
116, 3141-3142.
JA0661010
9
16296 J. AM. CHEM. SOC. VOL. 128, NO. 50, 2006