Strongly coupled porphyrin arrays featuring both π-cofacial and linear-π-conjugative interactions

Article abstract of DOI:10.1021/ic010871p

A combination of metal-catalyzed cross-coupling and metal-templated cycloaddition reactions have been utilized to establish multiporphyrin compounds 5-(5′-[15′,15″-bis(10″,20″-di[4- (3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]ethyne)-6- [(5?-10?,20?-di[4-(3-methoxy-3-methylbutoxy) phenyl]porphinato)zinc(II)]indane (1) and 5,6-bis(5′-15′,15″-bis[(10′,20′-di[4- (3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]ethyne)indane (2). Compounds 1 and 2 feature a covalently bridged cofacial bis(porphinato) metal core; ethyne bridging moieties conjugate directly one and two respective peripheral (porphinato)zinc(II) substituents to the macrocyclic framework of their corresponding face-to-face porphyrin units. Optical spectroscopy and electrochemical studies demonstrate substantive electronic interactions between the porphyrin subunits of these compounds. Notably, structural and ¹H NMR analyses verify that 1 and 2 possess open conformations necessary for binding small molecules within their respective cofacial (porphinato)metal cores.

Full text of DOI:10.1021/ic010871p

Inorg. Chem. 2002, 41, 331−341
Strongly Coupled Porphyrin Arrays Featuring Both π-Cofacial and
Linear-π-Conjugative Interactions
James T. Fletcher and Michael J. Therien*
Department of Chemistry, UniVersity of PennsylVania, Philadelphia, PennsylVania, 19104-6323
Received August 13, 2001
A combination of metal-catalyzed cross-coupling and metal-templated cycloaddition reactions have been utilized to
establish multiporphyrin compounds 5-(5′-[15′,15′′-bis(10′′,20′′-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)-
zinc(II)]ethyne)-6-[(5′′′-10′′′,20′′′-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (1) and 5,6-bis-
(5′-15′,15′′-bis[(10′,20′-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]ethyne)indane (2). Compounds 1
and 2 feature a covalently bridged cofacial bis(porphinato)metal core; ethyne bridging moieties conjugate directly
one and two respective peripheral (porphinato)zinc(II) substituents to the macrocyclic framework of their corresponding
face-to-face porphyrin units. Optical spectroscopy and electrochemical studies demonstrate substantive electronic
interactions between the porphyrin subunits of these compounds. Notably, structural and 1H NMR analyses verify
that 1 and 2 possess open conformations necessary for binding small molecules within their respective cofacial
(porphinato)metal cores.
Introduction
With respect to small molecule activation, the cofacial
(porphinato)metal structural motif12-14 has shown particular
catalytic efficacy in a wide range of multielectron redox
transformations.15-24 This catalytic diversity derives from
both the rich coordination chemistry of redox-active metal-
loporphyrin compounds, and the ease at which appropriate
metal-metal distances can be accommodated in such
structures. We report herein new archetypes that feature
substantial conjugation expansion of the classic cofacial bis-
(Porphinato)metal species bearing metal complexes1-8 or
other redox active entities9,10 as macrocycle substituents have
been examined for their potential utility as multielectron
oxidation and reduction catalysts. In these systems, the por-
phyrin-pendant substituents are envisaged to serve as electron
reservoirs or sinks, delivering or removing multiple electrons
from the focal catalytic unit during substrate turnover. While
the utility of such assemblies has been demonstrated,1,2,4,9,11
in practice, less than optimal electronic coupling between
the redox active moieties and the catalytic core often limits
the catalytic effectiveness of these supramolecular species.
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* To whom correspondence should be addessed. E-mail: herien@
a.chem.upenn.edu.
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10.1021/ic010871p CCC: $22.00 © 2002 American Chemical Society
Published on Web 01/04/2002
Inorganic Chemistry, Vol. 41, No. 2, 2002 331

Fletcher and Therien
(porphyrin) structural motif. These multiporphyrin com-
pounds exploit a face-to-face bis(porphinato)metal core and
auxiliary (porphinato)metal units that are linked to this
structure via an ethyne-based macrocycle-to-macrocycle
linkage topology, a mode of porphyrin-to-porphyrin con-
nectivity that enables exceptional ground- and excited-state
electronic communication between porphyrin centers.25-32
Such oligo[(porphinato)metal] structures, featuring extensive
porphyrin-porphyrin frontier orbital interactions enabled by
both π-stacking and the cylindrically π-symmetric ethyne
moiety, define potentially attractive ligand platforms from
which to evolve new multielectron redox systems.
Experimental Section
All manipulations were carried out under nitrogen prepurified
by passage through an O2 scrubbing tower (Schweizerhall R3-11
catalyst) and a drying tower (Linde 3Å molecular sieves) unless
otherwise stated. Air-sensitive solids were handled in a Braun
150-M glovebox. Standard Schlenk techniques were employed to
manipulate air sensitive solutions. A syringe pump was utilized to
control reproducibly the time-dependent concentration of reagents
in these cycloaddition reactions.
Unless otherwise noted, all solvents utilized in this work were
obtained from Fisher Scientific (HPLC grade); tetrahydrofuran and
toluene were distilled from Na/benzophenone under N2, and
triethylamine was distilled from CaH2 under N2, while dioxane
(anhydrous) was used as received from Aldrich. The catalysts
Pd2dba3, Pd(PPh3)2Cl2, AsPh3, and Co2(CO)8 (Strem), as well as
the reagents 1,6-heptadiyne, TBAF, iodobenzene, ethynylbenzene,
CuI (Aldrich), trimethylacetylene, and triisopropylacetylene (GFS
Chemicals) were used as received.
(5-Bromo-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphi-
nato)zinc(II), (5-ethynyl-10,20-di[4-(3-methoxy-3-methylbutoxy)-
phenyl]porphinato)zinc(II), and (5,15-dibromo-10,20-di[4-(3-methoxy-
3-methylbutoxy)phenyl]porphinato)zinc(II) were synthesized by
methodology established previously.25,40 Syntheses of spectroscopic
benchmarks 12 and 13 are described in the Supporting Information.
Chromatographic purification (Silica 60, 230-400 mesh, EM
Science, and Bio-Beads S-X1, 200-400 mesh, Bio-Rad) of all
compounds was performed on the benchtop. Chemical shifts for
1H NMR spectra are relative to residual protium in the deuterated
solvents (CDCl3, δ 7.24 ppm). All coupling constants are reported
in Hertz.
The fabrication of these species takes advantage of a new
synthesis of 1,2-phenylene-bridged cofacial porphyrins33 that
exploits ethyne-bridged multiporphyrin precursors con-
structed via sequential Pd-catalyzed cross-coupling25,34-40 and
metal-templated [2+2+2] cycloaddition41-44 reactions. In this
study, we utilize this chemistry to synthesize face-to-face
bis[(porphinato)metal] species that bear macrocycle-ethyne
substituents; further application of Pd-catalyzed cross-coup-
ling methodology extends conjugation of the cofacial (por-
phinato)metal core to additional porphyrin units, giving tris-
and tetrakis[(porphinato)metal] compounds 1 and 2, new
multiporphyrin archetypes that feature macrocycle-to-mac-
rocycle electronic communication that stems from both
π-cofacial and π-conjugative interactions.
Instrumentation. Electronic spectra were recorded on an OLIS
UV-vis-NIR spectrophotometry system that is based on the optics
of a Cary 14 spectrophotometer. NMR experiments were performed
on a 250 MHz Bru¨ker instrument. HRMS data were obtained at
the Mass Spectral Laboratories of the Department of Chemistry,
University of Pennsylvania. MALDI-TOF mass spectroscopic data
were obtained with a Perseptive Voyager DE instrument in the
Laboratories of Dr. Virgil Percec, Department of Chemistry,
University of Pennsylvania. Samples were prepared as micromolar
solutions in THF, and dithranol (Aldrich) was utilized as the matrix.
Cyclic voltammetric experiments were performed with an EG&G
Princeton Applied Research model 273A potentiostat/galvanostat.
The cyclic voltammetric experiments utilized a single-compartment
electrochemical cell with a platinum working electrode.
Bis[(5,5′-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]por-
phinato)zinc(II)]ethyne (10). (5-Bromo-10,20-di[4-(3-methoxy-
3-methylbutoxy)phenyl]porphinato)zinc(II) (53 mg, 0.063 mmol),
(5-ethynyl-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphi-
nato)zinc(II) (45 mg, 0.058 mmol), Pd2(dba)3 (9 mg, 0.0093 mmol),
and AsPh3 (23 mg, 0.074 mmol) were added to a 50 mL Schlenk
tube under N2. THF (10 mL) and triethylamine (2 mL) were added
via syringe, giving a deep green solution which was stirred for 3 h
at 35 °C. The resulting green-brown solution was evaporated and
the residue purified via chromatography (silica gel, 1/1 hexanes/
THF). The green-brown band was collected and the solvent
evaporated. The recovered solid was purified further via size-
exclusion chromatography (SX-1 biobeads, THF). The dark green
band was isolated, giving desired product 10. Isolated yield ) 83
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nines 1999, 3, 5-31.
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332 Inorganic Chemistry, Vol. 41, No. 2, 2002

Strongly Coupled Porphyrin Arrays
1
mg (93% based on 45 mg of the porphyrin starting material). H
NMR (250 MHz, 50/1 CDCl3/d5-pyridine): δ 10.45 (d, J ) 4.53
Hz, 4H, â), 10.04 (s, 2H, meso), 9.24 (d, J ) 4.43 Hz, 4H, â),
9.15 (d, J ) 4.43 Hz, 4H, â), 8.98 (d, J ) 4.35 Hz, 4H, â), 8.16
(d, J ) 8.43 Hz, 8H, Ph), 7.31 (d, J ) 8.53 Hz, 8H, Ph), 4.38 (t,
J ) 7.26 Hz, 8H, CH2), 3.33 (s, 12H, OCH3), 2.22 (t, J ) 6.98 Hz,
8H, CH2), 1.37 (s, 24H, CH3). Vis (THF): 403 (5.08), 411 (5.08),
430 (5.00), 478 (5.46), 548 (4.21), 565 (4.18), 701 (4.69). MS
(MALDI-TOF) m/z: 1535 (calcd for C90H86N8O8Zn2 1535).
) 49 mg (13% based on 300 mg of the porphyrin starting material).
1H NMR (250 MHz, 50/1 CDCl3/d5-pyridine): δ 9.63 (d, J ) 4.50
Hz, 4H, â), 8.84 (d, J ) 4.44 Hz, 4H, â), 8.01 (d, J ) 8.59 Hz,
4H, Ph), 7.22 (d, J ) 8.59 Hz, 4H, Ph), 4.34 (t, J ) 7.27 Hz, 4H,
CH2), 3.32 (s, 6H, OCH3), 2.20 (t, J ) 6.97 Hz, 4H, CH2), 1.39 (s,
42H, TIPS), 1.35 (s, 12H, CH3). The third dark green band isolated
corresponded to the (5,15-diethynyl-10,20-di[4-(3-methoxy-3-
methylbutoxy)phenyl]porphinato)zinc(II) side product. Isolated yield
) 110 mg (42% based on 300 mg of the porphyrin starting
1
material). H NMR (250 MHz, 50/1 CDCl3/d5-pyridine): δ 9.62
5,6-Bis[(5,5′-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]-
porphinato)zinc(II)]indane (11). A 50 mL Schlenk tube was
charged with 10 (50 mg, 33 µmol), Co2(CO)8 (11 mg, 33 µmol),
dioxane (2.5 mL), and toluene (10 mL) under N2. The resulting
green solution was heated to 100 °C, following which 10 mL of a
toluene solution containing 1,6-heptadiyne (38 µL, 330 µmol) and
Co2(CO)8 (11 mg, 33 µmol) were added dropwise over an 18 h
period. After the addition was complete, the solution was evaporated
and the residue purified by chromatography (3/2 hexanes/THF).
The red band was isolated, giving desired product 11. Isolated yield
) 50 mg (93% based on 50 mg of the porphyrin starting material).
1H NMR (250 MHz, d5-pyridine): δ 10.31 (d, J ) 4.65 Hz, 4H,
â), 10.11 (s, 2H, meso), 9.29 (d, J ) 4.50 Hz, 4H, â), 9.13 (d, J )
4.68 Hz, 4H, â), 8.95 (d, J ) 4.48 Hz, 4H, â), 8.64 (s, 2H, In CH),
8.02 (d, J ) 8.28 Hz, 4H, Ph), 7.66 (d, J ) 8.25 Hz, 4H, Ph), 7.32
(d, J ) 8.33 Hz, 4H, Ph), 7.25 (d, J ) 8.45 Hz, 4H, Ph), 4.43 (t,
J ) 7.06 Hz, 8H, R CH2), 3.41 (t, J ) 6.88 Hz, 4H, In CH2), 3.30
(s, 12H, OCH3), 2.40 (m, 2H, In CH2), 2.26 (t, J ) 6.98 Hz, 8H,
R CH2), 1.36 (s, 24H, CH3). Vis (THF): 411 (5.54), 434 (4.74),
558 (4.32), 589 (3.72), 599 (3.71). MS (MALDI-TOF) m/z: 1627
(calcd for C97H94N8O8Zn2 1627).
(d, J ) 4.62 Hz, 4H, â), 8.86 (d, J ) 4.65 Hz, 4H, â), 8.02 (d, J
) 8.60 Hz, 4H, Ph), 7.24 (d, J ) 8.59 Hz, 4H, Ph), 4.34 (t, J )
7.15 Hz, 4H, CH2), 4.11 (s, 2H, CCH), 3.31 (s, 6H, OCH3), 2.20
(t, J ) 7.15 Hz, 4H, CH2), 1.35 (s, 12H, CH3).
(5-Triisoproplysilylethynyl-15,15′-bis[(10,20-di[4-(3-methoxy-
3-methylbutoxy)phenyl]porphinato)zinc(II)])ethyne (6). (5-
Bromo-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)-
zinc(II) (107 mg, 0.128 mmol), 5 (113 mg, 0.118 mmol), Pd2(dba)3
(17 mg, 0.019 mmol), and AsPh3 (46 mg, 0.15 mmol) were added
to a 100 mL Schlenk tube under N2. THF (15 mL) and triethylamine
(3 mL) were added via syringe, giving a green solution which was
stirred for 4 h at 40 °C. Following evaporation of volatiles, the
residue was purified via chromatography (silica gel, 1/1 hexanes/
THF). A dark green-brown band was collected, which was purified
further via size-exclusion chromatography (SX-1 biobeads, THF),
giving desired product 6. Isolated yield ) 0.186 g (92% based on
1
113 mg of starting material 5). H NMR (250 MHz, 50/1 CDCl3/
d5-pyridine): δ 10.40 (d, J ) 4.60 Hz, 2H, â), 10.34 (d, J ) 4.55
Hz, 2H, â), 10.03 (s, 1H, meso), 9.65 (d, J ) 4.58 Hz, 2H, â),
9.22 (d, J ) 4.50 Hz, 2H, â), 9.13 (d, J ) 4.58 Hz, 2H, â), 9.02
(d, J ) 4.53 Hz, 2H, â), 8.96 (d, J ) 4.45 Hz, 2H, â), 8.88 (d, J
) 4.53 Hz, 2H, â), 8.14 (d, J ) 8.63 Hz, 4H, Ph), 8.09 (d, J )
8.70 Hz, 4H, Ph), 7.29 (d, J ) 8.50 Hz, 4H, Ph), 7.26 (d, J ) 8.58
Hz, 4H, Ph), 4.37 (t, J ) 7.12 Hz, 4H, CH2), 4.36 (t, J ) 7.12 Hz,
4H, CH2), 3.31 (s, 12H, OCH3), 2.20 (t, J ) 7.12 Hz, 8H, CH2),
1.40 (m, 21H, TIPS), 1.35 (s, 24H, CH3). Vis (THF): 412 (5.13),
423 (5.13), 448 (5.01), 482 (5.48), 558 (4.26), 727 (4.84). MS
(MALDI-TOF) m/z: 1715 (calcd for C101H106N8O8SiZn2 1714).
(5-Ethynyl-15-triisopropylsilylethynyl-10,20-di[4-(3-methoxy-
3-methylbutoxy)phenyl]porphinato)zinc(II) (5). (5,15-Dibromo-
10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc-
(II) (300 mg, 0.327 mmol), triisopropylsilylacetylene (0.47 mL,
2.094 mmol), trimethylsilylacetylene (0.10 mL, 0.698 mmol), Pd-
(PPh3)2Cl2 (24 mg, 0.035 mmol), and CuI (7 mg, 0.035 mmol) were
added to a 50 mL Schlenk tube under N2. THF (10 mL) and
triethylamine (3 mL) were transferred to the Schlenk tube via
syringe; the resulting deep green solution was stirred for 24 h at
45 °C. Over the course of the reaction, the solution became
increasingly fluorescent when exposed to long wavelength UV
irradiation from a hand-held lamp. After evaporation of volatiles,
the residue was purified via chromatography (silica gel, 3/1 hexanes/
THF). The dark green band was collected, which contained a
mixture of three porphyrinic products. This mixture was dissolved
in 50 mL of 1/1 THF/methanol, following which 1 M aqueous
NaOH (2 mL) was added. After stirring 5 min at room temperature,
the reaction was partitioned between CH2Cl2 and water, and the
organic layer evaporated. The resulting mixture was purified via
chromatography (silica gel, 7/3 hexanes/THF). The second dark
green band isolated corresponded to the desired product 5. Isolated
yield ) 138 mg (44% based on 300 mg of the porphyrin starting
5-[(5′-15′-Triisopropylsilylethynyl-10′,20′-di[4-(3-methoxy-
3-methylbutoxy)phenyl]porphinato)zinc(II)]-6-[(5′′-10′′,20′′-di-
[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc-
(II)]indane (8). A 50 mL Schlenk tube was charged with 6 (80
mg, 47 µmol), Co2(CO)8 (25 mg, 71 µmol), dioxane (2.5 mL), and
toluene (10 mL). The resulting green solution was heated to 100
°C, following which 5 mL of a toluene solution containing 1,6-
heptadiyne (54 µL, 470 µmol) were added dropwise over a 17 h
period. After the addition was complete, the solution was evaporated
and the residue purified by chromatography (silica gel, 7/3 hexanes/
THF). The purple-green band was isolated giving the desired
product 8. Isolated yield ) 58 mg (68% based on 80 mg of the
1
porphyrin starting material). H NMR (250 MHz, 50/1 CDCl3/d5-
pyridine): δ 9.73 (s, 1H, meso), 9.65 (d, J ) 4.67 Hz, 2H, â),
9.60 (d, J ) 4.69 Hz, 2H, â), 9.38 (d, J ) 4.43 Hz, 2H, â), 8.97
(d, J ) 4.57 Hz, 2H, â), 8.66 (d, J ) 4.42 Hz, 2H, â), 8.63 (d, J
) 4.40 Hz, 2H, â), 8.55 (d, J ) 4.51 Hz, 2H, â), 8.49 (d, J ) 4.68
Hz, 2H, â), 8.33 (s, 1H, In CH), 8.30 (s, 1H, In CH), 7.75 (m, 4H,
Ph), 7.50 (m, 4H, Ph), 7.11 (m, 8H, Ph), 4.31 (t, J ) 7.04 Hz, 4H,
R CH2), 4.30 (t, J ) 6.88 Hz, 4H, R CH2), 3.43 (t, J ) 6.99 Hz,
4H, In CH2), 3.31 (s, 12H, OCH3), 2.55 (m, 2H, In CH2), 2.19 (t,
J ) 7.11 Hz, 4H, R CH2), 2.17 (t, J ) 7.11 Hz, 4H, R CH2), 1.35
(s, 24H, CH3), 1.27 (s, 21H, TIPS). Vis (THF): 416 (5.60), 443
(5.04), 557 (4.30), 572 (4.28), 623 (4.28). MS (MALDI-TOF)
m/z: 1806 (calcd for C108H114N8O8SiZn2 1807). A trailing brown
1
material). H NMR (250 MHz, 50/1 CDCl3/d5-pyridine): δ 9.65
(d, J ) 4.55 Hz, 2H, â), 9.60 (d, J ) 4.57 Hz, 2H, â), 8.86 (d, J
) 4.56 Hz, 2H, â), 8.85 (d, J ) 4.56 Hz, 2H, â), 8.02 (d, J ) 8.57
Hz, 4H, Ph), 7.24 (d, J ) 8.58 Hz, 4H, Ph), 4.34 (t, J ) 7.16 Hz,
4H, CH2), 4.10 (s, 1H, CCH), 3.32 (s, 6H, OCH3), 2.20 (t, J )
7.13 Hz, 4H, CH2), 1.39 (s, 21H, TIPS), 1.35 (s, 12H, CH3). Vis
(THF): 434 (5.50), 446 (5.35), 538 (3.48), 582 (4.06), 632 (4.46).
HRMS (ESI+) m/z: 960.396104 (calcd for C57H64N4O4SiZn
960.398831). The first dark green band isolated corresponded to
the (5,15-bis[triisoproplysilylethynyl]-10,20-di[4-(3-methoxy-3-
methylbutoxy)phenyl]porphinato)zinc(II) side product. Isolated yield
Inorganic Chemistry, Vol. 41, No. 2, 2002 333

Fletcher and Therien
band was also isolated, which corresponded to pure starting material
6. Isolated yield ) 26 mg (32% recovery based on 80 mg of the
porphyrin starting material).
tography (silica gel, 3/2 hexanes/THF). The green-brown band was
isolated, giving desired product 7. Isolated yield ) 0.235 g (92%
based on 0.130 g of starting material 5). 1H NMR (250 MHz, 50/1
CDCl3/d5-pyridine): δ 10.29 (d, J ) 4.53 Hz, 4H, â), 9.65 (d, J )
4.60 Hz, 4H, â), 9.01 (d, J ) 4.55 Hz, 4H, â), 8.85 (d, J ) 4.58
Hz, 4H, â), 8.09 (d, J ) 8.43 Hz, 8H, Ph), 7.27 (d, J ) 8.63 Hz,
8H, Ph), 4.36 (t, J ) 7.09 Hz, 8H, CH2), 3.32 (s, 12H, OCH3),
2.20 (t, J ) 7.13 Hz, 8H, CH2), 1.39 (m, 42H, TIPS), 1.36 (s, 24H,
CH3). Vis (THF): 424 (5.22), 436 (5.20), 488 (5.47), 576 (4.25),
747 (4.91). MS (MALDI-TOF) m/z: 1895 (calcd for C112H126N8O8-
Si2Zn2 1895).
5-[(5′-15′-Ethynyl-10′,20′-di[4-(3-methoxy-3-methylbutoxy)-
phenyl]porphinato)zinc(II)]-6-[(5′′-10′′,20′′-di[4-(3-methoxy-3-
methylbutoxy)phenyl]porphinato)zinc(II)]indane (3). A 50 mL
Schlenk tube was charged with 8 (58 mg, 0.032 mmol), THF (5
mL), and tetrabutylammonium fluoride (1.0 M in THF, 0.068 mL,
0.068 mmol). After stirring 10 min at room temperature, CHCl3
(100 mL) was added to the reaction. The resulting solution was
washed with NaHCO3 (aq), following which the organic layer was
separated, evaporated, and purified via chromatography (silica gel,
3/2 hexanes/THF). The purple-brown band was isolated, giving the
desired product 3. Isolated yield ) 44 mg (83% based on 58 mg
of the porphyrin starting material). 1H NMR (250 MHz, 50/1 CDCl3/
d5-pyridine): δ 9.74 (s, 1H, meso), 9.65 (d, J ) 4.65 Hz, 2H, â),
9.62 (d, J ) 4.62 Hz, 2H, â), 9.35 (d, J ) 4.68 Hz, 2H, â), 8.98
(d, J ) 4.48 Hz, 2H, â), 8.66 (d, J ) 4.46 Hz, 2H, â), 8.62 (d, J
) 4.59 Hz, 2H, â), 8.56 (d, J ) 4.64 Hz, 2H, â), 8.50 (d, J ) 4.64
Hz, 2H, â), 8.34 (s, 1H, In CH), 8.32 (s, 1H, In CH), 7.76 (m, 4H,
Ph), 7.50 (m, 4H, Ph), 7.12 (m, 8H, Ph), 4.32 (t, J ) 7.12 Hz, 8H,
R CH2), 3.91 (s, 1H, CCH), 4.31 (t, J ) 7.16 Hz, 8H, R CH2),
3.45 (t, J ) 7.16 Hz, 4H, In CH2), 3.32 (s, 12H, OCH3), 2.56 (m,
2H, In CH2), 2.19 (t, J ) 7.12 Hz, 8H, R CH2), 1.37 (s, 24H, CH3).
Vis (THF): 416 (5.60), 443 (5.04), 557 (4.30), 572 (4.28), 623
(4.28). MS (MALDI-TOF) m/z: 1651 (calcd for C99H94N8O8Zn2
1651).
5,6-Bis[(5′-15′-triisopropylsilylethynyl-10′,20′-di[4-(3-methoxy-
3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (9). A 50 mL
Schlenk tube was charged with 7 (65 mg, 34.3 µmol), Co2(CO)8
(18 mg, 51.5 µmol), dioxane (2.5 mL), and toluene (10 mL). The
resulting brown solution was heated to 100 °C, following which 5
mL of a toluene solution containing 1,6-heptadiyne (40 µL, 343
µmol) were added dropwise over a 17 h period. After the addition
was complete, the resulting green solution was evaporated and the
residue purified by chromatography (silica gel, 7/3 hexanes/THF).
The green band was isolated giving the desired product 9. Isolated
yield ) 50 mg (73% based on 65 mg of the porphyrin starting
1
material). H NMR (250 MHz, 50/1 CDCl3/d5-pyridine): δ 9.56
(d, J ) 4.71 Hz, 4H, â), 9.40 (d, J ) 4.45 Hz, 4H, â), 8.57 (d, J
) 4.44 Hz, 4H, â), 8.50 (d, J ) 4.70 Hz, 4H, â), 8.29 (s, 2H, In
CH), 7.75 (m, 4H, Ph), 7.48 (m, 4H, Ph), 7.11 (m, 8H, Ph), 4.31
(t, J ) 7.13 Hz, 8H, R CH2), 3.44 (t, J ) 7.00 Hz, 4H, In CH2),
3.30 (s, 12H, OCH3), 2.55 (m, 2H, In CH2), 2.20 (t, J ) 7.08 Hz,
8H, R CH2), 1.37 (s, 24H, CH3), 1.23 (m, 42H, TIPS). Vis (THF):
423 (5.43), 428 (5.43), 454 (4.87), 577 (4.29), 613 (4.22), 625
(4.32). MS (MALDI-TOF) m/z: 1986 (calcd for C119H134N8O8Si2-
Zn2 1987). A trailing brown band was also isolated, which
corresponded to pure porphyrinic starting material. Isolated yield
) 17 mg (26% recovery based on 65 mg of compound 7).
5,6-Bis[(5′,5′′-15′-ethynyl-10′,20′-di[4-(3-methoxy-3-methylbu-
toxy)phenyl]porphinato)zinc(II)]indane (4). A 50 mL Schlenk
tube was charged with 9 (58 mg, 0.029 mmol), THF (5 mL), and
tetrabutylammonium fluoride (1.0 M in THF, 0.09 mL, 0.09 mmol).
After stirring 10 min at room temperature, CHCl3 (100 mL) was
added, and the resulting solution was washed with NaHCO3 (aq).
The organic layer was separated, evaporated, and purified via
chromatography (silica gel, 7/3 hexanes/THF). The green band was
isolated, giving desired product 4. Isolated yield ) 47 mg (98%
based on 58 mg of the porphyrin starting material). 1H NMR (250
MHz, 50/1 CDCl3/d5-pyridine): δ 9.56 (d, J ) 4.52 Hz, 4H, â),
9.36 (d, J ) 4.61 Hz, 4H, â), 8.57 (d, J ) 4.63 Hz, 4H, â), 8.50
(d, J ) 4.66 Hz, 4H, â), 8.30 (s, 2H, In CH), 7.73 (m, 4H, Ph),
7.47 (m, 4H, Ph), 7.11 (m, 8H, Ph), 4.31 (t, J ) 7.12 Hz, 8H, R
CH2), 3.92 (s, 2H, CCH), 3.44 (t, J ) 7.14 Hz, 4H, In CH2), 3.32
(s, 12H, OCH3), 2.55 (m, 2H, In CH2), 2.19 (t, J ) 7.12 Hz, 8H,
R CH2), 1.36 (s, 24H, CH3). Vis (THF): 423 (5.43), 428 (5.43),
454 (4.87), 577 (4.29), 613 (4.22), 625 (4.32). MS (MALDI-TOF)
m/z: 1671 (calcd for C101H94N8O8Zn2 1675).
5-(5′-[15′,15′′-Bis(10′′,20′′-di[4-(3-methoxy-3-methylbutoxy)-
phenyl]porphinato)zinc(II)]ethyne)-6-[(5′′′-10′′′,20′′′-di[4-(3-
methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane (1).
(5-Bromo-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphi-
nato)zinc(II) (17 mg, 0.0203 mmol), 3 (28 mg, 0.0170 mmol), Pd2-
(dba)3 (3 mg, 0.0033 mmol), and AsPh3 (8 mg, 0.0262 mmol) were
added to a 50 mL Schlenk tube under N2. THF (5 mL) and
triethylamine (1 mL) were added via syringe, and the reaction was
stirred for 16 h at 45 °C. Following evaporation of volatiles, the
residue was purified via chromatography (silica gel, 3/2 hexanes/
THF). The brown band was isolated giving desired product 1.
Isolated yield ) 32 mg (78% based on 28 mg of starting material
3). 1H NMR (250 MHz, 50/1 CDCl3/d5-pyridine): δ 10.27 (d, J )
4.55 Hz, 2H, â), 10.10 (d, J ) 4.50 Hz, 2H, â), 9.99 (s, 1H, meso),
9.74 (s, 1H, meso), 9.70 (d, J ) 4.68 Hz, 2H, â), 9.63 (d, J ) 4.70
Hz, 2H, â), 9.19 (d, J ) 4.43 Hz, 2H, â), 9.03 (d, J ) 4.55 Hz,
2H, â), 8.99 (d, J ) 4.40 Hz, 2H, â), 8.92 (d, J ) 4.33 Hz, 2H, â),
8.74 (d, J ) 4.58 Hz, 2H, â), 8.68 (d, J ) 4.43 Hz, 2H, â), 8.66
(d, J ) 4.65 Hz, 2H, â), 8.54 (d, J ) 4.65 Hz, 2H, â), 8.36 (s, 1H,
In CH), 8.35 (s, 1H, In CH), 8.08 (d, J ) 8.28 Hz, 4H, Ph), 7.81
(m, 4H, Ph), 7.57 (m, 4H, Ph), 7.25 (d, J ) 7.40 Hz, 4H, Ph), 7.14
(m, 8H, Ph), 4.34 (t, J ) 7.04 Hz, 4H, R CH2), 4.33 (t, J ) 7.09
Hz, 4H, R CH2), 4.32 (t, J ) 7.05 Hz, 4H, R CH2), 3.46 (m, 4H,
In CH2), 3.33 (s, 6H, OCH3), 3.32 (s, 6H, OCH3), 3.31 (s, 6H,
OCH3), 2.57 (m, 2H, In CH2), 2.20 (t, J ) 7.03 Hz, 4H, R CH2),
2.19 (t, J ) 7.00 Hz, 8H, R CH2), 1.38 (s, 12H, CH3), 1.37 (s,
12H, CH3), 1.35 (s, 12H, CH3). Vis (THF): 411 (5.44), 487 (5.27),
557 (4.41), 714 (4.70). MS (MALDI-TOF) m/z: 2406 (calcd for
5,6-Bis(5′-15′,15′′-bis[(10′,20′-di[4-(3-methoxy-3-methyl-
butoxy)phenyl]porphinato)zinc(II)]ethyne)indane (2). (5-Bromo-
10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc-
(II) (31 mg, 0.0370 mmol), 4 (30 mg, 0.0180 mmol), Pd2(dba)3 (5
mg, 0.0054 mmol), AsPh3 (0.013 g, 0.043 mmol), THF (10 mL),
and triethylamine (2 mL) were added to a 50 mL Schlenk tube.
The resulting solution was stirred for 23 h at 40 °C. Following
evaporation of volatiles, the residue was purified via chromatog-
raphy (silica gel, 1/1 hexanes/THF). The brown band was collected
and purified further via size-exclusion chromatography (SX-1
C143H138N12O12Zn3 2407).
Bis[(5,5′-15-triisopropylsilylethynyl-10,20-di[4-(3-methoxy-3-
methylbutoxy)phenyl]porphinato)zinc(II)]ethyne (7). A 50 mL
Schlenk tube was charged with 14 (0.152 g, 0.150 mmol), 5 (0.130
mg, 0.135 mmol), Pd2(dba)3 (0.020 g, 0.022 mmol), AsPh3 (0.053
g, 0.172 mmol), THF (15 mL), and triethylamine (3 mL), giving a
deep green solution, which was stirred for 4 h at 40 °C. Following
evaporation of the solvent, the residue was purified via chroma-
334 Inorganic Chemistry, Vol. 41, No. 2, 2002

Strongly Coupled Porphyrin Arrays
Table 1. Summary of Structure Determination of 5,6-Bis[(5′-15′-
triisopropylsilylethynyl-10′,20′-di[4-(3-methoxy-3-methylbutoxy)-
phenyl]porphinato)zinc(II)]indane)‚(Ethanol)2 (9‚(EtOH)2)
biobeads, THF), giving desired product 2. Isolated yield ) 36 mg
(63% based on 30 mg of starting material 4). 1H NMR (250 MHz,
50/1 CDCl3/d5-pyridine): δ 10.27 (d, J ) 4.55 Hz, 4H, â), 10.13
(d, J ) 4.63 Hz, 4H, â), 9.98 (s, 2H, meso), 9.63 (d, J ) 4.70 Hz,
4H, â), 9.18 (d, J ) 4.45 Hz, 4H, â), 9.02 (d, J ) 4.50 Hz, 4H, â),
8.91 (d, J ) 4.45 Hz, 4H, â), 8.78 (d, J ) 4.50 Hz, 4H, â), 8.59
(d, J ) 4.58 Hz, 4H, â), 8.36 (s, 2H, In CH), 8.07 (d, J ) 8.43 Hz,
8H, Ph), 7.86 (m, 4H, Ph), 7.63 (m, 4H, Ph), 7.20 (m, 16H, Ph),
4.35 (t, J ) 7.13 Hz, 8H, R CH2), 4.32 (t, J ) 7.13 Hz, 8H, R
CH2), 3.48 (t, J ) 7.03 Hz, 4H, In CH2), 3.35 (s, 12H, OCH3),
3.29 (s, 12H, OCH3), 2.58 (m, 2H, In CH2), 2.22 (t, J ) 7.13 Hz,
8H, R CH2), 2.19 (t, J ) 7.13 Hz, 8H, R CH2), 1.40 (s, 24H, CH3),
1.33 (s, 24H, CH3). Vis (THF): 419 (5.39), 479 (5.35), 558 (4.51),
713 (4.85). MS (MALDI-TOF) m/z: 3182 (calcd for C189H178N16O16-
Zn4 3183).
formula
fw
cryst class
space group
Zn2C123H146Si2N8O10
2083.40
triclinic
P1h (No. 2)
2
Z
cell constants
a
b
c
hind;1gR
b
19.5111(7) Å
20.9667(6) Å
17.5249(6) Å
103.699(2)°
110.344(2)°
hind;1gγ
V
86.690(3)°
6528.3(4) Å3
4.39 cm-1
µ
crystal size, mm3
Dcalcd
0.30 × 0.25 × 0.20
1.060 g/cm3
X-ray Crystallographic Structural Determination of 5,6-
Bis[(5′-15′-triisopropylsilylethynyl-10′,20′-di[4-(3-methoxy-3-
methylbutoxy)phenyl]porphinato)zinc(II)]indane)‚(Ethanol)2
(9‚(EtOH)2). X-ray quality crystals of 9‚(EtOH)2 were obtained
from slow diffusion of ethanol into a chloroform solution of 9.
The crystal dimensions were 0.30 × 0.25 × 0.20 mm3. Compound
9‚(EtOH)2 crystallizes in the triclinic space group P1h with a )
19.5111(7) Å, b ) 20.9667(6) Å, c ) 17.5249(6) Å, R ) 103.699-
(2)°, â ) 110.344(2)°, γ ) 86.690(3)°, V ) 6528.3(4) Å3, Z ) 2,
and dcalcd ) 1.060 g/cm3. X-ray intensity data were collected on a
Rigaku R-AXIS IIc area detector employing graphite-monochro-
mated Mo KR radiation (λ ) 0.710 69 Å) at a temperature of 200
K. Indexing was performed from a series of 1° oscillation images
with exposures of 200 s per frame. A hemisphere of data was
collected using 4° oscillation angles with exposures of 1200 s per
frame and a crystal-to-detector distance of 82 mm. Oscillation
images were processed using bioteX,45 producing a listing of
unaveraged F2 and σ(F2) values which were then passed to the
teXsan46 program package for further processing and structure
solution on a Silicon Graphics Indigo R4000 computer. A total of
46 248 reflections were measured over the ranges 5.02 e 2θ e
50.7°, -23 e h e 23, -25 e k e 25, -21 e l e 21 yielding
20 964 unique reflections (Rint ) 0.0632). The intensity data were
corrected for Lorentz and polarization effects but not for absorption.
The structure of 9‚(EtOH)2 was solved by Patterson methods
(DIRDIF).47 Table 1 contains details of the crystal and data
collection parameters. The structure was determined by Dr. Patrick
Carroll at the X-ray facility at the Department of Chemistry,
University of Pennsylvania.
F(000)
radiation
2θ range
hkl collected
2216
Mo KR (λ ) 0.710 69 Å)
5.02-50.7°
-23 e h e 23; -25 e k e 25;
-21e l e 21
46 248
20 964 (Rint ) 0.0632)
15 783 (F > 4σ)
20 964
no. reflns measured
no. unique reflns
no. obsd reflns
no. reflns used in refinement
no. params
1324
R indices (F > 4σ)
R1 ) 0.1041
wR2 ) 0.2366
R1 ) 0.1321
wR2 ) 0.2533
1.160
R indices (all data)
GOF
final difference peaks, e/Å3
+0.713, -0.381
Scheme 1
a Trimethylsilylacetylene (2 equiv), triisopropylsilylacetylene (6 equiv),
Pd(PPh3)2Cl2 (10 mol %), CuI (10 mol %), THF/TEA 10/3, 45 °C,
24 h. b 1.0 M NaOH (1 equiv), THF/MeOH 1/1, 25 °C, 10 min (5,
44%). c (5-Bromo-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphi-
nato)zinc(II) (1.1 equiv), Pd2dba3 (15 mol %), AsPh3 (1.2 equiv), THF/
TEA 5/1, 40 °C, 4 h (6, 93%). d (5-Bromo-15-triisopropylsilylethynyl-
10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)zinc(II) (1.1
equiv), Pd2dba3 (15 mol %), AsPh3 (1.2 equiv), THF/TEA 5/1, 40 °C, 4 h
(7, 92%).
Refinement was by full-matrix least squares based on F2 using
SHELXL-93.48 All reflections were used during refinement (F2
values that were experimentally negative were replaced by F2 )
0). The weighting scheme used was w ) 1/[σ2(Fo ) + 0.1010P2 +
2
2
22.8370P] where P ) (Fo + 2Fc2)/3. Non-hydrogen atoms were
refined anisotropically, and hydrogen atoms were refined using a
“riding” model. Refinement converged to R1 ) 0.1041 and wR2
) 0.2366 for 15 783 reflections for which F > 4σ(F), and R1 )
0.1321, wR2 ) 0.2533, and GOF ) 1.160 for all 20 964 unique,
nonzero reflections and 1324 variables.49 The maximum ∆/σ in
the final cycle of least squares was -0.003, and the two most
prominent peaks in the final difference Fourier were +0.713 and
-0.381 e/Å3.
Results and Discussion
Synthesis. Scheme 1 outlines the syntheses of (5-triiso-
propylsilylethynyl-15,15′-bis[(10,20-di[4-(3-methoxy-3-
methylbutoxy)phenyl]porphinato)zinc(II)])ethyne (6) and bis-
[(5,5′-15-triisopropylsilylethynyl-10,20-di[4-(3-methoxy-3-
(45) bioteX: A suite of Programs for the Collection, Reduction and
Interpretation of Imaging Plate Data; Molecular Structure Corpora-
tion: The Woodlands, TX, 1995.
(46) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corporation: The Woodlands, TX, 1985, 1992.
(47) DIRDIF: Parthasavathi, V.; Beurskens, P. T.; Slot, H. J. B. Acta
Crystallogr. 1983, A39, 860.
(48) Sheldrick, G. M. SHELXL-93: Program for the Refinement of Crystal
Structures; University of Go¨ttingen: Germany, 1993.
(49) R1 ) ∑||Fo| - |Fc||/∑|Fo|, wR2 ) {∑w(Fo - Fc )2/∑w(Fo )2}1/2
,
2
2
2
2
2
GOF ) {∑w(Fo - Fc )2/∑(n - p)}1/2, where n ) the number of
reflections and p ) the number of parameters refined.
Inorganic Chemistry, Vol. 41, No. 2, 2002 335

Fletcher and Therien
Scheme 2
Scheme 3
a (5-Bromo-10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphina-
to)zinc(II) (1.2 equiv), Pd2dba3 (18 mol %), AsPh3 (1.4 equiv), THF/TEA
5/1, 45 °C, 5 h (1, 78%). b (5-Bromo-10,20-di[4-(3-methoxy-3-methylbu-
toxy)phenyl]porphinato)zinc(II) (2.2 equiv), Pd2dba3 (30 mol %), AsPh3
(2.4 equiv), THF/TEA 5/1, 40 °C, 23 h (2, 65%).
a 1,6-Heptadiyne (10 equiv), Co2(CO)8 (1.5 equiv), dioxane/toluene 4/1,
100 °C, 17 h (8, 68%). b 1,6-Heptadiyne (10 equiv), Co2(CO)8 (1.5 equiv),
dioxane/toluene 4/1, 100 °C, 17 h (9, 73%). c 1,6-Heptadiyne (10 equiv),
Co2(CO)8 (2 equiv), dioxane/toluene 4/1, 100 °C, 18 h (11, 94%).
Structural Studies. The ORTEP representation of 5,6-
bis[(5′-15′-triisopropylsilylethynyl-10′,20′-di[4-(3-meth-
oxy-3-methylbutoxy)phenyl]porphinato)zinc(II)]indane)‚
(ethanol)2 (9‚(EtOH)2) is shown in Figure 1, with thermal
ellipsoids displayed at 30% probability. This structurally
characterized 1,2-phenylene-linked bis(porphyrin) species
featuring a cavity-bound ethanol constitutes an additional
example of the open “Pac-Man”53 conformation.33 Key
metrical parameters for 9‚(EtOH)2 include a Zn-Zn dis-
tance of 6.92 Å, a substantial 64.5° dihedral angle between
the least squares planes defined by the respective four central
nitrogen atoms (N4 plane) of its (porphinato)zinc(II) units,
and a lateral shift54 between the two porphyryl Zn atoms of
4.16 Å.
Congruent with the open structure of 9‚(EtOH)2, small
amplitude bond length and bond angle distortions are evident
at the juncture where the indanyl 5- and 6-carbon atoms are
linked to the 5′-(porphinato)zinc(II) meso positions (Figures
1-2, Table 2). The indanyl C6/C5-to-meso carbon distances
(C17-C58 and C66-C68) are elongated slightly (∼0.02 Å)
relative to typical Cmeso-to-arene bonds. Likewise, the cor-
responding C17-C58-C66 and C68-C66-C58 bond angles
(∼123.2°) reflect the steric crowding at the 5,6-indanyl bridge
that links the two (porphinato)metal units.
Each porphyrin macrocycle of 9‚(EtOH)2 exhibits a
combination of ruffling and saddling distortions (Figure 2).
The mean deviations of the macrocyclic carbon atoms from
the N4 planes are 0.133 and 0.119 Å, respectively, for the
Zn1 and Zn2 ring systems. For the Zn1 ring system, the
typical Cmeso and Câ displacements from the porphyrin least
squares plane are respectively 0.184 and 0.114 Å, respec-
tively, while the corresponding Cmeso and Câ displacements
within the Zn2 macrocycle are 0.146 and 0.121 Å. The
closest nonbonded contact between each of the porphyrin
methylbutoxy)phenyl]porphinato)zinc(II)]ethyne (7), key pre-
cursors to structures 1 and 2. The synthetic strategy exploits
the facts that cobalt-catalyzed [2+2+2] cycloaddition reac-
tions are sensitive to alkyne steric properties,41,50 and that
[5-(trimethylsilylethynyl)-15-(triisopropylsilylethynyl)-10,-
20-diarylporphinato]zinc(II) species can be prepared readily.
Selective deprotection of the trimethylsilyl (TMS) group
using standard methods35,51 gives [5-ethynyl-15-(triisopro-
pylsilylethynyl)-10,20-di[4-(3-methoxy-3-methylbutoxy)phe-
nyl]porphinato]zinc(II) (5); reaction of TIPS-protected 5 with
the corresponding 5-bromo- and 5-bromo-15-triisopropylsi-
lylethynyl-substituted 10,20-diarayl(porphinato)zinc(II) com-
pounds under previously established reaction conditions25,52
gives 6 and 7.
Meso-to-meso ethyne-bridged bis(porphinato)zinc(II) spe-
cies 6 and 7 undergo [2+2+2] cycloadditions with 1,6-
heptadiyne exclusively at the ethynyl moiety that links the
two porphyryl macrocycles (Scheme 2) to yield cofacial bis-
[(porphinato)zinc(II)] species 8 and 9. These reactions occur
in yields (∼70%, based on the porphyrinic starting material)
comparable to that delineated for the conversion of the simple
conjugated dimeric (porphinato)zinc(II) species 10 to face-
to-face 11.33
Compounds 8 and 9 can be deprotected using tetra-n-bu-
tylammonium fluoride to yield 3 and 4, respectively; subse-
quent Pd-catalyzed cross-coupling reactions of synthons 3
and 4 with [5-bromo-10,20-di[4-(3-methoxy-3-methylbutoxy)-
phenyl]porphinato]zinc(II) complete the syntheses of super-
molecular (porphinato)metal species 1 and 2 (Scheme 3).
(50) Hillard, R. L., III; Vollhardt, K. P. C. J. Am. Chem. Soc. 1977, 99,
4058-4069.
(51) Zehner, R. W.; Parsons, B. F.; Hsung, R. P.; Sita, L. R. Langmuir
1999, 15, 1121-1127.
(53) Guilard, R.; Brandes, S.; Tardieux, C.; Tabard, A.; L’Her, M.; Miry,
C.; Gouerec, P.; Knop, Y.; Collman, J. P. J. Am. Chem. Soc. 1995,
117, 11721-11729.
(52) Wagner, R. W.; Johnson, T. E.; Li, F.; Lindsey, J. S. J. Org. Chem.
1995, 60, 5266-5273.
(54) Scheidt, W. R.; Lee, Y. J. Struct. Bonding (Berlin) 1987, 64, 1-70.
336 Inorganic Chemistry, Vol. 41, No. 2, 2002

Strongly Coupled Porphyrin Arrays
Figure 1. ORTEP representations of compound 9‚(EtOH)2 with thermal ellipsoids at 30% probability. (A) View down the indanyl bridge; (B) view
orthogonal to the indanyl plane. Phenyl group alkyl substituents have been omitted for clarity.
Table 2. Selected Bond Distances and Angles for 9‚(EtOH)2
bond
distance, Å
bond
distance, Å
C2-C21
C12-C44
C17-C58
1.488(8)
1.493(8)
1.511(7)
C73-C87
C83-C110
C66-C68
1.494(9)
1.490(9)
1.505(8)
angle
angle, deg
angle
angle, deg
C2-C21-C22
C2-C21-C26
C17-C58-C59
C17-C58-C66
121.9(6)
121.1(6)
117.9(5)
123.4(5)
C73-C87-C88
C73-C87-C92
C68-C66-C65
C68-C66-C58
121.1(7)
122.1(7)
117.5(6)
122.9(5)
dihedral
angle, deg
dihedral
angle, deg
C1-C2-C21-C22
C3-C3-C21-C22
C16-C17-C58-C66
81.4(8) C72-C73-C87-C88
100.8(7) C74-C73-C87-C88 101.1(8)
75.8(6)
77.6(8)
64.4(5) C67-C68-C66-C58
C18-C17-C58-C66 110.5(6) C69-C68-C66-C58 108.4(6)
der Waals contact distance (3.40 Å).55 Interestingly, an
additional close interporphyrin contact exists between the
C19 and C70 â-carbon atoms; these nuclei are separated by
only 3.143(7) Å, and drive the anomalously large average
perpendicular displacements (0.44 Å) observed at the C19
and C20 â carbons of 9‚(EtOH)2’s Zn1 macrocycle.
The origin of the sub-van der Waals separation between
the C19 and C70 â-carbons derives likely from steric
interactions caused by the orientation of the ethanol moiety
bound within the pocket of the cofacial bis[(porphinato)-
zinc(II)] complex. Ethanol carbon atoms C56 and C57 are
suspended 3.476(6) and 3.820(8) Å, respectively, above the
N4 plane of the Zn2 macrocycle; note that the C56 methylene
carbon of the Zn1-ligated ethanol lies above the N5-C84
bond (nonbonded distances: C56-N5, 3.553(9) Å; C56-
C84, 3.613(8) Å). This interaction augments the CR-Cmeso
-
C5-indanyl-C6-indanyl dihedral angle (C16-C17-C58-C66)
involving the Zn1 macrocycle, with respect to the analogous
C67-C68-C66-C58 dihedral entailing the Zn2 porphyrin
ring (Table 2), resulting in an asymmetric tilting of the Zn1
(64°) and Zn2 (76°) porphyrin least squares planes relative
Figure 2. Diagrammatic representations of the porphyrin cores of
9‚(EtOH)2 illustrating the extent of the macrocycle saddling and ruffling
distortions. The numbers adjacent to the atom labels signify the perpen-
dicular displacements, in units of 0.01 Å, from the respective least squares
plane as defined by the four porphyrin nitrogen atoms.
macrocycles is at the bridging meso positions; note that the
C17-C68 separation is only 3.056(7) Å, well below the van
(55) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960.
Inorganic Chemistry, Vol. 41, No. 2, 2002 337

Fletcher and Therien
indicators of the relative proximity of the porphyrin rings in
cofacial orientations. Note that these signals appear as
doublets for compound 7 (δ ) 8.1 and 7.3 ppm; Figure 4A).
In the analogous compound 9 spectrum (Figure 4B), the
inequivalence of the H(o) and H(m) aryl protons that point
toward and away from the cofacial pocket is clearly
apparent: the H(o) resonances shift upfield and are split into
two multiplets (labeled H(o)in and H(o)out), while the meta-
phenyl resonances shift upfield and appear as a closely
overlapping pair of multiplets (labeled H(m)in and H(m)out).
These characteristic shifts for the o-phenyl protons of 7
and 9 can be used to discern basic solution structural features
1
of 2. Note that the H NMR spectrum for 2 (Figure 4C)
evinces a simple doublet at δ ) 8.15 ppm and multiplets at
δ ) 7.95 and 7.65 ppm that integrate in a 2/1/1 ratio: these
spectral signatures correspond to the respective o-phenyl
proton resonances observed for bis[(porphinato)zinc(II)]
species 7 and 9. These data show that 2 possesses two
inequivalent pairs of porphyryl units: one set of these signals
corresponds to the H(o) resonances for the closely spaced 1,2-
phenylene-bridged bis[(porphinato)zinc(II)] core, while the
second set delineates a pair of terminal porphyrin moieties
that are separated by a distance sufficiently large such that
the macrocycle ring currents do not significantly perturb aryl
ring chemical shifts relative to the compound 7 benchmark.
In this regard, two other compound 2 spectral features
deserve comment: (i) the substantial distance between the
outer porphyryl rings cannot derive from an extensive lateral
shift,54 as the â proton resonances reflect a plane of symmetry
defined by the indanyl bridge, and (ii) the distinct resonance
pattern between 9.0 and 10.5 ppm denotes two chemically
equivalent meso-to-meso ethyne-bridged bis[(porphinato)-
zinc(II)] scaffolds.25
Electronic Absorption Spectroscopy. Electronic spectral
features of tris- and tetrakis[(porphinato)zinc(II)] complexes
1 and 2 are consistent with their solution structures elucidated
by NMR methods. Figure 5A,B displays reference spectra
for the cofacial 1,2-phenylene-bridged and linear meso-to-
meso ethyne-linked bis[(porphinato)zinc(II)] species 11 and
10, respectively; the electronic structural characteristics of
these classes of coupled bis(porphyrin) systems have been
discussed previously.25-27,57,58 With respect to compound 11,
note that an optical hallmark of the cofacial porphyrin
structural motif is the presence of a B-state exciton band
that is intensified and blue shifted relative to the Soret
transition of an appropriate reference monomeric porphyrin.
Consistent with this, the 411 nm band of compound 11
(Figure 5A) is observed to lie 634 cm-1 higher in energy
with respect to the B-band transition for 5-phenyl-6-[(5′-
10′,20′-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)-
zinc(II)]indane (12) (Figure 6A).
Figure 3. Molecular model of compound 2‚(EtOH)4 generated from the
CaChe MM2 computational package and data obtained from the X-ray
crystallographic structure of 9‚(EtOH)2.
to the indanyl bridge least squares plane. The marked 4.16
Å lateral shift, coupled with (i) the significant observed
atomic perpendicular displacements from the macrocycle
least squares planes and (ii) the asymmetric tilting of the
two (porphinato)zinc(II) units with respect to the indanyl
bridge, serve to further illustrate the flexibility inherent to
the 1,2-phenylene-based porphyrin-to-porphyrin linkage to-
pology and the ease by which small molecules can be
accommodated within the cavities of such cofacial bis-
(porphyrin) ligand frameworks.33
The X-ray crystallographic data obtained for 9‚(EtOH)2
can be utilized to estimate a typical distance that separates
the porphyrin macrocycles appended via ethyne groups to
the cofacial bis[(porphinato)metal] core of compound 2 in
coordinating solvent. The Si-Si separation distance between
the two peripheral TIPS groups in 9‚(EtOH)2 is 13.81 Å;
simple replacement of each TIPS group with a 5′-(porphi-
nato)zinc(II) unit within a molecular mechanics computa-
tional package56 approximates a Zn-Zn separation of 15.7
Å between the central metal ions of the outer porphyrin rings
(Figure 3). This analysis highlights the fact that supplemental
π-cofacial interactions are essentially absent between the
outer porphyrin rings of 2 in an open “Pac-Man” conforma-
tion and suggests that the observed electrooptic perturbations
manifest in 2 relative to simple 1,2-phenylene-bridged bis-
[(porphinato)metal] compounds (e.g., 11; vide infra) in
coordinating solvents arise solely from substituent effects
inherent to the (5-ethynylporphinato)zinc(II) moiety.
NMR Spectroscopy. The open conformation of 2 was
confirmed via 1H NMR experiments. Figure 4 highlights the
resonances spanning the 7.0-10.5 ppm spectral domain for
compounds 7, 9, and 2. The 1H NMR chemical shifts
corresponding to the ortho and meta protons of the porphyryl
5- and 15-aryl substituents (labeled H(o) and H(m)) are key
As evidenced in Figure 5C,E, the key spectral signatures
that delineate cofacial bis(porphyrin) structures are also
manifest in ethyne-bearing precursor structures 7 and 8.
Elaboration of 7 and 8 into supermolecular structures 1 and
(57) Chang, C. K. AdV. Chem. Ser. 1979, 173, 162-177.
(58) Osuka, A.; Nakajima, S.; Maruyama, K. J. Org. Chem. 1992, 57,
7355-7359.
(56) Molecular Mechanics, CaChe v. 4.5; CaChe Scientific: Beaverton,
OR, 2000.
338 Inorganic Chemistry, Vol. 41, No. 2, 2002

Strongly Coupled Porphyrin Arrays
Figure 4. 250 MHz 1H NMR spectra of (A) 7, (B) 9, and (C) 2 in 50/1 CDCl3/d5-pyridine spanning the 11.0-6.8 ppm spectral window. S ) solvent peak.
2 gives rise to species that display electronic spectral
characteristics of both cofacial and meso-to-meso ethyne-
linked oligo[(porphinato)zinc(II)] compounds (Figure 5D,F).
The optical spectrum of compound 1, for example, shows
an intense transition at 411 nm (ꢀ ) 275 500 M-1 cm-1), a
wavelength identical to that observed for 11’s allowed B-state
exciton band (Figure 5A), suggesting a cofacial exciton
coupling energy similar to that manifest in the dimeric
reference compound; 1’s Q-state manifold spectral features,
as well as the energetic splitting between its prominent
B-state absorptions (3288 cm-1), are reminiscent of those
observed for meso-to-meso ethyne-bridged 10.25,26
The electronic absorption spectrum of tetrakis[(porphina-
to)zinc(II)] complex 2 displays the gross spectral features
of a meso-to-meso ethyne-bridged [(porphinato)zinc(II)]
dimer. Comparison of the Figure 5F spectrum with that for
the reference compound, [(5-15-[5′′-6′′-(phenyl)indanyl)]-
10,20-di[4-(3-methoxy-3-methylbutoxy)phenyl]porphinato)-
zinc(II)]-[(5′-10′,20′-di[4-(3-methoxy-3-methylbutoxy)phenyl]-
porphinato)zinc(II)]ethyne (13, Figure 6B), shows a striking
correspondence of the λmax values for the key optical
transitions. The effects of cofacial exciton coupling in 2,
however, are readily apparent, causing an increase in oscil-
lator strength of the high energy B-state transition manifold
centered at 419 nm and a general broadening of the visible
regime absorptive signature relative to that manifest for 13.
Note that the full-width-at-half-maximum (fwhm) of the
B-band region (∼360-525 nm) increases by 1133 cm-1 in
2 (5399 cm-1) relative to 13 (4266 cm-1); furthermore,
simplex fitting shows that the fwhm of 2’s low energy Soret
transition envelope centered at 479 nm has increased
substantially (fwhm ) 1045 cm-1) with respect to the ana-
logous low energy B-state spectral domain of 13 (fwhm )
438 cm-1).
Electrochemical Data. Potentiometric data for reference
monomer 12, reference dimers 11 and 13, as well as
compounds 1 and 2 are summarized in Table 3. As
expected,25,59 cyclic voltammetric experiments show that the
first oxidation processes for both cofacial and meso-to-meso
ethyne-bridged bis[(porphinato)zinc(II)] systems porphyrin
dimers are split into two one-electron steps. Typical of bis-
[(porphinato)metal] compounds featuring close interplanar
contacts,59,60 the initial step of the first oxidation process for
cofacial reference dimer 11 is destabilized relative to that
determined for benchmark porphyrin monomer 12. Such
redox behavior derives from the filled π-π interactions
characteristic of two closely spaced aromatic macrocycles.59
Following removal of the first electron from such cofacial
bis[(porphinato)zinc(II)] compounds, electronic delocaliza-
tion serves to stabilize the second step of 11’s first oxidation
(59) Le Mest, Y.; L’Her, M.; Hendricks, N. H.; Kim, K.; Collman, J. P.
Inorg. Chem. 1992, 31, 835-847.
(60) Osuka, A.; Nakajima, S.; Nagata, T.; Maruyama, K.; Toriumi, K.
Angew. Chem., Int. Ed. Engl. 1991, 30, 582-584.
Inorganic Chemistry, Vol. 41, No. 2, 2002 339

Fletcher and Therien
Figure 5. Electronic absorption spectra of (A) 11, (B) 10, (C) 7, (D) 1, (E) 8, and (F) 2 in THF.
Figure 6. Electronic absorption spectra of (A) 12 and (B) 13 in THF.
process relative to the E1/2(ZnP/ZnP+) potential determined
for 12.
[(porphinato)zinc(II)] benchmarks (Table 3). The anodic
cyclic voltammetric responses observed for the tetrakis-
[(porphinato)zinc(II)] complex 2 are similar to those observed
for 1 (Table 3); notably, the first step of the first oxidation
process for 2 is 2e in nature and is shifted cathodically 15
mV relative to 1’s initial oxidation potential. These poten-
tiometric data for compounds 1, 2, and 11-13 thus show (i)
that the extensive π-conjugation enabled by the meso-to-
meso ethyne-bridged porphyrin-to-porphyrin linkage topol-
ogy, which gives rise to substantial redox splitting, deter-
mines essentially the anodic current versus potential profiles
observed in the cyclic voltammetric studies of compounds
The first oxidation process for tris[(porphinato)zinc(II)] 1
is split into two observable steps, with a redox splitting (215
mV) reminiscent of that manifest for meso-to-meso ethyne-
bridged 13. The first step, one-electron (1e) in nature, occurs
at +555 mV and is shifted cathodically 15 mV with respect
to 13’s initially observed 1e oxidation potential. The second
step of 1’s first oxidation process is 2e in nature and occurs
at a potential (770 mV vs SCE) intermediate between those
determined for the second 1e redox steps of the first oxidation
processes of the cofacial (11) and ethyne-bridged (13) bis-
340 Inorganic Chemistry, Vol. 41, No. 2, 2002

Strongly Coupled Porphyrin Arrays
Table 3. Cyclic Voltammetric Data (mV)a
those determined for the initial reductive events of the
cofacial and meso-to-meso ethyne-bridged bis[(porphinato)-
zinc(II)] benchmarks 11 and 13 (Table 3).
compound
ZnP/ZnP+
705 (1)
620 (1), 750 (1) 1070 (1), 1250 (1) -1720 (2)
570 (1), 790 (1) 1255 (2)
555 (1), 770 (2) 1270 (3)
540 (2), 770 (2) 1280 (4)
ZnP+/ZnP2+
ZnP/ZnP-
12
11
13
1
1010 (1)
-1495 (1)
-1235 (1), -1335 (1)
-1420 (3)
-1425 (4)
Conclusions
2
Sequential cobalt-catalyzed [2+2+2] cycloadditions and
palladium-catalyzed cross-coupling reactions provide access
to supermolecular structures that manifest both classic
structural motifs that have been demonstrated to provide
substantial electronic communication between (porphinato)-
metal centers: face-to-face organization and direct macro-
cycle-to-macrocycle linkage via cylindrically π-symmetric
bridging moieties. We report two archetypal multiporphyrin
structures that manifest both 1,2-phenylene- and ethyne-based
meso-to-meso linkage topologies; structural, spectroscopic,
and potentiometric properties of these systems show that (i)
the 1,2-phenylene-bridged cofacial bis[(porphinato)zinc(II)]
component of these systems can adopt the open conformation
required for substrate binding and (ii) ethynyl(porphinato)-
metal moieties appended directly to either macrocycle of the
cofacial porphyrin core are strongly coupled to this unit. We
posit that the now established combination of these structural
elements holds promise for the elaboration of new classes
of redox catalysts competent to both bind small molecule
substrates and effect concerted, multielectron redox trans-
formations.
a Experimental conditions: solvent ) benzonitrile; [porphyrin] ) 1 mM;
[TBAClO4] ) 0.1 M; scan rate ) 100-1000 mV/s; reference electrode )
Ag wire. E1/2 values reported are relative to SCE; the ferrocene/ferrocenium
redox couple (0.43 V vs SCE, benzonitrile) was used as an internal standard.
The number in parentheses following each potential denotes the number of
electrons involved in that redox process.
1 and 2, and (ii) while both porphyrin-porphyrin π-cofacial
and π-conjugative electronic interactions deriving from the
ethynyl linkage topology serve to destabilize the HOMO of
the composite supermolecular complex, the extent to which
the HOMOs of 1 and 2 are further destabilized relative to
13 by their respective supplemental π-cofacial interactions
is only on the order of 10-30 mV.
The cathodic electrochemistry observed for reference bis-
[(porphinato)zinc(II)] compounds 11 and 13 shows that these
species display the signature current-potential responses for
their respective first reduction processes noted previously
for cofacial and meso-to-meso ethyne-bridged bis[(porphi-
nato)zinc(II)] structures.25,59 It is important to appreciate that
while the cofacial porphyrin motif destabilizes the LUMO,
giving rise to E1/2(ZnP-/ZnP) values that are substantially
lower than those determined for appropriate benchmark
(porphinato)zinc(II) compounds, a meso-to-meso ethyne-
bridging linkage topology stabilizes significantly the LUMO
with respect to that of its simple (porphinato)zinc(II) building
block. For the compounds listed in Table 3, it can be seen
that the magnitudes of these electronic perturbations are
approximately equal and opposite. Note that the potential
of cofacial 11’s initial 2e reduction is suppressed 225 mV
relative to that observed for monomer 12, while the potential
of the initial 1e step of meso-to-meso ethyne-bridged 13’s
first cathodic redox process is increased by 260 mV relative
to the compound 12 benchmark. These electronic effects that
derive from these two classes of porphyrin-porphyrin
linkage motifs apparently conspire in compounds 1 and 2 to
give rise to cathodic cyclic voltammetric responses that are
multielectron in nature at potentials intermediate between
Acknowledgment. This work was supported in part by
the MRSEC Program of the National Science Foundation
(DMR00-79909) and the Office of Naval Research (N00014-
98-1-0187). M.J.T. acknowledges the Camille and Henry
Dreyfus Foundation for a research fellowship. J.T.F. thanks
the International Precious Metals Institute (IPMI) for a
graduate student research award. The structure of compound
9 was determined by Dr. Patrick Carroll (X-ray Facility,
Department of Chemistry, University of Pennsylvania).
Supporting Information Available: Characterization data and
detailed syntheses of compounds 12-17, tables of crystal data, and
a labeled ORTEP diagram (22 pages PDF); X-ray crystallographic
file for 9 (CIF format). This material is free of charge via the
Internet at http://pubs.asc.org.
IC010871P
Inorganic Chemistry, Vol. 41, No. 2, 2002 341