Synthesis and complexation of back-to-back capped bis-dioxocyclams

Article abstract of DOI:10.1021/ic0502731

Pyridine-capped 5,12-dioxocyclams were coupled back-to-back directly, with one or two intervening phenyl groups, an ethynyl group, or a diazo group via Suzuki, Sonogashira, or reductive coupling of the 4-nitropyridine monocyclam. These bis-dioxocyclams linked through extended π-conjugated systems were complexed to copper(II) and cobalt-(III), producing bis-metal complexes which were characterized spectroscopically and electrochemically. These studies gave little evidence for electronic communication between metal centers across the π-conjugated linkers.

Full text of DOI:10.1021/ic0502731

Inorg. Chem. 2005, 44, 5858−5865
Synthesis and Complexation of “Back-to-Back” Capped
Bis-dioxocyclams
Jun Mo Gil, Scott David, Angela L. Reiff, and Louis S. Hegedus*
Department of Chemistry, Colorado State UniVersity, Fort Collins, Colorado 80523
Received February 21, 2005
Pyridine-capped 5,12-dioxocyclams were coupled “back-to-back” directly, with one or two intervening phenyl groups,
an ethynyl group, or a diazo group via Suzuki, Sonogashira, or reductive coupling of the 4-nitropyridine monocyclam.
These bis-dioxocyclams linked through extended
(III), producing bis-metal complexes which were characterized spectroscopically and electrochemically. These studies
gave little evidence for electronic communication between metal centers across the -conjugated linkers.
π-conjugated systems were complexed to copper(II) and cobalt-
π
Introduction
the ability to coordinate additional metals at this site.6
Application of this methodology to the synthesis of bis-
dioxocyclams which are linked back-to-back with conjugated
capping groups, as well as their cobalt(III) cyanide com-
plexes, which can form coordinate links to other metals, is
described below.
Coordinated transition metal centers covalently connected
by π-conjugated linkers of various constitution and length,
capable of electron or energy transfer, have been extensively
investigated for use in areas ranging from the development
of “molecular wires” to the modeling of photosynthesis.1
Transition metal arrays connected via coordination linkages
with ligands capable of transmitting electronic or magnetic
information across the π system of the linking ligands have
become important to the study of long-range electron transfer
and magnetic interactions.2 Complexes having the potential
to form extended π networks via both covalent and coordi-
nation linkages are less common and may share the physical
properties of both types of systems, as well as have unique
properties. Initial studies directed toward the synthesis of
this class of complex are described below.
Experimental Section
General Procedures. Acetonitrile was distilled over calcium
hydride. Methanol was distilled over calcium hydride and dried
over 4 Å molecular sieves. NMR spectra were recorded on Varian
JS-300 or JS 400 spectrometers. Infrared spectra were recorded on
a Nicolet Magna-IR 760 spectrometer. UV-vis spectra were
recorded on an Agilent G 1103 spectrometer. Electrochemical
measurements were conducted with an EG and G, Princeton Applied
Research, model 75 universal programmer, model 179 digital
coulometer, and model 173 potentiostat/galvanostat. The complex
was dissolved in a 0.1 M solution of tetrabutylammonium hexafluo-
rophosphate in acetonitrile or CH2Cl2. The working electrode was
glassy carbon, and the counter electrode was a platinum wire. The
reference electrode was SCE, and potentials were reported versus
Recent research in these laboratories has focused on the
synthesis and metal complexation studies of dioxocyclams,3
bis-dioxocyclams,4 and capped dioxocyclams having ad-
ditional ligand sites external to the macrocycle,5 as well as
* To whom correspondence should be addressed. E-mail: hegedus@
lamar.colostate.edu.
(3) (a) Betschart, C.; Hegedus, L. S. J. Am. Chem. Soc. 1992, 114, 5010.
(b) Moser, W. H.; Hegedus, L. S. J. Org. Chem. 1994, 59, 7779. (c)
Hegedus, L. S.; Greenberg, M. M.; Wendling, J. J.; Bullock, J. P. J.
Org. Chem. 2003, 68, 4179.
(4) (a) Dumas, S.; Lastra, E.; Hegedus, L. S. J. Am. Chem. Soc. 1995,
117, 7, 3368. (b) Hsiao, Y.; Hegedus, L. S. J. Org. Chem. 1997, 62,
3568. (c) Kuester, E.; Hegedus, L. S. Organometallics 1999, 18, 5318.
(d) Puntener, K.; Hellman, M. D.; Kuester, E.; Hegedus, L. S. J. Org.
Chem. 2000, 65, 8301. (e) Brugel, T. A.; Hegedus, L. S. J. Org. Chem.
2003, 68, 8409.
(5) (a) Wynn, T.; Hegedus, L. S. J. Am. Chem. Soc. 2000, 122, 5034. (b)
Achmatowicz, M.; Hegedus, L. S.; David, S. J. Org. Chem. 2003, 68,
7661.
(6) Hegedus, L. S.; Sundermann, M. J.; Dorhout, P. K. Inorg. Chem. 2003,
42, 4396.
(1) For recent reviews, see: (a) Zeissel, R.; Hissler, M.; El-ghayoury,
A.; Harriman, A. Coord. Chem. ReV. 1998, 178-180, 1251. (b)
Barigelletti, F.; Flamigni, L. Chem. Soc. ReV. 2000, 19, 1. (c) Launay,
J.-P. Chem. Soc. ReV. 2001, 30, 386. (d) See also the extensive work
of Lindsey et. al.: Ambroise, A.; Kirmaier, C.; Wagner, R. W.; Loewe,
R. S.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Org. Chem. 2002,
67, 3811.
(2) For a recent review, see: (a) Baranoff, E.; Collin, J.-P.; Flamigni, L.;
Sauvage, J.-P Chem. Soc. ReV. 2004, 33, 147. (b) Yu, L.; Muthuku-
maran, K.; Sazanovich, I. V.; Kirmaier, C.; Hindin, E.; Diers, J. R.;
Boyle, P. D.; Bocian, D. F.; Holton, D.; Lindsey, J. S. Inorg. Chem.
2003, 42, 6629. (c) Flay, M.-L.; Vahrenkamp, H. Eur. J. Inorg. Chem.
2003, 1719. (d) Geiss, A.; Vahrenkamp, H. Inorg. Chem. 2000, 39,
4029.
5858 Inorganic Chemistry, Vol. 44, No. 16, 2005
10.1021/ic0502731 CCC: $30.25
© 2005 American Chemical Society
Published on Web 07/12/2005

Synthesis and Complexation of Capped Bis-dioxocyclams
SCE. Cyclic voltammograms were obtained at a scan rate of 100
mV/s. Data were plotted with the x axis equal to 100 mV/cm.
Microwave reactions were performed in a GE countertop microwave
oven, model number JES1339WC, which had a capacity of 1.3 ft3
and a watt output of 1100 W. Because the compounds all occlude
solvent on crystallization, melting points are broad and elemental
analyses are unreliable. Constitution was assessed by high-resolution
mass spectroscopy, and purity by high-resolution 1H and 13C NMR
spectroscopy (see Supporting Information).
46.4; IR (Nujol) 2965, 1459 cm-1; HRMS (FAB+, m/z) Calcd for
C
157 °C.
14H13N2Cl4 (M + H+), 348.9833; found, 348.9832; mp ) 154-
4,4′-Bipyridine-Capped Bis-dioxocyclam 1a. Dioxocyclam (5)3a
(0.235 g, 0.634 mmol), 4b (0.110 g, 0.316 mmol), Na2CO3 (0.268
g, 2.52 mmol), and NaI (0.047 g, 0.316 mmol) were added to an
argon-flushed pressure tube. After dissolution in distilled CH3CN
(100 mL), the reaction was purged with argon. The pressure tube
was tightly sealed and placed into a 60-70 °C oil bath with stirring
for 4 days. After being cooled to ambient temperature, the reaction
mixture was transferred to a 250 mL round-bottom flask and
concentrated under reduced pressure. The residue was dissolved
in CH2Cl2 (100 mL) and H2O (50 mL) and stirred for 1 h, and the
two layers were partitioned. The aqueous layer was extracted with
CH2Cl2 (100 mL × 3). The combined organic extracts were dried
over MgSO4, filtered, and concentrated under vacuum. Purification
by flash silica gel chromatography using 0-25% MeOH in EtOAc
afforded the solid product (0.230 g, 0.242 mmol). Yield: 77%.
X-ray quality crystals were formed from slow evaporation of CH2-
2,2′,6,6′-Tetrakis(hydroxymethyl)-4,4′-bipyridine 3. 2,2′,6,6′-
Tetra(carboxymethyl)-4,4′-bipyridine (2)8 (0.504 g, 1.3 mmol) was
placed into a 100 mL round-bottom flask and dissolved in dry
absolute EtOH (10 mL). The flask was equipped with a condenser
and flushed with Ar. The flask was cooled to 0 °C, and NaBH4
(0.385 g, 11.0 mmol) was added in portions. The blue solution was
kept at 0 °C for 1.5 h then warmed to reflux for 24 h under Ar.
H2O (20 mL) was then added to the tan solution and stirred for
6 h at low heat. Solvent was removed under reduced pressure, and
the residue was purified using silica gel chromatography eluting
with MeOH to afford the white powder (0.307 g, 1.1 mmol).
Yield: 85%. 1H NMR (CD3OD, 300 MHz) δ 7.79 (s, 4H), 4.77 (s,
8H); 13C NMR (CD3OD, 75 MHz) δ 163.2, 149.3, 118.0, 65.6; IR
(Nujol) ν 2963, 1459 cm-1; HRMS (FAB+, m/z) Calcd for
C14H17N2O4 (M + H+), 277.01188; found, 277.01176; mp ) 210
°C dec.
1
Cl2/hexane; H NMR (CDCl3, 400 MHz) δ 9.06 (s, 1H), 9.05(s,
1H), 7.98 (s, 1H), 7.97 (s, 1H), 7.20 (s, 1H), 7.19 (s, 1H), 7.17 (s,
1H), 7.16 (s, 1H), 4.23 (d, J ) 16.8 Hz 2H), 4.14 (d, J ) 17.2 Hz
2H), 4.08 (d, J ) 17.2 Hz 2H), 4.023 (d, J ) 17.2 Hz 1H), 4.016
(d, J ) 17.2 Hz 1H), 3.43 (s, 6H), 3.23 (d, J ) 14.0 Hz 2H), 3.02-
2.90 (m, 10H), 2.60 (d, J ) 14.0 Hz 2H), 2.51 (s, 3H), 2.50 (s,
3H), 2.35 (d, J ) 14.4 Hz 2H), 1.47 (s, 6H), 1.44 (s, 6H), 1.37 (s,
6H), 1.33 (s, 6H), 1.21 (s, 6H), 1.142 (s, 3H), 1.137 (s, 3H); 13C
NMR (CDCl3, 100 MHz) δ 173.4, 172.7, 164.3, 159.8, 147.4, 147.2,
117.1, 117.0, 116.8, 116.6, 82.7, 79.6, 74.6, 72.7, 69.5, 69.4, 67.4,
65.7, 64.7, 56.0, 54.8, 51.9, 50.3, 26.3, 25.6, 23.6, 23.5, 19.2; FT-
IR (film) ν 1661 cm-1 (CdO); UV-vis (CHCl3) λmax (nm) [ꢀ (M-1
cm-1)] 280 (sh) [5980]; MS (FAB+, m/z) for C50H81N10O8 (M +
H+) found, 949.15.
2,2′,6,6′-Tetrakis(bromomethyl)-4,4′-bipyridine 4a. 2,2′,6,6′-
Tetrakis(hydroxymethyl)-4,4′-bipyridine (3) (0.127 g, 0.46 mmol)
and 2 drops of DMF were placed into a 10 mL round-bottom flask
equipped with a drying tube, and SOBr2 (6 mL) was added slowly
and stirred for 16 h. The reaction solution was transferred to a 250
mL flask, and CH2Cl2 (50 mL) was added to the reaction mixture
followed by the slow addition of H2O (50 mL) (Caution:
exothermic!). Then 40% KOH was added until pH 11 was reached.
After partitioning of the two layers, the aqueous solution was
extracted with CH2Cl2 (50 mL × 2). The combined organic phase
was dried over Na2SO4 and filtered. Concentration under reduced
pressure afforded a white powder (0.135 g, 0.26 mmol). Yield:
4-Bromo-2,6-bis(chloromethyl)pyridine 4c. To dimethyl-4-
bromo-2,6-pyridinedicarboxylate8 (3.3 g, 12 mmol) solution in
absolute EtOH (150 mL) was added NaBH4 (1.82 g, 48 mmol)
portionwise at 0 °C. After being stirred for 2 h, the reaction mixture
was warmed to ambient temperature, stirred overnight, and refluxed
for 10 min. After being cooled to room temperature, the solvent
was removed under reduced pressure until the mixture became a
slurry. H2O (15 mL) was added, the mixture extracted with CH2-
Cl2 (50 mL × 4), and the combined organic extracts were dried
over MgSO4, filtered, and concentrated under vacuum. Without
further purification, the obtained white solid (2.3 g) was dissolved
in DMF (23 mL) and was cooled to -10 °C. Then, SOCl2 (3.8
mL) was added dropwise. After the mixture was stirred for 1 h at
0 °C, CH2Cl2 (50 mL) and EtOAC (100 mL) were added and then
H2O (30 mL) was added slowly to quench the remaining SOCl2 at
0 °C. After the reaction was stirred for 30 min, 10 N NaOH solution
was added at 0 °C until pH 8-9 was achieved and the solution
was warmed to room temperature. After partitioning of the two
layers, the aqueous solution was extracted with EtOAc (50 mL ×
4). The combined organic extracts were dried over MgSO4, filtered,
and concentrated under vacuum. Purification by flash silica gel
chromatography using 10% EtOAc in hexane afforded the solid
56%; 1H NMR (CDCl3, 300 MHz) δ 7.59 (s, 4H), 4.61(s, 8H) 13
C
NMR (CD3OD, 75 MHz) δ 158.3, 147.6, 120.9, 33.24; IR (Nujol)
2955, 1460 cm-1; Elemental analysis: Calcd for C14H13N2Br4, C
31.85, H 2.29, N 5.31, Br 60.55; found, C 32.04, H 2.18, N 5.12,
Br 60.27; mp ) 190 °C dec.
2,2′,6,6′-Tetrakis(chloromethyl)-4,4′-bipyridine 4b. 2,2′,6,6′-
Tetrakis(hydroxymethyl)-4,4′-bipyridine (3) (0.101 g, 0.36 mmol)
and 4 drops of DMF were placed into a 10 mL round-bottom flask
equipped with a drying tube, and SOCl2 (6 mL) was added slowly
and stirred for 16 h. The reaction solution was transferred to a 250
mL flask, and CH2Cl2 (50 mL) was added to the reaction mixture
followed by the slow addition of H2O (50 mL) (Caution:
exothermic!). The solution was brought to pH 8 by slow addition
of solid NaHCO3. After partitioning of the two layers, the aqueous
solution was extracted with CH2Cl2 (50 mL × 2). The combined
organic solution was dried over Na2SO4 and filtered. Concentration
under reduced pressure afforded a white powder (0.090 g, 0.26
1
mmol). Yield: 71%; H NMR (CDCl3, 300 MHz) δ 7.68 (s, 4H),
4.75(s, 8H) 13C NMR (CD3OD, 75 MHz) δ 157.9, 147.8, 120.2,
1
product (2.2 g, 8.73 mmol). Yield: 73%; H NMR (CDCl3, 300
MHz) δ 7.63 (s, 2H), 4.62 (s, 4H).
(7) For extensive studies of capped cyclams, see the work of Guilard et.
al.: (a) Meyer, M.; Fremond, L.; Espinosa, E.; Guilard, R.; Ou, Z.;
Kadish, K. M. Inorg. Chem. 2004, 43, 5572. (b) Fremond, L.; Espinosa,
E.; Meyer, M.; Denat, F.; Suilard, R.; Huch, V.; Veith, M. New J.
Chem. 2000, 24, 959. For a review, see: (c) Denat, F.; Brandes, S.;
Guilard, R. Synlett 2000, 561.
4-Bromopyridine-Capped Dioxocyclam 7.5b Dioxocyclam (5)3a
(0.86 g, 2.3 mmol), 4c (0.65 g, 2.5 mmol), Na2CO3 (0.98 g, 9.24
mmol), and NaI (0.17 g, 1.2 mmol) were placed in an argon-flushed
pressure tube. After the mixture was dissolved in distilled CH3CN
(250 mL), the procedure above afforded the desired product (1.21
(8) Hueing, S.; Wehner, P. Synthesis 1989, 7, 552.
Inorganic Chemistry, Vol. 44, No. 16, 2005 5859

Gil et al.
g, 2.19 mmol). Yield: 95%. The physical properties of this
compound were identical to those previously reported.5b
vacuum. Recrystallization from CH2Cl2/hexane (1:5), washing the
precipitate with hexane, and drying under reduced pressure afforded
the white solid product (1.1 g, 3.8 mmol). Yield: 76%; H NMR
1
1,4-Bis(1,3,2-dioxaborolanyl)benzene 6a. In freshly distilled
THF (100 mL), p-dibromobenzene (2.36 g, 10 mmol) and magne-
sium turnings (0.535 g, 22 mmol) were added and refluxed for 2
days under purging with Ar (white cloudy solution). After cooling
to -78 °C, B(OEt)3 (4.25 mL, 25 mmol, neat) was added by
syringe. After warming to ambient temperature slowly and stirring
for 3 h, the reaction mixture was concentrated under reduced
pressure. The obtained white solid was dissolved in ethylene glycol
(50 mL) and toluene (100 mL) and then refluxed for 13 h. After
the reaction cooled to ambient temperature, the two layers were
partitioned. The glycol layer was extracted with toluene (100 mL
× 2). The combined toluene extracts were concentrated under
vacuum. Recrystallization from CH2Cl2/hexane (1:5), washing the
precipitate with hexane and drying, under reduced pressure afforded
the white solid product (0.436 g, 2.00 mmol). Yield: 20%; 1H NMR
(CDCl3, 400 MHz) δ 7.84 (s, 4H), 4.40(s, 8H); 13C NMR (CDCl3,
100 MHz) δ 134.3, 117.6, 66.3; FT-IR (solid) ν 2980, 2908, 1519,
1328.
(CDCl3, 300 MHz) δ 7.91 (d, J ) 7.8 Hz 4H), 7.68 (d, J ) 8.1 Hz
4H), 4.43 (s, 8H).
4,4′-Bis-(4-pyridyl)biphenyl-Capped Bis-dioxocyclam 1c. 7
(0.11 g, 0.19 mmol), 6b (0.026 g, 0.09 mmol), K2CO3 (0.097 g,
0.701 mmol), and Pd(PPh3)4 (0.022 g, 0.019 mmol) were placed
in an argon-flushed pressure tube. Following the procedure above
afforded the desired product as a white solid (0.090 g, 0.082 mmol).
Yield: 91%; 1H NMR (CDCl3, 300 MHz) δ 9.16 (s, 2H), 8.07 (s,
2H), 7.77 (s, 8H), 7.23 (s, 2H), 7.20 (s, 2H), 4.25 (d, J ) 16.8 Hz
2H), 4.17 (d, J ) 17.1 Hz 2H), 4.11 (d, J ) 16.8 Hz 2H), 4.03 (d,
J ) 17.1 Hz 2H), 3.45 (s, 6H), 3.24 (d, J ) 13.8 Hz 2H), 3.01-
2.90 (m, 10H), 2.64 (d, J ) 14.1 Hz 2H), 2.56 (s, 6H), 2.40 (d, J
) 14.4 Hz 2H), 1.49 (s, 6H), 1.46 (s, 6H), 1.42 (s, 6H), 1.34 (s,
6H), 1.22 (s, 6H), 1.16 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ
173.5, 172.9, 163.8, 159.2, 149.3, 141.2, 137.8, 128.0, 127.8, 117.1,
116.9, 82.7, 79.7, 74.7, 72.7, 69.6, 67.5, 65.8, 64.8, 56.0, 54.9, 52.0,
50.4, 26.3, 25.7, 23.7, 23.5, 19.3; FT-IR (film) ν 1656 cm-1 (Cd
O); UV-vis: λmax (nm) [ꢀ (M-1 cm-1)] 306 [69100]; HRMS
(FAB+, m/z) Calcd for C62H89N10O8 (M + H+), 1101.6865; found,
1101.6864; mp ) 220-225 °C dec.
1,4-Bis(4-Pyridyl)benzene-Capped Bis-dioxocyclam 1b. 7
(0.106 g, 0.19 mmol), bis-borate ester (6a) (0.020 g, 0.092 mmol),
K2CO3 (0.054 g, 0.386 mmol), and Pd(PPh3)4 (0.022 g, 0.019 mmol)
were placed in an argon-flushed pressure tube. After being dissolved
in distilled MeOH (4 mL), the reaction mixture was degassed by
repeating a freeze-pump-thaw sequence three times and was
purged with argon. The pressure tube was tightly sealed and placed
into a 90-110 °C oil bath with stirring for 4 days. After being
cooled to ambient temperature, the resulting brownish reaction
mixture was passed through a Celite pad and concentrated under
reduced pressure. The mixture was dissolved in CH2Cl2 (30 mL)
and H2O (20 mL) and stirred for 1 h, and the two layers were
partitioned. The aqueous layer was extracted with CH2Cl2 (30 mL
× 2). The combined organic extracts were dried over MgSO4,
filtered, and concentrated under vacuum. Purification by flash silica
gel chromatography using 10-25% MeOH in EtOAc afforded the
1,2-Bis(4-pyridyl)ethyne-Capped Bis-dioxocyclam 1d. 7 (0.055
g, 0.100 mmol), 4-ethynylpyridine-capped dioxocyclam (8)7 (0.050)
g, 0.100 mmol), CuI (0.002 g, 0.010 mmol), and PdBr2(PPh3)2
(0.008 g, 0.010 mmol) were placed in an argon-flushed pressure
tube. After being dissolved in distilled MeOH (2 mL) and Et3N (2
mL), the reaction mixture was degassed by repeating a freeze-
pump-thaw sequence three times and was purged with argon. The
pressure tube was tightly sealed and placed into 95-100 °C oil
bath with stirring for 3 days. After being cooled to ambient
temperature, the resulting brownish reaction mixture was passed
through a Celite pad and concentrated under reduced pressure. The
mixture was dissolved in CH2Cl2 (30 mL) and saturated NaHCO3
(20 mL) and stirred for 1 h, and the two layers were partitioned.
The aqueous layer was extracted with CH2Cl2 (30 mL × 3). The
combined organic extracts were dried over MgSO4, filtered, and
concentrated under vacuum. Purification by flash silica gel chro-
matography using 10% MeOH in EtOAc afforded the desired
1
desired product (0.091 g, 0.089 mmol). Yield: 97%; H NMR
(CDCl3, 400 MHz) δ 9.13 (s, 2H), 8.06(s, 1H), 8.05 (s, 1H), 7.77
(s, 4H), 7.21 (s, 2H), 7.18 (s, 2H), 4.24 (d, J ) 16.8 Hz 2H), 4.16
(d, J ) 17.2 Hz 2H), 4.09 (d, J ) 16.8 Hz 2H), 4.03 (d, J ) 17.2
Hz 2H), 3.44 (s, 6H), 3.24 (d, J ) 13.6 Hz 2H), 3.01-2.89 (m,
10H), 2.62 (d, J ) 14.0 Hz 2H), 2.55 (s, 6H), 2.39 (d, J ) 14.0 Hz
2H), 1.48 (s, 6H), 1.45 (s, 6H), 1.40 (s, 6H), 1.34 (s, 6H), 1.21 (s,
6H), 1.15 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 173.5, 172.8,
163.9, 159.3, 148.9, 139.3, 127.9, 117.1, 116.9, 82.7, 79.7, 74.7,
72.7, 69.5, 67.5, 65.8, 64.8, 56.0, 54.9, 51.9, 50.3, 26.3, 25.7, 23.7,
23.5, 19.3; FT-IR (film) 1660 ν cm-1 (CdO); UV-vis: λmax (nm)
[ꢀ (M-1 cm-1)] 282 [62400]; HRMS (FAB+, m/z) Calcd for
C56H85N10O8 (M + H+), 1025.6552; found, 1025.6560; mp ) 230-
240 °C dec.
1
product as a white solid (0.060 g, 0.062 mmol). Yield: 62%; H
NMR (CDCl3, 400 MHz) δ 8.95 (s, 2H), 7.90 (s, 2H), 7.08 (s,
2H), 7.05 (s, 2H), 4.17 (d, J ) 17.2 Hz 2H), 4.08 (d, J ) 17.2 Hz
2H), 4.02 (d, J ) 17.2 Hz 2H), 3.95 (d, J ) 17.2 Hz 2H), 3.42 (s,
6H), 3.21 (d, J ) 13.6 Hz 2H), 2.99-2.87 (m, 10H), 2.57 (d, J )
14.0 Hz 2H), 2.56 (s, 6H), 2.32 (d, J ) 14.4 Hz 2H), 1.45 (s, 6H),
1.42 (s, 6H), 1.35 (s, 6H), 1.31 (s, 6H), 1.20 (s, 6H), 1.14 (s, 6H);
13C NMR (CDCl3, 100 MHz) δ 173.3, 172.7, 163.6, 159.0, 131.3,
121.3, 120.8, 90.6, 82.7, 79.6, 74.6, 72.8, 69.2, 67.4, 65.5, 64.8,
56.0, 54.8, 52.0, 50.4, 26.3, 25.7, 23.6, 23.5, 19.3; FT-IR (film) ν
1660 cm-1 (CdO); UV-vis: λmax (nm) [ꢀ (M-1 cm-1)] 280
[27900]; HRMS (FAB+, m/z) Calcd for C52H81N10O8 (M + H+),
973.6239; found, 973.6211; mp ) 230-240 °C dec.
1,2-Di(pyridine-4-yl)diazine-Capped Bis-Dioxocyclam 1e. 4-Ni-
tropyridine-capped dioxocyclam 95b (0.180 g, 0.350 mmol) was
dissolved in distilled THF (20 mL) in a round-bottomed flask
equipped for reflux. After the flask was flushed with Ar, NaBH4
(0.039 g, 1.04 mmol) was added into the reaction. With flowing
Ar, the reaction was heated at reflux for a day. EtOH (2 mL) was
added to the reaction, and then the refluxing was continued for 3
days (orange-colored solution). After being cooled to ambient
temperature, H2O (50 mL) was added for quenching. After the
reaction was stirred for a day, EtOAc (50 mL) was added and the
4,4′-Bis(1,3,2-dioxaborolanyl)biphenyl 6b. 4,4′-Dibromobiphe-
nyl (1.56 g, 5.00 mmol) was dissolved in distilled THF (70 mL),
and the reaction mixture was cooled to -78 °C. n-BuLi (1.6 M in
hexane, 6.88 mL, 11 mmol) was added by syringe. After the reaction
was stirred for 1.5 h at -78 °C, B(OEt)3 (neat, 2.6 mL, 15 mmol)
was added by syringe and the reaction mixture was stirred for 1 h
at -78 °C and warmed to ambient temperature. After being stirred
at room temperature for 2 h, the reaction mixture was concentrated
under reduced pressure. The obtained white solid was dissolved in
ethylene glycol (50 mL) and toluene (150 mL) and then refluxed
for 2 days. After being cooled to ambient temperature, the two layers
were partitioned. The glycol layer was extracted with toluene (100
mL × 2). The combined toluene extracts were concentrated under
5860 Inorganic Chemistry, Vol. 44, No. 16, 2005

Synthesis and Complexation of Capped Bis-dioxocyclams
two layers were partitioned. The aqueous layer was extracted with
CH2Cl2 (30 mL × 2). The combined organic extracts were dried
over MgSO4, filtered, and concentrated under vacuum. Purification
by flash silica gel chromatography 15% MeOH in EtOAc afforded
the orange solid product (0.111 g, 0.114 mmol). Yield: 65%. X-ray
quality crystals were obtained from EtOAc by slow evaporation;
1H NMR (CDCl3, 400 MHz) δ 8.96 (s, 2H), 7.95 (s, 1H), 7.94 (s,
1H), 7.38 (s, 2H), 7.37 (s, 2H), 4.31 (d, J ) 17.2 Hz 2H), 4.18 (d,
J ) 17.2 Hz 2H), 4.12 (d, J ) 15.6 Hz 2H), 4.08 (d, J ) 16.8 Hz
2H), 3.42 (s, 6H), 3.22 (d, J ) 13.6 Hz 2H), 3.00-2.90 (m, 10H),
2.61 (d, J ) 14.4 Hz 2H), 2.53 (s, 6H), 2.37 (d, J ) 14.4 Hz 2H),
1.47 (s, 6H), 1.44 (s, 6H), 1.36 (s, 6H), 1.32 (s, 6H), 1.20 (s, 6H),
1.14 (s, 6H); 13C NMR (CDCl3, 100 MHz) δ 173.4, 172.7, 165.5,
160.8, 158.4, 112.5, 111.2, 82.6, 79.6, 74.5, 72.7, 69.5, 67.4, 65.8,
64.7, 55.9, 54.8, 51.9, 50.3, 26.2, 25.6, 23.6, 23.4, 19.2; FT-IR
(film) ν 1657 cm-1 (CdO); UV-vis: λmax (nm) [ꢀ (M-1 cm-1)]
290 [21 100], 460 (sh) [430]; HRMS (FAB+, m/z) Calcd for
C50H81N12O8 (M + H+), 977.6300; found, 977.6328; mp ) 230-
240 °C dec.
through a Celite pad and washed with excess MeOH. The obtained
greenish solution was concentrated under reduced pressure and
purified using silica gel pretreated with eluent (eluent: 2% Et3N
in MeOH). The obtained green eluent was concentrated, and the
residue dissolved in CH2Cl2 (3 mL), precipitated by the diffusion
with hexane, and filtered through a cotton pad. The precipitate was
washed with excess EtOAc and hexane. Dissolving the greenish
precipitate from the cotton pad using excess CHCl3 and concentra-
tion in a vacuum afforded the desired product (0.020 g, 0.016
mmol). Yield: 67%; FT-IR (film) ν 1586 cm-1 (CdO); UV-vis:
λmax (nm) [ꢀ (M-1 cm-1)] 308 [62 900], 375 [8187], 668 [232];
MS (electro spray) Calcd for C62H84Cu2N10O8 (M+), 1224.507;
found, 1223.47 (-H), 1225.27 (+H); ESR: symmetrical one
harmonic G value: 2.0173; mp ) 230-240 °C dec.
Bis-copper(II) Complex 10e. 1e (0.052 g, 0.053 mmol), K2-
CO3 (0.138 g, 1.00 mmol), and Cu(BF4)2‚xH2O (0.237 g, ≈1 mmol)
were placed in a 20 mL pressure tube, and the mixture was
suspended in dry distilled MeOH (4 mL). The pressure tube was
flushed with Ar, tightly sealed, and heated at 90 °C for 4 days.
After being cooled to ambient temperature, the reaction mixture
was filtered through a Celite pad and washed with excess MeOH.
The resulting brown solution was concentrated under reduced
pressure and purified using silica gel pretreated with eluent
(eluent: 2% Et3N in MeOH). The brown eluent was concentrated,
and the residue dissolved in CH2Cl2 (3 mL), precipitated by the
diffusion of hexane, filtered through a cotton pad, and washed with
excess EtOAc and hexane. Dissolving the brownish precipitate from
the cotton pad using excess CHCl3 and concentration in a vacuum
afforded the desired product (0.044 g, 0.040 mmol). Yield: 75%;
Bis-copper(II) Complex 10a. 1a (0.018 g, 0.200 mmol), K2-
CO3 (0.027 g, 0.200 mmol), and Cu(BF4)2‚xH2O (0.47 g, ≈2 mmol)
were placed in a 20 mL pressure tube, and the mixture was
suspended in dry distilled MeOH (3 mL). The pressure tube was
flushed with Ar, tightly sealed, and heated to 85 °C for 4 days.
After being cooled to ambient temperature, the reaction mixture
was filtered through a Celite pad and washed with MeOH. The
obtained greenish solution was concentrated under reduced pressure.
The residue was taken up in CH2Cl2 and filtered through a pad of
Celite, which was washed with CH2Cl2. The solvent was removed
under reduced pressure to yield the desired product (0.030 g, 0.016
mmol) as a light-green powder. Yield: 78%. X-ray quality crystals
were produced by vapor diffusion using CHCl3 and n-pentane. FT-
FT-IR (film) ν 1586 cm-1 (CdO); UV-vis: λ
(nm) [ꢀ (M-1
max
cm-1)] 277 [20 600], 375 [4970], 660 [130]; MS (electrospray)
Calcd for C50H79Cu2N12O8 (M+ + H), 1100.45; found, 1101.20;
ESR: symmetrical one harmonic G value: 2.0182; mp ) 230-
240 °C dec.
IR (film) ν 1570 cm-1; UV-vis: λ
(nm) [ꢀ (M-1 cm-1)] 685
max
[150]; MS (FAB+, m/z) C50H77Cu2N10O8 (M + H+) found, 1071.7;
ESR: unsymmetrical two harmonics G value: 2.1319(major),
2.0473(minor); mp ) 230-240 °C dec.
Procedure for the Preparation of a Commercial Microwave
Oven for Reaction Use. To prepare a commercial microwave oven
for reaction conditions, the focus point of the microwave radiation
must be determined. The rotation wheel was removed from under
the glass plate of the microwave. The plate was then covered evenly
with (1/4 in.) 4 Å mol sieves. The microwave was then operated at
high power until one area of the sieves started to glow. This spot
was marked on the glass plate. This determined the focus point on
the horizontal plane. For the vertical plane, a pressure tube was
rotated 360° on the marked spot until maximum microwave
radiation was found. This was determined by preparation of a
cobalt(III) complex. When not in the focus point, the tube would
become warm but the solution would remain pink. When in the
focus point, the pressure tube would become warm and the solution
would turn purple. The direction the tube should point was then
marked on the glass plate. This setup procedure is necessary only
once to find the focus point. All reactions were performed behind
a blast shield starting at a power level of 10% and a time of 30 s.
The power level and time were increased until appropriate condi-
tions were determined, and all reactions were cooled to room
temperature between microwave sets. The power level and time
were never increased above 20% and 3 min, respectively. To
prevent explosions or bumping, all reactions were shaken prior to
a microwave set. This is especially important if the reaction forms
a precipitate. The precipitate must be suspended in solution prior
to each microwave set. When all of these precautions were followed,
our laboratories safely performed several thousand cycles with no
adverse side affects such as explosions.
Bis-copper(II) Complex 10b. 1b (0.093 g, 0.090 mmol), K2-
CO3 (0.125 g, 0.900 mmol), and Cu(BF4)2‚xH2O (0.214 g, ≈0.9
mmol) were placed in a 20 mL pressure tube, and the mixture was
suspended in dry distilled MeOH (5 mL). The pressure tube was
flushed with Ar, tightly sealed, and heated at 90 °C for 3 days.
After being cooled to ambient temperature, the reaction mixture
was filtered through a Celite pad and washed with excess MeOH.
The obtained greenish solution was concentrated under reduced
pressure and purified using silica gel pretreated with 2% Et3N in
MeOH (eluent: from MeOH to 5% Et3N in MeOH). The obtained
green solution was concentrated, dissolved in CHCl3 (3 mL), and
filtered through a cotton pad. The filtrate was precipitated by the
diffusion of hexane, filtered through a cotton pad again, and the
precipitate washed with hexane. Washing out the greenish precipi-
tate from the cotton pad using excess CHCl3 and concentration
under vacuum afforded the desired product (0.044 g, 0.038 mmol).
Yield: 42%; FT-IR (film) ν 1590 cm-1 (CdO); UV-vis: λmax
(nm) [ꢀ (M-1 cm-1)] 285 (sh) [32 200], 365 (sh) [3640], 676 [190];
MS (electrospray) found for C56H81Cu2N10O8 (M+ + H), 1149.5;
ESR: symmetrical one harmonic G value: 2.1273; mp ) 230-
240 °C dec.
Bis-copper(II) Complex 10c. 1c (0.027 g, 0.025 mmol), K2-
CO3 (0.034 g, 0.250 mmol), and Cu(BF4)2‚xH2O (0.058 g, ≈0.25
mmol) were placed in a 20 mL pressure tube, and the mixture was
dissolved in dry distilled MeOH (3 mL). The pressure tube was
flushed with Ar, tightly sealed, and heated at 90 °C for 3 days.
After being cooled to ambient temperature, the reaction was filtered
Bis-cobalt(III) Complex 11a. 1a (0.215 g, 0.227 mmol), Co-
(CH3CO2)2‚4H2O (1.13 g, 4.53 mmol), and (i-Pr)2NEt (0.586 g,
Inorganic Chemistry, Vol. 44, No. 16, 2005 5861

Gil et al.
4.53 mmol) were placed in a 20 mL pressure tube, and the mixture
was dissolved in distilled MeOH (5 mL). The pressure tube was
tightly sealed, placed in the microwave oven, and subjected to
microwave irradiation for a sequence of 10 2-min sessions at 20%
power. The resulting mixture was filtered through a Celite pad and
washed with excess MeOH. Air was bubbled through the obtained
red solution overnight, followed by concentration under reduced
pressure. Purification by column chromatography on neutral
alumina, eluting traces of the monocobalt complex with 3% MeOH
in EtOAc followed by elution with 5% MeOH in EtOAc, gave the
desired bis-cobalt complex as the acetate. Dissolution in MeOH (6
mL) containing NaCN (0.220 g, 4.53 mmol) and stirring the reaction
for 2 days produced the bis-cyano complex, which was purified
using neutral alumina column chromatography (eluent: 5% MeOH
in CH2Cl2). The resulting orange solution was concentrated, and
the residue was dissolved in CH2Cl2 (4 mL), precipitated by the
diffusion of hexane (5 mL), filtered through a cotton pad, and
washed with excess EtOAc. Dissolving the orange precipitate from
the cotton pad using excess MeOH and concentration in a vacuum
afforded the desired product (0.116 g, 0.104 mmol). Yield: 46%;
Figure 1.
Scheme 1
1
X-ray quality crystals were formed from CH2Cl2. H NMR (CD3-
OD, 400 MHz) δ 7.94 (s, 4H), 5.80 (d, J ) 18.8 Hz 2H), 5.10 (d,
J ) 20 Hz 2H), 4.93 (d, J ) 20 Hz 2H), 4.77 (d, J ) 18.8 Hz 2H),
3.81 (d, J ) 13.2 Hz 2H), 3.64 (d, J ) 12.8 Hz 2H), 3.53 (d, J )
12 Hz 2H), 3.50 (d, J ) 14 Hz 2H), 3.37 (s 6H), 3.34 (d, J ) 16.8
Hz 2H), 3.10 (s, 3H), 3.097 (s, 3H), 3.09 (d, J ) 13.2 Hz 2H),
3.01 (d, J ) 12.4 Hz 2H), 2.91 (d, J ) 12.4 Hz 2H), 1.67 (s, 6H),
1.63 (s, 6H), 1.48 (s, 6H), 1.43 (s, 6H), 1.41 (s, 6H), 1.37 (s, 6H);1H
NMR (CDCl3, 400 MHz) δ 7.53 (s, 1H), 7.48 (s, 1H), 7.41 (s,
1H), 7.35 (s, 1H), 6.12 (d, J ) 20.8 Hz 1H), 6.06 (d, J ) 21.2 Hz
1H), 5.11 (d, J ) 18.4 Hz 2H), 4.78 (d, J ) 17.6 Hz 1H), 4.76 (d,
J ) 18.4 Hz 1H), 4.49 (d, J ) 18.0 Hz 1H), 4.47 (d, J ) 18.8 Hz
1H), 3.99 (d, J ) 12.4 Hz 2H), 3.82-3.68 (m, 6H), 3.48 (s, 6H),
3.30 (s, 3H), 3.26 (s, 3H), 3.12 (d, J ) 13.6 Hz 2H), 2.94 (d, J )
12.8 Hz 2H), 2.73 (d, J ) 11.6 Hz 2H), 2.62 (d, J ) 12.4 Hz 2H),
1.73-1.41 (m, 36H); 13C NMR (CD3OD, 100 MHz) δ 174.8, 174.6,
164.8, 162.5, 149.59, 149.55, 133.2, 118.92, 118.86, 82.9, 81.9,
81.4, 80.1, 70.0, 69.6, 69.5, 69.1, 65.0, 64.3, 52.8, 51.1, 29.6, 28.8,
28.6, 28.4, 27.7, 22.9; FT-IR (film) ν 2126 (CN), 1566 (CdO)
cm-1; UV-vis (CHCl3) λ (nm) [ꢀ (M-1 cm-1)] 280 [17 000], 460
[1200]; HRMS (FAB+, m/z) Calcd for C52H77N12O8Co2 (M + H+),
1115.4651; found, 1115.4661; mp ) 230-240 °C dec.
1
Yield: 41%; H NMR (CDCl3, 400 MHz) δ 7.82 (d, J ) 8.4 Hz
4H), 7.71 (d, J ) 8.4 Hz 4H), 7.46 (s, 4H), 6.10 (d, J ) 18.4 Hz
2H), 5.07 (d, J ) 18.8 Hz 2H), 4.70 (d, J ) 18.8 Hz 2H), 4.44 (d,
J ) 18.4 Hz 2H), 4.04 (d, J ) 13.6 Hz 2H), 3.83 (d, J ) 12.0 Hz
2H), 3.81 (d, J ) 13.6 Hz 2H), 3.71 (d, J ) 12.4 Hz 2H), 3.52 (s,
6H), 3.32 (s, 6H), 3.12 (d, J ) 14.0 Hz 2H), 2.94 (d, J ) 13.2 Hz
2H), 2.72 (d, J ) 12.0 Hz 2H), 2.60 (d, J ) 12.4 Hz 2H), 1.73 (s,
6H), 1.68 (s, 6H), 1.60 (s, 6H), 1.52 (s, 6H), 1.50 (s, 6H), 1.48 (s,
6H); 13C NMR (CDCl3, 100 MHz) δ 173.7, 172.6, 162.2, 159.6,
152.2, 142.2, 135.6, 130.1, 128.6, 128.2, 116.8, 116.4, 82.7, 82.1,
79.6, 78.5, 69.4, 69.3, 68.4, 67.8, 63.7, 62.8, 52.7, 51.6, 30.7, 28.8,
28.5, 27.7, 27.1, 23.3; FT-IR (film) ν 2126, 1571 cm-1; UV-vis
(CHCl3) λmax (nm) [ꢀ (M-1 cm-1)] 323 [48 400], 457 [630]; HRMS
(FAB+, m/z) Calcd for C64H84N12O8Co2 (M+), 1266.5199; found,
1266.5159; mp ) 230-240 °C dec.
Bis-cobalt(III) Cyanide Complex 11b. 1b (0.087 g, 0.085
mmol), Co(CH3CO2)2‚4H2O (0.423 g, 1.70 mmol), and (i-Pr)2NEt
(0.220 g, 1.70 mmol) were used for the reaction. The above
procedure afforded the desired product (0.044 g, 0.037 mmol).
1
Yield: 43%; H NMR (CDCl3, 400 MHz) δ 7.76 (s, 4H), 7.47(s,
2H), 7.46 (s, 2H), 6.09 (d, J ) 18.4 Hz 1H), 6.07 (d, J ) 18.0 Hz
1H), 5.06 (d, J ) 18.8 Hz 2H), 4.72 (d, J ) 18.8 Hz 2H), 4.44 (d,
J ) 18.0 Hz 2H), 4.00 (d, J ) 13.2 Hz 2H), 3.79 (d, J ) 11.6 Hz
2H), 3.77 (d, J ) 11.6 Hz 2H), 3.68 (d, J ) 12.4 Hz 2H), 3.48 (s,
6H), 3.29 (s, 3H), 3.28 (s, 3H), 3.11 (d, J ) 13.6 Hz 2H), 2.93 (d,
J ) 13.2 Hz 2H), 2.72 (d, J ) 12.0 Hz 2H), 2.60 (d, J ) 12.4 Hz
2H), 1.70-1.45 (m, 36H); 13C NMR (CDCl3, 100 MHz) δ 173.9,
172.6, 162.5, 159.9, 151.5, 138.3, 129.7, 128.8, 117.0, 116.6, 82.7,
82.0, 79.6, 78.5, 69.3, 68.4, 67.8, 63.7, 62.9, 52.7, 51.6, 30.6, 28.8,
28.6, 28.5, 27.6, 27.1, 23.3; FT-IR (film) ν 2121, 1563 cm-1; UV-
vis (CHCl3) λmax (nm) [ꢀ (M-1 cm-1)] 300 [31 900], 460 [590];
HRMS (FAB+, m/z) Calcd for C58H81N12O8Co2 (M + H+),
1191.4964; found, 1191.4986; mp ) 230-240 °C dec.
Results and Discussion
Ligand Synthesis. The targeted class of ligands was
pyridine-capped bis-dioxocyclams7 connected through the
4-position of the pyridine group by conjugated groups (Figure
1). The parent bipyridine complex 1a was synthesized as in
Scheme 1. Starting with bipyridine tetraester 2 (synthesized
in overall 35% yield in three steps from 2,6-dimethylpyri-
dine),8 reduction of the ester followed by treatment with
thionyl chloride or thionyl bromide produced the desired
bipyridine capping agents 4a and 4b in fair to good yield.
Reaction of the bromo capper, 4a, with bis-dioxocylam 5
resulted in decomposition of 4a and recovery of 5, while
use of chloro compound 4b resulted in no reaction. Suc-
Bis-cobalt(III) Cyanide Complex 11c. 1c (0.090 g, 0.082
mmol), Co(CH3CO2)2‚4H2O (0.408 g, 1.64 mmol), and (i-Pr)2NEt
(0.212 g, 1.64 mmol) were used for the reaction. The above
procedure afforded the desired product (0.043 g, 0.034 mmol).
5862 Inorganic Chemistry, Vol. 44, No. 16, 2005

Synthesis and Complexation of Capped Bis-dioxocyclams
Scheme 2
Complexation Studies
As anticipated from previous complexation studies5,6 with
capped dioxocyclams, ligands 1a-c and 1e readily took up
copper(II) when treated with copper(II) tetrafluoroborate
(Scheme 5). (Complexation of 1d to copper was not
attempted). In contrast, cobalt(III) was more difficult to
introduce into these macrocycles and required microwave
irradiation in the presence of Hu¨nig’s base (Scheme 6).11
The products were mixtures of cobalt(III) acetates, methox-
ides, and hydroxides, (by electrospray mass spectroscopy)
and were converted to the corresponding cyanide complexes
by treatment with sodium cyanide in methanol. Macrocycles
1a-c produced cobalt(III) cyanide complexes in modest
yield, while 1d and 1e produced complex, inseparable
mixtures.
Properties
The spectroscopic and electrochemical properties of the
free ligands and their copper(II) and cobalt(III) complexes
are summarized in Table 1. As observed previously,3-6 the
CO stretching frequencies of the amide carbonyl groups were
sensitive to complexation, appearing at ≈1660 cm-1 in the
free ligand and shifting to 1560-1590 cm-1 in the metal
complexes. In marked contrast, the 13C chemical shift of these
carbonyl groups remained virtually the same upon complex-
ation to cobalt(III), (δ ≈ 173 ppm). The CtN stretching
frequency in the cobalt(III) cyanide complexes 11a-11c
ranged from 2121 to 2126 cm-1, consonant with that
observed for the corresponding cobalt(III) cyanide complexes
of capped monocyclams.11 The 13C chemical shift of the
cyanide group similarly appeared at between δ 130 and 140
ppm. Surprisingly, although all of these bis-dioxocyclam
ligands and complexes had to be mixtures of diastereoiso-
mers, their 13C spectra showed a simple set of peaks
consistent with the presence of a single diastereoisomer. The
1H NMR spectra in CDCl3 were more informative on the
issue of diastereoisomers, even though all of the peaks on
the dioxocyclam ring again indicated the presence of a single
diastereoisomer. However, the signals from the pyridine
linkers proved diagnostic. For the free, uncomplexed 4-bro-
mopyridine-capped mono dioxocyclam 7, the two protons
on the pyridine ring appeared as two singlets at δ ≈ 7.1
ppm, and the methylene groups connecting the pyridine to
the dioxocyclam appeared as a cluster of doublets (J = 17
Hz) centered at δ ≈ 4.0 ppm. In the corresponding cobalt-
(III) cyanide complex, the pyridine singlets moved to δ ≈
7.5 ppm, while the methylene doublets separated and
appeared at 4.4, 4.6, 4.9, and 5.8. For the bipyridine-bridged
bis-dioxocyclam 1a, the most upfield methylene signal
appeared as two overlapping one-proton doublets, while the
pyridine proton signals were four singlets clustered around
δ 7.3 ppm. The 1H-NMR spectrum of the cobalt(III) cyanide
complex 11a similarly had four singlets centered around δ
7.4 ppm for the pyridine signals, and three of the four
methylene signals were doubled. Interestingly, in CD3OD,
Scheme 3
cessful capping was achieved under Finkelstein conditions
utilizing 1 mol of NaI/mol 4b (Scheme 1). Higher amounts
of NaI resulted in lower yields, presumably due to decom-
position of the in-situ-formed benzylic iodide.
Extended back-to-back capped bis-dioxocyclams 1b and
1c were efficiently synthesized by Suzuki coupling of
4-bromopyridine-capped cyclam 75b with the appropriate aryl
bis-boronic ester (Scheme 2).9
The acetylide-linked bis-dioxocyclam 1d was synthesized
by Sonogashira10 coupling of 4-ethynylpyridine-capped
dioxocyclam5b with 7 in fair yield (Scheme 3). Azo-linked
bis-dioxocyclam 1e was made by reductive coupling11 of
4-nitropyridine-capped dioxocyclam 9 (Scheme 4). It should
be noted that, although uncapped dioxocyclam 5 is achiral,
two new chiral centers at nitrogen are created by capping,
since nitrogen inversion is prevented by the rigidity of the
system.5a Capped dioxocyclams such as 7 are thus produced
as a racemic mixture of enantiomers. Synthesis of bis-
dioxocyclams from achiral 5 or racemic capped mono-
dioxocyclams must produce two diastereoisomeric products,
a racemic pair of enatiomers, and a “meso” compound.5a
Only one diastereoisomer is shown for clarity. With these
materials in hand, introduction of metals into these ligand
systems was addressed.
(9) Patoux, C.; Launay, J.-P.; Beley, M.; Chodorowski-Kimmes, S.; Collin,
J.-P.; James, S.; Sauvage, J.-P. J. Am. Chem. Soc. 1998, 120, 3717.
(10) Evans, R. F.; Brown, H. C. J. Org. Chem. 1962, 27, 1665.
(11) Reiff, A.; Garcia-Frutos, E.; Gil, J. M.; Hegedus, L. S. submitted for
publication.
1
these differences disappeared, and the H-NMR spectrum
of 11a displayed four clean doublets for the methylene
protons and a singlet for the four pyridine protons! As the
Inorganic Chemistry, Vol. 44, No. 16, 2005 5863

Gil et al.
Scheme 4
Scheme 5
responding cobalt(III) cyanide complex, 11b, displayed
doubling of only the lowest methylene signal to indicate the
1
presence of diastereoisomers. Finally, the H-NMR spectra
of 1c and 11c showed no indication of the presence of
diastereoisomers, presumably because of the increased
distance between the two cyclam rings.
The UV-vis spectra of the copper complexes 10a, b, c
all showed well-resolved, although broad, absorption maxima.
Interestingly, the bipy-bridged complex 10a absorbed exactly
where the 4-pyridylpyridine-capped mono-dioxocyclam cop-
per(II) complex11 did, at 685 nm (ꢀ ≈ 150). With the
interspersion of additional phenyl groups between the two
pyridine units (10b, 10c), the absorption moved to shorter
wavelengths, (676 and 668 nm, respectively) approaching
that of the pyridine-capped mono-dioxocyclam copper(II)
complex (658 nm).5a (The long-wavelength absorption for
10e was masked by strong tailing of the azo visible
absorption at ≈500 nm). In contrast, the spectra for cobalt-
(III) complexes 11a-c, had no distinct maxima but rather
presented broad shoulders tailing from intense, shorter-
wavelength absorptions, all in the region of ≈460 nm. For
comparison, a range of substituted pyridine-capped mono-
dioxocyclam cobalt(III) cyanide complexes (Py, Pz, 4-Py-
Py, 4Me2NPhPy, 4-BrPy, 4MeOPy)11 all had distinct maxima
between 454 and 463 nm, indicating insensitivity to the
nature of the capping agent. This stands in contrast to the
corresponding copper(II) complexes.
Scheme 6
Table 1. Spectroscopic and Electrochemical Data for Compounds 1,
10, and 11
ν, cm-1
13C δ, ppm
compound (CO, CN)
γ
max, nm; ꢀ
(CO, CN)
CV, V/SCE
la
1611
280; 5980
173.4, 172.7 E1/2 ) -1.9;
∆E ) 160 mV
282; 62 400 173.5, 172.9
306; 69 100 173.5, 172.8
280; 27 900 173.3, 172.7
290; 21 100 173.4, 171.7
460; 430
1b
lc
1d
1e
1660
1656
1660
1657
Electrochemistry
10a
10b
1570
1590
685; 150
E1/2 ) -1.4;
Guilard7a has reported an E1/2 ) -1.14 V/SCE reduction
of Cu(II) to Cu(I) in the unsubstituted pyridine-capped 5,-
12-dioxo-monocyclam copper(II) complex. The uncomplexed
bipyridyl-capped bis-dioxocyclam 1a underwent a quasi-
reversible reduction at E1/2 ) -1.9 V/SCE (∆E ) 160 mV),
presumably due to reduction of the bipyridine group. In
contrast, the corresponding Cu(II) complex 10a underwent
a quasi-reversible two-electron reduction at E1/2 ) -1.4
V/SCE (∆E ) 100 mV) (CuII f CuI based on ref 7a) and
an irreversible reduction at Ep ) -2.0 V/SCE. The phenyl-
extended analogue 10b underwent a reversible two-electron
reduction at E1/2 ) -1.5 V/SCE (∆E ) 70 mV) and two
irreversible reductions at Ep ) -1.8 and -2.0 V/SCE. The
fact that there is no detectable (by cyclic voltammetry)
difference in the reduction potentials of the two metal centers
implies little, if any, electronic communication between the
two metals.
∆E ) 100 mV (2e-)
EPC ) -2.0
285; 32 225
E1/2 ) -1.35;
∆E ) 70 mV (2e-)
EPC ) -1.8, -2.0
365; sh
10c
10e
11a
1586
1586
1566,
308; 62 900
668; 240
375; sh
660; br. tail
280; 17 000 174.8, 174.6 EPC ) -1.2(2e-);
∆E ) 60 mV
2126, CN 460; 1200
133.2, CN
E1/2 ) -1.3,-1.9;
∆E ) 130 mV
11b
11c
1563
2121, CN 460; 590
300; 31 900 173.9, 172.6 EPC ) -1.3(2e-)
138.3, CN
E1/2 ) -1.5,-1.6;
∆E ) 120 mV
∆E ) 110 mV
1571
323; 48 400 173.7, 172.6 EPC ) -1.4
130.1, CN E1/2 ) -1.7
2126, CN 457; 630
separation between dioxocyclam rings was increased by the
interspersion of one (1b, 11b) and two (1c, 11c) phenyl
groups, these differences disappeared. The H-NMR spec-
trum of 1b was indistinguishable from that of a 4-substituted
1
The electrochemistry of the corresponding cobalt(III)
cyanide complexes 11a-11c was markedly different. The
pyridine-capped 5,12-dioxo-mono-cyclam cobalt(III) cyanide
pyridine-capped mono-dioxocyclam, while that of the cor-
5864 Inorganic Chemistry, Vol. 44, No. 16, 2005

Synthesis and Complexation of Capped Bis-dioxocyclams
complex underwent irreversible reduction at Ep ) -1.36
V/SCE.11,12 The bipyridyl-capped bis-dioxocyclam cobalt-
(III) cyanide complex 11a underwent an irreversible two-
electron reduction at Ep ) -1.2 V/SCE (Co(III) f Co(II)), a
reversible one-electron reduction at E1/2 ) -1.3 V (∆E 60
mV) and a quasi-reversible reduction at -1.9 V/SCE (∆E
130 mV). The phenyl-extended analogue 11b underwent an
irreversible two-electron (Co(III) f Co(II)) reduction at Ep )
acquired, but none of them were of sufficient quality to assign
accurate bond lengths because of twinning and/or highly
disordered solvents of crystallization. Thus, although accurate
bond lengths and bond angles cannot be reported, the gross
structure of these compounds has been confirmed.
Summary
-1.3V/SCE and two quasi-reversible reductions at E1/2
)
A series of bis-dioxocyclams linked back-to-back by
conjugated 4-substituted pyridine capping groups via the
secondary amine nitrogens were synthesized and fully
characterized. Copper(II) and cobalt(III) cyanide complexes
of these ligands were prepared and characterized by spec-
troscopic and electrochemical methods. The copper(II)
complex of the bipyridyl-linked systems 10a and 10b
underwent reversible two-electron reductions (CuII f CuI)
at E1/2 ) -1.4 to -1.5 V/SCE. In contrast, the cobalt cyanide
complexes 10a-10c underwent irreversible two-electron
reductions (Co(III) f Co(II)) at -1.2 to 1.4 V/SCE and showed
no indication of electronic communication between the
metals. X-ray crystal structures for 1a, 10a, and 11a (five
data sets) were acquired, but none were of publishable
quality.
-1.5 V (∆E 110 mV) and -1.6 V (∆E ) 120 mV)/SCE.
The biphenyl-extended analogue 11c underwent an irrevers-
ible two-electron reduction at Ep ) -1.4 V, and a quasi-
reversible two-electron reduction at E1/2 ) -1.6 V/SCE (∆E
130 mV).
The fact that there is no detectable (by cyclic voltamme-
try)13 difference in the reduction potentials of the two cobalts
again implies little, if any, electronic communication between
the two metal centers. The two quasi-reVersible reductions
observed are likely due to the bypyridyl linker, since similar
reversible reductions were observed with the 4-(pyridyl)-
pyridine-capped mono-cyclam cobalt cyanide complex.11 As
the two pyridine groups are separated by one or two phenyl
groups, the degree of communication between the two
pyridine groups decreases to zero and both reduce at the same
potential.
Acknowledgment. The authors thank Professor Mike
Elliott for providing electrochemical equipment and expertise
and Andy Bolig for acquiring electrochemical data. Support
for this research was provided by the National Science
Foundation (CHE 9908661). Mass spectra were obtained on
instruments supported by National Institutes of Health Grant
No. GM49631. X-ray crystal structures were determined on
a Bruker SMART CCD X-ray diffractometer purchased
through the NIH Shared Instrument Grant Program. The
authors thank Susie Miller for extensive assistance with the
X-ray structural studies.
Structural Studies
Although X-ray crystal structures of the bipyridine-linked
free ligand 1a, the bis-copper(II) complex 10a, and the bis-
cobalt(III) cyanide complex 11a were obtained, none of the
data were of publishable quality, having final R indices of
0.1131 and 0.2979 for the free ligand 1a and of 0.1501 and
0.3819 for copper complex 10a. Five data sets on different
crystals of cobalt complex 11a from different solvents were
(12) The reversibility of the CoIII/II couple for macrocyclic tetraamine
ligands was shown to be dependent on the electrode and ring size.
See: (a) Bernhardt, P. V.; Macpherson, P.; Martinez, M. Inorg. Chem.
2000, 39, 5203. The non-Nernstian behavior of the CoIII/II cyclam
couple has been attributed to slow axial ligand exchange in conjunction
with electron transfer. See: (b) Simon, E.; L’Haridon, P.; Pichon, R.;
L’Her, M. Inorg. Chim. Acta 1998, 282, 173.
(13) If the splitting between the two reductions waves is small, it may not
be detected by cyclic voltammetric measurements. See: Geiss, A.;
Kolm, J. J.; Janiak, D.; Vahrenkamp, H. Inorg. Chem. 2000, 39, 4037.
Supporting Information Available: 1H and 13C NMR spectra
of 1a, 1b, 1c, 1e, 11a, 11b, and 11c. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC0502731
Inorganic Chemistry, Vol. 44, No. 16, 2005 5865