A practical synthesis of tris(pyrazolyl)methylaryls

Article abstract of DOI:10.1021/jo701924w

(Figure Presented) The preparation of three tris(pyrazolyl)toluidines from trifluoromethylaniline reagents is described that likely takes advantage of (quinoidal) resonance-stabilized activation of the C-F bonds. Subsequent transformations lead to two add

Full text of DOI:10.1021/jo701924w

functionalized at the “back” boron or methine position). That
is, the synthetic methodology and coordination chemistry of
aryltris(pyrazolyl)borates (Figure 1, left) have been well-
developed,4 which has permitted significant advances in iron-
(II) spin-crossover chemistry.5 On the other hand, the chemistry
of analogous tris(pyrazolyl)methane derivatives (Figure 1, right)
are almost unknown because synthetic difficulties render these
derivatives nearly inaccessible by standard routes. The lone
reported example of a tris(pyrazolyl)methyl bound directly to
an arene is PhC(pz2py)3, prepared in a mere 8% yield from
trichlorotoluene and the sodium pyrazolide.6 To make matters
more grim, similar reactions with other pyrazolyls fail to give
usable quantities of desired products.7 It occurred to us during
the course of our investigations into developing new fluorescent
turn-on sensors based on modified aniline derivatives8 that it
may be possible to take advantage of the quinoidal resonance
forms of electron donors such as commercially available
trifluoromethylaniline to provide access to tris(pyrazolyl)-
toluidines via an elimination-addition mechanism, as depicted
in Scheme 1. Derivatives such as H2NC6H4C(pz)3 would also
be appealing since they would contain a built-in entry point for
further functionalization (including the possibility of serving
as monomers for new polyanilines). We now communicate the
successful implementation of this strategy for the preparation
of three new electroactive tris(pyrazolyl)toluidines, p- and o-H2-
NC6H4C(pz)3 and p-EtNHC6H4C(pz)3. Subsequent conversion
of the former to p-BrC6H4C(pz)3 or to p-Et2NHC6H4C(pz)3 is
also described. Future reports will elaborate on the organic and
coordination chemistry of these derivatives.
A Practical Synthesis of
Tris(pyrazolyl)methylaryls
Brendan J. Liddle and James R. Gardinier*
Department of Chemistry, Marquette UniVersity, P.O. Box 1881,
Milwaukee, Wisconsin 53201-1881
james.gardinier@marquette.edu
ReceiVed September 5, 2007
The preparation of three tris(pyrazolyl)toluidines from trif-
luoromethylaniline reagents is described that likely takes
advantage of (quinoidal) resonance-stabilized activation of
the C-F bonds. Subsequent transformations lead to two
additional (for a total of five new) tris(pyrazolyl)methylaryls.
This simple reaction is remarkable because only one other
tris(pyrazolyl)methylaryl has been reported previously, be-
cause it is usually very difficult to activate fluoroalkane C-F
bonds, and because of the potential scope of the reaction.
Since the seminal reports on the preparation and coordination
chemistry of tris(pyrazolyl)borates and tris(pyrazolyl)methanes,1
variations on these so-called scorpionate ligands have permeated
all aspects of inorganic chemistry. Substantial research effort
first went into developing multiple generations of tris(pyrazolyl)-
borates, such as developing bulky derivatives to stabilize unusual
coordination complexes.2 On the other hand, the chemistry of
the parent tris(pyrazolyl)methane, HC(pz)3 (pz ) pyrazolyl),
and its derivatives was relegated to near obscurity until an
efficient high-yield synthetic route reported by the Reger group
incited vigorous research on these derivatives (nearly 30 years
after the initial report).3 Currently, there exists a disparity in
the chemistry of certain “third-generation” scorpionates (ligands
FIGURE 1. Third generation scorpionates based on tris(pyrazolyl)-
borates (left) and tris(pyrazolyl)methanes (right).
The optimized one-pot preparative route to tris(pyrazolyl)-
toluidines is found in Scheme 2. A summary of synthetic
variants is presented in Table 1. Several details are worth noting
(4) (a) Dias, H. V. R.; Wu, J.; Wang, X.; Rangan, K. Inorg. Chem. 2007,
46, 1960. (b) Kisko, J. L.; Hascall, T.; Kimblin, C.; Parkin, G. J. Chem.
Soc., Dalton Trans. 1999, 12, 1929. (c) Sohrin, Y.; Kokusen, H.; Matsui,
M. Inorg. Chem. 1995, 34, 3928. (d) White, D. L.; Faller, J. W. J. Am.
Chem. Soc. 1982, 104, 1548.
(5) (a) Reger, D. L.; Gardinier, J. R.; Elgin, J. D.; Smith, M. D.; Hautot,
D.; Long, G. J.; Grandjean, F. Inorg. Chem. 2006, 45, 8862. (b) Reger, D.
L.; Gardinier, J. R.; Bakbak, S.; Semeniuc, R. F.; Bunz, U. H. F.; Smith,
M. D. New J. Chem. 2005, 29, 1035. (c) Reger, D. L.; Gardinier, J. R.;
Smith, M. D.; Shahin, A. M.; Long, G. J.; Rebbouh, L.; Grandjean, F. Inorg.
Chem. 2005, 44, 1852. Reger, D. L.; Gardinier, J. R.; Gemmill, W. R.;
Smith, M. D.; Shahin, A. M.; Long, Gary J.; Rebbouh, L.; Grandjean, F. J.
Am. Chem. Soc. 2005, 127, 2303.
(1) (a) Trofimenko, S. J. Am. Chem. Soc. 1966, 88, 1842. (b) Trofimenko,
S. J. Am. Chem. Soc. 1970, 92, 5118. (c) Trofimenko, S. Scorpionates:
The Coordination Chemistry of Polypyrazolylborate Ligands; Imperial
College Press: London, UK, 1999.
(2) For example: (a) Kisko, J. L.; Hascall, T.; Parkin, G. J. Am. Chem.
Soc. 1998, 120, 10561. (b) Han, R.; Looney, A.; McNeill, K.; Parkin, G.;
Rheingold, A. L.; Haggerty, B. S. J. Inorg. Biochem. 1993, 49, 105. (c)
Han, R.; Gorrell, I. B.; Looney, A. G.; Parkin, G. J. Chem. Soc., Chem.
Commun. 1991, 10, 717. (d) Gorrell, I. B.; Parkin, G. Inorg. Chem. 1990,
29, 2452.
(6) Humphrey, E. R.; Mann, K. L. V.; Reeves, Z. R.; Behrendt, A.;
Jeffery, J. C.; Maher, J. P.; McCleverty, J. A.; Ward, M. D. New J. Chem.
1999, 23, 417.
(3) (a) Pettinari, C.; Pettinari, R. Coord. Chem. ReV. 2005, 249 (5-6),
525. (b) Reger, D. L.; Grattan, T. C.; Brown, K. J.; Little, C. A.; Lamba,
J. J. S.; Rheingold, A. L.; Sommer, R. D. J. Organomet. Chem. 2000, 607,
120. (c) Jameson, D. L.; Castellano, R. K.; Reger, D. L.; Collins, J. E.;
Tolman, W. B.; Tokar, C. J. Inorg. Synth. 1998, 32, 51.
(7) Reger, D. L. Private communication.
(8) (a) Liddle, B. J.; Silva, R. M.; Morin, T. J.; Macedo, F. P.; Shukla,
R.; Lindeman, S. V.; Gardinier, J. R. J. Org. Chem. 2007, 72, 5637. (b)
Liddle, B. J.; Lindeman, S. V.; Reger, D. L.; Gardinier, J. R. Inorg. Chem.
2007, 46, 8484.
10.1021/jo701924w CCC: $37.00 © 2007 American Chemical Society
Published on Web 11/10/2007
9794
J. Org. Chem. 2007, 72, 9794-9797

SCHEME 1. Retrosynthetic Approach to
Tris(pyrazolyl)toluidines
SCHEME 2. Preparative Route to Tris(pyrazolyl)toluidines
FIGURE 2. ORTEP drawing (50% ellipsoids) with atom labeling of
p- (left) and o-H2NC6H4C(pz)3 (right).
infra). Given that p-Et2NC6H4CF3 is the strongest electron donor
of the three para-substituted anilines, hydrogen bonding involv-
ing the NH-group may play a significant role in facilitating the
reaction. Other solvent systems (Ph2O, xylenes, toluene, xylene/
H2O with phase transfer catalyst) and Bronsted base combina-
tions were also explored (some, but not all, are found in Table
1); however, low solubility of the base typically led to
significantly lower yields, longer reaction times, and in the case
of Ph2O, also to extensive decomposition due to this solvent’s
high boiling point. Noteworthy is that the reaction employing
(NEt4)(OH) in DMSO was more sluggish and gave lower yields
than that with either NaOH or KOH, indicating an important
role for the metal cation (presumably facilitating fluoride
abstraction).
Scheme 3 summarizes the initial demonstrations of using tris-
(pyrazolyl)toluidines as synthetically viable reagents. First, p-Et2-
NC6H4C(pz)3, a derivative that could not be prepared directly
from p-Et2NC6H4CF3, was obtained in modest yield from H2-
NC6H4C(pz)3 and ethyl iodide. Also, p-H2NC6H4C(pz)3 was
converted to p-BrC6H4C(pz)3 in good yield (74%) by adapting
a literature method.10
TABLE 1. Attempted Preparations of Tris(pyrazolyl)methylaryls
reagent
base
solvent
time (h)
yielda (%)
p-H2NC6H4CF3
NaOH
KOH
DMSO
DMSO
DMSO
DMSO
DMSO
Ph2O
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
1
1
2
0.5
1
2
12
1
5
1
5
80
82
22
41
46
22
16
46
0
NEt4(OH)
Cs2CO3
K2CO3
K2CO3
Na2CO3
KOH
KOH
KOH
K2CO3
KOH
KOH
p-EtNHC6H4CF3
p-Et2NC6H4CF3
o-H2NC6H4CF3
70
5
0
m-H2NC6H4CF3
C6H5CF3
3
3
0
a Isolated scorpionate of the type ArylC(pz)3.
SCHEME 3. Preparative Route to
Tris(pyrazolyl)methylaryls
The new scorpionates have been characterized by multiple
methods including by single-crystal X-ray diffraction studies
of each p- and o-H2NC6H4C(pz)3, Figures 2 and 3, respectively.
In both, the molecules are associated into polymeric chains via
intermolecular hydrogen bonding interactions involving the
amino group hydrogens and pyrazolyl nitrogens of neighboring
molecules (Figure 3). There are two independent molecules in
the unit cell of the para derivative. One molecule serves as a
hydrogen donor to two neighboring molecules while the other
only donates to one other molecule, forming the polymeric tape
as in Figure 3a. The ortho derivative has one accessible N-H
hydrogen for intermolecular hydrogen bonding (to the pyrazolyl
nitrogen of a neighboring molecule) and therefore forms a
single-stranded polymer chain as in Figure 3b. The thermal
properties of the o-H2NC6H4C(pz)3 are quite interesting as this
compound forms a clear yellow glass upon heating past ca.
185 °C and retains its appearance on cooling. Subsequent
reheating to 80 °C causes recrystallization then “remelting” upon
reaching 185 °C; all other derivatives simply form a glass but
do not exhibit this unusual recrystallization behavior. Finally,
since it is established that aniline derivatives undergo one-
First, only p- and o-trifluoromethylaniline derivatives gave the
desired scorpionate in good yields. The yield of the deriviative
from o-H2NC6H4CF3 was slightly lower than that from p-H2-
NC6H4CF3, presumably due to steric hindrance between the
o-NH2 group and pyrazolyls.
Both m-H2NC6H4CF3 and C6H5CF3 remained unchanged
under the reaction conditions. Such observations diminish the
possibility of an SN2-type mechanistic pathway but might be
expected if the ionic resonance form in Scheme 1 were
operative. Here, the electron-donating amino group plays a vital
role since it is usually very difficult to activate C-F fluoroalkane
bonds.9 Interestingly, p-EtNHC6H4CF3 gave the desired scor-
pionate but p-Et2NC6H4CF3 did not undergo any reaction (the
desired p-Et2NC6H4C(pz)3 had to be prepared indirectly, vide
(9) See for instance: (a) Haeffner, F.; Marquez, M.; Gonzalez, C. J.
Phys. Chem. A 2007, 111, 268. (b) Kiplinger, J. L.; Richmond, T. G.;
Osterberg, C. E. Chem. ReV. 1994, 94, 373.
(10) Doyle, M. P.; Siegfried, B.; Dellaria, J. F., Jr. J. Org. Chem. 1977,
42, 2426.
J. Org. Chem, Vol. 72, No. 25, 2007 9795

silent in the solvent potential window. As anticipated from
inductive effects, the tris(pyrazolyl)toluidines are easier to
oxidize than the trifluoromethylanilines and oxidation also
becomes more favorable with increasing N-ethyl substitution.
The greater electron donating effect of para versus ortho
substitution is also demonstrated by comparing the oxidation
potentials of the two H2NC6H4C(F or pz)3 isomers.
In conclusion, a simple, high-yielding route to tris(pyrazolyl)-
toluidines (“third-generation” scorpionates with an aniline
groups bound to the “back” methine position) has been
discovered that is likely facilitated by ionic quinoidal intermedi-
ates derived from trifluoromethylaniline starting materials. The
electron donating amino group is vital since it is usually very
difficult to otherwise activate fluoroalkane C-F bonds. Both
resonance and steric effects are operatives as only para and ortho
isomers of H2NC6H4CF3 afforded the desired tris(pyrazolyl)-
methylanilines (with the yield of the para being higher than that
of the ortho); neither m-H2NC6H4CF3 nor C6H5CF3 gives any
desired products under comparable or more forcing conditions.
Hydrogen bonding may play a role in arbitrating the reaction
pathway since yields decrease on substituting one N-H with
an N-ethyl as in EtNHC6H4CF3 and vanish for the di-N-ethyl
derivative. The feasibility of using p-H2NC6H4C(pz)3 as a
reagent was also demonstrated in the preparation of two other
scorpionates p-XC6H4C(pz)3 (X ) Et2N, Br). For the latter,
further derivatization via Pd-catalyzed coupling reactions can
be envisioned. Future reports will elaborate on the organic
transformations and coordination chemistry of these and related
derivatives and will address the scope of this resonance-assisted
elimination/addition reaction involving trifluoromethylanilines.
FIGURE 3. Views of hydrogen bonding interactions (red dashed lines)
resulting in (A) a polymeric tape of p-H2NC6H4C(pz)3 and (B) a
polymeric chain of o-H2NC6H4C(pz)3.
TABLE 2. Oxidation Potentials (V vs Ag/AgCl) of Aniline
Derivativesa
compd
Epa
Epc
p-H2NC6H4CF3
1.31
1.22
1.15
1.43
1.15
1.08
1.01
1.25
p-EtNHC6H4CF3
p-Et2NC6H4CF3
o-H2NC6H4CF3
p-H2NC6H4C(pz)3
p-EtNHC6H4C(pz)3
p-Et2NC6H4C(pz)3
o-H2NC6H4C(pz)3
Experimental Section
0.99
Preparation of p-H2NC6H4C(pz)3. A mixture of 1.61 g (9.99
mmol) of p-H2NC6H4CF3, 1.68 g (29.9 mmol) of KOH, and 2.04
g (30.0 mmol) of pyrazole in 10 mL of DMSO was heated at reflux
for 1 h. After cooling to room temperature, 50 mL each of water
and CH2Cl2 was added. The organic and aqueous layers were
separated, the aqueous layer was extracted twice with 50 mL of
CH2Cl2, and the combined organics were dried over MgSO4.
Purification of the organic fraction by flash chromatography on
SiO2 with Et2O yields unreacted aniline in the band near the solvent
front then the desired product in the following pale yellow band
(Rf 0.4). After removing solvent, the resulting waxy solid was
triturated with Et2O to afford 2.50 g (82%) of pure p-H2NC6H4C-
(pz)3 as a very pale yellow solid after collecting by filtration and
drying under vacuum. Mp 127-129 °C dec to yellow glass. Anal.
Calcd (found) for C16H15N7: C, 62.94 (63.32); H, 4.95 (4.87); N,
32.11 (32.48). 1H NMR (300 MHz, CDCl3) δH 7.71 (d, J ) 1 Hz,
3H), 7.53 (d, J ) 2 Hz, 3H), 6.86 (part of AA′BB′, 2H), 6.63 (part
of AA′BB′, 2H), 6.34 (dd, J ) 2, 1 Hz, 3H), 3.88 (br s, 2H). 13C
NMR (75.5 MHz, CDCl3) δC 148.3, 141.1, 132.2, 129.8, 126.4,
114.1, 106.2, 93.3. HRMS-direct probe (m/z): calcd (found) for
C16H15N7 305.1389 (305.1386). Crystals suitable for X-ray diffrac-
tion were grown by layering a benzene solution with hexanes and
allowing solvents to slowly diffuse overnight.
0.84
a CH3CN, NBu4(PF6) supporting electrolyte, scan rate 0.1 V/s.
FIGURE 4. Cyclic voltammograms of CH3CN solutions of p-Et2-
NC6H4CF3 (blue) and of p-Et2NC6H4C(pz)3 (black) acquired at a scan
rate of 0.1 V/s with NBu4(PF6) as the supporting electrolyte.
The following two derivatives were prepared analogously with
the same amount of solvent, millimoles of (appropriate) reagents,
and identical heating time. Therefore only the purification proce-
dure, yield, and characterization data are provided.
electron oxidation,11 the electrochemistry of the starting materi-
als and new derivatives was investigated and the results are
summarized in Table 2 and Figure 4. The N,N-diethyl derivatives
were unique in that they exhibit (quasi)reversible oxidation
(Figure 4); all other aniline derivatives are irreversibly oxidized
and display only anodic waves in their cyclic voltammograms
(Supporting Information); p-BrC6H4C(pz)3 is electrochemically
(11) (a) Galus, Z.; Adams, R. N. J. Phys. Chem. 1963, 67, 862. (b) Bacon,
J.; Adams, R. N. J. Am. Chem. Soc. 1968, 90, 6596. (c) Hand, R. L.; Nelsen,
R. F. J. Am. Chem. Soc. 1974, 96, 850. (d) MacDiarmid, A. G.; Epstein, A.
J. Faraday Discuss. Chem. Soc. 1989, 88, 317. (e) MacDiarmid, A. G.
Angew. Chem., Int. Ed. 2001, 40, 2581. (f) Heeger, A. J. Angew. Chem.,
Int. Ed. 2001, 40, 2591.
9796 J. Org. Chem., Vol. 72, No. 25, 2007

o-H2NC6H4C(pz)3. Column chromatography with Et2O (Rf 0.7)
afforded 2.14 g (70%) of pure p-H2NC6H4C(pz)3 as a colorless solid
after trituration with Et2O, filtration, and drying as above. Mp 185-
187 °C dec to yellow glass. Anal. Calcd (found) for C16H15N7: C,
62.94 (62.57); H, 4.95 (5.18); N, 32.11 (31.88). 1H NMR (300 MHz,
CDCl3) δH 7.74 (d, J ) 2 Hz, 3H), 7.73 (d, J ) 1 Hz, 3H), 7.30
(m, 2H), 6.77-6.70 (br m, 4H), 6.40 (dd, J ) 2, 1 Hz, 3H), 5.93
(part of AA′BB′, 2H), 3.57 (br s, 2H). 13C NMR (75.5 MHz, CDCl3)
δC 145.44, 145.39, 141.5, 132.8, 131.9, 128.2, 122.5, 118.80,
118.76, 117.6, 107.1, 93.1. HRMS-direct probe (m/z): calcd (found)
for C16H15N7 305.1389 (305.1393). Crystals suitable for X-ray
diffraction were grown by layering a benzene solution with hexanes
and allowing solvents to slowly diffuse overnight.
few hours. Mp 115-117 °C dec to yellow glass. Anal. Calcd
(found) for C20H23N7: C, 66.46 (66.55); H, 6.41 (6.80); N, 27.13
1
(26.82). H NMR (300 MHz, CDCl3) δH 7.72 (d, J ) 1 Hz, 3H),
7.57 (d, J ) 2 Hz, 3H), 6.87 (part of AA′BB′, 2H), 6.60 (part of
AA′BB′, 2H), 6.34 (dd, J ) 2, 1 Hz, 3H), 3.36 (q, J ) 7.3 Hz,
4H), 1.16 (t, J ) 7.3 Hz, 6H). 13C NMR (75.5 MHz, CDCl3) δC
149.0, 141.2, 132.4, 129.9, 123.1, 110.4, 106.2, 93.7, 44.4, 12.7.
HRMS-direct probe (m/z): calcd (found) for C20H23N7 361.2015
(361.2008).
p-BrC6H4C(pz)3. A 0.813 g (2.66 mmol) sample of solid p-H2-
NC6H4C(pz)3 was added to a nitrogen-purged solution of 0.595 g
(2.66 mmol) of CuBr2 and 0.65 mL (5.46 mmol) of tBuONO in 20
mL of anhydrous CH3CN. Gas evolution concomitant with a
solution color change from deep green to purple occurred im-
mediately on mixing. The reaction mixture was heated at reflux
for 30 min until gas evolution was no longer detected via an attached
oil bubbler. Aqueous workup followed by separation by column
chromatography on silica gel with Et2O as an eluent (Rf 0.8)
afforded 0.731 g (74%) of pure p-BrC6H4C(pz)3 as a colorless solid.
Colorless crystals can be grown by cooling a nearly saturated Et2O
solution in a -30 °C freezer overnight. Mp 120-121 °C. Anal.
Calcd (found) for C16H13BrN6: C, 52.05 (51.86); H, 3.55 (3.69);
p-EtNHC6H4C(pz)3. Column chromatography of the organic
fraction from workup with Et2O (Rf 0.8) as an eluent afforded 2.14
g (46%) of pure p-H2NC6H4C(pz)3 as a colorless solid after
trituration with Et2O, filtration, and drying as above. Crystals are
obtained either by cooling hot concentrated hexanes solution or
layering a benzene solution with hexanes. Mp 134-135 °C dec to
yellow glass. Anal. Calcd (found) for C18H19N7: C, 64.85 (65.13);
1
H, 5.74 (6.02); N, 29.41 (29.18). H NMR (300 MHz, CDCl3) δH
7.72 (d, J ) 1 Hz, 3H), 7.55 (d, J ) 2 Hz, 3H), 6.86 (part of
AA′BB′, 2H), 6.54 (part of AA′BB′, 2H), 6.34 (dd, J ) 2, 1 Hz,
3H), 3.88 (br s, 1H), 3.16 (q, J ) 7.3 Hz, 2H), 1.25 (t, J ) 7.3 Hz,
3H). 13C NMR (75.5 MHz, CDCl3) δC 149.8, 141.2, 134.2, 129.9,
125.1, 111.6, 106.2, 93.5, 38.2, 14.9. HRMS-direct probe (m/z):
calcd (found) for C18H19N7 333.1702 (333.1696).
1
N, 22.76 (22.95). H NMR (300 MHz, CDCl3) δH 7.74 (d, J ) 1
Hz, 3H), 7.55 (part of AA′BB′, 2H), 7.43 (d, J ) 2 Hz, 3H), 7.08
(part of AA′BB′, 2H), 6.38 (dd, J ) 2, 1 Hz, 3H). 13C NMR (75.5
MHz, CDCl3) δC 141.7, 136.6, 132.3, 131.5, 130.7, 125.2, 106.9,
92.9. HRMS-direct probe (m/z): calcd (found) for C16H13BrN6
368.0385 (368.0373).
p-Et2NC6H4C(pz)3. A mixture of 1.00 g (3.38 mmol) of p-H2-
NC6H4C(pz)3, 1.60 mL (19.9 mmol) of ethyl iodide, and 2.68 g
(19.4 mmol) of K2CO3 in 10 mL of DMF was heated at reflux 4 h.
After cooling to room temperature, 25 mL each of H2O and CH2-
Cl2 were added. The organic and aqueous layers were separated,
the aqueous layer was extracted twice with 50 mL of CH2Cl2, the
combined organics were dried over MgSO4 and filtered onto 5 g
of silica gel, and solvent was removed by rotary evaporation to
adsorb the product mixture. The adsorbed mixture was added to a
short column of fresh silica and the desired compound was eluted
in the first band (Rf ca. 0.5) with 2:1 hexanes:ethyl acetate. After
triturating with Et2O, crude p-Et2NC6H4C(pz)3 was collected by
filtration. Colorless crystals (0.758 g, 64%) of pure p-Et2NC6H4C-
(pz)3 were grown by allowing a boiling supersaturated hexane
solution to slowly cool to room temperature over the course of a
Acknowledgment. J.R.G. thanks Marquette University, the
Petroleum Research Fund (74371-G), and an NSF instrumenta-
tion grant (CHE-0521323) for support, Sergey V. Lindeman for
the structure determinations, and Bill Cotham and Mike Walla
(University of South Carolina) for mass spectrometric measure-
ments.
Supporting Information Available: NMR spectra, voltammo-
grams, and crystallographic information files. This material is
available free of charge via the Internet at http://pubs.acs.org.
JO701924W
J. Org. Chem, Vol. 72, No. 25, 2007 9797