18-atom-ringed macrocyclic tetra-imidazoliums for preparation of monomeric tetra-carbene complexes

Article abstract of DOI:10.1021/om100625g

18-Atom-ringed macrocyclic tetra-imidazolium ligands have been synthesized by a two-step procedure and are the smallest free tetra-imidazoliums to date. The structures of the tetra-imidazoliums were characterized by multinuclear NMR and high-resolution ES

Full text of DOI:10.1021/om100625g

Organometallics 2010, 29, 3235–3238 3235
DOI: 10.1021/om100625g
18-Atom-Ringed Macrocyclic Tetra-imidazoliums for Preparation of
Monomeric Tetra-carbene Complexes
Heather M. Bass, S. Alan Cramer, Julia L. Price, and David M. Jenkins*
Department of Chemistry, The University of Tennessee, Knoxville, Tennessee 37996-1600
Received June 29, 2010
Summary: 18-Atom-ringed macrocyclic tetra-imidazolium li-
other beneficial properties, in particular their resistance to degra-
dation in the presence of O2.7 This communication presents
easy-to-synthesize, strong σ-donor macrocyclic tetra-NHCs that
exclusively produce monomeric transition metal complexes.
Recently synthesized tetra-N-heterocyclic carbene complexes
include the classes of tetra-monodentate carbenes, bis-bidentate
carbenes, and macrocyclic tetra-dentate carbenes.8 These tetra-
carbene complexes have found potential applications as near-
UV-phosphorescent emitters,9 radiopharmaceuticals,10 and cat-
alyst precursors.11 Yet, of these tetra-NHCs, only three exam-
ples of monomeric macrocyclic tetra-carbene complexes have
been prepared, and both synthetic approaches are somewhat
limited in scope. Hahn’s synthesis of the first macrocyclic tetra-
carbene complex requires a templating reaction on platinum.12
In addition to requiring a tetra-isocyanide complex as a pre-
cursor to the monodentate carbene ligands, the synthesis also
requires harsh reagents such as phosgene. The other two exam-
ples have been prepared from a macrocyclic tetra-imidazolium
ligand, and although a few macrocyclic tetra-imidazoliums have
been synthesized,13 only one of these species has been employed
as a ligand for synthesizing tetra-carbene complexes. Murphy’s
group was able to prepare a 24-atom-ringed tetra-imidazolium
using 1,3-diiodopropane as the key dielectrophile for ring
formation.14 This tetra-carbene ligand is so large and flexible
that some metal complexes are monomeric, such as palladium14
and cobalt,15 but others are dimeric, such as silver14 and
copper.14 Since most NHC complexes are prepared from
imidazoliums, this approach provides a wider ranging scope
than templating.
gands have been synthesized by a two-step procedure and are
the smallest free tetra-imidazoliums to date. The structures of
the tetra-imidazoliums were characterized by multinuclear
NMR and high-resolution ESI/MS to distinguish them from
the potential di-imidazolium species. These tetra-imidazolium
ligands form monomeric tetra-carbene complexes of platinum
through in situ deprotonation.
The stabilization of complexes that contain metal-ligand
multiple bonds, such as oxo and nitride ligands, is dependent
on the symmetry and donor strength of the auxiliary ligands
bound to the transition metal.1 Recent advancements in the
preparation of iron oxos and nitrides for bioinorganic models of
O2 and N2 activation have employed neutral tetra-dentate weak
σ-donors, such as cyclam, as the auxiliary macrocyclic ligand.2
Current research on 3-fold symmetry complexes of iron3 and
cobalt4 has demonstrated that increasing the σ-donor strength of
the auxiliary ligands stabilizes novel imido and nitride com-
plexes. To our knowledge, few neutral tetra-dentate strong
σ-donor ligands have been synthesized. In fact, few macrocyc-
lic tetra-dentate phosphines have been prepared and isolated,
due to their difficult syntheses, instability, and sensitivity to
O2.5 Lately, N-heterocyclic carbenes (NHCs) have become a
more attractive alternative to phosphines for many catalytic
applications.6 In addition to strong σ-donation, NHCs exhibit
*To whom correspondence should be addressed. E-mail: jenkins@
ion.chem.utk.edu.
(1) (a) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds:
The Chemistry of Transition Metal Complexes Containing Oxo, Nitrido,
Imido, Alkylidene, Or Alkylidyne Ligands; Wiley: New York, 1988. (b) Lin,
Z.; Hall, M. B. Coord. Chem. Rev. 1993, 123, 149.
Results and Discussion
We have synthesized 18-atom-ringed tetra-imidazolium
macrocycles that should exclusively favor monomeric com-
plexation. These imidazoliums were synthesized in multigram
(2) (a) Rohde, J.-U.; In, J.-H.; Lim, M. H.; Brennessel, W. W.; Bu-
kowski, M. R.; Stubna, A.; Muenck, E.; Nam, W.; Que, L. Science 2003,
299, 1037. (b) Li, F.; England, J.; Que, L. J. Am. Chem. Soc. 2010, 132, 2134.
(c) Meyer, K.; Bill, E.; Mienert, B.; Weyhermueller, T.; Wieghardt, K. J. Am.
Chem. Soc. 1999, 121, 4859. (d) Berry, J. F.; Bill, E.; Bothe, E.; DeBeer George,
S.; Mienert, B.; Neese, F.; Wieghardt, K. Science 2006, 312, 1937.
(3) (a) Scepaniak, J. J.; Fulton, M. D.; Bontchev, R. P.; Duesler,
E. N.; Kirk, M. L.; Smith, J. M. J. Am. Chem. Soc. 2008, 130, 10515. (b)
Vogel, C.; Heinemann, F. W.; Sutter, J.; Anthon, C.; Meyer, K. Angew.
Chem., Int. Ed. 2008, 47, 2681. (c) Betley, T. A.; Peters, J. C. J. Am. Chem.
Soc. 2004, 126, 6252. (d) Brown, S. D.; Betley, T. A.; Peters, J. C. J. Am.
Chem. Soc. 2003, 125, 322.
(4) (a) Jenkins, D. M.; Betley, T. A.; Peters, J. C. J. Am. Chem. Soc.
2002, 124, 11238. (b) Hu, X.; Meyer, K. J. Am. Chem. Soc. 2004, 126,
16322. (c) Shay, D. T.; Yap, G. P. A.; Zakharov, L. N.; Rheingold, A. L.;
Theopold, K. H. Angew. Chem., Int. Ed. 2005, 44, 1508.
(5) (a) Kyba, E. P.; Davis, R. E.; Hudson, C. W.; John, A. M.; Brown,
S. B.; McPhaul, M. J.; Liu, L.-K.; Glover, A. C. J. Am. Chem. Soc. 1981,
103, 3868. (b) Kyba, E. P.; Hudson, C. W.; McPhaul, M. J.; John, A. M. J.
Am. Chem. Soc. 1977, 99, 8053. (c) Mizuta, T.; Okano, A.; Sasaki, T.;
Nakazawa, H.; Miyoshi, K. Inorg. Chem. 1997, 36, 200.
(7) Strassner, T. Top. Organomet. Chem. 2007, 22, 125.
(8) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109, 3677.
(9) (a) Unger, Y.; Zeller, A.; Taige, M. A.; Strassner, T. Dalton Trans.
2009, 4786. (b) Unger, Y.; Zeller, A.; Ahrens, S.; Strassner, T. Chem.
Commun. 2008, 3263.
(10) Quezada, C. A.; Garrison, J. C.; Tessier, C. A.; Youngs, W. J.
J. Organomet. Chem. 2003, 671, 183.
(11) Lee, C.-S.; Pal, S.; Yang, W.-S.; Hwang, W.-S.; Lin, I. J. B.
J. Mol. Catal. A Chem. 2008, 280, 115.
(12) Hahn, F. E.; Langenhahn, V.; Luegger, T.; Pape, T.; Le Van, D.
Angew. Chem., Int. Ed. 2005, 44, 3759.
(13) (a) Sato, K.; Onitake, T.; Arai, S.; Yamagishi, T. Heterocycles
2003, 60, 779. (b) Shi, Z.; Thummel, R. P. J. Org. Chem. 1995, 60, 5935.
(c) Wong, W. W. H.; Vickers, M. S.; Cowley, A. R.; Paul, R. L.; Beer, P. D.
Org. Biomol. Chem. 2005, 3, 4201.
(14) McKie, R.; Murphy, J. A.; Park, S. R.; Spicer, M. D.; Zhou,
S.-Z. Angew. Chem., Int. Ed. 2007, 46, 6525.
(6) (a) Herrmann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290. (b)
Diez-Gonzalez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009, 109, 3612.
(15) Park, S. R.; Findlay, N. J.; Garnier, J.; Zhou, S.; Spicer, M. D.;
Murphy, J. A. Tetrahedron 2009, 65, 10756.
r
2010 American Chemical Society
Published on Web 07/14/2010
pubs.acs.org/Organometallics

3236 Organometallics, Vol. 29, No. 15, 2010
Bass et al.
Scheme 1
Figure 1. Example electrospray ionization mass spectrum mea-
sured for an acetonitrile solution of 2a (A) and 4a (B). (A) The
insets show highlights for the {(Me,EtTCH)(OTf)}3þ, {(Me,EtTCH)-
(OTf)2}2þ, and {(Me,EtTCH)(OTf)3}þ ions, which are denoted as
“3þ”, “2þ”, and “1þ”, respectively. (B) The insets show high-
lights for the [(Me,EtTCH)Pt]2þ and {[(Me,EtTCH)Pt](OTf)}þ
ions, which are denoted as “2þ” and “1þ”, respectively.
quantities using a simple two-step process starting from com-
mercially available imidazoles and without the use of dilute
solvent conditions (Scheme 1). We prepared 1,10-methylene(bis-
imidazole) (1a) using the methods of Diez-Barra16 and Clara-
munt.17 We synthesized 1,10-methylenebis(4,5-diphenylimida-
zole) (1b) in high yield by adding dibromomethane to a basic
solution of 4,5-diphenylimidazole in acetonitrile (Scheme 1).
Although previous syntheses of macrocyclic tetra-imidazolium
species have employed dihaloalkanes or dihaloxylenes as the key
dielectrophile for ring formation,13,14 we were unsuccessful in
our attempts at similar reactions to produce smaller sized mac-
rocycles with reagents such as diiodomethane and 1,2-diio-
doethane. However, utilizing the stronger dielectrophile 1,2-
bis(trifoxy)ethane18 allowed us to prepare the 18-atom-ringed
macrocyclic tetra-imidazoliums, (Me,EtTCH)(OTf)4 (2a) and
Scheme 2
To test the ability of 2 to form monomeric metal complexes,
we synthesized platinum complexes (Scheme 2). Bis-bidentate
platinum9,10 and palladium20 carbene complexes that are similar
in size to 4 have been prepared previously via in situ deprotona-
tion with a weak base from the free imidazolium ligands.
Thallium salts were employed in the reaction to remove any
iodide ions and prevent anion confusion during purification.
Spectroscopic characterization of 4 was consistent with a tetra-
carbene complex. The ESI/MS of 4a (Figure 1) shows peaks at
m/z 271.1 and 691.1 that are associated with [(Me,EtTCH)Pt]2þ
and {[(Me,EtTCH)Pt](OTf)}þ, respectively. The geminal AB
splitting pattern in the 1H NMR of the protons on the methylene
position on 4a demonstrates the rigidity of the ligand in solu-
tion,9,20b which is in direct contrast to Murphy’s complex.14 The
13C NMR of 4a is consistent with NHC formation with the
carbene peak at 158 ppm, for which platinum satellites could be
observed with a 195Pt-C coupling constant of 942 Hz.12 Similar
NMR and ESI/MS data were obtained for 4b, although the
platinum satellites on the carbene carbon in the 13C NMR could
not be resolved. To confirm the conformation of 4, a single crys-
tal of 4b was examined and a structure demonstrating connec-
tivity of the macrocyclic ligand was obtained (Figure 2). The
X-ray structure corroborates the high-resolution ESI/MS
evidence for 2 that demonstrates that these species are indeed
macrocycles.
(
Me,EtTCPh)(OTf)4 (2b), shown in Scheme 1, each in greater than
15% yield and within 3 days. We were then able to exchange the
counteranions from triflates to iodides by mixing 2a and 2b with
excess (nBu4N)I in an acetonitrile solution to yield (Me,EtTCH)-
(I)4 (2c) and (Me,EtTCPh)(I)4 (2d), respectively.
One challenge in these syntheses is distinguishing between the
di-imidazolium species (3) shown in Scheme 1 and the desired
macrocyclic species (2) since they are often synthesized con-
currently.13b,14 1H and 13C NMR for the white solids formed
were consistent with imidazolium formation, and although this
evidence was not sufficient to distinguish between 2 and 3,19
high-resolution ESI/MS conclusively confirmed the formation
of 2, as opposed to 3. The ESI/MS spectrum exhibited peaks at
m/z 167.1 and 799.1 (Figure 1), which are associated with
{(Me,EtTCH)(OTf)}3þ and {(Me,EtTCH)(OTf)3}þ, respectively,
and are unique to 2a. In addition, the peak at m/z325.1 exhibited
isotopomers that were 1/2 of a mass unit apart, which is con-
sistent with {(Me,EtTCH)(OTf)2}2þ from 2a and not with the 1þ
ion of 3a-OTf. The ratio of the isotopomers at m/z 325.1 is con-
sistent with only 2a and not a mixture of 2a and 3a.Furthermore,
no peak was found at m/z88.1, which would match the 2þ ion of
3a-2OTf. Combined, these data demonstrate that only the
macrocyclic 18-atom ring, 2a, was isolated from the reaction.
Similar data were obtained from the ESI/MS for 2b.
In conclusion, we have demonstrated a facile, two-step
synthesis of 18-atom-ringed tetra-imidazolium ligands that
employed 1,2-bis(trifoxy)ethane as the key dielectrophile.
The ligands can be prepared on a multigram scale quickly
(16) Diez-Barra, E.; De la Hoz, A.; Sanchez-Migallon, A.; Tejeda, J.
Heterocycles 1992, 34, 1365.
(17) Claramunt, R. M.; Elguero, J.; Meco, T. J. Heterocycl. Chem.
1983, 20, 1245.
(20) (a) Fehlhammer, W. P.; Bliss, T.; Kernbach, U.; Bruedgam, I.
J. Organomet. Chem. 1995, 490, 149. (b) Herrmann, W. A.; Schwarz, J.;
Gardiner, M. G.; Spiegler, M. J. Organomet. Chem. 1999, 575, 80.
(18) Lindner, E.; Von Au, G.; Eberle, H. J. Chem. Ber. 1981, 114, 810.
(19) Tapu, D.; Dixon, D. A.; Roe, C. Chem. Rev. 2009, 109, 3385.

Communication
Organometallics, Vol. 29, No. 15, 2010 3237
white solid. The white solid was collected over a 150 mL medium
sintered-glass frit and dried under reduced pressure to give the
product (12 g, 89% yield). 1H NMR (CDCl3, 300.1 MHz): δ 7.51
(m, 6H), 7.40 (dd, J1 = 7.8 Hz, J2 = 1.8 Hz, 4H), 7.19 (m, 10H),
6.77 (s, 2H), 5.73 (s, 2H). 13C NMR (CDCl3, 75.46 MHz): δ 139.1,
136.7, 133.8, 131.1, 129.8, 129.7, 129.6, 128.3, 127.4, 126.9, 126.6,
53.1. IR (neat): 3059, 1600, 1500, 1442, 1357, 1304, 1231, 1193,
1072, 1017, 950, 922, 790, 774 cm-1. DART MS (m/z): [M - H]þ
453.3. Anal. Calcd for C31H24N4: C, 82.27; H, 5.35; N, 12.38.
Found: C, 82.11; H, 5.21; N, 12.19.
Synthesis of 3,9,14,20-Tetraaza-1,6,12,17-tetraazoniapenta-
cyclohexacosane-1(23),4,6(26),10,12(25),15,17(24),21-octaene
Tetra-trifluoromethanesulfonate ((Me,EtTCH)(OTf)4), 2a. 1,10-
Methylene(bisimidazole) (1a) (7.39 g, 0.0499 mol) was dissolved
in acetonitrile (220 mL) in a 500 mL round-bottom flask, and
1,2-diylbis(trifluoromethanesulfonate)ethane (16.3 g, 0.0499
mol) was then slowly added into the stirring solution. The
solution was heated to reflux and stirred for 2 days. The solution
was then filtered hot through a 60 mL fine sintered-glass frit, and
a white solid was collected. The white solid was then dried under
Figure 2. Crystal structure of [(Me,EtTCPh)Pt](PF6)2 (4b). Or-
ange, blue, and gray ellipsoids (50% probability) represent Pt,
N, and C, respectively. Counteranions, solvent molecules, and
hydrogens have been omitted for clarity.
1
and cleanly without the use of dilute solvent conditions.
These 18-atom-ringed tetra-imidazoliums (2) ligate to form
monomeric transition metal complexes such as 4. Future
research will evaluate the catalytic properties of complexes
supported by 2.
reduced pressure to give the product (3.73 g, 15.8% yield). H
NMR (DMSO-d6, 300.1 MHz): δ 8.99 (s, 4H), 8.07 (s, 4H), 7.87
(s, 4H), 6.52 (s, 4H), 4.80 (s, 8H). 13C NMR (DMSO-d6, 75.46
MHz): δ 137.7, 123.6, 123.1, 120.7 (q, JFC = 322 Hz), 58.5, 48.9.
19F NMR (DMSO-d6, 282.3 MHz): δ -77.1. IR (neat): 3110,
1578, 1553, 1369, 1273, 1247, 1226, 1150, 1075, 1028, 886, 858,
774, 724 cm-1. ESI/MS (m/z): [M - OTf]þ 799.1, [M - 2OTf]2þ
325.0, [M - 3OTf]3þ 167.1. Anal. Calcd for C22H24F12N8O12S4:
C, 27.85; H, 2.55; N, 11.81. Found: C, 27.92; H, 2.47; N, 11.74.
Synthesis of 4,5,10,11,15,16,21,22-Octaphenyl-3,9,14,20-tet-
raaza-1,6,12,17-tetraazoniapentacyclohexacosane-1(23),4,6(26),
10,12(25),15,17(24),21-octaene Tetra-trifluoromethanesulfonate
((Me,EtTCPh)(OTf)4), 2b. 1,10-Methylenebis(4,5-diphenylimida-
zole) (1b) (10.0 g, 0.0222 mol) was added to a 500 mL round-
bottom flask, dissolved with acetonitrile (175 mL), and stirred
for 20 min. 1,2-Diylbis(trifluoromethanesulfonate)ethane (7.23 g,
0.0222 mol) was diluted with acetonitrile (5 mL) and pipetted into
the round-bottom flask. The reaction mixture was heated to reflux
for 72 h. After cooling to room temperature, a white solid was
collected by slowly pouring the solution over a 150 mL medium
sintered-glass frit a few milliliters at a time. Each aliquot was filtered
through before adding the next one. This slow filtration yielded the
product, which was dried under reduced pressure (3.25 g, 18.9%
yield). 1H NMR (DMSO-d6, 300.1 MHz): δ 10.02 (s, 4H), 7.46 (m,
16H), 7.29 (t, J = 7.2 Hz, 8H), 7.18 (d, J = 6.0 Hz, 8H), 7.00 (d,
J = 6.9 Hz, 8H), 6.61 (s, 4H), 4.68 (s, 8H). 13C NMR (DMSO-d6,
75.46 MHz): δ 136.8, 132.7, 132.3, 131.0, 130.7, 130.2, 129.4, 129.3,
123.2, 122.4, 120.6 (q, JF-C = 322 Hz), 56.0, 46.8. 19F NMR
(DMSO-d6, 282.3 MHz): δ -77.8. IR (neat): 3145, 3067, 1560,
Experimental Section
Syntheses of organic compounds were performed under normal
atmospheric conditions. Syntheses of platinum complexes were
performed under a dry nitrogen atmosphere with the use of either
a drybox or standard Schlenk techniques. Solvents were dried on an
Innovative Technologies (Newburgport, MA) Pure Solv MD-7
solvent purification system and degassed by three freeze-pump-
thaw cycles on a Schlenk line to remove O2 prior to use. DMSO-d6,
acetonitrile-d3, and chloroform-d were degassed by three freeze-
pump-thaw cycles prior to drying over activated molecular sieves.
These NMR solvents were then stored under N2 in a glovebox. The
compounds 1,10-methylene(bis-imidazole) (1a)16,17 and 1,2-diylbis-
(trifluoromethanesulfonate)ethane (also called 1,2-bis(trifoxy)-
ethane)18 were prepared as described previously. All other reagents
were purchased from commercial vendors and used without puri-
1
fication. H, 13C{1H}, and 19F NMR spectra were recorded at
ambient temperature on a Varian Mercury 300 MHz or a Varian
1
INOVA 600 MHz narrow-bore broadband system. H and 13C
NMR chemical shifts were referenced to the residual solvent. 19F
NMR chemical shifts are reported relative to an external standard
of neat CFCl3. All mass spectrometry analyses were conducted at
the Mass Spectrometry Center located in the Department of
Chemistry at the University of Tennessee. The DART analyses
were performed using a JEOL AccuTOF-D time-of-flight (TOF)
mass spectrometer with a DART (direct analysis in real time)
ionization source from JEOL USA, Inc. (Peabody, MA). The
ESI/MS analyses were performed using a QSTAR Elite quadrupole
time-of-flight (QTOF) mass spectrometer with an electrospray
ionization source from AB Sciex (Concord, Ontario, Canada).
All mass spectrometry sample solutions were prepared in acetoni-
trile. Infrared spectra were collected on a Thermo Scientific Nicolet
iS10 with a Smart iTR accessory for attenuated total reflectance.
Carbon, hydrogen, and nitrogen analyses were obtained from
Atlantic Microlab, Norcross, GA.
1445, 1372, 1336, 1278, 1254, 1241, 1226, 1177, 1027, 765 cm-1
.
ESI/MS (m/z): [M - OTf]þ 1407.2, [M - 2OTf]2þ 629.2, [M -
3OTf]3þ 369.8. Anal. Calcd for C70H56F12N8O12S4: C, 53.98; H,
3.62; N, 7.19. Found: C, 53.84; H, 3.47; N, 7.37.
Synthesis of 3,9,14,20-Tetraaza-1,6,12,17-tetraazoniapenta-
cyclohexacosane-1(23),4,6(26),10,12(25),15,17(24),21-octaene
Tetraiodide ((Me,EtTCH)(I)4), 2c. In a 120 mL jar with a Teflon
lid, acetonitrile (70 mL) and (Me,EtTCH)(OTf)4 (2a) (3.12 g,
0.00329 mol) were added and stirred. DMSO (14 mL) was added
dropwise until all of the solids dissolved. Tetrabutylammonium
iodide (12.2 g, 0.0329 mol) was then dissolved in acetonitrile (25
mL) in a 100 mL beaker. The tetrabutylammonium iodide
solution was poured into the 120 mL jar, immediately forming
a white precipitate. The acetonitrile mixture stirred overnight,
and the white solid was collected on a 60 mL fine sintered-glass
frit. The white solid was subsequently washed with THF (2 ꢀ 30
mL) and acetonitrile (1 ꢀ 30 mL) on the 60 mL fine sintered-
glass frit. The white solid was then dried under reduced pressure
to yield the product (2.28 g, 80.5% yield). 1H NMR (DMSO-d6,
300.1 MHz): δ 9.11 (s, 4H), 8.11 (s, 4H), 7.91 (s, 4H), 6.58 (s, 4H),
4.84 (s, 8H). 13C NMR (DMSO-d6, 75.46 MHz): δ 137.6, 123.5,
Synthesis of 1,10-Methylenebis(4,5-diphenylimidazole), 1b. 4,5-
Diphenylimidazole (13.2 g, 0.0610 mol) and potassium hydro-
xide powder (5.0 g, 0.089 mol) were added to a 240 mL glass jar
with a Teflon lid and dissolved with 100 mL of acetonitrile and
stirred for 15 min. Dibromomethane (5.2 g, 0.030 mol) was then
diluted with 3 mL of acetonitrile, and this solution was slowly
added to the glass jar. The reaction was then stirred for 72 h. After
the reaction was complete, 16 mL of ice cold water was added to the
mixture and stirred for an additional 15 min, which precipitated a

3238 Organometallics, Vol. 29, No. 15, 2010
Bass et al.
123.0, 58.4, 48.7. IR (neat): 3094, 3023, 1563, 1550, 1441, 1327,
1170, 1153, 1022, 824, 764, 750, 728 cm-1. Anal. Calcd for
C18H24I4N8: C, 25.14; H, 2.81; N, 13.03. Found: C, 25.09; H,
3.07; N, 12.39.
reaction mixture was removed from the heat and allowed to cool
to room temperature, thallium(I) hexafluorophosphate (0.219 g,
0.626 mmol) was dissolved in benzonitrile (2 mL), added to the
reaction mixture, and stirred for 24 h. The reaction mixture was
then filtered over Celite to remove thallium(I) iodide. Benzoni-
trile was then removed under reduced pressure to leave the crude
solid. The crude solid was dissolved in acetone (5 mL) and
filtered over Celite. The product was crystallized via vapor
diffusion of ether into the acetone solution. The collected
crystals were washed with methylene chloride (2 mL) and diethyl
ether (3 ꢀ 10 mL) (0.010 g, 6.6% yield). 1H NMR (DMSO-d6,
300.1 MHz): δ 7.45 (m, 16H), 7.39 (t, J = 7.9 Hz, 8H), 7.25 (t,
J = 7.7 Hz, 8H), 7.13 (d, J = 7.1 Hz, 8H), 6.14 (d, J = 14.1 Hz,
Synthesis of 4,5,10,11,15,16,21,22-Octaphenyl-3,9,14,20-tet-
raaza-1,6,12,17-tetraazoniapentacyclohexacosane-1(23),4,6(26),
10,12(25),15,17(24),21-octaene Tetraiodide ((Me,EtTCPh)(I)4),
2d. (Me,EtTCPh)(OTf)4 (2b) (9.36 g, 0.00602 mol) was added as
a solid to an acetonitrile (300 mL) solution of tetrabutylammo-
nium iodide (8.89 g, 0.0241 mol) in a 500 mL Erlenmeyer flask.
This mixture was stirred overnight, and the white solid was
collected on a 150 mL medium sintered-glass frit and dried
under reduced pressure to yield the pure product (8.84 g, 93.7%
yield). 1H NMR (DMSO-d6, 300.1 MHz): δ 10.65 (s, 4H), 7.59
(d, J = 6.6 Hz, 8H), 7.47 (m, 24 H), 7.21 (d, J = 7.5 Hz, 8H), 6.97
(s, 4H), 4.75 (s, 8H). 13C NMR (DMSO-d6, 75.46 MHz): δ 136.0,
133.2, 132.2, 131.7, 131.5, 131.2, 131.1, 129.6, 129.5, 123.8,
123.4, 57.7, 46.5. IR (neat): 2964, 1561, 1488, 1446, 1373,
1252, 1215, 1030, 759 cm-1. Anal. Calcd for C66H56I4N8: C,
53.97; H, 3.84; N, 7.63. Found: C, 52.33; H, 3.89; N, 7.26.
Synthesis of [(Me, EtTCH)Pt](OTf)2, 4a. (Me,EtTCH)(OTf)4 (2a)
(0.174 g, 0.184 mmol) was dissolved in DMSO (1 mL) in a 20 mL
vial. Platinum(II) iodide (0.0824 g, 0.184 mmol) was dissolved in
1 mL of DMSO and was added to the (Me,EtTCH)(OTf)4 solu-
tion. Triethylamine (0.0762 g, 0.753 mmol) was then added to
the reaction mixture. This solution was heated to 85 °C and
stirred for 48 h. After the reaction mixture was removed from the
heat and allowed to cool to room temperature, thallium(I)
trifluoromethanesulfonate (0.130 g, 0.367 mmol) was dissolved
in DMSO (1 mL) and was added to the reaction mixture. This
mixture was stirred for 15 min and then filtered over Celite to
remove thallium(I) iodide. DMSO was then removed under
reduced pressure to leave the crude solid. The crude solid was
washed with THF (3 ꢀ 10 mL) and dried under reduced
pressure, leaving a white solid. To further purify the white solid,
it was dissolved in acetonitrile (2 mL), and the resulting solution
was then filtered over Celite and crystallized via vapor diffusion
of ether into the acetonitrile solution. White crystals were
collected and dried under reduced pressure to give the pure
2H), 5.72 (d, J = 14.2 Hz, 2H), 4.79 (m, 4H), 4.5 (m, 4H). 13
C
NMR (DMSO-d6, 150.9 MHz): δ 158.8, 132.2, 131.1, 130.9,
130.2, 129.8, 129.7, 128.9, 128.8, 126.0, 125.3, 58.1, 46.8. 19F
NMR (DMSO-d6, 282.3 MHz): δ -70.1 (d, J = 711 Hz). IR
(neat): 1489, 1467, 1404, 1369, 1235, 828, 786, 766, 735 cm-1
.
ESI/MS (m/z): [M - PF6]þ 1297.34, [M - 2PF6]2þ 576.19. Anal.
Calcd for C66H52F12N8P2Pt: C, 54.97; H, 3.63; N, 7.77. Found:
C, 54.69; H, 3.54; N, 7.79.
X-ray Structure Determinations. X-ray diffraction measure-
ments were performed on single crystals coated with Paratone
oil and mounted on Kaptan loops. Each crystal was frozen
under a stream of N2 while data were collected on a Bruker
APEX diffractometer. A matrix scan using at least 20 centered
reflections was used to determine initial lattice parameters.
Reflections were merged and corrected for Lorenz and polari-
zation effects, scan speed, and background using SAINT 4.05.
Absorption corrections, including odd and even ordered sphe-
rical harmonics, were performed using SADABS. Space group
assignments were based upon systematic absences, E statistics,
and successful refinement of the structure. The structure was
solved by Patterson maps with the aid of successive difference
Fourier maps and was refined against all data using the
SHELXTL 5.0 software package. The structure of 4b was solved
in the space group Cc. The crystal suffered from twinning, which
led to a lower quality structure. Despite repeated attempts with
different solvent combinations, we were unable to grow crystals
that did not exhibit twinning. The carbon, nitrogen, platinum,
and phosphorus atoms were refined anisotropically, while the
disordered fluorine atoms were refined isotropically. Three of
the fluorine atoms (F4, F7, and F11) were split equally over two
positions to improve the electron density model of the PF6’s.
The solvent molecules in the unit cell were modeled as ethers.
They are disordered and were refined isotropically.
1
product (0.0715 g, 46.3% yield). H NMR (DMSO-d6, 300.1
MHz): δ 7.68 (d, J = 1.8 Hz, 4H), 7.57 (d, J = 2.1 Hz, 4H), 6.40
(d, J = 12.9 Hz, 2H), 5.95 (d, J = 13.5 Hz, 2H), 4.86 (m, 4H),
4.61 (m, 4H). 13C NMR (DMSO-d6, 150.9 MHz): δ 157.8 (s and
Pt satellites, JPt-C = 942 Hz for 195Pt (195Pt = 33.8% abun-
dance)), 123.3, 121.6, 120.6 (q, JF-C = 322 Hz), 62.5, 48.7. 19
F
NMR (DMSO-d6, 282.3 MHz): δ -77.0. IR (neat): 3131, 1574,
1428, 1244, 1224, 1152, 1026, 857, 812, 757, 707 cm-1. ESI/MS
(m/z): [M - OTf]þ 692.1, [M - 2OTf]2þ 271.6. Anal. Calcd for
C20H20F6N8O6PtS2: C, 28.54; H, 2.40; N, 13.31. Found: C,
28.67; H, 2.21; N, 13.16.
Acknowledgment. This research was funded by a start-
up grant from the University of Tennessee. The QStar
ESI/MS was purchased with funds from NSF grant
number CHE-0750364. We thank T. David Harris for
assistance with the crystallography.
Synthesis of [(Me, EtTCPh)Pt](PF6)2, 4b. (Me,EtTCPh)(I)4 (2d)
(0.153 g, 0.104 mmol) was dissolved in benzonitrile (10 mL) in a
20 mL vial. Dichlorobis(benzonitrile)platinum(II) (0.0492 g,
0.104 mmol) was dissolved in 2 mL of benzonitrile and was
added to the (Me,EtTCPh)(I)4 solution. Triethylamine (0.0528 g,
0.521 mmol) was then added to the reaction mixture. This
solution was heated to 90 °C and stirred for 24 h. After the
Supporting Information Available: X-ray crystallographic
files (CIF). These materials are available free of charge via the
Internet at http://pubs.acs.org.