Tripodal 4-pyridyl-derived host ligands and their metallo-supramolecular chemistry: Stella octangula and bowl-shaped assemblies

Article abstract of DOI:10.1021/ic901972h

The synthesis of five new cyclotriveratrylene derivatives with 4-pyridyl side arms is reported, along with the crystal structures of three of these. Three ligands with extended 4-pyridylphenyl side arms and a ligand derived from cyclotriphenolene have bee

Full text of DOI:10.1021/ic901972h

Inorg. Chem. 2010, 49, 675–685 675
DOI: 10.1021/ic901972h
Tripodal 4-Pyridyl-Derived Host Ligands and Their Metallo-Supramolecular
Chemistry: Stella Octangula and Bowl-Shaped Assemblies
Tanya K. Ronson,† Christopher Carruthers,† Julie Fisher,† Thierry Brotin,‡ Lindsay P. Harding,§
Pierre J. Rizkallah, and Michaele J. Hardie*,†
†
‡
ꢀ ꢀ
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom, Stereochimie
ꢀ
ꢀ
et Interactions Moleculaires, UMR 5532 CNRS/ENS-Lyon, 46 Allee d’Italie, 69364 Lyon 07, France,
§Department of Chemical and Biological Sciences, University of Huddersfield, Huddersfield, HD1 3DH,
United Kingdom, and STFC Daresbury Laboratory, Daresbury, Warrington, WA4 4AD, United Kingdom
Received October 6, 2009
The synthesis of five new cyclotriveratrylene derivatives with 4-pyridyl side arms is reported, along with the crystal
structures of three of these. Three ligands with extended 4-pyridylphenyl side arms and a ligand derived from
cyclotriphenolene have been shown to form [Pd6L8]12þ stella octangula assemblies using diffusion-ordered
spectroscopy NMR and electrospray MS techniques. This confirms the generality of the stella octagula assembly,
providing that the ligand arms show a degree of rigidity. The more flexible ether-linked ligand tris(4-pyridyl-
methyl)cyclotriguaiacylene forms a smaller [Pd3L4]6þ bowl-shaped assembly in the solid state and in solution. The
previously reported ligand tris(4-pyridylmethylamino)cyclotriguaiacylene forms a similar assembly in solution.
Introduction
organometallic cryptophanes,4 organo-gels,5 metallo-gels,6 anion
sensing,7 fullerene separations,8 metallo-supramolecular
assemblies,9-15 and coordination polymers.16 Both CTV
and its chiral analogs cyclotriguaiacylene (CTG) and tris-
amino cyclotriguaiacylene (aCTG) can be converted into
extended-arm host molecules through functionalization at
the upper rim.17
Cyclotriveratrylene (CTV) is a molecular host with a rela-
tively rigid shallow bowl-shaped cavity.1 Recent interest in CTV
chemistry includes applications in liquid crystals,2 gas-binding,3
*To whom correspondence should be addressed. E-mail: m.j.hardie@
leeds.ac.uk.
(1) For a review, see: Collet, A. Tetrahedron 1987, 43, 5725–5759.
(2) (a) Rio, Y.; Nierengarten, J.-F. Tetrahedron Lett. 2002, 43, 4321–4324.
(b) Felder, D.; Heinrich, B.; Guillon, D.; Nicoud, J.-F.; Nierengarten, J.-F.
Chem.;Eur. J. 2000, 6, 3501–3507.
The self-assembly of 3D metallo-supramolecular species
from transition metals ions and multifunctional ligands is
well established, and a huge range of polyhedral/prismatic
(3) Fogarty, H. A.; Berthault, P.; Brotin, T.; Huber, G.; Desvaux, H.;
Dutasta, J.-P. J. Am. Chem. Soc. 2007, 129, 10332–10333.
(4) Fairchild, R. M.; Holman, K. T. J. Am. Chem. Soc. 2005, 127, 16364–
16365.
(5) Bardelang, D.; Camerel, F.; Ziessel, R.; Schmutz, M.; Hannon, M. J.
J. Mater. Chem. 2008, 18, 489–494.
(6) Westcott, A.; Sumby, C. J.; Walshaw, R. D.; Hardie, M. J. New J.
Chem. 2009, 33, 902–912.
(7) (a) Zhang, S.; Echegoyen, L. J. Am. Chem. Soc. 2005, 127, 2006–2011.
(b) Gawenis, J. A.; Holman, T. K.; Atwood, J. L.; Jurisson, S. S. Inorg. Chem.
2002, 41, 6028–6031.
(8) Huerta, E.; Cequier, E.; de Mendoza, J. Chem. Commun. 2007, 5016–
5018.
(9) Sumby, C. J.; Fisher, J.; Prior, T. J.; Hardie, M. J. Chem.;Eur. J.
2006, 12, 2945–2959.
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6399.
(11) Sumby, C. J.; Carr, M. J.; Franken, A.; Kennedy, J. D.; Kilner, C. A.;
Hardie, M. J. New J. Chem. 2006, 30, 1390–1396.
(12) Ronson, T. K.; Fisher, J.; Harding, L. P.; Hardie, M. J. Angew.
Chem., Int. Ed. 2007, 46, 9086–9088.
(15) Zhong, Z.; Ikeda, A.; Shinkai, S.; Sakamoto, S.; Yamaguchi, K. Org.
Lett. 2001, 3, 1085–1087.
(16) (a) Sumby, C. J.; Hardie, M. J. Cryst. Growth Des. 2005, 5, 1321–
1324. (b) Hardie, M. J.; Sumby, C. J. Inorg. Chem. 2004, 43, 6872–6874. (c)
Ronson, T. K.; Hardie, M. J. CrystEngComm 2008, 10, 1731–1734. (d) Mough,
S. T.; Holman, K. T. Chem. Commun. 2008, 1407–1409.
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Halder, G. J.; Chapman, K. W.; Balde, C.; Letard, J.-F.; Murray, K. S.; Kepert,
C. J.; Batten, S. R. Angew. Chem., Int. Ed. 2009, 48, 2549–2552. (c) Lu, Z.;
Knobler, C. B.; Furukawa, H.; Wang, B.; Liu, G.; Yaghi, O. M. J. Am. Chem. Soc.
2009, 131, 12532–12533. (d) Ghosh, K.; Hu, J.; White, H. S.; Stang, P. J. J. Am.
Chem. Soc. 2009, 131, 6695–6697. (e) Ghosh, K.; Mukherjee, P. S. Organome-
tallics 2008, 27, 316–319. (f ) Oppel, I. M.; Foecker, K. Angew. Chem., Int. Ed.
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Seidel, S. R.; Stang, P. J. Acc. Chem. Res. 2002, 35, 972–983. (i) Fujita, M.;
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r
2009 American Chemical Society
Published on Web 12/14/2009
pubs.acs.org/IC

676 Inorganic Chemistry, Vol. 49, No. 2, 2010
Ronson et al.
Scheme 1. Self-Assembly of Stella Octangula [Pd6(1)8]12þ Cage with Detail from Crystal Structure (Box)12
structures have been reported.18-23 The majority of such
polyhedra utilize planar or linear ligands with a much smaller
number involving cavitand ligands. Many of these involve
dimeric capsule assemblies,19 with only rare examples of
higher assemblies with cavitand ligands known.20 Metal-
based assemblies incorporating 3-fold symmetric cyclotriver-
atrylene ligands are particularly unusual. The bowl shape of a
CTV derivative provides a convergent binding mode, and
such ligands can form assemblies with greater internal vo-
lumes than would a corresponding planar analog and give the
resulting assemblies a stellated aspect. Furthermore, the CTV-
type ligands impart embedded molecular recognition sites
within the assemblies, and it has been shown that simple
host-guest interactions at these sites can have a directing
influence on the overall self-assembly process.9 Shinkai and
co-workers have reported [M3L2] capsules involving CTV-
type ligands.15 We have reported [Ag2L2]2þ capsules,9,10
[Ag4L4]4þ “star-burst” tetrahedra9-11 as well as a [Ag4L4]4þ
self-included tetrahedra,21 a [M3L2]2 [2]catenane,13 and a
topologically nontrivial [Pd4L4]8þ “Solomon’s cube”.14
We have also recently reported a [Pd6L8]12þ metallo-
supramolecular assembly with a stella octangula structure
which forms from the reaction of tris(isonicotinoyl)cyclotri-
guaiacylene (1) with Pd(NO3)2 in dimethylsulfoxide (DMSO),
Scheme 1.12 Square planar Pd(II) with highly labile ligands
such as NO3- has been combined with multifunctional ligands
to give a number of 3D metallo-supramolecular assemblies.22
The [Pd6L8]12þ stella octangula features Pd(II) cations in an
octahedral arrangement and a ligand, 1, occupying each face
of the octahedron. A stella octangula is the first stellation of an
octahedron, which is where the edges of the octahedron are
extended until they meet at a point, resulting in a polyhedron
with a spiked appearance. The pyramidal shape of 1 means
that [Pd6L8]12þ has the appearance of a stella octangula. M6L8
metallo-supramolecular assemblies have also been reported
by several other groups.23
(19) For examples, see: (a) Gruppi, F.; Boccini, F.; Elviri, L.; Dalcanale,
E. Tetrahedron 2009, 65, 7289–7295. (b) Power, N. P.; Dalgarno, S. J.; Atwood,
J. L. New J. Chem. 2007, 31, 17–20. (c) Haino, T.; Kobayashi, M.; Chikaraishi,
M.; Fukazawa, Y. Chem. Commun. 2005, 2321–2323. (d) Kobayashi, K.;
Yamada, Y.; Yamanaka, M.; Sei, Y.; Yamaguchi, K. J. Am. Chem. Soc. 2004,
126, 13896–13897. (e) Pirondi, L.; Bertolini, F.; Cantadori, B.; Ugozzoli, F.;
Massera, C.; Dalcanale, E. Proc. Natl. Acad. Sci. U. S. A. 2002, 99, 4911–4915.
(20) (a) McKinlay, R. M.; Thallapally, P. K.; Atwood, J. L. Chem.
Commun. 2006, 2956–2958. (b) McKinlay, R. M.; Cave, G. W. V.; Atwood,
J. L. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 5944–5948. (c) McKinlay, R. M.;
Thallapally, P. K.; Cave, G. W. V.; Atwood, J. L. Angew. Chem., Int. Ed. 2005,
44, 5733–5736. (d) Fox, O. D.; Drew, M. G. B.; Beer, P. D. Angew. Chem., Int.
Ed. 2000, 39, 135–140. (e) Fox, O. D.; Drew, M. G. B.; Wilkinson, E. J. S.; Beer,
P. D. Chem. Commun. 2000, 391–392.
(21) Carruthers, C.; Ronson, T. K.; Sumby, C. J.; Westcott, A.; Harding,
L. P.; Prior, T. J.; Rizkallah, P.; Hardie, M. J. Chem.;Eur. J. 2008, 14,
10286–10296.
(22) For examples, see: (a) Chand, D. K.; Biradha, K.; Kawano, M.;
Sakamoto, S.; Yamaguchi, K.; Fujita, M. Chem. As. J. 2006, 1, 82–90. (b)
Sato, S.; Iida, J.; Suzuki, K.; Kawano, M.; Ozeki, T.; Fujita, M. Science 2006, 313,
1273–1276. (c) Suzuki, K.; Tominaga, M.; Kawano, M.; Fujita, M. Chem Comm.
2009, 1638–1640. (d) Suzuki, K.; Kawano, M.; Fujita, M. Angew. Chem., Int.
Ed. 2007, 46, 2819–2822. (e) Tominaga, M.; Suzuki, K.; Kawano, M.; Kusukawa,
T.; Ozeki, T.; Sakamoto, S.; Yamaguchi, K.; Fujita, M. Angew. Chem., Int. Ed.
2004, 43, 5621–5625.
(23) (a) Chand, D. K.; Biradha, K.; Fujita, M.; Sakamoto, S.; Yamaguchi,
K. Chem. Commun. 2002, 2486–2487. (b) Chand, D. K.; Fujita, M.; Biradha, K.;
Sakamoto, S.; Yamaguchi, K. Dalton Trans. 2003, 2750–2756. (c) Moon, D.; Kang,
S.; Park, J.; Lee, K.; John, R. P.; Won, H.; Seong, G. H.; Kim, Y. S.; Kim, G. H.;
Rhee, H.; Lah, M. S. J. Am. Chem. Soc. 2006, 128, 3530–3531. (d) Liu, H.-K.;
Tong, X. Chem. Commun. 2002, 1316–1317. (e) Ghosh, S.; Mukherjee, P. S.
J. Org. Chem. 2006, 71, 8412–8416. (f) Hiraoka, S.; Harano, K.; Shiro, M.; Ozawa,
Y.; Yasuda, N.; Toriumi, K.; Shionoya, M. Angew. Chem., Int. Ed. 2006, 45, 6488–
6491.
Having the binding pyridyl groups in the 4 position
in ligand 1 is an important aspect of the design of the
stella octangula, and we report herein our investigations
into whether other CTG-based or aCTG-based ligands
with pyridyl binding sites in a 4 disposition form analog-
ous [Pd6L8]12þ stella octangula cages. The cage complex
[Pd6(1)8]12þ has a significant internal volume as well as

Article
Inorganic Chemistry, Vol. 49, No. 2, 2010 677
Scheme 2. Synthetic Routes to New Ligands
internal binding sites, which gives it the potential to act as a
for [Pd6(1)8]12þ. Ligands investigated of the same size as 1 but
with more flexible linker groups between the CTG core and
4-pyridyl groups were tris(4-pyridylmethyl)cyclotriguaiacylene,
3, and the previously reported tris(4-pyridylmethylamino)-
cyclotriguaiacylene, 4.9 Ligands tris{4-(4-pyridyl)phenylester}-
cyclotriguaiacylene, 5; tris{4-(4-pyridyl)benzyl}cyclotriguai-
acylene, 6; and tris{4-(4-pyridyl)benzyl-amino}cyclotriguaiacy-
lene, 7, all feature longer 4-(4-pyridyl)phenyl “arms” extending
from the host core. With the majority of ligands investigated,
[Pd6L8]12þ cages were indeed formed, although an alternative
[Pd3L4]6þ open bowl-shaped assembly was found with two of
the more flexible ligands.
nanoscale vessel. The surface of [Pd6(1)8]12þ is not fully
˚
enclosed and has eight windows of ca. 7 ꢀ 9 A dimensions,
although access through these windows is partially blocked
by methoxy groups of the ligand. The series of ligands with
4-pyridyldonorgroups, 2-7, was designed in order to test the
generality of the stella octangula cage formation and to
manipulate both the size of the overall assembly and these
windows on its surface.
Results and Discussion
Ligand Synthesis and Structures. The synthetic routes
to previously unreported ligands are summarized in
Scheme 2. All ligands were isolated as racemic mixtures
in moderate to good yields. Tris(isonicotinoyl)cyclo-
triphenolene (2) was prepared by the reaction of cyclo-
triphenolene24 with isonicotinoyl chloride hydrochloride
in THF, in the presence of a base. Similarly, tris{4-(4-
pyridyl)phenylester}cyclotriguaiacylene (5) was prepared
by the reaction of 4-(4-pyridyl)benzoyl chloride hydro-
chloride with cyclotriguaiacylene (CTG)25 in the presence
of a base. The ether linked derivatives tris(4-pyridyl-
methyl)cyclotriguaiacylene (3) and tris{4-(4-pyridyl)-
benzyl}cyclotriguaiacylene (6) were prepared by the
reaction of CTG with 4-bromomethylpyridine or 4-[4-
(chloromethyl)phenyl]pyridine hydrochloride, repectively,
The ligand tris(isonicotinoyl)cyclotriphenolene 2 is di-
rectly analogous to 1 but based on a cyclotriphenolene core
without the OMe goups at the rim. It therefore has the
potential to form a cage with larger windows than were seen
(24) Brotin, T.; Roy, V.; Dutasta, J.-P. J. Org. Chem. 2005, 70, 6187–6195.
(25) Brotin, T.; Devic, T.; Lesage, A.; Emsley, L.; Collet, A. Chem.;Eur.
J. 2001, 7, 1561–1573.

678 Inorganic Chemistry, Vol. 49, No. 2, 2010
Ronson et al.
Figure 1. Section ofan aligned infinite columnfromthe crystalstructure
of 2.
in dry dimethylformamide (DMF) with NaH as a base.
Tris{4-(4-pyridyl)benzyl-amino}cyclotriguaiacylene (7) was
synthesized in two steps from the precursor 3,8,13-triamino-
2,7,12-trimethoxy-10,15-dihydro-5H-tribenzo[a,d,g]cyclono-
nene (aCTG),26 with initial formation of the imine through
reaction with 4-(4-pyridyl)benzaldehyde followed by reduc-
tion with sodium borohydride. All ligands were characterized
by NMR, IR, mass spectrometry, and elemental analysis.
Single crystals were obtained of 2and 3(in two phases) and of
a solvate of 5, and their X-ray structures are briefly described
below.
Figure 2. From the crystal structures of (a) 3a and (b) 3b. The asym-
metric units are shown of the left and misaligned columns of ligand 3 on
the rightwithcrystallographicallyequivalentmoleculesshown inthe same
colors.
Ligand 2 crystallizes in space group P1 with one
complete molecule in the asymmetric unit. The three
pyridyl arms are directed outward, forming an extended
cavity which acts as a host for another molecule of 2,
resulting in aligned infinite stacks of the ligand, Figure 1.
˚
The long centroid-centroid distances of 4.679 A between
the aromatic rings of adjacent ligands preclude any π-π
interactions.
Two phases of 3 were obtained from different crystal-
lization solvents. Phase 3a was isolated by vapor diffusion
of diisopropyl ether into a CDCl3 solution of 3, while
phase 3b was obtained from vapor diffusion of diethyl
ether into an acetonitrile solution. Neither crystal struc-
ture showed any appreciable inclusion of a solvent, as
indicated by low residual electron density from the crystal
structure refinements. With 3a, ligand 3 crystallizes in the
monoclinic cell with one molecule of 3 in the asymmetric
unit, Figure 2a. An offset infinite stack of ligands is
formed with one OMe group of each ligand being directed
into the molecular cavity of another, Figure 2a. A face-to-
face π-π stacking interaction occurs between a pyridyl
ring of one ligand and one of the aromatic rings of the
Figure 3. Detail from the crystal structure of 5 31/3MeCN 1/3H2O
showing host-guest interactions between 5 and CH3CN.
3
3
although this occurs in a distinct manner to that of 3a,
and an OMe group of one ligand is not directed into the
bowl of an adjacent ligand as for 3b, Figure 2b. Infinite
stacks of ligand 3 within 3b pack together in a manner that
˚
creates small circular channels approximately 10 A in
diameter.
Slow evaporation of a solution of 5 in acetonitrile gave
˚
CTV core at a ring centroid separation of 3.736 A. Phase
1
colorless crystals of 5 31/3MeCN /3H2O which crystal-
3
3
3b crystallizes in the rhombohedral space group R3, with
two molecules of 3 in the asymmetric unit, Figure 2b.
Phase 3b also shows offset infinite stacks of ligands,
lize in the trigonal space group P31c. The asymmetric unit
contains one molecule of 5, three acetonitrile solvate
molecules, and a further acetonitrile and water solvate
molecules located on special positions with fractional
occupancy. Each molecule of 5 is a host for an acetonitrile
molecule (Figure 3), with the hydrophobic end of the
^
(26) Garcia, C.; Malthete, J.; Collet, A. Bull. Soc. Chim. Fr. 1993, 130, 93–
95.

Article
Inorganic Chemistry, Vol. 49, No. 2, 2010 679
Scheme 3. Schematic Giving a Summary of the Formation of Stella Octangula or Open-Bowl Assemblies with the Different Ligands 1-7
acetonitrile molecule directed into the hydrophobic
cavity of the host and an additional weak C-H
Pd(NO3)2 shows a series of peaks at m/z 2826.2,
2103.6, 1670.5, and 1382.1 corresponding to {Pd6(6)8-
O
interaction (C O distance = 3.45 A) with one of the
3 3 3
xþ
˚
(NO3)(12-x)
}
(x = 3-6), Figure S2 (Supporting In-
3 3 3
ester oxygen atoms of 5. An additional acetonitrile also
forms a weak C-H O interaction (C O distance
formation). Freshly prepared solutions of ligand 7 with
Pd(NO3)2 show peaks at m/z 2816.9, 2096.7, 1664.8, and
3 3 3
3 3 3
1377.1 corresponding to {Pd6(7)8(NO3)(12-x)}
xþ (x =3-6),
˚
3.39 A) with an ester oxygen atom. The crystal lattice
has a complicated packing motif dominated by edge-to-
face π-stacking interactions and face-to-face π-π stack-
ing interactions, the latter between phenyl-pyridyl arms
of neighboring ligands at ring centroid separations of
indicating that the amine-linked derivative 7 also forms the
stella octangula assembly in solution, Figure S3 (Supporting
Information).
The 1H NMR spectra of 4:3 mixtures of the ligands 2, 5,
and 6 with Pd(NO3)2 in d6-DMSO are broad and show
coordination-induced shifts compared to the spectra of
the free ligands. In each case, the spectra show only one
set of ligand arm environments, indicating that the com-
plexes formed retain the C3 symmetry of the ligands.
DOSY has been used to further investigate the complexes
formed. DOSY has become a valuable tool for character-
izing large supramolecular assemblies in solution, allow-
ing the relative size of a molecule to be estimated from a
comparison of experimental diffusion rates.27 DOSY
NMR studies of a 4:3 mixture of 2 and Pd(NO3)2 in d6-
DMSO showed a band for the major solution component
with a diffusion coefficient of 0.642 ꢀ 10-10 m2 s-1. A
diffusion coefficient of 1.256 ꢀ 10-10 m2 s-1 was obtained
for a d6-DMSO solution of ligand 2 alone, giving a
Dcomplex/Dligand ratio of 0.51. Although this is larger than
the ratio of 0.43 observed for [Pd6(1)8](NO3)12,12 it is
significantly smaller than the ratio of 0.68 observed for
the previously studied [Ag4L4]4þ coordination cage with a
˚
ca. 3.79 A.
Metallo-Supramolecular Assemblies with Pd(II). For
each of the ligands 2-7, a 4:3 mixture of the ligand and
Pd(NO3)2 in DMSO or d6-DMSO was studied by electro-
spray ionization mass spectrometry (ESI-MS) and diffu-
1
sion-ordered (DOSY) H NMR spectroscopy. With the
exception of ligands 3 and 4, which form an open-bowl
assembly discussed in detail later in the text, these solu-
tion studies demonstrated that the [Pd6L8]12þ stella oc-
tangula is the dominant self-assembly product between
Pd(II) and these types of ligands, Scheme 3. The complex
[Pd6(7)8]12þ is not stable in solution, as the ligand de-
grades when allowed to stand in solution in the presence
of the metal cation.
ESI-MS provides excellent evidence that the self-
assembly of a [Pd6(L)8]12þ stella octangula cage occurs
in solution for ligand 2 and all of the longer-arm ligands
5-7. The electrospray mass spectrum of a DMSO solu-
tion of 2 with Pd(NO3)2 shows peaks at m/z 2087.6 and
1550.7, which are assigned to {Pd6(2)8(NO3)9}3þ (calcd
2088.3) and {Pd6(2)8(NO3)8}4þ (calcd 1550.7), Figure S1
(Supporting Information). The electrospray mass spec-
trum of the complex of 5 with Pd(NO3)2 and shows a
series of peaks at m/z 2187.7, 1737.8, and 1437.6 which
(27) For example: (a) Kamiya, N.; Tominaga, M.; Sato, S.; Fujita, M.
J. Am. Chem. Soc. 2007, 129, 3816–3817. (b) Allouche, L.; Marquis, A.; Lehn,
J.-M. Chem.;Eur. J. 2006, 12, 7520–7525. (c) Evan-Salem, T.; Baruch, I.;
Avram, L.; Cohen, Y.; Palmer, L. C.; Rebek, J., Jr. Proc. Natl. Acad. Sci. 2006,
103, 12296–12300. (d) Megyes, T.; Jude, H.; Grosz, T.; Bako, I.; Radnai, T.;
Tarkanyi, G.; Palinkas, G.; Stang, P. J. J. Am. Chem. Soc. 2005, 127, 10731–
10738. (e) Tidmarch, I. S.; Taylor, B. F.; Hardie, M. J.; Russo, L.; Clegg, W.;
Ward, M. D. New J. Chem. 2009, 33, 366–375.
can be assigned to {Pd6(5)8(NO3)(12-x)}
xþ (x = 4-6), all
arising from the octahedral core but with different num-
bers of anions, Figure 4. Likewise, a solution of 6 and

680 Inorganic Chemistry, Vol. 49, No. 2, 2010
Ronson et al.
Figure 4. Electrospray mass spectrum of 5 and Pd(NO3)2 in DMSO.
Inset: Theoretical and experimental isotopic distribution patterns for the
{Pd6(5)8(NO3)7}5þ peak.
Figure 5. Detail from the crystal structure of [Pd3(3)4](NO3)6
n(DMSO) m(H2O). Each ligand 3 is shown in a different color, and guest
3
3
NO3- and DMSO molecules inside the superbowl are shown as ball-and-
stick.
related aminocyclotriguaiacylene-based ligand9 and is
consistent with a very large species being present in
solution. Assuming that the solution species is approxi-
cell volume than was seen for the tetragonal crystals of
˚
3 12
˚
[Pd6(1)8] 12(NO3) n(DMSO) where V ∼ 33 400 A .
mately spherical, a hydrodynamic radius of 16.8 A can be
estimated using a Stokes-Einstein relationship, which is
3
3
Both ligands with relatively flexible linker groups and
4-pyridyl arms did not form the [Pd6L8]12þ stella octan-
gula assembly. Ligand 3 contains ether-linked 4-pyridyl
arms and is thus more flexible than the ester-linked
ligands 1 and 2. A solution containing a mixture of 3
and Pd(NO3)2 in DMSO gave small single crystals of
composition [Pd3(3)4](NO3)6 n(DMSO) m(H2O) upon
slow diffusion of acetone vapor. The single-crystal
X-ray structure was determined from data collected using
synchrotron radiation and reveals a [Pd3(3)4](NO3)6
assembly which resembles an open superbowl, Scheme 3
and Figure 5.
consistent with the crystal structure of [Pd6(1)8]12þ
˚
(diameter of ca. 30 A).
DOSY NMR studies of a 4:3 mixture of 5 and Pd-
(NO3)2 in d6-DMSO showed a band for the major solu-
tion component with a diffusion coefficient of 0.477 ꢀ
10-10 m2 s-1. A diffusion coefficient of 1.032 ꢀ 10-10 m2 s-1
was obtained for a d6-DMSO solution of ligand 5 alone,
giving a Dcomplex/Dligand ratio of 0.46. This is in good
3
3
agreement with the ratio of 0.43 observed for [Pd6(1)8]12þ
.
The hydrodynamic radius of [Pd6(5)8]12þ is estimated to
˚
be around 22.6 A, somewhat larger than the hydrody-
There is one [Pd3(3)4]6þ assembly in the asymmetric
unit of the crystal structure along with counteranions and
solvent. The [Pd3(3)4]6þ assembly displays approximately
C3 (noncrystallographic) molecular symmetry, and there
are two types of ligand binding modes observed. The
three Pd centers are arranged in a triangle, each with
square planar N4 coordination, and Pd-N distances
12þ
˚
namic radius of 19.4 A observed for [Pd6(1)8]
in
solution,12 as would be expected for the larger ligand.
Likewise, a 4:3 mixture of 6 and Pd(NO3)2 in d6-DMSO
showed a band with a diffusion coefficient of 0.4095 ꢀ
10-10 m2 s-1, and a solution of the ligand by itself had
a diffusion coefficient of 1.112 ꢀ 10-10 m2 s-1. The
Dcomplex/Dligand ratio of 0.37 is slightly less than that
observed for the other complexes. This is likely to be
due to a greater error margin in D in this case due to
broadened resonance and resonance overlap observed for
this system. The hydrodynamic radius of [Pd6(6)8]12þ is
˚
range from 1.973(15) to 2.054(11) A. The central ligand
forms the bottom of the bowl and bridges all three Pd
centers. The other three ligands form the sides of the bowl,
and each binds to only two Pd centers, with two pyridyl
arms binding to the same Pd center. This binding mode is
only possible due to the additional flexibility of 3 arising
from the ether linkages and leads to conformation of the
ligands within [Pd3(3)4]6þ differing significantly from the
conformation of ligand 1 within [Pd6(1)8]12þ, and indeed
from the conformations seen in the two crystalline phases
of 3 reported above. The Cphenyl-O-CH2-Cpyridyl tor-
sion angles seen for ligand 1 in the stella octangula and for
ligand 3 in both phases 3a and 3b are actually quite
similar. Phase 3a has torsion angles -174.0, þ161.9,
and þ171.3°, and phase 3b has -169.7, þ167.7, and
þ179.6°, while in the stella octangula the two crystal-
lographically independent ligands give angles of -172.6,
þ167.3, -177.9°, þ174.4, þ169.1, and þ174°.12 The
˚
estimated to be around 26.3 A. Solutions of ligand 7 and
Pd(NO3)2 were not investigated due to the instability of,
and difficulties in purifying, the ligand.
In all cases, crystal growth was attempted by the
diffusion of acetone vapors into the DMSO solutions.
Crystalline products were isolated with ligands 2, 5, and 6.
These crystals were highly solvated, and X-ray data
collected using rotating anode and synchrotron X-ray
sources were too weak to allow for structure determina-
tions. This is likely to be due to inherent disorder in the
crystals and the subsequent lack of high-angle X-ray data.
The unit cell parameters for crystals isolated from a
solution of 5 and Pd(NO3)2 were F-centered cubic with
˚
3
˚
a = 51.56 A and V ∼ 137 000 A . As would be expected
given the larger size of the ligand, this is a much larger unit
corresponding torsion angles for ligand 3 with

Article
Inorganic Chemistry, Vol. 49, No. 2, 2010 681
Figure 6. Detail from the crystal structure of [Pd3(3)4](NO3)6
3
n(DMSO) m(H2O), showing two of the [Pd3(3)4]6þ superbowls hydro-
gen-bonding together in the solid state.
3
Figure 7. Electrospray mass spectrum of 3 and [Pd(MeCN)4](BF4)2 in
DMSO. Inset: Theoreticaland experimentalisotopicdistribution patterns
for the {Pd3(3)4(BF4)4}2þ peak.
[Pd3(3)4]6þ are quite different at þ81.0, þ87.2, and þ87.8°
for the central ligand and, for example, þ70.5, þ81.9, and
-116.7° for one of the ligands at the side of the bowl. The
species in solution. DOSY NMR studies of a 4:3 mixture
of ligand 3 and Pd(NO3)2 in d6-DMSO showed a band for
a major solution component with a diffusion coefficient
of 0.711 ꢀ 10-10 m2 s-1. A diffusion coefficient of 1.320 ꢀ
10-10 m2 s-1 was obtained for a d6-DMSO solution of
ligand 3 alone, giving a Dcomplex/Dligand ratio of 0.54. The
appearance of the double-quantum filtered correlation
spectroscopy, nuclear Overhauser effect spectrometry,
and rotating-frame Overhauser enhancement spectro-
scopy (ROESY) spectra and 1D nuclear Overhauser
effect experiments are also consistent with a single solu-
tion species.
Pd Pd distances within the open-bowl assembly are
3 3 3
˚
9.742, 10.144, and 10.424 A and are significantly shorter
˚
than the Pd Pd distances of ca. 16.6 A in the octahedral
3 3 3
assembly [Pd6(1)8]12þ. The depth of the bowl is 14.5 A, as
˚
defined by the distance between the OCH3 groups of the
upper rim of the bowl and the -(CH2)3- plane of the
central ligand.
Overall, the [Pd3(3)4]6þ assembly is a molecular host for
five molecules of DMSO, Figure 5. Four of these DMSO
guest molecules form host-guest interactions, each with
an individual ligand, in which the hydrophobic methyl
group is directed into the molecule cavity. Distances
between the methyl carbon atom of the guest and the
lower rim -(CH2)3- plane of the host ligand range from
ESI-MS gives evidence of the [Pd3(3)4]6þ assembly
existing in solution with a peak at m/z 1646.9 correspond-
ing to {Pd3(3)4(NO3)4}2þ (calcd 1647.4), Figure S4
(Supporting Information). However, there are also in-
tense peaks at m/z 1530.5 and 849.2, corresponding to
the mononuclear species {Pd(3)(NO3)}þ and {Pd(3)2-
(NO3)}þ and a variety of other higher species including
Pd2(3)2, Pd2(3)3, Pd3(3)3, and Pd4(3)4 fragments. This
indicates that a mixture of species is present in the
spectrometer in the gas phase. The largest mass fragment
was at m/z 2216.2, which corresponds to the species
{Pd6(3)8(NO3)9}3þ (calcd 2217.5). This may indicate that
a small amount of the octahedral cage exists in solution or
that the hydrogen-bonded dimer of [Pd3(3)4]6þ bowls
observed in the solid state also forms in solution or within
the mass spectrometer. The ESI-MS of a 3:4 solution of
[Pd(MeCN)4](BF4)2 and 3 in DMSO provides further
strong evidence for the formation of the [Pd3(3)4]6þ
assembly in solution, Figure 7. Here, the spectrum shows
strong peaks at m/z 1696.4 corresponding to a {Pd3(3)4-
(BF4)4}2þ (calcd 1696.9) and at m/z 1102.3 corresponding
to {Pd3(3)4(BF4)3}3þ (calcd 1102.3), as well as weak peaks
at m/z 3479.8 for {Pd3(3)4(BF4)5}þ (calcd 3480.9) and m/z
2291.2 for the larger species {Pd6(3)8(BF4)9}3þ (calcd
2291.6).
˚
3.83 to 4.15 A. The fifth DMSO forms a weak axial
˚
interaction with one of the Pd centers (Pd-O 3.173 A).
In the solid state, the [Pd3(3)4]6þ bowls dimerize
through C-H O interactions with C O distances
3 3 3
3 3 3
in the range 3.11-3.31 A, Figure 6. Each [Pd3(3)4]6þ bowl
is homochiral, but the two bowls of the dimer have
opposite chiralities. The six Pd positions within the
{[Pd3(3)4]}2 dimer form a distorted octahedron with sig-
nificant elongation along one axis and the ligands posi-
tioned above each octahedral face. Hence, the hydrogen-
bonded dimer is akin to a stella octangula with an oblate
distortion, and its two halves are held together by weak
interactions. Its long axis measures 2.7 nm, taken from
the center of the C positions within the opposite lower rim
-(CH2)3- groups, which is marginally shorter than the
˚
equivalent distance of 3 nm in [Pd6(1)8]12þ
.
The 1H NMR spectrum of a 3:4 mixture of Pd(NO3)2
and 3 in d6-DMSO is complicated, and it has not proved
1
possible to specifically assign the H signals, Figure S9
(Supporting Information). However, there is one major
species, and it is notable that it does not show the C3
symmetry of the ligand. This is consistent with the four
pyridyl arm environments observed in the crystal struc-
ture of [Pd3(3)4]6þ. There was no significant change in the
1H NMR spectrum upon heating the sample to 50 °C,
which is consistent with the existence of a single major
Tris(4-pyridylmethylamino)cyclotriguaiacylene 4 also
has a flexible linker group between the host core and 4-
pyridyl binding group and behaves similarly to 3 when
reacted with Pd(NO3)2. As for [Pd3(3)4]6þ, the 1H NMR
spectrum of a 3:4 mixture of Pd(NO3)2 and 4 in d6-DMSO

682 Inorganic Chemistry, Vol. 49, No. 2, 2010
Ronson et al.
is of low symmetry and cannot be assigned, Figure S12
(Supporting Information). DOSY NMR studies of a 4:3
mixture of ligand 4 and Pd(NO3)2 in d6-DMSO showed a
band for a major solution component with a diffusion
coefficient of 0.778 ꢀ 10-10 m2 s-1. A diffusion coefficient
of 1.332 ꢀ 10-10 m2 s-1 was obtained for a d6-DMSO
solution of ligand 4 alone, giving a Dcomplex/Dligand ratio of
0.58. This ratio is very similar to that observed for
[Pd3(3)4]6þ. ESI-MS gives clear evidence of the formation
of a [Pd3(4)4]6þ molecular bowl. The electrospray mass
spectrum of a DMSO solution of 4 with [Pd(MeCN)4]-
(BF4)2 in a 4:3 ratio was recorded. The major peaks in
the spectrum were a þ2 peak at m/z 1691.0 corresponding
to a {Pd3(4)4(BF4)4}2þ species (calcd 1690.5) and a þ3 peak
at m/z 1098.4 corresponding to {Pd3(4)4(BF4)3}3þ (calcd
1098.0), Figure S5 (Supporting Information).
Synthesis. Preparation of 4-(4-Pyridyl)benzoic Acid. Pre-
pared with minor modifications to literature methods.28 Pd-
(PPh3)4 (0.53 g, 0.59 mmol) was added to a degassed solution of
4-carboxybenzene boronic acid (1.458 g, 8.786 mmol) and
4-bromopyridine hydrochloride (1.708 g, 8.783 mmol) in a
0.4 M Na2CO3 solution (45 mL) and acetonitrile (45 mL). The
mixture was heated at 90 °C under N2 for 16 h. The hot
suspension was filtered. The filtrate was acidified with 1 M
HCl and the volume reduced by half in vacuo. The white solid
was collected by filtration to give 4-(4-pyridyl)benzoic acid as
1
the hydrochloride salt (1.86 g, 90%). H NMR (500 MHz, d6-
DMSO): δ 9.00 (2H, d, pyridyl H2, J = 6.5 Hz), 8.40 (2H, d,
pyridyl H3, J = 6.5 Hz), 8.14 ppm (4H, m, phenyl H2, H3). 13
C
NMR (75 MHz, d6-DMSO): δ 167.0, 153.5, 144.0, 139.1, 133.3,
130.6, 128.5, 124.3 ppm. Elem anal. calcd (%) for C12H9NO2-
(HCl): C, 61.16; H, 4.27; N, 5.94. Found: C, 60.85; H, 4.30; N,
5.95.
Preparation of 4-(4-Pyridyl)benzoyl Chloride Hydrochloride.
4-(4-Pyridyl)benzoic acid hydrochloride (1.83 g, 7.77 mmol) was
refluxed under N2 in thionyl chloride (10 mL) containing a few
drops of DMF for 24 h. The thionyl chloride was removed in
vacuo and the off-white solid washed with diethyl ether to give
4-(4-pyridyl)benzoyl chloride hydrochloride in quantitative
Conclusion
[Pd6L8]12þ metallo-supramolecular assemblies with a stella
octangula structure can be constructed using a number of
different CTG-based ligands with 4-pyridyl donor groups.
The overall size of the assembly and the size of the windows
on its exterior surface can therefore be manipulated to
provide a family of potential superhosts. Tris(4-pyridylmethy-
lamino)cyclotriguaiacylene and tris(4-pyridylmethylamino)
cyclotriguaiacylene were found to be an exception to this,
and their more flexible ether and methyl-amine linkages allow
a different binding mode to the metal, and a [Pd3L4]6þ open
bowl is formed. In any event, dimerization of the open bowls
through weak hydrogen bonding gives an overall assembly
akin to the stella octangula, at least in the solid state.
1
yield. H NMR (500 MHz, d6-DMSO): δ 9.04 (2H, d, pyridyl
H2, J = 6.5 Hz), 8.49 (2H, d, pyridyl H3, J = 6.5 Hz), 8.16 ppm
(4H, m, phenyl H2, H3). Elem anal. calcd (%) for C12H8NOCl-
(HCl): C, 56.72; H, 3.57; N, 5.51; Cl, 27.9. Found: C, 55.00; H,
3.55; N, 5.25; Cl, 28.0.
Preparation of 4-[4-(Hydroxymethyl)phenyl]pyridine. A solu-
tion of NaBH4 (190 mg, 5 mmol) in NaOH (0.2 M, 1.5 mL) was
added dropwise to a solution of 4-(4-pyridyl)benzaldehyde (837
mg, 4.57 mmol) in MeOH (10 mL) at 0 °C and the mixture
stirred for 2 h at room temperature. Aqueous Na2CO3 solution
(0.4 M, 5 mL) was added and the mixture extracted with CH2Cl2
(3 ꢀ 50 mL). The combined organic layers were washed twice
with water and dried over MgSO4, and the solvent was evapo-
rated. The crude product was purified by column chromatog-
raphy (silica, 0-10% MeOH in CH2Cl2) to give 4-[4-(hydro-
xymethyl)phenyl]pyridine as an off-white powder (608 mg,
72%). 1H NMR (500 MHz, CDCl3): δ 8.65 (2H, d, pyridyl
H2, J = 6.0 Hz), 7.65 (2H, d, phenyl H3, J = 8.1 Hz), 7.48-7.30
Experimental Section
Cyclotriguaiacylene,25 cyclotriphenolene,24 3,8,13-triami-
no-2,7,12-trimethoxy-10,15-dihydro-5H-tribenzo[a,d,g]cyclo-
nonene hydrochloride (aCTG.3HCl),26 and ligand tris(4-pyri-
dylmethylamino)cyclotriguaiacylene, 4,9 were prepared accord-
ing to literature methods. Electrospray mass spectra were
collected at the University of Huddersfield and were measured
on a Bruker MicroTOF-Q instrument in the positive ion mode.
Samples of the complexes were prepared at concentrations of ca.
5 mM in DMSO and analyzed by direct infusion using a Cole
Parmer syringe pump at a flow rate of 3 mL/min. Spectra were
acquired over an m/z range of 50-4000; several scans were
averaged to provide the final spectrum. The charge of each
species (nþ) was confirmed by the spacing between the isotope
components, which were 1/n mass units. Unless otherwise
stated, reagents were obtained from commercial sources and
used as received. Elemental analyses were performed by the
School of Chemistry’s service at the University of Leeds.
(4H, m, phenyl H2 and pyridyl H3), 4.78 ppm (2H, s, CH2). 13
C
NMR (75 MHz, CDCl3): δ 150.6, 148.5, 142.5, 137.7, 128.0,
127.6, 122.0, 65.1 ppm. Elem anal. calcd (%) for C12H11NO-
(H2O)0.1: C, 77.06; H, 6.04; N, 7.49. Found: C, 76.80; H, 5.95; N,
7.15. All other data matched those previously reported.29
Preparation of 4-[4-(Chloromethyl)phenyl]pyridine Hydro-
chloride. Thionyl chloride (1 mL, 14 mmol, excess) was added
to a solution of 4-[4-(hydroxymethyl)phenyl]pyridine (608 mg,
3.28 mmol) in dry CHCl3 (50 mL) at room temperature. The
mixture was stirred overnight, and the solvent removed in
vacuo. The crude product was dried in vacuo for 2 h and used
without further purification.
Preparation of Tris(isonicotinoyl)cyclotriphenolene (2). Cyclo-
triphenolene (98 mg, 0.31 mmol) was dissolved in dry THF
(30 mL) under a N2 atmosphere and cooled to -78 °C in a dry
ice/acetone bath. Triethylamine (0.55 mL) was added to the
reaction, which was stirred for 30 min. Isonicotinoyl chloride
hydrochloride (192 mg, 1.08 mmol) was added to the solution,
which was stirred at -78 °C for 1 h, and then refluxed for 2 days.
The solution was taken to dryness in vacuo and the residue
triturated with ethanol to give 2 as a white solid (102 mg 52%).
Mp 248-241 °C. 1H NMR (500 MHz, CDCl3): δ 8.78 (6H, d,
DOSY NMR Measurements. DOSY NMR measurements
were measured in d6-DMSO on a Varian Inova 500 MHz
spectrometer operating under regulated temperature conditions
(20 °C), with a 5 mm probe. The pulse sequence employed was a
bipolar pulse pair simulated echo operating in the ONESHOT
experiment. Additional parameters: number of different gradi-
ent levels, 15; gradient stabilization delay, 0.002 s; gradient
length, 0.004 s; diffusion delay, 0.06 s; relaxation delay, 10 s;
Kappa (unbalancing factor), 0.2. Spectra were recorded for
4 mM solutions of the ligand with added Pd(NO3)2 2H2O (3:4
3
metal/ligand ratio). Hydrodynamic radii were estimated using a
Stokes-Einstein relationship.
(29) Blanco, V.; Abella, D.; Pia, E.; Platas-Iglesias, C.; Peinador, C.;
Quintela, J. M. Inorg. Chem. 2009, 48, 4098–4197.
(30) (a) Kamiya, N.; Tominaga, M.; Sato, S.; Fujita, M. J. Am. Chem.
Soc. 2007, 129, 3816–3817. (b) Allouche, L.; Marquis, A.; Lehn, J.-M. Chem.;
Eur. J. 2006, 12, 7520–7525.
(28) Gong, Y.; Pauls, H. W. Synlett. 2000, 829–831.

Article
Inorganic Chemistry, Vol. 49, No. 2, 2010 683
pyridyl H2, J = 5.6 Hz), 7.91 (6H, d, pyridyl H3, J = 5.6 Hz),
7.38 (3H, d, aryl CH), 7.19 (3H, dd, aryl CH), 6.95 (3H, dd, aryl
CH), 4.85 (3H, d, CH2, J = 13.7 Hz), 3.76 ppm (3H, d, CH2,
J = 13.7 Hz). 13C NMR (75 MHz, CDCl3): δ 162.7, 149.8, 148.3,
139.7, 135.9, 135.8, 130.4, 122.2, 121.6, 119.2, 35.7 ppm. HR MS
(ESþ): m/z 634.1969 (MHþ). Calcd for C39H28N3O6 634.1973.
Elem anal. calcd (%) for C39H27N3O6(H2O): C, 71.88; H, 4.49;
N, 6.45. Found: C, 72.35; H, 4.85; N, 6.25.
(5 ꢀ 100 mL) and dried (MgSO4) and the solvent removed in
vacuo. The residue was purified by column chromatography
(silica, 0-5% MeOH in CH2Cl2) to afford 6 as a white powder
(357 mg, 68%). Mp 143-145 °C. 1H NMR (500 MHz, CDCl3):
δ 8.66 (6H, d, pyridyl H2, J = 5.1 Hz), 7.64 (6H, d, phenyl H3,
J = 8.1 Hz), 7.48-7.55 (12H, m, phenyl H2 and pyridyl H3),
6.86 (3H, s, aryl CH), 6.71 (3H, s, aryl CH), 5.16 (6H, m,
CH2-O), 4.72 (3H, d, CTG CH2, J = 13.9 Hz), 3.67 (9H, s,
CH3), 3.49 ppm (3H, d, CTG CH2, J = 13.9 Hz). 13C NMR (75
MHz, CDCl3): δ 150.4, 148.5, 147.8, 147.0, 138.6, 137.7, 132.8,
131.8, 127.7, 127.2, 121.5, 116.2, 113.9, 71.1, 56.2, 36.5 ppm. HR
MS (ESþ): m/z 910.3824 (MHþ). Calcd for C60H52N3O6,
910.3851. Elem anal. calcd (%) for C60H51N3O6(H2O): C,
77.65; H, 5.76; N, 4.53. Found: C, 77.95; H, 5.75; N, 4.50.
Preparation of Tris[4-(4-pyridyl)benzylamino]cyclotriguaia-
Preparation of Tris(4-pyridylmethyl)cyclotriguaiacylene (3).
NaH (60% dispersion in mineral oil, 200 mg, 4.92 mmol) was
added in small portions to a solution of CTG (200 mg, 0.490
mmol) in dry DMF (7 mL) and the mixture stirred for 30 min
under N2. A solution of 4-bromomethylpyridine (2.45 mmol) in
dichloromethane (30 mL) was added by syringe and the mixture
stirred at room temperature for 48 h. Water (100 mL) and
CH2Cl2 (100 mL) were added and the aqueous layer washed
with CH2Cl2 (2 ꢀ 100 mL). The combined organic layers were
washed with water (5 ꢀ 100 mL), dried (MgSO4), and evapo-
rated in vacuo. The residue was purified by column chromatog-
raphy (silica, 5% MeOH in CH2Cl2) to afford 3 as an off-white
powder (262 mg, 79%). [4-Bromomethylpyridine was freshly
prepared before use by the following method: A saturated
aqueous Na2CO3 solution was added dropwise to a stirred
cylene (7). A mixture of aCTG 3HCl (445 mg, 0.864 mmol),
3
4-(4-pyridyl)benzaldehyde (500 mg, 2.73 mmol), and triethyla-
mine (1.75 mL) in ethanol (50 mL) was refluxed for 3 h to give a
yellow solution. The reaction mixture was cooled to room
temperature and the solvent removed in vacuo to give a bright
yellow solid. This was dissolved in a 1:1 mixture of dichloro-
methane and ethanol (40 mL), sodium borohydride (500 mg,
13.1 mmol) was added in small portions and the reaction
mixture stirred at room temperature for 72 h. The solvent was
removed in vacuo and the solid taken up in dichloromethane
(150 mL), the chlorinated extract washed with water (50 mL)
and then dried over MgSO4. The solvent was removed in vacuo
and the crude product purified by column chromatography
(silica, 5% MeOH in CH2Cl2 with a few drops of Et3N) to give
slightly impure 7 (∼90% purity by NMR). Yield: 382 mg, 48%.
All further attempts to purify the product were unsuccessful.
HR MS (ESþ): m/z 907.4308 (MHþ). Calcd for C60H55N6O3,
907.4330. 1H NMR (500 MHz, CDCl3): δ 8.65 (6H, d, pyridyl
H2, J = 4.9 Hz), 7.61 (6H, d, phenyl H3, J = 8.1 Hz), 7.50 (6H,
d, pyridyl H3, J = 4.9 Hz), 7.47 (6H, d, phenyl H2, J = 8.1 Hz),
6.50 (3H, s, aryl CH), 6.47 (3H, s, aryl CH), 4.68 (3H, d, CTG
CH2, J = 13.7 Hz), 4.41 (6H, s, br, NHCH2), 3.49 (9H, s, CH3),
3.37 ppm (3H, d, CTG CH2, J = 13.7 Hz).
solution of 4-bromomethylpyridine HBr (620 mg, 2.45 mmol)
3
in distilled water (20 mL) at 0 °C to reach ∼pH 7. Then,
4-bromomethylpyridine was extracted with CH2Cl2 (30 mL),
dried over MgSO4, and filtered. The filtrate was used without
further purification.] Mp 138-143 °C. 1H NMR (500 MHz,
CDCl3): δ 8.60 (6H, d, pyridyl H2, J = 6 Hz), 7.34 (6H, d,
pyridyl H4, J = 6 Hz), 6.78 (3H, s, aryl CH), 6.66 (3H, s, aryl
CH), 5.11 (6H, s, CH2-O), 4.70 (3H, d, CTG CH2, J = 13.8
Hz), 3.71 (9H, s, CH3) 3.46 ppm (3H, d, CTG CH2, J = 13.8
Hz). 13C NMR (75 MHz, CDCl3): δ 150.0, 148.5, 146.7, 146.5,
133.2, 131.6, 121.2, 116.3, 113.7, 70.0, 56.1, 36.5 ppm. HR MS
(ESþ): m/z 682.2932 (MHþ). Calcd for C42H40N3O6, 682.2912.
Elem anal. calcd (%) for C42H39N3O6(H2O)0.5: C, 73.03; H,
5.84; N, 6.08. Found: C, 72.95; H, 6.05; N, 5.75.
Preparation of Tris[4-(4-pyridyl)benzoyl]cyclotriguaiacylene
(5). Cyclotriguaiacylene (153 mg, 0.375 mmol) was dissolved
in dry THF (30 mL) under a N2 atmosphere and cooled to -78 °C
in a dry ice/acetone bath. Triethylamine (0.65 mL) was added to
the reaction, which was stirred for 30 min. 4-(4-Pyridyl)benzoyl
chloride hydrochloride (320 mg, 1.26 mmol) was added to the
solution, which was stirred at -78 °C for 1 h and then at room
temperature for 2 days. A further portion of 4-(4-pyridyl)-
benzoyl chloride hydrochloride (320 mg, 1.26 mmol) was added
and the mixture stirred for a further 2 days. The solution was
taken to dryness in vacuo and the residue triturated with ethanol
to give 5 as a white solid (287 mg, 80%). Mp 255-260 °C
Reaction of 2 with Pd(NO3)2. Pd(NO3)2 2H2O (5 mg, 0.019
3
mmol) was added to a solution of tris(isonicotinoyl)cyclo-
triphenolene (15 mg, 0.024 mmol) in DMSO (1.5 mL). Acetone
diffusion into the solution gave heavily solvated colorless crys-
tals of [Pd6(2)8](NO3)12, which were isolated by filtration and
dried in vacuo. Yield: 14 mg. 1H NMR (500 MHz, d6-DMSO): δ
9.54 (6H, d, pyridyl H2), 8.27 (6H, d, pyridyl H3), 7.56 (3H, m,
aryl CH), 7.39 (3H, s, br, aryl CH), 6.89 (3H, m, aryl CH), 4.85
(3H, s, br, CH2), 3.76 ppm (3H, s, br, CH2). IR (solid state): ν
3106 (w), 3056 (w), 3022 (w), 2916 (w), 1750 (s), 1654 (w), 1621
(w), 1586 (w), 1564 (w), 1494 (m), 1430 (m), 1343 (m), 1371 (s,
NO3-), 1234 (s), 1186 (m), 1148 (m), 1106 (m), 1084 (w), 1057
(m), 1020 (s), 951 (m), 862 (w), 829 (w), 763 (w), 753 (w), 693 (m),
620 (w), 577 cm-1 (w). ES MS (DMSO solution): m/z 2087.6
{Pd6(2)8(NO3)9}3þ (calcd 2088.3), 1550.7 {Pd6(2)8(NO3)8}4þ
(calcd 1550.7), 1434.3 {Pd(2)2(NO3)}þ (calcd 1434.3), 1233.6
{Pd3(2)3(NO3)4}2þ (calcd 1233.6), 801.1 {Pd(2)(NO3)}þ (calcd
801.1). The crystals of [Pd6(2)8](NO3)12 n(DMSO) m(H2O)
1
(decomposition). H NMR (500 MHz, CDCl3): δ 8.73 (6H, d,
pyridyl H2, J = 5.9 Hz), 8.31 (6H, d, phenyl H3, J = 8.4 Hz),
7.77 (6H, d, phenyl H2, J = 8.4 Hz), 7.56 (6H, d, pyridyl H3, J =
5.9 Hz), 7.20 (3H, s, aryl CH), 6.98 (3H, s, aryl CH), 4.86 (3H, d,
CTG CH2, J = 13.8 Hz), 3.82 (9H, s, CH3), 3.71 ppm (3H, d,
CTG CH2, J = 13.8 Hz). 13C NMR (75 MHz, CDCl3): δ 164.2,
150.5, 150.0, 147.1, 143.1, 138.6, 138.1, 131.6, 131.1, 130.0,
127.2, 124.1, 121.7, 114.3, 56.3, 36.6 ppm. HR MS (ESþ): m/z
952.3232 (MHþ). Calcd for C60H46N3O9, 952.3229. Elem anal.
calcd (%) for C60H45N3O9(H2O): C, 74.29; H, 4.88; N, 4.33.
Found: C, 74.45; H, 4.75; N, 4.20.
3
3
were highly solvated, and satisfactory microanalytical results
could not be obtained.
Preparation of [Pd3(3)4](NO3)6 n(DMSO) m(H2O). Pd-
3
3
(NO3)2 2H2O (12 mg, 0.045 mmol) was added to a solution of
3
Preparation of Tris{4-(4-pyridyl)benzyl}cyclotriguaiacylene
(6). NaH (60% dispersion in mineral oil, 470 mg, 11.8 mmol)
was added in small portions to a solution of CTG (236 mg, 0.578
mmol) in dry DMF (7 mL) and the mixture stirred for 30 min.
Solid 4-[4-(chloromethyl)phenyl]pyridine hydrochloride (694
mg, 2.89 mmol) was added and the mixture stirred at room
temperature for 48 h. Water (100 mL) and CH2Cl2 (100 mL)
were added, and the aqueous layer washed with CH2Cl2 (2 ꢀ 100
mL). The combined organic layers were washed with water
tris(4-pyridylmethyl)cyclotriguaiacylene (40 mg, 0.059 mmol) in
DMSO (5 mL). Acetone diffusion into the solution gave heavily
solvated colorless crystals of [Pd3(3)4](NO3)6 n(DMSO)
m(H2O) which were isolated by filtration and dried in vacuo
(33 mg). IR (solid state): ν 3097 (w), 2983 (w), 2932 (w), 2852 (w),
1655 (w), 1609 (m), 1508 (s), 1479 (w), 1434 (m), 1397 (w), 1339
(s, NO3-), 1275 (m), 1257 (s), 1214 (m), 1198 (m), 1144 (m), 1086
(m), 1063 (w), 1021 (s), 994 (w), 948 (m), 928 (w), 892 (w), 848
(m), 829 (w), 813 (m), 741 (m), 705 (w), 665 (w), 647 (w), 618 (m),
3
3

684 Inorganic Chemistry, Vol. 49, No. 2, 2010
Ronson et al.
Table 1. Details of Data Collections and Structure Refinements for X-Ray Structures
2
3a
3b
5 31/3MeCN 1/3H2O
[Pd3(3)4](NO3)6
3
3
formula
Mr
C39H27N3O6
633.64
C42H39N3O6
681.76
0.50 ꢀ 0.15 ꢀ 0.08
monoclinic
P2(1)/n
16.2129(19)
7.9897(9)
27.423(3)
90
103.168(6)
90
3458.8(7)
4
1.309
0.088
1.34 to 31.53
67963
C42H39N3O6
681.76
0.12 ꢀ 0.10 ꢀ 0.05
rhombohedral
R3
62.828(4)
62.828(4)
9.8070(13)
90
90
120
33525(5)
36
1.216
0.082
1.12 to 25.00
157844
C66.67H55.67 N6.33O9.33
1094.84
0.50 ꢀ 0.40 ꢀ 0.20
trigonal
P31c
19.3666(4)
19.3666(4)
28.7185(16)
90
90
120
9328.2(6)
6
1.169
C184H209N15O43.5Pd8S3
4274.04
0.15 ꢀ 0.10 ꢀ 0.06
monoclinic
C2/c
43.49(3)
28.10(3)
40.83(4)
90
100.545(15)
90
49058(79)
8
1.157
0.659
3.19 to 17.75
70813
cryst size [mm]
cryst syst
space group
0.20 ꢀ 0.18 ꢀ 0.17
triclinic
P1
˚
a [A]
4.6791(4)
14.1061(10)
24.9786(18)
74.971(4)
88.487(4)
80.645(4)
1570.9(2)
2
1.340
0.092
0.84 to 26.00
26374
˚
b [A]
˚
c [A]
R [deg]
β [deg]
γ [deg]
3
˚
V [A ]
Z
F
calcd [g cm-3
]
μ [cm-1
θ range [deg]
data collected
]
0.079
1.21 to 25.00
165090
unique data, Rint
obs. data [I > 2σ (I )]
data/restraints/params
R1 [obs. data]
wR2 [all data]
absolute structure parameter
GOF
6142, 0.0299
4400
6142/0/433
0.0437
0.1312
11517, 0.0290
8317
11517/0/463
0.0464
0.1516
13127, 0.0928
7986
13127/0/925
0.0598
0.2249
10939, 0.0346
9211
10939/1/718
0.0763
0.2447
15312, 0.1208
9929
15312/48/1123
0.1122
0.3267
0.4(14)
1.091
0.978
1.039
1.080
1.071
1
531 cm-1 (w). ES MS (DMSO solution): m/z 2216.2 {Pd6(3)8-
(NO3)9}3þ (calcd 2216.9), 1762.4 {Pd2(3)2(NO3)3}þ and {Pd4(3)4-
(NO3)6}2þ (calcd 1762.3), 1646.9 {Pd3(3)4(NO3)4}2þ (calcd
1646.9), 1530.5 {Pd(3)2(NO3)}þ (calcd 1530.5), 1306.3 {Pd3(3)3-
(NO3)4}2þ (calcd 1305.8), 1190.8 {Pd2(3)3(NO3)2}2þ (calcd 1190.8),
849.2 {Pd(3)(NO3)}þ (calcd 849.2). Microanalytical results indicate
the crystals were highly solvated. Example of elemental analysis,
calcd (%) for Pd3(C42H39N3O6)4(NO3)6(C2H6SO)12(H2O)6: C,
51.66; H, 5.42; N, 5.65; S, 8.62. Found: C, 51.60; H, 5.55; N, 5.75;
S, 8.45.
DMSO solution with a 3:4 metal/ligand ratio. H NMR (500
MHz, d6-DMSO): δ 9.35 (6H, s, br), 8.16 (6H, s, br), 7.91 (6H,
d), 7.53 (6H, d), 7.25 (3H, s, aryl CH), 7.17 (3H, s, aryl CH), 5.07
(3H, s, br), 4.51-4.54 (6H, m), 3.50-3.53 ppm (9H, m, CTG
CH2 and CH3). ES MS (DMSO solution): m/z 2826.2 {Pd6(6)8-
(NO3)9}3þ (calcd 2825.4), 2103.6 {Pd6(6)8(NO3)8}4þ (calcd
2103.6), 1987.7 {Pd(6)2(NO3)}þ and {Pd2(6)4(NO3)2}2þ (calcd
1986.6), 1670.5 {Pd6(6)8(NO3)7}5þ (calcd 1670.5), 1533.0 {Pd2-
(6)3(NO3)2}2þ and {Pd4(6)6(NO3)4}4þ (calcd 1533.5), 1382.1
{Pd6(6)8(NO3)6}6þ (calcd 1381.7), 1077.3 {Pd(6)(NO3)}þ and
{Pd2(6)2(NO3)2}2þ (calcd 1077.3), 1002.0 {Pd2(6)3(NO3)}3þ
(calcd 1001.6), 962.4 {Pd(6)2}2þ (calcd 962.3). Crystals were
highly solvated, and satisfactory microanalysis could not be
obtained.
Reaction of 5 with Pd(NO3)2. Pd(NO3)2 2H2O (4 mg, 0.015
3
mmol) was added to a solution of tris[4-(4-pyridyl)benzoyl]-
cyclotriguaiacylene (15 mg, 0.016 mmol) in DMSO (2 mL).
Acetone diffusion into the solution gave heavily solvated color-
less crystals of [Pd6(5)8](NO3)12, which were isolated by filtra-
tion and dried in vacuo (15 mg). Crystals of [Pd6(5)8](NO3)12 can
also be isolated from acetone diffusion into a DMSO solution
with a 3:4 metal/ligand ratio. 1H NMR (500 MHz, d6-DMSO): δ
9.46 (6H, s, br, pyridyl H2), 8.22 (6H, s, br), 8.17 (6H, s, br), 8.10
(6H, s, br), 7.49 (3H, s, aryl CH), 7.31 (3H, s, aryl CH), 4.91(3H,
s, br, CTG CH2), 3.45 ppm (12H, m, CTG CH2 and CH3). IR
(solid state): ν 3007 (w), 2918 (w), 1735 (s), 1643 (m), 1615 (s),
1508 (s), 1466 (w), 1436 (m), 1403 (m), 1329 (s, NO3-), 1266 (s),
1206 (m), 1179 (s), 1139 (m), 1092 (m), 1062 (w), 1013 (s), 951 (s),
901 (w), 871 (w), 836 (m), 767 (m), 736 (w), 704 (m), 623 (w),
567 (w), 530 (w), 510 cm-1 (w);. ES MS (DMSO solution):
m/z 2187.7 {Pd6(5)8(NO3)8}4þ (calcd 2187.5), 1737.8 {Pd6(5)8-
(NO3)7}5þ (calcd 1737.6), 1596.4 {Pd2(5)3(NO3)2}2þ and {Pd4-
(5)6(NO3)4}4þ (calcd 1596.4), 1437.6 {Pd3(5)4(NO3)3}3þ and
{Pd6(5)8(NO3)6}6þ (calcd 1437.6), 1361.0 {Pd2(5)4(NO3)}3þ
(calcd 1360.7), 1119.2 {Pd(5)(NO3)}þ (calcd 1119.2), 1062.2
{Pd3(5)4(NO3)2}4þ (calcd 1062.7). The crystals of [Pd6(5)8]-
(NO3)12 were highly solvated. Example of elemental analysis,
calcd (%) for Pd6(C60H45N3O9)8(NO3)12(C2H6SO)8(H2O)25: C,
59.14; H, 4.59; N, 5.01; S, 2.54. Found: C, 59.10; H, 4.30; N,
4.70; S, 2.40; %.
X-Ray Crystallography. Crystals were mounted under oil on a
glass fiber and X-ray diffraction data collected at 150(1) K with
either Mo KR radiation (λ = 0.71073 A) using a Bruker Nonius
X-8 diffractometer with ApexII detector and FR591 rotating
anode generator, or with synchrotron radiation at STFC Dares-
˚
˚
bury laboratory station 16.2SMX (λ = 0.7977 A). Data sets
were corrected for absorption using a multiscan method, and
structures were solved by direct methods using SHELXS-9731
and refined by full-matrix least-squares on F2 by SHELXL-97,32
interfaced through the program X-Seed.33 In general, all non-
hydrogen atoms were refined anisotropically, and hydrogen
atoms were included as invariants at geometrically estimated
positions, unless specified otherwise. Details of data collections
and structure refinements are given in Table 1. Crystallographic
data have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publications CCDC 742268-
742272.
Crystals of [Pd3(3)4](NO3)6 n(DMSO) m(H2O) were poorly
3
3
diffracting, even with synchrotron radiation, and only data with
2θ e 45° were used in the final refinement. SAME and SADI
restraints were applied to the poorly ordered DMSO solvent
molecules and nitrate anions to ensure a stable refinement.
Hydrogen atoms were included as invariants at geometrically
Reaction of 6 with Pd(NO3)2. Pd(NO3)2 2H2O (4 mg, 0.015
3
mmol) was added to a solution of tris{4-(4-pyridyl)benzyl}-
cyclotriguaiacylene (15 mg, 0.016 mmol) in DMSO (2 mL).
Acetone diffusion into the solution gave a small amount of
colorless crystals. The product was not isolated in sufficient
quantities for solid-state characterization. Crystals of [Pd6(6)8]-
(NO3)12 can also be isolated from acetone diffusion into a
€
€
(31) Sheldrick, G. M. SHELXS-97; University of Gottingen: Gottingen,
Germany, 1990.
€
€
(32) Sheldrick, G. M. SHELXL-97; University of Gottingen: Gottingen,
Germany, 1997.
(33) Barbour, L. J. J. Supramol. Chem. 2003, 1, 189–191.

Article
Inorganic Chemistry, Vol. 49, No. 2, 2010 685
estimated positions, aside from those of a disordered DMSO
molecule and water molecules, which were excluded. Only three
of the expected six anions could be located, and these were
refined with isotropic displacement parameters. The
SQUEEZE34 function was applied to remove areas of diffuse
electron density, which could not be modeled, which presum-
ably accounts for the remaining anions and severely disordered
solvent molecules.
Acknowledgment. We thank the EPSRC for their financial
support of this research, and thank STFC Daresbury laboratory
for access to microdiffraction facilities, Ian Blakeley for per-
forming elemental analyses, and Tanya Marinko-Covell for
some mass spectrometry measurements.
Supporting Information Available: ESI-MS spectra; 1-D,
DOSY, and ROESY NMR spectra; and crystallographic in-
formation files (CIF) are available. This information is available
free of charge via the Internet at http://pubs.acs.org.
(34) Spek, A.; van der Sluis, P. Acta Crystallogr., Sect. A 1990, 46, 194.