Metal template synthesis of a tripodal tris(bipyridyl) receptor that encapsulates a proton and an iron(ii) centre in a pseudo cage

Article abstract of DOI:10.1071/CH11501

The Fe(ii) template synthesis of the first member of a new category of tripodal tris-bipyridine ligands incorporating a nitrogen bridgehead is reported. The X-ray structure of the reaction product shows that the ligand adopts a pseudo cage-like structure that encapsulates both a proton and an Fe(ii) ion in its cavity. The complex shows an extended helical arrangement that is effectively 'capped' at its open end by a hydrogen bonded PF6-counter ion that is symmetrically aligned with the 3-fold axis of the helix. A 1H NMR study demonstrated that the encapsulated proton can be reversibly exchanged under acid/base conditions in CD3CN.

Full text of DOI:10.1071/CH11501

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2012, 65, 1371–1376
Full Paper
http://dx.doi.org/10.1071/CH11501
Metal Template Synthesis of a Tripodal Tris(bipyridyl)
Receptor that Encapsulates a Proton and an Iron(II)
Centre in a Pseudo Cage*
A
A E
,
B
Christopher R. K. Glasson, George V. Meehan, Cherie A. Motti,
Jack K. Clegg,
C D
,
A
C E
,
Murray S. Davies, and Leonard F. Lindoy
A
School of Pharmacy and Molecular Sciences, James Cook University, Townsville,
Qld 4814, Australia.
B
The Australian Institute of Marine Science, Townsville, Qld 4810, Australia.
C
School of Chemistry, F11, The University of Sydney, NSW 2006, Australia.
D
Department of Chemistry, The University of Cambridge, Lensfield Rd,
Cambridge, CB2 1EW, UK.
E
Corresponding authors. Email: George.Meehan@jcu.edu.au;
lindoy@chem.usyd.edu.au
The Fe(II) template synthesis of the first member of a new category of tripodal tris-bipyridine ligands incorporating a
nitrogen bridgehead is reported. The X-ray structure of the reaction product shows that the ligand adopts a pseudo cage-
like structure that encapsulates both a proton and an Fe(II) ion in its cavity. The complex shows an extended helical
arrangement that is effectively ‘capped’ at its open end by a hydrogen bonded PFꢀ6 counter ion that is symmetrically
aligned with the 3-fold axis of the helix. A 1H NMR study demonstrated that the encapsulated proton can be reversibly
exchanged under acid/base conditions in CD3CN.
Manuscript received: 22 December 2011.
Manuscript accepted: 29 January 2012.
Published online: 7 March 2012.
Introduction
of an unsymmetrical mono-aldehyde analogue of 2 might be
expected to give rise to fac- and mer-isomers of the intermediate
tris-ligand, mono-aldehyde derivative complex. Clearly if both
isomers are initially formed, it was of interest to probe whether
isomerization, possibly associated with dynamic covalent imine
chemistry,[3] might occur to yield the resulting pseudo-cage
product in reasonable yield. To this end, Fe(II) was chosen as the
templating metal because of its well established propensity to
yield strong, low-spin (diamagnetic) complexes incorporating a
tris-bipyridyl coordination environment[4] and thus allowing
In a previous study our group investigated the metal template
synthesis of Mn(II), Co(II), Fe(II), and Cu(II) complexes of fully
closed tris-bipyridyl cages of type 1 (Fig. 1) that adopt extended
helical structures on binding to the metal ion.[1] The encapsu-
lation procedure involved a series of reductive amination reac-
tions involving three molecules of the dialdehyde precursor of
type 2 (Fig. 1) and ammonium acetate (as a source of ammonia),
together with sodium cyanoborohydride, as reactants. The pro-
cedure was carried out either as a one-pot reaction in the pres-
ence of the metal ion or in a two-step fashion involving initial
isolation of the corresponding octahedral [ML3]2þ (L ¼ 2) pre-
cursor as its hexafluorophosphate salt followed by reaction with
excess ammonium acetate and sodium cyanoborohydride.
As an extension of this study we were interested in applying
the above general procedure to the synthesis of the correspond-
ing Fe(II) complex of the related tripodal ligand 3 (Fig. 2), hence
giving rise to a pseudo-cage derivative in which the expected
triple helix would have one end ‘open’; in part, a motivation for
this study was to act as a foundation for further synthesis aimed
at producing new anion receptors related to those reported
previously based on tris-bipyridine ligand derivatives.[2] Never-
theless, it was realized that the synthesis of a complex of the
above type could well be less than straight forward since the use
1
ready investigation of the reaction outcome by H NMR. The
moderate kinetic inertness associated with the use of low-spin
Fe(II) (d6 electronic configuration) was not expected to signifi-
cantly impede such a rearrangement within the timescale of the
synthetic procedure.
Results and Discussion
Ligand Precursors
An outline of the synthesis of the mono-aldehyde precursor 6
starting from 5,50-dimethyl-2,20-bipyridine is given in
Scheme 1; precursor 5-trimethylsilylmethyl-50-methyl-2,20-
bipyridine (4) was prepared by a literature procedure.[5] Silane 4
was then converted to 5-chloromethyl-50-methyl-2,20-bipyridine
*Dedicated to Roger Bishop – a fine supramolecular chemist.
Journal compilation Ó CSIRO 2012
www.publish.csiro.au/journals/ajc

1372
C. R. K. Glasson et al.
(5) in 85% yield by reaction with Cl3CCCl3 and CsF.[6]
A Williamson condensation of 5 with salicylaldehyde in dimethyl-
formamide resulted in the target mono-aldehyde 6 whose 1H NMR
spectrum is given in Fig. 3a.
Metal-Template Preparation of Pseudo Cage 3
The protonated cation, [Fe(HL)3]3þ (L ¼ 6) (see below), was
prepared in a one pot procedure involving the initial interaction
of three equivalents of mono-aldehyde 6 with Fe(BF4)2ꢁ6H2O in
refluxing acetonitrile. To monitor the progress of the reaction,
a small aliquot of the reaction solution was removed and the
product isolated as its PF6ꢀ salt; the 1H NMR spectrum (Fig. 3b)
of this product in CD3CN was consistent with the formation of
[FeL3](PF6)2 (L ¼ 6) as a mixture of its mer/fac isomers. The
latter is most clearly illustrated by the observation of four signals
R
R
1
N
O
O
N
O
O
for the aldehyde protons of 6 in the H NMR spectrum of the
product (see expanded region of the spectrum in Fig. 3b).
Reductive amination of the bulk solution then involved
addition of NH4OAc followed by excess NaCNBH3 to the
stirred red solution at 08C for 2 h; the solution was then allowed
to warm to room temperature and stirring was continued
overnight. The product was isolated as its PFꢀ6 salt and further
purified by chromatography on silica gel and the product
reisolated as its PF6ꢀ salt to afford [Fe(HL)3](PF6)3ꢁCH3CN
(L ¼ 3) as a purplish red crystalline solid in 55 % yield. The
microanalysis and HRMS data are in accord with the above
N
R
N
N
O
N
O
R
N
N
R
R
R
R
1; R ϭ H, t-Bu
1
formulation (see Experimental). As anticipated, the H NMR
spectrum of this product was markedly simplified (see Fig. 3c)
relative to the mono-aldehyde precursor complex, [FeL3]2þ
(L ¼ 6) and is again consistent with the formation of an Fe(II)
complex of the above stoichiometry. In particular, the spectrum
shows AB spin systems centred at 3.97 and 5.07 ppm in the
aliphatic region that correspond to proton resonances for meth-
ylene groups adjacent to the nitrogen bridgehead atom and the
benzyl ethers, respectively. The 1H NMR spectrum of the
deprotonated form of the above complex, namely [Fe(L)]
(PF6)2 (L ¼ 3) is shown in Fig. 3d. Deprotonation was achieved
by treatment of the NMR sample of [Fe(HL)](PF6)3 (L ¼ 3) in
CD3CN with K2CO3; interestingly, no colour change was
observed on deprotonation. The aforementioned AB spin system
peaks are significantly further resolved in the 1H NMR spectrum
of the deprotonated species, consistent with a decreased equiva-
lence of the respective geminally related protons. As might be
expected, proton resonances corresponding to the methylene
groups adjacent to the nitrogen bridgehead atom are now shifted
upfield by 0.82 ppm to be centred at 3.15 ppm.
O
N
N
O
O
O
2; R ϭ H, t-Bu
Fig. 1. Structures of compounds 1 and 2.
N
N
N
O
O
N
N
N
O
N
1H NMR evidence also indicates that reprotonation of the
above species is readily achieved. Thus addition of two equiva-
lents of trifluoroacetic acid to the above NMR solution results in
3
Fig. 2. Structure of compound 3.
(i) LDA
(ii) Me3SiCl
N
N
Me3Si
N
N
4
Cl3CCCl3, CsF
in CH3CN
Salicylaldehyde
K2CO3
ϩ
O
N
N
in DMF
N
N
Cl
6
5
O
Scheme 1. Synthesis of precursors for pseudo cage 3.

Template Synthesis of a Tris(bipyridyl) Receptor
1373
regeneration of the spectrum of the protonated [Fe(HL)3]3þ
species. The 1H NMR spectral differences between the methy-
lene and aromatic resonances in [Fe(HL)3](PF6)3 (L = 3) and
[Fe(L)3](PF6)2 (L ¼ 3) are in keeping with a significant confor-
mational rearrangement of the tertiary amine capping unit
occurring in generating the latter species.
X-Ray Structure and Modelling Studies
Slow diffusion of diethyl ether into an acetonitrile solution of the
product obtained from the template synthesis yielded purplish-
red crystals suitable for X-ray diffraction. The structure deter-
mination of [Fe(HL)](PF6)3 (L ¼ 3) (Fig. 4) confirmed that
(a)
(b)
R-CH3
CD3CN
H2O
(c)
R-CH3
CD3CN
H2O
H2O
(d )
CD3CN
R-CH3
10.5 10.0 9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
ppm
Fig. 3. 1H NMR spectrum of (a) mono-aldehyde 6 in CDCl3, (b) mixture of mer and fac isomers of [Fe(6)3](PF6)2 in CD3CN, (c) [Fe(HL)](PF6)3 (L ¼ 3)
in CD3CN and (d) [Fe(L)](PF6)2 (L ¼ 3) in CD3CN.

1374
C. R. K. Glasson et al.
Fig. 4. X-ray structure of [Fe(HL)](PF6)3 (L ¼ 3). Left: view approximately perpendicular to the C3-axis (two anions removed for
clarity). Right: view of the cationic section down the C3-axis. Dashed lines indicate hydrogen bonds, dotted lines CHmethyl-F
interactions.
protonation of the bridgehead nitrogen had occurred. The com-
ꢀ
plex crystallizes in the centric trigonal space group R3 with one-
third of the molecule in the asymmetric unit. The optically active
metal centres are, as expected, coordinated in a fac tris-chelate
fashion to the three 2,20-bipyridine units resulting in an octa-
hedral configuration showing typical Fe-N bond lengths of
with four adjacent [Fe(HL)]3þ (L ¼ 3) cations through six
˚
CHphenylene?F or CHpyridyl?F contacts of less than 2.9 A,
while the P(2)-containing anion undergoes two similar interac-
˚
tions of 2.3 A, as well as several weaker methylene?F contacts
and also two anion–p interactions with the comparatively
electron poor pyridyl rings (indicated by a F?ring centroid
[11]
˚
˚
˚
distance of 2.9 A).
1.977(4) A and 1.974(4) A and a bite angle of 81.68(16)8.
The twist angle of 528 is also similar to that observed (548) in
tris(5,50-dimethyl-2,20-bipyridine)iron(II).[1] The protonated
bridgehead nitrogen is arranged endo towards the metal
centre – an arrangement stabilized by hydrogen bonding
between this proton and the three adjacent ether oxygen
In order to investigate the possibility of encapsulation of
other guest species, the volume of the cavity of [Fe(HL)](PF6)3
(L ¼ 3) was estimated using the X-ray crystallographic data. The
phenoxy oxygens were treated as the limits to the cavity size in
these calculations. The average oxygen to oxygen distance is
˚
˚
atoms (N-H?O 2.44(5) A, 117(3)8) (Fig. 4). A related
3.77 A. Consideration of the van der Waals radius of oxygen
[12]
˚
(1.52 A)
arrangement has been observed in metal complexes of zwit-
terionic polyphenolic ligands[7] but not previously observed for
phenol-ethers.
results in an equilateral triangle (for which the
apices are represented by the three phenoxy-oxygen atoms) with
˚
side length of 0.73 A. Using Euclidean geometry the diameter of
a sphere representative of the cavity volume was calculated to be
The presence of the metal-ion imparts a helical twist on the
˚
3
˚
˚
ligand that extends ,13.3 A down the length of the mole-
0.84 A (volume ¼ 0.31 A ). The effect of deprotonation of
[Fe(HL)](PF6)3 (L ¼ 3) was then investigated using an energy
minimized model generated via the semi-empirical PM3
method.[13] The structure was optimized with atom coordinates
for the donor atoms and the Fe(II) metal centre fixed at their
X-ray values. The oxgyen to oxygen distances increased to an
cule.[1,8] The helical twist experienced by the ligand along this
˚
distance is 1318 implying a pitch length of 36.5 A, which is a
similar pitch length to both mononuclear and dinuclear
bipyridine-containing helicates and tetrahedra previously
reported by our group,[1,8–10] in keeping with the degree of
chiral twist experienced by all these complexes being a function
of the metal chelate twist angle. The extension of this twist
results in the methyl groups at the termini of the ligand being
arranged ,6.4 A apart producing a binding pocket which is a
good size and shape match for a face of the hexafluorophosphate
anions present. Indeed, a PF6ꢀ anion (containing atom P(1)) is
located in a position to take advantage of weak CHmethyl
fluorine interactions, with each methyl group interacting with
two fluorines to form bifurcated hydrogen bonds with CH?F
distances of 2.70 A and 2.95 A (Fig. 4). There are therefore a
total of six such interactions between each cation and the face of
the anion binding to it; a similar arrangement is observed in a
dinuclear ruthenium(II) complex formed from quaterpyridine
ligands.[9]
While there are several weak offset face-to-face p-p
˚
(Cpyridyl-Cpyridyl distances of 3.3 A) and methylene–p interactions
(CHmethylene-Cphenyl distances of ,2.9 A) present between
molecules in the lattice, the packing is dominated by CH?F
interactions that result in a complicated three-dimensional
network. For example, in addition to the methyl-fluorine inter-
action described above, each P(1)-containing anion interacts
˚
average of 4.07 A. Consideration of van der Waals radii of
oxygen now resulted in an equilateral triangle side length of
˚
1.03 A, allowing the diameter of the sphere representing the
3
˚
˚
˚
cavity volume to be calculated as 1.18 A (volume ¼ 0.86 A ).
Clearly this is in accord with the encapsulated proton being a
snug fit for the cavity of the [Fe(L)](PF6)2 (L ¼ 3) host. Inter-
estingly, the model gives clear evidence of a significant confor-
mational change of the tris-salicyloxyamine capping unit
consistent with the NMR spectral changes observed upon
deprotonation of [Fe(HL)](PF6)3 (L ¼ 3).
?
˚
˚
Conclusion
The results presented in this report are in accordance with a
mixture of fac/mer isomers present in the intermediate mono-
aldehyde Fe(II) complex, [FeL3](PF6)2 (L ¼ 6), undergoing
significant isomerization from mer to fac during the course of
the reductive amination reaction. Although not specifically
identified for the present system, it seems likely that the Fe(II)
template isomerization process may be associated with some
degree of dynamic imine exchange behaviour. The result is the
˚

Template Synthesis of a Tris(bipyridyl) Receptor
1375
Fe(II) complex of a new tripodal (pseudo cage) ligand showing
an extended helical structure. Further, in the solid state the
arrangement is effectively ‘capped’ through symmetrical hydro-
gen bond interactions with an axially aligned PFꢀ6 counter ion.
8.1, 1H), 8.36 (d, 3J 8.1, 1H), 8.48 (dd, 4J 1.8, 5J 0.6, 1H), 8.63
(d, 4J 2.4, 1H). dC 18.60, 43.36, 120.98, 121.07, 133.10, 134.05,
137.39, 137.93, 149.15, 149.70, 153.05, 156.27. m/z (ESI-
HRMS) Calc. for [M þ H]þ ¼ 219.0683, found 219.0676; calc.
for [M þ Na]þ ¼ 241.0503, found ¼ 241.0497.
Experimental
2-((50-Methyl-[2,2’-bipyridin]-5-yl)methoxy)
benzaldehyde (6)
All reagents were of analytical grade unless otherwise indicated.
Chromatography grade solvents were distilled through a frac-
A
DMF (10 cm3) solution of salicylaldehyde (230 mg,
1
tionation column packed with glass helices. H and 13C NMR
1.88 mmol) and 5-chloromethyl-50-methyl-2,20-bipyridine
(343 mg, 1.57 mmol) in the presence of K2CO3 (650 mg,
4.7 mmol) was stirred at room temperature for 10 h. H2O
(20 cm3) was then added to the reaction mixture, and the
resulting precipitate was filtered off and washed with water
followed by a minimum volume of chilled MeOH. The crude
product was purified by chromatography on silica gel with
dichloromethane (98.75 %), MeOH (1 %) and saturated NH3
(0.25 %) as eluent to afford the product (477 mg, 94 %) as a
white solid. dH 2.41 (s, 3H), 5.27 (s, 2H), 7.06 (d, 3J 8.4 Hz, 1H),
7.13 (dd, 3J 7.8, 3J 7.2, 1H), 7.56 (ddd, 3J 8.4, 3J 7.8, 4J 1.8, 1H),
7.67 (dd, 3J 8.1, 4J 1.5, 1H), 7.88 (dd, 3J 7.8, 4J 1.8, 1H), 7.93
(dd, 3J 8.1, 4J 2.1, 1H), 8.31 (d, 3J 8.1, 1H), 8.45 (d, 3J 8.1, 1H),
8.53 (d, 4J 1.5, 1H), 8.75 (d, 4J 2.1, 1H), 10.55 (s, 1H). dC 18.64,
68.19, 113.01, 121.24, 121.27, 121.68, 125.42, 129.02, 131.77,
134.31, 136.18, 136.55, 138.46, 148.39, 149.32, 152.76, 155.88,
160.73, 189.62. m/z (ESI-HRMS) Calc. for [M þ Na]þ ¼
327.1104, found ¼ 327.1117.
spectra were recorded on a Bruker AM-300 or a Varian Mercury
300 MHz spectrometer (300.133 MHz) at 298 K. NMR of
organic species was recorded in CDCl3 and for metal complexes
in CD3CN. 1H and 13C NMR resonance are quoted in ppm and
the coupling constants (J) in Hertz (Hz). 1H NMR spectra were
referenced according to residual proton resonances for CDCl3
(7.24 ppm) and CD3CN (1.94 ppm). 13C NMR spectra were
referenced to solvent peaks for CDCl3 (77.0 ppm) and CD3CN
(1.39 ppm). Positive ion electrospray ionization high resolution
(ESI-HR): Fourier transform ion cyclotron resonance mass
spectrometry (FTICR-MS) measurements were obtained on a
Bruker BioAPEX 47e mass spectrometer equipped with an
Analytica of Branford electrospray ionization (ESI) source.
Microanalyzes were performed by the Campbell Microanalyti-
cal Laboratory, Chemistry Department, University of Otago,
Dunedin.
5-Trimethylsilylmethyl-50-methyl-2,20-bipyridine (4)
Lithium diisopropylamide (LDA) was prepared by adding 1.5 M
n-BuLi (4.4 cm3) dropwise to a stirred solution of dry diiso-
propylamine (0.758 g, 7.5 mmol) in THF (15 cm3) at ꢀ788C.
This solution was stirred for a further 0.5 h and allowed to warm
to 08C for 10 min. The resulting LDA solution was cooled to
ꢀ788C and a solution of 5,50-dimethyl-2,20-bipyridine (552 mg,
3 mmol) in THF was added dropwise. The reaction was allowed
to continue for 2 h and Me3SiCl (760 mg, 7 mmol) was then
added rapidly and the reaction was quenched with 3 cm3 of
MeOH after 3 min. The solvent was then removed under vacuum
and the resulting paste was taken up in dichloromethane and the
solution filtered. The dichloromethane was then removed under
vacuum and the solid that remained was purified by chroma-
tography on deactivated silica gel with 60 % petroleum and 40 %
ethyl acetate as eluent to afford the product as a waxy white solid
(614 mg, 80 %). dH 0.02 (s, 9H), 2.11 (s, 2H), 2.38 (s, 3H), 7.44
(dd, 3J 8.3, 4J 2.1, 1H), 7.61 (ddd, 3J 8.1, 4J 2.1, 5J 0.6, 1H), 8.22
(d, 3J 8.3, 1H), 8.24 (d, 3J 8.1, 1H), 8.34 (d, 4J 2.1, 1H), 8.48 (dd,
[FeHL](PF6)3ꢁCH3CN (L 5 3)
Astirredsolutionof 2-(50-methyl-[2,20]bipyridinyl-5-ylmethoxy)-
benzaldehyde 6 (61 mg, 0.2 mmol) and Fe(BF4)2ꢁ6H2O (23 mg,
0.067 mmol) in acetonitrile (10 cm3) was refluxed for 40 min
(for the 1H NMR spectrum of [Fe(6)3](BF4)2, see Fig. 3b). The
reaction mixture was cooled to room temperature and further
acetonitrile (90 cm3) added. To this, NH4OAc (77 mg,
1.0 mmol) was added and the resulting mixture stirred for 0.5 h.
The reaction mixture was then cooled to 08C in an ice bath
followed by the addition of NaCNBH3 (124 mg, 2.0 mmol).
After 2 h the reaction mixture was allowed to warm to room
temperature and stirred overnight and the solvent volume was
reduced under vacuum to ,5 cm3 and excess KPF6 in H2O
(15 cm3) was added. The resulting precipitate was isolated by
filtration and washed with H2O and a minimum volume of cold
MeOH then purified by chromatography on silica gel with
CH3CN, H2O, and saturated KNO3 (7 : 1 : 0.5) as eluent. The
product was then isolated as its PF6 salt (see above) affording a
purplish red solid (51 mg, 55 %). dH 2.24 (s, 9H), 3.94 (d, 2J 13.2,
3H), 4.01 (d, 2J 13.2, 3H), 5.04 (d, 2J 12.0, 3H), 5.09 (d, 2J 12.0,
3H), 7.05 ꢀ 7.20 (m, 12H), 7.41 (br s, 3H), 7.54 (ddd, 3J 7.5, 3J
7.5, 4J 1.8, 3H), 7.80 (br s, 3H), 7.98 (d, 3J 8.3, 3H), 8.02 (d, 3J
5
4J 2.1, J 0.6, 1H). dC ꢀ1.79, 18.55, 24.21, 120.44, 120.64,
133.12, 136.46, 136.65, 137.81, 148.47, 149.57, 152.27, 153.80.
5-Chloromethyl-50-methyl-2,20-bipyridine (5)
A solution of 5-trimethylsilylmethyl-50-methyl-2,20-bipyridine
(475 mg, 1.85 mmol), hexachloroethane (876 mg, 3.70 mmol)
and anhydrous CsF (562 mg, 3.70 mmol) in acetonitrile (20 cm3)
was heated at 608C with stirring for 6 h. The acetonitrile was
removed and replaced with dichloromethane (50 cm3) and the
resulting mixture was filtered. The filtrate was washed with
water (30 cm3) then brine (30 cm3) and was then dried over
anhydrous Na2SO4. The solvent was removed under vacuum
and the solid that remained was chromatographed on silica gel
with dichloromethane (97.5 %), MeOH (2 %) and saturated NH3
(0.5 %) as eluent to afford the pure product (344 mg, 85 %) as a
white crystalline solid. dH 2.37 (s, 3H), 4.62 (s, 2H), 7.62 (ddd, 3J
8.1, 4J 1.8, 5J 0.6, 1H), 7.82 (dd, 3J 8.1, 4J 2.4, 1H), 8.27 (d, 3J
3
3
8.3, 3H), 8.44 (d, J 8.3, 3H), 8.49 (d, J 8.3, 3H). dC 18.11,
51.64, 67.20, 112.37, 121.90, 123.74, 123.97, 132.70, 133.88,
136.52, 138.05, 138.88, 139.47, 152.29, 154.44, 156.45, 157.45,
157.42, 159.53. m/z (ESI-HRMS) Calc. for [M ꢀ 3PF6]3þ
¼
312.7822, found ¼ 312.7834. Anal. Calc. for C57H52FeN7O3P3F18ꢁ
CH3CN: C 50.08, H 3.92, N 7.92. Found: C 50.15, H 4.03,
N 8.02.
The deprotonated form of this compound was obtained by
treatment of the CD3CN NMR sample with K2CO3. dH 2.20 (s,
9H), 3.08 (d, 2J 11.4, 3H), 3.21 (d, 2J 11.4, 3H), 4.92 (d, 2J 12.7,
3H), 5.14 (d, 2J 12.7, 3H), 6.87 – 6.99 (m, 9H), 7.09 (d, 4J 0.9,
3
4
3
3H), 7.94 (dd, J 8.3, J 1.8, 6H), 8.00 (br s, 3H), 8.41 (d, J

1376
C. R. K. Glasson et al.
8.3, 3H), 8.45 (d, 3J 8.3, 3H). m/z (ESI-HRMS) Calc. for
[M ꢀ PF6]þ ¼ 1082.3041, found ¼ 1082.3004; calc. for [M ꢀ
2PF6]2þ ¼ 468.6697, found 468.6699.
(c) K. Sato, Y. Sadamitsu, S. Arai, T. Yamagishi, Tetrahedron Lett.
2007, 48, 1493. doi:10.1016/J.TETLET.2006.12.118
[3] (a) D. Xu, R. Warmuth, J. Am. Chem. Soc. 2008, 130, 7520.
doi:10.1021/JA800803C
(b) C. D. Meyer, C. S. Joiner, J. F. Stoddart, Chem. Soc. Rev. 2007, 36,
1705. doi:10.1039/B513441M
(c) J. Nitschke, Acc. Chem. Res. 2007, 40, 103. doi:10.1021/
AR068185N
(d) B. H. Northrop, F. Arico, N. Tangchiavang, J. D. Badjic,
J. F. Stoddart, Org. Lett. 2006, 8, 3899. doi:10.1021/OL061262U
(e) P. T. Corbett, J. Leclaire, L. Vial, K. R. West, J.-L. Wietor,
J. K. M. Sanders, S. Otto, Chem. Rev. 2006, 106, 3652. doi:10.1021/
CR020452P
X-Ray Structure Determination
Data were collected on a Bruker-Nonius APEX2-X8-FR591
diffractometer employing graphite-monochromated Mo-Ka
˚
radiation generated from a rotating anode (0.71073 A) with v
and c scans to ,568 2y at 150(2) K. Data integration and
reduction were undertaken with SAINT and XPREP.[14] Subse-
quent computations were carried out using the WinGX-32
graphical user interface.[15] The structure was solved by direct
methods using SIR97.[16] Multi-scan empirical absorption cor-
rections were applied to the dataset using the program
SADABS.[17] Data were refined and extended with SHELXL-
97.[18] Non-hydrogen atoms were refined anisotropically.
Carbon-bound hydrogen atoms were included in idealized posi-
tions and refined using a riding model. Nitrogen bound hydro-
gen atoms were first located in the difference Fourier map before
refinement. There is a small amount of thermal motion evident
in the fluorine atoms of the anions and subsequently the thermal
parameters of these atoms on the opposite sides of the molecule
were restrained to be equal. CCDC 855907 contains the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
(f) S. J. Rowan, S. J. Cantrill, G. R. L. Cousins, J. K. M. Sanders, J. F.
Stoddart, Angew. Chem. Int. Edit. 2002, 41, 898. doi:10.1002/1521-
3773(20020315)41:6,898::AID-ANIE898.3.0.CO;2-E
[4] L. F. Lindoy, S. E. Livingstone, Coord. Chem. Rev. 1967, 2, 173.
doi:10.1016/S0010-8545(00)80204-0
[5] U. S. Schubert, C. Eschbaumer, G. Hochwimmer, Tetrahedron Lett.
1998, 39, 8643. doi:10.1016/S0040-4039(98)02041-3
[6] S. A. Savage, A. P. Smith, C. L. Fraser, J. Org. Chem. 1998, 63, 10048.
doi:10.1021/JO981505Z
[7] (a) M. G. Davidson, C. L. Doherty, A. L. Johnson, M. F. Mahon, Chem.
Commun. (Camb.) 2003, 1832. doi:10.1039/B303618A
(b) J. D. Chartres, A. Dahir, P. A. Tasker, F. J. White, Inorg. Chem.
Commun. 2007, 10, 1154. doi:10.1016/J.INOCHE.2007.06.004
[8] D. F. Perkins, L. F. Lindoy, G. V. Meehan, P. Turner, Chem. Commun.
(Camb.) 2004, 152. doi:10.1039/B312716H
[9] C. R. K. Glasson, G. V. Meehan, J. K. Clegg, L. F. Lindoy, J. A. Smith,
F. R. Keene, C. Motti, Chem. – Eur. J. 2008, 14, 10535. doi:10.1002/
CHEM.200801790
Crystallographic Data
[10] (a) C. R. K. Glasson, G. V. Meehan, C. A. Motti, J. K. Clegg, P. Turner,
P. Jensen, L. F. Lindoy, Dalton Trans. 2011, 40, 10481. doi:10.1039/
C1DT10667H
Formula C57H52F18FeN7O3P3, M 1373.82, trigonal, space group
˚
ꢀ
R 3(#148), a 14.7878(9), b 14.7878(9), c 45.461(6) A, g 120.008,
3
V 8609.5(14) A , Dc 1.590 g cmꢀ3, Z 6, crystal size 0.250 by
˚
(b) C. R. K. Glasson, G. V. Meehan, J. K. Clegg, L. F. Lindoy,
P. Turner, M. B. Duriska, R. Willis, Chem. Commun. (Camb.) 2008,
1190. doi:10.1039/B717740B
0.150 by 0.100 mm, colour purplish red, habit prism, T 150(2) K,
l(MoKa) 0.71073 A, m(MoKa) 0.458mmꢀ1, T(SADABS)min,max
˚
0.6494, 0.7457, 2qmax 50.00, hkl range ꢀ17 17, ꢀ16 17, ꢀ52 54,
N 20775, Nind 3381(Rmerge 0.0654), Nobs 2480(I . 2s(I)),
Nvar 267, residualsA R1(F) 0.0793, wR2(F2) 0.2291, GoF(all)
(c) C. R. K. Glasson, J. K. Clegg, J. C. McMurtrie, G. V. Meehan,
L. F. Lindoy, C. A. Motti, B. Moubaraki, K. S. Murray, J. D. Cashion,
Chem. Sci. 2011, 2, 540. doi:10.1039/C0SC00523A
ꢀ3
1.094, Drmin,max ꢀ1.118, 1.603 eꢀ
A
.
˚
[11] M. C. T. Fyfe, G. T. Glink, S. Menser, J. F. Stoddart, A. J. P. White,
D. J. Williams, Angew. Chem. Int. Edit. 1997, 36, 2068. doi:10.1002/
ANIE.199720681
[12] A. Bondi, J. Phys. Chem. 1964, 68, 441. doi:10.1021/J100785A001
[13] J. J. P. Stewart, J. Comput. Chem. 1989, 10, 209. doi:10.1002/JCC.
540100208
Acknowledgement
We thank the Australian Research Council and the Marie Curie IIF scheme
of the 7th EU Framework Program for support.
[14] Bruker-Nonius, APEX v2.1, SAINT v.7 and XPREP v.6.14 2003
(Bruker AXS Inc.: Madison, WI).
References
[15] L. J. Farrugia, J. Appl. Cryst. 1999, 32, 837.
[16] A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Gioca-
vazzo, A. Guagliardi, A. G. C. Moliterni, G. Polidori, S. Spagna,
J. Appl. Cryst. 1999, 32, 115. doi:10.1107/S0021889898007717
[17] G. M. Sheldrick, SADABS: Empirical Absorption and Correction
Software 1999–2008 (University of Go¨ttingen: Go¨ttingen).
[18] G. M. Sheldrick, SHELXL-97: Programs for Crystal Structure
Analysis 1997 (University of Go¨ttingen: Go¨ttingen).
[1] D. F. Perkins, L. F. Lindoy, A. McAuley, G. V. Meehan, P. Turner,
Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 532. doi:10.1073/PNAS.
0508539103
[2] (a) B. Wu, J. Yang, X. Huang, S. Li, C. Jia, X.-J. Yang, N. Tang,
C. Janiak, Dalton Trans. 2011, 40, 5687. doi:10.1039/C0DT01561J
(b) V. Amendola, M. Boiocchi, B. Colasson, L. Fabbrizzi, E. Monzani,
M. J. Douton-Rodriguez, C. Spadin, Inorg. Chem. 2008, 47, 4808.
doi:10.1021/IC800099J
P
P
P
P
AR1 ¼ 99Fo9 ꢀ 9Fc99/ 9Fo9 for Fo . 2s(Fo); wR2 ¼ ( w(F2o ꢀ Fc2)2/ (wF2c)2)1/2 all reflections w ¼ 1/[s2(F2o) þ (0.1085P)2 þ 86.3000P] where
P ¼ (F2o þ 2F2c)/3.