Synthesis of new bulky bis(pyrazolyl)methane carboxylate (heteroscorpionate) ligands and their complexes with iron, manganese and nickel

Article abstract of DOI:10.1039/c2dt31859h

Three new sterically demanding ligands based on the bispyrazolylacetic acid motif have been prepared and complexes with Fe(ii), Fe(iii), Ni(ii) and Mn(ii) have been synthesised and characterised. Single crystal X-ray structures are included for two of the ligands in the protonated form and ten other complexes. Additionally, a new general route to amide derivatives has been established, a range of amide derivatives synthesised and their coordination chemistry investigated. Only one metal complex was synthesised from the amide ligands, and was bound via the hydroxylamine groups in preference to the pyrazole and carboxylate donor set. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt31859h

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PAPER
Synthesis of new bulky bis(pyrazolyl)methane carboxylate
(heteroscorpionate) ligands and their complexes with iron, manganese and
nickel†
Michael W. Jones,* Jack E. Baldwin, Andrew R. Cowley, Jonathan R. Dilworth, Alexei Karpov,
Nicolas Smiljanic, Amber L. Thompson and Robert M. Adlington*
Received 14th August 2012, Accepted 28th September 2012
DOI: 10.1039/c2dt31859h
Three new sterically demanding ligands based on the bispyrazolylacetic acid motif have been prepared
and complexes with Fe(II), Fe(III), Ni(II) and Mn(II) have been synthesised and characterised. Single
crystal X-ray structures are included for two of the ligands in the protonated form and ten other
complexes. Additionally, a new general route to amide derivatives has been established, a range of
amide derivatives synthesised and their coordination chemistry investigated. Only one metal complex
was synthesised from the amide ligands, and was bound via the hydroxylamine groups in preference to
the pyrazole and carboxylate donor set.
complexes which have labile ligands in the remaining coordi-
nation sites to allow further chemistry to occur.
Introduction
Bis(pyrazolyl)methanecarboxylates (bpmc) are a class of ligand
that has attracted much attention in recent years due to their
ready coordination to metals in a facial arrangement and their
generally higher stability than related pyrazolyl boron based
systems. Their coordination chemistry has been explored with
metals such as Zn, Y, Ti and Sc in the context of catalysis1,2
whereas with Tc and Re3–6 the focus moved in part to radiophar-
maceuticals. The coordination chemistry of this class of ligand
has been the subject of several reviews.7–9 However, the major
thrust of the research to date has been models for the active site
of several prominent metalloenzyme active sites i.e. isopenicillin
N-synthase (IPNS;10 see Fig. 1 for abbreviated structures of the
active site of the IPNS enzyme and intermediate with ACV
(δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine) substrate) tyrosine
hydroxylase,11 and extradiol catechol dioxygenase12 which
incorporate the his-his-asp triad.13–15
Increasing the steric bulk of the ligand is one obvious strategy
to prevent both dimer formation and complexes with the 2 : 1
stoichiometry. To date tert-butyl groups,17 menthone18 and
camphor19 groups are the bulkiest pyrazole substituents that have
been deployed. The camphor and menthone groups were fused
directly to the pyrazole rings and hence would not have been
expected to exert steric effects on the coordination sphere as the
primary interest of such research was for the introduction of
chiral centres. The use of tert-butyl groups was more successful
and monomeric 1 : 1 complexes were obtained with both Fe(II)
and Fe(III).17 We have been interested for some time in the chem-
istry of aryl substituted pyrazoles both in terms of their steric
requirements and because one- or two-photon fluorescent com-
plexes can be made, offering the possibility of tracking com-
plexes or ligands in cells. As a further variant we have sought to
introduce one or two methoxy or isopropoxy substituents at the
2- and 6-positions on the pyrazole phenyl groups. Here we
hoped to observe hemilabile behaviour involving coordination of
However, problems have arisen in the preparation of mono-
nuclear complexes with transition metals such as Fe, due to the
tendency either to form inactive dimeric carboxylate bridged
complexes or unreactive octahedral complexes of the type ML2
(L = bpmc).16 This has made it difficult to obtain mononuclear
Chemistry Research Laboratory, The University of Oxford, 12 Mansfield
Road, Oxford, OX1 3TA, UK. E-mail: michael.jones@chem.ox.ac.uk,
robert.adlington@chem.ox.ac.uk; Fax: +44 (0)1865 285002;
Tel: +44 (0)1865 275626
†Electronic supplementary information (ESI) available: The Supplemen-
tary Information contains thermal ellipsoid plots of all of the X-ray struc-
tures, the cif of the X-ray structures, the Slant Fourier map of the iron-
aquo environment indicating the electron density attributed to the protons
of the aquo ligand and a histogram of the Fe-OR2 (ether) distances from
the CCDC. CCDC 896640–896655. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/c2dt31859h
Fig. 1 Structure of the active site of the IPNS enzyme showing
the change that takes place on addition of ACV. AA
=
L-δ-(α-aminoadipoyl).
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Fig. 2 Structures of the bis(pyrazolyl)methanecarboxylate ligands
investigated in this study [R = Ph (HL1a), 2-(OMe)-C6H4 (HL1b),
2-(OiPr)-C6H4 (HL1c), 2,6-di(OMe)-C6H3 (HL1d), Ad (HL1e),
Me (HL1f)].
the ether oxygens which would favour reactive mononuclear
complexes. It has been shown that attachment of amide groups
to the pyrazoles of a phenoxybis(pyrazolyl)methane ligand leads
to coordination of the amide carboxyl oxygen as a bridging
group between two Ni(II) ions.20 Here we describe the impact on
the coordination chemistry of Fe(II), Fe(III) and Ni(II) on two
phenyl, 2-methoxyphenyl or 2-isopropoxyphenyl substituents at
the 3- and 5-positions of the pyrazole rings. We also prepared
new Mn(II) complexes. To the best of our knowledge, no Mn(II)
complexes of this class of ligand have been reported (Fig. 2).
Scheme 1 Reagents/conditions: (a) N2H4·H2O, MeOH, reflux, 3 h; (b)
K2CO3, KOH, TEBAC, CH2Cl2, reflux, 18 h; (c) (i) nBuLi, THF
−78 °C → 0 °C, 2 h, N2 (ii) ClCO2Et, −78 °C → RT, N2, 18 h;
LiOH·H2O, THF, H2O, RT, 20 h. (*NB: 4e was prepared via this route
Results and discussion
Ligand synthesis and characterisation
but has already been reported.23
)
The synthesis of the ligands in this study has not been previously
reported but follows similar approaches to those employed on
different, but related systems by other workers in the
field.16,17,21,22 Construction of the bpmc ligand was achieved in
five steps from commercially available materials via the route
described in Scheme 1.
1,3-Diketones 2a–2d were obtained via a Claisen conden-
sation between methyl benzoate and acetophenone (2a), the
requisite 2-alkoxyoxy substituted ester and ketone for 2b and 2c
or adamantyl pair for 2e.24 Treatment of the diketones with
hydrazine hydrate in refluxing methanol led directly to the pyra-
zoles 3a, 3b and 3c in 92, 98 and 67% yield, respectively.
Attempts to prepare the 2,6-dimethoxyaryl derivative 2d via a
Claisen condensation failed to give 2d (presumably due to steric
hindrance) so a second generation ynone route was chosen
(Scheme 2).
From a variety of syntheses of ynones, the approach based on
oxidation of propargylic alcohol 8 was selected. It is worthy to
mention that other possible transformations such as via Weinreb
amide or Sonogashira-coupling were unsuccessful. Furthermore,
the resultant ynone 9 did not initially cyclize to the desired pyra-
zole using methanol as solvent, which was successful for the
synthesis of the other pyrazoles from the 1,3-diketone precur-
sors. This resulted in only the isolation of the Michael adduct
from the addition of hydrazine to the activated triple bond. All
further attempts to induce cyclization by heating the Michael
adduct with Dean Stark apparatus in toluene, different proton
sources or Lewis acids did not lead to pyrazole formation. Chan-
ging the solvent to ethanol resulted in the formation of the
desired pyrazole 4d in good yield.
excess of base and triethylbenzylammonium chloride (TEBAC),
as a phase transfer catalyst. The addition of the carboxylate
group has been reported previously, either by treatment of the
starting pyrazole with dibromoacetic acid in the presence of
base17 or by quenching the anion of bispyrazolylmethane with
carbon dioxide.21 However, neither of these methods gave access
to the desired ligands in acceptable yields. For ligands HL1a–c
this was instead this was achieved over two separate steps, firstly
quenching of the anion with ethyl chloroformate, followed by
saponification of the ester with lithium hydroxide. This afforded
the three ligands HL1a–1c, and the X-ray crystal structures of
HL1b and HL1c are illustrated in Fig. 3. The presence of the car-
boxylic acid functionality was confirmed by a resonance at δ
164.5–165.0 ppm in the 13C NMR spectra and strong absorp-
tions at 1753 cm−1 (HL1a), 1774 cm−1 (HL1b) and 1759 cm−1
(HL1c) in the infra-red spectra.
It is evident from the X-ray structure of HL1b that the ligand
is preorganised to bind in the conventional facial geometry, the
scorpion-like carboxylate tail projecting directly forward into a
favourable binding arrangement near the pyrazole nitrogens. At
first glance there appears to be a degree of intramolecular π–π
stacking between the aryl rings in the 3 and 3′ positions of the
ligand HL1b; however, the distance of 3.95 Å or 4.23 Å does not
support this. In both of the crystallographically-distinct mole-
cules in the asymmetric unit, there is a short intramolecular
hydrogen bond between the hydroxyl group and a nitrogen atom
(O(2)⋯N(2) 2.6515(19), O(8)⋯N(6) 2.711(2) Å). The O–H
bonds are unusually long (1.11(4) and 1.04(3) Å respectively),
suggesting that the hydrogen bonding is significantly perturbing
these O–H bonds. Similar features were observed for the HL1c
Conversion of all of the pyrazoles to the bispyrazolylmethanes
was readily achieved with dichloromethane in the presence of an
Dalton Trans.
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presumably due to excessive steric congestion with no possibility
of rotation about the pyrazole C-phenyl bond to direct the
methoxy groups away from the bridging methylene group. This
can be rationalised in that the methylene bridge is too sterically
hindered by the two ortho-methoxyl substituents for derivatisa-
tion (at least with the desired carboxylate motif) in this fashion.
Bis(3,5-bis(adamantyl)-1H-pyrazol-1-yl)methane 4e23 was used
in an effort to introduce non-coordinating, sterically demanding
groups. Additionally, the adamantyl motif is not planar, unlike the
phenyl substituted compounds synthesised in this study, and more
like the tert-butyl group employed by Burzlaff and co-workers for
their bpmc ligands.16 Introducing the carboxylate functionality to
form ester 5e from 4e was problematic, and all efforts to optimise
the conditions with a variety of bases, temperatures and carboxy-
late sources did not lead to an improvement of the low yield
through the nBuLi/ClCO2Et couple (Scheme 3).
We were then unable to saponify the ester 5e using the standard
LiOH, or other MOH bases, and only the starting ester 5e was
recovered. Reduction of the ester 5e to the alcohol 10 was success-
ful using LiAlH4. All attempts to oxidize the alcohol 10 directly
to the desired carboxylic acid HL1e were unsuccessful and led to
recovery of starting alcohol 10 or decomposition of the starting
material. The alcohol 10 was then oxidized to the aldehyde 11
using a Swern oxidation.25 However, we were sadly unable to
oxidize 11 further to the carboxylic acid HL1e. It appears that
steric effects have to be finely balanced to provide control of the
coordination sphere without compromising the ligand synthesis.
n
Scheme 2 Conditions: (a) BuLi, THF, −5 °C → RT, 2 h, then DMF,
−60 °C; (b) HCuCMgBr, THF, −20 °C → RT, 2 h; (c) 2,6-dimethoxy-
iodobenzene, Pd(PPh3)2Cl2 (2 mol%), CuI (4 mol%), DIPEA, THF, reflux,
24 h; (d) MnO2, CHCl3, RT, 48 h; (e) N2H4·H2O, EtOH, reflux, 24 h.
Fig. 3 X-ray crystal structures of ligand HL1b and HL1c. Thermal
ellipsoids drawn at 50% probability and hydrogen atoms removed for
clarity.
structure, with again a short intramolecular N–H bond between
one pyrazole nitrogen and the hydroxyl proton.
The other two ligands HL1d and HL1e proved much more
difficult to prepare despite investigating a number of alternative
approaches. In spite of the circuitous route employed to obtain
the bis(pyrazolyl)methane 4d, and a number of different con-
ditions (bases, temperatures, carboxylate sources) all attempts to
introduce a carboxylate group at the bridgehead carbon failed,
Scheme 3 Reagents/conditions: (a) nBuLi, THF, −78 °C, N2 (ii)
−20 °C, 2 h (iii) ClCO2Et, −78 °C → RT; (b) LiAlH4, THF, N2, reflux;
(c) (COCl)2, DMSO, CH2Cl2, NEt3, −78 °C, N2.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

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Fig. 4 X-ray crystal structure of complex [Mn(L1a)2] 12. Thermal
ellipsoids drawn at 50% probability and hydrogen atoms, solvent and
disorder removed for clarity.
Scheme 4 Reagents/conditions: (a) MCl2 or MCl3 or Fe(BF4)2·6H2O,
KOtBu, THF, N2, RT or reflux (12 M = Mn(II), R = Ph, 14 M = Mn(II),
R = o-PhOiPr, 15 M = Fe(II), R = Ph, 17 M = Fe(II), R = o-PhOMe, 18
M = Fe(II), R = o-PhOiPr, 19 M = Fe(III), R = o-PhOMe, 20 M = Ni(II),
R = Ph, 21 M = Ni(II), R = o-PhOMe, 22 M = Ni(II), R = o-PhOiPr); (b)
MCl2, KOtBu, THF, N2, RT or reflux (13 M = Mn(II), R = o-PhOMe, 16
M = Fe(II); R = o-PhOMe).
Coordination to first row transition metals
The bpmc ligands HL1a–1c were then reacted directly with a
selection of transition metal chlorides or tetrafluoroborates under
the conditions outlined in Scheme 4 to give either neutral or cat-
ionic pseudo-octahedral ML2 complexes or dimeric [{MLX}2]22
species (M = Mn, X = Cl) or [{MLX}2]2+ (M = Fe, X = H2O).
The resulting complexes were characterized predominantly by
X-ray crystallography but supported by HPLC, mass spec-
trometry, elemental analysis and infra-red spectroscopy. Initially,
it was anticipated that using stoichiometric amounts of metal salt
and ligand could control the outcome, however, it was found that
the same result was obtained regardless of the ratio of LH to
MXn. This suggests that the reaction favours the formation of
either the stable pseudo-octahedral complex or the carboxylate
bridged dimer.
Fig. 5 X-ray crystal structure of complex [{MnL1bCl}2] 13. Thermal
ellipsoids drawn at 40% probability and hydrogen atoms and solvent
removed for clarity.
[{MnL1bCl}2] 13 was formed (Fig. 5), a result thought to be due
to the more bulky ether substituents in HL1b which appear to
stabilize the distorted trigonal bipyrimidal coordination mode
through weak interactions {2.762(2) to 3.294(2) Å} with the
metal. This is discussed in further detail in the section on X-ray
structures below.
This dimeric species consists of two metal centres each co-
ordinated by one tridentate scorpionate ligand with the coordi-
nated carboxylate oxygen bridging the second metal centre
(related by a crystallographic inversion centre). The coordination
is completed by a single chloride resulting in an oxygen bridged,
metal dimer. As would be expected, the bridging oxygen is
asymmetrically coordinated, with M–O distances of 2.114(3)
and 2.286(3) Å leading to a distorted trigonal bipyramidal
coordination at the metal (Fig. 5, Table 1). The structure is
directly analogous to the Fe(II) complex reported previously16
and related to that of Fe(II) with L1b (16) described below. It is
interesting to note that a small manipulation, like the addition of
a methoxy group at the 2-position of the phenyl rings appears to
give rise to such a major difference in the coordination geometry
Complexes with Mn(II) 12–14
The initial interest in Mn2+ was based on its introduction into the
active site of the IPNS enzyme, and crystallisation of X-ray
quality crystals of an intermediate in the enzyme active site.26 In
addition, manganese(II) is less prone to the oxidation that often
plagues the chemistry of iron(II). Ligand HL1a, even when
reacted at a ratio of 1 : 1 ligand to metal with MnCl2 in THF in
the presence of potassium tert-butoxide as base formed a
pseudo-octahedral complex [Mn(L1a)2] 12 (Fig. 4). The same
result was observed even when excess MnCl2 was used.
However, when ligand HL1b was reacted with anhydrous MnCl2
under analogous conditions, the very different complex
Dalton Trans.
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Table 1 Polyhedral volumes (Å3) for the metal complexes
Pseudo-octahedral
Trigonal bipyrimidal
Mn(II) Ph 12
Mn(II) OiPr 14
Fe(II) Ph 15
Fe(II) OMe 17
Fe(II) OiPr 18
Fe(III) OMe 19
Ni(II) Ph 20
14.92
14.70
13.46
13.25
13.66
13.38
12.30
12.37
12.42
Mn(II) OMe 13
Fe(II) OMe 16
14.75
14.00
Ni(II) OMe 21
Ni(II) OiPr 22
in the complexes. Interestingly, using the more sterically demand-
ing isopropoxyaryl ligand HL1c under identical conditions led to
the formation of a pseudo-octahedral complex [Mn(L1c)2] 14,
similar to that of complex 12. Single crystal X-ray analysis,
elemental analysis and accurate mass spectrometry supported the
formation of the ML2 complex. Further discussion of the X-ray
structures follows in a separate section below. We were encour-
aged at this stage to take these findings to the more complicated
Fe(II) systems, while being conscious of the possibility of partici-
pation of the ether groups in coordinating and hence stabilizing
the metal complexes.
Fig. 6 X-ray crystal structure of complex [Fe(L1b)2] 17. Thermal ellip-
soids drawn at 50% probability and hydrogen atoms removed for clarity.
Complexes with Fe(II) and Fe(III) 15–19
When Fe(BF4)2·6H2O was used in place of MnCl2 under similar
reaction conditions, neutral complexes displaying the ML2 (L =
L1a, L1b) stoichiometry were isolated with both ligands (Fig. 6),
even when a 1 : 1 metal : ligand ratio was used. There was no
evidence for dimeric complexes with this Fe(II) precursor. Altera-
tion of the iron precursor to FeCl2 and reaction with the ligands
HL1a and HL1b under the same reaction conditions gave the
identical [FeL1a2] complex 15 and the dimeric complex
[{Fe(H2O)L1b}2][FeCl4]2 16 (Fig. 7), respectively.
Fig. 7 X-ray crystal structure of complex [{Fe(H2O)L1b}2][FeCl4]2 16.
Thermal ellipsoids drawn at 50% probability and hydrogen atoms,
solvent and counterions removed for clarity.
water is the correct assignment in this structure. The identity of
the [FeCl4]− anion was confirmed by the tetrahedral bond angles
The structure for complex 16 is formally analogous to that of
the Mn complex 13 above but with a water molecule replacing
the chloride. The origin of the water molecules may be the nomi-
nally anhydrous THF or FeCl2 or they may have been introduced
during the recrystallisation process which was carried out
without the exclusion of air. The identity of the coordinated
aquo ligand over a hydroxide ion was lent support by the water
molecule forming hydrogen bonds with both protons. One of
these is formed to the free O atom of the carboxylate ligand
triply-coordinated to the second Fe atom in the complex
(O(7)⋯O(2)′ 2.740(3) Å, symmetry operator −x, −y, 1 − z) and
the second to the O atom of a molecule of Et2O (O(7)⋯O(8)
2.632(4) Å). Additionally, careful examination of the difference
Fourier map (see Fig. SI1 in the ESI†) suggests the presence of
two peaks due to the location of two hydrogen atoms which is
consistent with the structure containing water. The possibility
that the structure contains hydroxyl rather than water and that the
hydrogen atom is disordered between these two positions was
excluded by conducting refinement of the positional parameters
and isotropic temperature factor with the occupancy set to 0.5.
This led to an increase in R1 from 4.818% to 4.828% and both
the displacement parameters became unrealistically small. Thus,
although it is impossible to be 100% certain we believe that
−
and Fe–Cl distances of 2.1784(11)–2.1951(8) Å for the FeCl4
counterion being in close agreement to the reported values
2.163(4)–2.21(2) Å.27–29 The presence of the [FeCl4]2− anion
was eliminated on the basis of X-ray crystallography, which has
reported bond lengths of 2.2780(13)–2.3626(13) Å and a depar-
ture from tetrahedral geometry.30
The trigonal bipyramidal coordination for compound 16 was
not followed for either the unsubstituted phenyl or more hin-
dered isopropoxyaryl ligands, HL1a or HL1c, when the FeCl2
precursor was used under identical conditions. This was surpris-
ing for HL1c, as it was anticipated that the isopropyl ethers
would be of sufficient size to assist in stabilisation of the trigonal
bipyrimidal coordination mode. In each case ML2 structures of
pseudo-octahedral geometry were prepared and the crystal struc-
tures determined.
Clearly there is a delicate balance between the monomeric and
dimeric species which can be perturbed both by the nature of the
ligand (as with Mn) or by the choice of precursor (for Fe(II)).
Finally, the reaction of FeCl3 with ligand HL1b led to the for-
mation of a Fe(III), cationic [ML2]+ type complex 19 exhibiting
pseudo-octahedral coordination at the metal centre with both
[FeCl4]− and
a
protonated decarboxylated ligand as the
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Dalton Trans.

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counterion. The Fe–Cl distances in the counterion identified this
as being Fe(III). A [Fe(OAr)4]NEt4 complex 2331,32 was used in
the hope that the introduction of bulky groups on the Fe(III) pre-
cursor with a stoichiometry of M : L of 1 : 1 would lead to mono-
meric species. However, complicated inseparable mixtures were
formed under a variety of reaction conditions.
Complexes with Ni(II) 20–22
Fig. 9 Close-up of the coordination sphere of the pseudo-octahedral
(left) and trigonal bipyrimidal (right) coordination modes for the metal
complexes.
Nickel(II) complexes of bispyrazolylcarboxylates have not been
previously reported, and were studied as they do not suffer from
the problems of oxygen sensitivity which can cause problems
with Fe(II) derivatives. All three of the nickel(II) complexes
20–22, formed as a pale green coloured precipitate with bpmc
ligands in the ratio of M : L (1 : 2). X-Ray crystallography
revealed classic pseudo-octahedral geometry about the Ni(II)
centre (Fig. 8). A detailed comparison of the X-ray crystal struc-
tures appears below.
on the tris(pyrazolyl)borate system.36 Correspondingly, the poly-
hedral volume also decreases across the series, manganese exhi-
biting the largest polyhedral volume, the iron complexes
intermediary and finally the nickel complexes (with the smallest
ionic radius) having the smallest polyhedral volumes.
The influence of increasing the size of the ligand is most
obvious for the nickel complexes where, as the size of the pyra-
zolyl sidegroups becomes bulkier, the entire N,N,O-donor set
becomes more ‘pinched’. This is demonstrated by the nitrogen–
nitrogen distance decreasing from 2.966(2) Å(Ph) to 2.810(3) Å
(2-(OiPr)Ph) and the N–O–N angle (between the metal bound
atoms) also decreasing from 62.05(6)° to 57.51(6)° for the same
examples with the ortho-methoxy compound 21 in the middle in
each case. One other less expected difference between the metal
complexes was the differentiation in bond lengths of the metal–
pyrazolyl nitrogen bond in the same bpmc, again, as the size of
the ligand increased. Complexes incorporating the phenyl deriva-
tive (L1a) exhibited almost the same M–N bond lengths (within
uncertainty), whereas the complexes with ligands L1b or L1c
showed a disparity between the N–M bonds which were up to
0.189 Å different for complex 22. The shorter M–N distances
and longer M–O (carboxylate) bonds for the dimeric species, (13
and 16), compared to the ML2 complexes, was in keeping with
the trend observed by Burzlaff and co-workers for their series of
iron N,N,O-heteroscorpionate complexes.16
The τ (tau) parameter introduced by Addison and co-
workers37 is a useful index to ascribe the degree of trigonality of
5-coordinate complexes. We found τ values of 0.76 and 0.41, for
complex 13 and 16 respectively. With τ = 0 (square pyramidal)
and τ = 1 (trigonal bipyrimidal) the Mn complex 13 is closer to
trigonal bipyrimidal than the Fe complex 16 which has four of
its substituents lying considerably closer to a plane. Comparison
of the trigonal bipyramidal structures with those in the literature
revealed a shorter Fe–Fe distance of 3.406(1) Å for complex 16
compared with that of the Fe–Fe distance of 3.670(4) Å for the
tert-butyl derivative prepared by Burzlaff and co-workers,16
which was unexpected. This may be attributable to either the pla-
narity of the aryl rings allowing closer approach than for the tert-
butyl system which has more three-dimensional bulk. Alterna-
tively, it could be an influence of the ortho-methoxyl groups,
which have close approach in the range of 2.762(2) to 3.294(2) Å
for the Mn and Fe complexes 13 and 16. A ConQuest search of
the CCDC for iron–(O)ether interactions was made in the range
0–5 Å. The histogram plot (see SI2†) illustrates that the distances
for our Fe–O(R2) interactions of 2.762(2) to 3.294(2) Å for the
Mn and Fe complexes 13 and 16 are considerably shorter than
X-ray crystal structures
Despite 1H NMR spectroscopy being a useful tool in the solution
state analysis of some paramagnetic species, the 1H NMR analy-
sis of the complexes in hand did not provide us with useful
information and all that was observed was a broadening of the
proton resonances and decreased resolution of the signal to noise
ratio. Hence, it was important to establish unequivocal (albeit,
solid state) structures by X-ray crystallography. Of the two types
of complex, the effects of changing metal, charge or coordi-
nation type were most obvious when the bond distances and
angles, and the polyhedral volume33 were calculated using
IVTON34 and considered (Fig. 9). A table of the key bond
lengths and angles for the X-ray structures are summarised in
Tables 1 and 2.
On examination of the structural data for the complexes,
several trends became evident. Progressing across the group, the
metal–oxygen bond distance becomes shorter. This is readily
accounted for by the decreasing atomic radius of the metal ion
across the series in line with the Irving–Williams35 series which
has also been probed in some depth by Solomon and co-workers
Fig. 8 X-ray crystal structure of complex [Ni(L1c)2] 22. Thermal ellip-
soids drawn at 30% probability and the molecule of THF and the hydro-
gen atoms removed for clarity.
Dalton Trans.
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Table 2 Key bond lengths and distances (Å) and angles (°) for the metal complexes
M–N1
M–N2
M–O
N–Na
N1–O–N2b
Mn(II) Ph 12 (PO)
Mn(II) OMe 13 (TBP)c
Mn(II) OiPr 14 (PO)
Fe(II) Ph 15 (PO)
2.3411(14)
2.264(3)
2.2861(13)
2.2106(12)
2.101(2)
2.206(9)
2.2307(16)
2.169(3)
2.3057(14)
2.241(3)
2.4040(13)
2.2723(12)
2.134(2)
2.286(8)
2.3403(17)
2.287(3)
2.1148(12)
2.286(3)
2.0652(11)
2.0241(10)
2.1461(17)
2.003(8)
1.999(14)
2.055(3)
1.9996(14)
1.997(4)
3.110(2)
2.973(5)
2.999(2)
3.033(2)
2.897(3)
2.922(12)
2.971(2)
2.878(5)
2.966(2)
2.874(7)
2.810(3)
63.89(5)
62.30(11)
61.00(4)
62.88(4)
61.10(7)
60.35(28)
60.99(5)
57.57(10)
62.05(6)
59.76(17)
57.51(6)
Fe(II) OMe 16 (TBP)d
Fe(II) OMe 17 (PO)
Fe(II) OiPr 18 (PO)
Fe(III) OMe 19 (PO)
Ni(II) Ph 20 (PO)
2.1545(17)
2.119(5)
2.094(2)
2.1478(17)
2.211(5)
2.285(2)
Ni(II) OMe 21 (PO)
Ni(II) OiPr 22 (PO)
1.9845(18)
a This is the distance between the two metal bound nitrogens on the same bpmc ligand. b This is the angle between the atoms that are coordinated to
the metal centre from the same bmpc. c Mn–Cl 2.3574(12) Å, Mn–O′ 2.114(3) Å. d Fe–OH2 2.014(2) Å, Fe–O′ 2.0894(17) Å.
Chemistry of amide heteroscorpionate ligands
Since the introduction of steric bulk had not alone been sufficient
to block carboxylate bridging we also investigated replacement
of the carboxylate motif by an amide group. The synthesis of bis
(pyrazolyl)methane amide ligands directly by lithiation of the
bis(pyrazolyl)methane followed by reaction with an isocyanate
and finally ‘quenching’ in situ by the addition of the metal salt
have been described.38 There have also been reports of the
coordination chemistry of ligands where the amide groups are
directly attached to the pyrazole groups. Using first the simple
pyrazole derivative HL1f for the optimisation studies and then
Fig. 10 Close-up of the binding environment of the metal atom in the
the bulkier o-PhOMe derivative HL1b, a selection of seven
X-ray crystal structure of complexes 13 and 16. Thermal ellipsoids at
amides were synthesised using DIC (N,N-diisopropylcarbodi-
imide), HOBt (hydroxybenzotriazole), DIPEA (N,N-diisopropy-
lethylamine) and DMF as solvent under relatively standard
peptide coupling conditions (Scheme 5). Other peptide coupling
procedures were found to be ineffective or gave unacceptably
low yields.
The amide ligands all formed as colourless solids and
were characterised by 1H and 13C NMR, infra-red and mass
spectrometry. Absorptions at ca. 3122–3442 cm−1 for the N–H
stretching frequency and a shift to lower wave number for the
CvO stretch in the infra-red spectra (to approximately
1715–1669 cm−1), in addition to other strong supporting
data (i.e. NMR and accurate mass spectra) were indicative
of the amide functionality being present. The X-ray crystal struc-
ture was determined for the isopropyl derivative 27 (Fig. 11)
crystallised by evaporation of a methanolic solution of the
ligand.
The crystal structure contained two inequivalent molecules of
methanol for each molecule of isopropyl derivative 27, and there
is an intermolecular hydrogen bonding network involving the
amide group. This was stabilised by a two-point intermolecular
interaction of the isopropyl hydrogen, CH(CH3)2 with the
methoxyl carbon and the meta-hydrogen on the aryl ring with
the carbonyl oxygen. A hydrogen bond was also present
between the pyrazole nitrogen and the amide proton, similar to
the pyrazole–hydroxyl H-bond observed for HL1b and HL1c.
Hydrogenation of the benzyloxy derivative 30 in the presence of
palladium on carbon catalyst provided access to the hydroxamic
acid derivative 31.
50% probability.
most examples and occur in the lowest 30 percentile. Addition-
ally, closer inspection of the X-ray structure, and comparison
with other similar examples from the CCDC reveal that the lone
pairs of the alkoxyl oxygens are correctly aligned to interact with
the Fe or Mn. A close-up of the binding environment of the two
distorted trigonal bipyramidal species 13 and 16 indicates the
orientations of the methyl ether groups (Fig. 10).
The coordination achieved by these ligand systems is very
sensitively balanced, as the isopropoxyl ethers resulted in
pseudo-octahedral coordination to all metals in this study and
did not participate in any type of stabilisation. In fact, in all com-
plexes containing L1c the aryl rings were orientated with the iso-
propoxyl groups directed away from the metal. In each of these
cases the aryl group is rotated 180° from the trigonal bipyramidal
examples with the ether projecting away from the metal, and
playing no apparent part in coordination.
The results obtained with the ligands studied above demon-
strated that the steric effects and donor characteristics of
the bpmc ligand substituents required further modification to
achieve monomeric coordination sensitive and needs careful
consideration. The smaller 2,6-dimethylaryl or a donating group
(2-NMe2) to assist in the stabilisation of the coordination sphere
are two such ways in which this could be accomplished and are
the source of ongoing investigation in our laboratory. The failure
to prepare the 2,5-dimethoxyaryl ligand HL1d via the routes we
attempted means that other avenues had to be explored.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

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Scheme 5 Reagents/conditions: (a) RNH2 or RNH2·HCl, DIC, HOBt,
DIPEA, DMF, 0 °C–RT, N2, 20 h; (b) H2 (g), Pd/C, EtOAc, RT, 18 h;
(c) Fe(BF4)2·6H2O or FeCl2, KOtBu, THF, RT.
Fig. 12 X-ray crystal structure of complex 32. Thermal ellipsoids at
30% probability and the hydrogen atoms, solvent molecules and the
minor component of disorder have been removed for clarity.
pyrazolyl nitrogens to give octahedral 32 (Fig. 12). The X-ray
data for 32 was of low quality due to the size of the crystals and
volatile solvents (CH2Cl2 and Et2O) present in the crystal struc-
ture. Two of the ligands refined well, but the third ligand gave
very prolate displacement parameters suggesting that the third
ligand does not have a single ideal position. This can be mod-
elled with one set of atoms; however it is more usual to use two
or more sites so that the geometry is not distorted. In this case,
the size of the ligand and the close proximity of the two com-
ponents of the disorder mean that the number of parameters (and
restraints) that would be required would be large. For this
reason, the disordered ligand was modelled with isotropic displa-
cement parameters. While this is less than ideal it was considered
the best option and there is little doubt as to the connectivity.
This structure, while disappointing in the fact that the pyrazo-
lyl based ligand did not bind in the desired facial manner, does
open up the possibility of generating multi-metallic complexes
utilising the free pyrazole groups to bind other metals.
Fig. 11 X-ray crystal structure of compound 27. Thermal ellipsoids at
50% probability and hydrogen atoms and solvent molecules have been
removed for clarity.
The hydroxamic acid derivative 31 could in principle create
different chelate ring size and coordination behaviour if the term-
inal hydroxyl group were to bind. Under a range of conditions
the amide functionalised ligands gave intractable polymeric mix-
tures, except in the case of the hydroxamic acid derivative 31.
This was found to readily react with Fe(BF4)2·6H2O or anhy-
drous FeCl2 and crystals of 32 suitable for single crystal X-ray
analysis were obtained by the slow infusion of diethyl ether into
a saturated CH2Cl2 solution of complex. It was found that with
31, the very high affinity of the iron for the hydroxylamido
group39,40 overrode the tridentate, facial binding mode and 31
behaved as a bidentate ligand with no participation of the
Experimental
General information
All reactions involving water-sensitive compounds were carried
out in oven-dried Schlenk glassware under nitrogen atmosphere
unless stated otherwise. Nitrogen gas was dried by passage
through phosphorus pentoxide and self-indicating silica gel. All
solvents were dried according to standard procedures and were
distilled prior to use. All reagents were purchased from Aldrich
and used without further purification. Column chromatography
was performed on silica gel 60 M (mesh 230–400) Macherey-
Dalton Trans.
This journal is © The Royal Society of Chemistry 2012

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Nagel. Thin layer chromatography (TLC): silica gel layered
2331,32,51 and bispyrazolyl acetic acid HL1f 17,21 were all syn-
thesised according to reported procedures. 2′-Isopropoxyaceto-
phenone52 and methyl-2-isopropoxybenzoate53 were prepared by
O-alkylation of 2′-hydroxyacetophenone and methyl salicylate,
respectively by treatment with 2-bromopropane, K2CO3 and
DMF at 80 °C and had identical NMR spectra to those reported
in the literature.
NB: It must be noted as a safety precaution that the inhalation
of ethyl chloroformate as a liquid or spray mist is very hazar-
dous and can lead to severe irritation of the mucus membranes
of the eyes, mouth and respiratory tract, and in very severe cases
even death. Please refer to the MSDS before proceeding and use
all appropriate safety equipment when dealing with this reagent.
1
aluminum foil (60 F254 Merck, Darmstadt). H-, 13C-, DEPT-,
NOESY-, COSY-, HMQC-, and HMBC-spectra were recorded
on Bruker DQX 400 spectrometers using CDCl3 as solvent
unless otherwise stated. The resonances (δ values) were
measured relative to the signals for CDCl3 (7.27) and CDCl3
(77.0), respectively. The assignments of quaternary C, CH, CH2
and CH3 were made on the basis of DEPT, HMQC and HMBC
spectra. IR spectra were obtained for thin films on KBr-plates on
a Bruker Tensor 27 FT-IR spectrophotometer. Mass spectra were
recorded on Jeol JMS-700 and Finnigan TSQ 700 spectrometers.
The melting points (uncorrected) were measured on Reichert-
Jung Thermovar apparatus. HPLC characterisation (analytical
HPLC) of compounds was performed by using a Varian C-18
column (Pursuit XRs 5 4.6 × 150 mm) with UV/Vis detection at
λobs = 254 nm with a 1.0 mL min−1 gradient elution method
(Solvent A: MeCN, Solvent B: H2O): start 5% A, gradient over
1–12.5 min reaching 100% A, hold until 18.5 min at 100% A,
reverse gradient 18.5–19.75 min reaching 5% A, then hold to
21.5 min at 5% A. Elemental analyses were performed either by
the microanalysis service by Mr S. Boyer, at London Metro-
politan University.
1,3-Bis(2-isopropoxyphenyl)propane-1,3-dione 2c. NaH (60%
in mineral oil, 2.74 g, 68.61 mmol) was added in small portions
over 5 min to a stirred mixture of 2′-isopropoxyacetophenone
(4.07 g, 22.87 mmol) and methyl-2-isopropoxybenzoate (4.44 g,
22.87 mmol) in anhyd. THF (60 mL) at RT under N2 atmos-
phere. The resultant mixture was heated at reflux with stirring for
18 h. The orange coloured suspension was then cooled to RT,
and quenched slowly with water (3 mL), then added to 1 M HCl
(100 mL) and CH2Cl2 (50 mL). The layers were separated and
the aqueous layer extracted with CH2Cl2 (3 × 50 mL). The com-
bined organic extracts were washed with sat. NaCl(aq) (3 ×
50 mL) then dried over anhyd. MgSO4, filtered and concentrated
to dryness in vacuo. The gummy residue was purified by flash
chromatography with an elution gradient starting with 1 : 4
Et2O–petroleum ether and finishing with 1 : 2 Et2O–petroleum
ether to furnish the title product 2c as a pale yellow coloured oil
(4.98 g, 64%). The NMR data indicated the presence of both the
diketone and enol forms in the relative ratio of 1 : 2 favouring
Single crystal X-ray diffraction data were obtained for com-
pounds HL1b, HL1c, 4b, 12–22, 27 and 32. In each case, a
typical crystal was mounted using the oil drop technique, in
perfluoropolyether oil at 150(2) K using a Cryostream N2 open-
flow cooling device.41 Diffraction data were collected using
graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) on a
Nonius Kappa CCD diffractometer or an Oxford Diffraction
SuperNova (λ = 1.54180 Å; structures 14 and 18). For all data
collections, series of ω-scans were performed in such a way as to
collect a complete data set to a maximum resolution of 0.77 Å or
0.83 Å (for data collected with molybdenum and copper radia-
tion respectively). Data reduction including unit cell refinement
and inter-frame scaling was carried out using DENZO-SMN/
SCALEPACK42 or CrysAlisPro43 as appropriate. Intensity data
were processed and corrected for absorption effects by the multi-
scan method, based on repeat measurements of identical and
Laue equivalent reflections. Structure solution was carried out
with direct methods using the programs SIR9244 within the
CRYSTALS software suite.45 In general, coordinates and aniso-
tropic displacement parameters of all non-hydrogen atoms were
refined freely except where disorder necessitated the use of
“same distance restraints” together with thermal similarity and
vibrational restraints to maintain sensible geometry/displacement
parameters. Hydrogen atoms were generally visible in the differ-
ence map and refined with soft restraints prior to inclusion in the
final refinement using a riding model.46 In the case of compound
21, the difference Fourier map indicated the presence of diffuse
electron density believed to be disordered solvent. PLATON/
SQUEEZE47–49 was used leaving a void from which the electron
density was removed. Crystallographic data (excluding structure
factors) for all the structures have been deposited with the Cam-
bridge Crystallographic Data Centre (CCDC 896640–896655).
Ortep depictions of the single crystal X-ray structures are in the
ESI, Fig. SI3–SI18.† Tables summarising the X-ray crystallo-
graphic data follow (Tables 3 and 4).
1
the enol form. Enol H NMR (CDCl3, 400 MHz) δ: 1.15 (12H,
m, 4 × CH3), 4.40 (2H, m, 2 × CH(CH3)2), 6.73 (2H, m, Ph),
6.77 (2H, m, Ph), 7.15 (1H, m, COCHvCOH), 7.25 (2H, m,
Ph), 7.75 (2H, m, Ph). 13C NMR (CDCl3, 100 MHz) δ: 22.1
(CH3), 71.8 (CH(CH3)2), 103.7 (COCHvCOH), 113.1 (ArCH),
120.1 (ArCH), 127.0 (Cq), 131.3 (ArCH), 134.0 (ArCH), 157.5
(Cq), 184.9 (COH), 195.8 (CO). Diketone 1H NMR (CDCl3,
400 MHz) δ: 1.06 (12H, m, 4 × CH3), 4.46 (2H, m, 2 × CH-
(CH3)2), 4.52 (2H, m, CH2), 6.79 (2H, m, Ph), 6.83 (2H, m, Ph),
7.21 (2H, m, Ph), 7.68 (2H, m, Ph). 13C NMR (CDCl3,
100 MHz) δ: 21.7 (CH3), 60.2 (CH2), 70.3 (CH(CH3)2), 115.2
(ArCH), 120.6 (ArCH), 127.3 (Cq), 130.2 (ArCH), 132.4
(ArCH), 156.8 (Cq), 184.9 (CO). HRMS-ES+ Found 341.1744
[C21H24O4 + H]+ requires 341.1747.
General procedure for conversion of 1,3-diketones to
1H-pyrazoles
Hydrazine hydrate (2 mol equiv.) was added to a stirred solution
of 1,3-bis(aryl)propane-1,3-dione 2 (1 mol equiv.) in MeOH at
RT. The reaction mixture was heated at reflux for 3 h, concen-
trated in vacuo and the residue dissolved in CH2Cl2. The
aqueous layer was separated and extracted three times with
CH2Cl2. The combined organic extracts were dried over anhyd.
Na2SO4 and concentrated to approximately 10% of the original
volume in vacuo. Pentane (200 mL) was added and the
1,3-Bis(2-methoxyphenyl)propane-1,3-dione 2b,24 1,3-bis-
((3,5-diphenyl)-1H-pyrazol-1-yl)methane 4a,50 [Fe(OAr)4]NEt4
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

Table 3 Summary of the X-ray crystallographic data for compounds HL1b and HL1c and 4b, 12–16
HL1b
HL1c
4b
12
13
14
15
16
Chemical formula
C
36H32N4O6
C44H48N4O6
C35H32N4O4
C64H46MnN8O4·
0.56(CH2Cl2)
1094.03
Monoclinic
C12/c1
C
72H62Cl2Mn2N8O12
·
C
88H94MnN8O12
·
C
64H46FeN8O4
C72H66Fe2N8O14·2(C4H10O)·
2(FeCl4)·2(CH2Cl2)
2092.48
Triclinic
ˉ
P1
2.734(CH2Cl2)
1644.37
Monoclinic
P121/n1
2(CH2Cl2)
1680.55
Triclinic
P1
Colourless
FW
616.67
Triclinic
P1
Colourless
728.89
Monoclinic
P21/n
572.66
Triclinic
ˉ
P1
1046.97
Monoclinic
P21/c
Crystal system
Space group
Crystal colour
Crystal size (mm)
a (Å)
b (Å)
c (Å)
α (°)
β (°)
ˉ
ˉ
Colourless
Colourless
Colourless
Pale brown
Pale green
Yellow
0.20 × 0.24 × 0.38 0.13 × 0.23 × 0.38 0.20 × 0.26 × 0.26 0.24 × 0.28 × 0.28 0.12 × 0.16 × 0.16
0.05 × 0.10 × 0.20 0.10 × 0.18 × 0.20 0.20 × 0.26 × 0.26
12.1397(2)
12.9915(2)
19.7574(2)
91.9180(3)
94.7670(3)
93.8292(5)
3095.90(8)
4
1.323
0.091
1296
48 725
13.9875(1)
17.3504(2)
16.4504(2)
90
102.2764(6)
90
3901.03(7)
4
1.241
0.083
1552
63 778
8830 (0.035)
0.0480
0.1044
11.2058(2)
11.4803(2)
12.5044(2)
68.4885(9)
76.8457(8)
78.7278(8)
1446.14(4)
2
1.315
0.087
604
20 353
31.0387(4)
12.8870(3)
14.3510(2)
90
108.5904(10)
90
5440.82(17)
4
1.336
0.356
2266.8
27 287
6190 (0.045)
0.0435
11.7772(3)
19.0933(5)
16.9997(4)
90
95.7201(11)
90
3803.61(17)
2
1.436
0.660
1689.732
40 355
8666 (0.059)
0.0623
0.1159
12.6238(3)
13.0182(3)
14.6494(4)
79.745(2)
66.043(2)
84.906(2)
2164.56(10)
1
1.289
2.899
883
101 578
9047 (0.056)
0.0414
13.8206(2)
12.3235(2)
15.5858(2)
90
95.0494(6)
90
2644.24(7)
2
1.315
0.344
1088
58 363
6705 (0.020)
0.0367
0.0941
12.7160(2)
13.7894(2)
15.7739(2)
69.5889(6)
68.2544(6)
77.5909(6)
2396.07(6)
1
1.450
0.992
1074
35 573
γ (°)
V (Å3)
Z
Dcalcd (g cm−3
)
μ (mm−1
F (000)
)
Reflections collected
Unique reflections (Rint
R1 (I > 2σ(I))
)
14 010 (0.044)
0.0366
0.0750
6563 (0.050)
0.0384
0.0723
10 885 (0.030)
0.0482
0.0730
wR′2 (all data)
0.0518
0.0984
Table 4 Summary of the X-ray crystallographic data for compounds 17–22, 27 and 32
17 18 19
C108H102Cl12Fe3N12O18 C64H46N8NiO4
20
21
22
27
32
Chemical formula
C72H62FeN8O12 C88H94FeN8O12
2(CH2Cl2)
·
C72H62N8NiO12
C88H94N8NiO12
0.5(C4H8O)
1658.29
Monoclinic
P121/n1
Pale green
·
C39H39N5O5·
2(CH3OH)
721.85
Monoclinic
P121/c1
Colourless
C108H96FeN15O18·
2(C4H10O)·CH2Cl2
2181.07
Monoclinic
P21/n
Orange
FW
1287.18
Triclinic
P1
1681.47
Triclinic
P1
2451.06
Triclinic
P1
1049.83
Monoclinic
P121/c1
1290.04
Triclinic
ˉ
P1
Crystal system
Space group
Crystal colour
Crystal size (mm)
ˉ
ˉ
ˉ
Green
0.19
Yellow
Yellow
Pale green
Pale green
0.04 × 0.08 × 0.14 0.08 × 0.12 × 0.26
0.06 × 0.09 × 0.12 0.12 × 0.13 × 0.14 0.24 × 0.27 × 0.28 0.17 × 0.19 × 0.20 0.04 × 0.08 × 0.34
× 0.20 × 0.21
11.167(2)
12.168(2)
13.514(2)
110.506(6)
111.012(8)
99.483(8)
1541.4(5)
1
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
12.5703(5)
13.0224(5)
14.5998(6)
80.272(3)
66.147(4)
85.055(3)
2153.94(16)
1
12.0788(2)
14.7551(2)
17.4330(2)
65.7920(5)
83.7864(4)
86.3306(5)
2816.45(7)
1
13.8042(2)
11.9718(2)
15.9231(3)
90
96.2482(9)
90
2615.84(8)
2
1.333
11.4357(3)
13.5314(3)
16.1192(6)
109.6213(10)
94.1992(11)
108.888(2)
2176.15(12)
1
13.8101(2)
16.6015(3)
18.5646(3)
90
96.6213(9)
90
4227.89(12)
2
1.303
14.1426(2)
22.5440(4)
11.9542(2)
90
90.603(1)
90
3811.16(11)
4
1.258
20.2222(4)
23.5384(5)
23.4924(5)
90
92.4789(9)
90
11 171.9(4)
4
1.297
Dcalcd (g cm−3
)
1.411
0.324
672
1.296
3.071
884
1.445
0.736
1262
0.984
0.275
674
μ (mm−1
F (000)
)
0.430
1092
0.301
1763
0.087
1536
0.258
4580
Reflections collected
Unique reflections (Rint
R1 (I > 2σ(I))
18 323
6073 (0.093)
0.1448
22 779
8892 (0.035)
0.0456
48 417
12 808 (0.38)
0.0621
45 801
5958 (0.070)
0.0425
0.1154
33 033
9622 (0.091)
0.0936
42 745
41 684
8649 (0.038)
0.0551
0.1651
95 334
)
9640 (0.031)
0.0525
0.1120
20 309 (0.152)
0.1220
0.0881
wR′2 (all data)
0.3122
0.1234
0.0947
0.3102

View Online
Bis(3,5-bis(isopropoxyphenyl)-1H-pyrazol-1-yl)methane 4c.
3,5-Bis(isopropoxyphenyl)-1H-pyrazole 3c (2.84 g, 9.47 mmol),
KOH (2.12 g, 37.87 mmol), K2CO3 (5.23 g, 37.87 mmol), ben-
zyltriethylammonium chloride (0.22 g, 0.95 mmol) and CH2Cl2
(70 mL) were treated by the general procedure to afford a colour-
less solid. The residue was purified by flash chromatography
using Et2O–petroleum ether (1 : 9) and the major fraction crystal-
lized directly from the eluent to afford the title compound 4c as
colourless prisms (1.72 g, 53%) m.p. 153–155 °C. 1H NMR
(CDCl3, 400 MHz) δ: 1.18 (12H, d, J 6.0 Hz, 4 × CH3), 1.30
(12H, d, J 6.0 Hz, 4 × CH3), 4.38 (2H, spt, J 6.0 Hz, 2 × CH-
(CH3)2), 4.55 (2H, spt, J 6.0 Hz, 2 × CH(CH3)2), 6.31 (2H, s,
CH2), 6.76 (2H, s, 2 × pzCH), 6.95 (8H, m, Ph), 7.19 (2H, td, J
7.5, 2.0 Hz, Ph), 7.26 (2H, obsc. d, Ph), 7.35 (2H, m, Ph), 7.87
(2H, dd, J 7.5, 2.0 Hz, Ph). 13C NMR (CDCl3, 100 MHz) δ:
22.0 (CH3), 22.2 (CH3), 62.8 (CH2), 70.7 (CH(CH3)2), 71.1 (CH-
(CH3)2), 109.1 (pzCH), 114.4 (ArCH), 114.7 (ArCH), 120.5
(ArCH), 120.8 (ArCH), 121.5 (Cq), 123.6 (Cq), 128.1 (ArCH),
128.8 (ArCH), 129.8 (ArCH), 132.5 (ArCH), 141.0 (Cq), 147.8
(Cq), 155.01 (Cq). Found 707.3571 [C43H48N4O4 + Na]+
requires 707.3568.
colourless precipitate was collected by vacuum filtration to give
the desired product 3 as a colourless solid.
3,5-Bis(2-methoxyphenyl)-1H-pyrazole 3b. Hydrazine hydrate
(2.84 mL, 58.4 mmol), 1,3-bis(2-methoxyphenyl)propane-1,3-
dione 2b24 (8.34 g, 29.4 mmol) and MeOH (80 mL) were
treated by the general procedure to give the desired product 3b
1
as a colourless solid (8.11 g, 98%) m.p. 130–132 °C. H NMR
(CDCl3, 400 MHz) δ: 3.98 (6H, s, 2 × OCH3), 7.06 (4H, m, Ph),
7.20 (1H, s, pzCH), 7.32 (2H, m, Ph), 7.90 (2H, dd, J 7.5 Hz,
J 2.0 Hz, Ph), 9.64 (1H, br s, NH). 13C NMR (CDCl3,
100 MHz) δ: 55.7 (CH3), 103.7 (CH), 111.5 (CH), 120.1 (Cq),
121.1 (CH), 128.4 (CH), 129.0 (CH), 144.7 (Cq), 156.4 (Cq).
ESI+ (m/z (%)): 281 ([M + H]+, 100). HRMS-ES+ Found
281.1285. [C17H16N2O2 + H+]+ requires 281.1290.
3,5-Bis(2-isopropoxyphenyl)-1H-pyrazole 3c. Hydrazine
hydrate (1.50 mL, 30.85 mmol), 1,3-bis(2-isopropyloxyphenyl)-
propane-1,3-dione 2c (4.96 g, 14.57 mmol) and MeOH (75 mL)
were treated by the general procedure to afford a colourless gum.
This was purified by flash chromatography using Et2O–
petroleum (1 : 1) to afford the title product 3c as an off-white
solid (3.28 g, 67%) m.p. 105–107 °C. 1H NMR (CDCl3,
400 MHz) δ: 1.46 (12H, d, J 6.0 Hz, 4 × CH3), 4.73 (2H, spt,
J 6.0 Hz, 2 × CH(CH3)2), 7.04 (4H, m, Ph), 7.28 (2H, m, Ph),
7.31 (1H, s, pzCH), 7.91 (2H, d, J 7.5 Hz, Ph). 13C NMR
(CDCl3, 100 MHz) δ: 22.3 (CH3), 70.9 (CH(CH3)2), 103.9 (pzCH),
114.1 (ArCH), 121.0 (ArCH), 128.2 (ArCH), 128.3 (Cq),
128.6 (ArCH), 144.7 (Cq), 154.6 (Cq). HRMS-ES+ Found
337.1907 [C21H24N2O2 + H+]+ requires 337.1905
Bis(3,5-bis(2,6-dimethoxyphenyl)-1H-pyrazol-1-yl)methane 4d.
3,5-Bis(2,6-dimethoxyphenyl)-1H-pyrazole 31 (1.00 g, 2.94 mmol),
KOH (0.658 g, 11.7 mmol), K2CO3 (1.62 g, 11.7 mmol),
benzyltriethylammonium chloride (0.109 g, 0.59 mmol),
CH2Br2 (30 mL) were treated according to the general procedure
to afford a solid, which was purified by flash chromatography
using EtOAc as eluent then the major fraction was recrystallised
from pentane to afford the title compound 4d as a colourless
solid (0.725 g, 71%). 1H NMR (CDCl3, 400 MHz) δ: 3.53
(12H, s, 4 × OCH3), 3.69 (12H, s, 4 × OCH3), 6.25 (2H, s, CH2)
6.31 (2H, s, 2 × pzCH), 6.39 (4H, d, J 8.5 Hz, 4 × m-ArCH),
6.59 (4H, d, J 8.5 Hz, 4 × m-ArCH), 7.14 (2H, t, J 8.5 Hz,
2 × p-ArCH), 7.20 (2H, t, J 8.5 Hz, 2 × p-ArCH). 13C NMR
(CDCl3, 100 MHz) δ: 55.9 (OCH3), 56.5 (OCH3), 62.3 (CH2),
105.0 (m-ArCH), 105.2 (m-ArCH), 108.5 (Cq), 111.0 (pzCH),
113.7 (Cq), 128.7 (p-ArCH), 129.8 (p-ArCH), 134.4 (Cq),
144.1 (Cq), 153.2 (Cq), 158.9 (Cq). HRMS-ES+ Found
693.2918 [C39H40N4O8 + H]+ requires 693.2919.
General procedure for conversion of 3,5-disubstituted-1H-
pyrazoles into bis(3,5-bis(2-aryl)-1H-pyrazol-1-yl)methanes
A stirred mixture of 3,5-bis(aryl)-1H-pyrazole 3 (1 mol), KOH
(4 mol equiv.), K2CO3 (4 mol equiv.) and benzyltriethylammo-
nium chloride (0.1 mol equiv.) in CH2Cl2 (or CH2Br2 in the case
of 4d) were heated at reflux for 12 h. The reaction mixture was
then cooled to RT and the solids were removed by vacuum fil-
tration. The solids were washed well with CH2Cl2 and filtrate
was concentrated to dryness in vacuo.
General procedure for preparation of ethyl 2,2-bis(3,5-bis(aryl)-
1H-pyrazol-1-yl)acetates 5
Bis(3,5-bis(2-methoxyphenyl)-1H-pyrazol-1-yl)methane 4b.
3,5-Bis(2-methoxyphenyl)-1H-pyrazole 3b (22.7 g, 81.0 mmol),
KOH (18.1 g, 0.32 mol), K2CO3 (44.6 g, 0.32 mol), benzyl-
triethylammonium chloride (2.70 g, 16.2 mmol) and CH2Cl2
(300 mL) were treated by the general procedure to afford an off-
white solid. The residue was crystallized from EtOH to afford
the title compound 4b as a colourless solid (22.3 g, 96%) m.
p. 190–191 °C. 1H NMR (CDCl3, 400 MHz) δ: 3.75 (6 H, s, 2 ×
OCH3), 3.84 (6 H, s, 2 × OCH3), 6.36 (2H, s, CH2), 6.74 (2H, s,
2 × pzCH), 6.92 (4H, d, J 8.5 Hz, Ph), 6.97 (4H, dt, J 7.5 Hz,
J 1.0 Hz, Ph), 7.25 (4H, m, Ph), 7.39 (2H, m, Ph), 7.84 (2H, dd,
J 8.0 Hz, J 2.0 Hz, Ph). 13C NMR (CDCl3, 100 MHz) δ:
55.4 (CH3), 63.0 (CH2), 109.1 (CH), 110.8 (CH), 111.2 (CH),
119.4 (Cq), 120.6 (CH), 122.0 (Cq), 128.6 (CH), 128.7 (CH),
130.3 (CH), 132.0 (CH), 140.9 (Cq), 147.5 (Cq), 156.6 (Cq),
156.8 (Cq). ESI+ (m/z (%): 573 ([M + H]+, 100). HRMS-ES+
Found 573.2510 [C35H32N4O4 + H]+ requires 573.2502.
nBuLi (1.6 M in hexanes, 1.1 mol equiv.) was added to a stirred
mixture of bis(3,5-diaryl)-1H-pyrazol-1-yl)methane 4 (1 mol
equiv.) in anhyd. THF at −78 °C under N2 atmosphere. The reac-
tion mixture was allowed to warm up to 0 °C and stirred at this
temperature for a further 1 h. A solution of ethyl chloroformate
(3 mol equiv.) in anhyd. THF was added slowly to the lithiate
through a cannula at −78 °C under N2 atmosphere. The reaction
mixture was then allowed to warm to RT overnight before
quenching with sat. NH4Cl(aq). The layers were separated and the
aqueous phase extracted three times with EtOAc, before the
combined organic extracts were dried over anhyd. Na2SO4 and
concentrated to dryness in vacuo to afford a colourless gum.
Ethyl 2,2-bis(3,5-diphenyl-1H-pyrazol-1-yl)acetate 5a. nBuLi
(1.6 M in hexanes, 12.5 mL, 20.0 mmol), bis((3,5-diphenyl)-
This journal is © The Royal Society of Chemistry 2012
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1H-pyrazol-1-yl)methane 4a50 (8.061 g, 19.0 mmol) in anhyd.
THF (150 mL), and ethyl chloroformate (5.70 mL, 57.0 mmol)
in anhyd. THF (50 mL) was treated by the general procedure to
afford a colourless gum. The residue was recrystallized twice
from EtOH to afford the title compound 5a as a colourless solid
(7.61 g, 76%) m.p. 144–145 °C. 1H NMR (CDCl3, 400 MHz) δ:
1.23 (3H, t, J 7.5 Hz, CH3), 4.22 (2H, q, J 7.5 Hz, CH2), 6.64
(2H, s, 2 × pzCH), 7.00 (1H, s, CH), 7.32 (12H, m, Ph), 7.41
(4H, m, Ph), 7.84 (4H, m, Ph). 13C NMR (CDCl3, 100 MHz) δ:
14.0 (CH3), 62.9 (CH2), 71.6 (CH), 104.9 (CH), 126.0 (CH),
127.9 (CH), 128.4 (CH), 128.6 (CH), 128.9 (CH), 129.1 (CH),
129.6 (Cq), 133.0 (Cq), 146.2 (Cq), 151.7 (Cq), 164.9 (Cq).
ESI+ (m/z (%)): 525 ([M + H]+, 100). HRMS-ES+ Found
525.2285 [C34H28N4O2 + H]+ requires 525.2290.
(Cq), 120.87 (ArCH), 120.92 (ArCH), 124.2 (Cq), 128.1
(ArCH), 129.8 (ArCH), 131.9 (ArCH), 141.3 (Cq), 148.4 (Cq),
154.9 (Cq), 155.0 (Cq), 164.7 (Cq). HRMS-ES+ Found
757.3969 [C46H52N4O6 + H]+ requires 757.3960.
Bis(3,5-bis(2,6-dimethoxyphenyl)-1H-pyrazol-1-yl)methane
4d. A mixture of 3,5-bis(2,6-dimethoxyphenyl)-1H-pyrazole 3d
(1.00 g, 2.94 mmol), KOH (0.658 g, 11.7 mmol), K2CO3
(1.62 g, 11.7 mmol) and TEBAC (0.109 g, 0.59 mmol) in
CH2Br2 (30 mL) was treated by the general procedure to afford a
solid, which was purified by flash chromatography using EtOAc
as eluent then the major fraction was recrystallised from pentane
to afford the title compound 4d as a colourless solid (0.725 g,
71%). 1H NMR (CDCl3, 400 MHz) δ: 3.53 (12H, s, 4 × OCH3),
3.69 (12H, s, 4 × OCH3), 6.25 (2H, s, CH2) 6.31 (2H, s, 2 ×
pzCH), 6.39 (4H, d, J 8.5 Hz, 4 × m-ArCH), 6.59 (4H, d, J 8.5
Hz, 4 × m-ArCH), 7.14 (2H, t, J 8.5 Hz, 2 × p-ArCH), 7.20 (2H,
t, J 8.5 Hz, 2 × p-ArCH). 13C NMR (CDCl3, 100 MHz) δ: 55.9
(OCH3), 56.5 (OCH3), 62.3 (CH2), 105.0 (m-ArCH), 105.2 (m-
ArCH), 108.5 (Cq), 111.0 (pzCH), 113.7 (Cq), 128.7 (p-ArCH),
129.8 (p-ArCH), 134.4 (Cq), 144.1 (Cq), 153.2 (Cq), 158.9
(Cq). HRMS-ES+ Found 693.2918 [C39H40N4O8 + H]+ requires
693.2919.
Ethyl
2,2-bis(3,5-bis(2-methoxyphenyl)-1H-pyrazol-1-yl)
acetate 5b. nBuLi (1.6 M in hexanes, 15.4 mL, 24.6 mmol), bis-
(3,5-bis(2-methoxyphenyl)-1H-pyrazol-1-yl)methane 4b (13.4 g,
23.4 mmol) and ethyl chloroformate (7.00 mL, 70.2 mmol) in
anhyd. THF (70 mL) at −78 °C was treated by the general pro-
cedure to afford a colourless solid. The residue was recrystallized
twice from EtOH to afford the title compound 5b as a colourless
solid (12.3 g, 82%) m.p. 184–186 °C. νmax (KBr, cm−1) 1758
(CvO), 1584 (CvN). 1H NMR (CDCl3, 400 MHz) δ: 1.43
(3H, t, J 7.0 Hz, CH3), 3.55 (6H, s, 2 × OCH3), 3.84 (6H, s, 2 ×
OCH3), 4.50 (2H, q, J 7.0 Hz, CH2), 6.68 (2H, d, J 8.5 Hz, Ph),
6.72 (2H, s, 2 × pzCH), 6.82 (4H, m, Ph), 6.90 (1H, s, CH),
6.92 (2H, d, J 8.0 Hz, Ph), 6.97 (2H, dt, J 7.5 Hz, J 1.0 Hz, Ph),
7.26 (4H, m, Ph), 8.10 (2H, dd, J 7.5 Hz, J 2.0 Hz, Ph). 13C
NMR (CDCl3, 100 MHz) δ: 14.4 (CH3), 54.9 (CH3), 55.4
(CH3), 62.0 (CH2), 71.0 (CH), 109.0 (CH), 110.6 (CH), 111.1
(CH), 118.6 (Cq), 120.7 (CH), 120.8 (CH), 122.3 (Cq), 128.5
(CH), 129.5 (CH), 130.2 (CH), 131.9 (CH), 141.2 (Cq), 148.3
(Cq), 155.9 (Cq), 156.8 (Cq), 165.0 (Cq). ESI+ (m/z (%)): 645
([M + H]+, 100). HRMS-ES+ Found 667.2545 [C38H36N4O6 +
Na]+ requires 667.2533.
General procedure for preparation of 2,2-bis(3,5-bis(aryl)-1H-
pyrazol-1-yl)acetic acids HL1a–c
A solution of LiOH·H2O (4 mol equiv.) in H2O was added to a
stirred solution of ethyl 2,2-bis(3,5-diaryl-1H-pyrazol-1-yl)-
acetate 5 (1 mol equiv.) in THF at RT. The reaction mixture was
stirred at RT overnight, then the THF was evaporated in vacuo
and 1 M HCl(aq) was added until pH 1 upon cooling with ice
bath. The resultant solution was extracted three times with
EtOAc, then the combined organic extracts were dried over
anhyd. Na2SO4 and concentrated to dryness in vacuo. An excess
of Et2O or pentane, with the presence of ultrasonication in
several cases, were added to induce precipitation. The colourless
precipitate was collected by vacuum filtration to afford the
desired product scorpionate ligands as colourless solids.
Ethyl
acetate 5c. nBuLi (1.6 M in hexanes, 1.0 mL, 1.58 mmol), bis-
(3,5-bis(2-isopropoxyphenyl)-1H-pyrazol-1-yl)methane 4c
2,2-bis(3,5-bis(2-isopropoxyphenyl)-1H-pyrazol-1-yl)
2,2-Bis(3,5-diphenyl-1H-pyrazol-1-yl)acetic
acid
HL1a.
(0.986 g, 1.44 mmol) in anhyd. THF (15 mL) and ethyl chloro-
formate (0.41 mL, 4.32 mmol) in anhyd. THF (5 mL) was
treated by the general procedure to afford a colourless gum. The
residue was purified by flash chromatography using Et2O–
petroleum ether (1 : 9) and the major fraction recrystallized from
EtOH to afford the title compound 5c as a colourless solid
(0.831 g, 76%) m.p. 117–118 °C. νmax (KBr, cm−1) 1768
(CvO), 1603 (CvN), 1582 (CvN). 1H NMR (CDCl3,
400 MHz) δ: 1.04 (6H, d, J 6.0 Hz, 2 × CH3), 1.21 (6H, d, J 6.0
Hz, 2 × CH3), 1.27 (6H, d, J 6.0 Hz, 2 × CH3), 1.29 (6H, d, J
6.0 Hz, 2 × CH3), 1.38 (3H, t, J 7.0 Hz, COCH2CH3), 4.18 (2H,
spt, J 6.0 Hz, 2 × CH(CH3)2), 4.46 (2H, q, J 7.0 Hz, CH2), 4.52
(2H, spt, J 6.0 Hz, CH(CH3)2), 6.69 (2H, s, 2 × pzCH), 6.71
(4H, m, Ph), 6.78 (2H, td, J 7.5, 1.0 Hz, Ph), 6.93 (4H, m, Ph),
6.97 (1H, s, CHCO2Et), 7.21 (4H, m, Ph), 8.05 (2H, dd, J 8.0,
2.0 Hz, Ph). 13C NMR (CDCl3, 100 MHz) δ: 14.2 (CH2CH3),
21.5 (CH3), 22.0 (CH3), 22.2 (CH3), 22.3 (CH3), 61.7
(CH2CH3), 70.9 (CHCO2Et), 71.1 (CH(CH3)2), 72.2 (CH-
(CH3)2), 109.1 (pzCH), 114.97 (ArCH), 115.02 (ArCH), 120.7
LiOH·H2O (210 mg, 45.0 mmol) in H2O (90 mL) and ethyl
2,2-bis(3,5-diphenyl-1H-pyrazol-1-yl)acetate 5a (6.63 g,
12.6 mmol) in THF (270 mL) was treated by the general pro-
cedure to afford a colourless solid. This was recrystallised from
EtOH to afford the desired product HL1a as a colourless solid
(5.13 g, 82%) m.p. 190–191 °C. νmax (KBr, cm−1) 1753
(CO2H), 1554 (CvN). 1H NMR (CDCl3, 400 MHz) δ: 6.55
(2H, s, 2 × pzCH), 7.18 (9H, m, Ph, CH), 7.29 (2H, m, Ph),
7.38 (2H, m, Ph), 7.44 (4H, m, Ph), 7.85 (4H, m, Ph), 9.80 (1H,
br s, OH). 13C NMR (CDCl3, 100 MHz) δ: 67.4 (CH), 105.1
(CH), 126.1 (CH), 128.1 (Cq), 128.5 (CH), 128.7 (CH), 128.9
(CH), 129.3 (CH), 131.8 (Cq), 146.7 (Cq), 152.0 (Cq), 165.0
(Cq). ESI+ (m/z (%)): 497 ([M + H]+, 100). HRMS-ES+ Found
519.1791 [C32H24N4O2 + Na]+ requires 519.1797. HPLC
Rf = 9.25 min.
2,2-Bis(3,5-bis(2-methoxyphenyl)-1H-pyrazol-1-yl)acetic acid
HL1b. LiOH·H2O (0.210 g, 5.00 mmol) in H2O (12 mL) and
ethyl 2,2-bis(3,5-bis(2-methoxyphenyl)-1H-pyrazol-1-yl)acetate
Dalton Trans.
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5b (0.91 g, 1.41 mmol) in THF (35 mL) was treated by the
general procedure to afford a colourless solid. This was recrystal-
lised from EtOH to afford the desired product HL1b as colour-
less prisms suitable for single crystal X-ray diffraction (0.82 g,
94%) m.p. 193–194 °C. νmax (KBr, cm−1) 1774 (CO2H), 1604
(CvN), 1584 (CvN). 1H NMR (CDCl3, 400 MHz) δ: 3.68
(6H, s, 2 × OCH3), 3.85 (6H, s, 2 × OCH3), 6.64 (2H, d, J 8.5
Hz, Ph), 6.71 (2H, s, 2 × pzCH), 6.82 (2H, t, J 7.5 Hz, Ph), 6.95
(2H, d, J 8.5 Hz, Ph), 6.98 (4H, m, Ph), 7.08 (1H, s, CH), 7.24
(2H, dt, J 8.0, 1.5 Hz, Ph), 7.31 (2H, dt, J 7.5, 2.0 Hz, Ph), 8.03
(2H, dd, J 7.5 Hz, J 2.0 Hz, Ph), 9.20 (1H, br s, OH). 13C NMR
(CDCl3, 100 MHz) δ: 55.1 (CH3), 55.4 (CH3), 69.7 (CH), 109.4
(CH), 110.5 (CH), 111.3 (CH), 117.3 (Cq), 120.7 (CH), 120.8
(CH), 121.0 (Cq), 129.1 (CH), 129.4 (CH), 130.8 (CH), 131.3
(CH), 141.7 (Cq), 149.0 (Cq), 155.7 (Cq), 156.9 (Cq), 164.5
(Cq). ESI+ (m/z (%)): 639 ([M + Na]+, 70). HRMS-ES+ Found
639.2216 [C36H32N4O6 + Na]+ requires 639.2220. HPLC
Rf = 9.64 min.
(10 mL) was added to a stirred solution of ethynyl magnesium
bromide (0.5 M solution in THF, 45 mL, 22.50 mmol) in THF
(80 mL) at −20 °C under nitrogen atmosphere. After 0.25 h, the
cooling bath was removed and the mixture allowed to warm to
RT over 2 h. Saturated NH4Cl (30 mL) was added, followed by
EtOAc (50 mL). The layers were separated then the aqueous
layer was extracted with EtOAc (3 × 50 mL), then the combined
organic extracts were dried over anhyd. Na2SO4, filtered and
concentrated to dryness in vacuo to afford the product 7 as a
yellow coloured solid (3.2 g, 92%). 1H NMR (CDCl3,
400 MHz) δ: 2.45 (1H, d, J 2.5 Hz, CuCH), 3.89 (6H, s, 2 ×
OCH3), 4.12 (1H, d, J 11.5 Hz, OH), 5.93 (1H, dd, J 11.5,
2.4 Hz, CHOH), 6.60 (2H, d, J 8.5 Hz, ArCH-3,-5), 7.24 (1H, t,
J 8.5 Hz, ArCH-4). 13C NMR (CDCl3, 100 MHz) δ: 55.9
(HCOH), 56.3 (2 × OCH3), 71.0 (CuCH), 84.7 (CuCH), 104.5
(CH), 116.9 (Cq), 129.5 (CH), 157.4 (Cq). HRMS-ES+ Found
215.0678 [C11H12O3 + Na]+ requires 215.0679.
(NB: This compound has also been prepared by Whalley and
co-workers,54 but by a different technique, and without quoting
any other physical data other than the melting point (88 °C) and
elemental analysis.)
2,2-Bis(3,5-bis(2-isopropoxyphenyl)-1H-pyrazol-1-yl)acetic
acid HL1c. LiOH·H2O (0.083 g, 1.98 mmol) in H2O (5 mL) and
ethyl
2,2-bis(3,5-bis(2-isopropoxyphenyl)-1H-pyrazol-1-yl)-
acetate 5c (0.50 g, 0.66 mmol) in THF (15 mL) was treated
according to the general procedure to afford a colourless solid.
This solid was recrystallised from EtOAc/CH2Cl2 to afford the
title compound HL1c as colourless prisms suitable for single
crystal X-ray diffraction (0.475 g, 99%). m.p. 174–176 °C. νmax
(KBr, cm−1) 1759 (CO2H), 1603 (CvN), 1583 (CvN). 1H
NMR (CDCl3, 400 MHz) δ: 1.10 (6H, d, J 6.0 Hz, 2 × CH3),
1.31 (6H, d, J 6.5 Hz, 2 × CH3), 1.34 (12H, d, J 6.5 Hz, 4 ×
CH3), 4.30 (2H, m, 2 × CH(CH3)2), 4.60 (2H, spt, J 6.0 Hz, 2 ×
CH(CH3)2), 6.62 (2H, d, J 8.0 Hz, Ph), 6.72 (2H, s, 2 × pzCH),
6.77 (2H, t, J 7.5 Hz, Ph), 6.94 (2H, d, J 8.0 Hz, Ph), 7.00 (2H,
m, Ph), 7.01 (2H, m, Ph), 7.16 (1H, s, CH), 7.18 (2H, m, Ph),
7.26 (2H, obsc. td, Ph), 8.08 (2H, dd, J 7.5, 2.0 Hz, Ph). 13C
NMR (CDCl3, 100 MHz) δ: 21.7 (CH3), 21.8 (CH3), 22.1
(CH3), 22.2 (CH3), 69.4 (CHCO2H), 70.6 (CH(CH3)2), 71.2
(CH(CH3)2), 109.6 (pzCH), 113.7 (ArCH), 113.9 (ArCH), 118.9
(Cq), 120.5 (ArCH), 120.6 (ArCH), 122.3 (Cq), 129.0 (ArCH),
129.3 (ArCH), 130.2 (ArCH), 131.2 (ArCH), 141.8 (Cq), 149.1
(Cq), 154.5 (Cq), 155.2 (Cq), 164.7 (Cq). Found 751.3469
[C44H48N4O6 + Na]+ requires 751.3466.
Preparation of 1,3-bis(2,6-dimethoxyphenyl)-propyn-3-ol 8. A
mixture of 2,6-dimethoxyiodobenzene (4.125 g, 15.6 mmol), Pd-
(PPh3)2Cl2 (0.218 g, 0.311 mmol), CuI (0.109 g, 0.572 mmol)
and DIPEA (39 mL) in anhyd. THF (40 mL) was degassed for
0.5 h. A solution of 3-(2,6-dimethoxyphenyl)-propyn-3-ol 7
(2.95 g, 15.3 mmol) in anhyd. THF (20 mL) was then added
drop-wise and the resultant mixture heated at reflux with stirring
for 24 h. The mixture was then cooled to RT, filtered through
Celite™ and concentrated to dryness in vacuo. The residue was
purified by flash chromatography using CH2Cl2–EtOAc (4 : 1)
and the major fraction recrystallised from pentane to afford the
1
title compound 8 as a colourless solid (2.10 g, 42%). H NMR
(CDCl3, 400 MHz) δ: 3.82 (6H, s, 2 × OCH3), 3.90 (6H, s, 2 ×
OCH3), 4.05 (1H, dd, J 11.5, 8.5 Hz, OH), 6.21 (1H, d, J
11.5 Hz, CHOH), 6.48 (2H, d, J 8.5 Hz, m-CH), 6.59 (2H, d, J
8.5 Hz, m-CH), 7.17 (1H, t, J 8.5 Hz, p-CH), 7.21 (1H, t, J 8.5
Hz, p-CH). 13C NMR (CDCl3, 100 MHz) δ: 55.96 (OCH3),
56.03 (OCH3), 57.2 (CH), 75.2 (Cq), 98.8 (Cq), 103.5 (CH),
104.7 (CH), 118.3 (Cq), 129.1 (CH), 129.4 (CH), 157.7 (Cq),
161.6 (Cq). HRMS-ES+ Found 351.1203 [C19H20O5 + Na]+
requires 351.1203.
Preparation of 2,6-dimethoxybenzaldehyde 6. To a solution of
nBuLi (2.5 M in hexanes, 34 mL, 87 mmol) in THF (50 mL) at
−5 °C under atmosphere of nitrogen was added 1,3-dimethoxy-
benzene (10.0 g, 9.22 mL, 72.4 mmol). Over the next 1 h the
temperature was allowed to warm to 25 °C, then cooled to
−50 °C and DMF (7.11 mL, 100 mmol) was added. The reaction
mixture was poured onto a mixture of HCl (36%, 30 g, 25 mL)
and H2O (300 mL) at 0 °C. The mixture was extracted with
EtOAc (3 × 100 mL) to afford the title compound 6 as a colour-
Preparation of 1,3-bis(2,6-dimethoxyphenyl)-propyn-3-one
9. MnO2 (4.61 g, 53 mmol) was added to a stirred solution
of 1,3-bis(2,6-dimethoxyphenyl)-propyn-3-ol
8
(1.16 g,
3.53 mmol) in CHCl3 (15 mL) at RT and the resultant mixture
stirred at RT for 2 days. After this time the mixture was filtered
through Celite™, evaporated to dryness in vacuo and the residue
recrystallised from pentane to afford the title compound 9 as a
1
1
colourless solid (1.00 g, 86%). H NMR (CDCl3, 400 MHz) δ:
less solid (7.4 g, 62%). H NMR (CDCl3, 400 MHz) δ: 3.90
3.84 (6H, s, 2 × OCH3), 3.85 (6H, s 2 × OCH3), 6.49 (2H, d, J
8.5 Hz, 2 × m-CH), 6.58 (2H, d, J 8.5 Hz, 2 × m-CH), 7.30 (2H,
m, 2 × p-CH). 13C NMR (CDCl3, 100 MHz) δ: 56.00 (OCH3),
56.04 (OCH3), 84.5 (Cq), 98.8 (Cq), 99.3 (Cq), 103.3 (m-
ArCH), 104.3 (m-ArCH), 119.6 (Cq), 131.7 (p-ArCH), 132.3
(p-ArCH), 158.4 (Cq), 163.0 (Cq), 178.0 (CvO). HRMS-ES+
Found 349.1046 [C19H18O5 + Na]+ requires 349.1046.
(6H, s, 2 × OCH3), 6.58 (2H, d, J 8.5 Hz, m-CH), 7.45 (1H, t, J
8.5 Hz, p-CH), 10.51 (1H, s, CHO). 13C NMR (CDCl3,
100 MHz) δ: 56.0 (OCH3), 103.8 (CH), 114.3 (Cq), 135.9 (CH),
162.1 (Cq), 189.4 (CHO).
Preparation of 3-(2,6-dimethoxyphenyl)-propyn-3-ol 7. 2,6-
Dimethoxybenzaldehyde 6 (3.0 g, 18.05 mmol) in anhyd. THF
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3,5-Bis(2,6-dimethoxyphenyl)-1H-pyrazole 3d. To a stirred
slurry of 1,3-bis(2,6-dimethoxyphenyl)-propyn-3-one 9 (1.62 g,
4.96 mmol) and N2H4·H2O (65% H2O v/v, 0.407 mL,
5.46 mmol) in EtOH (50 mL) was heated at reflux overnight
with stirring. The mixture was then evaporated to dryness in
vacuo, and the residue recrystallised from pentane to afford the
concentrated to dryness in vacuo to afford a colourless solid.
This was purified by flash chromatography using a pentanes-
Et2O elution gradient, followed by recrystallisation with abs.
EtOH of the major fraction to furnish the title compound 10 as
colourless cubes (0.945 g, 63%) m.p. 200–201 °C. νmax (KBr,
cm−1) 3510, 2903, 2848, 1540, 1451, 1102, 1065, 792. 1H
NMR (CDCl3, 400 MHz) δ: 1.72 (24H, m, 12 × CH2), 1.88
(24H, m, 12 × CH2), 2.01, (12H, m, 6 × CH2), 4.34 (1H, dd, J
6.5, 6.5 Hz, OH), 4.41 (2H, dd, J 6.5, 6.5 Hz, CH2OH), 5.96
(2H, s, 2 × pzCH), 6.85 (1H, dd, J 6.0, 6.0 Hz, CH). 13C NMR
(CDCl3, 100 MHz) δ: 28.5 (CH), 28.7 (CH), 33.8 (Cq), 34.8
(Cq), 36.4 (CH2), 37.0 (CH2), 41.8 (CH2), 42.4 (CH2), 64.7
(CH2OH), 75.8 (CH), 101.6 (CH), 153.6 (Cq), 159.6 (Cq). ESI
m/z 715 (MH+, 100%). HRMS Found 737.5129 [C48H66N4O +
Na]+ requires 737.5129.
1
title product 3d as a colourless solid (1.518 g, 90%). H NMR
(CDCl3, 400 MHz) δ: 3.87 (12H, s, 4 × OCH3), 6.68 (4H, d, J
8.5 Hz, m-CH), 7.10 (1H, s, pzCH), 7.28 (2H, t, J 8.5 Hz,
p-CH). 13C NMR (CDCl3, 100 MHz) δ: 56.0 (OCH3), 104.4
(CH), 109.7 (CH), 128.8 (CH), 158.3 (Cq). (NB: Resonances
corresponding to the ipso-Cq and the pz-Cq were not visible
with multiple scans or using a Bruker AVC500 at 125.8 MHz.)
HRMS-ES+ Found 341.1495 [C19H20N2O4 + H]+ requires
341.1496.
Preparation of 2,2-bis[3,5-bis(adamantyl)-1H-pyrazol-1-yl]-
ethanal 11. Conducted under Swern conditions,25 a solution of
DMSO (0.16 mL, 2.307 mmol) was added to a stirred solution
of oxalyl chloride (0.20 mL, 2.307 mmol) in anhyd. CH2Cl2
(15 mL) at −78 °C, under N2. The resultant mixture was stirred
at −78 °C for 1 h, then a mixture of alcohol 10 (1.500 g,
2.098 mmol) and NEt3 (0.73 mL, 5.244 mmol) in anhyd.
CH2Cl2 (30 mL) was added drop-wise via cannula. The resultant
mixture was stirred at −78 °C for 3 h and then quenched by the
slow addition of sat. NaCl(aq) (40 mL) and warmed to RT. The
layers were separated and the aqueous layer extracted with
CH2Cl2 (3 × 25 mL). The combined organic extracts were dried
over anhyd. Na2SO4, filtered and concentrated to dryness in
vacuo to afford the title compound 11 as a colourless solid
(1.488 g, 99%). νmax (KBr, cm−1) 2904, 2848, 1748(CvO),
Preparation of ethyl bis[3,5-bis(adamantyl)-1H-pyrazol-1-yl]-
acetate 5e. nBuLi (1.6 M in hexanes, 17.99 mL, 28.783 mmol
was added drop-wise to a stirred solution of bis(3,5-bis(adaman-
tyl)-1H-pyrazol-1-yl)methane 4e (18.764 g, 27.412 mmol) in
anhyd. THF (285 mL) at −78 °C under N2 atmosphere. The
resultant mixture was allowed to slowly warm to −20 °C over
2 h, and then cooled once again to −78 °C and quenched by the
addition of ClCO2Et (2.88 mL, 30.153 mmol). The resultant
mixture was allowed to warm slowly to RT with stirring over-
night. Sat. NH4Cl(aq) (300 mL), followed by CH2Cl2 (250 mL)
were then added and the layers separated. The aqueous layer was
extracted with CH2Cl2 (3 × 70 mL) and then the combined
organic extracts were dried over anhyd. Na2SO4, filtered and
concentrated to dryness in vacuo to afford a pale yellow coloured
foam. This was found to be a mixture of the starting dimer 4e
and ester 5e, which was purified by flash chromatography using
Et2O–pentanes (1 : 9) to afford, in order of elution, starting
dimer 4e (13.510 g, 72% recovery) and ester 5e (2.586 g, 14%).
The ester was recrystallised from EtOH to afford the desired
compound as colourless prisms. m.p. 169.5–170.5 °C. νmax
(KBr, cm−1) 3050, 2937, 2836, 1747, 1604, 1584, 1471, 1247,
1
1542, 1451, 1359, 1304, 1253, 1189, 1102, 794, 733. H NMR
(CDCl3, 400 MHz) δ: 1.69 (24H, m, 12 × CH2), 1.89 (24H, m,
12 × CH2), 1.99 (12H, m, 6 × CH2), 6.01 (2H, s, 2 × pzCH),
7.14 (1H, s, CH), 9.91 (1H, s, CHO).13C NMR (CDCl3,
100 MHz) δ: 28.4 (CH), 28.7 (CH), 34.0 (Cq), 34.4 (Cq), 36.3
(CH2), 37.0 (CH2), 41.3 (CH2), 42.3 (CH2); 80.4 (CH), 102.0
(CH), 154.4 (Cq), 160.1 (Cq), 190.4 (CHO). HRMS Found
713.5154 [C48H64N4O + H]+ requires 713.5153.
1
1189, 1116, 1023, 753. H NMR (CDCl3, 400 MHz) δ: 1.28,
(3H, t, J 7.0 Hz, CH2CH3), 1.71 (24H, br s, 12 × CH2), 1.86
(24H, m, 12 × CH2), 1.99 (12H, br s, 6 × CH2), 4.29 (2H, q, J
7.0 Hz, CH2CH3), 5.93 (2H, s, 2 × pzCH), 7.17 (1H, s, CH).
13C NMR (CDCl3, 100 MHz) δ: 14.2 (CH3), 28.5 (CH), 28.8
(CH), 33.8 (Cq), 34.3 (Cq), 36.5 (CH2), 37.1 (CH2), 41.7 (CH2),
42.3 (CH2), 61.8 (CH2), 75.6 (CH), 101.1 (CH), 152.8 (Cq),
159.4 (Cq), 166.3 (Cq). ESI m/z 757 (MH+, 100%). HRMS
Found 757.5407 [C50H68N4O2 + H]+ requires 757.5415.
General procedure for metal complex formation for type ML2
or (ML)2 12–22
The requisite metal salt (1.05 mol equiv.) was added to a stirred
mixture of HL1a, HL1b or HL1c (1 mol equiv.) and KOtBu (1.05
or 3 mol equiv.) in degassed anhyd. THF (ca. 15 mL mmol−1 of
ligand) in a Schlenk flask at RT under N2 atmosphere. The resul-
tant mixture was stirred either at RT or with heating until com-
plete, before the mixture was cooled to RT and the resultant
precipitate collected by filtration. The solid was washed well
with Et2O to yield the desired complexes.
Preparation of 2,2-bis[3,5-bis(adamantyl)-1H-pyrazol-1-yl]-
ethanol 10. A solution of ester 5e (1.586 g, 2.097 mmol) in
anhyd. THF (20 mL) was added drop-wise to an ice-cold slurry
of LiAlH4 (0.513 g, 13.546 mmol) in anhyd. THF (30 mL)
under N2 atmosphere. The once addition was complete, the
resultant mixture was heated to reflux overnight. After this time
the mixture was cooled to 0 °C and quenched by the slow
addition of H2O (50 mL). EtOAc (50 mL) was then added and
the mixture filtered. The solids were washed well with EtOAc
and H2O, before the layers were separated. The aqueous layer
was extracted with EtOAc (3 × 30 mL), then the combined
organic extracts were dried over anhyd. Na2SO4, filtered and
[Mn(II)(L1a)2] 12. Ligand HL1a (0.200 g, 0.40 mmol) and
KOtBu (0.049 g, 0.43 mmol) and anhyd. THF (5 mL) were suc-
cessively added to a Schlenk flask under N2 atmosphere. The
reaction mixture was stirred for 0.5 h at the RT, degassed and
anhyd. MnCl2 (0.055 g, 0.43 mmol) was added, which resulted
in the immediate formation of a colourless precipitate. The reac-
tion mixture was heated to reflux for 1 h, cooled to RT and
Dalton Trans.
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stirred for 24 h. The beige precipitate was removed by vacuum
filtration and washed with THF, the filtrate was concentrated and
colourless crystals appropriate for X-ray analysis were obtained
by slow diffusion of Et2O into CH2Cl2 solution (0.105 g, 50%).
m.p. >230 °C. νmax (KBr, cm−1) 1670 (CO2−), 1556 (CvN).
Found 1068.2942 [C64H46MnN8O4 + Na]+ requires 1068.2915.
HPLC Rf = 9.78 min.
for 24 h. A precipitate was removed by vacuum filtration and
washed with THF, the filtrate was concentrated to afford the title
compound as yellow coloured powder (0.180 g, 69%). Yellow
crystals were obtained by slow diffusion of Et2O into CH2Cl2
solution (0.103 g, 39%). m.p. 220 °C (dec.) νmax (KBr, cm−1
)
=
1672 (CO2−), 1608 (CvN), 1584 (CvN). HPLC Rf
10.09 min. Found: C, 48.66; H, 3.60; N, 6.44.
C72H66Cl8Fe4N8O14 requires: C, 48.74; H, 3.75; N, 6.32. NB:
Attempts to visualise the predicted isotope distribution pattern of
the molecular ion through a variety of mass spectrometry tech-
niques i.e. ES+/−, FAB, EI, FI and MALDI were unsuccessful
and did not show the molecular ion or an easily rationalised
fragment.
[Mn(II)ClL1b]2 13. MnCl2 (0.044 g, 0.35 mmol), ligand HL1b
(0.200 g, 0.33 mmol) and KOtBu (0.040 g, 0.35 mmol) in
anhyd. THF (5 mL) under N2 atmosphere were heated to reflux
for 1 h, cooled to RT and stirred for 24 h. A colourless precipi-
tate was removed by vacuum filtration and washed with THF, the
filtrate was concentrated to give a beige powder (0.200 g). The
precipitate was redissolved in CH2Cl2 (5 mL) and Et2O (50 mL)
was added to cause precipitation of the title compound as colour-
less powder (0.184 g, 79%). Colourless crystals appropriate for
X-ray analysis were obtained by slow diffusion of Et2O into a
CH2Cl2 solution. m.p. >230 °C. νmax (KBr, cm−1) 1656 (CO2−),
1608 (CvN), 1585 (CvN). HPLC Rf = 9.92 min. Found: C,
60.98; H, 4.42; N, 7.89. C72H62Cl2Mn2N8O12 requires: C,
61.24; H, 4.43; N, 7.94. NB: Attempts to visualise the predicted
isotope distribution pattern of the molecular ion through a
variety of mass spectrometry techniques i.e. ES+/−, FAB, EI, FI
and MALDI were unsuccessful and did not show the molecular
ion or an easily rationalised fragment.
[Fe(II)(L1b)2] 17. Fe(BF4)2·6H2O (0.110 g, 0.325 mmol) was
added to a stirred mixture of ligand HL1b (0.200 g, 0.325 mmol)
and KOtBu (0.038 g, 0.341 mmol) in degassed THF (5 mL) at
RT under N2 atmosphere. The resultant mixture was stirred for
4 h, before Et2O (5 mL) was added and the precipitate collected
by filtration. This was recrystallised from EtOH/CHCl3 to afford
the title complex as small, pale green coloured prisms (0.186 g,
78%) that were suitable for single crystal X-ray analysis. m.p.
>250 °C (dec.) νmax (KBr, cm−1) 1661 (CO2−), 1607 (CvN).
Found 1309.3782 [C72H62FeN8O12 + Na]+ requires 1309.3731.
HPLC Rf = 9.31 min.
[Fe(II)(L1c)2] 18. FeCl2 (0.022 g, 0.11 mmol), ligand HL1c
(0.075 g, 0.10 mmol) and KOtBu (0.012 g, 0.11 mmol) in
anhyd. THF (5 mL) under N2 atmosphere and were heated to
reflux for 1 h, cooled to RT and stirred for 24 h. A precipitate
was formed which was collected by suction filtration and washed
with THF, followed by Et2O. The solid was then dissolved in
CH2Cl2, filtered through a plug of Celite™ and then the CH2Cl2
solution containing the product was placed in a jar containing
Et2O. Green coloured crystals of the title compound were sub-
sequently obtained by slow diffusion of Et2O into the CH2Cl2
solution (0.056 g, 72%). m.p. >240 °C. νmax (KBr, cm−1) 1669
[Mn(II)(L1c)2] 14. MnCl2 (0.014 g, 0.11 mmol), ligand HL1c
(0.075 g, 0.10 mmol) and KOtBu (0.012 g, 0.11 mmol) in
anhyd. THF (5 mL) under N2 atmosphere and were heated to
reflux for 1 h, cooled to RT and stirred for 24 h. A precipitate
was formed which was collected by suction filtration and washed
with THF, followed by Et2O. The solid was then dissolved in
CH2Cl2, filtered through a plug of Celite™ and then the CH2Cl2
solution containing the product was placed in a jar containing
Et2O. Colourless crystals of the title compound were sub-
sequently obtained by slow diffusion of Et2O into the CH2Cl2
solution (0.068 g, 87%) m.p. >240 °C. νmax (KBr, cm−1) 1667
(CO2−), 1605 (CvN). Found 1533.6294 [C88H94FeN8O12
+
(CO2−), 1607 (CvN). Found 1533.6294 [C88H94FeN8O12
+
Na]+ requires 1533.6236. Found: C, 69.82; H, 6.17; N, 7.29.
C88H94FeN8O12 requires: C, 69.92; H, 6.27; N, 7.41.
Na]+ requires 1533.6236. Found: C, 69.87; H, 6.19; N, 7.35.
C88H94MnN8O12 requires: C, 69.96; H, 6.27; N, 7.42.
[Fe(III)(L1b)2][Fe(III)Cl4] 19. FeCl3 (0.057 g, 0.35 mmol),
ligand HL1b (0.200 g, 0.33 mmol) and KOtBu (0.040 g,
0.35 mmol) in anhyd. THF (5 mL) were treated by the general
procedure to give a yellow-brown mixture. The reaction mixture
was heated to reflux for 1 h, cooled to RT and stirred for 2 days.
A yellow precipitate was removed by vacuum filtration and
washed with THF, the filtrate was concentrated and the desired
complex was obtained by precipitation from CH2Cl2 solution
with Et2O to afford the complex as beige powder (0.095 g,
39%). Yellow prisms appropriate for X-ray analysis were
obtained by slow evaporation of CH2Cl2 solution. m.p. >250 °C.
[Fe(II)(L1a)2] 15. Fe(BF4)2·6H2O (0.056 g, 0.166 mmol) was
added to a stirred mixture of ligand HL1a (0.150 g, 0.302 mmol)
and KOtBu (0.102 g, 0.906 mmol) in degassed THF (5 mL) at
RT under N2 atmosphere. The resultant mixture was stirred for
4 h, before Et2O (5 mL) was added and the precipitate collected
by filtration. This was recrystallised from EtOH/CHCl3 to afford
the title complex as beige coloured powder (0.149 g, 94%). Pale
green coloured crystals suitable for single crystal X-ray analysis
were obtained upon slow infusion of Et2O into a CH2Cl2 of the
complex m.p. >250 °C (dec.). νmax (KBr, cm−1) 1669 (CO2−),
1556 (CvN). Found 1069.2898 [C64H46FeN8O4 + Na]+ requires
1069.2885. HPLC Rf = 9.62 min. Found: C, 73.53; H, 4.26; N,
10.68. C64H46FeN8O4 requires: C, 73.42; H, 4.43; N, 10.70.
νmax (KBr, cm−1
)
1584 (CvN). Found 1309.3771
−
[C72H62FeN8O12 − FeCl4 + Na]+ requires 1309.3731. HPLC
Rf = 9.92 min.
[{Fe(II)(H2O)L1b}2][Fe(III)Cl4]2
16. FeCl2
(0.044
g,
[Ni(II)(L1a)2] 20. Anhyd. NiCl2 (0.020 g, 0.151 mmol) was
added to a stirred mixture of ligand HL1a (0.150 g, 0.302 mmol)
and KOtBu (0.050 g, 0.454 mmol) in degassed anhyd. THF
(5 mL) at RT under atmosphere of N2. The resultant mixture was
0.35 mmol), ligand HL1b (0.200 g, 0.33 mmol) and KOtBu
(0.040 g, 0.35 mmol) in anhyd. THF (5 mL) under N2 atmos-
phere and were heated to reflux for 1 h, cooled to RT and stirred
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stirred for 4 h, before Et2O (5 mL) was added and the precipitate
collected by filtration. This was recrystallised from EtOH/CHCl3
to afford the title complex as small, pale green coloured prisms
(0.129 g, 82%) that were suitable for single crystal X-ray analy-
sis. m.p. >250 °C. νmax (KBr, cm−1) 1631 (CO2−), 1613
sequentially and the mixture allowed to warm to RT overnight
with stirring under nitrogen atmosphere. After this time the
solvent was removed in vacuo and the residue taken up in
EtOAc and brine. The layers were separated and the organic
layer was washed twice with brine, before being dried over
anhyd. Na2SO4, filtered and concentrated to dryness in vacuo.
The crude products were purified by either direct recrystallisation
or flash chromatography followed by recrystallisation.
(CvN), 1550 (CvN). Found 1071.2871 [C64H46N8NiO4
+
Na]+ requires 1071.2888. HPLC Rf = 9.93 min.
[Ni(II)(L1b)2] 21. Anhyd. NiCl2 (0.021 g, 0.155 mmol) was
added to a stirred mixture of ligand HL1b (0.100 g, 0.155 mmol)
and KOtBu (0.027 g, 0.243 mmol) in degassed anhyd. THF
(2.5 mL) at RT under atmosphere of N2. The resultant mixture
was stirred for 4 h, before Et2O (2.5 mL) was added and the pre-
cipitate collected by filtration. This was recrystallised by slow
diffusion of Et2O into CH2Cl2 solution to afford the title
complex as small, pale green coloured prisms (0.086 g, 86%)
that were suitable for single crystal X-ray analysis. m.p. >250 °C
νmax (KBr, cm−1) 1663 (CO2−), 1608 (CvN). Found 1311.3762
Pz-NHiPr 24. Ligand HL1f 17,21 (0.200 g, 1.04 mmol),
iPrNH2 (0.106 mL, 1.25 mmol), DIC (0.806 mL, 5.20 mmol),
HOBt (0.703 g, 5.20 mmol), DIPEA (1.72 mL, 10.7 mmol) and
DMF (10 mL) was treated by the general procedure to afford the
crude off-white product. This was purified by flash chromato-
graphy using 1 : 1 EtOAc–petroleum ether to afford the title
compound 24 as a colourless microcrystalline solid (0.130 g,
53%). m.p. 103–105 °C. νmax (KBr, cm−1) 3298 (NH), 1669
(CvO), 1575 (CvN), 1555 (CvN). 1H NMR (CDCl3,
400 MHz) δ: 1.08 (6H, d, J 6.5 Hz, 2 × CH3), 4.05 (1H, m,
CH), 6.25 (2H, dd, J 2.5, 2.5 Hz, pzCH), 7.11 (1H, s, CH), 7.43
(1H, d, J 7.5 Hz, NH), 7.55 (2H, d, J 2.5 Hz, pzCH), 7.70 (2H,
d, J 2.5 Hz, pzCH). 13C NMR (CDCl3, 100 MHz) δ: 22.1
(CH3), 42.1 (CH), 75.2 (CH), 107.0 (pzCH), 141.2 (pzCH),
162.9 (CO). HRMS-ES+ Found 234.1349 [C11H15N5O + H]+
requires 234.1349.
[C72H62N8NiO12 + Na]+ requires 1311.3733. HPLC Rf
=
9.95 min.
[Ni(II)(L1c)2] 22. Anhyd. NiCl2 (0.014 g, 0.11 mmol), ligand
HL1c (0.075 g, 0.10 mmol) and KOtBu (0.012 g, 0.11 mmol) in
anhyd. THF (5 mL) under N2 atmosphere and were heated to
reflux for 1 h, cooled to RT and stirred for 24 h. A precipitate
was formed which was collected by suction filtration and washed
with THF, followed by Et2O. The solid was then dissolved in
CH2Cl2, filtered through a plug of Celite™ and then the CH2Cl2
solution containing the product was placed in a jar containing
Et2O. Colourless crystals of the title compound were sub-
sequently obtained by slow diffusion of Et2O into the CH2Cl2
solution (0.053 g, 68%) that were suitable for single crystal
X-ray analysis. m.p. >240 °C. νmax (KBr, cm−1) 1671 (CO2−),
1607 (CvN). Found 1535.6298 [C88H94N8NiO12 + Na]+
requires 1535.6237. Found: C, 69.67; H, 6.19; N, 7.38.
C88H94N8NiO12 requires: C, 69.79; H, 6.26; N, 7.41.
Pz-NHBn 25. Ligand HL1f 17,21 (0.200 g, 1.04 mmol),
BnNH2 (0.136 mL, 1.25 mmol), DIC (0.806 mL, 5.20 mmol),
HOBt (0.703 g, 5.20 mmol), DIPEA (1.72 mL, 10.7 mmol) and
DMF (10 mL) was treated by the general procedure to afford the
crude off-white product. This was purified by flash chromato-
graphy using 1 : 1 EtOAc–petroleum ether and the major fraction
recrystallised from CH2Cl2/Et2O to afford the title compound 25
as a colourless microcrystalline solid (0.180 g, 62%). m.p.
105–107 °C. νmax (KBr, cm−1) 3229 (NH), 1691 (CvO), 1568
1
(CvN). H NMR (CDCl3, 400 MHz) δ: 4.50 (2H, d, J 6.0 Hz,
CH2), 6.31 (2H, dd, J 2.5, 1.5 Hz, pzCH), 7.14 (1H, s, CH),
7.30 (5H, m, Ph), 7.59 (2H, d, J 1.5 Hz, pzCH), 7.71 (2H, d, J
2.5 Hz, pzCH), 7.86 (1H, br s, NH). 13C NMR (CDCl3,
100 MHz) δ: 43.9 (CH2), 75.4 (CH), 107.2 (pzCH), 127.6
(ArCH), 128.7 (ArCH), 130.4 (pzCH), 137.2 (ArCq), 141.5
(pzCH), 163.9 (CO). HRMS-ES+ Found 304.1166 [C15H15N5O
+ Na]+ requires 304.1169.
Preparation of [Fe(OAr)4]NEt4 (OAr = o-2,6-Me2-C6H3)
2331,32,51
2,6-Dimethylphenol (15.063 g, 123.31 mmol) was added to a
stirred mixture of FeCl3 (5.000 g, 30.83 mmol), NEt4Br
(6.503 g, 30.83 mmol) and NEt3 (17.2 mL, 123.31 mmol) in
abs. EtOH (190 mL) at RT under atmosphere of N2. The resul-
tant mixture was heated at reflux for 3 h and then cooled to RT
and then to 0 °C. The dark red coloured solid was isolated by fil-
tration and this was purified by recrystallisation from MeOH to
afford the title complex as small red/brown clusters (11.993 g,
58%). m.p. >300 °C. νmax (KBr, cm−1) 3385, 2942, 2909, 1587,
1466, 1421, 1269, 1232, 1089, 863.
Pz-NHOBn 26. Ligand HL1f 17,21 (2.00 g, 10.41 mmol),
BnONH2 (3.18 mL, 20.83 mmol), DIC (2.88 mL, 20.83 mmol),
HOBt (2.66 g, 20.83 mmol), DIPEA (8.28 mL, 52.07 mmol)
and DMF (15 mL) was treated by the general procedure to afford
the crude off-white product. This was purified by flash chrom-
atography using 1 : 1 EtOAc–petroleum ether to afford the title
compound 26 as a colourless microcrystalline solid (1.51 g,
56%). m.p. 108.5–110.5 °C. νmax (KBr, cm−1) 3122 (NH), 1705
(CvO), 1499 (CvN). 1H NMR (CDCl3, 400 MHz) δ: 4.95
(2H, d, J 6.0 Hz, CH2), 6.30 (2H, m, pzCH), 7.00 (1H, s, CH),
7.35 (5H, m, Ph), 7.53 (2H, d, J 1.5 Hz, pzCH), 7.69 (2H, d, J
2.0 Hz, pzCH), 10.33 (1H, s, NH). 13C NMR (CDCl3,
100 MHz) δ: 74.4 (CH2), 78.4 (CH), 107.3 (pzCH), 128.6
(pzCH), 129.0 (ArCq), 129.4 (ArCH), 130.3 (ArCH), 141.5
(pzCH), 165.7 (CvO). HRMS-ES+ Found 320.1123
[C15H15N5O2 + Na]+ requires 320.1118.
General procedure for the preparation of the amides 24–30
(Scheme 5 of paper)
The requisite acid (HL1b or HL1f) and requisite amine were dis-
solved in anhyd. DMF at RT under nitrogen atmosphere and
then cooled to 0 °C with the aid of an ice bath for 20 min. DIC
(N,N-diisopropylcarbodiimide), HOBt (hydroxybenzotriazole)
and finally DIPEA (diisopropylethylamine) were then added
Dalton Trans.
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Pz(PhOMe)-NHiPr 27. Ligand HL1b (0.515 g, 0.836 mmol),
iPrNH2 (0.083 mL, 1.10 mmol), DIC (0.65 mL, 4.173 mmol),
HOBt (0.564 g, 4.173 mmol), DIPEA (1.38 mL, 8.329 mmol)
and DMF (10 mL) were treated by the general procedure to
afford an off-white solid. This was purified by flash chromato-
graphy 1 : 1 EtOAc–petroleum ether and recrystallised from
EtOH to afford the title compound 27 as a colourless microcrys-
talline solid (0.530 g, 96%). Crystals suitable for single crystal
X-ray diffraction were obtained upon recrystallisation from
MeOH. m.p. 148–150 °C. νmax (KBr, cm−1) 3442 (NH), 1690
(CvO), 1605 (CvN), 1584 (CvN). 1H NMR (CDCl3,
400 MHz) δ: 1.36 (6H, d, J 6.5 Hz, 2 × CH3), 3.63 (6H, s, 2 ×
OCH3), 3.85 (6H, s, 2 × OCH3), 4.28 (1H, p, J 6.5 Hz, CH-
(CH3)2), 6.65 (2H, d, J 8.0 Hz, Ph), 6.70 (2H, s, pzCH), 6.73
(1H, s, CH), 6.78 (2H, td, J 7.0, 1.0 Hz, Ph), 6.84 (2H, dd, J
7.5, 2.0 Hz, Ph), 6.96 (2H, d, J 8.5 Hz, Ph), 7.03 (2H, t, J 7.5
Hz, Ph), 7.27 (4H, ddd, J 7.5, 2.5, 2.5 Hz, Ph), 8.12 (3H, m, Ph,
NH). 13C NMR (CDCl3, 100 MHz) δ: 22.7 (CH3), 42.0 (CH-
(CH3)2), 55.0 (OCH3), 55.4 (OCH3), 71.7 (CH), 109.0 (pzCH),
110.4 (ArCH), 111.3 (ArCH), 118.3 (ArCq), 120.5 (ArCH),
120.7 (ArCH), 122.4 (ArCq), 128.6 (ArCH), 128.8 (ArCH),
130.3 (ArCH), 131.4 (ArCH), 141.5 (ArCq), 148.5 (ArCq),
155.9 (ArCq), 156.9 (ArCq), 164.1 (CvO). HRMS-ES+ Found
658.3018 [C39H39N5O5 + H+]+ requires 658.3024.
1.0 Hz, Ph), 6.82 (1H, s, CHC(O)NHOCH3), 6.83 (2H, dd,
J 7.5, 2.0 Hz, Ph), 6.97 (2H, d, J 8.5 Hz, Ph), 7.03 (2H,
dt, J 7.5, 1.0 Hz, Ph), 7.28 (4H, m, Ph), 8.08 (2H, dd, J 7.5,
2.0 Hz, Ph). 13C NMR (CDCl3, 100 MHz) δ: 55.0 (OCH3),
55.4 (OCH3), 64.3 (NOCH3), 71.4 (CHC(O)NHOCH3), 109.2
(pzCH), 110.4 (ArCH), 111.3 (ArCH), 118.0 (ArCq), 120.6
(ArCH), 120.7 (ArCH), 122.1 (ArCq), 128.91 (ArCH),
128.99 (ArCH), 130.5 (ArCH), 131.4 (ArCH), 141.7 (pzCq),
148.9 (pzCq), 155.8 (ArCq), 156.9 (ArCq), 162.5 (CvO).
HRMS-ES+ Found 646.2663 [C37H35N5O6 + H]+ requires
646.2660.
Pz(PhOMe)-NHOBn 30. Ligand HL1b (1.000 g, 1.62 mmol),
BnONH2·HCl (0.310 g, 1.94 mmol), DIC (0.50 mL,
3.24 mmol), HOBt (0.437 g, 3.24 mmol), DIPEA (1.34 mL,
8.10 mmol) and DMF (15 mL) were treated by the general pro-
cedure to afford an off-white solid. This recrystallised from
EtOH to afford the title compound 30 as colourless prisms
(1.010 g, 85%). m.p. 164–166 °C. νmax (KBr, cm−1) 3292 (NH),
1
1715 (CvO). H NMR (CDCl3, 400 MHz) δ: 3.65 (6H, s, 2 ×
OCH3), 3.81 (6H, s, 2 × OCH3), 5.18 (2H, s, CH2), 6.63 (2H,
obscured d, Ph), 6.65 (2H, s, pzCH), 6.77 (2H, td, J 7.2, 0.9 Hz,
Ph), 6.83 (1H, s, CH), 6.84 (2H, dd, J 7.5, 1.8 Hz, Ph), 6.92
(2H, dd, J 7.5, 0.9 Hz, Ph), 6.96 (2H, dd, J 8.1, 0.9 Hz, Ph),
7.21 (2H, m, Ph), 7.27 (2H, m, Ph), 7.33 (2H, m, Ph), 7.64 (2H,
m, Ph), 7.90 (2H, dd, J 7.8, 1.8 Hz, Ph), 10.62 (1H, br s, NH).
13C NMR (CDCl3, 100 MHz) δ: 55.0 (OCH3), 55.4 (OCH3),
71.2 (CH), 78.4 (CH2), 109.2 (pzCH), 110.4 (ArCH), 111.2
(ArCH), 118.0 (ArCq), 120.7 (ArCH), 122.0 (ArCq), 128.5
(ArCH), 128.6 (ArCH), 128.8 (ArCH), 129.06 (ArCH), 129.2
(ArCH), 129.9 (ArCH), 130.5 (ArCH), 131.4 (ArCH), 135.4
(ArCq), 141.8 (ArCq), 149.0 (ArCq), 155.8 (ArCq), 156.9
(ArCq), 162.3 (CvO). HRMS-ES+ Found 744.2797
[C43H39N5O6 + Na]+ requires 744.2793.
Pz(PhOMe)-NHBn 28. Ligand HL1b (0.600 g, 0.973 mmol),
BnNH2 (0.141 mL, 1.07 mmol), DIC (0.750 mL, 4.86 mmol),
HOBt (0.654 g, 4.86 mmol), DIPEA (1.6 mL, 10.84 mmol) and
DMF (10 mL) were treated by the general procedure to afford an
off-white solid. This recrystallised from EtOH to afford the title
compound 28 as colourless prisms (0.510 g, 72%). m.p.
1
161–162.5 °C. νmax (KBr, cm−1) 3346 (NH), 1689 (CvO). H
NMR (CDCl3, 400 MHz) δ: 3.60 (6H, s, 2 × OCH3), 3.81 (6H,
s, 2 × OCH3), 4.73 (2H, d, J 6.0 Hz, CH2), 6.64 (2H, d, J 8.0
Hz, Ph), 6.68 (2H, s, 2 × pzCH), 6.78 (2H, td, J 7.5, 1.0 Hz,
Ph), 6.84 (2H, dd, J 7.5, 2.0 Hz, Ph), 6.85 (1H, s, CHC(O)
NHBn), 6.92 (2H, td, J 8.0, 1.0 Hz, Ph), 6.97 (2H, td, J 7.5,
1.0 Hz, Ph), 7.28 (7H, m, Ph), 7.62 (2H, dd, J 8.0, 1.5 Hz, Ph),
Preparation of pz(PhOMe)-NHOH 31
Pz(PhOMe)-NHOBn 30 (0.300 g, 0.416 mmol) and Pd/C (10%
w/w, 0.025 g) in EtOAc (50 mL) was stirred at RT under a
balloon of hydrogen gas for 18 h. The mixture was then filtered
through Celite™ and the solids washed well with EtOAc. The
filtrate was concentrated in vacuo and then pentanes were added
to induce precipitation. The colourless precipitate was collected
by vacuum filtration to afford the title compound 31 as a colour-
8.02 (2H, dd, J 8.5, 2.0 Hz, Ph), 8.67 (1H, t, J 6.0 Hz, NH). 13
C
NMR (CDCl3, 100 MHz) δ: 43.4 (CH2), 55.0 (OCH3), 55.4
(OCH3), 71.7 (CH), 109.2 (pzCH), 110.4 (ArCH), 111.2
(ArCH), 118.3 (ArCq), 120.6 (ArCH), 120.7 (ArCH), 122.2
(ArCq), 126.9 (ArCq), 127.4(ArCH), 128.5 (ArCH), 128.7
(ArCH), 129.2 (ArCH), 130.4 (ArCH), 131.4 (ArCH), 138.5
(ArCq), 141.6 (ArCq), 148.8 (ArCq), 155.9 (ArCq), 156.9
(ArCq), 165.1 (CvO). HRMS-ES+ Found 728.2841
[C43H39N5O5 + Na]+ requires 728.2843.
less solid (0.246 g, 94%). m.p. 125–127 °C. νmax (KBr, cm−1
)
3230 (NH), 1690 (CvO). 1H NMR (CDCl3, 400 MHz) δ:
3.60 (6H, s, 2 × OCH3), 3.82 (6H, s, 2 × OCH3), 6.58 (2H, d,
J 8.5 Hz, Ph), 6.65 (2H, s, pzCH), 6.77 (2H, t, J 7.5 Hz, Ph),
6.85 (2H, dd, J 7.5, 1.5 Hz, Ph), 6.89 (1H, s, CH), 6.91 (2H, d,
J 8.0 Hz, Ph), 6.99 (2H, t, J 7.5 Hz, Ph), 7.23 (4H, m, Ph), 8.06
(2H, dd, J 8.0, 1.5 Hz, Ph), 9.35 (1H, br s, NH), 10.37 (1H,
br s, OH). 13C NMR (CDCl3, 100 MHz) δ: 55.1 (OCH3),
55.4 (OCH3), 70.5 (CHC(O)NHOH), 109.2 (pzCH), 110.4
(ArCH), 111.1 (ArCH), 117.8 (ArCq), 120.6 (ArCH), 120.8
(ArCH), 121.8 (ArCq), 129.1 (ArCH), 129.3 (ArCH), 130.5
(ArCH), 131.3 (ArCH), 141.9 (pzCq), 149.3 (pzCq), 155.8
(ArCq), 156.8 (ArCq), 163.1 (CvO). HRMS-ES+ Found
632.2503 [C36H33N5O6 + H]+ requires 632.2504. HPLC Rf =
14.82 min.
Pz(PhOMe)-NHOMe 29. Ligand HL1b (1.000 g, 1.62 mmol),
MeONH2·HCl (0.162, 1.94 mmol), DIC (0.500 mL,
3.24 mmol), HOBt (0.430 g, 3.24 mmol), DIPEA (2.6 mL) and
DMF (10 mL) were treated by the general procedure to afford an
off-white solid. This was purified by flash chromatography with
7 : 3 EtOAc–petroleum ether and the major fraction recrystallised
from EtOH to afford the title compound 29 as colourless prisms
(0.892 g, 85%). m.p. 165–167 °C. νmax (KBr, cm−1) 3257 (NH),
1
1717 (CvO). H NMR (CDCl3, 400 MHz) δ: 3.67 (6H, s, 2 ×
OCH3), 3.85 (6H, s, 2 × OCH3), 4.03 (3H, s, NOCH3), 6.66
(2H, d, J 8.5 Hz, Ph), 6.68 (2H, s, pzCH), 6.80 (2H, dt, J 7.5,
This journal is © The Royal Society of Chemistry 2012
Dalton Trans.

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Preparation of [Fe(pz(PhOMe)-NHO)3]·2Et2O·CH2Cl2 32
KOtBu (0.015 g, 0.133 mmol) was added to a stirred solution of
ligand 31 (0.07 g, 0.111 mmol) in anhyd. THF (5 mL) at RT
under N2 atmosphere. The mixture was degassed for 0.5 h, and
then FeCl2 (0.014 g, 0.111 mmol) was added. The resultant
mixture became bright orange and was stirred at RT overnight.
The orange precipitate was collected by vacuum filtration and
recrystallised by infusing Et2O into a CH2Cl2 solution of the
complex to afford the title compound 32 as small orange prisms
that were suitable for X-ray crystallographic analysis (0.056 g,
78%) that lost solvent rapidly on exposure to air. m.p.
203–205 °C. νmax (KBr, cm−1) 1606 (CvO), 1584 (CvN).
Found 1969.6317 [C108H96FeN15O18
+
Na]+ requires
1969.6301. HPLC Rf = 14.95 min.
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Conclusions
The heteroscorpionate ligands prepared in this study represent
new bulky ligand systems which coordinate to metal ions in the
expected facial arrangement. However, increasing the bulk of the
ligands by the installation of aryl substituents at the 3- and 5
positions of the pyrazole rings failed to give the monomeric
complexes with the 1 : 1 (M : L) stoichiometry required for an
IPNS oxidase model. Instead dimeric complexes with either a
6-coordinate octahedral or a 5-coordinate trigonal bipyrimidal
coordination and bridging carboxylates were obtained. In two
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the trigonal bipyrimidal coordination mode. Ni, Mn, and Fe
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Acknowledgements
MWJ, AK and NNS thank the EPSRC for funding. The authors
also wish to thank Prof Stephen Faulkner, Dr Jeffrey Harmer,
Dr Jason Holland, Dr Philip Waghorn and Dr David Watkin
for helpful discussions.
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Dalton Trans.