Synthesis, stereocontrol and structural studies of highly luminescent chiral tris-amidepyridyl-triazacyclononane lanthanide complexes

Article abstract of DOI:10.1039/c3dt53000k

The configuration of the remote amide chiral moiety determines the helicity of the metal complex in Ln(iii) complexes of nonadentate N₆O ₃ ligands based on triazacyclononane. Solution NMR studies revealed the presence of a dominant isomer whose proportion varies from 9:1 to 4:1 from Ce to Yb and X-ray crystallographic studies at 120 K of the Yb and two enantiomeric Eu complexes confirmed the configuration as S-Δ-λ in the major isomer. Global minimisation methods allowed magnetic susceptibility and electronic relaxation times of the lanthanide ions to be estimated by analysis of variable field longitudinal relaxation rate (R₁) data sets. A set of four europium complexes, containing different para-substituted pyridinyl-aryl groups, exist as one major isomer (15:1), and absorb light strongly via an ICT transition in the range 320 to 355 nm (ε = 55 to 65000 M^-1 cm^-1). The two examples absorbing light at 332 nm, possess overall emission quantum yields of 35 and 37% in aerated water, making these systems as bright as any Eu complex in solution. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c3dt53000k

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Synthesis, stereocontrol and structural studies of
highly luminescent chiral tris-amidepyridyl-
triazacyclononane lanthanide complexes†
Cite this: Dalton Trans., 2014, 43,
5490
Emily R. Neil, Alexander M. Funk, Dmitry S. Yufit and David Parker*
The configuration of the remote amide chiral moiety determines the helicity of the metal complex in
Ln(III) complexes of nonadentate N6O3 ligands based on triazacyclononane. Solution NMR studies
revealed the presence of a dominant isomer whose proportion varies from 9 : 1 to 4 : 1 from Ce to Yb and
X-ray crystallographic studies at 120 K of the Yb and two enantiomeric Eu complexes confirmed the
configuration as S-Δ-λ in the major isomer. Global minimisation methods allowed magnetic susceptibility
and electronic relaxation times of the lanthanide ions to be estimated by analysis of variable field
longitudinal relaxation rate (R1) data sets. A set of four europium complexes, containing different para-
substituted pyridinyl-aryl groups, exist as one major isomer (15 : 1), and absorb light strongly via an ICT
transition in the range 320 to 355 nm (ε = 55 to 65 000 M−1 cm−1). The two examples absorbing light at
332 nm, possess overall emission quantum yields of 35 and 37% in aerated water, making these systems
as bright as any Eu complex in solution.
Received 24th October 2013,
Accepted 7th February 2014
DOI: 10.1039/c3dt53000k
www.rsc.org/dalton
torsion angle, where the nature of X and Y is defined by the
constitution of the ligating moiety.7 A number of strategies
Introduction
Triazacyclononane is a small macrocycle that is easily functio- exist that allow the preparation of enantiopure complexes. For
nalised to generate hexadentate and nonadentate ligands that example, such complexes can be synthesised through incor-
give rise to thermodynamically and kinetically stable metal poration of a remote chiral centre within the ligand frame-
complexes of the d and f block elements.1–6 The ring nitrogen work. Introduction of a stereogenic centre may occur on the
atoms act as donors and have been substituted with carboxy- macrocyclic ring8,9 or in the ring N substituent, leading to pre-
late, phosphonate, phosphinate, phenolate, thiolate and sub- ferential stabilization of a particular stereoisomer. Complexes
stituted pyridyl moieties to form a large family of well-defined with Δ or Λ configuration are formed with partial or total
C3 symmetric complexes. Initial work concentrated on tricarb- stereocontrol. This approach was recently studied for the ring
oxymethyl systems2b,3 and related triphosphinate complexes C-substituted series of lanthanide complexes with pyridyltri-
have also been examined, for example with the late d-block carboxylate or triphosphinate donors.8 Complete stereochemi-
elements and In(III) and Ga(III).1j,2a Nine coordinate tris-pyridyl- cal control has also been achieved in 9-coordinate cationic
carboxylate triazacyclononane complexes of Ln(III) ions have lanthanide complexes, [Ln·L(H2O)]3+, based on 12-N4 tetra-
been reported by Latva, Mazzanti and co-workers,1d–g and were amide ligands in C4 symmetry. The stereogenic centre at
shown to exist in the solid state in a tri-capped trigonal pris- carbon was derived from a precursor enantiopure amine, such
matic coordination geometry. More recent variants include a as α-methylbenzylamine.10
series of tri-pyridylphosphinate systems that define an iso-
In this work, we have set out to prepare ligand L1 using a
similar stereochemical approach, in order to assess the degree
structural series across the lanthanide block.4,5
The hexadentate or nonadentate complexes in C3 symmetry of stereocontrol in lanthanide complex formation. By analogy
exist as Δ or Λ isomers, as revealed by the sign of the NCXY with recent work, the related ligands L2a–d were also prepared,
as the introduction of the aralkynyl moiety greatly enhances
the absorption characteristics of the ligand and permits
efficient sensitization of Eu emission.6 Furthermore, these
complexes, and their derivatives, are attractive candidates as
Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK.
E-mail: david.parker@dur.ac.uk; Tel: +44 (0)191 33 42033
†Electronic supplementary information (ESI) available: General experimental
the basis of probes for circularly polarised emission studies,
methods and instrumentation; selected VT NMR spectra and emission spectra.
and this work underpins the development of new luminescent
chiral probes.7,11–13 In addition, their coordination chemistry
CCDC 965909–965911. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c3dt53000k
5490 | Dalton Trans., 2014, 43, 5490–5504
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can be directly compared to the kinetically stable triphosphi- obtained and was separated by column chromatography on
nate, tricarboxylate and tris-diethylcarboxamide analogues, neutral alumina. The di- and tri-substituted S-L1 ligands were
[Ln·L3,4,5],6,1e,g allowing us to deepen our understanding of isolated in yields of 22% and 55% respectively. The enantio-
ligand field effects in lanthanide complexes of high symmetry.
meric ligand R-L1 was made by an identical pathway, and their
Results and discussion
Ligand and complex synthesis
The parent ligand L1 was prepared in six steps from commer-
cially available precursors (Scheme 1). The amide coupling
reaction of 6-methylpyridine-2-carboxylic acid with S-α-methyl-
benzylamine14 afforded the desired amide S-1a, in good yield.
The amide, S-1a was treated with mCPBA in chloroform to give
the N-oxide in 83% yield. The N-oxide, 1b, was subsequently
transformed to a 6-acetoxymethyl-pyridine derivative using
acetic anhydride at 120 °C. This rearrangement reaction was
followed by ester solvolysis, catalysed by ethoxide, to furnish
the alcohol, S-1d, in 85% yield. Mesylation under standard
conditions gave S-1e, which was used directly in the next step
without further purification. Alkylation of 9-N3 was carried out
using the crude mesylate in acetonitrile in the presence of
Scheme 1 (i) S-PhCHMeNH2/EDC/DIPEA/HOBt/DMF; (ii) mCPBA/
CHCl3; (iii) Ac2O/Δ; (iv) EtOH/cat. NaOEt; (v) MsCl/Et3N/THF; (vi) K2CO3/
K2CO3. A mixture of mono-, di- and trialkylated products was MeCN/9-N3.
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Structural analysis of Eu and Yb complexes of L1
Crystals of [LnL1](CF3SO3)3 grew readily from aqueous metha-
nol (1 : 1). The complexes R-[EuL1](CF3SO3)3 and S-[EuL1]-
(CF3SO3)3 crystallize in the trigonal space group R3. Crystallo-
graphic analysis of S-[YbL1]3+ revealed that it was isostructural
with the Eu complexes, strongly suggesting that the series of
lanthanide complexes of L1 would also adopt a common struc-
ture, at least from Eu to Yb, as has been verified for [Ln·L3]
and [Ln·L4]. The anions were slightly disordered, and a severely
disordered solvent molecule was present in each structure. The
lanthanide ion is coordinated by the three N atoms of the
macrocyclic ring, each pyridyl N and the amide O atoms. A C3
axis passes through the metal atom and the centre of the
macrocyclic ring (Fig. 1).
Analysis of the lengths of the lanthanide-donor atom
bonds, compared to the values reported for [Ln·L3]4,5 revealed
longer Ln–O and Ln–Npy bonds, as expected with a neutral
amide donor, and a shorter Ln–N distance, indicating that the
Ln ion is sitting closer to the plane of the N3 ring (Table 1).
The complexes each adopted a distorted tricapped trigonal
prism structure. The distortion angle is defined by the twist of
the mean plane of the 9-N3 ring with reference to the three
bound oxygen atoms of the amide, phosphinate or carboxylate
groups (Fig. 2). No significant differences in twist angle were
found for the Eu/Yb complexes of L1, compared to the values
for the corresponding complexes of L3 and L4.
Scheme 2 (i) NaOH/EtOH/H2O; (ii) S-PhCHMeNH2/EDC/DIPEA/HOBt/
DMF-CH2Cl2; (iii) Pd(dppf)Cl2/CuI/NEt3/X-Ph-CCH/THF; (iv) MsCl/Et3N/
THF; (v) K2CO3/MeCN/9-N3.
lanthanide complexes were made by reaction with one equi-
valent of the lanthanide triflate salt in dry MeCN. Trituration
with cold ether yielded the lanthanide complexes S-[LnL1]-
(CF3SO3)3 in quantitative yield (Ln = Ce, Pr, Nd, Eu, Gd, Tb, Dy,
Ho, Er, Tm, Yb).
For the synthesis of L2a–d, a five-step synthetic route was
devised (Scheme 2) beginning with preparation of the mono-
hydroxymethyl p-iodo mono-carboxylic acid. Formation of the
amide bond proved slightly troublesome, but by stirring the
coupling reagents, base and amine in a solvent mixture of
DCM–DMF (1 : 1) followed by slow, dropwise addition of
the carboxylic acid, the amide, S-2b, was formed in reasonable
yield (58%). The alkynes, S-4a–d, were synthesised by a
Sonogashira cross-coupling reaction between the p-iodo-
pyridyl amide, 2b, and various p-substituted aralkynes, using
catalytic Pd(dppf)Cl2 and CuI in degassed THF. Mesylation fol-
lowed by alkylation of 9-N3 were carried out using standard
conditions to give S-L2a–d. Complexation with Eu(OTf)3 in
acetonitrile at 80 °C gave the triflate salt of the europium
complexes, S-[EuL2a–d](CF3SO3)3, following trituration with
cold ether.
The crystal structures show that the major diastereoisomer
of the complex derived from the enantiopure S ligand system
Table 1 Selected mean distances of ligand donor atoms to the lantha-
nide iona (Å, 0.01) for [Ln·Ln] (Ln = Eu, Yb, n = 1, 3)b
[Ln·Ln]
Eu
Yb
Ln·L1-O
Ln·L3-O
Ln·L1-N
Ln·L3-N
Ln·L1-Npy
Ln·L3-Npy
2.40
2.33
2.63
2.68
2.57
2.66
2.34
2.25
2.57
2.62
2.49
2.62
a Effective ionic radii (Å) in 9-coordinate systems are 1.12 (Eu) and
1.04 Å (Yb). b Data for [Ln·L3] are taken from ref. 4 and 5.
Fig. 1 Views of the structures of the tripositively charged cations of S-Δ-(λλλ)-[EuL1] (left) and R-Λ-(δδδ)-[EuL1] (right) (120 K), showing the twist
angle (23.7°) associated with trigonal prismatic distortion, compared to 19.5° for [Eu·L3] and 22.3° for [Eu·L4]. CCDC 965909–965911.
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consistent with a trend induced by the lanthanide contraction.
Proton NMR spectra were obtained in CD3OD for the crystals
isolated and indicated that, in each case, it was the major solu-
tion diastereoisomer that had crystallized out of solution. The
isomers could also be separated by reverse phase HPLC. Intri-
guingly, the ratio of isomers for [Eu·L2a–d 3+
was 15 : 1 (ESI†)
]
suggesting that in these systems the more polarisable pyridine
N may have a shorter bond to the lanthanide ion, enhancing
the impact of the steric demand of the proximate chiral centre.
The isomer ratio observed for [Yb·L1] was invariant with temp-
erature over the range 278 to 353 K (D2O, 14.1 T) and the
variation of the chemical shift followed the expected T−2
dependence, consistent with Bleaney’s theory of magnetic an-
isotropy. No evidence was therefore found for chemical
exchange between the two isomeric species, on the NMR
timescale.
Fig. 2 1H NMR spectrum of [EuL1]3+ (CD3OD, 295 K, 9.4 T), showing the
two diastereoisomeric species in ratio 7 : 1, examining the most shifted
axial ring protons at −6.6 and −5.2 ppm. The major species is assigned
as S-Δ-(λλλ), whilst the minor isomer is most likely to be S-Δ-δδδ. Ratios
of isomeric species were estimated at 4.7 and 9.4 T by integration and
were within 10%.
The assignment of each ligand resonance was greatly
assisted by the previous studies with [Ln·L3].5 In addition,
longitudinal relaxation rate data (R1) were measured for each
ligand resonance at five magnetic fields, from 4.7 to 16.5 T.
Resonances that are closer to the paramagnetic centre relax
faster (via the r−6 dependence of R1, vide infra), allowing a
simple internal check of spectral assignments (Tables 2
and 3).
Paramagnetic longitudinal relaxation in these lanthanide
complexes arises from rotational and conformational modu-
lation of the electron-nuclear dipolar interaction, as in the
equation below,
had a Δ configuration (NCCNpy = +36.5°) and a λ conformation
for each 5-ring chelate derived from the 9-N3 ring (NCCN =
−46.9°). The europium complex derived from the enantiopure
R ligand system is enantiomeric, with Λ helicity and a δ
LnNCCN chelate ring conformation. The same sense of asym-
metric induction was observed in tris-lanthanide Eu complexes
of 2,6-picolinamides11 and in many examples with related
12-N4 based tetra-amides.10,15 In each case, the chiral amide
moiety is derived from S-PhCHMeNH2 or its analogues.
Solution NMR studies
ꢂ
ꢃ
ꢀ
ꢁ
2
2
μ0
γ2NgL2nμ2B Jð J þ 1Þ
T1e
T2e
1 þ ω2eT22e
The series of lanthanide complexes of L1 was examined by
proton NMR in CD3OD, revealing that two C3 symmetric
species were present in each case (Fig. 2). The ratio of these
isomers fell from 9 : 1 (Ce) to 4 : 1 (Yb) across the series,
R1 ¼
3
þ 7
15 4π
r6
1 þ ω2NT12e
ꢂ
ꢃ
ꢀ
ꢁ
2
2
μ0
ω2Nμ4eff
ð3kBTÞ r6
τr
þ
3
2
5 4π
1 þ ω2Nτ2r
Table 2 Proton NMR assignments (δH/ppm) of the major isomeric species observed for paramagnetically shifted ligand resonances in [Ln·L1]3+
(Ln = Tm, Yb, Eu; 295 K, CD3OD)a,b, showing distances to the Eu centre based on X-ray analysis
Ln
Hax
H′
eq
Heq
pyCHN
CH3
CHNH
Ho
Hp
Hm
H′
ex
H5
H4
H3
pyCH′N
Tm
Yb
Eu
−79.8
−18.8
−6.6
−30.5
−6.7
−2.2
−29.0
−4.2
−1.5
−22.0
−2.8
−0.7
−7.5
−1.1
+1.2
+9.3
+6.2
+4.0
10.8
7.6
5.7
10.7
8.2
6.9
10.4
8.3
6.7
11.3
8.9
5.1
19.2
11.4
7.4
19.6
11.2
7.3
23.0
11.6
7.5
+70.4
+22.3
+7.6
a Data for other Ln complexes are given in the Experimental but were not fully assigned due to severe line-broadening of certain protons
within 4.5 Å of the metal ion. b The isomer ratio was 7 : 1 for [Eu·L1]3+, and increased to 15 : 1 for [Eu·L2a–d 3+
]
. Chemical shift values were more or
less unchanged in DMF vs. CD3OD, consistent with encapsulation of the Ln ion by the ligand.
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Table 3 Selected relaxation rate data (R1, s−1), determined at five fields for Yb and Tm complexes of L1 (CD3OD, 295 K). Full sets are given (ESI), for
the Tb, Dy, Ho and Er analogues
Complex
[Yb·L1]3+
Bo/T
Hax
H′
Heq
pyCHN
H3
H4
pyCH′N
eq
4.7
9.4
11.7
14.1
16.4
4.7
43(0.5)
62(1.2)
78(0.6)
89(0.3)
102(0.1)
158(2)
377(9)
479(5)
589(4)
699(5)
34(0.3)
48(1.1)
63(0.3)
73(0.4)
83(0.3)
130(23)
327(10)
411(8)
501(5)
580(9)
30(0.4)
43(0.9)
56(0.2)
65(0.5)
74(0.5)
118(2)
283(5)
366(4)
443(4)
512(8)
19(0.1)
29(0.5)
39(0.2)
46(0.3)
53(0.4)
80(1)
202(6)
256(3)
314(4)
363(3)
7(0.4)
12(0.3)
15(0.4)
17(0.6)
21(0.1)
31(1)
5.0(0.5)
7.3(0.3)
8.6(0.1)
10.1(0.3)
10.7(0.1)
18(0.5)
40(1)
53(1)
63(1)
73(1)
129(2)
215(3)
275(9)
317(3)
359(1.5)
566(19)
1413(97)
1718(20)
2088(43)
2482(76)
[Tm·L1]3+
9.4
75(2)
11.7
14.1
16.4
105(1)
125(2)
149(2)
Table 4 Calculated values of magnetic susceptibilityc (μeff/μB) and electronic relaxation times (T1e, ps) for [Ln·Ln] (n = 1, 3, 4), derived from global
fitting of the field dependence of longitudinal relaxation rate (R1) dataa,b (CD3OD, 295 K)d
[Ln·L1]
[Ln·L3]
[Ln·L4]
Ln
μeff/μB
T1e/ps
μeff/μB
T1e/ps
μeff/μB
T1e/ps
Tb
Dy
Ho
Er
Tm
Yb
9.59(03)
10.09(03)
10.31(02)
8.80(03)
7.77(02)
4.56(04)
0.27(03)
0.29(03)
0.21(03)
0.22(04)
0.15(03)
0.17(04)
9.40(03)
10.21(03)
10.22(01)
9.05(02)
7.66(03)
4.36(03)
0.21(04)
0.32(03)
0.11(02)
0.26(03)
0.09(04)
0.12(06)
9.65(02)
10.47(01)
10.44(01)
9.23(02)
7.43(01)
4.27(02)
0.26(03)
0.28(02)
0.17(02)
0.23(03)
0.08(02)
0.09(04)
a Values of τr estimated simultaneously were: [Ln·L1], 196(1) ps; [Ln·L3] 205(6) ps; [Ln·L4], 132(1) ps. b In each case, for every set of resonances
considered, the distance r from the proton to the Ln ion was taken from the X-ray crystallographic analysis. c Literature μeff values for the aqua
ions are typically as follows: Tb, 9.8; Dy, 10.3; Ho, 10.4; Er, 9.4; Tm, 7.6; Yb, 4.3 BM.18–20 These values relate to a ‘weak’ ligand field (less than or
close to kT), as is the case here. d Data for [Ln·L4] were recorded in D2O; earlier work has shown that T1e values are independent of solvent
viscosity.17
Table 5 Solvatochromisma data observed with [Eu·L2a–d 3+
(295 K)
]
where µ0 is vacuum permeability, gN is the magnetogyric ratio
of the nucleus, gLn is the Landé factor of the fundamental multi-
plet J of the free Ln3+ ion, µB is the Bohr magneton (BM), τr is
λmax/nm
E3T0 normalised
[Eu·L2a
]
[Eu·L2b
]
[Eu·L2c
]
[Eu·L2d
]
the rotational correlation time, ωN is the nuclear Larmor fre-
Solvent
2
quency, ωe is the electron Larmor frequency, (μeff
)
is the
H2O
1.00
0.76
0.65
0.55
0.40
332b
332
331
320
308
328b
328
327
324
316
356
355
355
336
332
352
352
349
344
336
square of the effective magnetic moment, T1e and T2e are the
relaxation times of the electron spin and r is the electron-
nuclear distance. Normally, it is assumed that T1e equals T2e.
Using values of r derived from the X-ray analysis, it is poss-
ible to estimate the values of μeff, τr and T1e, by globally mini-
mising the data sets simultaneously. Such an approach has
been demonstrated recently to be effective at estimating these
variables, especially as the rotational correlation time, τr, is not
expected to vary significantly from one lanthanide complex to
another.16,17 Data obtained in this manner (Table 4), for
[Ln·L1], allowed a comparison to be made with results
obtained with [Ln·L3,4]. The values of T1e and τr obtained fell
in the range expected for such complexes with rather weak
ligand fields (vide infra for emission analysis). Furthermore,
the estimates of the magnetic susceptibility values were also
found to be in reasonable agreement with literature values that
are derived from aqua ion or solid-state metal oxide data.18–20
MeOH
EtOH
iPrOH
DMF
a E3T0 values are based on Reichardt’s normalised solvent polarity scale.
b Europium emission was an order of magnitude greater in water for
these complexes, compared to organic solvents or to [Eu·L2c–2d].
in the complexes of L2a–2d. Indeed, this band was very intense
(ε values in MeOH ranged from 63 000 to 69 000 M−1 cm−1 to
about 55 000 M−1 cm−1 in water) consistent with its ICT char-
acter, and in accord with earlier work on related lanthanide
complexes with carboxylate or phosphinate donors.6,1b The
position of the absorption band was particularly sensitive to
solvent polarity, and there was a hypsochromic shift in sol-
vents of lower polarity (Table 5). Such behaviour is consistent
with the lowering of the energy of the relaxed ICT excited state
in more polar protic solvents. The chloride salt complexes
of L2c and L2d were the least soluble in water of the four
Absorption and emission spectral studies
The series of lanthanide complexes of L1 possess an absorp-
tion band at 280 nm, which shifted to the red by up to 75 nm complexes examined.
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The aralkynyl chromophore acts as an efficient sensitiser of
In water at pH 6.5, the emission quantum yields for the Eu
europium emission, and quantum yields in methanol were 5 complexes of L2a and L2b (X = H and CO2Me) were 35 and 37%
( 3)% for the complexes with ligands L2a–d (Table 6). The euro- respectively (Table 6). These are amongst the highest values
pium emission spectrum for all of the complexes was very reported for sensitized emission of any europium complex in
similar (Fig. 3), and almost identical to the behaviour of aqueous solution, and compare to 39% for a closely related
[Eu·L3,4] and their extended chromophore analogues, consist- tris-phenylphosphinate, based on [Eu·L3], that possesses the
ent with time-averaged C3 symmetry.5,6
same core chromophore as the L2 series of ligands used here.6
The lower quantum yields and emission lifetimes for Emission intensities were unchanged in 0.1 M NaCl solution
[Eu·L2c] and [Eu·L2d] (Table 6) suggested that the intramole- and in 0.1 M HEPES buffer at pH 7.4. The emission intensities
cular energy transfer step from the relaxed excited ICT state may of solutions of [Eu·L2c]3+ and [Eu·L2a]3+, in the presence of a
be partially reversible, and therefore is thermally activated. As thousand fold excess of EDTA at pH 6.5, were monitored as a
the temperature was lowered, the emission intensity increased function of time over a period of 7 days; after an initial 15%
by a factor of 5 over the range 295 to 235 K, in accord with this reduction, no significant change in intensity was observed in
premise, and consistent with a suppression of thermally acti- each case, consistent with the high kinetic stability of these
5
vated back energy transfer from the excited Eu D0 state to the systems with respect to dissociative ligand exchange.
ICT excited state. The phosphorescence spectrum of [GdL2d],
The absorption and emission spectral behaviour of the
recorded at 85 K in a glass of ether–isopentane–ethanol complexes of L2c and L2d, absorbing at longer wavelength in
(5 : 5 : 2), showed a very broad band at low temperature, protic solvents, were also sensitive to the apparent pH. In an
i
centred at 450 nm (530 nm shoulder), consistent with the 80/20 PrOH–water mixture, as the apparent pH was varied,
intermediacy of an excited state with predominant ICT charac- both the absorbance at 348 nm and the europium emission
ter, rather than a ligand centred triplet excited state.1b
spectral form varied (Fig. 4). The spectral changes observed
were completely reversible. The emission spectral changes
were particularly striking and led to the appearance of
additional transitions, consistent with a lowering of the sym-
metry around the Eu ion, and a change in the Eu coordination
environment. These changes were most apparent in the ΔJ = 1
transitions around 595 nm, which evolved from a broad single
manifold, to a set of three distinct transitions. For Eu com-
plexes, three transitions are symmetry-allowed in systems
lacking a Cn symmetry axis. The absorption spectral change
was characterized by a shift to the blue at higher pH, moving
Table 6 Photophysical data for the complexes S-[EuL2a–d]Cl3 (295 K,
MeOH)a,b
Complex
λmax/nm
ε/M−1 cm−1
τ/ms
ϕem
[EuL2a 3+
]
332
328
355
352
69 000
63 000
65 000
65 000
0.80
0.81
0.49
0.54
0.08
0.03
0.04
0.03
[EuL2b 3+
[EuL2c 3+
[EuL2d 3+
]
]
]
a In water at pH 6.5, emission lifetimes for [Eu·L2a] and [Eu·L2b] were
0.81 (1.10 ms in D2O, hence the hydration state,26 q = 0) and 0.80 ms, the primary absorption band from 355 to 328 nm (Fig. 5).
and overall quantum yields 35% and 37% respectively whilst for
Values of the apparent pKa for the ground and excited states,
derived by iterative fitting of the observed spectral changes to
[Eu·L2c] and [Eu·L2d], corresponding values were 0.49 and 0.46 ms,
with quantum yields of 2%, in each case. Extinction coefficients in
water were lower: 55( 4) mM−1 cm−1 b For the parent complexes in a two-state equilibrium, were estimated to be 9.1 in each case.
.
water: [TbL1]: λmax = 280 nm, ε = 15 400 M−1 cm−1, τ = 1.87 ms, (τ(D2O)
= 2.12 ms), ϕem = 50%; [EuL1]: λmax = 280 nm, ε = 15 500 M−1 cm−1, τ =
0.98 ms, (τ(D2O) = 1.42 ms), ϕem = 7%. In comparison, [EuL5] has an
overall emission quantum yield of 0.2% in water, with a lifetime of
1.01 ms, (λmax = 281 nm, ε = 20 500 M−1 cm−1).1e
Taken, together, this behaviour is consistent with deproto-
nation of one amide NH proton, reversibly generating an
Fig. 4 Variation of the Ln(III) emission spectrum as a function of pH for
S-[EuL2c]Cl3 (iPrOH–H2O 80 : 20 v/v, 5 μM complex, 298 K, λexc 348 nm).
Top right: absorbance changes at 348 nm with pH (filled circles), and
variation of the ΔJ = 2/ΔJ = 4 relative emission intensity ratio with pH
(open circles) (pKa 9.10 ( 0.13)).
Fig. 3 Emission spectrum of S-[EuL2c](CF3SO3)3 (MeOH, 295 K, λexc
355 nm).
=
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Fig. 5 UV-absorption spectra of S-[EuL2c]Cl3 in iPrOH–H2O (80 : 20
v/v) at an apparent pH of 10.3 (blue) and pH 4.4 (red).
Fig. 7 Circularly polarized luminescence emission spectra for S-Δ
(green) and R-Λ (blue) [Eu·L2d] (λexc 348 nm; pH 5, water, 295 K).
amide enolate in which the anionic oxygen is coordinated to
the europium centre. Indeed, in several examples of 12-N4
lanthanide tetra-amide complexes, similar pKa values (range
7.9 to 11.1) have been associated with amide deprotonation in
aqueous media.21–23
transitions was found to be 70 cm−1, corresponding to a B20
value of +233 cm−1, compared to +110 cm−1 for [Eu·L3] and
+75 cm−1 for [Eu·L4].17 As this parameter also determines the
magnitude of the dipolar shift in NMR, this trend was also
reflected in the relative shifts of the ligand protons, best illus-
trated in the 1H NMR chemical shift data for the Yb complexes
of ligands L1–3 (Table 2 and ref. 5). Thus, the most shifted ring
proton (Hax, see Fig. 2) resonates at −18.8, −13.8 and
−4.8 ppm for [YbL1], [Yb·L3] and [Yb·L4] respectively, and the
total spectral width is 30, 24 and 14 ppm in that sequence.
These examples also highlight the fact that the sign of B20 in
these C3 symmetric complexes is positive and opposite to that
of the multitudinous C4 12-N4 analogues, explaining the
different sense of the NMR shifts observed.
Chiroptical spectral behaviour
Circularly polarized luminescence spectroscopy is a sensitive
means of interrogating the excited state chirality of lanthanide
complexes.7,24 The CPL spectra of the Δ and Λ complexes of
[Ln·L1] were examined and showed mirror image behaviour
(Fig. 6). Furthermore, when the sign and magnitude of the
CPL transitions for Δ-[Tb·L1] and Δ-[Tb·L3] were compared4
they were very similar, in accord with their common configur-
ation. In the latter case, the absolute configuration at each
phosphorus is S, as is the case with this amide complex.
The CPL spectra of the Δ and Λ complexes of [Tb·L1]3+ and
[Eu·L2d 3+
were also recorded (Fig. 6 and 7). With these
]
Summary and conclusions
examples, CPL spectroscopy allowed the two components of
the ΔJ = 1 manifold in the Eu spectrum to be more clearly
resolved. Analysis of the energies of these transitions allows an
estimate to be made of the second order crystal field term,
B20.25 For [Eu·L1]3+, for example, the splitting of the two
Structural determinations using crystallographic, NMR and
CPL methods have shown that the configuration of the stereo-
genic centre in the remote amide moiety determines the heli-
city of the metal complex in this new range of Ln(III) complexes
of nonadentate N6O3 ligands based on triazacyclononane. The
NMR studies revealed the presence of a dominant isomer in
solution that was isolated by crystallization. The proportion of
the major isomer present in solution was 9 : 1 for Ce and Pr, 7
or 6 : 1 from Nd to Tm and 4 : 1 for Yb. The level of remote
stereocontrol in complex formation is inferior to that created
by C-substitution of the 9-N3 ring. In that case, even the intro-
duction of a single methyl substituent led to preferential for-
mation of one (>96%) enantiomeric complex.8
In four analogous europium complexes, containing para-
substituted pyridinyl-aryl groups, stereocontrol is higher and
the complex exists as one major isomer in solution in a ratio
of 15 : 1. Each complex absorbs light strongly via an ICT tran-
sition in the range 320 to 355 nm (ε = 55 000 M−1 cm−1 in
water) that is strongly solvatochromic. Two examples absorb-
ing light around 332 nm, albeit with a broad transition that
extends to 365 nm, possess overall emission quantum yields at
Eu of 35 and 37% in aerated water. These values are amongst
Fig. 6 Circularly polarized luminescence emission spectra for S-Δ
(green) and R-Λ (blue) [Tb·L1] (λexc 280 nm; H2O, pH 6.5, 295 K;
Δ-complex: gem (539) +0.11; gem(623) −0.35).
5496 | Dalton Trans., 2014, 43, 5490–5504
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the highest ever observed for sensitised europium emission in washed successively with water (1 × 10 mL) and brine (1 ×
water, rendering them particularly ‘bright’ complexes. Such be- 10 mL), dried over MgSO4 and the solvent removed under
haviour augurs well for the use of analogues of these systems reduced pressure. The crude mixture was purified by flash
as the basis of CPL probes, in which the sign, intensity and column chromatography (silica, gradient elution starting from
form of selected CPL transitions can be used to probe the local 30% EtOAc in hexane to 60% EtOAc in hexane) to afford com-
chiral environment.
pound S-1a as a yellow oil (1.32 g, 75%). TLC analysis Rf 0.24
(silica, 30% EtOAc in hexane); 1H NMR (295 K, 400 MHz,
3
3
CDCl3) δH 8.38 (1H, d, J 7.5, NH), 7.94 (1H, d, J 7.5, py-H3),
3
3
7.64 (1H, t, J 7.5, py-H4), 7.41 (2H, d, J 7.5, Ph-Ho), 7.35 (2H,
t, 3J 7.5, Ph-Hm), 7.27–7.25 (2H, m, Ph-Hp, py-H5) 5.26 (1H, dq,
3J 7, 3J 7.5 CHCH3), 2.49 (3H, s, py-CH3), 1.56 (3H, d, 3J 7,
CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC 163.4 (CvO),
157.0 (py-C6), 149.1 (py-C2), 143.3 (Ph-Ci), 137.4 (py-C4), 128.5
(Ph-Cm), 127.2 (Ph-Cp), 126.2 (Ph-Co), 125.8 (py-C5), 119.3 (py-
C3), 48.6 (CHCH3), 24.1 (py-CH3), 21.9 (CHCH3); m/z (HRMS+)
241.1334 (C15H17ON2 requires 241.1335).
Experimental
Details of the general procedures, and instrumentation used
are given in the ESI.†
Crystal structure determinations of Δ and Λ-[EuL1] and
Δ-[Yb·L1]
Crystals of [EuL1] suitable for single crystal structure determi-
nation were grown by slow evaporation of a CH3OH solution.
The crystals of Eu-complexes are shattered by flash-freezing, so
they were gradually cooled at the rate of 120° per hour from
250 K to 120 K. The X-ray single crystal data for all compounds
were collected at 120 K on a Bruker SMART CCD 6000
diffractometer (graphite monochromator, MoKα, λ = 0.71073 Å)
equipped with a Cryostream (Oxford Cryosystems) open-flow
nitrogen cryostat. The structures were solved by direct methods
and refined by full-matrix least squares on F2 for all data using
Olex227 and SHELXTL28 software. In all compounds the coun-
terions are linked by N–H⋯O hydrogen bonds and triflate
anions are disordered over two positions. All non-disordered
non-hydrogen atoms were refined anisotropically, disordered
atoms were refined isotropically with fixed SOF = 0.5. Hydro-
gen atoms in Eu-complexes were found in the difference
Fourier maps and refined isotropically while H-atoms in Yb-
complex were placed in the calculated positions and refined in
riding mode. The structures of all complexes contain small
amounts of severely disordered solvent molecules (av. 15 elec-
trons per independent part of unit cell) that could not be
reliably modelled and have been taken into account using
the MASK procedure of the Olex2 programme package.
The absolute configuration of the compounds was established
by measurements of anomalous dispersion effects. CCDC
965909–965911.
(S)-6-Methyl-2-((1-phenylethyl)carbamoyl)pyridine 1-oxide
(S-1b). m-CPBA (1.89 g, 10.9 mmol) was added to a stirred
solution of amide S-1a (1.32 g, 5.49 mmol) in anhydrous
CHCl3 (16 mL). The resulting solution was stirred at rt for 18 h
under an argon atmosphere. The solution was washed with
NaHCO3 (aq.) (0.5 M, 25 mL) and extracted with DCM (3 ×
20 mL). The organic layers were combined, dried over MgSO4
and the solvent removed under reduced pressure. The crude
mixture was purified by flash column chromatography (silica,
gradient elution starting from 40% EtOAc in hexane to 70%
EtOAc in hexane) to yield compound S-1b as a white crystalline
solid (1.17 g, 83%). TLC analysis Rf 0.21 (silica, 60% EtOAc in
1
hexane); m.p. 70–71 °C; H NMR (295 K, 400 MHz, CDCl3) δH
3
3
4
11.91 (1H, d, J 7.5, NH), 8.34 (1H, dd, J 8, J 2, py-H3), 7.40
(2H, m, Ph-Ho), 7.38 (1H, dd, 3J 8, 4J 2, py-H5), 7.34 (3H, m, Ph-
Hm, Ph-Hp), 7.25–7.23 (1H, m, py-H4), 5.31 (1H, dq, J 7, J 7.5
CHCH3), 2.57 (3H, s, py-CH3), 1.62 (3H, d, 3J 7, CHCH3); 13C
NMR (295 K, 100 MHz, CDCl3) δC 159.4 (CvO), 150.3 (py-C6),
143.5 (Ph-Ci), 141 (py-C2), 128.9 (Ph-C), 128.1 (py-C5), 127.4
(py-C4), 127.1 (py-C3), 126.5 (Ph-C), 126.4 (Ph-Co), 49.8
(CHCH3), 22.8 (CHCH3), 18.4 (py-CH3); m/z (HRMS+) 257.1280
(C15H17N2O2 requires 257.1290).
3
3
(S)-(2-((1-Phenylethyl)carbamoyl)pyrdin-2-yl)methyl acetate
(S-1c).
Ligand syntheses
(S)-6-Methyl-N-(1-phenylethyl)picolinamide (S-1a).
The N-oxide S-1b (700 mg, 2.73 mmol) was dissolved in acetic
anhydride (14 mL) and the solution was heated to 120 °C for
24 h with stirring. The reaction progress was monitored by
6-Methylpyridine-2-carboxylic acid (1.00 g, 7.29 mmol), LCMS and TLC (silica, 50% EtOAc in hexane, Rf(product) 0.38,
HOBt·H2O (1.48 g, 10.9 mmol), EDC (1.70 g, 10.94 mmol) and Rf(reactant) 0.16). The solvent was removed under reduced
DIPEA (3.17 mL, 18.2 mmol) were dissolved in anhydrous pressure and the residue purified by column chromatography
DMF (20 mL). (S)-(−)-α-Methylbenzyl amine (0.93 mL, (silica, gradient elution starting from 20% EtOAc in hexane to
7.29 mmol) was added dropwise to the solution and the 70% EtOAc in hexane) to give S-1c as dark yellow oil (476 mg,
mixture was stirred at rt for 22 h under an argon atmosphere. 59%). TLC analysis Rf 0.38 (silica, 50% EtOAc in hexane); 1H
3
Water was added (25 mL) and the mixture extracted with NMR (295 K, 400 MHz, CDCl3) δH 8.26 (1H, d, J 7.5, NH), 8.14
3
3
3
EtOAc (3 × 10 mL). The organic layers were combined and (1H, d, J 8, py-H3), 7.86 (1H, t, J 8, py-H4), 7.48 (1H, d, J 8,
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3
3
py-H5), 7.42–7.25 (5H, m, Ph-H), 5.36–5.28 (1H, dq, J 7, J 7.5, δC 162.8 (CONH), 152.5 (py-C6), 149.9 (py-C2), 143.3 (Ph-Ci),
CHCH3), 5.24 (2H, s, py-CH2), 2.16 (3H, s, COCH3), 1.63 (3H, d, 138.7 (py-C4), 128.8 (Ph-Cm), 127.5 (Ph-Cp), 126.4 (Ph-Co),
3J 7, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC 170.6 124.6 (py-C3), 122.4 (py-C5), 70.8 (py-CH2), 49.0 (CHCH3), 38.3
(COCH3), 163.2 (CONH), 154.7 (py-C2), 149.7 (py-C6), 143.4 (OSO2CH3), 22.1 (CHCH3); m/z [HRMS]+ 335.1066 [M + H]+
(Ph-Ci), 138.3 (py-C4), 128.8 (Ph-Cm), 127.5 (Ph-Cp), 126.4 (Ph- (C16H19N2O4S requires 335.1060).
Co), 124.1 (py-C5), 121.6 (py-C3), 66.5 (py-CH2), 49.0 (CHCH3),
6,6′,6″-((1,4,7-Triazacyclononane-1,4,7-triyl)tris(methylene))-
22.2 (CHCH3), 21.0 (COCH3); m/z (HRMS+) 299.1373 [M + H]+
tris(N-((S)-1-phenylethyl)picolinamide (S-L1)
(C17H19N2O3 requires 299.1396).
(S)-6-(Hydroxymethyl)-N-(1-phenylethyl)picolinamide (S-1d).
1,4,7-Triazacyclononane (55 mg, 0.427 mmol) and the mesylate,
S-1e, (428 mg, 1.28 mmol) were dissolved in anhydrous CH3CN
(19.5 mL) and K2CO3 (59 mg, 0.427 mmol) was added. The
mixture was stirred under argon at 78 °C. After 21 h the reaction
was cooled and filtered to remove excess potassium salts. The
solvent was removed under reduced pressure and the crude
The ester, S-1c, (350 mg, 1.16 mmol) was dissolved in anhy- material purified by column chromatography (alumina, gradient
drous CH3CH2OH (12 mL). A small amount of sodium metal elution starting from 100% CH2Cl2 to 5% CH3OH in CH2Cl2) to
(∼5 mg) was added and the solution stirred at 40 °C under give S-L1 as a yellow glassy solid (180 mg, 55%); TLC analysis Rf
argon for 2 h. The solution was concentrated under reduced 0.21 (alumina, CH2Cl2 : CH3OH 1%); 1H NMR (295 K, 400 MHz,
3
3
pressure and the residue dissolved in DCM (100 mL). The CDCl3) δH 8.53 (3H, d, J 7, CONH), 8.08 (3H, d, J 7.5, py-H3),
sodium salts were extracted by washing with water (1 × 25 mL) 7.77 (3H, t, py-H4), 7.51 (3H, d, J 7, py-H5), 7.43–7.17 (15H, m,
3
3
3
and the aqueous layer was re-extracted with DCM (3 × 20 mL). Ph-H), 5.35 (3H, dq, J 7, J 7.5, CHCH3), 3.78 (6H, s, py-CH2),
The organic layers were combined, dried over MgSO4, filtered 2.79 (12H, s, ring Hs), 1.62 (9H, d, 3J 7, CHCH3); 13C NMR
and the solvent removed under reduced pressure. The crude (295 K, 100 MHz, CDCl3) δC 163.7 (CONH), 159.3 (py-C2), 149.5
residue was purified by column chromatography (silica, gradi- (py-C6), 143.6 (Ph-Ci), 137.9 (py-C4), 128.8 (Ph-Cm), 127.5 (Ph-
ent elution starting from 40% EtOAc 100% EtOAc) to yield Cp), 126.6 (Ph-Co), 125.9 (py-C5), 120.9 (py-C3), 64.6 (py-CH2),
compound S-1d as a white solid (330 mg, 85%). TLC analysis 56.3 (ring Cs), 49.0 (ring Cs), 46.0 (CHCH3), 22.05 (CHCH3); m/z
Rf 0.35 (silica, 70% EtOAc in hexane); m.p. 152–154 °C; 1H NMR (HRMS+) 844.4683 [M + H]+ (C51H58N9O3 requires 844.4663).
(295 K, 400 MHz, CDCl3) δH 8.21 (1H, s, 3J 7.5, NH), 8.16 (1H, d,
S-[EuL1](CF3SO3)3. Europium(III) triflate (14 mg, 0.024 mmol)
3J 7.5, py-H3), 7.89 (1H, t, 3J 7.5, py-H4), 7.49 (1H, d, 3J 7.5, was added to a solution of ligand, S-L1, (19 mg, 0.024 mmol)
3
3
py-H5), 7.43–7.25 (5H, m, Ph-H), 5.37–5.30 (1H, dq, J 7, J 7.5, in anhydrous acetonitrile (2 mL) and the mixture heated at
CHCH3), 4.83 (2H, s, py-CH2), 2.91 (1H, br s, OH), 1.64 (3H, d, reflux for 20 h. The solution was concentrated under vacuum
3J 7, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC 163.1 and cold diethyl ether (2 mL) was added dropwise to the solu-
(CONH), 158.4 (py-C6), 149.1 (py-C2), 143.2 (Ph-Ci), 138.7 (py-C4), tion. The resulting white solid was filtered and dried in vacuo
128.9 (Ph-Cm), 127.6 (Ph-Cp), 126.4 (Ph-Co), 123.5 (py-C5), 121.7 to yield S-[EuL1](CF3SO3)3 as a white solid (20 mg, 85%). 1H
(py-C3), 64.6 (py-CH2), 49.1 (CHCH3), 22.1 (CHCH3); m/z NMR (295 K, 400 MHz, CD3OD) δH major diastereoisomer 7.6
(HRMS+) 257.1282 [M + H]+ (C15H17N2O2 requires 257.1290).
(pyCH′N), 7.5 (py-H3), 7.4 (py-H5), 7.3 (py-H4), 6.9 (Ph-Hp), 6.7
(S)-(6-((1-Phenylethyl)carbamoyl)pyridine-2-yl)methyl methane (Ph-Hm), 5.7 (Ph-Ho), 5.1 (NCH′ ), 4.0 (CHCH3), 1.2 (CHCH3),
ax
sulfonate (S-1e). The alcohol, S-1d, (227 mg, 0.886 mmol) was −0.7 (pyCHN), −1.5 (NCHeq), −2.2 (NCH′ ), −6.6 (NCHax); m/z
eq
dissolved in anhydrous THF (5.5 mL) and NEt3 (0.37 mL, HRMS+ 992.3646 [M
−
2H]+ (C51H55N9O3151Eu requires
2.66 mmol) was added. The mixture was stirred at 5 °C, methane- 992.3626). τ(H2O) = 0.98 ms, τ(D2O) = 1.42 ms (q = 0) and ϕem
sulfonyl chloride (0.12 mL, 1.49 mmol) was added and the (H2O) = 7%. tR = 5.63 min.
reaction stirred at rt for 30 minutes and monitored by TLC
Crystals of the europium complex were grown by slow evap-
(silica, 100% ethyl acetate, Rf(product) 0.63, Rf(reactant) 0.53). oration of aqueous methanol (1 : 1 v/v) and examined by X-ray
The solvent was removed under reduced pressure and the crystallography.
residue dissolved in DCM (25 mL) and washed with saturated
Crystal data: C51H57EuN9O3 × 3CF3SO3, Mr = 1443.22, tri-
aqueous NaCl solution (15 mL). The aqueous layer was re- gonal (R3); a = 21.6392(5) Å, c = 11.4683(4) Å, V = 4650.6(2) Å3,
extracted with DCM (3 × 10 mL) and the organic layers were Z = 3; µ = 1.205 mm−1, Dcalc = 1.546 mg mm−3, T = 120 K; 62 469
combined, dried over MgSO4, filtered and the solvent removed reflections were measured (2.18 ≤ 2Θ ≤ 62.06), 5722 indepen-
under reduced pressure to leave compound S-1e, as a bright dent reflections (Rint = 0.0336), R1 = 0.0412 (5684 I ≥ 2σ(I)), ωR2
yellow oil, which was used directly in the next step without = 0.1043 (all data), GOOF = 1.026. Flack parameter −0.0013
further purification. TLC analysis Rf 0.63 (silica, 100% ethyl (11), Hooft parameter 0.004(5), CCDC 965909.
acetate); 1H NMR (295 K, 400 MHz, CDCl3) δH 8.25 (1H, d, 3J 8,
S-[CeL1](CF3SO3)3. An analogous method to that for
NH), 8.19 (1H, d, 3J 8, py-H5), 7.91 (1H, t, 3J 8, py-H4), 7.59 (1H, S-[EuL1]3+ using cerium(III) triflate (7 mg, 0.012 mmol) and the
3
d, J 8, py-H3), 7.42–7.26 (5H, m, Ph-H), 6.36 (2H, s, py-CH2), ligand S-L1 (10 mg, 0.012 mmol) in dry acetonitrile (2 mL) was
5.34–5.28 (1H, dq, 3J 7, 3J 8, CHCH3), 3.07 (3H, s, SO2CH3), followed to yield S-[CeL1](CF3SO3)3 as a white solid (10 mg,
3
1.63 (3H, d, J 7, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) 85%). 1H NMR (295 K, 400 MHz, CD3OD) δH major diastereoisomer
5498 | Dalton Trans., 2014, 43, 5490–5504
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9.6 (py-H3), 9.4 (py-H4), 8.4 (py-H5), 7.7 (Ph-H), 7.6 (Ph-H), 6.2 H4), 7.5 (Ph-HP), 6.9 (Ph-Hm), 6.1 (Ph-Ho), 3.6, 1.9 (CHCH3), 1.8
(NCH′ ), 4.5 (CHCH3), 4.1 (pyCHN), 1.6 (NCH′ ), 1.3 (CHCH3), (pyCHN), 0.9 (CHCH3), −5.0 (NCHeq), −5.1 (NCH′ ), −8.8
ax
eq
eq
0.3 (NCHeq), −1.0 (NCHax); m/z (HRMS+) 981.3506 [M − 2H]+ (NCHax); m/z HRMS+ 1009.380 [M − 2H]+ (C51H55N9O3168Er
(C51H55N9O3140Ce requires 981.3482).
requires 1009.377).
S-[TmL1](CF3SO3)3. 1H NMR (295 K, 400 MHz, CD3OD) δH
major diastereoisomer 70.4 (pyCH′N), 23.0 (py-H3), 19.6 (py-
S-[PrL1](CF3SO3)3. An analogous method to that for
S-[EuL1]3+ using praseodymium(III) triflate (7 mg, 0.012 mmol)
and the ligand S-L1 (10 mg, 0.012 mmol) in dry acetonitrile
(2 mL) was followed to yield S-[PrL1](CF3SO3)3, as a white solid
(10 mg, 85%). 1H NMR (295 K, 400 MHz, CD3OD) δH major dia-
stereoisomer 11.1 (py-H3), 10.5 (py-H4), 10.1 (py-H5), 9.4
H4), 19.2 (py-H5), 11.3 (NCH′ ), 10.8 (Ph-Ho), 10.7 (Ph-Hp),
ax
10.4 (Ph-Hm), 9.3 (CHCH3), −7.5 (CHCH3), −22.0 (pyCHN),
−29.0 (NCHeq), −30.5 (NCH′ ), −79.8 (NCHax); m/z HRMS+
eq
1010.375 [M − 2H]+ (C51H55N9O3169Tm requires 1010.376).
S-[YbL1](CF3SO3)3. 1H NMR (295 K, 400 MHz, CD3OD) δH
major diastereoisomer 22.3 (pyCH′N), 11.6 (py-H3), 11.4 (py-
(NCH′ ), 8.4 (Ph-H), 8.2 (Ph-H), 8.1 (Ph-H), 6.4 (pyCHN), 4.1
ax
(CHCH3), 1.6 (NCHeq), 1.1 (CHCH3), 0.5 (pyCH′N), −1.3
H5), 11.2 (py-H4), 8.9 (NCH′ ), 8.3 (Ph-Hm), 8.2 (Ph-Hp), 7.6
(NCH′ ), −5.5 (NCHax); m/z HRMS+ 982.3493 [M − 2H]+
ax
eq
(Ph-Ho), 6.2 (CHCH3), −1.1 (CHCH3), −2.8 (pyCHN), −4.2
(NCHeq), −6.7 (NCH′eq), −18.8 (NCHax); m/z HRMS+ 1012.382
[M − 2H]+ (C51H55N9O3171Yb requires 1012.379). Crystals of the
ytterbium complex were grown by slow evaporation of aqueous
methanol (1 : 1 v/v) and examined by X-ray crystallography.
Crystal data: C54H57F9N9O12S3Yb, Mr = 1464.30, trigonal
(R3); a = 21.836(2), c = 11.1868(17) Å, V = 4619.5(10) Å3, Z = 3; µ
= 1.713 mm−1, Dcalc = 1.579 mg mm−3, T = 120 K; 65 596 reflec-
tions measured (2.16 ≤ 2Θ ≤ 62.06), 5472 independent reflec-
tions (Rint = 0.0398), R1 = 0.0437 (5432 I ≥ 2σ(I)), ωR2 = 0.1116
(all data), GOOF = 1.053, Flack parameter −0.018(11), Hooft
parameter 0.003(3). CCDC 965911.
(C51H55N9O3141Pr requires 982.3499).
S-[NdL1](CF3SO3)3. An analogous method to that for
S-[EuL1]3+ using neodymium(III) triflate (7 mg, 0.012 mmol) and
the ligand S-L1 (10 mg, 0.012 mmol) in dry acetonitrile (2 mL)
was followed to yield [NdL1]3+, as a white solid (9 mg, 72%). 1H
NMR (295 K, 400 MHz, CD3OD) δH major diastereoisomer 10.2
(py-H3), 9.3 (py-H4), 8.9 (py-H5), 7.5 (Ph-H), 7.2 (pyCHN), 6.4
(Ph-H), 5.8 (NCHax), 5.3 (CHCH3), 4.1 (NCH′ ), 2.7 (NCHeq), 2.6
ax
(NCH′ ), 1.6 (CHCH3), 0.4 (pyCH′N); m/z (HRMS+) 983.3505 [M
eq
− 2H]+ (C51H55N9O3142Nd requires 983.3530).
S-[TbL1](CF3SO3)3. An analogous method to that for
S-[EuL1]3+ using terbium(III) triflate (10 mg, 0.017 mmol) and the
ligand S-L1 (15 mg, 0.017 mmol) in dry acetonitrile (2 mL) was
followed to yield S-[TbL1](CF3SO3)3, as a white solid (16 mg,
R-L1 and R-L2 were synthesised in an analogous manner to
the S series starting from R-(+)-α-methylbenzyl amine.
R-[EuL1](CF3SO3)3. 1H NMR (295 K, 400 MHz, CD3OD) δH
major diastereoisomer 7.6 (pyCH′N), 7.5 (py-H3), 7.4 (py-H5),
7.3 (py-H4), 6.9 (Ph-Hp), 6.7 (Ph-Hm), 5.7 (Ph-Ho), 5.1 (NCH′ax)
4.0 (CHCH3), 1.2 (CHCH3), −0.7 (pyCHN), −1.5 (NCHeq), −2.2
(NCH′eq), −6.6 (NCHax); m/z [HRMS]+ 992.3674 [M − 2H]+
(C51H55N9O3151Eu requires 992.3626). Crystals of the europium
complex were grown by slow evaporation of aqueous methanol
(1 : 1 v/v) and examined by X-ray crystallography.
1
92%). H NMR (295 K, 400 MHz, CD3OD) δH major diastereo-
isomer; partial assignment: 57.5 (NCHax), 29.9 (NCH′ ), 23.9
eq
(NCHeq), 8.6 (CHCH3), 5.8 (CHCH3), 4.5 (Ph-Hm), 2.0 (Ph-Ho),
−3.2 (py-H4), −4.4 (py-H5), −11.0 (py-H3), −12.4 (NCH′ ),
ax
2H]+
−45.5 (pyCH′N); m/z HRMS+ 1000.369 [M
−
(C51H55N9O3159Tb requires 1000.368). τ(H2O) = 1.87 ms, τ(D2O)
= 2.12 ms and ϕem (H2O) = 50%.
S-[DyL1](CF3SO3)3. An analogous method to that for
S-[EuL1]3+ using dysprosium(III) triflate (11 mg, 0.017 mmol) and
the ligand S-L1 (15 mg, 0.017 mmol) in dry acetonitrile (2 mL)
was followed to yield S-[DyL1](CF3SO3)3, as a white solid
(15 mg, 88%). 1H NMR (295 K, 400 MHz, CD3OD) δH major dia-
Crystal data C51H57EuN9O3 × 3CF3SO3, Mr = 1443.22, tri-
gonal (R3); a = 21.6423(8), c = 11.5027 Å, V = 4665.9 Å3, Z = 3; µ =
1.201 mm−1, Dcalc = 1.541 mg mm−3, T = 120 K; 29 561 reflec-
tions were measured (3.76 ≤ 2Θ ≤ 62), 6082 independent
reflections (Rint = 0.0267), R1 = 0.0281 (6077 I ≥ 2σ(I)), ωR2
0.0740 (all data), GOOF = 1.029, Flack parameter −0.012(7),
Hooft parameter -0.009(2). CCDC 965910.
=
stereoisomer, partial assignment: 22.5 (NCH′ ), 18.2, 11.1, 7.0,
ax
6.5 (Ph-H), 6.2 (Ph-H), 5.6, 5.0 (py-H4), 3.0 (py-H5), 1.9 (py-H3),
−1.5, −3.7 (pyCHN), −4.8, −14.0, 18.0; m/z HRMS+ 1002.371
[M − 2H]+ (C51H55N9O3161Dy requires 1002.370). τ(H2O) =
0.04 ms and ϕem (H2O) = 1.2%.
R-[TbL1](CF3SO3)3. 1H NMR (295 K, 400 MHz, CD3OD) δH
major diastereoisomer, partial assignment: 57.5 (NCHax), 29.9
(NCH′eq), 23.9 (NCHeq), 8.6 (CHCH3), 5.8 (CHCH3), 4.5 (Ph-
Hm), 2.0 (Ph-Ho), −3.2 (py-H4), −4.4 (py-H5), −11.0 (py-H3),
−12.4 (NCH′ax), −45.5 (pyCH′N); m/z [HRMS]+ 1000.368
[M − 2H]+ (C51H55N9O3159Tb requires 1000.368).
S-[HoL1](CF3SO3)3. An analogous method to that for
S-[EuL1]3+ using holmium(III) triflate (8 mg, 0.013 mmol) and
the ligand S-L1 (11 mg, 0.013 mmol) in dry acetonitrile (2 mL)
was followed to yield S-[HoL1](CF3SO3)3, as a white solid
(13 mg, 99%). 1H NMR (295 K, 400 MHz, CD3OD) δH major dia-
6-(Hydroxymethyl)-4-iodopicolinic acid (S-2a)
stereoisomer, partial assignment: 47.3 (NCHax), 23.3 (NCH′ ),
eq
22.6 (NCHeq), 11.9, 10.2, 9.8, 7.2 (CHCH3), 5.8 (CHCH3), 5.5
(Ph-Hm), 5.1 (Ph-Ho), 0.5 (py-H5), −0.4 (py-H4), −3.7 (NCH′ ),
ax
−5.5 (py-H3), −32.0 (pyCH′N); m/z HRMS+ 1006.374 [M − 2H]+
(C51H55N9O3165Ho requires 1006.373).
S-[ErL1](CF3SO3)3. 1H NMR (295 K, 400 MHz, CD3OD) δH Methyl
6-(hydroxymethyl)-4-iodopicolinate
(200
mg,
major diastereoisomer 12.8, 8.2 (py-H3), 8.0 (py-H5), 7.9 (py- 0.683 mmol) was dissolved in a 1 : 1 v/v mixture of ethanol–
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water (6 mL) and NaOH (2 M, 0.5 mL) was added dropwise. 10 mL). The organic layers were combined, dried over MgSO4,
The solution was stirred at room temperature for 1 h. The filtered and the solvent removed under reduced pressure to
ethanol was removed under reduced pressure and the aqueous yield the compound 3a as a pale brown solid. TLC analysis Rf
1
layer was acidified to pH = 4 using a 2 M HCl solution until a 0.32 (silica, 50% EtOAc in hexane); m.p. 152–153 °C; H NMR
white precipitate was formed. The solid was extracted into (295 K, 400 MHz, CDCl3) δH 7.47–7.40 (4H, m, Ar-H), 2.17 (3H,
EtOAc (4 × 50 mL), dried over MgSO4 and concentrated under s, COCH3), 0.24 (9H, s, Si(CH3)3); 13C NMR (295 K, 100 MHz,
reduced pressure to yield the compound S-2a as a white solid CDCl3) δC 168.3 (COCH3), 138.2 (Ar-C), 132.9 (Ar-C), 119.3 (Ar-
(168 mg, 88%) which was used in the next step without further C), 118.9 (Ar-C), 104.9 (alkyne C), 93.8 (alkyne C), 24.9
purification. TLC analysis Rf 0.08 (silica, 15% CH3OH in (COCH3), 0.1 (Si(CH3)3); m/z (HRMS+) 232.1148 [M + H]+
CH2Cl2); m.p. >190 °C (dec.); 1H NMR (295 K, 400 MHz, (C13H18NOSi requires 232.1158).
MeOD) δH 8.38 (1H, s, py-H3), 8.16 (1H, s, py-H5), 4.72 (2H, s,
py-CH2); 13C NMR (295 K, 100 MHz, MeOD) δC 166 (COOH),
N-(4-Ethynylphenyl)acetamide (3b) CAS: 35447-83-7
164 (py-C6), 149 (py-C2), 134 (py-C5), 133 (py-C3), 108 (py-C4),
64.7 (py-CH2); m/z (HRMS+) 279.9478 [M + H]+ (C7H7NO3127I
requires 279.9471).
(S)-6-(Hydroxymethyl)-4-iodo-N-(1-phenylethyl)picolinamide
(S-2b)
(4-(Trimethylsilyl)ethynyl)acetanilide (213 mg, 0.921 mmol)
was dissolved in anhydrous THF (3.5 mL) and triethylammo-
nium trihydrofluoride (1.50 mL, 9.21 mmol) was added. The
mixture was stirred at 35 °C under argon for 48 h. The solvent
was removed under vacuum to give an off-white solid which
was purified by column chromatography (silica, gradient
HOBt·H2O (442 mg, 3.27 mmol), EDC (507 mg, 3.27 mmol),
DIPEA (0.76 mL, 4.36 mmol) and (S)-(–)-α-methylbenzyl amine
(0.30 mL, 2.40 mmol) were dissolved in anhydrous 1 : 1 DMF–
DCM (4 mL). The carboxylic acid, S-2a, (608 mg, 2.18 mmol in
1 mL DMF) was added slowly and dropwise to the solution and
the mixture stirred at rt for 22 h under an argon atmosphere.
The solvent was removed under reduced pressure, water was
elution starting from 100% hexane to 40% EtOAc in hexane) to
afford compound 3b as a white solid (104 mg, 71%). TLC ana-
lysis Rf 0.31 (silica, 40% EtOAc in hexane); 1H NMR (295 K,
3
400 MHz, CDCl3) δH 7.64 (1H, s, NH), 7.48 (2H, d, J 8.5, Ar-
added to the crude residue and the mixture extracted with
H2,2′), 7.43 (2H, d, J 8.5, Ar-H3,3′), 3.04 (1H, s, H6), 2.17 (3H, s,
3
EtOAc (4 × 40 mL). The organic layers were combined and
washed successively with water (1 × 40 mL) and brine (1 ×
COCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC 168.7 (COCH3),
138.5 (Ar-C1), 133.0 (Ar-C3,3′), 119.5 (Ar-C2,2′), 117.8 (C4), 83.5
40 mL), dried over MgSO4 and the solvent removed under
(C5), 76.8 (C6), 24.8 (COCH3); m/z (HRMS+) 160.0751 [M + H]+
reduced pressure. The crude mixture was purified by flash
column chromatography (silica, gradient elution starting from
20% EtOAc in hexane to 50% EtOAc in hexane) to afford S-2b
(C10H10NO requires 160.0762); m.p. 115–117 °C (lit.
115–119 °C).29
as a yellow oil (510 mg, 61%). TLC analysis Rf 0.38 (silica, 50%
EtOAc in hexane); 1H NMR (295 K, 400 MHz, CDCl3) δH 8.48
(S)-6-(Hydroxymethyl)-N-(1-phenylethyl)-4-(phenylethynyl)-
(1H, s, py-H3), 8.08 (1H, d, 3J 8.5, NH), 7.92 (1H, s, py-H5),
picolinamide (S-4a)
7.39–7.38 (2H, m, Ph-Ho), 7.36–7.34 (2H, m, Ph- Hm), 7.29–7.27
3
3
(1H, m, Ph-Hp), 5.32 (1H, dq, J 8.5, J 7, CHCH3), 4.76 (2H, s,
py-CH2), 1.62 (3H, d, J 7, CHCH3); 13C NMR (295 K, 100 MHz,
3
CDCl3) δC 161.9 (CONH), 159.5 (py-C6), 149.3 (py-C2), 143.0
(Ph-Ci), 132.6 (py-C5), 130.9 (py-C3), 128.9 (Ph-Cm), 127.6 (Ph-
Cp), 126.4 (Ph-Co), 108.0 (py-C4), 64.3 (py-CH2), 49.1 (CHCH3),
21.9 (CHCH3); m/z (HRMS+) 383.0271 [M + H]+ (C15H16N2O2I127
requires 383.0257).
General Sonogashira cross coupling reaction. The com-
pound S-2b (100 mg, 0.262 mmol) was dissolved in anhydrous
(4-(Trimethylsilyl)ethynyl)acetanilide (3a) CAS: 81854-47-9
4-((Trimethylsilyl)ethynyl)aniline (200 mg, 1.06 mmol) was dis- THF (2 mL) and the solution was degassed (freeze–thaw cycle)
solved in anhydrous CH2Cl2 (3 mL) and acetic anhydride three times. Phenylacetylene (40 μL, 0.393 mmol) and triethyl-
(0.12 mL, 1.27 mmol) was added dropwise. The solution was amine (0.18 mL, 1.31 mmol) were added and the solution was
stirred at room temperature under an argon atmosphere for degassed (freeze–thaw cycle) once more. [1,1-Bis(diphenyl-
2 h. The reaction mixture was washed with saturated aqueous phosphino)ferrocene]dichloropalladium(II) (19 mg, 26 µmol)
Na2CO3 solution (10 mL) and extracted into CH2Cl2 (2 × and CuI (10 mg, 52 µmol) were added and the resulting brown
5500 | Dalton Trans., 2014, 43, 5490–5504
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solution was stirred at 65 °C under argon for 24 h. The solvent C), 127.6 (Ph-C), 126.4 (Ph-C) 124.7 (py-C5), 123.4 (py-C3),
was removed under reduced pressure and the resulting brown 114.4 (Ar-C2,2′), 114.0 (py-C4), 96.0 (C5), 85.6 (C6), 64.7 (py-
oil was purified by column chromatography (silica, gradient CH2), 55.5 (OCH3), 49.0 (CHCH3), 22.0 (CHCH3); m/z (HRMS+)
elution starting from 100% CH2Cl2 to 2% CH3OH in CH2Cl2 in 387.1701 [M + H]+ (C24H23N2O3 requires 387.1709).
0.2% increments) to give the compound S-4a as a yellow oil
(S)-4-((4-Acetamidophenyl)ethynyl)-6-(hydroxymethyl)-
N-(1-phenylethyl)picolinamide (S-4d)
(91 mg, 98%). TLC analysis Rf 0.32 (silica, 1% CH3OH in
CH2Cl2); H NMR (295 K, 400 MHz, CDCl3) δH 8.19 (1H, br s,
1
py-H3), 8.15 (1H, d, 3J 9, CONH), 7.57–7.54 (3H, m, Ar-H3,3′, py- The compound S-4d was obtained as a yellow oil (122 mg,
H5), 7.42–7.27 (8H, m, Ar-H1, Ar-H2,2′, Ph-H), 5.35 (1H, dq, 3J 9, 68%) according to the general cross coupling procedure. TLC
3J 7, CHCH3), 4.80 (2H, s, py-CH2), 1.63 (3H, d, J 7 CHCH3); analysis Rf 0.49 (silica, 5% CH3OH in CH2Cl2); m.p. >200 °C
3
13C NMR (295 K, 100 MHz, CDCl3) δC 162.9 (CONH), 159.1 (py- (dec.); 1H NMR (295 K, 400 MHz, d6-DMSO) δH 10.19 (1H, s,
C6), 149.2 (py-C2), 143.1 (Ph-Ci), 134.0 (C4), 132.1 (Ar-C), 129.6 NHOAc), 9.01 (1H, d, 3J 8.5, CONH), 7.89 (1H, br s, py-H3),
(Ar-C), 128.8 (Ph-C), 128.6 (Ph-C), 127.5 (py-C5), 126.4 (Ph-C), 7.68–7.67 (3H, m, py-H5, Ar-H3,3′), 7.59–7.57 (2H, m, Ar-H2,2′),
124.9 (py-C4), 123.4 (py-C3), 121.9 (C1), 95.4 (C5), 86.5 (C6), 7.42–7.33 (4H, m, Ph-Ho, Ph-Hm), 7.24 (1H, t, 3J 7, Ph-Hp), 5.59
3
3
3
64.7 (py-CH2), 49.0 (CHCH3), 21.9 (CHCH3); m/z (HRMS+) (1H, br t, J 6.5, OH), 5.21 (1H, dq, J 8.5, J 7, CHCH3), 4.68
3
3
357.1608 [M + H]+ (C23H21N2O2 requires 357.1603).
(2H, d, J 6.3, py-CH2), 2.07 (3H, s, NHCOCH3), 1.54 (3H, d, J
7, CHCH3); 13C NMR (295 K, 100 MHz, d6-DMSO) δC 168.7
(NHCOCH3), 162.4 (CONH), 161.6 (py-C6), 149.5 (py-CH2),
144.1 (Ci), 140.7 (Ar-C1), 132.7 (Ar-C2,2′), 128.3 (Cm), 126.8 (Cp),
126.2 (Co), 123.9 (py-C5), 121.3 (py-C3), 118.8 (Ar-C3,3′), 114.9
(Ar-C4), 94.7 (C5), 85.9 (C6), 63.6 (py-CH2), 48.2 (CHCH3), 24.1
(NHCOCH3), 21.9 (CHCH3); m/z (HRMS+) 414.1803 [M + H]+
(C25H24N3O3 requires 414.1818).
(S)-Methyl 4-((2-(hydroxymethyl)-6-(1-phenylethylcarbamoyl)-
pyridin-4-yl)ethynyl)benzoate (S-4b)
(S)-(6-(1-Phenylethylcarbamoyl)-4-(phenylethynyl)pyridin-2-yl)-
methyl methanesulfonate (S-5a)
General mesylation procedure. The compound S-4a (91 mg,
0.256 mmol) was dissolved in anhydrous THF (2 mL) and NEt3
(0.12 mL, 0.896 mmol) was added. The mixture was stirred at
5 °C and methanesulfonyl chloride (30 µL, 0.383 mmol) was
added and the reaction stirred at rt for 30 minutes and moni-
tored by TLC. The solvent was removed under reduced
pressure and the residue dissolved in CH2Cl2 (15 mL) and
washed with NaCl solution (saturated, 15 mL). The aqueous
layer was re-extracted with CH2Cl2 (3 × 15 mL) and the organic
layers were combined, dried over MgSO4, filtered and the
solvent removed under reduced pressure to yield the com-
pound S-5a, as a bright yellow oil (111 mg, 99%), which was
used directly in the next step without further purification. TLC
analysis Rf = 0.75 (silica, 100% EtOAc); 1H NMR (295 K,
The compound S-4b was obtained as a yellow oil (97 mg, 89%)
according to the general cross coupling procedure. TLC analy-
sis Rf 0.19 (silica, 1% CH3OH in CH2Cl2); 1H NMR (295 K,
400 MHz, CDCl3) δH 8.21 (1H, br s, py-H5), 8.13 (1H, d, 3J 7,
3
CONH), 8.04 (2H, d, J 8, Ar-H2,2′), 7.62–7.60 (3H, m, Ar-H3,3′
,
py-H3), 7.42–7.28 (5H, m, Ph-H), 5.35 (1H, dq, 3J 7, 3J 7,
CHCH3), 4.82 (2H, s, py-CH2), 3.94 (3H, s, CO2CH3), 2.80 (1H,
br s, OH), (1.64, 3H, d, 3J 7, CHCH3); 13C NMR (295 K,
100 MHz, CDCl3) δC 166.4 (CO2Me), 162.8 (CONH), 159.4 (py-
C2), 149.4 (py-C6), 143.0 (Ph-Ci), 133.4 (Ar-C4), 132.0 (Ar-C3,3′),
130.7 (Ar-C1), 129.7 (Ar-C2,2′), 128.8 (Ph-Cm), 127.6 (Ph-Cp),
126.4 (Ph-Co), 125.0 (py-C3), 123.4 (py-C5), 94.1 (C5), 89.0 (C6),
64.7 (py-CH2), 52.5, 49.0 (CHCH3), 21.9 (CHCH3); m/z (HRMS+)
415.1643 [M + H]+ (C25H23N2O4 requires 415.1658).
4
3
400 MHz, CDCl3) δH 8.25 (1H, d, J 2, py-H5), 8.22 (1H, d, J 9,
CONH), 7.65 (1H, d, 4J 2, py-H3), 7.58–7.56 (2H, m, Ar-H),
7.43–7.27 (8H, m, Ar-H, Ph-H), 5.35 (2H, s, py-CH2), 5.33 (1H,
(S)-6-(Hydroxymethyl)-4-((4-methoxyphenyl)-N-(1-phenylethyl)-
picolinamide (S-4c)
3
3
3
dq, J 9, J 7, CHCH3), 3.10 (3H, s, SO2CH3), 1.64 (3H, d, J 7,
CHCH3); m/z (HRMS)+ 435.1374 [M + H]+ (C24H23N2O4S
The compound S-4c was obtained as a yellow oil (190 mg, requires 435.1379).
94%) according to the general cross coupling procedure. TLC
(S)-Methyl 4-((2-((methylsulfonyloxy)methyl)-
6-(1-phenylethylcarbamoyl)pyridin-4-yl)ethynyl)benzoate
(S-5b)
analysis Rf 0.18 (silica, 1% CH3OH in CH2Cl2); 1H NMR (295 K,
3
400 MHz, CDCl3) δH 8.17 (1H, br s, py-H3), 8.12 (1H, d, J 7.5,
4
3
CONH), 7.53 (1H, br s, py-H5), 7.49 (2H, dt, J 2, J 9, Ar-H3,3′),
7.42–7.35 (4H, m, Ph-Ho, Ph-Hm), 7.29–7.27 (1H, m, Ph-Hp), The compound S-5b was obtained as a yellow oil (101 mg,
6.90 (2H, dt, 4J 2, 3J 9, Ar-H2,2′), 5.36 (1H, dq, 3J 7.5, 3J 7, 88%) according to the general mesylation procedure. TLC ana-
1
CHCH3), 4.80 (2H, s, py-CH2), 3.84 (3H, s, OCH3), 2.77 (1H, br lysis Rf 0.75 (silica, 100% EtOAc); H NMR (295 K, 400 MHz,
3
s, OH), 1.64 (3H, d, J 7, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δH 8.27 (1H, br s, py-H5), 8.21 (1H, d, 3J 8.5, CONH),
CDCl3) δC 162.9 (CONH), 160.7 (Ar-C1), 158.7 (py-C6), 149.4 8.06 (2H, d, J 8.5, Ar-H2,2′), 7.67 (1H, br s, py-H3), 7.63 (2H, d,
3
(py-C2), 143.2 (Ph-Ci), 134.5 (Ar-C4), 133.8 (Ar-C3,3′), 128.9 (Ph- 3J 8.5, Ar-H3,3′), 7.43–7.35 (4H, m, Ph-Ho, Ph-Hm), 7.28 (1H, t,
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3J 7, Ph-Hp), 5.36 (2H, s, py-CH2), 5.33 (1H, dq 3J 8.5, 3J 7, reaction was cooled and filtered to remove excess potassium
CHCH3), 3.94 (3H, s, CO2CH3), 3.11 (3H, s, SO2CH3), 1.64 (3H, salts. The solvent was removed under reduced pressure and
d, 3J 7, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC 166.4 the crude material purified by column chromatography (silica,
(CO2CH3), 162.2 (CONH), 153.0 (py-C6), 150.2 (py-C2), 143.1 gradient elution starting from 100% CH2Cl2 to 10% CH3OH in
(Ph-Ci), 134.0 (Ar-C4), 132.1 (Ar-C3,3′), 130.9 (Ar-C1), 129.8 (Ar- CH2Cl2) to give S-L2a as a yellow glassy solid (35 mg, 36%). TLC
C2,2′), 128.9 (Ph-Cm), 127.6 (Ph-Cp), 126.4 (Ph-Co), 125.9 (py- analysis Rf 0.42 (silica, 5% CH3OH in CH2Cl2); 1H NMR (295 K,
C3), 124.4 (py-C5), 94.9 (C5), 88.5 (C6), 70.2 (py-CH2), 52.5 400 MHz, CDCl3) δH 8.21 (3H, br s, py-H3), 7.51 (6H, d, 3J 7, Ar-
(CO2CH3), 49.1 (CHCH3), 38.4 (SO2CH3), 22.1 (CHCH3); m/z H3,3′), 7.42–7.33 (15H, m, py-H5, Ar-H1, Ar-H2,2′, Ph-Ho), 7.24
3
3
(HRMS)+ 493.1421 [M + H]+ (C26H25N2O6S requires 493.1433).
(6H, m, Ph-Hm), 7.16 (3H, t, J 7.2, Ph-Hp), 5.34 (3H, q, J 6.5,
CHCH3), 3.87 (6H, s, py-CH2), 2.84 (12H, br s, ring Hs), 1.63
3
(9H, d, J 6.5, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC
(S)-(4-((4-Methoxyphenyl)ethynyl-6-((1-phenylethylcarbamoyl)-
pyridine-2-yl)methyl methane sulfonate (S-5c)
163.1 (CONH), 159.4 (py-C6), 149.8 (py-C2), 143.3 (Ph-Ci), 133.4
(Ar-C4), 132.1 (Ar-C), 129.5 (Ar-C), 128.7 (Ph-Cm), 127.4 (Ph-Cp),
127.1 (py-C5), 126.4 (Ph-Co), 122.9 (py-C3), 122.0 (Ar-C1), 94.8
(C5), 86.8 (C6), 64.1 (py-CH2), 56.2 (ring Cs), 48.9 (CHCH3), 21.9
(CHCH3); m/z (HRMS+) 1144.562 [M
+
H]+ (C75H70N9O3
requires 1144.560).
Trimethyl 4,4′,4″-(S,S)-6,6′,6″-(1,4,7-triazacyclononane-
1,4,7-triyl)tris(methylene)tris(2-((S)-1-phenylethylcarbamoyl)-
pyridine-6,4-diyl)tris(ethyne-2,1-diyl)tribenzoate (S-L2b
)
The compound S-5c was obtained as a yellow oil (165 mg,
The compound S-L2b was obtained as a yellow oil (58 mg, 55%)
according to the general alkylation procedure. TLC analysis Rf
98%) according to the general mesylation procedure. TLC ana-
1
lysis Rf 0.78 (silica, 100% EtOAc); H NMR (295 K, 400 MHz,
1
CDCl3) δH 8.23 (1H, br s, py-H5), 8.12 (1H, br s, CONH), 7.62
(1H, br s, py-H3), 7.51 (2H, d, 3J 8.5, Ar-H3,3′), 7.42–7.28 (5H, m,
0.47 (silica, 5% CH3OH in CH2Cl2); H NMR (295 K, 700 MHz,
3
CDCl3) δH 8.41 (3H, d, J 6, CONH), 8.17 (3H, br s, py-H3), 8.02
(6H, d, 3J 8.5, Ar-H2,2′), 7.64 (3H, br s, py-H5), 7.56 (6H, d, 3J
8.5, Ar-H3,3′), 7.38–7.36 (6H, m, Ph-Ho), 7.2–7.25 (6H, m, Ph-
3
Ph-H), 6.91 (2H, d, J 8.5, Ar-H2,2′), 5.34 (2H, s, py-CH2), 5.32
3
(1H, t, J 7, CHCH3), 3.85 (3H, s, OCH3), 3.10 (OSO2CH3), 1.64
3
3
3
Hm), 7.20 (3H, t, J 7, Ph-Hp), 5.33 (3H, dq, J 6, J 7, CHCH3),
(3H, d, 3J 7, CHCH3); 13C NMR (295 K, 100 MHz, CDCl3) δC
162.5 (CONH), 160.8 (Ar-C1), 152.7 (py-C2), 150.1 (py-C6), 143.2
(Ph-Ci), 135.0 (Ar-C4), 133.9 (Ar-C3,3′), 128.9 (Ph-C), 127.6 (Ph-
C), 126.4 (Ph-C) 125.7 (py-C3), 124.2 (py-C5), 114.4 (Ar-C2,2′),
96.7 (C5), 85.4 (C6), 70.4 (py-CH2), 55.5 (OCH3), 49.1 (CHCH3),
38.4 (OSO2CH3), 22.1 (CHCH3).
3.93 (9H, s, CO2CH3), 3.81 (6H, m, py-CH2), 2.83 (12H, br s,
3
ring Hs), 1.60 (9H, d, J 7, CHCH3); 13C NMR (295 K, 100 MHz,
CDCl3) δC 166.4 (CO2CH3), 163.0 (CONH), 159.6 (py-C6), 149.9
(py-C2), 143.3 (Ci), 132.9 (Ar-C4), 132.0 (Ar-C3,3′), 130.7 (Ar-C1),
129.8 (Ar-C2,2′), 128.7 (Ph-Cm), 127.5 (Ph-Cp), 127.1 (py-C5),
126.4 (Ph-Co), 123.0 (py-H3), 93.7 (C5), 89.3 (C6), 64.1 (py-CH2),
56.1 (ring Cs), 52.5 (CO2CH3), 48.9 (CHCH3), 21.9 (CHCH3); m/z
(HRMS+) 1318.623 [M + H]+ (C78H76N9O6 requires 1318.627).
(S)-(4-((4-Acetamidophenyl)ethynyl)-
6-(1-phenylethylcarbamoyl)pyridin-2-yl)methyl
methanesulfonate (S-5d)
6,6′,6″-((1,4,7-Triazacyclononane-1,4,7-triyl)tris(methylene))-
tris(4-((4-methoxyphenyl)ethynyl)-N-((S)-1-phenylethyl)-
picolinamide) (S-L2c)
The compound S-5d was obtained as a yellow oil (110 mg,
84%) according to the general mesylation procedure. TLC ana-
1
lysis Rf 0.51 (silica, 100% EtOAc); H NMR (295 K, 400 MHz,
3
d3-acetonitrile) δH 8.50 (1H, s, NHCOCH3), 8.45 (1H, d, J 8.5,
The compound S-L2c was obtained as a yellow oil (42 mg, 28%)
according to the general alkylation procedure. TLC analysis Rf
4
4
CONH), 8.05 (1H, d, J 2, py-H5), 7.67 (1H, d, J 2, py-H3), 7.61
(2H, dt, 3J 9, 4J 2, Ar-H3,3′), 7.52 (2H, dt, 3J 9, 4J 2, Ar-H2,2′),
1
0.68 (silica, 7% CH3OH in CH2Cl2); H NMR (295 K, 400 MHz,
3
CDCl3) δH 8.47 (3H, d, 3J 8.5, CONH), 8.13 (3H, br s, py-H3),
7.45 (6H, d, 3J 9, Ar-H3,3′), 7.38–7.18 (18H, m, Ph-H, py-H5),
7.39–7.21 (5H, m, Ph-H), 5.33 (2H, s, py-CH2), 5.18 (1H, dq, J
8.5, 3J 7, CHCH3), 3.12 (3H, s, SO2CH3), 2.04 (3H, s,
NHCOCH3), 1.53 (3H, d, 3J 7, CHCH3)H; m/z (HRMS+) 492.1594
[M + H]+ (C26H26N3O5S requires 492.1593).
3
3
3
6.87 (6H, d, J 9, Ar-H2,2′), 5.33 (3H, dq, J 8.5, J 6.5, CHCH3),
3.82 (9H, s, OCH3), 3.80–3.75 (6H, m, py-CH2), 2.85–2.79 (12H,
m, ring Hs), 1.60 (9H, d, 3J 6.5, CHCH3); 13C NMR (295 K,
100 MHz, CDCl3) δC 163.0 (CONH), 160.4 (Ar-C1), 159.1 (py-C6),
149.5 (py-C2), 143.2 (Ph-Ci), 133.6 (Ar-C4), 133.5 (Ar-C3,3′), 128.5
6,6′,6″-(1,4,7-Triazacyclononane-1,4,7-triyl)tris(methylene)tris-
(N-((S)-1-phenylethyl)-4-(phenylethynyl)picolinamide) (S-L2a)
General alkylation procedure. 1,4,7-Triazacyclononane tri- (Ph-C), 127.2 (Ph-C), 126.7 (Ph-C), 126.2 (py-C5), 122.6 (py-C3),
hydrochloride (20 mg, 0.085 mmol) and the mesylate, S-5a, 114.2 (Ar-C2,2′), 113.9 (py-C4), 95.0 (C5), 85.7 (C6), 63.9 (py-
(111 mg, 0.256 mmol) were dissolved in anhydrous CH3CN CH2), 56.0 (ring Cs), 55.3 (OCH3), 48.7 (CHCH3), 21.8 (CHCH3);
(4.5 mL) and K2CO3 (71 mg, 0.512 mmol) was added. The m/z (HRMS+) 1234.592 [M
+
H]+ (C78H76N9O6 requires
mixture was stirred under argon at 78 °C. After 24 h the 1234.592).
5502 | Dalton Trans., 2014, 43, 5490–5504
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Dalton Transactions
Paper
6,6′,6″-(1,4,7-Triazacyclononane-1,4,7-triyl)tris(methylene)-
tris(4-((4-acetamidophenyl)ethynyl)-N-((S)-1-phenylethyl)-
S-[EuL2d] (CF3SO3)3
The complex S-[EuL2d](CF3SO3)3 was obtained according to the
general complexation procedure, using the ligand S-L2d, as a
picolinamide) (S-L2d
)
The compound S-L2d was obtained as a yellow oil (50 mg, 43%) yellow glassy solid (8 mg, 72%). 1H NMR (295 K, 200 MHz,
according to the general alkylation procedure. TLC analysis Rf CD3OD) δH major diastereoisomer, partial assignment 7.8, 7.6,
0.63 (silica, 15% CH3OH in CH2Cl2); 1H NMR (295 K, 7.4, 7.1, 7.0, 6.9, 5.9, 4.1, 2.2, 1.2 (CHCH3), 0.7, −1.5 (NCHeq),
400 MHz, CD3OD) δH 7.94 (3H, s, py-H3), 7.58 (6H, d, 3J 8.5, Ar- −2.2 (NCH′eq), −6.6 (NCHax); m/z (HRMS)+ 1463.523 [M − 2H]+
H3,3′), 7.54 (3H, s, py-H5), 7.36–7.16 (21H, m, Ph-H, Ar-H2,2′), (C81H76N12O6151Eu) requires 1463.520). tR = 8.0 min.
5.20 (1H, s, CHCH3), 4.04 (6H, br s, py-CH2), 3.02 (12H, br s,
3
ring Hs), 2.10 (9H, s, NHCOCH3), 1.53 (9H, d, J 6.5, CHCH3);
13C NMR (295 K, 100 MHz, CD3OD) δC 171.6 (NHCOCH3),
164.7 (CONH), 151.4 (py-C6), 144.4 (Ci), 141.5 (py-C2), 135.4
(Ar-C4), 133.8 (Ar-C3,3′), 129.7 (Ph-Co), 128.5 (py-C5), 127.3 (Ph-
Cm), 124.2 (py-C4), 123.0 (py-C3), 120.6 (Ar-C2,2′), 117.6 (Ar-C1),
86.6 (C5), 79.1 (C6), 64.6 (py-CH2), 50.4 (CHCH3), 24.1
(NHCOCH3), 22.1 (CHCH3); m/z (HRMS+) 1315.621 [M + H]+
(C81H76N12O6 requires 1315.624).
Acknowledgements
This work was supported by the ERC (ERN, AMF, DP;
FCC 266804). We thank Dr Robert Pal and Mr Robert Puckrin
for their assistance with the CPL measurements.
R-L2d was synthesised in an analogous manner to the S
series starting from R-(+)-α-methylbenzyl amine.
Notes and references
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S-[EuL2a](CF3SO3)3
General complexation procedure. Europium(III) triflate
(9 mg, 0.015 mmol) was added to a solution of ligand, S-L2a,
(18 mg, 0.015 mmol) in anhydrous acetonitrile (2 mL) and the
mixture heated at reflux for 20 h. The solution was concen-
trated under vacuum and cold diethyl ether (2 mL) was added
dropwise to the solution. The resulting solid was isolated and
dried in vacuo to yield S-[EuL2a](CF3SO3)3 as a yellow glassy
solid (10 mg, 50%). 1H NMR (295 K, 200 MHz, CD3OD) δH
major diastereoisomer, partial assignment: 7.7 (pyCH′N), 7.6,
7.4, 7.1, 7.0, 5.9, 4.1, 3.5, 1.2 (CHCH3), 0.8, −1.5 (NCHeq), −2.1
(NCH′eq), −6.5 (NCHax); m/z (HRMS)+ 1292.455 [M − 2H]+
(C75H67N9O3151Eu requires 1292.456). tR = 8.4 min.
S-[EuL2b](CF3SO3)3
The complex S-[EuL2b](CF3SO3)3 was obtained according to the
general complexation procedure, using the ligand S-L2b, as a
1
white solid (10 mg, 52%). H NMR (295 K, 400 MHz, CD3OD)
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5.1, 3.9, 1.2 (CHCH3), 0.8, −1.6 (NCHeq), −2.5 (NCH′eq), −6.7
(NCHax); m/z (HRMS)+ 734.7366 [M − H]2+ (C81H72N9O9151Eu
requires 734.7418). tR = 8.8 min.
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J. Chem. Soc., Chem. Commun., 1989, 1793; (b) C. J. Broan,
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S-[EuL2c] (CF3SO3)3
The complex S-[EuL2c](CF3SO3)3 was obtained according to the
general complexation procedure, using the ligand S-L2c, as a
1
white solid (20 mg, 70%). H NMR (295 K, 400 MHz, CD3OD)
δH (major diastereoisomer, partial assignment: 7.6 (pyCH′N),
7.5, 7.3, 7.1, 7.0, 6.7, 5.8, 4.2, 3.9, 3.5, 2.0, 1.1 (CHCH3), −0.8
(pyCHN), −1.5 (NCHeq), −2.0 (NCH′eq), −6.5 (NCHax); m/z
(HRMS+) 1382.492 [M − 2H]+ (C78H73N9O6151Eu requires
1382.488). tR = 8.4 min.
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5504 | Dalton Trans., 2014, 43, 5490–5504
This journal is © The Royal Society of Chemistry 2014