Chiral lanthanoid dimers ligated by carbohydrate-based diketonates: Catalytic and luminescent properties

Article abstract of DOI:10.1002/ejic.201100505

The reaction of hydrated lanthanoid chlorides (Ln = La, Eu) with chiral, carbohydrate-based diketonate ligands has yielded dimeric species with Ln ₂L₆ composition as determined by MALDI mass spectrometry and single-crystal X-ray crystallography. The X-ray crystallographic analysis identified a chiral cavity formed by interligand repulsion able to coordinate dimethylformamide, prompting investigation of the catalytic properties of the dimers. Preliminary results indicate that the dimers display catalytic activity in thio-Michael addition reactions as well as metal-based luminescence in the case of europium.

Full text of DOI:10.1002/ejic.201100505

FULL PAPER
DOI: 10.1002/ejic.201100505
Chiral Lanthanoid Dimers Ligated by Carbohydrate-Based Diketonates:
Catalytic and Luminescent Properties
William J. Gee,[a] Judith Hierold,[a] Jonathan G. MacLellan,[a] Philip C. Andrews,[a]
David W. Lupton,[a] and Peter C. Junk*[a]
Keywords: Rare earths / Lanthanoids / Asymmetric catalysis / Luminescence / Enantioselectivity / Lewis acids / Diketonates
The reaction of hydrated lanthanoid chlorides (Ln = La, Eu)
with chiral, carbohydrate-based diketonate ligands has
to coordinate dimethylformamide, prompting investigation of
the catalytic properties of the dimers. Preliminary results
yielded dimeric species with Ln2L6 composition as deter- indicate that the dimers display catalytic activity in thio-
mined by MALDI mass spectrometry and single-crystal X-
ray crystallography. The X-ray crystallographic analysis
identified a chiral cavity formed by interligand repulsion able
Michael addition reactions as well as metal-based lumines-
cence in the case of europium.
lecular magnetism.[9] Such species have been synthesised by
ligation of amino acids,[9b,10] chiral amine chelates[8,11] and
coordination-induced species.[9a,9c]
Introduction
The synthesis of new, enantiopure catalysts incorporating
the lanthanoid elements constitutes a fascinating challenge
revolving around the search for chiral ligands suited to de-
sired applications.[1] The lanthanoid series, replete with a
highly electropositive nature coupled with a flexible coordi-
nation sphere, have been shown to catalyse a range of
chemo- and stereoselective reactions, varying according to
ligand class.[1b] Such reactions include hydrosilylations,[2]
hydroaminations,[2,3] polymerisations,[4] Mukaiyama aldol
reactions[5] and thio-Michael reactions,[6] to name but a few.
Prior ligand classes investigated include alkoxide complex-
es,[1b] heterometallic BINOL complexes,[1c] phosphate com-
plexes[1b] and a range of neutral O- and N-donor com-
plexes.[7] Diketonate ligands have been largely overlooked
since the early inception of asymmetric lanthanoid cataly-
sis.[1b] Similarly, with the notable exception of a range of d-
glucose-derived bifunctional asymmetric catalysts reported
by Shibasaki et al.,[1e–1g] the potential of lanthanoid carbo-
hydrate complexes has remained largely unexplored. Carbo-
hydrates represent the most abundant group of natural
products known and hence have the ability to impart versa-
tility and cost-effectiveness to a catalyst series. Further-
more, the isolation of polynuclear chiral lanthanoid species,
either by chelation of ligands containing a chiral centre or
by induced chirality through coordination, has been garner-
ing increasing attention over the past decade, owing to their
potential application to carbon dioxide fixation[8] and mo-
Herein we report the synthesis of lanthanum and euro-
pium dimers ligated by diketonate ligands incorporating a
chiral protected galactose moiety. The dimers contain a
binding pocket which has been visualised in the solid state
by X-ray crystallography, while possessing luminescent
properties measured for the europium species. An investiga-
tion of the catalytic properties of both dimers in the 1,4-
addition of thiols to α,β-unsaturated carbonyl compounds
revealed high catalytic activity, at low catalyst loadings,
whilst employing mild conditions.
Results and Discussion
The asymmetric diketonate ligand central to this study
incorporates both a chiral terminus, to promote asymmetric
induction, and an achiral phenyl terminus to ease steric
constraints within the coordination environment. The core
of the ligand, d-Galactose, imparts a source of chiral diols
that have been extended to give greater steric bulk by simple
conversion to acetonide groups.[12] Subsequent oxidation,
acid chloride formation and direct coupling to lithium
1-phenylenolate yields the chiral diketone Hhpp
(Scheme 1).[13] Each step of the ligand synthesis was moni-
tored using optical rotation measurements, with values sim-
ilar to these reported for intermediate species. The reaction
of Hhpp with hydrated lanthanoid chloride salts using es-
tablished methodologies for cluster synthesis[14] yielded chi-
ral dimers with the composition [Ln2(hpp)6] [Ln = La (1),
Eu (2)]. The solid-state structure of lanthanum species 1
was elucidated by X-ray diffraction studies performed on
single crystals generated by the slow infusion of hexane into
[a] School of Chemistry, Monash University,
Clayton, Victoria, 3800, Australia
E-mail: peter.junk@monash.edu
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100505.
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P. C. Junk et al.
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a toluene solution of 1 containing 1% dimethylformamide pocket containing two lanthanum atoms (Figure 2). It is
(Figure 1). The compound was found to crystallise in the postulated that the sterically bulky acetonide groups inhibit
chiral space group P41212.
the regular ligand spacing around the exterior that can be
seen for analogous lanthanoid dimers.[15]
Scheme 1. Reagents and conditions: (a) acetone, ZnCl2, 8 h; (b) 0.5
m aqueous NaOH, KMnO4, 12 h; (c) neat SOCl2, reflux, 3 h; (d)
1 equiv. lithium 1-phenylenolate, –78 °CǞroom temp., 2 h.
Figure 2. Space-filling model of the binding pocket of 1 viewed
from above. The coordinating DMF molecule has been omitted to
highlight the exposed lanthanoid atoms.
A crystallographic structural determination could not be
made for europium species 2, however there is considerable
evidence supporting retention of the dimeric motif. Aside
from consistent infrared and elemental analyses, MALDI
mass spectrometry yielded a dominant cationic fragment
consistent with the [Ln2(hpp)5]+ species in each case
(Table 1). The observed isotopic profiles were in each in-
stance consistent with the dimeric form. Analysis of crystal-
line 1 by 1H NMR spectroscopy gave a spectrum consistent
with the crystal structure shown in Figure 1. Evidence for
both the enolic proton, determined from Hhpp to be lo-
cated at δ = 15.99 ppm, and resonances derived from the
keto tautomer were absent. The greatest shifts in resonances
relative to the free ligand corresponded to protons assigned
Figure 1. The molecular structure of 1 coordinating a molecule of
DMF. Hydrogen atoms have been omitted for clarity.
Performing the symmetry operation (y, x, –z) generated to the pyranose ring, owing to the changes in the local mag-
the anticipated [La2(hpp)6] dimeric motif containing an un- netic environment caused by metal coordination for two of
expected bridging DMF molecule. The bridging DMF is the six tridentate ligands. Nonequivalence of the methyl res-
disordered over two positions with symmetry transforma- onances of the acetonide groups also suggests two distinct
tions generating the reciprocal molecule. Each of the metal magnetic environments for the ligand groups, although as-
centres has a coordination number of nine and is μ2-bridged signment of the signals proved impossible. Methyl reso-
by both O(22) of the DMF, and the central oxygen atoms nances for the coordinated DMF molecule were observed
[O(17), OЈ(17)] of two ligands. The La–O–La angles vary at δ = 2.88 and 2.94 ppm, while the aldehyde proton was
only slightly between that of the ligands and that of the shifted upfield to 6.65 ppm. The latter resonance, corre-
DMF [102.3(9)° and 103.3(8)°, respectively]. The two bridg- sponding to the DMF aldehyde proton, represents a signifi-
ing ligands are tridentate, coordinating through both oxy- cant shift relative to the aldehyde of a noncoordinated sol-
gen atoms of the diketonate and the oxygen of the pyranose vent sample, which is located at δ = 8.02 ppm.[16] The up-
ring, giving an overall coordination mode of μ2- field shift can be justified as increased imine character over
η2(O,OЈ)η2(OЈ,PyO). The solely chelating diketonates give the C–N bond in response to polarisation of the aldehyde
the closest oxygen-to-metal contacts, with La–O distances carbonyl group. The crystallographic evidence supports this
averaging 2.46 Å. This compares with a bridging diketonate assertion, with a longer C–O distance of 1.289(10) Å, and
La–O distance of 2.485(3) Å for the outer ketone, 2.62 Å shorter C–N distance of 1.268(10) Å observed relative to a
(averaged) for the bridging ketone and 2.703(2) Å for the noncoordinated DMF molecule [C–O: 1.221 Å; C–N:
pyranose oxygen. The bridging ketone oxygen slightly fav- 1.315(7) Å].[17] The europium dimer 2 exhibited an analo-
1
ours one of the lanthanum atoms with La–O and LaЈ–O gous H spectrum to the lanthanum species, however pro-
distances of 2.587(3) and 2.656(2) Å, respectively. Removal tons located in closer proximity to the europium centres
of the DMF molecule allows visualisation of the binding exhibited an increasing degree of upfield paramagnetic
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Chiral Lanthanoid Dimers Ligated Diketonates
shifting (see Supporting Information). The shifts in the % without significant loss of reactivity (Table 2, entries 1a–
NMR resonances observed for the europium species arise c). A control experiment omitting the catalyst confirmed
from low-lying excited states and are typical of such sys- only minor uncatalysed thio-Michael addition (Table 2, en-
tems.
try 1d). The optimised reaction conditions, using 5 mol-%
lanthanum dimer 1, were employed with both ketone- and
aldehyde-derived α,β-unsaturated carbonyl compounds
(Table 2, entries 1a, 2–4), with constantly high isolated
yields. Furthermore, both aliphatic and aromatic thiols
were shown to be competent nucleophiles (Table 2, entries
1a, 5–6).
Table 1. Observed MALDI fragments for dimers 1 and 2.
Cation
Predicted m/z (relative
Observed m/z (relative
intensity %)[a]
intensity %)[a]
[La2(hpp)5]+
2154.5379 (100)
2153.5346 (90)
2155.5413 (61)
2179.5630 (100)
2181.5697 (97)
2180.5663 (95)
2182.5677 (70)
2154.6017 (100)
2153.6297 (90)
2155.5664 (60)
2180.4300 (100)
2182.4214 (99)
2181.4241 (94)
2183.4165 (70)
[Eu2(hpp)5]+
Table 2. Dimers 1 and 2 as catalysts in thio-Michael addition reac-
tions.
[a] Only peaks with relative intensities greater than 50% have been
listed.
The luminescent properties of europium dimer 2 were
next investigated by fluorescence spectroscopy. Excitation
of a chloroform solution of the europium dimer with ultra-
violet radiation (λ = 396 nm) resulted in characteristic red
5
7
emission of the D0 excited state to a suitable end state FJ
(J = 0–6).[18] The first five transitions corresponding to pho-
ton emission from D0Ǟ7FJ (J = 0–4) are shown in Fig-
5
ure 3. Low intensity transitions, 5D0Ǟ7F5 and 5D0Ǟ7F6,
have been omitted. The D0Ǟ7F1 transition has a low in-
5
tensity, attributed to the noncentrosymmetrical position of
Eu3+ atoms, which is consistent with prior reports.[15]
[a] Isolated yield following flash column chromatography. (b)
5 mol-% 1 used as catalyst. (c) Reaction time 6 h. (d) Reaction
stopped after 24 h.
Figure 3. Emission spectra of europium dimer 2 with an excitation
wavelength of 396 nm.
Lanthanoid species have been shown to act as reliable
As the chiral nature of the binding cavity suggests poten-
catalysts in thio-Michael addition reactions, which is attrib- tial for asymmetric induction, the enantiomeric excess of
uted to their Lewis acidity and oxophilic nature.[6] To inves- the thio-Michael products were evaluated. Unfortunately,
tigate the catalytic activity of the dimers the addition of using the described reaction conditions (Table 2, entry 1a)
benzyl mercaptan to benzalacetone was initially studied. To the thio-Michael adduct was obtained in Ͻ10% ee.
eliminate competitive DMF binding in the chiral pocket the Decreasing the reaction temperature to 0 °C increased the
catalysts were precipitated as amorphous powders in the enantioselectivity, with the adduct being formed in 95% ee,
absence of DMF. Both MALDI and elemental analyses for however the yield was now very modest (Scheme 2). Fur-
both lanthanum and europium powders remained consis- ther optimisation did not lead to reaction conditions cap-
tent with the [Ln2(hpp)6] motif. It was found that the reac- able of both good yields and high enantioselectivities.
tion proceeded smoothly at room temperature under nonin-
We postulate that at lower temperatures the ligand con-
ert conditions without the need for solvent, yielding selec- formation and binding pocket corresponds to that shown
tively the β-addition product (Table 2, entry 1). Whilst a in Figures 1 and 2 promoting enantioselectivity. Unfortu-
catalyst loading of 5 mol-% gave complete conversion in nately at these temperatures the thio-Michael reaction is ki-
90 min with both dimers 1 and 2 (isolated yields 96% and netically disfavoured when catalysed by dimers 1 or 2. At
91%, respectively), the loading could be lowered to 1 mol- higher temperatures the thio-Michael reaction becomes ki-
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P. C. Junk et al.
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enced to the solvent. Solid-state IR spectra were recorded with a
Perkin–Elmer 1600 series FTIR or a Bruker Equinox 55 Infrared
Spectrometer fitted with a Specac Diamond ATR source. Infrared
band frequencies are reported in wavenumbers (cm–1) and inten-
sities are reported as strong (s), medium (m) or weak (w). Solution
Real-Time Infrared (RTIR) scanning measurements were recorded
with a Mettler Toledo ReactIR 10 spectrometer fitted with a Di-
Comp probe connected to an MCT detector by a K6 Conduit and
scanning in the region of 4000 to 650 wavenumbers at 8 wave-
number resolution. HRMS were recorded with a Bruker BioApex
47e FTMS fitted with an Analytica electrospray source using NaI
for accurate mass calibration. Melting points were measured with
a Stuart Scientific Melting Point Apparatus in an open capillary.
Elemental analyses were performed by Campbell Microanalytical
Laboratory, Department of Chemistry, University of Otago, Dune-
Scheme 2. Low-yielding synthesis of thio-Michael addition product
(Table 2, entry 5) at 0 °C in 95% ee.
netically favourable, however ligand lability, which has been
reported for analogous species at this temperature,[14c] likely
negates the selectivity of the chiral binding pocket, allowing
indiscriminate reaction.
While these studies have achieved moderate enantio-
selectivities they provide important proof of principle that
chiral β-diketone carbohydrate lanthanoid complexes are
capable of enantioselective catalysis. Currently several stra- din, New Zealand. Optical rotation was measured with a PolAAr
2001 automatic polarimeter at the sodium D line (587 nm) at 25 °C.
HPLC analysis was performed with a Perkin–Elmer LC200 and a
Daicel AD-H column.
tegies to improving the enantioselectivity at elevated tem-
peratures are under investigation. They include screening a
greater range of lanthanoid elements to observe the effects
of ionic size on enantioselectivity, and altering the aceto-
nide groups to incorporate more bulky functionalities such
Synthesis of (Z)-3-Hydroxy-3-phenyl-1-(1,2:3,4-di-O-isopropylidene-
α-D-galactopyranose)prop-2-en-1-one (Hhpp): The ligand Hhpp was
as phenyl rings. We believe that future generations of such obtained by a modified literature procedure.[13] 1,2:3,4-Di-O-iso-
propylidene-α-d-galacturonyl chloride (2.00 g, 7.30 mmol) was dis-
solved in dry THF (5 mL) and rapidly stirred under nitrogen. In a
separate flask cooled to –78 °C a solution of dry acetophenone
(1.64 mL, 14.00 mmol) in dry THF (10 mL) was lithiated with
freshly prepared LiHMDS (14.2 mmol) under nitrogen. The solu-
tion of enolate was transferred in one portion to the acid chloride
catalysts have the potential for widespread application to a
range of asymmetric lanthanoid-catalysed reactions.
Conclusions
We have synthesised the first example of a diketonate solution at –78 °C with rapid stirring. The reaction was then
warmed to room temperature, after which time the solution was
quenched with water (ca. 30 mL) and neutralized with hydrochloric
acid (10%) and extracted with ethyl acetate (3ϫ100 mL). The or-
ganic washes were combined, dried (MgSO4) and concentrated to
dryness under reduced pressure yielding a brown oil. Purification
was done by gradient column chromatography (n-hexane Ǟ
EtOAc/n-hexane, 1:2) to yield the title compound as a pale yellow
ligand bearing a protected carbohydrate group chelating a
lanthanoid species. A single crystal diffraction study of the
resultant lanthanoid adducts identified a [La2(hpp)6] motif
containing a chiral cavity occupied by a coordinated mole-
cule of DMF. MALDI mass spectrometry and elemental
analyses confirmed the europium moiety to be iso-
structural, with a luminescence study on dimer 2 identifying
a characteristic red wavelength emission when exposed to
ultraviolet radiation (λ = 396 nm). Both 1 and 2 show excel-
crystalline solid; yield 2.08 g (76%); m.p. 88.8–90.2 °C. [α]D
=
–170.2. C20H24O7 (376.41): calcd. C 63.8, H 6.4; found C 64.1, H
1
6.5. H NMR (CDCl3, 500 MHz): δ = 1.34 (s, 3 H, CH3), 1.35 (s,
lent activity as Lewis acid catalysts. However, the transfer 3 H, CH3), 1.42 (s, 3 H, CH3), 1.53 (s, 3 H, CH3), 4.31–4.49 (m, 2
H, H2 H3), 4.61–4.80 (m, 2 H, H4 H5), 5.67 (d, J = 5.0 Hz, 1 H,
of chiral information during the catalyzed reactions under
optimal reaction conditions remains a challenge. These fin-
dings define a new range of chiral lanthanoid complexes
with vast potential for modification and tuning to act as
H1), 6.63 (s, J = 7.5 Hz, 1 H, H7), 7.44 (t, J = 7.5 Hz, 2 H, H10),
7.51 (t, J = 7.5 Hz, 1 H, H12), 7.91 (d, J = 7.5 Hz, 2 H, H11), 15.99
(s, 1 H, OH) ppm. 13C NMR (CDCl3, 125 MHz): δ = 24.59, 25.01,
26.02, 26.08, 70.23, 70.86, 70.89, 72.15, 94.55, 96.71, 109.20,
109.92, 127.40, 128.72, 132.54, 134.58, 182.06, 194.81 ppm. IR
chiral catalysts.
(ATR): ν
= 2987 (m), 2938 (m), 1599 (s), 1569 (s), 1493 (m),
˜
max
1459 (s), 1379 (s), 1324 (w), 1259 (s), 1208 (s), 1166 (s), 1143 (w),
1114 (m), 1064 (s), 1001 (s), 930 (s), 900 (w), 869 (m), 849 (m), 836
(m), 817 (m), 770 (s), 693 (s), 658 (w) cm–1. MS (ESI) calcd. for [M
+ Na]+: 399.1, found: 399.3; for [M + H]+: 377.2, found 377.2.
Experimental Section
General Considerations: 1,2:3,4-Di-O-isopropylidene-α-d-galact-
uronyl chloride was obtained by refluxing 1,2:3,4-di-O-isopropylid-
ene-α-d-galacturonic acid in thionyl chloride for 3 h followed by
removal of volatile impurities under high vacuum. All other chemi-
cals were obtained from Sigma–Aldrich and were used as received.
Flash chromatography was performed on silica gel (Davisil LC60A,
40–63-μm silica media) using compressed air. The solvent system
employed was an increasing gradient of ethyl acetate in hexane ini-
tiating from neat hexane unless otherwise stated. TLC was per-
formed using aluminium-backed plates coated with 0.2 mm silica
(Merck; 60 F254 plates). Eluted plates were visualised using a 254-
nm UV lamp or by treatment with a suitable stain. 1H and 13C
NMR spectra were recorded with a Varian Unity Nova 500 spec-
trometer. Chemical shifts were recorded on the δ scale and refer-
Synthesis of Dimers 1 and 2: To a round-bottomed flask equipped
with a stirrer bead were added Hhpp and the appropriate lan-
thanoid trichloride in a 1:1 molar ratio. The starting materials were
dissolved in methanol, followed by a slow, dropwise addition of
4 equiv. of triethylamine. The reactions were stirred for 16 h. After
this time the solvent was removed and the residue stirred in toluene
(ca. 5 mL) for 1 h. The solution was then filtered to remove trieth-
ylammonium chloride, and the toluene removed under high vac-
uum yielding the dimeric complex.
[La2(hpp)6(DMF)] (1): Colourless crystals were obtained after the
slow infusion of hexane into a toluene solution of 1 infused with
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Chiral Lanthanoid Dimers Ligated Diketonates
1% dimethylformamide; yield 63%; m.p. 145–151 °C (dec.).
C123H145La2NO43 (2603.29): calcd. C 56.7, H 5.6, N 0.5; found C
3-(Benzylthio)cyclohexanone:[19] (Table 2, Entry 4), yield 98%. 1H
NMR (CDCl3, 400 MHz): δ = 1.57–1.65 (m, 2 H), 2.00–2.05 (m, 2
56.6, H 5.3, N 0.4. 1H NMR (CDCl3, 500 MHz): δ = 1.26–1.54 (m, H), 2.22–2.26 (m, 2 H), 2.30 (ddd, J = 14.0, 10.4, 0.8 Hz, 1 H),
72 H, 24ϫ CH3), 2.88 [s, 3 H, CH3(DMF)], 2.95 [s, 3 H,
CH3(DMF)], 4.25–4.75 (m, 24 H, H5 H6 H7 H8), 5.65 (s, 6 H, H9), 5 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 24.21, 31.41, 35.05,
6.46–6.66 (m, 6 H, H3), 6.65 (s, 1 H, DMF), 7.20–7.70 (m, 18 H,
41.03, 42.08, 47.91, 127.24, 128.70, 128.82, 138.01, 208.75 ppm. IR
PhH), 7.76–8.19 (m, 12 H, PhH) ppm. IR (ATR): νmax = 2983 (m), (NaCl): ν = 3028 (w), 2941 (m), 1712 (s), 1601 (w), 1494 (m),
2.57–2.62 (m, 1 H), 2.83–2.89 (m, 1 H), 3.69 (s, 2 H), 7.14–7.24 (m,
˜
˜
max
2929 (m), 1654 (w), 1598 (s), 1570 (m), 1517 (s), 1485 (m), 1453 (s), 1453 (m), 1421 (w), 1314 (m), 1221 (m), 1175 (w), 1069 (m), 703
1425 (s), 1377 (s), 1252 (m), 1208 (s), 1165 (m), 1064 (s), 1000 (s),
899 (m), 767 (m), 695 (m), 667 (w) cm–1. HRMS (MALDI) calcd.
for [La2(gph)5]+: 2154.54 (100), 2153.53 (90), 2155.54 (61), 2156.54
(25), 2157.55 (9); found 2154.60 (100), 2153.63 (90), 2155.57 (60),
2156.55 (23), 2157.53 (7).
(m) cm–1.
4-(Butylthio)-4-phenylbutan-2-one:[6c] (Table 2, Entry 5), yield 81%.
1H NMR (CDCl3, 400 MHz): δ = 0.83 (t, J = 7.6 Hz, 3 H), 1.27–
1.34 (m, 2 H), 1.42–1.51 (m, 2 H), 2.08 (s, 3 H), 2.19–2.36 (m, 2
H), 2.96 (d, J = 7.2 Hz, 2 H), 4.31 (t, J = 7.2 Hz, 1 H), 7.20–7.28
(m, 5 H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 13.72, 22.06,
30.86, 31.16, 31.36, 44.30, 50.33, 127.39, 127.85, 128.66, 142.19,
[Eu2(hpp)6] (2): Removal of toluene yielded 2 as a yellow powder;
yield 57%; m.p. 102–116 °C (dec.). C120H138Eu2O42 (2556.31):
calcd. C 56.4, H 5.4; found C 56.0, H 5.3. 1H NMR (CDCl3,
500 MHz): δ = –1.43 (s, 6 H, H9), 0.43 (s, 18 H, 6ϫ CH3), 0.83 (s,
18 H, 6ϫ CH3), 1.24–1.53 (m, 36 H, 12ϫ CH3), 3.96–4.78 (m, 24
H, H5 H6 H7 H8), 5.77 (m, 6 H, H3), 6.20–6.26 (m, 12 H, PhH),
6.26–6.48 (m, 6 H, PhH), 7.39–7.45 (m, 12 H, PhH) ppm. IR
205.68 ppm. IR (NaCl): ν
= 2957 (s), 2929 (s), 2872 (m), 1716
˜
max
(s), 1600 (w), 1492 (m), 1453 (m), 1359 (m), 1152 (m), 1021 (w),
699 (s) cm–1. HRMS (ESI) calcd. for [M + Na]+: 259.1133; found
259.1123; HPLC Daicel AD-H, λ = 238 nm, hexane/iPrOH, 98:2,
0.5 mL/min, fraction tr = 13.6 (major enantiomer) and 14.7 (minor
enantiomer).
(ATR): νmax = 2984 (m), 2936 (m), 1595 (s), 1565 (s), 1517 (s), 1486
˜
(m), 1452 (m), 1413 (s), 1378 (s), 1288 (w), 1251 (m), 1209 (m),
1165 (s), 1139 (m), 1107 (w), 1062 (s), 991 (s), 939 (m), 899 (m),
871 (m), 842 (m), 782 (m), 711 (m) cm–1. HRMS (MALDI) calcd.
for [Eu2(gph)5]+: 2180.56 (100), 2182.56 (98), 2181.56 (94), 2183.57
(69), 2179.56 (40), 2184.57 (37), 2178.56 (37); found 2180.43 (100),
2182.42 (98), 2181.42 (94), 2183.42 (69), 2179.43 (40), 2184.43 (37),
2178.44 (37).
4-Phenyl-4-(phenylthio)butan-2-one:[19] (Table 2, Entry 6), yield
96%. 1H NMR (CDCl3, 400 MHz): δ = 2.05 (s, 3 H), 3.02–3.05
(m, 2 H), 4.69 (t, J = 7.2 Hz, 1 H), 7.18–7.29 (m, 10 H) ppm. 13C
NMR (CDCl3, 100 MHz): δ = 30.80, 48.19, 49.64, 127.55, 127.73,
127.82, 128.60, 128.95, 133.01, 134.17, 141.16, 205.60 ppm. IR
(NaCl): ν
= 3059 (m), 3029 (m), 1715 (s), 1600 (w), 1582 (m),
˜
max
1480 (m), 1453 (m), 1438 (m), 1359 (m), 1152 (m), 1023 (m), 748
(s), 696 (s) cm–1.
General Synthetic Procedure for Thio-Michael Additions: To a vial
equipped with a stirrer bead was added the α,β-unsaturated carb-
onyl compound (0.5 mmol), thiol (1.0 mmol) and [Eu2(hpp)6] 2
(64 mg, 25 μmol, 5 mol-%). The mixture was stirred at room tem-
perature until TLC analysis indicated complete conversion. The
product was purified via flash column chromatography (EtOAc/n-
hexane, 1:9).
4-(Benzylthio)-4-phenylbutan-2-one:[19] (Table 2, Entry 1), yield
96%. 1H NMR (CDCl3, 400 MHz): δ = 2.00 (s, 3 H), 2.91–2.93
(m, 2 H), 3.45 (d, J = 13.2 Hz, 1 H), 3.52 (d, J = 13.2 Hz, 1 H),
4.20 (t, J = 7.2 Hz, 1 H), 7.19–7.32 (m, 10 H) ppm. 13C NMR
(CDCl3, 100 MHz): δ = 30.62, 35.89, 44.10, 50.16, 127.16, 127.53,
128.09, 128.59, 128.72, 129.06, 137.97, 141.67, 205.42 ppm. IR
X-ray Crystallography: Crystal data was collected at 123(2) K at the
Australian synchrotron MX1 beam-line. The data collection and
integration were performed within Blu-Ice[21] and XDS[22] software
programs. Structural solution and refinement was carried out with
SHELXL-97[23] utilising the graphical interface X-Seed.[24] Data
were corrected for absorption using the SADABS[25] or SORTAV[26]
packages.
Refinement of F2 was carried out against ALL reflections. The
weighted R factor wR and goodness of fit S are based on F2, con-
ventional R-factors R are based on F, with F set to zero for negative
F2. The threshold expression of F2 Ͼ 2σ(F2) is used only for calcu-
lating R-factors(gt) etc., and is not relevant to the choice of reflec-
tions for refinement. R-factors based on F2 are statistically about
twice as large as those based on F, and R-factors based on ALL
data will be even larger. There are considerable solvent accessible
voids within the asymmetric unit (4919 Å3). However, the low con-
centration of electron density compared to the cluster core com-
bined with a large amount of thermal motions and disorder meant
that the solvent could not be adequately modelled and therefore
the residual electron density was removed using Platon[27] squeeze.
The electron count within the void is 462. Two of the phenyl rings,
attached to ligands one and three are disordered over two positions
with occupancies of the major component of 70% and 50%,
respectively. Because of this disorder the rings on ligand three could
not sustain anisotropic refinement.
(ATR): ν
= 3027 (w), 2915 (w), 1714 (s), 1601 (w), 1493 (m),
˜
max
1452 (m), 1416 (m), 1359 (m), 1154 (m), 1073 (m), 1025 (m), 762
(m), 699 (s) cm–1.
1
3-(Benzylthio)-3-phenylpropanal: (Table 2, Entry 2), yield 75%. H
NMR (CDCl3, 400 MHz): δ = 2.82 (ddd, J = 7.6, 3.2, 2.0 Hz, 2
H), 3.40 (d, J = 13.6 Hz, 1 H), 3.50 (d, J = 13.6 Hz, 1 H), 4.11 (t,
J = 7.6 Hz, 1 H), 7.13–7.28 (m, 10 H), 9.52 (t, J = 2.0 Hz, 1
H) ppm. 13C NMR (CDCl3, 100 MHz): δ = 35.74, 42.93, 49.75,
127.30, 127.82, 128.04, 128.67, 128.92, 129.09, 137.79, 141.04,
199.51 ppm. IR (NaCl): νmax = 3061 (w), 3028 (m), 2918 (w), 2826
˜
(w), 2727 (w), 1723 (s), 1677 (m), 1601 (w), 1493 (s), 1453 (s), 1071
(m), 1028 (m), 751 (m), 699 (s) cm–1. HRMS (ESI) calcd. for [M +
NH4]+: 274.1266; found 274.1260.
3-(Benzylthio)butanal:[20] (Table 2, Entry 3), yield 94%. 1H NMR
(CDCl3, 400 MHz): δ = 1.33 (d, J = 7.2 Hz, 3 H), 2.51–2.65 (m, 2
H), 3.16 (sext, J = 7.2 Hz, 1 H), 3.78 (s, 2 H), 7.24–7.33 (m, 5 H),
9.67 (t, J = 2.0 Hz. 1 H) ppm. 13C NMR (CDCl3, 100 MHz): δ =
21.58, 33.84, 35.44, 50.33, 127.28, 128.73, 128.93, 138.15,
CCDC-822445 contains the supplementary crystallographic data
for this publication. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
200.66 ppm. IR (NaCl): νmax = 3028 (m), 2961 (m), 2923 (m), 2825 Supporting Information (see footnote on the first page of this arti-
˜
(m), 2726 (m), 1720 (s), 1601 (m), 1494 (s), 1453 (s), 1377 (m), 1240 cle): Additional X-ray crystallographic data for complex 1,
(m), 1116 (m), 1070 (m), 1028 (m), 769 (m), 704 (s) cm–1.
MALDI mass spectra and 1H NMR spectra of complexes 1 and
Eur. J. Inorg. Chem. 2011, 3755–3760
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3759

P. C. Junk et al.
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Acknowledgments
We gratefully acknowledge the Australian Research Council and
Monash University for supporting this work including, but not lim-
ited to, the granting of a Postgraduate Publication Award. This
research was, in part, undertaken on the macromolecular crystal-
lography (MX1) beamline at the Australian Synchrotron, Victoria,
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Received: May 18, 2011
Published Online: August 2, 2011
3760
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 3755–3760