Heteronuclear 3 d/DyIII coordination clusters as catalysts in a domino reaction

Article abstract of DOI:10.1002/chem.201500505

Three isoskeletal tetranuclear coordination clusters with general formula [M^II₂Dy^III₂L₄(EtOH)₆](ClO₄)₂·2 EtOH, (M=Co, 1; M=Ni, 2) and [Ni^II₂Dy

Full text of DOI:10.1002/chem.201500505

DOI: 10.1002/chem.201500505
Communication
&
Homogeneous Catalysis
Heteronuclear 3d/DyIII Coordination Clusters as Catalysts in
a Domino Reaction
Kieran Griffiths, Christopher W. D. Gallop, Alaa Abdul-Sada, Alfredo Vargas, Oscar Navarro,
and George E. Kostakis*[a]
In memory of Prof. Yiannis Elemes
pose. H2L supports a defect dicubane topology bearing two di-
valent 3d ions and two trivalent 4f ions[18,19] in the absence of
Abstract: Three isoskeletal tetranuclear coordination clus-
ters with general formula [MII2DyIII L4(EtOH)6](ClO4)2·2EtOH,
any additional bridging atom. Indeed, the combination in
2
(M=Co, 1; M=Ni, 2) and [NiII2DyIII L4Cl2(CH3CN)2]·2CH3CN
open air of H2L with Dy(OTf)3 and Co(ClO4)2·6H2O or Ni(-
2
ClO4)2·6H2O in the presence of Et3N in EtOH afforded air-stable
tetranuclear defect dicubane compounds with the general for-
(3), have been synthesized and characterized. These air-
stable compounds, and in particular 3, display efficient ho-
mogeneous catalytic behavior in the room-temperature
synthesis of trans-4,5-diaminocyclopent-2-enones from 2-
furaldehyde and primary or secondary amines under
a non-inert atmosphere.
mula [MII2DyIII L4(EtOH)6]-(ClO4)2·2EtOH (M=Co, 1; M=Ni, 2)
2
(Figure 1). Each 3d metal has an octahedral geometry and each
In the last two decades interest in the construction of polynuc-
lear 3d/4f coordination clusters[1] was driven by their aestheti-
cally pleasing structures,[2–4] however the interest burgeoned
due to the magnetic properties that such species display.[5–7]
The synthesis of such species can be aptly described by the
term “serendipitous self-assembly”[8] but, in recent years, tre-
mendous attention has been given on the selection of the ap-
propriate organic ligands to develop the syntheses of such co-
ordination clusters. Apart from the employment of an hepta-
nuclear CeIVMnIV coordination cluster for the oxidation of
6
benzyl alcohol to benzaldehyde, less attention has been given
to the catalytic properties of such heteronuclear compounds.[9]
For instance, dysprosium triflate, due to its mild nature, has
proven to be an excellent catalyst for reactions where both ni-
trogen and oxygen functionalities are present.[10] Of particular
interest is its ability to retain catalytic activity in the presence
of Lewis-basic nitrogen groups, allowing its use in transforma-
tions involving unprotected amines.[11–16]
Figure 1. Molecular structure of 2 (1 is isostructural with CoII atoms in the
NiII positions). Color code: NiII: green; DyIII: light blue; O: red; N: blue; C:
black. Hydrogen atoms and perchlorate are omitted for clarity.
DyIII center has a square-antiprismatic geometry. Two different
coordination modes can be found for the organic ligand (see
Scheme S1 in the Supporting Information), occupying five and
six vertices for the 3d and the DyIII centers, respectively. The re-
maining vertices are occupied by one (3d) and two (DyIII) etha-
nol molecules. To further confirm the identity of compounds
1 and 2 in solution, we performed a broad electrospray ioniza-
tion mass (ESI-MS) spectrometry study. For 1, we observed two
peaks in the MS (positive-ion mode) at m/z 1506.9719 and at
m/z 736.0393 which perfectly correspond to two fragments,
[CoII2DyIII L4(ClO4)ÀH]+ and [CoII2DyIII L4(MeOH)2ÀH]2+, respec-
We recently initiated a project aimed at developing dual cat-
alytic coordination clusters and to achieve this goal, com-
pounds that retain their topology in solution are required. 3d/
DyIII coordination clusters possessing a defect dicubane topolo-
gy derived from (E)-2-(2-hydroxy-3-methoxybenzylidene-ami-
no)phenol (H2L),[17] pose as ideal candidates to serve this pur-
2
2
[a] K. Griffiths, Dr. C. W. D. Gallop, Dr. A. Abdul-Sada, Dr. A. Vargas,
Dr. O. Navarro, Dr. G. E. Kostakis
tively (see Figures S1 and S2). Similarly, for 2, peaks at m/z
1520.0169 and m/z 744.55 correspond to {[NiII DyIII L4-
Department of Chemistry,
School of Life Sciences, University of Sussex
Brighton BN1 9QJ (UK)
2
2
(MeOH)2(EtOH)]+2H}+
and
{[NiII2DyIII L4(MeOH)À(EtOH)]+
2
2H}2+ fragments (see Figures S3 and S4), respectively. There-
E-mail: G.Kostakis@sussex.ac.uk
fore, in both cases, the ESI-MS data indicate that the dicationic
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201500505.
[MII2DyIII L4]2+ cores remain intact.
2
Chem. Eur. J. 2015, 21, 1 – 5
1
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Communication
With the coordination clusters in hand, the next step was to
identify a challenging catalytic reaction. Batey and co-workers
reported on the use of Dy(OTf)3 as a Lewis acid catalyst for the
domino condensation/ring-opening/electrocyclization of sec-
ondary amines and 2-furaldehyde,[14] leading to the synthesis
of exclusively trans-4,5-diaminocyclopent-2-enones. This is a re-
markably atom-efficient reaction with only one equivalent of
water generated as a side product. The authors postulated
that the reaction proceeds through a deprotonated Stenhouse
salt intermediate,[20] although they showed that the lanthanide
is not involved in the cyclization step (Scheme 1). Primary
amines required the use of more expensive Sc(OTf)3 to pro-
duce the corresponding products, albeit in considerably lower
yields.
Table 1. Comparison of catalytic activity for compounds 1, 2 and 3.[a]
Entries
Catalyst
T
Loading
[mol%][b]
Time
[h]
Yield
[%]
1
2
3
4
5
6
7
8
Dy(OTf)3
1
2
1
2
1
1
1
r.t.
r.t.
r.t.
10
10
10
10
10
5
2.5
1
5
2.5
1
10
10
10
1
16
16
16
2
2
2
2
2
2
2
quantitative[14]
55
41
93
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
reflux
r.t.
95
92[c]
90[c]
79[c]
9
2
2
2
94[c]
10
11
12
13
14
15
94[c]
2
2
2
2
80[c]
Dy(OTf)3
63
0
0
Co(ClO4)2·6H2O
Ni(ClO4)2·6H2O
3
16
quantitative
[a] Reaction conditions: amine, 1 mmol; 2-furaldehyde, 0.5 mmol; 4 ꢁ MS,
100 mg; catalyst; anhydrous MeCN, 4 mL; room temperature. [b] Catalyst
loading calculated per equivalent of Dy. [c] Determined by 1H NMR spec-
troscopy.
Scheme 1. Proposed mechanism for the DyIII-catalyzed synthesis of trans-4,5-
diaminocyclopent-2-enones
[NiII2DyIII L4Cl2(CH3CN)2]·2CH3CN (3) (Figure 2).[21] A similar coor-
2
dination behavior to 1 and 2 (see Scheme S1) is observed for
the organic moieties in 3 but, interestingly, a perchlorate to
chlorine transformation is observed.[22] The NiII atoms have an
octahedral geometry with one vertex occupied by a CH3CN
molecule, while DyIII has almost ideal pentagonal bipyramidal
geometry; one phenolic oxygen and the chlorine atoms
occupy the axial positions. ESI-MS studies showed that 3 re-
tains its topology in solution. Only two fragments are observed
and the two main peaks at m/z 1556.1150 and m/z 703.5109
correspond to {[NiII DyIII L4Cl2(CH3CN)(CH3OH)]+4H}+ and
In this protocol, the reactions were performed in acetonitrile
under a nitrogen atmosphere, at room temperature and using
a catalyst loading of 10 mol%.[14] Under these conditions, the
reaction between 2-furaldehyde and morpholine led to a quan-
titative amount of (4S,5R)-dimorpholinocyclopent-2-enone
(Table 1, entry 1). This reaction was chosen to test the catalytic
activity of coordination clusters 1 and 2. To make the protocol
more user-friendly, all reactions were carried out in open air.
Both complexes afforded moderate yields of the desired prod-
uct after 16 h (Table 1, entries 2 and 3). Upon increasing the
temperature (reflux), both complexes allowed the reaction to
take place in excellent yields, in almost one order of magni-
tude less time (2 h) (Table 1, entries 4 and 5). At this tempera-
ture and in both cases, the catalyst loading could be decreased
to 2.5 mol% with only a slight decrease in the yields (Table 1,
entries 6–11). Interestingly, the use of Dy(OTf)3 under these
conditions led to a considerable decrease in the yield when
compared with the reaction at room temperature (Table 1,
entry 12). As expected, neither Co(ClO4)2·6H2O nor Ni-
(ClO4)2·6H2O, the 3d metal precursors used in the synthesis of
the coordination clusters, showed catalytic behavior (Table 1,
entries 13 and 14).
2
2
{[NiII2DyIII L4]ÀH}2+ fragments (Figures S5 and S6), respectively.
2
The excellent results at high temperature, using low catalyst
loadings, prompted us to consider the possibility that 1 and 2
were undergoing changes under our reaction conditions. To in-
vestigate this hypothesis, the best performing coordination
cluster, 2, was refluxed in acetonitrile for 1 h, affording an air-
Figure 2. Molecular structure of 3. Color code: NiII: green; DyIII: light blue; O:
stable,
compound
formulated
as
red; N: blue; C: black; Cl: purple. Hydrogen atoms are omitted for clarity.
&
&
Chem. Eur. J. 2015, 21, 1 – 5
www.chemeurj.org
2
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
The use of only 1 mol% of 3 at room temperature in our
test catalytic reaction led to the quantitative formation of the
desired product (Table 1, entry 15). This is a decrease of cata-
lyst loading of one order of magnitude when compared to the
state-of-the-art for this multicomponent reaction, as well as
a more user-friendly protocol that does not require the use of
an inert atmosphere. Realizing the convenience of circumvent-
ing the need to synthesize 2 to obtain 3, we modified the orig-
inal procedure for the synthesis of 2 by substituting ethanol
by acetonitrile and refluxing for 1 h, affording 3 in 68% yield.
We then explored the scope of the reaction by employing
a variety of secondary amines as substrates (Table 2). In all
cases, the reactions proceeded smoothly and it was possible to
isolate the corresponding products 4a–4e in excellent yields.
To our delight, when the same conditions were applied to pri-
mary amines, 3 catalyzed the formation of the corresponding
deprotonated Stenhouse salts (5a–d). The combination of 5a
or 5b with very dilute HCl or silica gel promoted the ring-clos-
ing leading to the corresponding trans-4,5-diaminocyclopent-
2-enones in very high yields (95% and 56% overall yield, for
4 f and 4g, respectively, see Scheme S2). The latter transforma-
tions are consistent with Batey’s proposition that DyIII is not in-
volved in the cyclization step. Interestingly, the same treatment
applied to 5c and 5d did not afford the cyclized products to
any extent, the substrates remaining unaltered.
To further identify the formation of the deprotonated Sten-
house salt intermediate a computational study was undertak-
en. Energy minimization calculations within the Kohn–Sham
density functional theory (DFT) at the B3LYP/6-311G** level
employing the polarizable continuum media (PCM) formalism
were carried out on model compounds 4 f, 5a, 6, and 7
(Figure 3). The overall energy profile together with the calculat-
ed NMR data (Table T1 in the Supporting Information) highly
suggests that a) the pathway
Table 2. DyIII-catalysed condensation/ring-opening/cyclization of secon-
dary amines with 2-furaldehyde and condensation/ring-opening of pri-
mary amines with 2-furaldehyde.
[a] Reaction conditions: amine, 1 mmol; 2-furaldehyde, 0.5 mmol; 4 ꢁ MS,
100 mg; catalyst; anhydrous MeCN, 4 mL; room temperature.
from intermediate 6–5a towards
the final product is highly favor-
able—which thus confirms that
the catalysis takes place prior to
this step, b) intermediate 6–5a
likely resembles a configuration
somewhere between 6 (in which
the nitrogen bears a hydrogen)
and 5a (in which the hydrogen
the migrates to the neighboring
oxygen), c) one factor that
highly affects the total electronic
energy of 7 concerns a pyrami-
dal-to-planar evolution of the
beta-nitrogen, a key feature that
is likely involved in the catalytic
process.
In conclusion, we report
herein the first examples of
a series of custom-designed, cat-
alytically active 3d/DyIII coordina-
tion clusters. These are the first
results towards the development Figure 3. Energy profile of the reaction with aniline of the ring-opening (5a) and -closure (4 f) products.
Chem. Eur. J. 2015, 21, 1 – 5 www.chemeurj.org ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3
&
&
These are not the final page numbers! ÞÞ

Communication
0.1336, Rsigma =0.1333) which were used in all calculations. The final
R1 was 0.0655 (I> 2s(I)) and wR2 was 0.1584 (all data).
of dual catalytic coordination clusters. A careful choice of the
organic ligand has allowed the synthesis of coordination clus-
ters that remain intact in solution and display a remarkable
catalytic activity. The catalytic performance can be improved
by modifying the coordination environment of the DyIII ion.
This control allows, for the first time, a thorough catalytic in-
vestigation of this species. NMR spectroscopy of the diamag-
CCDC-1012311 (1), CCDC-1012312 (2), CCDC-1038641 (3) contain
the supplementary crystallographic data for this paper. These data
can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
netic (NiII2YIII ) analogue as well theoretical studies of the active
2
Acknowledgements
catalytic species are underway. As the synthetic strategy to
obtain 1–3 is simple, high yielding and based on accessible
building blocks, the approach is likely widely applicable and
new reactivity, including the 3d part, can be uncovered.
We thank the EPSRC UK National Crystallography Service at the
University of Southampton for the collection of the crystallo-
graphic data for compound 3. G.E.K. acknowledges the Univer-
sity of Sussex for offering a PhD position (K.G.).
Experimental Section
Keywords: amines · coordination clusters · domino reactions ·
dysprosium · homogeneous catalysis
Synthesis
Compounds 1 and 2: Dy(OTf)3 (61 mg, 0.1 mmol), M(ClO4)2 6H2O
(37 mg for 1 or 37 mg for 2, 0.1 mmol), LH2 (48 mg, 0.2 mmol) and
Et3N (69 mL, 0.5 mmol) were added in EtOH (20 mL), and the result-
ing mixture was stirred for one hour. After filtration, yellow-green-
ish (for 1) and orange (for 2) crystals were obtained in 49% (for 1)
and 57% (for 2) yield and collected by filtration, washed with Et2O
and dried in air.
[1] L. Cronin, J. Fielden, Coordination Clusters in Encyclopedia of Supra-
molecular Chemistry, Taylor and Francis, London, 2007, pp. 1–10.
[2] X.-J. Kong, Y.-P. Ren, W.-X. Chen, L.-S. Long, Z. Zheng, R.-B. Huang, L.-S.
Zheng, Angew. Chem. Int. Ed. 2008, 47, 2398–2401; Angew. Chem. 2008,
120, 2432–2435.
[3] Z. M. Zhang, L. Y. Pan, W. Q. Lin, J. D. Leng, F. S. Guo, Y. C. Chen, J. L. Liu,
M. L. Tong, Chem. Commun. 2013, 49, 8081–8083.
[4] C. Papatriantafyllopoulou, T. C. Stamatatos, C. G. Efthymiou, L. Cunha-
Silva, F. A. A. Paz, S. P. Perlepes, G. Christou, Inorg. Chem. 2010, 49,
9743–9745.
[5] R. Sessoli, A. K. Powell, Coord. Chem. Rev. 2009, 253, 2328–2341.
[6] K. S. Pedersen, J. Bendix, R. Clꢂrac, Chem. Commun. 2014, 50, 4396–
4415.
[7] J. W. Sharples, D. Collison, Coord. Chem. Rev. 2014, 260, 1–20.
[8] R. E. P. Winpenny, J. Chem. Soc. Dalton Trans. 2002, 1–10.
[9] G. Maayan, G. Christou, Inorg. Chem. 2011, 50, 7015–7021.
[10] G. K. Veits, J. Read deAlaniz, Tetrahedron 2012, 68, 2015–2026.
[11] P. A. Duspara, R. A. Batey, Angew. Chem. Int. Ed. 2013, 52, 10862–10866;
Angew. Chem. 2013, 125, 11062–11066.
Compound 3: Dy(OTf)3 (61 mg, 0.1 mmol), Ni(ClO4)2·6H2O (37 mg,
0.1 mmol), LH2 (48 mg, 0.2 mmol) and Et3N (69 mL, 0.5 mmol) were
added in CH3CN (20 mL), and the resulting mixture was refluxed
for one hour. After filtration, yellow-greenish crystals were ob-
tained in 68% yield and collected by filtration, washed with Et2O
and dried in air. Compound 3 can be synthesized in the same yield
by altering Ni(ClO4)2·6H2O for NiCl2 6H2O.
Crystallography
C72H92Cl2Co2Dy2N4O28 (1): M=1975.25 gmolÀ1, monoclinic, space
group P21/n (no. 14), a=12.8246(4), b=20.9395(5), c=
15.3815(5) ꢁ, b=108.997(4)8, V=3905.6(2) ꢁ3, Z=2, T=173.0 K,
m(CuKa)=14.667 mmÀ1, 1calcd =1.680 gcmÀ3, 25962 reflections mea-
[12] G. K. Veits, D. R. Wenz, J. Read deAlaniz, Angew. Chem. Int. Ed. 2010, 49,
9484–9487; Angew. Chem. 2010, 122, 9674–9677.
[13] L. I. Palmer, J. Read deAlaniz, Angew. Chem. Int. Ed. 2011, 50, 7167–
7170; Angew. Chem. 2011, 123, 7305–7308.
[14] S.-W. Li, R. A. Batey, Chem. Commun. 2007, 3759–3761.
[15] D. R. Wenz, J. Read deAlaniz, Org. Lett. 2013, 15, 3250–3253.
[16] L. I. Palmer, J. Read deAlaniz, Org. Lett. 2013, 15, 476–479.
[17] R. Kannappan, D. M. Tooke, A. L. Spek, J. Reedijk, Inorg. Chim. Acta
2006, 359, 334–338.
[18] K. C. Mondal, G. E. Kostakis, Y. Lan, W. Wernsdorfer, C. E. Anson, A. K.
Powell, Inorg. Chem. 2011, 50, 11604–11611.
[19] K. C. Mondal, A. Sundt, Y. Lan, G. E. Kostakis, O. Waldmann, L. Ungur,
L. F. Chibotaru, C. E. Anson, A. K. Powell, Angew. Chem. Int. Ed. 2012, 51,
7550–7554; Angew. Chem. 2012, 124, 7668–7672.
[20] J. Stenhouse, Justus Liebigs Ann. Chem. 1850, 74, 278–279.
[21] S. J. Coles, P. A. Gale, Chem. Sci. 2012, 3, 683–689.
[22] B. Bhattacharya, R. Dey, D. K. Maity, D. Ghoshal, CrystEngComm 2013,
15, 9457–9464.
sured (7.48 ꢀ 2V ꢀ 142.8988), 7561 unique (Rint =0.0490, Rsigma
=
0.0482) which were used in all calculations. The final R1 was 0.0378
(I> 2s(I)) and wR2 was 0.0981 (all data).
C72H92Cl2Dy2N4Ni2O28 (2): M=1974.81 gmolÀ1, monoclinic, space
group P21/n (no. 14), a=12.7440(4), b=20.9329(5), c=
15.3458(5) ꢁ, b=108.920(4)8, V=3872.6(2) ꢁ3, Z=2, T=173 K,
m(MoKa)=2.539 mmÀ1, 1calcd =1.694 gcmÀ3, 19340 reflections mea-
sured (4.7988 ꢀ 2V ꢀ 58.678), 8980 unique (Rint =0.0330, Rsigma
=
0.0510) which were used in all calculations. The final R1 was 0.0374
(I> 2s(I)) and wR2 was 0.0883 (all data).
C64H56Cl2Dy2N8Ni2O12 (3): M=1642.48 gmolÀ1
,
triclinic, space
¯
group P1 (no. 2), a=11.696(3), b=11.973(4), c=13.084(4) ꢁ, a=
88.597(16)8, b=64.494(10)8, g=81.504(15)8, V=1633.9(9) ꢁ3, Z=1,
T=100 K, m(MoKa)=2.975 mmÀ1, 1calcd =1.669 gcmÀ3, 17540 reflec-
Received: February 7, 2015
tions measured (4.7688 ꢀ 2V ꢀ 50.1668), 5747 unique (Rint
=
Published online on && &&, 0000
&
&
Chem. Eur. J. 2015, 21, 1 – 5
www.chemeurj.org
4
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Communication
COMMUNICATION
&
Homogeneous Catalysis
K. Griffiths, C. W. D. Gallop,
A. Abdul-Sada, A. Vargas, O. Navarro,
G. E. Kostakis*
&& – &&
Heteronuclear 3d/DyIII Coordination
Clusters as Catalysts in a Domino
Reaction
Custom-designed catalysts: Three air-
cient homogeneous catalytic behavior
in the room-temperature synthesis of
trans-4,5-diaminocyclopent-2-enones
from 2-furaldehyde and primary or sec-
ondary amines under a non-inert atmos-
phere.
stable compounds formulated as
[MII2DyIII L4(EtOH)6](ClO4)2 2EtOH,
2
[M=Co (1) and Ni (2)] and
[NiII2DyIII L4Cl2(CH3CN)2] 2CH3CN (3), have
2
been characterized. Compound 3, in
particular, displays for the first time effi-
Chem. Eur. J. 2015, 21, 1 – 5
www.chemeurj.org
5
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ