Allyl complexes of scandium: Synthesis and structure of neutral, cationic and anionic derivatives

Article abstract of DOI:10.1039/c1cc14180e

Neutral, cationic and anionic allyl compounds of scandium contain highly fluxional allyl ligands in solution, whilst in the solid state both η¹- and η³-binding modes are detected.

Full text of DOI:10.1039/c1cc14180e

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COMMUNICATION
Allyl complexes of scandium: synthesis and structure of neutral, cationic
and anionic derivativesw
Sabine Standfuss, Elise Abinet, Thomas P. Spaniol and Jun Okuda*
Received 12th July 2011, Accepted 12th September 2011
DOI: 10.1039/c1cc14180e
Neutral, cationic and anionic allyl compounds of scandium
contain highly fluxional allyl ligands in solution, whilst in the
1
3
solid state both g - and g -binding modes are detected.
Allyl complexes of the rare earth metals are initiators for the
1–3
homogeneous stereoselective polymerization of dienes.
1
3
Scheme 1 Synthesis of [Sc(Z -C
3 5 3 5 2 2
H )(Z -C H ) (THF) ] (1a) and
Although tris(allyl) complexes of the rare earth metals
3
3 5 3
[Sc(C H ) ] (1b).
[
Ln(Z -C
3 5 3
H ) (L)] (L = THF, 1,4-dioxane) are a versatile source
1–12
for neutral and cationic allyl derivatives,
THF beside a doublet and a quintet for the allyl ligands,
consistent with the homoleptic compound [Sc(C H ) ]
peculiarly the parent
3
5 3
tris(allyl) complex of scandium has remained elusive so far. Only
cyclopentadienyl-supported allyl complexes of scandium have
(
Fig. S2, ESIw).
Single crystals of 1a were obtained by slow crystallization from
3
13a
13b,14
been reported: [Cp Sc(Z -C H )] (Cp = C Me , C H
5
or
3
2
3
5
5
5
5
15
5
3
13c
a THF solution at ꢀ40 1C within five days. X-Ray diffraction
studyz revealed two crystallographically independent molecules
in the unit cell. Both show trigonal bipyramidal configuration
with two THF ligands in the axial positions (O1–Sc1–O2
C Me H ), [{SiMe (Z -C H ) }Sc(Z -C H )],
[Cp*Sc(Z -
5
4
2
5
4 2
3
5
5
2
0
3
2a
C H ) ] (Cp*
5 2
=
Z -C Me ), [Cp Sc(Z -C H ) ] ,b and
3
5
5
0
3
5 2
0
3
+
]
5
2a
[
Cp Sc(Z -C
3
H
5
)(THF)
2
(Cp = Z -C
5
Me SiMe
4
3
). Recent
and
theoretical
studies
of
homoleptic
bis(allyl)-
3
3
177.82(11)1). Two allyl ligands are Z - and one allyl ligand is
tris(allyl)scandium using DFT calculations showed Z -binding
mode for all allyl ligands. We report here that starting from
1
1
4
Z -coordinated consistent with the formula [Sc(Z -C H )-
3
3
5
(
Z -C
3 5 2 2
H ) (THF) ] (1a) (Fig. 1). The manganese complex
3 5 3 n
the neutral compound tris(allyl)scandium [Sc(C H ) (THF) ] (1a:
3
1
17a
[Li(THF)
4
][Mn{Z -(Me
3
2
Si) C
3
H
3
}{Z -(Me
3
Si)
2
C
3
H
3
}
2
]
contains
n = 2; 1b: n = 0) both cationic (2) and anionic (3) derivatives are
3
1
accessible which contain Z - and Z -allyl ligands in the solid state.
Tris(allyl)scandium compounds [Sc(C H ) (THF) ]
1a: n = 2; 1b: n = 0) were obtained by the reaction of
3
5 3
n
(
1
6
anhydrous ScCl with three equivalents of allylpotassium or
3
5
with 1.5 equivalents of bis(allyl)calcium in THF at 0 1C in
7
1
0% yield (Scheme 1). The H NMR spectrum of 1 in THF-d
8
indicates highly fluxional behavior of all three allyl ligands in
solution on the NMR time scale with one doublet for the
terminal allyl protons at d = 2.97 ppm and one quintet for the
methine proton at d = 6.18 ppm. Below ꢀ80 1C, broadening
of the signal for the terminal protons is observed
(
Fig. S1c, ESIw). At ꢀ95 1C, the signal is broad (2.2–3.5 ppm)
but decoalescence was not observed (Fig. S1d, ESIw). The
coordinated THF ligands in 1a are lost by drying in vacuo for
1
h. The crystalline product slowly changed into a yellow
1
powder of 1b and its H NMR spectrum shows only traces of
1
3
Fig. 1 Molecular structure of [Sc(Z -C
3
H
5
)(Z -C
Displacement ellipsoids are shown at 50% probability; hydrogen
3
H
5
)
2
(THF)
2
] (1a).
Institute of Inorganic Chemistry, RWTH Aachen University,
Landoltweg 1, 52056 Aachen, Germany
E-mail: jun.okuda@ac.rwth-aachen.de; Fax: +49 241 8092644
w Electronic supplementary information (ESI) available: Synthesis
and characterization of 1a–b, 2a–c, 3a–c and 4. CCDC 832188 (1a),
˚
atoms are omitted for clarity. Selected interatomic distances [A] and
angles [1]: Sc1–C1 2.373(4), Sc1–C4 2.434(4), Sc1–C5 2.479(4),
Sc1–C6
2.557(4),
Sc1–C7
2.493(4),
Sc1–C8
2.485(4),
Sc1–C9 2.447(4), Sc1–O1 2.225(3), Sc1–O2 2.208(3), C1–C2 1.477(5),
C2–C3 1.310(6), O1–Sc1–O2 177.82(11), C1–Sc1–O1 89.46(11),
C1–Sc1–O2 90.85(11).
832189 (2a), 832190 (3c). For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1cc14180e.
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11441–11443 11441

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1
3
2+
two Z - and one Z -coordinated allyl fragments (r(Mn ) =
0
3
+
18
˚ ˚
.66 A, CN = 4; r(Sc ) = 0.745 A, CN = 6).
˚
The metal atom only deviates by 0.040(3) A from the plane
formed by C2, C5 and C8. The Sc1–C1 bond length is 2.373(4)
1
˚
A for the Z -allyl ligand and the average distance from Sc1 to
3
˚
the carbon atoms of the Z -allyl ligands of 2.48 A (ranging
4
from 2.434(4) to 2.557(4) A) is within the expected range. The
˚
˚
interatomic distance C2–C3 of 1.310(6) A is as expected in the
1
range of a C–C double bond and the C–C distances within
2
3
˚
the Z -coordinated fragments of 1.38 A (ranging from 1.359(6)
3
3–6
˚
to 1.421(6) A) are as expected for Z -allyl ligands.
The related compounds with larger metal centers [Ln(Z -
3
3
3
6a
3
C H
)
5 3
(THF)
3
2
], (Ln = Ce, Pr), [Nd(Z -C
3
H
5
)
3
(m-C
4 8 2 n
H O )]
4
5
3
and [Ca(Z -C H ) (triglyme-k )] contain Z -coordinated allyl
3
5 2
3
ligands in the solid state. The tris(allyl)indium compound
1
Fig. 2 Molecular structure of the cationic part of [Sc(Z -
C H ) (THF) ][B(C H ) ] (2a). Displacement ellipsoids shown at
[
In(Z -C H ) (m-C H O )] with
a
smaller ionic radius
3
5 3
4
8
2
n
3
5 2
3
6
5 4
3
+
18
r(In ) = 0.62 A, CN = 4) and a more covalent character
ꢀ
˚
(
50% probability; hydrogen atoms and the anion [BPh ] are omitted
4
1
12
for clarity; only one of the two split positions of C5 is shown. Selected
˚
displays Z -coordinated allyl ligands in the solid state.
The neutral compound 1a was protonated by the Brønsted
acids [NEt H][BPh ], [NMe H][B(C Cl (4) and
H][B(C ] in THF to give the bis(allyl) cation
(THF)
interatomic distances [A] and angles [1]: Sc1–C1 2.5071(16),
Sc1–C2 2.4662(16), Sc1–C3 2.4117(16), Sc1–C4 2.3854(16), Sc1–C5a
3
4
3
H
6 3
2 4
) ]
2
.474(2), Sc1–C5b 2.486(6), Sc1–C6 2.5870(17), C1–C2 1.378(2),
C2–C3 1.382(2), C4–C5a 1.417(3), C5a–C6 1.331(3), C4–C5b
.434(8), C5b–C6 1.257(7), Sc1–O1 2.1814(10), Sc1–O2 2.2379(10),
[
[
NPhMe
2
3
6 5 4
F )
3
+
Sc(Z -C
H
5
)
2
3
]
in 2a–c. These compounds precipi-
1
tated within 5 min at room temperature as yellow powder in
Sc1–O3 2.2071(10), O1–Sc1–O3 175.44(4), O1–Sc1–O2 85.96(4),
O2–Sc1–O3 89.48(4), C2–Sc1–C5a 136.54(7), C2–Sc1–C5b 141.14(18).
6
8–80% isolated yield (Scheme 2).
1
The H NMR spectrum of 2a in THF-d shows two signals for
8
both allyl ligands: a doublet for the terminal protons at d =
.10 ppm and a quintet for the methine protons at d = 5.99 ppm.
The CH resonances are shifted towards lower field as compared to
3
2
1
a and the dynamic behavior is comparable to 1a. Similar behavior
is found for the cations in [Sc(C (THF) ][B(C Cl ] (2b)
and in [Sc(C (THF) ][B(C ] (2c).
3
H
5
)
2
3
6
H
3
2 4
)
3
H
5
)
2
3
6
F
5
)
4
Scheme 3 Synthesis of K[Sc(C
5 4 6 3 5 4 2
H ) ] (3a), [Ca(THF) ][Sc(C H ) ]
3
By cooling the filtered reaction mixture of 2a to ꢀ40 1C, single
(3b) and [Mg(THF) ][Sc(C H ) ] (3c).
6
3
5 4 2
crystals suitable for X-ray diffraction were obtained. The cation
3
+
]
1
[
Sc(Z -C
center. Both allyl ligands are within the equatorial plane
Fig. 2). As in 1a, the axial positions are occupied by two THF
3
H
5
)
2
(THF)
3
contains a five-coordinate scandium
The H NMR spectra of 3a and 3b in THF-d
doublet and a quintet for the allyl groups at d = 2.70 ppm
(CH ) and d = 6.09 ppm (CH), indicating fluxional behavior
8
show a
(
2
ligands (O1–Sc1–O3 175.44(4)1). The average distance from the
scandium center to the carbon atoms of the Z -allyl ligands is
in solution. The resonances for the methylene protons are
shifted towards higher field compared to 1a. At ꢀ95 1C, all
signals retain their multiplicity and are slightly shifted to
higher field (Fig. S7b, ESIw).
3
˚
˚
2
.47 A (ranging from 2.3854(16) to 2.5870(17) A) and similar to
3
that in 1a. The C–C distances within the Z -coordinated frag-
19
˚
ments of 1.37 A (ranging from 1.257(7) to 1.434(8) A) are as
˚
When ScCl
was reacted with [Mg(C H )Cl], single crystals of
3 5
3
3
3–6
expected for Z -allyl ligands. Cationic lanthanide bis(allyl) and
[Mg(THF) ][Sc(C H ) ]
3 5 4 2
6
(3c) suitable for X-ray diffraction
3
+
mono(allyl) complexes [Ln(Z -C
3
H
5
)
2
(THF)
4
]
(Ln = La, Ce,
3
precipitated from a THF/n-pentane solution at ꢀ40 1C. The
3
0
3
+ 2a
Nd) and [Cp Sc(Z -C
3
H
5
)(THF)
2
]
contain Z -coordinated
molecular structure in the solid state shows that two allyl ligands
1
3
allyl ligands in the solid state.
are Z - and two ligands are Z -coordinated to the scandium center
(Fig. 3). The geometry around the metal center is best described as
distorted tetrahedral. The angle C7–Sc1–C10 of 96.1(2)1 between
When 1a was treated with one equivalent of allylpotassium
in THF at 0 1C, the ate complex K[Sc(C H ) ] (3a) was
obtained. Compound 3a was also synthesized directly by
3
5 4
1
the Z -coordinated allyl ligands is less than expected for tetra-
hedral geometry and reflects this distorted geometry. The average
treating ScCl with four equivalents of allylpotassium. With
3
5
bis(allyl)calcium, [Ca(THF) ][Sc(C H ) ] (3b) was obtained
distance between the scandium center and the carbon atoms of the
3
6
3
5 4 2
˚
in THF at 0 1C (Scheme 3).
Z -coordinated allyl ligands is 2.45 A (ranging from 2.424(5) to
˚
.488(5) A) and very similar to the neutral 1a and the cationic 2a.
2
1
The distances to the Z -coordinated allyl ligands of 2.271(5) and
˚
.277(5) A are smaller than in 1a explained by the smaller
2
coordination number in 3c. In comparison, [Mg(THF)
6
]-
and
with the larger atoms samar-
3
7
3
20
H ) ]
3 5 4
[
Sm(Z -C
Li(m-C
ium, cerium and lanthanum contain four Z -coordinated allyl
3
H
5
)
4
]
2
,
[Li
2
3
(m-C
3
H
5
)(C
4
H
8
O
2
)
3
][Ce(Z -C
6b
[
4
H
8
O
2
)
3 5 4
3/2][La(Z -C H ) ]
3
3
Scheme 2 Synthesis of [Sc(Z -C
3
H
5
)
2
(THF)
3
][BPh
4
3 5 2
] (2a), [Sc(C H ) -
1
21
H ) ]
3 5 4 2
(
THF)
3
6
][B(C H
3
Cl
2
)
4
] (2b) and [Sc(C
3
H
5
)
2
(THF)
3
6
][B(C F
5
)
4
] (2c).
fragments. The anionic parts in [K(15-crown-5)
2
][Al(Z -C
1
1442 Chem. Commun., 2011, 47, 11441–11443
This journal is c The Royal Society of Chemistry 2011

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2ymax = 53.421, 41 084 reflections measured, 7333 unique, Rint = 0.1140,
GoF = 0.974, R
data for 2a: C18
C2/c, a = 31.6886(18), b = 9.9269(6), c = 23.1586(13) A, b =
1
[I 4 2s(I)] = 0.0753, wR
2
(all data) = 0.2238. Crystal
ꢀ1
H
34
O
3
ScꢁC24 20B, M = 662.62 g mol , monoclinic,
H
˚
3
ꢀ1
,
˚
9
3.9940(10)1, V = 7267.3(7) A , Z = 8, m(MoK
T = 100(2) K, 2ymax = 60.981, 53 345 reflections measured, 10 704
unique, Rint = 0.0840, GoF = 0.947, R [I 4 2s(I)] = 0.0475, wR (all
data) 0.1134. Crystal data for 3c: 48MgO 20Sc)ꢁ
ꢁ2(C12
(C /n, a = 13.0491(12),
b = 11.3146(10), c = 20.4870(18) A, b = 97.444(4)1, V = 2999.3(5) A ,
a
) = 0.240 mm
1
2
=
24
C H
6
H
ꢀ1
2
4
H O), M = 1019.62 g mol , monoclinic, P2
8
1
3
˚
˚
ꢀ
1
Z = 2, m(MoK
a
) = 0.284 mm , T = 130(2) K, 2ymax = 52.981, 43819
reflections measured, 6000 unique, Rint = 0.2219, GoF = 0.841, R
(all data) = 0.1759.
1
[
I 4 2s(I)] = 0.0670, wR
2
Fig. 3 Molecular structure of the anionic part of [Mg(THF)
1
6
]-
3
[
Sc(Z -C
3
H
5
)
2
(Z -C
3
H
5
)
2
]
2
(3c). Displacement ellipsoids shown at 50%
1 (a) L. Friebe, O. Nuyken and W. Obrecht, Adv. Polym. Sci., 2006,
04, 1; (b) S. M. Guillaume, E. Kirillov, Y. Sarazin and
J.-F. Carpentier, C. R. Chim., 2010, 13, 608.
2+
2
probability; hydrogen atoms and cation [Mg(THF)
6
]
are omitted for
˚
clarity. Selected interatomic distances [A] and angles [1]: Sc1–C1 2.450(5),
Sc1–C2 2.436(6), Sc1–C3 2.450(6), Sc1–C4 2.488(5), Sc1–C5 2.453(5),
Sc1–C6 2.424(5), Sc1–C7 2.271(5), Sc1–C10 2.277(5), C1–Sc1–C7
2
(a) N. Yu, M. Nishiura, X. Li, Z. Xi and Z. Hou, Chem.–Asian J.,
2
008, 3, 1406; (b) Z. Jian, D. Cui, Z. Hou and X. Li, Chem.
Commun., 2010, 46, 3022; (c) L. Zhang, T. Suzuki, Y. Luo,
M. Nishiura and Z. Hou, Angew. Chem., Int. Ed., 2007, 46, 1909.
D. Robert, E. Abinet, T. P. Spaniol and J. Okuda, Chem.–Eur. J.,
110.2(2), C6–Sc1–C10 109.6(2), C7–Sc1–C10 96.1(2).
3
1
17b
and [{MgCl(THF)
2
}
3
(m
3
-C
3
H
5
)
2
]
2
[Mg(Z -C
3
H
5
)
4
]
contain four
2
009, 15, 11937.
1
Z -coordinated allyl fragments to the smaller metal centers
aluminium and magnesium. The anion in [Li(TMEDA) ]-
)] with the smaller nickel(II) center
4 M. P. Pu, Q. Li, Y. Xie, R. B. King and H. F. Schaefer, J. Phys.
Chem. A, 2011, 115, 4491.
5 P. Jochmann, T. Dols, T. P. Spaniol, L. Perrin, L. Maron and
J. Okuda, Angew. Chem., Int. Ed., 2009, 48, 5715.
6 (a) R. Taube, J. Organomet. Chem., 1996, 513, 49; (b) R. Taube,
2
1
3
[
Ni(Z -C
3
H
5
)
2
(Z -C
3 5
H
3
1
22
contains one Z - and two Z -coordinated allyl ligands.
The neutral (tris)allyl compound 1 was also observed as
only product from 2a with one equivalent of 3a containing the
1
cationic as well as the anionic fragment in a H NMR experi-
¨
H. Windisch, F. H. Gorlitz and H. Schumann, J. Organomet.
Chem., 1993, 445, 85; (c) R. Taube, S. Maiwald and J. Sieler,
J. Organomet. Chem., 2001, 621, 327.
L. F. Sanchez-Barba, D. L. Hughes, S. M. Humphrey and
´
7
ment (Fig. S3, ESIw). Furthermore, 3a reacted with two
equivalents of the Brønsted acid [NEt H][BPh ] to give 2a.
M. Bochmann, Organometallics, 2005, 24, 5329.
8
9
E. Abinet, T. P. Spaniol and J. Okuda, Chem.–Asian J., 2011, 6, 389.
S. C. Chmely, C. N. Carlson, T. P. Hanusa and A. L. Rheingold,
J. Am. Chem. Soc., 2009, 131, 6344.
0 E. G. Hoffmann, R. Kallweit, G. Schroth, K. Seevogel,
W. Stempfle and G. Wilke, J. Organomet. Chem., 1975, 97, 183.
3
4
Cationic allyl compounds are known to catalyze the poly-
1
–3
merization of olefins.
Since 2c is better soluble in organic
1
solvents than 2a and 2b, this compound was tested for the
3
,23
polymerization of styrene and 1,3-butadiene in toluene.
Atactic polystyrene was isolated in modest yield after 1 h at
11 N. Yue, E. Hollink, F. Gue
2
´
rin and D. W. Stephan, Organometallics,
001, 20, 4424.
2 I. Peckermann, G. Raabe, T. P. Spaniol and J. Okuda, Chem.
Commun., 2011, 47, 5061.
1
1
5
0 1C. Polymerization of 1,3-butadiene gave a mixture of
,4-polybutadiene (cis/trans ratio = 2 : 1) and 1,2-polybutadiene
3 (a) M. E. Thompson, S. M. Baxter, A. R. Bulls, B. J. Burger,
M. C. Nolan, B. D. Santarsiero, W. P. Schaefer and J. E. Bercaw,
J. Am. Chem. Soc., 1987, 109, 203; (b) M. B. Abrams, J. C. Yoder,
C. Loeber, M. W. Day and J. E. Bercaw, Organometallics, 1999,
18, 1389; (c) J. C. Yoder, M. W. Day and J. E. Bercaw, Organo-
metallics, 1998, 17, 4946.
4 R. Coutts and P. C. Wailes, J. Organomet. Chem., 1970, 25, 117.
5 (a) S. Demir, S. E. Lorenz, M. Fang, F. Furche, G. Meyer,
J. W. Ziller and W. J. Evans, J. Am. Chem. Soc., 2010, 132,
11151; (b) S. Demir, E. Montalvo, J. W. Ziller, G. Meyer and
W. J. Evans, Organometallics, 2010, 29, 6608; (c) S. Demir,
T. J. Mueller, J. W. Ziller and W. J. Evans, Organometallics, 2011,
1
in moderate yield after 15 min at 25 1C. This is comparable to the
reported polymerizations of 1,3-butadiene using the analogous
3
3
neodymium catalyst [Nd(Z -C H ) (THF) ][BPh ].
3
5 2
3
4
In conclusion, we have structurally characterized the neutral,
cationic and anionic allyl compounds of scandium 1–3. Fluxional
behavior of the coordination manner of the allyl ligands is found
1
1
1
in solution. Even at ꢀ95 1C the H NMR spectra of 1a and 3a do
not show decoalescence. The crystal structure of the anionic part
1
3
of 3c contains two Z - and two Z -coordinated allyl ligands, the
scandium atom in the neutral compound 1a is bonded to one
30, 3083.
16 J. B. Wilkes, J. Org. Chem., 1967, 32, 3231.
1
3
1
1
7 (a) R. A. Layfield and S. M. Humphrey, Angew. Chem., Int. Ed.,
2004, 43, 3067; (b) T. H. Bullock, F. Garcıa, S. M. Humphrey,
P. Schuler and R. A. Layfield, Chem. Commun., 2006, 2039.
Z - and two Z -coordinated allyl ligands and the cationic part in
3
´
2
a contains two Z -coordinated allyl ligands. The smallest
¨
rare earth metal scandium represents a borderline case for
3
8 R. D. Shannon, Acta Crystallogr., Sect. A: Cryst. Phys., Diffr.,
Theor. Gen. Crystallogr., 1976, 32, 751.
19 S. O’Brien, M. Fishwick, B. McDermott, M. G. H. Wallbridge and
G. A. Wright, Inorg. Synth., 1971, 13, 73.
0 Z. Huang, M. Chen, W. Qiu and W. Wu, Inorg. Chim. Acta, 1987,
Z -coordination of allyl ligands that is common for all larger,
1
–8,11,13–15,20,24
less electronegative metals.
The high activity of
some scandium complexes in polymerizations may be corre-
1
2
2
2
2
3
lated with the propensity to both Z - and Z -allyl binding
modes in the reactive intermediate prior to olefin insertion.
139, 203.
1 C. Lichtenberg, T. P. Spaniol and J. Okuda, Organometallics, 2011,
1
3b
3
2 D. Alberti, R. Goddard, A. Rufin
0, 4409.
We are grateful to the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie for financial support.
´
ska and K.-R. Po
¨
rschke,
Organometallics, 2003, 22, 4025.
3 General conditions for polymerization: m(2c)
= 15 mg;
[
2
monomer]/[2c] = 1000; [Al(CH
0 mL; styrene: 50 1C, 1 h; 1,3-butadiene: 25 1C, 15 min.
2 2 3
CHMe ) ]/[2c] = 5; Vtotal =
Notes and references
ꢀ
1
z Crystal data for 1a: C17
P2 /c, a = 14.341(6), b = 21.027(9), c = 11.963(5) A, b = 104.738(7)1,
V = 3489(3) A , Z = 8, m(MoK
H
31
O
2
Sc, M = 312.38 g mol , monoclinic,
24 Metrical parameters for allyl bonds for 1a,b and the anion of 3a–c
are in good agreement with those obtained by DFT calculations;
Prof. L. Maron, personal communication.
˚
1
3
ꢀ1
˚
a
) = 0.422 mm , T = 100(2) K,
This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 11441–11443 11443