Spontaneous resolution versus formation of racemic crystals of indenylpotassium complexes

Article abstract of DOI:10.1016/j.jorganchem.2013.05.045

During a study of stereochemically labile organometallic reagents, we found that crystallisation of [K(ind)(pmdta)]n (ind = indenyl, pmdta = N,N,N',N'',N''-pentamethyldiethylenetriamine) from tetrahydrofuran (THF) gave rise to three different crystalline phases depending on the concentration. The more concentrated solutions gave racemic crystals of the previously known coordination polymer [K(ind)(pmdta)]n, a-1. More dilute solutions gave crystals of a new phase, b-1, which was found to undergo spontaneous resolution. From even more dilute solutions, we were able to isolate a chiral inclusion compound with THF, 2, which also undergoes spontaneous resolution. Crystals of b-1 and 2 were enantiomerically pure, and since b-1 is a reactive organometallic reagent, attempts were made to use the crystals in enantioselective synthesis. Reacting single crystals with N-chlorosuccinimide gave rise to chiral 1-chloroindene, but no enantiomeric excess was observed.

Full text of DOI:10.1016/j.jorganchem.2013.05.045

Journal of Organometallic Chemistry 741-742 (2013) 131e135
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Spontaneous resolution versus formation of racemic crystals
of indenylpotassium complexes
Susanne Olsson , Anders Lennartson , Mikael Håkansson a
a
,
b
*
a
Department of Chemistry and Molecular Biology, University of Gothenburg, SE-412 96 Gothenburg, Sweden
Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 February 2013
Received in revised form
During a study of stereochemically labile organometallic reagents, we found that crystallisation of
[
K(ind)(pmdta)]
n
(ind ¼ indenyl, pmdta ¼ N,N,N’,N’’,N’’-pentamethyldiethylenetriamine) from tetrahy-
drofuran (THF) gave rise to three different crystalline phases depending on the concentration. The more
concentrated solutions gave racemic crystals of the previously known coordination polymer
22 May 2013
Accepted 29 May 2013
[
K(ind)(pmdta)]
dergo spontaneous resolution. From even more dilute solutions, we were able to isolate a chiral inclusion
compound with THF, 2, which also undergoes spontaneous resolution. Crystals of -1 and 2 were
enantiomerically pure, and since -1 is a reactive organometallic reagent, attempts were made to use the
n
, a-1. More dilute solutions gave crystals of a new phase, b-1, which was found to un-
Keywords:
b
Organopotassium reagents
Asymmetric synthesis
Concomitant polymorphism
Spontaneous resolution
b
crystals in enantioselective synthesis. Reacting single crystals with N-chlorosuccinimide gave rise to
chiral 1-chloroindene, but no enantiomeric excess was observed.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
only one nucleation event, all crystals will be of the same enan-
tiomorph and a racemic solute may be quantitatively transformed
Syntheses of optically active products from achiral or racemic
starting materials, without the presence of any optically active
species may be examples of absolute asymmetric synthesis [1,2].
We have previously studied the use of chiral organometallic re-
agents in absolute asymmetric synthesis, starting with the dis-
covery that Grignard reagents may assume chiral octahedral
into a pure enantiomer on crystallisation. Since an optically active
product thus is produced from racemic starting materials, this may
be regarded as a form of absolute asymmetric synthesis. Although
the complexes are stereochemically labile in solution, the config-
uration is retained in the solid state, and crystals of cis-[(p-
3 6 4 2 3 2
CH C H )MgBr(dme) ] and cis-[Mg(CH )(thf)(dme) ]I gives opti-
coordination geometries [3]. Two such reagents, cis-[(p-CH
MgBr(dme) ] and cis-[Mg(CH )(thf)(dme) ]I, were found to crys-
tallise in the Sohncke [4] space group P2 [5]. A substance
3
C
6
H
4
)
cally active 1-p-tolyl-butan-1-ol and 2-pentanol, respectively,
after solventeless reactions with butyraldehyde [5]. The enantio-
meric excesses (ee) were moderate, however: 5e21% and 5e22%,
respectively. We argued that a higher enantioselectivity could be
attained by using organometallic reagents displaying chirogenic
2
3
2
1 1 1
2 2
crystallising in a Sohncke space group crystallises as a conglom-
erate and is said to undergo spontaneous resolution. The two en-
antiomers will appear in separate crystals, making each single-
crystal enantiopure. Since the octahedral Grignard reagents are
highly labile in solution, they may undergo total spontaneous res-
olution (crystallisation-induced asymmetric transformation) [6].
This phenomenon occurs for stereochemically labile conglomer-
ates, and implies that an excess of one enantiomorph may be ob-
tained on crystallisation. This is possible when the solution remains
racemic during the crystallisation, even though one enantiomer
crystallises preferentially. In a case where crystallisation starts with
a
-carbon atoms. A reaction with an achiral electrophile, such as CO
2
or Br , could trap the configuration of the reactive chirogenic car-
2
bon centre, without the need to form a new chirogenic centre. Such
reactions may proceed with a high degree of stereochemical
retention (or inversion). For example, (ꢀ)-menthylchloride gives
menthyllithium when treated with lithium metal in hydrocarbon
solution, and subsequent carbonation yields 3-p-menthane-
carboxylic acid in almost enantiomerically pure form [7]. A study of
indenylzinc complexes revealed that zinc coordinates the indenyl
1
anions in a
h
-mode, with the
a
-carbon atom being a chirogenic
1
centre. It was found that di(3-picoline)-di(1-
h -indenyl)zinc crys-
tallises in space group P2 and that selected single-crystals
react with N-chlorosuccinimide (NCS) in the presence of meth-
anol and p-benzoquinone [8]. The product, 1-chloroindene, was
1 1 1
2 2
*
Corresponding author. Tel.: þ46 031 786 9106x9025.
E-mail addresses: susanne.olsson@chem.gu.se (S. Olsson), hson@chem.gu.se
(
M. Håkansson).
0
022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.05.045

132
S. Olsson et al. / Journal of Organometallic Chemistry 741-742 (2013) 131e135
obtained with high ee (89%). Bulk samples gave up to 71% ee
without optimisation of the crystallisation conditions. Di(indenyl)
zinc is best prepared by transmetallation of indenylpotassium with
C14
C13
zinc chloride in THF [9]. We found that a small excess of inden-
C15
1
ylpotassium facilitated the crystallisation of di(3-picoline)-di(1-
h
-
C16
C17
N2
C1
indenyl)zinc, and our manipulations with indenylpotassium led to
the accidental discovery of two indenylpotassium complexes
crystallising as conglomerates. Our investigations of these com-
plexes will be described in this paper.
C12
N3
N1
K1
C18
C11
C5
C10
C3
C4
C2
2
. Results and discussion
C9
C6
C8
2.1. Crystallisation
C7
Crystallisation of [K(ind)(pmdta)]
n
from benzene has been re-
-1, belong to the
ca. Like crystallisation from benzene, we
found that cooling a concentrated THF solution of [K(ind)(pmdta)]
invariably gave crystals of -1. (An excess of PMDTA was necessary,
ported previously [10], and the crystals obtained,
polar space group P2
a
1
n
a
however, to avoid precipitation of an unknown solid, presumably a
coordination polymer containing THF.) Upon cooling dilute solu-
Fig. 1. Molecular structure of b-1 displaying the crystallographic numbering scheme.
Displacement ellipsoids are drawn at the 50% probability level and all H atoms have
been omitted for clarity.
tions of [K(ind)(pmdta)]
space group P2 . We have not observed any indication of twinning-
by-inversion in -1 and crystallisation of -1 can therefore be
described as spontaneous resolution. In order to see whether -1
n
, a new phase (b-1) crystallised in Sohncke
1
shaped polymeric chains are centred on the 2
formationally chiral.
The same type of chains centred on 2
the main difference between the two structures is that adjacent
chains assume the same sense of chirality in -1, while -1 is
racemic. The calculated densities for -1 and -1 are similar: 1.134
1
-axes and are con-
b
b
b
1
-axes are found in a-1, and
had undergone total spontaneous resolution, two samples con-
sisting of relatively few crystals (which had formed slowly) were
examined, but enantiomorphic crystals were found within the
same sample. A well-known method in such cases is crystallisation
under slow stirring [11,12], but can be difficult to achieve at
depressed temperature over prolonged periods of time. In contrast
b
a
a
b
ꢀ
3
and 1.137 g cm , respectively. This indicates a similar packing ef-
ficiency [20], and explains the fact that the two phases may crys-
tallise concomitantly.
3 6 4 2
to e.g. the chiral reagents cis-[(p-CH C H )MgBr(dme) ] and cis-
The crystal structure of 2 displays the same type of polymeric
[
Mg(CH
3
)(thf)(dme)
2
]I, which crystallise as conglomerates at
ꢁ
chains as in
are separated by channels occupied by THF molecules (Fig. 2). As a
result, the structure is slightly less densely packed than -1 and -1,
a-1 and b-1, the largest difference being that the chains
ambient temperature and as racemic phases at ꢀ60 C [5], the
crystallisation of 1 does not appear to depend on the temperature,
a
b
since
b-1 has been obtained both at ambient temperature (by
ꢀ
3
ꢁ
ꢁ
the density being 1.128 g cm . The THF molecules form two CHeO
interactions with the PMDTA ligand, the O1eH18a and O1eH15b
layering the solution with n-hexane), at ꢀ30 C or at ꢀ80 C.
Following the method outlined in the experimental section, the
ꢀ
distances both being 2.66 A.
synthesis of
b-1 is perfectly reproducible. At intermediate con-
centrations, concomitant [13] crystallisation of the two phases was
observed. Concomitant crystallisation of racemates and conglom-
erates have attracted some attention [13,14], and we have observed
such phenomena for 10-nitro-phenantren-9-yl phenyl sulphide
2.3. Reactions with N-chlorosuccinimide
The crystal structure of
b
-1 is very different from that of di(3-
1
[
15], di(2,4-dimethylpyridino)-dichlorozinc [16] and di(3-picoline)-
picoline)-di(1-
nuclear molecules displaying indenyl anions bound in a
resulting in chirogenic -carbon atoms, while the polymeric
exhibits indenyl anions that are sandwiched between two K ions.
The two sides of the indenyl group in -1 are different; one side is
mode, while the opposite side is more
coordination. Investigation of the local
structure reveals that if the electrophile approaches an isolated
chain in -1, an ee would be obtained if the attack takes place
h -indenyl)zinc. The latter forms discrete mono-
1
1
di(1-
Cooling a very dilute solution to ꢀ80 C may initiate crystal-
lisation of the inclusion compound [K(ind)(pmdta)] (THF) (2), and
these crystals were found to belong to space group P2 . A Flack
h
-indenyl)zinc [8].
h
fashion,
-1
ꢁ
a
b
n
n
1
b
5
parameter [17e19] of ꢀ0.02(4) indicates that the analysed crystal
was enantiomerically pure, with no indication of twinning-by-
inversion. Of the two conglomerates, our efforts towards total
coordinated by a K ion in a h
3
accessible due to a
h
spontaneous resolution were concentrated on
b-1, which could be
b
obtained in the form of large single-crystals, while synthesis of 2
generally yields very small crystals. The synthesis of 2 is also
perfectly reproducible.
selectively on the less hindered side (Fig. 3).
When the complete crystal structure is examined, the difference
between the two sides of the indenyl anion is affected, since the
adjacent chains will fill up the space created in the grooves of the
zigzag chains. Nevertheless, it seemed to be worth trying to use
2.2. Crystal structures
crystals of b-1 in an asymmetric synthesis. Complex b-1 forms large
The three phases
the same type of polymeric chains. For example, each indenyl group
in -1 is coordinated by two K atoms exhibiting two different co-
ordination modes (Fig.1): K1 coordinates in a
other side of the indenyl plane, K1 (ꢀx, 1/2 þ y, ꢀz) coordinates in a
a
-1,
b
-1 and 2 are closely related and display
well-developed crystals, which make reactions on single-crystals
fairly simple. By performing reactions on single-crystals, one can
be sure to have an optically pure starting material. In the case of an
ee in a single-crystal reaction, reactions on bulk samples can be
performed; with knowledge of the ee obtained from a single-crystal,
b
5
h
-mode while, at the
3
h
-mode to C1, C8 and C9. Atom C8 is a part of the phenyl ring
one can get a rough estimate of the enantiomerical purity of the bulk
1
system rather than the cyclopentadienyl ring system. The zigzag
sample. During our investigations of di(3-picoline)-di(1-
h
-indenyl)

S. Olsson et al. / Journal of Organometallic Chemistry 741-742 (2013) 131e135
133
C21
C22
C20
C13
C12
C15
C16
C10
N2
N1
O1
C19
C14
C18
K1
N3
C17
C11
C5
C3
C4
C2
C6
C1
C9
C8
C7
Fig. 2. Molecular structure of 2 displaying the crystallographic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and all H atoms have been
omitted for clarity.
zinc we found that NCS was a suitable electrophile [8]. Other elec-
trophiles were tested as well, however, carbon dioxide gave only
achiral product, since indene-1-carboxylic acid rapidly rearranges
to achiral indene-3-carboxylic acid [21]. Bromine gave a complex
mixture of products due to addition of bromine to the double bond
acetonitrile is less likely to give rise to a high ee in the case of b-1,
since dissolution most probably will break the polymeric chains,
with total loss of chirality. If, on the other hand, dissolution leads to
3
the formation of intermediate discrete chains in solution, the
h
face
of the indenyl anion could be exposed and an ee could be obtained.
Performing the reaction in the presence of methanol resulted in
indene, along with only traces of any chlorinated products, as re-
flected by the considerably higher basicity of organopotassium
compounds compared to organozinc compounds. On replacing
methanol with acetonitrile, the reaction mixture contained 48e64%
1-chloroindene, but again no ee was observed. Addition of p-ben-
zoquinone did not improve the results [8]. Reactions in diethyl ether
gave similar results, 51e72% racemic 1-chloroindene. The crystals of
2 obtained so far have generally been too small to allow single-
crystal reactions.
and trimethylsilyl chloride gave only racemic product. Crystals of
b-
1
were selected at low temperature [22] and ground with NCS under
nitrogen atmosphere in a phial at liquid nitrogen temperature. The
phial was sealed and the mixture was allowed to slowly reach
ambient temperature. Initially, we had problems obtaining a
reproducible reaction product; HPLC indicated that the extracted
product could consist either of almost pure indene, or mixtures of
indene and up to 70% 3-chloroindene. The samples contained only
traces of the desired 1-chloroindene and there was no correlation
between reaction time and conversion. A sample quenched directly
with water before reaching ambient temperature gave a product
consisting of 49% indene, 29% 1-chloroindene (racemic) and 22% 3-
chloroindene, as indicated by HPLC. Higher yields of 1-chloroindene
3. Conclusions
ꢁ
were obtained when n-hexane was slowlyadded at ꢀ196 C, and the
It was found that crystallisation of [K(ind)(pmdta)]
n
from THF
mixture ground during thawing. Upon HPLC-analysis, the hexane
gave rise to two different phases of [K(ind)(pmdta)]
n
(
a
-1 and -1),
b
solution contained a mixture of indene and 41e49% 1-chloroindene,
and an inclusion compound containing co-crystallised THF (2). By
adjusting the concentration, it was found possible to obtain the
which unfortunately was racemic. Unlike the case of di(3-picoline)-
1
di(1-
h
-indenyl)zinc, the use of solvents like methanol and
desired phase selectively:
solutions, while -1 and 2 are obtained from more dilute solutions.
One of the phases, -1, has been reported previously and forms
racemic crystals, while -1 and 2 were found to undergo sponta-
neous resolution. Although single crystals of -1 were found to be
enantiopure, both enantiomorphs were found when examining
an entire crystal batch. Since -1 is a reactive organometallic re-
a-1 crystallises from more concentrated
b
a
b
b
b
agent, attempts were made to use the crystals in enantioselective
synthesis, but no ee was observed upon reaction with N-chloro
succinimide.
4. Experimental part
4.1. General
Fig. 3. Individual polymeric chains in b-1 are chiral, and one of the faces of the indenyl
anion is more accessible than the other side. In the case of an isolated chain, an ee
All experiments were performed under nitrogen atmosphere
would be expected on reaction with an electrophile.
using Schlenk or low-temperature techniques [22]. All glass

134
S. Olsson et al. / Journal of Organometallic Chemistry 741-742 (2013) 131e135
ꢁ
equipment was dried at 130 C over night. THF was distilled from
sodium/benzophenone shortly prior to use. PMDTA (Aldrich) and
Table 1
Selected bond distances for b-1 and 2.
indene (Aldrich) were distilled from CaH
2
prior to use. HPLC anal-
b-1
2
ysis was carried out on a Varian system with a 9010 Solvent De-
livery System and a 9065 Polychrom UV-DAD detector coupled
with a PDR-Chiral Inc. Advanced Laser Polarimeter. Separation was
achieved using a Daicel Chiracel OD column and a mobile phase
consisting of n-hexane/2-propanol 99:1.
a
a
a
b
h3
K(1)eC(1)
K(1)eC(8)
K(1)eC(9)
K(1)eC(1)
3.1788(14)
3.2910(14)
3.3236(13)
3.0700(13)
3.0129(13)
3.0621(14)
3.1423(13)
3.1506(13)
2.8359(12)
2.8321(11)
2.8966(12)
3.079(3)
3.254(3)
3.196(3)
3.088(3)
3.029(3)
3.098(3)
3.212(3)
3.200(3)
2.827(2)
2.888(2)
2.913(2)
3
3
5
5
5
5
5
h
h
h
h
h
h
h
K(1)eC(2)b
b
K(1)eC(3)
K(1)eC(4)b
K(1)eC(9)b
K(1)eN(1)
K(1)eN(2)
K(1)eN(3)
4.2. Indenylpotassium in THF
e
e
e
Potassium (1.43 g, 0.037 mol) was cut into small pieces, and THF
ꢁ
(
(
17 mL) was added. The mixture was stirred at 0 C, and indene
4.25 mL, 0.037 mol) was added in small portions over 0.5 h. The
a
Symmetry codes: ꢀx, ꢀ1/2 þ y, ꢀz.
b
Symmetry codes:
b
-1: x, y, z; 2: 1 ꢀ x, 1/2 þ y, ꢀz.
mixture was stirred at ambient temperature until all the potassium
was dissolved (c. 6 h). A clear, amber-coloured solution was ob-
tained. The solution is extremely air-sensitive, and darkens on
exposure of minute amounts of oxygen, but may be stored
4.7. Reaction between (
b
-1) and NCS/p-benzoquinone in solution
-1 was carefully selected at
ꢁ
at ꢀ80 C for a few weeks. The concentration was determined by
A crystal (c. 0.5 ꢂ 0.5 ꢂ 0.5 mm) of
b
titration with 0.10 M hydrochloric acid, and was found to be
low temperature under nitrogen atmosphere using microscope
ꢁ
1
.96 M.
.3. [K(ind)(pmdta)]
PMDTA (0.5 mL, 2.4 mmol) and THF (0.9 mL) was added to
[22] and transferred to a phial. The phial was cooled to ꢀ196 C, and
the crystal was ground using a metal rod. A mixture of NCS (c.
65 mg) and p-benzoquinone (c. 9 mg) was added, and the reaction
4
n
(b-1)
ꢁ
mixture was ground at ꢀ196 C. Acetonitrile (0.2 mL) was slowly
ꢁ
added at ꢀ196 C. The frozen mixture was thawed and ground until
indenylpotassium (1.96 M in THF, 0.5 mL, 0.98 mmol). The solution
it reached ambient temperature. Hydroquinone (c. 100 mg) was
added to precipitate the benzoquinone, the reaction mixture was
extracted with hexane (c. 0.2 mL), the hexane phase was washed
with 2.5 M HCl and analysed by HPLC.
ꢁ
was cooled to ꢀ30 C, where crystals formed over night. Several
crystals were picked for X-ray diffraction, all of which were iden-
tified as
Yield: 0.25 g, 77%. If the solution is diluted with 0.8 mL of THF,
concomitant crystallisation of -1 and -1 may occur. More
concentrated solutions invariably deposited crystals of -1.
b-1 without any signs of concomitant crystallisation of a-1.
a
b
4
.8. X-ray crystallography
a
Crystals were carefully selected using microscope at low tem-
ꢁ
4
.4. [K(ind)(pmdta)]
n
(THF)
n
,(2)
perature [22]. Data were recorded at ꢀ173 C using a Rigaku R-AXIS
IIc area detector with graphite monochromated Mo-Ka radiation
ꢀ
PMDTA (0.20 mL, 0.96 mmol) was added to indenylpotassium
(l
¼ 0.71073 A) from a Rigaku RU-H3R rotating anode, operating at
ꢁ
(
1.96 M in THF, 0.2 mL, 0.39 mmol) diluted with THF (2.0 mL). The
50 kV and 90 mA. 90 oscillation photos with a rotation angle of 2
ꢁ
solution was placed at ꢀ80 C where colourless needles of 2 formed
over night. Yield: 0.15 g, 94%.
Table 2
Crystal and refinement data for
b-1 and 2.
4
.5. Solid state reaction between (
b
-1) and NCS
-1 was carefully selected at
Parameter
b
-1
2
A crystal (c. 0.5 ꢂ 0.5 ꢂ 0.5 mm) of
b
Empirical formula
KC18
H
30
N
3
38 3
KC22H N O
ꢀ
1
low temperature under nitrogen atmosphere using microscope
M/g mol
327.55
Monoclinic
P2
9.534(2)
10.9451(19)
9.724(2)
90
109.471(8)
90
956.6(3)
2
1.137
0.279
100(2)
0.4 ꢂ 0.3 ꢂ 0.3
4.26e25.50
5093
2622 (0.0203)
204
399.65
Monoclinic
P2
ꢁ
[
22] and transferred to a phial. The phial was cooled to ꢀ196 C, and
Crystal system
Space group
1
1
the crystal was ground using a metal rod. NCS (c. 65 mg) was added,
ꢀ
a/A
9.474(2)
10.518(3)
11.885(3)
90
96.375(8)
90
1177.0(5)
2
1.128
ꢁ
and the mixture was ground at ꢀ196 C. The phial was sealed with a
ꢀ
b/A
rubber septum and allowed to reach ambient temperature. Water
ꢀ
c/A
ꢁ
ꢁ
(c. 0.1 mL) and n-hexane (c. 0.2 mL) was added. The hexane phase
a/
b
/
was washed with 2.5 M HCl and analysed by HPLC.
ꢁ
/
g
ꢀ
3
V/A
4
.6. Reaction between (
b
-1) and NCS in solution
-1 was carefully selected at
Z
D
m
/g cm 3
(Mo K
)/mm 1
T/K
ꢀ
c
ꢀ
a
0.241
100(2)
A crystal (c. 0.5 ꢂ 0.5 ꢂ 0.5 mm) of
b
low temperature under nitrogen atmosphere using microscope
Crystal size/mm
0.4 ꢂ 0.2 ꢂ 0.2
1.72e25.50
7956
4212 (0.0504)
249
ꢁ
[
22] and transferred to a phial. The phial was cooled to ꢀ196 C, and
ꢁ
q
Range/
the crystal was ground using a metal rod. NCS (c. 65 mg) was added,
Reflections collected
Unique reflections, Rint
No. of parameters
ꢁ
and the mixture was ground at ꢀ196 C. Solvent (n-hexane,
methanol, acetonitrile or diethyl ether, 0.2 mL) was slowly added
Absolute structure parameter
ꢀ0.02(2)
ꢀ0.02(4)
ꢁ
at ꢀ196 C. The frozen mixture was thawed and ground until it
GOF on F2
1.029
1.054
a
2 b
reached ambient temperature. The reaction mixture was extracted
Final R (F) (I > 2
s
(I))/wR (F )
0.0212/0.0535
0.0214/0.0536
0.0476/0.0937
0.0574/0.0966
1
2
a
2 b
with hexane (c. 0.2 mL), and the hexane phase was washed with
2
solvent was evaporated in a stream of nitrogen before extraction.
R
1
/wR
2
(F ) (all data)
.5 M HCl and analysed by HPLC. In the case of diethyl ether, the
a
R
wR
1
(F) ¼ S(jjF
o
j ꢀ jF
c
jj)/SjF j.
o
b
2
2
2
2
2
2
(F ) ¼ {S[w(F
o
ꢀ F

S. Olsson et al. / Journal of Organometallic Chemistry 741-742 (2013) 131e135
135
were collected. Data were processed using the CrystalClear soft-
ware package [23], and an empirical absorption correction was
applied using the REQAB program. The structures were solved us-
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Acknowledgements
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Financial support from the Swedish Research Council (VR) is
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Appendix A. Supplementary material
CCDC 923404, 923405; contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
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