Probing the salt-metathesis route to bis(aryl)calcium compounds: Structure of an arylcalcate complex

Article abstract of DOI:10.1002/ejic.201501178

1,3-Diisopropoxybenzene can be selectively metalated by nBuLi or by the superbase mixtures nBuLi/NaOC(Me)₂Et or nBuLi/KOC(Me)₂Et to give 2,6-diisopropoxyphenyllithium (71 %), 2,6-diisopropoxyphenylsodium (61 %), or 2,6-diisopropoxyph

Full text of DOI:10.1002/ejic.201501178

FULL PAPER
DOI:10.1002/ejic.201501178
Probing the Salt-Metathesis Route to Bis(aryl)calcium
Compounds: Structure of an Arylcalcate Complex
[a]
[b]
Sjoerd Harder* and Christian Ruspic
Dedicated to Professor Rudi van Eldik on the occasion of his 70th birthday
Keywords: Alkaline earth metals / Grignard reagents / Sodium / Calcium / Salt metathesis
1
,3-Diisopropoxybenzene can be selectively metalated by
nBuLi or by the superbase mixtures nBuLi/NaOC(Me) Et or
nBuLi/KOC(Me) Et to give 2,6-diisopropoxyphenyllithium
71%), 2,6-diisopropoxyphenylsodium (61%), or 2,6-diiso-
phenyl)calcium by the same approach using 2,6-diisoprop-
oxyphenylpotassium and CaI gave the calcate complex
Ca] K , which is the first arylcalcate complex
2
2
–
+
2
[{(iPrO)
2 6 3 3
C H }
1
3
(
to have been structurally characterized. The trend in the
C
propoxyphenylpotassium (59%) as isolated products. The at-
tempted synthesis of bis(2,6-diisopropoxyphenyl)calcium by
the salt metathesis route using 2,6-diisopropoxyphenylsod-
NMR chemical shifts of the aryl Cipso atoms shows that
the calcate complex displays an aryl–metal bond polarity
(nucleophilicity/basicity) similar to that in arylsodium com-
pounds.
ium and CaI
2
gave an undefined mixture of products,
whereas the attempted synthesis of bis(2,6-diisopropoxy-
Introduction
ety of reactive heavier alkaline-earth metal complexes has
been extended further to [(Me Si) CH]M·(thf) (M/x = Ca/
3
2
x
Although the discovery and widespread application of
Grignard reagents is more than a century old,[ notable de-
velopment of the organometallic chemistry of the heavier
alkaline-earth metals (Ca, Sr, Ba) only started a few dec-
[14]
2
, Sr/3, Ba/3) and complexes with the phenyl-substituted
1]
–
– [11,15]
carbanions Ph C and Ph CH .
3
2
[
2]
ades ago. Organocalcium chemistry, in particular, has
[3]
seen major breakthroughs with applications as initiators
in polymer chemistry,[
4,5]
the exploitation of their lanthan-
[6]
ide-like properties in homogeneous catalysis and their use
in chemical vapour deposition.[
7]
Application of organocalcium complexes in stereoselec-
tive styrene polymerization[ initiated the challenging goal
of developing highly reactive and nucleophilic organocal-
4]
[
8]
cium reagents. As historically known cyclopentadienyl,
tris(trimethylsilyl)methyl[ and 1,3-bis(trimethylsilyl)allyl
9]
[10]
complexes of calcium were not suitable as initiators for styr-
ene polymerization, benzylcalcium complexes of increasing
reactivity have been developed (1[ Ͻ2 Ͻ3 Ͻ4 ).
Routes to benzyl complexes of the heavier alkaline-earth
metals have also recently been reported.[ Subsequently,
unsubstituted bis(allyl)calcium was found to be a potent
precursor in organocalcium chemistry.[ The growing vari-
4a]
[4b]
[4f]
[11]
12]
13]
The most reactive organocalcium compounds are un-
doubtedly the “heavy” arylcalcium Grignard complexes.[
It was not until 2005 that well-defined arylcalcium com-
plexes appeared in the literature: three groups indepen-
dently reported the synthesis and crystal structures of aryl-
13]
[
[
a] Inorganic and Organometallic Chemistry,
University Erlangen-Nürnberg,
Egerlandstrasse 1, 91058 Erlangen, Germany
www.harder-research.com
b] Anorganische Chemie, Universität Duisburg-Essen,
Universitätsstrasse 5, 45117 Essen, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201501178.
[
16]
calcium complexes. Niemeyer and co-workers treated the
in situ prepared (C F ) Ca with a triazene ligand to obtain
6
5 2
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the first well-defined heteroleptic arylcalcium compound yields by tedious fractional crystallization of a Ca Grignard
[
16a]
[22]
[
Equation (1)].
Our attempts to synthesize a homoleptic mixture,
the Schlenk equilibrium [Equation (4)] can be
[
23]
bis(aryl)calcium complex with tamed reactivity through a simply shifted by the addition of KOtBu. In this case the
salt-metathesis route led to a tetrameric cluster with incor- intermediate ArCaOtBu is in equilibrium with CaAr and
2
2
–
[16b]
porated O [Equation (2)].
Careful analysis of first Ca(OtBu) , and precipitation of the insoluble [Ca(OtBu) ]
2
2
ϱ
structural data of the arylcalcium moiety showed aryl ring drives the equilibrium to the homoleptic CaAr2 [Equa-
distortions typical of polar arylmetal compounds.[ As the tion (5)].
extent of this distortion is dependent on the polarity of the
17]
metal–carbon bond, it could be concluded that C–Ca and
C–Li bonds have approximately similar polarity. West-
erhausen and co-workers[
16c]
reported a similar tetrameric
2–
arylcalcium cluster, Ph Ca I O, with incorporated O ,
3
4 3
which was synthesized by the Grignard method [Equa-
2
–
tion (3)]. The incorporated O could originate from oxid-
ation by traces of air[
16b]
or by ether cleavage,
[16c]
which is
Following our earlier synthetic protocol, we report herein
our attempts to synthesize a bis(aryl)calcium complex by
the salt-metathesis route, which is most efficient for CaI2
precursors partially dissolved in a polar solvent like thf and
with M = K or Na [Equation (6)]. The driving force for the
reaction is the insolubility of KI or NaI. Because arylsod-
ium and -potassium compounds generally show high reac-
tivity towards polar solvents like thf, we used an aryl anion
of tamed reactivity and with increased steric bulk. We de-
scribe the synthesis and isolation of the precursors 2,6-
a well-established process in polar organometallic chemis-
try.[
18]
(
(
iPrO) -phenyllithium, 2,6-(iPrO) -phenylsodium and 2,6-
2
2
iPrO) -phenylpotassium. The crystal structure of the tetra-
2
meric aggregate [2,6-(iPrO) -phenylsodium] presents one
2
4
of the few structures of a solvent-free arylsodium complex.
Further reaction of these reagents with CaI did not lead
2
to the anticipated bis(aryl)calcium compound, but instead,
the first example of an arylcalcate complex was isolated:
–
+
[
Ar Ca] K . In addition, we describe the structure of an
3
accidental oxidation product, ArOCaI·(thf), obtained from
the metathesis reaction.
Results and Discussion
The bulky 1,3-diisopropoxybenzene, (iPrO) C H , was
2
6
4
Westerhausen and co-workers achieved a major break- prepared in 75% yield according to the procedure of Ya-
[
24]
through by showing that careful activation of Ca and syn- suda and co-workers (Scheme 1).
thesis at low temperatures could give arylcalcium iodide erature procedure, in which (iPrO) C H was lithiated in
In contrast to the lit-
2
6
4
compounds by the Grignard route. The isolated complexes situ by nBuLi in thf to give 2,6-diisopropoxyphenyllithium
[
24]
could be obtained in crystalline purity and the first crystal and subsequently converted,
we aimed to isolate a sol-
vent-free product. Therefore we performed the lithiation in
This set the stage for a decade of “heavy” Grignard chemis- hexane at reflux and isolated the pure product (iPrO)2-
[
19]
structure of a Ca Grignard, MesCaI·(thf) , was obtained.
4
try.[
3c–3h]
It was immediately clear that these post-Grignard C H Li in 29% yield. The low yield of this “directed ortho-
6 3
reagents are highly reactive and first reports mention thf metallation” reflects the steric pressure of the two iPrO sub-
cleavage at temperatures as low as –30 °C.[20] However, a stituents: the analogous lithiation of the less bulky 1,3-di-
recent detailed investigation showed that Ca Grignard rea- methoxybenzene to 2,6-dimethoxyphenyllithium is
a
gents are more stable than initially expected[ and this cer- straightforward procedure (yield: 95%).
21]
[25]
Attempts to
tainly widens the scope for the application of these potent convert 2,6-diisopropoxyphenyllithium into 2,6-diisoprop-
reagents. Their stability in ethereal solvents is dependent oxyphenylsodium and -potassium by transmetallation with
on temperature, concentration and solvent, but can also be NaOC(Me) Et and KOC(Me) Et in hexane, benzene or thf,
2
2
2
+
influenced by the second anionic ligand on Ca .
respectively, failed. In all cases, the starting material
Ca Grignard reagents are important building blocks for (iPrO) C H Li was isolated. This is likely due to the fact
2
6
3
the synthesis of bis(aryl)calcium compounds. Although the that this lithium compound is quite insoluble even in thf.
first bis(aryl)calcium complexes were obtained in poor However, the corresponding sodium and potassium com-
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pounds could be obtained by direct metallation of 1,3-diiso-
propoxybenzene with the superbase mixtures, nBuLi/
NaOC(Me) Et and nBuLi/KOC(Me) Et, respectively, in
2
2
hexane, with the products precipitating from solution. The
solvent-free sodium compound (iPrO) C H Na is remarka-
2
6
3
bly soluble in hexane and could even be obtained in the
form of large well-defined crystals by the slow cooling of a
hexane solution. Because the literature describes only two
crystal structures of solvent-free arylsodium compounds
[
26]
[27]
(
5
and 6 ) and a handful of tmeda-solvated arylsodium
[
28–31]
dimers (7
), we determined the structure of (iPrO)2-
C H Na by single-crystal X-ray diffraction.
6
3
cupied by the two chelating iPrO arms. One of the iPrO
+
arms bridges two Na ions, and therefore the total coordi-
+
nation number of each Na ion is six. The C–Na distances
are in the relatively narrow range of 2.6267(8)–2.7268(9) Å,
and considerably longer than those in 5 [2.523(5)–
2.579(5) Å] or 6 [2.572(2)–2.609(2) Å]. This is likely due to
the much higher coordination number of six for Na in the
structure of (iPrO) C H Na (cf. Na in 5 is five-coordinate
2
6
3
and Na in 6 is four-coordinate). There are two types of
Na–O bonds in [(iPrO) C H Na] : the bridging iPrO sub-
2
6
3
4
stituents show much longer Na–O bonds [2.5143(6)–
.6861(8) Å] than the iPrO groups that are coordinated to
2
+
a single Na ion [2.2908(7) Å].
It is of interest to compare the structure of [(iPrO)2-
C H Na] with those of similar aryllithium compounds.
6
3
4
Scheme 1.
2,6-Dimethoxyphenyllithium (8) also crystallizes as a tetra-
mer, but displays a completely different structure that could
(
iPrO) C H Na crystallizes in the tetragonal space group be envisaged to consist of two stacked dimers in which the
2 6 3
P-42 c with two tetrameric aggregates in the unit cell (Fig- Cipso atoms are involved in 3-centre–2-electron bonding.[
17d]
1
ure 1, Table 1). The structure of [(iPrO) C H Na] shows The Li atoms within the dimeric subunits interact with the
2
6
3
4
2
very high crystallographic S symmetry. The tetramer can C sp orbital, whereas contacts between the dimeric sub-
be described as a distorted cube consisting of four Na ions units are formed by interaction along the C p orbital. This
4
+
and the four Cipso atoms of the aryl anions, a structure type view is apparent from the significantly shorter C–Li bonds
typical of organolithium tetramers. The Cipso atoms can be within the dimer compared with those between dimers and
envisaged to be involved in 4-centre–2-electron bonding. Al- from their different 13C– Li magnetic coupling constants.
though the terminology “4-centre–2-electron bonding” im- Thus, the tetramer 8 is constructed of two loosely bound
plies a covalent bonding model, it should be noted that dimeric subunits. The subunit itself has attracted consider-
6
[
32]
bonding in organoalkalimetal complexes is largely ionic.
able interest for formally containing a planar four-coordi-
However, the bonding geometry is quite clearly defined by nate carbon atom. The difference between the Li and Na
such terminology and therefore we chose to use this de- structures originates from the much larger ionic radius of
+
+
+
[33]
scription. The remaining coordination sites on Na are oc- Na compared with Li (1.02 vs. 0.74 Å, six-coordinate).
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sors all show a single set of signals (see the Exp. Sect.).
Although a thf solution of (iPrO) C H Li is stable, the
2
6
3
heavier alkali metal compounds (iPrO) C H Na and
2
6
3
1
(
iPrO) C H K both slowly decompose in solution.
H
2
6
3
NMR monitoring shows continuous growth of a set of sig-
nals that can be assigned to propene (which was also inde-
[
35]
pendently detected by a GC–MS analysis). Therefore, de-
composition is not due to a reaction with thf, but caused
by an intramolecular rearrangement: the intramolecular de-
protonation of the Me substituent of iPr leads to an imme-
diate Wittig-type rearrangement giving propene and pre-
sumably a phenolate complex (Scheme 1).
As the decomposition of the Na and K compounds is
relatively slow (half-life about 2 days), we continued to tar-
get the synthesis of the bis(aryl)calcium compound by a
salt-metathesis reaction with CaI . The driving force in this
2
reaction is the formation and precipitation of the very
stable, insoluble salt (NaI) or (KI) (due to the good solu-
ϱ
ϱ
bility of LiI in thf, use of the Li precursor would be disad-
vantageous).
Figure 1. a) Crystal structure of [(iPrO)
2
C
6
H
3
Na]
4
. Hydrogen
After many attempts, the reaction of 2 equivalents of
atoms and iPr substituents are not shown for clarity. b) Graphical (iPrO) C H Na with anhydrous CaI in thf did not give
2
6
3
2
presentation of the partial structure showing the geometry of the
distorted C Na cube and the C–Na/O–Na bonding geometry.
pure or crystalline products that could be identified as the
desired product [(iPrO) C H ] Ca. In one case we isolated
4
4
2
6
3 2
a small batch of colourless well-defined crystals (yield
2 6 3 4 2
Table 1. Selected bond lengths for [(iPrO) C H Na] , {[(iPrO) -
Ͻ 10%) that were identified as [(iPrO) C H O]CaI·thf,
–
+
2
6
3
C
6
H
3
O]CaI·thf}
Bond Bond length [Å]
(iPrO) Na]
2 2 6 3 3
and [{(iPrO) C H } Ca] K .
likely formed after partial oxidation by O from traces of
2
Bond
Bond length [Å]
air (ether-substituted phenyl anions are oxidation-sensi-
[
16b]
[
2
C
6
H
3
4
tive).
The decomposition product crystallized as a cen-
trosymmetric dimer in the monoclinic space group P2 /c
Na1–C2
Na1a–C2
Na1b–C2
2.7268(9)
2.6267(8)
2.6784(8)
Na1–O1
Na1a–O1
Na1b–O2
2.6861(8)
2.5143(6)
2.2908(7)
1
(Figure 2, Table 1). Two aryloxide anions bridge two Ca2
ions in such a way that both iPrO substituents can form
intramolecular Ca–O bonds. O,OЈ,OЈЈ-Chelation of the
+
{
[(iPrO)
2
2
C
6
6
H
3
3
O]CaI·thf}
2
2
(
,6-di-iPrO-phenoxy ligands leads to a nearly planar
Ca–O1
Ca–O2
Ca–O4
2.2457(12)
2.5657(13)
2.3686(13)
Ca–I
Ca–O1Ј
Ca–O2Ј
3.0702(4)
2.2508(12)
2.5544(12)
ArOCa)2 framework in which the Ca2 ions lie only
+
0.237(1) Å out of the ArO least-squares plane. The coordi-
nation spheres of both Ca2 ions are completed by iodide
and thf ligands. The terminal Ca–I bond of 3.0702(4) Å is
significantly shorter than that in (p-tolyl)CaI·(thf)4
+
–
+
[{(iPrO)
C
H
3
} Ca] K
Ca–C2
Ca–C14
Ca–C26
Ca–O2
Ca–O4
Ca–O5
2.5498(15)
2.5352(13)
2.5416(14)
2.4258(11)
2.4566(12)
2.4348(11)
K–C2
3.0607(15)
2.9914(14)
3.0523(12)
2.6784(12)
2.8442(11)
K–C26
K–O2
K–O6
K–O3ЈЈ
This allows for 4-centre–2-electron bonding and the higher
coordination number of six in the arylsodium structure. The
crystal structure of 2,6-di-tert-butoxyphenyllithium (9)
shows a completely different structure type: in this case an
unusual trimeric aggregate is formed that has no resem-
[34]
blance to the structure of [(iPrO) C H Na] .
2
6
3
4
The sodium compound (iPrO) C H Na shows good sol-
2
6
3
ubility in benzene and even dissolves in hexane, but the
potassium compound (iPrO) C H K only dissolves in thf.
2
6
3
We were unable to grow single crystals of (iPrO) C H K,
2
6
3
but based on its insolubility in aromatic solvents and the
+
[33]
much larger ionic radius for K (1.38 Å, six-coordinate),
1
13
it is likely a coordination polymer. The H and C NMR
spectra of the aryllithium, -sodium and -potassium precur- Hydrogen atoms are not shown for clarity.
2 6 3 2
Figure 2. Crystal structure of the dimer {[(iPrO) C H O]CaI·thf} .
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[
3.172(1) Å],[20] which also features a hexacoordinate Ca2+ bond length of 2.749(4) Å in Ar Ca O [see Equation (2)] in
6 4
ion. This may be explained by the unusual coordination ge- which the Cipso atom also bridges two Ca2 ions.
+
[16b]
The
ometry of Ca in [(iPrO) C H O]CaI·thf, in which a large average Ca–C bond is similar in length to the terminal Ca–
2
6
3
[
20]
part of the coordination sphere is not occupied by ligands Cipso bond in (p-tolyl)CaI·(thf) (2.556 Å).
4
but shielded by iPr groups. As [(iPrO) C H O]CaI·thf is an
Although there are examples of arylpotassium com-
2
6
3
accidental product, the development of a high-yielding syn- pounds embedded in mixed-metal “ate” complexes,[ no
thetic route and further analysis was not pursued. crystal structure has been reported of a “pure” arylpotas-
Failure of the salt-metathesis route using (iPrO) C H Na sium compound that does not contain other metal cations.
36]
2
6
3
may be due to the partial decomposition of the precursor However, there are some examples of structurally charac-
see above) or insufficient precipitation of NaI resulting in terized alkyl,[37] benzyl and acetylide potassium com-
[38]
[39]
(
a mixture of products. Salt metathesis using (iPrO) C H K plexes. The C–K bond lengths vary between 2.90–3.10 Å,
2
6
3
may be advantageous on account of the lower solubility which means that the C–K bonds in the current calcate
of KI. The reaction of 2 equivalents of (iPrO) C H K with complex are of similar length to those in regular organopot-
2
6
3
anhydrous CaI in thf, followed by evaporation of all sol- assium compounds. As primary (stronger) bonds should be
2
vents and extraction with benzene gave, after crystalli- formed with the higher charged, more electronegative Ca,
zation, a batch of colourless crystals that were identified as this may seem counterintuitive. However, one should also
–
+
a rare calcate complex, [{(iPrO) C H } Ca] K , by single- consider the directionality of the Cipso–metal bond. The
2
6
3 3
2
crystal X-ray diffraction. The use of different (iPrO)2- more compact Cipso sp lone pair forms shorter C–metal
C H K/CaI ratios either led to complex reaction mixtures bonds than the extended perpendicular p-type orbital. For
6
3
2
or isolation of the calcate complex. The crystallized yield this reason, the structures of mixed-metal “ate” complexes
of 12% is low, but likely due to the partial decomposition often show that the harder, smaller and higher charged cat-
2
of the potassium precursor and the presence of other prod- ions are aligned along the sp lone pair whereas the softer
ucts in the reaction mixture.
and larger alkali metal cations are bound by the p-type
–
+
The complex [{(iPrO) C H } Ca] K crystallizes in the orbital. Indeed, the “ate” complex (tmp) PhMgK (tmp =
2
6
3 3
2
[36a]
monoclinic space group P2 /c (Figure 3, Table 1). The cen- tetramethylpiperidide) with incorporated PhK units
1
2
+
2+
2
tral Ca ion is surrounded by three Ar anions each of shows bonding of Mg along the Cipso sp lone pair and
+
which chelate the metal in a bidentate bonding mode bonding of K along the p-type orbital. Its average C–K
through the Cipso atom and one of the iPrO oxygen atoms. bond length of 3.046(5) Å is similar to that in the current
This results in quite an unusual ligand–metal bonding ge- calcate structure.
ometry with very narrow C–Ca–O bite angles [55.38(5)–
Other evidence for the primary bond to Ca2+ in the cur-
+
2
5
5.83(5)°]. The K ion is less strongly bound at the fringe rent structure is found in the directionality of the sp lone
of the calcate anion by two C,O-chelating aryl anions and pairs, which point more towards Ca2 than to K . The
+
+
a K–O3 contact to a neighbouring calcate anion. This ar- angles C5···C2–Ca1 (146.62°) and C29···C26–Ca (145.70°)
rangement results in a linear coordination polymer in which are considerably larger than the angles C5···C2–K (99.67°)
+
K
ions bridge the calcate units. The C
atoms C2 and and C29···C26–K (128.64°). It is also interesting to note
ipso
2
+
+
2
C26 bridge the Ca and K ions. The Ca–C bond lengths that the sp lone pair at C14, which does not bridge cations
do not show much variation and its average value of but forms a terminal Ca–C bond, is not directed towards
.542(1) Å is considerably shorter than the average Ca–C the metal. The shift of Ca2 away from the sp axis is due
+
2
2
to the strong intramolecular coordination of the iPrO sub-
stituent through a strained four-membered Ca–C–C–O
ring. In the current calcate structure, these observations
point to a primary bond between the aryl C
atoms and
ipso
2+
+
Ca and to a much weaker bond between Cipso and K .
Although there is precedent for C–Ca bonded organo-
[
37b,40]
–
calcate complexes,
the complex [{(iPrO) C H } Ca] -
2 6 3 3
+
K
is the first example of an arylcalcate complex of type
Ar Ca] M . As one can control the nucleophilicity/basicity
–
+
[
3
of the carbanion through the nature of the second metal
cation, “ate” complexes are of interest as superbases,
[
41]
mixed-metal reagents or TURBO Grignards. On account
–
of the negative charge on Ar Ca , the Ar–Ca bond should
3
be more ionic than that in neutral Ar Ca and ArCaI com-
2
plexes. One parameter to probe aryl–metal bond ionicity is
[
17]
the deformation of the aryl ring. Although the aryl ring
–
+
in the calcate complex [{(iPrO) C H } Ca] K shows an
2
6
3 3
unusually acute C–C–C angle at Cipso [average: 113.0(1)°],
changes in this parameter are also influenced by other sub-
stituents and are not accurate enough for a strong conclu-
2
Figure 3. Crystal structure of the calcate complex [{(iPrO) -
C H } Ca] K (linear coordination polymer). Hydrogen atoms are
6 3 3
not shown for clarity.
–
+
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sion on bond ionicity. There is, however, another parameter NMR spectra.[44] The 1H NMR chemical shift of the
that can be linked to the charge localization at C and N(SiMe ) anion is dependent on the Ca/K ratio and repre-
ipso
3 2
1
3
Cipso–M bond ionicity. The C NMR chemical shift of sents an average signal of different species among which is
Cipso in a metallated phenyl ring is very sensitive to charge the known calcate complex [{(Me Si) N} Ca] K .
–
+ [45]
Salt
3
2
3
localization. Compared with the neutral aromatic ligand, metathesis is therefore not the method of choice for the syn-
an enormous downfield shift is observed. This is caused by thesis of arylcalcium complexes. The direct Grignard route
increased σ-electron density and decreased π-electron den- gives less complications due to the presence of only one
sity at the metallated carbon atom and can be used to evalu- kind of metal cation.
ate aggregation numbers in aryllithium chemistry: the
downfield shift increases with decreasing aggregation. In good measure of aryl–metal bond polarity. Although aryl-
The 13C NMR chemical shift of the aryl Cipso atom is a
[
42]
the series of (iPrO) C H M complexes introduced in this calcium compounds show a bond polarity similar to that
2
6
3
work, we also find a distinct influence of the metal on the of aryllithium compounds, the calcate complex displays an
1
3
C chemical shift of Cipso: Li (152.2)Ͻ Na (154.6)Ͻ K aryl–metal bond polarity similar to that of arylsodium
161.8 ppm). The downfield shift increases with the polarity compounds. The much higher reactivity (nucleophilicity/
(
of the C–M bond. Because the chemical shift of the Cipso basicity) of calcate complexes can be exploited in catalyst
atom is also strongly influenced by ortho-alkoxy substitu- design.
ents, only direct comparisons with similar lead structures
are possible. The dinuclear complex [(MeO) C H ] -
2
6
22]
3 3
[
Ca I·(tmeda) shows a chemical shift of 152.0 ppm
and
2
2
Experimental Section
for the cluster [(MeO) C H ] Ca O the C signal is found
2
6
3 6
4
ipso
at δ = 150.2 ppm. This means that the polarity of the aryl– General Methods: Solvents were dried by standard methods and
Ca bond compares well with that of aryllithium com- distilled from sodium/benzophenone prior to use. All moisture- and
–
+
pounds. The present calcate [{(iPrO) C H } Ca] K shows air-sensitive reactions were carried out under argon using standard
a
2
6
3 3
1
3
Schlenk techniques. Samples prepared for NMR measurements,
elemental analysis as well as for the reactions were handled in a
glovebox.
C signal for Cipso at δ = 156.3 ppm, which relates to
an average bond polarity similar to that of organosodium
compounds. The high nucleophilicity/basicity of calcate
complexes is in line with a recent report on a highly active NaOC(Me)
2
Et and KOC(Me)
2
Et were prepared by heating a two-
Et with metallic Na or K at
ate” complex in catalysis.[
43]
“
fold excess of the alcohol HOC(Me)
2
reflux for 18 h after which excess alcohol was removed under vac-
uum and the remaining white powder dried at 100 °C under high
vacuum. The alcoholates were used without further analysis.
nBuNa was prepared by the addition of nBuLi in hexane to a solu-
tion of NaOC(Me) Et (20% excess) in hexane at –30 °C after which
2
the suspension was warmed to room temperature and the isolated
Conclusions
1,3-Diisopropoxybenzene has been cleanly metallated at
the 2-position and the compounds (iPrO) C H M (M = Li,
Na, K) have been isolated. The crystal structure of the
2
6
3
precipitate was washed with hexane to remove LiOC(Me) Et. The
2
remaining white powder was dried under high vacuum and used
tetramer [(iPrO) C H Na] is a rare example of solvent-free without further analysis. 1,3-(iPrO) C H was prepared according
2
6
3
4
2
6
4
arylsodium complex that is even soluble in hexane. The salt- to a literature procedure.[
24]
metathesis reaction between CaI and (iPrO) C H Na only
2
2
6
3
NMR spectra were recorded with a Bruker DPX300 or Avance III
HD400 spectrometer. Single crystal structures were determined by
X-ray diffraction with a Siemens SMART diffractometer (APEXII
detector) or a Supernova diffractometer (Rigaku-Oxford diffrac-
led to complex reaction mixtures. On one occasion, crystals
of the oxidation product {[(iPrO) C H O]CaI·thf} were
2
6
3
2
obtained. The use of (iPrO) C H K in the salt-metathesis
2
6
3
reaction gave a well-defined product that could be structur- tions; AtlasS2 detector). Elemental analyses were performed with
ally characterized and represents the first arylcalcate com- a CEInstruments EA1110 elemental analyser (samples were applied
–
+
to a high vacuum before measurements). On account of the high
air-sensitivity of the complexes, the data obtained were not always
satisfactory. Propene was detected by GC–MS with a HP quadru-
pole mass spectrometer (Agilent 5973N MSD) in conjunction with
a HP gas chromatograph (Type 6890).
plex [{(iPrO) C H } Ca] K .
2
6
3 3
The unintended isolation of the calcate complex illus-
trates one of the main problems inherent to salt-metathesis
reactions. The exchange of different anions and cations may
lead to complex mixtures of compounds in which certain
combinations might be favoured, or in the case that the Synthesis of 2,6-(iPrO)
2
C
6
H
3
Li: nBuLi (9.20 mL, 2.46 m in hexane,
2.6 mmol) was added to a solution of 1,3-(iPrO) (4.40 g,
2.6 mmol) in hexane (30 mL). The reaction mixture was heated at
2
2
2 6 4
C H
product is obtained by crystallization, the least soluble spe-
cies will be obtained. Similar problems have been encoun-
tered in alkylcalcium chemistry: Lappert and co-workers re-
ported that the reaction of CaI with [(Me Si) CH]K gave
reflux for 1 h during which time a fine white precipitate was
formed. The mixture was centrifuged and the precipitate washed
with hexane (2ϫ 15 mL). Drying under high vacuum (0.01 Torr,
2
3
2
–
+
the calcate species [{(Me Si) CH} Ca] K , irrespective of
3
2
37b]
3
2
1
0 °C, 30 min) yielded the product as a white powder (3.16 g,
5.8 mmol, 70%). H NMR ([D ]thf, 300 MHz): δ = 1.29 (d, J =
8
the reaction stoichiometry.[
Hanusa and co-workers
1
showed that Ca[N(SiMe ) ] prepared from KN(SiMe3)2
3
2 2
6.0 Hz, 12 H), 4.60 (sept, J = 6.0 Hz, 2 H), 6.25 (d, J = 7.5 Hz, 2
1
3
and CaI by the salt-metathesis route can contain consider- H), 6.77 (t, J = 7.5 Hz, 1 H) ppm. C ([D ]thf, 75 MHz): δ = 23.0
2
8
able amounts of KN(SiMe3)2 that are not visible in its (iPr-Me), 68.5 (iPr-CH), 105.0 (Ar-m), 126.0 (Ar-p), 152.2 (C-Li),
5748
Eur. J. Inorg. Chem. 2015, 5743–5750
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
2
168.1 (Ar-o) ppm. C12H17LiO (200.21): C 71.99, H 8.56; found C
70.83, H 8.02.
[1] V. Grignard, Ann. Chim. 1901, 24, 433.
[
[
2] T. P. Hanusa, Coord. Chem. Rev. 2000, 210, 329.
3] For reviews, see: a) M. Westerhausen, Angew. Chem. Int. Ed.
001, 40, 2975; Angew. Chem. 2001, 113, 3063; b) J. S. Alexan-
Synthesis of 2,6-(iPrO)
2
C
6
H
3
Na: 1,3-(iPrO)
2
C
6
H
4
(2.60 g,
13.4 mmol) dissolved in hexane (10 mL) was added to a suspension
2
of nBuNa (0.97 g, 12.1 mmol) in hexane (10 mL). After complete
addition, the precipitate dissolved instantaneously to give a yellow
solution. The solution was stirred for 2 h at room temperature and
subsequently all solvents were removed under vacuum. The re-
sulting solid was washed with cold hexane (2ϫ 5 mL). Drying
under high vacuum (0.01 Torr, 20 °C, 30 min) yielded the product
as a white powder (1.60 g, 7.40 mmol, 61%). The product can also
der, K. Ruhlandt-Senge, Eur. J. Inorg. Chem. 2002, 2761; c) M.
Westerhausen, M. Gärtner, R. Fischer, J. Langer, L. Yu, M.
Reiher, Chem. Eur. J. 2007, 13, 6292; d) M. Westerhausen, M.
Gärtner, R. Fischer, J. Langer, Angew. Chem. Int. Ed. 2007, 46,
1
950; Angew. Chem. 2007, 119, 1994; e) M. Westerhausen, Co-
ord. Chem. Rev. 2008, 252, 1516; f) M. Westerhausen, Z. Anorg.
Allg. Chem. 2009, 635, 13; g) A. Torvisco, K. Ruhlandt-Senge,
Top. Organomet. Chem. 2013, 45, 1; h) M. Westerhausen, J.
Langer, S. Krieck, R. Fischer, H. Görls, M. Köhler, Top. Or-
ganomet. Chem. 2013, 45, 29.
be obtained in a similar yield by slow evaporation of the solvent
1
from a hexane solution. H NMR (C
6
D
6
, 300 MHz): δ = 0.97 (d,
J = 6.2 Hz, 12 H), 4.33 (sept, J = 6.2 Hz, 2 H), 6.48 (d, J = 7.5 Hz,
H), 7.22 (t, J = 7.5 Hz, 1 H) ppm. 1 C (C
3
[4] For the polymerization of styrene, see: a) F. Feil, S. Harder,
Organometallics 2000, 19, 5010; b) S. Harder, F. Feil, A.
Weeber, Organometallics 2001, 20, 1044; c) S. Harder, F. Feil,
K. Knoll, Angew. Chem. Int. Ed. 2001, 40, 4261; Angew. Chem.
2
6 6
D , 75 MHz): δ = 22.4
(iPr-Me), 67.8 (iPr-CH), 104.0 (Ar-m), 127.2 (Ar-p), 154.6 (C-Na),
1
6
67.3 (Ar-o) ppm. C12
6.29, H 7.98.
H17NaO
2
(216.26): C 66.65, H 7.92; found C
K: 1,3-(iPrO) (6.50 g,
2001, 113, 4391; d) F. Feil, S. Harder, Macromolecules 2003,
Synthesis of 2,6-(iPrO)
3.5 mmol) and KOC(Me)
2
C
6
H
3
2
C
6
H
4
36, 3446; e) S. Harder, F. Feil, Organometallics 2002, 21, 2268;
f) F. Feil, C. Müller, S. Harder, J. Organomet. Chem. 2003, 683,
3
2
Et (3.55 g, 28.1 mmol) were dissolved
5
6; g) F. Feil, S. Harder, Eur. J. Inorg. Chem. 2003, 3401; h)
D. F.-J. Piesik, K. Häbe, S. Harder, Eur. J. Inorg. Chem. 2007,
652.
in hexane (40 mL) and the mixture was cooled to –50 °C. Then
nBuLi (11.4 mL, 2.46 m in hexane, 28.1 mmol) was added slowly
and a white precipitate formed immediately. While still in the cool-
ing bath, the reaction mixture was slowly warmed to 5 °C and
stirred for a further 2 h at this temperature. Subsequently, the reac-
tion mixture was centrifuged and the precipitate washed with hex-
ane (3ϫ 30 mL). Drying under high vacuum (0.01 Torr, 20 °C,
5
[
5] For the polymerization of polar cyclic ethers, see: a) M. H. Chi-
sholm, D. Navarro-Llobet, W. J. Simonsick Jr., Macromolecules
2
001, 34, 8851; b) S. Schneiderbauer, P. J. Dijkstra, C. Birg, M.
Westerhausen, J. Feijen, Macromolecules 2001, 34, 3863; c) Z.
Zhong, M. J. K. Ankoné, P. J. Dijkstra, C. Birg, M. Westerhau-
sen, J. Feijen, Polym. Bull. 2001, 46, 51; d) M. Westerhausen,
S. Schneiderbauer, A. N. Kneifel, Y. Söltl, P. Mayer, H. Nöth,
Z. Zhong, P. J. Dijkstra, J. Feijen, Eur. J. Inorg. Chem. 2003,
3432; e) M. H. Chisholm, J. Gallucci, K. Phomphrai, Inorg.
Chem. 2004, 43, 6717; f) M. H. Chisholm, J. C. Gallucci, G.
Yaman, Inorg. Chem. 2007, 46, 8676; g) D. J. Darensbourg, W.
Choi, C. P. Richers, Macromolecules 2007, 40, 3521; h) D. J.
Darensbourg, W. Choi, O. Karroonnirun, N. Bhuvanesh, Mac-
romolecules 2008, 41, 3493; i) N. Barros, P. Mountford, S. G.
Guillaume, L. Maron, Chem. Eur. J. 2008, 14, 5507; j) M. H.
Chisholm, J. C. Gallucci, G. Yaman, T. Young, Chem. Com-
mun. 2009, 1828; k) Y. Sarazin, V. Poirier, T. Roisnel, J.-F.
Carpentier, Eur. J. Inorg. Chem. 2010, 3423; l) M. G. Cushion,
P. Mountford, Chem. Commun. 2011, 47, 2276; m) Y. Sarazin,
B. Liu, T. Roisnel, L. Maron, J.-F. Carpentier, J. Am. Chem.
Soc. 2011, 133, 9069.
3
9
0 min) yielded the product as a white powder (6.00 g, 25.8 mmol,
2%). H NMR ([D ]thf, 300 MHz): δ = 1.22 (d, J = 6.2 Hz, 12
8
1
H), 4.72 (sept, J = 6.2 Hz, 2 H), 6.15 (d, J = 7.5 Hz, 2 H), 6.67 (t,
J = 7.5 Hz, 1 H) ppm. 1 C ([D
4.7 (iPr-CH), 102.3 (Ar-m), 122.5 (Ar-p), 161.8 (C-K), 166.1
Ar-o) ppm. Elemental analysis was troublesome due to the high
sensitivity of 2,6-(iPrO) K towards traces of air.
Synthesis of [{2,6-(iPrO)
2
3
8
]thf, 75 MHz): δ = 20.7 (iPr-Me),
6
(
2 6 3
C H
–
+
2
C
6
H
3
}
3
Ca] K : A suspension of CaI
3.05 g, 10.4 mmol) in thf (10 mL) was added to a solution of 2,6-
iPrO) K (5.30 g, 22.8 mmol) in thf (30 mL). After stirring for
8 h at room temperature, the solvent was removed in vacuo. The
(
(
4
2 6 3
C H
residue was extracted with benzene (3ϫ 15 mL) and the combined
benzene layers were concentrated and dried in vacuo. The residue
was washed with hexane (2ϫ 15 mL) and crystallized from benzene
by slow diffusion of hexane to give the product as large colourless
crystalline blocks (600 mg, 0.91 mmol, 12% relative to the potas-
sium precursor). Variation of the K/Ca ratio did not lead to isola-
[
6] a) S. Harder, Chem. Rev. 2010, 110, 3852; b) A. G. M. Barrett,
M. R. Crimmin, M. S. Hill, P. A. Procopiou, Proc. R. Soc. Lon-
don, Ser. A 2010, 466, 927; c) M. R. Crimmin, M. S. Hill, Top.
Organomet. Chem. 2013, 45, 191.
tion of [2,6-(iPrO)
complex. 1H NMR (C
.2 Hz, 36 H), 4.60 (sept, J = 6.2 Hz, 6 H), 6.43 (d, J = 7.8 Hz, 6
2
C
6
H
3
]
2
Ca or to increased yields of the calcate
6
D
6
/[D ]thf, 400 MHz): δ = 1.12 (d, J = [7] a) H. M. El-Kaderi, M. J. Heeg, C. H. Winter, Organometallics
8
6
2004, 23, 4995; b) H. M. El-Kaderi, M. J. Heeg, C. H. Winter,
Polyhedron 2006, 25, 224; c) S. Nath, R. Tu, T. Goto, Surf.
Coat. Technol. 2010, 205, 2618; d) W. D. Buchanan, M. A. Gu-
ino-o, K. Ruhlandt-Senge, Inorg. Chem. 2010, 49, 7144; e)
W. D. Buchanan, M. A. Guino-o, K. Ruhlandt-Senge, Chem.
Eur. J. 2013, 19, 10708.
13
H), 6.96 (t, J = 7.8 Hz, 3 H) ppm. C NMR (C
00 MHz): δ = 22.3 (iPr-Me), 68.9 (iPr-CH), 107.2 (Ar-m), 126.3
Ar-p), 156.3 (C-Ca), 166.6 (Ar-o) ppm. C36 51CaKO (658.98): C
6 6 8
D /[D ]thf,
1
(
H
6
6
5.62, H 7.80; found C 65.47, H 7.99.
Na]
2 6 3 3
) and -1426807 (for {[(iPrO) C H ] Ca }K )
CCDC-1426805 (for [(iPrO)
O]CaI·THF}
2
C
6
H
3
4 2
), -1426806 (for {[(iPrO) -
[
8] a) T. P. Hanusa, Polyhedron 1990, 9, 1345; b) T. P. Hanusa,
Chem. Rev. 1993, 93, 1023; c) D. J. Burkey, T. P. Hanusa, Com-
ments Inorg. Chem. 1995, 17, 41; d) M. L. Hays, T. P. Hanusa,
Adv. Organomet. Chem. 1996, 40, 117; e) P. Jutzi, N. Burford,
Chem. Rev. 1999, 99, 969.
9] a) F. G. N. Cloke, P. B. Hitchcock, M. F. Lappert, G. A. Law-
less, B. Royo, J. Chem. Soc., Chem. Commun. 1991, 724; b)
C. Eaborn, S. A. Hawkes, P. B. Hitchcock, J. D. Smith, Chem.
Commun. 1997, 1961.
–
+
C
6
H
3
2
contain the supplementary crystallographic 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.
[
Acknowledgments
[
10] M. G. Harvey, T. P. Hanusa, V. G. Young Jr., Angew. Chem. Int.
D. Bläser and Prof. Dr. R. Boese are kindly acknowledged for part
of the X-ray data collection.
Ed. 1999, 38, 217; Angew. Chem. 1999, 111, 241.
[11] S. Harder, S. Müller, E. Hübner, Organometallics 2004, 23, 178.
Eur. J. Inorg. Chem. 2015, 5743–5750
5749
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[
[
12] a) A. Weeber, S. Harder, H.-H. Brintzinger, K. Knoll, Organo-
[30] [2-Me
2
N-C
6
H
4
Na·tmeda]
2
: D. R. Armstrong, L. Balloch, E.
metallics 2000, 19, 1325; b) K. Izod, P. G. Waddell, Organome-
tallics 2015, 34, 2726.
13] a) P. Jochmann, T. S. Dols, T. P. Spaniol, L. Perrin, L. Maron,
J. Okuda, Angew. Chem. Int. Ed. 2009, 48, 5715; Angew. Chem.
Hevia, A. R. Kennedy, R. E. Mulvey, C. T. O’Hara, S. D. Rob-
ertson, Beilstein J. Org. Chem. 2011, 7, 1234.
31] [2-CF -C H Na·tmeda] and [2-CF -C H Na·PMDTA] : J. A.
3 6 4 2 3 6 4 2
[
Garden, D. R. Armstrong, W. Clegg, J. García-Alvarez, E.
Hevia, A. R. Kennedy, R. E. Mulvey, S. D. Robertson, L.
Russo, Organometallics 2013, 32, 5481.
2
009, 121, 5825; b) P. Jochmann, T. S. Dols, T. P. Spaniol, L.
Perrin, L. Maron, J. Okuda, Angew. Chem. Int. Ed. 2010, 49,
795; Angew. Chem. 2010, 122, 7962; c) P. Jochmann, V. Leich,
[
[
[
[
32] C. Lambert, P. von Rague Schleyer, Angew. Chem. Int. Ed.
7
Engl. 1994, 33, 1129; Angew. Chem. 1994, 106, 1187.
T. P. Spaniol, J. Okuda, Chem. Eur. J. 2011, 17, 12115.
14] M. R. Crimmin, A. G. M. Barrett, M. S. Hill, D. J. MacDou-
gall, M. F. Mahon, P. A. Procopiou, Chem. Eur. J. 2008, 14,
33] R. D. Shannon, C. T. Prewitt, Acta Crystallogr., Sect. B 1969,
[
[
[
25, 925.
34] S. Harder, J. Boersma, L. Brandsma, J. A. Kanters, A. J. M.
Duisenberg, J. H. Van Lenthe, Organometallics 1991, 10, 1623.
35] G. R. Fulmer, A. J. M. Miller, N. H. Sherden, H. E. Gottlieb,
A. Nudelman, B. M. Stolz, J. E. Bercaw, K. I. Goldberg, Orga-
nometallics 2010, 29, 2176.
1
1292.
15] a) J. S. Alexander, K. Ruhlandt-Senge, Chem. Eur. J. 2004, 10,
274; b) M. A. Guino-o, A. Torvisco, W. Teng, K. Ruhlandt-
1
Senge, Inorg. Chim. Acta 2012, 389, 122.
16] a) S.-O. Hauber, F. Lissner, G. B. Deacon, M. Niemeyer, An-
gew. Chem. Int. Ed. 2005, 44, 5871; Angew. Chem. 2005, 117,
[36] a) P. C. Andrews, A. R. Kennedy, R. E. Mulvey, C. L. Raston,
B. A. Roberts, R. B. Rowlings, Angew. Chem. Int. Ed. 2000,
39, 1960; Angew. Chem. 2000, 112, 2036; b) A. J. Martínez-
Martínez, D. R. Armstrong, B. Conway, B. J. Fleming, J. Klett,
A. R. Kennedy, R. E. Mulvey, S. D. Robertson, C. T. O’Hara,
Chem. Sci. 2014, 5, 771.
6021; b) C. Ruspic, S. Harder, Organometallics 2005, 24, 5506;
c) R. Fischer, H. Görls, M. Westerhausen, Inorg. Chem. Com-
mun. 2005, 8, 1159.
[
17] a) D. Thoennes, E. Weiss, Chem. Ber. 1978, 111, 3157; b) A.
[
37] a) W. M. Boesveld, P. B. Hitchcock, M. F. Lappert, D.-S. Liu,
S. Tian, Organometallics 2000, 19, 4030; b) P. B. Hitchcock,
A. V. Khvostov, M. F. Lappert, J. Organomet. Chem. 2002, 663,
Domenicano, P. Murray-Rust, Tetrahedron Lett. 1979, 24,
2
283; c) S. Harder, P. F. Ekhart, L. Brandsma, J. A. Kanters,
A. J. M. Duisenberg, P. v. R. Schleyer, Organometallics 1992,
1, 2623; d) S. Harder, J. Boersma, L. Brandsma, A. van Het-
263; c) F. Antolini, P. B. Hitchcock, M. F. Lappert, X.-H. Wei,
1
Organometallics 2003, 22, 2505; d) W. Clegg, B. Conway, A. R.
Kennedy, J. Klett, R. E. Mulvey, L. Russo, Eur. J. Inorg. Chem.
eren, J. A. Kanters, W. Bauer, P. v. R. Schleyer, J. Am. Chem.
Soc. 1988, 110, 7802.
2011, 721; e) K. Yan, G. Schoendorff, B. M. Upton, A. Ellern,
[
[
18] R. E. Mulvey, V. L. Blair, W. Clegg, A. R. Kennedy, J. Klett,
L. Russo, Nature Chem. 2010, 2, 588.
19] R. Fischer, M. Gärtner, H. Görls, M. Westerhausen, Angew.
Chem. Int. Ed. 2006, 45, 609; Angew. Chem. 2006, 118, 624.
20] R. Fischer, M. Gärtner, H. Görls, M. Westerhausen, Organo-
metallics 2006, 25, 3496.
T. L. Windus, A. D. Sadow, Organometallics 2013, 32, 1300.
38] a) H. Viebrock, T. Panther, U. Behrens, E. Weiss, J. Organomet.
Chem. 1995, 491, 19; b) F. Feil, S. Harder, Organometallics
[
2001, 20, 4616; c) H. Schumann, D. M. M. Freckmann, S. De-
[
[
[
chert, Organometallics 2006, 25, 2696; d) D. R. Armstrong,
M. G. Davidson, D. Garcia-Vivo, A. R. Kennedy, R. E. Mul-
vey, S. D. Robertson, Inorg. Chem. 2013, 52, 12023.
21] M. Köhler, J. Langer, H. Görls, M. Westerhausen, Organome-
tallics 2014, 33, 6381.
[39] T. Kähler, F. Olbrich, private communication to the Cambridge
Structural Database (BADPOM).
[40] M. A. Guino-o, C. F. Campana, K. Ruhlandt-Senge, Chem.
Commun. 2008, 1692.
22] R. Fischer, M. Gärtner, H. Görls, L. Yu, M. Reiher, M. West-
erhausen, Angew. Chem. Int. Ed. 2007, 46, 1618; Angew. Chem.
2007, 119, 1642.
[
[
[
23] J. Langer, S. Krieck, H. Gorls, M. Westerhausen, Angew. Chem.
Int. Ed. 2009, 48, 5741; Angew. Chem. 2009, 121, 5851.
24] E. Ihara, Y. Adachi, H. Yasuda, H. Hashimoto, N. Kanehisa,
Y. Kai, J. Organomet. Chem. 1998, 569, 147.
25] a) G. Wittig, in: Neuere Methoden der Praparativen Organischen
Chemie, 4th ed. (Ed.: W. Foerst), Verlag Chemie, Weinheim,
Germany, 1963, vol. 1, p. 476; b) C. Ruspic, S. Harder, unpub-
lished results.
[41] a) R. E. Mulvey, Acc. Chem. Res. 2009, 42, 743; b) E. Hevia,
R. E. Mulvey, Angew. Chem. Int. Ed. 2011, 50, 6448; Angew.
Chem. 2011, 123, 6576; c) R. E. Mulvey, S. D. Robertson, Top.
Organomet. Chem. 2013, 45, 103; d) R. E. Mulvey, S. D. Rob-
ertson, Angew. Chem. Int. Ed. 2013, 52, 11470; Angew. Chem.
2013, 125, 11682; e) H. Ila, O. Baron, A. J. Wagner, P. Knochel,
Chem. Commun. 2006, 583; f) R. L.-Y. Bao, R. Zhao, L. Shi,
Chem. Commun. 2015, 51, 6884.
[26] R. den Besten, M. T. Lakin, N. Veldman, A. L. Spek, L.
[42] a) D. Seebach, R. Hilssig, J. Gabriel, Helv. Chim. Acta 1983,
66, 308; b) W. Bauer, W. R. Winchester, P. v. R. Schleyer, Orga-
nometallics 1987, 6, 2371.
Brandsma, J. Organomet. Chem. 1996, 514, 191.
[
[
27] M. Niemeyer, P. P. Power, Organometallics 1997, 16, 3258.
28] [2-tBuS-C
6
H
4
Na·tmeda]
2
: R. den Besten, L. Brandsma, A. L.
[43] F. M. Younis, S. Krieck, H. Görls, M. Westerhausen, Organo-
metallics 2015, 34, 3577.
Spek, private communication to the Cambridge Structural Da-
tabase (LEDQOA).
[44] A. M. Johns, S. C. Chmely, T. P. Hanusa, Inorg. Chem. 2009,
6 4 2
[29] [2-(N-Me-piperazinium)-C H Na·tmeda] : R. den Besten, L.
48, 1380.
Brandsma, A. L. Spek, private communication to the Cam-
bridge Structural Database (AFADIV).
[45] X. He, B. C. Noll, A. Beatty, R. E. Mulvey, K. W. Henderson,
J. Am. Chem. Soc. 2004, 126, 7444.
Received: October 15, 2015
Published Online: November 13, 2015
Eur. J. Inorg. Chem. 2015, 5743–5750
5750
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