Organic heterobimetallic complexes of the alkaline earth metals (Ae = Ca, Sr, Ba) with tetrahedral metallate anions of three-valent metals (M = B, Al, Ga, and V)

Article abstract of DOI:10.1039/c0nj00136h

Heterobimetallic compounds with complex cations of the very electropositive alkaline earth metals (Ae) and organic tetrahedral anions of trivalent elements (M) form solvent-separated ions. Depending on the metals, they can be prepared by addition of carbanions or amides to MR₃, via reduction of VMes₄ with the alkaline earth metals and by transmetallation of VMes₃. For comparison reasons selected alkali metal derivatives are also included in this study. Average structural parameters of the boranates [Ca(thf)₆][BPh₄]₂ (1) and [CaI(thf) ₅][BPh₄] (2), the alanates [Li(thf)₂(tmeda)] [AlPh₃(tmp)] (3), [(thf)₂K(N-carbazolyl) ₂AlMes₂] (4), and [Sr(thf)₇][AlPh ₄]₂ (5), of the gallate [Ca(dme)₄][GaEt ₃(N-carbazolyl)]₂ (6), and of the vanadates [Li(thf) ₄][VMes₄] (7), [CaI(thf)₅][VMes₄] (8), [Ca(thf)₆][VMes₄]₂ (9), and [Sr(thf) ₆][VMes₄]₂ (10), are discussed. All these complexes contain complex cations of the type [(L)_nM]⁺, and tetrahedral anions of the type [ER₄]^-. Only 4 crystallizes as a contact ion pair because the soft K⁺ cation shows no preference for hard bases such as ethers or for soft arene π-systems.

Full text of DOI:10.1039/c0nj00136h

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PAPER
www.rsc.org/njc | New Journal of Chemistry
Organic heterobimetallic complexes of the alkaline earth metals
(Ae = Ca, Sr, Ba) with tetrahedral metallate anions of three-valent
metals (M = B, Al, Ga, and V)wzy
a
a
b
c
a
¨
¨
Jens Langer, Sven Krieck, Helmar Gorls, Gunter Kreisel, Wolfgang Seidel and
Matthias Westerhausen*a
Received (in Victoria, Australia) 19th February 2010, Accepted 13th April 2010
DOI: 10.1039/c0nj00136h
Heterobimetallic compounds with complex cations of the very electropositive alkaline earth
metals (Ae) and organic tetrahedral anions of trivalent elements (M) form solvent-separated ions.
Depending on the metals, they can be prepared by addition of carbanions or amides to MR3, via
reduction of VMes4 with the alkaline earth metals and by transmetallation of VMes3. For
comparison reasons selected alkali metal derivatives are also included in this study. Average
structural parameters of the boranates [Ca(thf)6][BPh4]2 (1) and [CaI(thf)5][BPh4] (2), the alanates
[Li(thf)2(tmeda)][AlPh3(tmp)] (3), [(thf)2K(N-carbazolyl)2AlMes2] (4), and [Sr(thf)7][AlPh4]2 (5), of
the gallate [Ca(dme)4][GaEt3(N-carbazolyl)]2 (6), and of the vanadates [Li(thf)4][VMes4] (7),
[CaI(thf)5][VMes4] (8), [Ca(thf)6][VMes4]2 (9), and [Sr(thf)6][VMes4]2 (10), are discussed. All these
complexes contain complex cations of the type [(L)nM]+, and tetrahedral anions of the type
[ER4]ꢀ. Only 4 crystallizes as a contact ion pair because the soft K+ cation shows no preference
for hard bases such as ethers or for soft arene p-systems.
alkaline earth metals has been revived in this area.8–16 In
Introduction
contrast to the nearly uninvestigated organometallic ‘‘ate’’
chemistry of calcium and its heavier congeners, first structural
investigations of a magnesium alanate, Mg(AlMe4)2, were
published more than 40 years ago.17 The first structural
investigations of heterobimetallic organocalcium derivatives
were performed on [(Cp*)2Ca{m-Me3Al(thf)}].18 Recent
reinvestigations of calcium alkylalanates 19 showed their similarity
to the ytterbium derivatives (contact ions in [(phen)Ca(AlMe4)2]
The chemistry of heterobimetallic compounds represents a
vastly growing field because these compounds exhibit strongly
different properties and reactivity than their homoleptic
congeners. Therefore, metal metallates represent a substance
class with a long history.1 If the electronegativity of the
involved metals differs significantly the formation of ‘‘ate’’
complexes is observed and solvent-separated or contact ion
pairs are found. Often the s-block metals (alkali (A) and
alkaline earth metals (Ae))2,3 form the cation which can be
coordinated by neutral Lewis bases such as ethers or amines,
whereas the complex ‘‘ate’’ anions contain the nobler and
more electronegative metal. In the case of rather similar
electronegativities of the metals, the heterobimetallic complexes
often prefer the formation of molecular cage or ring
compounds. Despite the fact that the organometallic ‘‘ate’’
chemistry of the heavy alkaline earth metals, calcium, strontium,
and barium, has a long tradition and that early reviews have
already discussed their alanates,4 boranates and zincates,5–7
the development of an organometallic chemistry of the heavy
and polymeric [Ca(AlEt4)2]N) and their tendency to
degrade tetrahydrofuran leading to solvent-separated
{[(thf)4Ca(m-O-CH=CH2)] [AlMe4]}2. Mixed alkyl/aryl
alanates show redistribution reactions leading to solvent-
sepaꢀrated [Ca(thf)6][AlMe4ꢀxPhx]2.20 Boranates with the
BH4 anion of the heavier alkaline earth metals are well-
known.21 A partial substitution of the hydrogen atoms by
organyl groups leads to very reactive boranates such as e.g.
[CaCp0(HBEt3)(thf)2].22 Recent reinvestigations on calcium
tetraphenylboranates showed that these [BPh4]ꢀ units are
weakly coordinating anions which support the formation of
solvent-separated ions.23
Alkaline earth metal metallates of transition metals also
gained attention in the last few years. However, the late
transition metals copper and zinc form cuprates(I) and zincates(II)
with the anions, [CuR2]ꢀ with linear C–Cu–C units24,25
and [ZnR3]ꢀ with zinc atoms, in distorted trigonal planar
environments,2,3,26 respectively. A contact ion pair with a
distorted tetrahedrally coordinated transition metal was
reported for a calcium manganate(II).27 Metallates with
tetrahedrally coordinated metal centers are also known for
vanadium(III).28–30 These investigations showed that bulky
mesityl groups have to be employed in order to stabilize the
coordination number of four at vanadium. The smaller phenyl
a Institut fur Anorganische und Analytische Chemie,
¨
Friedrich-Schiller-Universita¨t Jena, August-Bebel-Str. 2,
D-07743 Jena, Germany. E-mail: m.we@uni-jena.de;
Fax: +49 3641 948102
b Institut fur Anorganische und Analytische Chemie,
¨
Friedrich-Schiller-Universitat Jena, Lessingstr. 8, D-07743 Jena,
¨
Germany
c Institut fur Technische Chemie und Umweltchemie,
Friedrich-Schiller-Universitat Jena, Lessingstr. 12, D-07743 Jena,
¨
¨
Germany
w In memoriam Professor Pascal Le Floch.
z This article is part of a themed issue on Main Group chemistry.
y CCDC reference numbers 765641–765650. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c0nj00136h
ꢁc
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substituents allow the synthesis of vanadates(II) with octa-
hedrally coordinated metal centers in [{Li(Et2O)}4VPh6].31,32
In order to isolate vanadates(III) with tetra-coordinate metal
atoms, larger aryl groups have to be bound at the V(III)
center. Thus, larger groups such as mesityl29,33 or
2,6-dimethoxyphenyl34 are suitable substituents. Heteroleptic
distorted tetrahedral vanadates with lithoxy,35–37 siloxy
groups38 and others39 are also feasible if the bulkiness of the
substituents enforces a coordination number of four. Tetra-
hedral vanadates(III) were isolated too, from the metathesis
reaction of [VCl3(thf)3] with LiC6Cl5, yielding [V(C6Cl5)4]ꢀ
anions,40 whereas the smaller pentafluorophenyl groups
form penta-coordinate vanadates(III) of the metal center in a
trigonal bipyramidal environment.41 Reduction of [V(Mes)3(thf)]
by sodium or potassium in the presence of nitrogen led to the
formation of [(diglyme)2Na][Na(Mes)3V–N2–V(Mes)3] and
[(diglyme)2K][(Mes)3V–N2–V(Mes)3], respectively.42,43
results in immediate precipitation of [Ca(thf)6][BPh4]2 (1)
besides minor amounts of silver. Stepwise cooling of the
mother liquor to ꢀ40 1C led to further crops of 1. A silver-
containing product of the reaction could not be isolated,
precipitation of AgI did not occur. When the mother liquor
of the reaction was further concentrated at low temperatures,
a yellow-orange oil was obtained which did not crystallize even
at ꢀ78 1C. It can be assumed that this residue contains
organometallic silver complexes. Slow warm-up of this residue
to room temperature led to decolorization and subsequent
precipitation of metallic silver in agreement with the thermal
lability of such organometallic silver compounds. Additionally,
colorless crystals of [CaI(thf)5][BPh4] (2) were deposited
during this process. The analytical data obtained for 2 are in
good agreement with related derivatives and therefore need no
further discussion (see experimental section).
In the case of the higher homologue aluminium, the use of
silver salts is not promising for the preparation of organo-
metallic alkaline earth metal alanates, since the higher arylating
power of organometallic aluminium compounds, in comparison
with their borane analogs, would probably lead to labile
argentates instead. However, other redox reactions like that
of alanes and alkaline earth metals offer a suitable access
to heterobimetallic alanates like Ca(AlEt4)2.45,46 Tetraaryl-
substituted derivatives can be prepared by reaction of Al(aryl)3
and the corresponding arylalkaline earth metal derivatives as
reported for calcium.20
Following our previous investigation,47 the synthesis of
further amido-substituted organoalanates was attempted. Besides
group transfer reactions from calcium amides to alanes, the
metathesis reaction of calcium halides and alkali metal alanates
might offer a suitable pathway to such compounds. The
starting materials [Li(thf)2(tmeda)][AlPh3(tmp)] (3) (tmp =
tetramethypiperidide) and [(thf)2K(N-carbazolyl)2AlMes2] (4)
were prepared in good yields from [(Et2O)AlPh3] or
[(Et2O)AlCl(Mes)2] and the corresponding alkali metal amides
(see eqn (1) and (2)).
In order to explore heterobimetallic complexes of the heavy
alkaline earth metals with tetrahedrally coordinated metallate
anions we have chosen the lighter elements of the boron group
as well as vanadium. The Allred–Rochow electronegativity
values of these elements (B: 2.01, Al: 1.47, Ga: 1.82, and V:
1.45) are significantly larger than the values of the heavier
alkaline earth metals (Ca: 1.04, Sr: 0.99, and Ba: 0.97);
therefore, solvent-separated alkaline earth metal metallates
can be expected for tetraarylmetallates of these elements.
Recent developments in the field of heavy Grignard
reagents, in particular of aryl alkaline earth metal halides,
paved the way for the synthesis of heterobimetallic
organylalanates, zincates, and cuprates of the heavy alkaline
earth metals. Extending these previous investigations, we
herein extend this interesting chemistry to other trivalent
metallates of boron, gallium, and vanadium.
Results and discussion
Synthesis and characterization
LiðtmpÞ þ ðEt2OÞAlPh3
THF=toluene
ꢀ
Due to the higher stability of the BPh4 anion in comparison
ð1Þ
to the corresponding alanate, alkaline earth metal tetraphenyl-
boranates are easier to handle than their higher homologues.
Different synthetic procedures have been developed to synthesize
derivatives of Ca, Sr and Ba. Harder et al. reported the
preparation of [{CaBr(thf)4}2][BPh4]2 by metathesis reaction
of [CaBr2(thf)4] and NaBPh4.44 Recently, Ruhlandt-Senge and
co-workers developed an alternative approach via a trans-
amination reaction between M[N(SiMe3)2]2 and [HNR3][BPh4].23
Several tetraphenylboranates of Ca, Sr and Ba were prepared
in this manner in the presence of additional neutral donors.
Inspired by recent advances in the synthesis of calcium
organocuprates via transmetallation reactions, where the
reduction of organocopper compounds by metallic calcium
is the initial step,24,25 an alternative route to alkaline earth
metal boranates by reduction of Ag[BPh4] was envisioned.
Although the reaction of the activated metal powders of Ca, Sr
and especially Ba took place smoothly and silver was deposited,
we were not able to isolate well defined alkaline earth metal
boranates from these reaction solutions in THF. However, an
alternative reaction of Ag[BPh4] and [CaI(Tolyl)(thf)4] at 0 1C
ꢀ! ½ðthfÞ2ðtmedaÞLiꢂþ½Ph3AlðtmpÞꢂꢀ
tmeda
2KðN-carbazolylÞ þ ðEt2OÞAlMes2Cl
THF=Et2O
ꢀ! ½ðthfÞ2K-Z6ðN-carbazolylÞ2AlMes2ꢂ ð2Þ
ꢀKCl
However, metathesis reaction of 3 with calcium iodide results
in a complicated reaction mixture and no well defined reaction
product was obtained. Similar results were obtained from the
reaction of 4 and calcium iodide. Although precipitation of
potassium iodide occurred, the isolation of a pure product
failed. On the one hand, this behaviour is most likely
associated to the well known redistribution reactions of
substituents in alanates.20 On the other hand, the multihapto
coordination mode of potassium with the mesityl groups by
p-arene–metal interactions in 4 additionally stabilizes the
complex and hampers an effective metathesis reaction. Due
to these unsatisfying results observed in the case of calcium,
only the synthesis of homoleptic tetraaryl alanates via aryl
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group transfer was envisioned for the heavier alkaline earth
metals strontium and barium.
agreement with the literature where the chemistry of the
species of type [Ga(Ar)4]ꢀ is nearly exclusively limited to the
[Ga(C6F5)4]ꢀ anion.54–57 Mes3Ga is an exceedingly weak
Lewis acid and there are no stable adducts known with Lewis
bases such as THF or Et2O. In contrast to the aluminium-
triorganyls (which form Lewis acid–base adducts immediately),
the considerably reduced Lewis acidity of Ga(aryl)3 results in a
nearly trigonal planar arrangement around the gallium center
with the mesityl groups in a propeller-like arrangement.58,59 In
order to demonstrate that the group transfer from calcium
to an organometallic gallium species represents a suitable
procedure for the synthesis of calcium gallates, we varied the
substituents at calcium as well as at gallium. Hence, the
addition reaction of triethylgallane and [Ca(dme)2(NPh2)2]
yielded the organometallic derivative of the formula
[Ca(dme)4][GaEt3(N-carbazolyl)]2 (6) (eqn (4)). Compound 6
was formed during a period of two weeks by successive
precipitation of a white solid, which was completely insoluble
in common organic solvents. The diphenylamido group was
dehydrogenated by oxidative C–H bond functionalization,
resulting in cyclization and formation of the carbazolyl
moiety. This type of reaction normally occurs by treatment of
palladium acetate under reflux or microwave irradiation.60 NMR
spectroscopic investigations indicate the presence of only one
species and there are no signs of ligand redistribution equilibria
in contrast to the observations for alanate ions [AlMe4ꢀxPhx]ꢀ in
solution. Interestingly, a similar reaction, which was carried out
with triethylalane instead of triethylgallane, does not lead to a
comparable ring closure in NMR experiments; instead, solely the
expected addition reaction was observed.
Unfortunately, the organometallic chemistry of strontium
and barium is still underdeveloped in comparison to the
organocalcium chemistry. For instance, there are only a few
structurally characterized aryl derivatives of strontium and
barium known. The first were synthesized by Niemeyer and
co-workers via aryl transfer from mercury to the heavier
alkaline earth metals.48
Although a Grignard-type reaction of those metals and aryl
halides (especially iodides) is possible too, an active Schlenk
equilibrium in combination with an altered reactivity in
solvent degradation reactions has prevented the isolation of
simple aryl derivatives of strontium and barium thus far.
However, the recent isolation of such solvent degradation
products, which contained residual phenyl groups, underlined
the initial formation of arylstrontium and arylbarium halides in
these reactions.49 The high alkalinity of the reaction solutions
additionally indicates that the lack of aryl derivatives of strontium
and barium is more related to problems of isolation but not
formation of these derivatives.50 Following this assumption,
such solutions should be useful as synthetic equivalents for
isolated organostrontium or organobarium derivatives.
Consequently, the reaction of a solution, obtained from
activated strontium and iodobenzene in THF, and AlPh3,
resulted in formation of the expected strontium tetraphenyl-
alanate (5) which was isolated in good yield (see eqn (3)).
THF
fð thfÞ SrPh2gþ2ðEt OÞAlPh3 ꢀ! ½ðthfÞ7Srꢂ2þ2½Ph4Alꢂꢀ
x
2
ð3Þ
The 27Al-NMR experiment clearly shows the presence of the
solvent-separated and highly symmetrical alanate species in
the characteristic field range for tetracoordinated aluminium
atoms (125–180 ppm). The tetrahedral environment is
reflected in the 27Al shift of 132.9 ppm and a small half-height
width of 23 Hz ([CaI(thf)5][AlPh4]2: 132.9 ppm).20 The
linewidth increases markedly with the bulkiness of the ligands
and the resulting distortion of the geometry of the complex.51
Compounds 3 and 4 show half-height widths of more than
4000 Hz for 3 and of 3848 Hz for 4, and lie in the region for
comparable systems such as [AlEt2(NEt2)] (1220 Hz)52 and
[AlPh3(tmeda)] (3900 Hz).53
2ðdmeÞ2CaðNPh2Þ2 þ 2GaEt3
toluene
ꢀ! ½ðdmeÞ4Caꢂ2 þ2½Et3GaðN-carbazolylÞꢂꢀ ð4Þ
ꢀ}CaH2}
ꢀ2}Ph2NH}
With vanadium, a transition metal is included, which resembles
gallium with respect to its ion radius, while its electronegativity
is more similar to aluminium (Al 1.47, V 1.45, Ga 1.82; Allred-
Rochow). In contrast to gallium, tetramesityl vanadates are well
known. A look at the alkali metal derivatives guides the way to
the related chemistry of the alkaline earth metals. Besides the
transmetallation reaction of LiMes and [VMes3(thf)], the
reaction of alkali metals with [VMes3(thf)] is suitable to
generate such alkali metal tetramesityl vanadates.28 This
chemistry has been well known for decades and [Li(thf)4]-
[VMes4] (7) was originally prepared from LiMes and VMes3.
Here we present the crystal structure of [Li(thf)4][VMes4] (7).
The same strategy as used for the lithium compound
allowed the preparation of the calcium derivative too.
However, the reaction between [CaI(Mes)(thf)4] and [VMes3(thf)]
is challenging because the high reactivity of the mesitylcalcium
derivative promotes solvent degradation and rearrangement
reactions.61 These side reactions led to a product mixture from
which pure [CaI(thf)5][VMes4] (8) was obtained via fractional
crystallization in low yield. The violet crystals are extremely
air-sensitive and react upon exposure to air, as observed for
the lithium derivative, to red VMes4 as the major vanadium-
containing species.62 Alternatively, the reaction of metallic
calcium and [VMes3(thf)] yields small amounts of
Attempts to isolate a corresponding barium alanate failed
due to the extreme reactivity of the arylbarium species in ether,
leading to degradation reactions, and the high solubility of
organobarium species.49
Besides alanes, the corresponding gallanes were also
included in this investigation. In order to obtain a similar
geometry around the group 13 metal center, the mesityl
derivative Mes3Ga was chosen as a starting material instead
of Ph3Ga to compensate for the growing ionic radius from
aluminium (53 pm) to gallium (61 pm). In contrast to their
lighter homologues, no well defined gallanates of the heavier
alkaline earth metals were isolated from the reaction of
Mes3Ga with [Ae(aryl)I] (aryl = Ph, Mes; M = Ca, Sr, Ba).
Instead, depending on the reaction conditions employed,
amorphous powders or oils containing several unidentified
products were obtained. This unsatisfying finding is in
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[Ca(thf)6][VMes4]2 (9). The stabilization and isolation of low-
valent vanadium species formed in the course of the reaction,
as postulated for the related reaction of potassium and
[VMes3(thf)],28 was attempted by addition of cyclo-
octadiene, but failed. In light of the previous results, an
alternative strategy to alkaline earth metal tetraarylvanadates
seems highly desirable. The vanadium(IV) compound [VMes4]
is a promising starting material. Therefore, the reversal of
its formation by oxidation of tetramesityl vanadates was
investigated. Highly divided metal powders of the heavier
alkaline earth metals, calcium, strontium and barium, were
employed as reducing agents in THF. While the reaction
proceeded smoothly for barium, in the case of strontium much
longer reaction times were necessary. Even after two days,
only about one fifth of the starting material was consumed.
However, the separation of the product and the educts is
simple (see experimental section) and pure {[Sr(thf)6][VMes4]2}
(10) was obtained. In the case of calcium no reaction at all was
observed. These differences in reactivity seem to be not only
related to their reducing power, but also to the affinity of those
metals or their cations to aromatic p-systems. Probably, the
side-on coordination of metal species to the mesityl group is
an important step in the reduction of the highly shielded
vanadium(IV) center in V(aryl)4. Some additional evidence
for this hypothesis is provided by the reaction of barium with
VMes4. While the reaction solution in THF showed the typical
dark violet color of the [VMes4]ꢀ anion, precipitation of the
product with diethyl ether yielded a green solid. This color
change might be related to a coordination of the barium cation
to the mesityl groups under formation of a contact ion pair in the
solid state. In addition, the reduction can also be performed in
toluene, leading to a similar green product. If the compound is
dissolved in donor solvents such as THF or 1,2-dimethoxyethane
(DME), the dark violet color reappears and solvent-separated
ions of [Ba(dme)5][VMes4]2ꢃnDME are formed.
Fig.
2
Molecular structure and numbering scheme of
[CaI(thf)5][BPh4] (2). Selected bond lengths (pm): Ca1–I1 306.60(7),
Ca1–O1 234.3(2), Ca1–O2 234.4(2), Ca1–O3 233.9(2), Ca1–O4
238.3(2), Ca1–O5 236.4(3), B1–C21 164.2(5), B1–C 27 164.2(5),
B1–C33 164.8(5), B1–C39 165.0(5). Angles (deg.): C21–B1–C27
107.4(3), C21–B1–C33 109.2(3), C21–B1–C39 110.4(3), C27–B1–C33
110.4(3), C27–B1–C39 111.0(3), C33–B1–C39 108.4(3).
Fig. 3 Molecular structure and numbering scheme of [Li(thf)2(tmeda)]-
[AlPh3(tmp)] (3). Selected bond lengths (pm): Li1–O1 193.2(9), Li1–O2
194.0(9), Li1–N2 209.2(9), Li1–N3 208.0(9), Al1–N1 189.1(3), Al1–C10
203.4(4), Al1–C16 201.5(4), Al1–C22 202.0(4). Angles (deg.): N1–Al1–C10
115.4(2), N1–Al1–C16 116.7(2), N1–Al1–C22 108.4(2), C10–Al1–C16
100.7(2), C10–Al1–C22 108.1(2), C16–Al1–C22 106.8(2).
Structural investigations
The compounds 1 to 10 are displayed in Fig. 1–10. In all these
representations the ellipsoids show a probability level of 40%
and the hydrogen atoms are neglected for clarity. Average
values of selected structural parameters are listed in Table 1.
Most of these molecules consist of solvent-separated ions
and have tetrahedral anions in common. Due to the fact that
cations as well as anions can be considered as large soft ball-
shaped ions, we do not expect to find short intermolecular
distances. The contact ion pair [(thf)2K(N-carbazolyl)2AlMes2]
(4) represents the only exception. The hardness and softness of
metal cations can be judged on the basis of the radius r(Mn+
)
of the cation and the charge n. The absolute hardness, based
on ionization potential and electron affinity,63–66 of the relevant
alkali (Li+ 35.12, Na+ 21.08, K+ 13.64) and alkaline earth
metal cations (Ca2+ 19.52, Sr2+ 16.3, Ba2+ 12.8) increases
with the charge, and decreases with the size. Hard Lewis acids
favour the coordination of hard bases such as ethers and
amines, whereas soft cations prefer soft bases such as aryl
p-systems. The cations Ca2+ and Na+ show a rather similar
Fig.
1 Molecular structure and numbering scheme of
[Ca(thf)6][BPh4]2 (1). Symmetry-related atoms (ꢀx + 1, ꢀy, ꢀz + 1)
are marked with an ‘‘A’’; the symmetry-related [BPh4ꢀ] anion is
omitted for clarity. Selected bond lengths (pm): Ca1–O1 234.2(3),
Ca1–O2 232.5(3), Ca1–O3 234.1(3), B1–C13 164.7(6), B1–C19
165.9(6), B1–C25 165.2(6), B1–C31 164.1(6). Angles (deg.):
C13–B1–C19 110.5(3), C13–B1–C25 107.7(3), C13–B1–C31 109.9(3),
C19–B1–C25 109.8(3), C19–B1–C31 108.6(3), C25–B1–C31 110.3(3).
hardness, while the softer K+ cation is comparable to Ba2+
The latter also show rather similar radii (K+: 152 pm, Ba2+
.
:
149 pm),67 but due to a larger charge of the alkaline earth
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Fig. 6 Molecular structure and numbering scheme of [Ca(dme)4]-
[GaEt3(carbazolyl)]2 (6). The anions are distinguished by the letters
‘‘A’’ and ‘‘B’’. Selected bond lengths (pm): Ca1–O1 247.3(3), Ca1–O2
244.2(4), Ca1–O3 249.9(4), Ca1–O4 248.2(4), Ca1–O5 247.2(3),
Ca1–O6 249.5(4), Ca1–O7 243.6(4), Ca1–O8 242.3(4), Ga1A–N1A
201.3(4), Ga1A-C13A 200.9(6), Ga1A-C15A 200.4(6), Ga1A-C17A
201.4(6), Ga1B-N1B 203.9(5), Ga1B-C13B 201.6(6), Ga1B-C15B
200.2(6), Ga1B-C17B 200.1(7).
Fig. 4 Molecular structure and numbering scheme of (4). The
asymmetric unit contains two molecules [(Et2O)(thf)2K(N-carbazolyl)2-
AlMes2] (4A) and [(thf)2K(N-carbazolyl)2AlMes2] (4B). Selected
bond lengths (pm): K1A–O1A 273.1(4), K1A–O2A 274.0(4),
K1A–O3A 279.7(6), K1B–O1B 268.2(4), K1B–O2B 262.4(5),
Al1A–N1A 192.0(4), Al1A–N2A 191.6(4), Al1A–C25A 202.7(4),
Al1A–C 34A 201.9(4), Al1B–N1B 191.8(4), Al1B–N2B 193.0(5),
Al1B–C 25B 202.4(5), Al1B–C34B 202.2(5). Angles (deg.): N1A–
Al1A–N2A 95.7(2), N1B–Al1B–N2B 96.2(2).
Fig.
7 Molecular structure and numbering scheme of
[Li(thf)4][VMes4] (7). Selected bond lengths (pm): Li1–O1 191.5(6),
Li1–O2 194.0(6), Li1–O3 192.9(6), Li1–O4 192.8(6), V–C1 214.5(3),
V–C10 214.8(3), V–C19 215.2(3), V–C28 214.5(3). Angles (deg.):
C1–V–C10 117.0(1), C1–V–C19 115.3(1), C1–V–C28 96.8(1),
C10–V–C19 96.7(1), C10–V–C28 115.4(1), C19–V–C28 117.1(1).
Fig.
5 Molecular structure and numbering scheme of
[Sr(thf)7][AlPh4]2 (5). Selected bond lengths (pm): Sr1–O1 257.7(3),
Sr1–O2 255.7(3), Sr1–O3 255.6(3), Sr1–O4 257.6(3), Sr1–O5 256.1(3),
Sr1–O6 254.8(3), Sr1–O7 258.4(3), Al1–C1 201.0(4), Al1–C7 200.3(4),
Al1–C13 202.5(4), Al1–C19 199.8(4), Al2–C25 200.6(4), Al2–C31
199.8(5), Al2–C37 200.8(4), Al2–C43 201.3(5).
Fig.
8 Molecular structure and numbering scheme of
[CaI(thf)5][VMes4] (8). Selected bond lengths (pm): Ca–I 302.86(9),
Ca–O1 240.1(3), Ca–O2 233.7(3), Ca–O3 234.5(3), Ca–O4 235.3(3),
Ca–O5 234.4(3), V–C21 215.4(4), V–C30 215.3(3), V–C39 215.2(3),
V–C48 213.4(4). Angles (deg.): C21–V–C30 97.7(1), C21–V–C39
115.6(1), C21–V–C48 115.8(1), C30–V–C39 115.0(1), C30–V–C48
116.0(1), C39–V–C48 97.9(1).
metal cation the preference of soft arene bases is less pronounced.
The tetraphenylboranate (1, 2) and tetraphenylalanate (5)
anions show only small distortions of the tetrahedral geometry,
whereas the substitution of one phenyl group by a bulky
tetramethylpiperidino moiety in 3 enhances steric strain,
ꢁc
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and four large C–E–C angles is approx. 201 and is observed for
the vanadates 8 to 11. Such distortions are characteristic for
tetrahedrons which are compressed along a C2 axis. A direct
comparison with the phenyl derivative is not possible because
the smaller phenyl group leads to the formation of vanadate
anions with larger coordination numbers (see above). In 4 the
steric pressure is induced by the bulky mesityl groups, the
amino units and the coordination of the carbazolyl p-systems
to potassium, leading to a rather small N1–Al–N2 angle of
approx. 961. It is also noteworthy that the Al–C and Ga–C
bond lengths show very similar values due to the d-block
contraction of the radii, but the Ga–N distance to a carbazolyl
group in 6 is approx 10 pm larger than the Al–N values in 3
and 4. This fact can be attributed to the bulkiness of the
attached organyl substituents (ethyl at Ga, less demanding
phenyl at Al) and to their inductive effects (alkyl: +I, aryl: ꢀI
effect). Despite a similar size of Al and Ga, the gallium atom
contains many more electrons which should enhance the
repulsion to anions. Therefore this effect strongly influences
substituents with strongly electrovalent (ionic) bonds, whereas
this effect is much smaller for covalently bound organyl
groups.
Fig. 9 Molecular structure and numbering scheme of [Ca(thf)6]-
[VMes4]2 (9). Symmetry-related atoms (ꢀx + 1, ꢀy + 1, ꢀz + 2)
are marked with an ‘‘A’’. The second symmetry-related anion is not
shown for clarity. Selected bond lengths (pm): Ca–O1 234.4(2), Ca–O2
233.1(2), Ca–O3 237.7(2), V–C1 214.1(3), V–C10 215.3(3), V–C19
214.3(3), V–C28 214.2(3). Angles (deg.): C1–V–C10 114.8(1),
C1–V–C19 118.2(1), C1–V–C28 97.3(1), C10–V–C19 97.0(1),
C10–V–C28 117.7(1), C19–V–C28 113.2(1).
The metal atoms are enwrapped by Lewis bases leading to
sterically saturated cations. The coordination numbers
strongly depend on the size of the metal and of the bulkiness
of the Lewis bases. Tetra-coordinate lithium cations are very
common68,69 and are also found in 3.
The heavy alkaline earth metal cations tend to enhance the
coordination numbers as far as possible. Tetrahydrofuran
molecules stabilize hexa-coordinate calcium cations leading
to [(thf)6Ca]2+ as in 1 and 9 or to [(thf)5CaI]+ as in 2 and 8.
Slightly larger strontium cations allow both, hexa- and hepta-
coordination as observed for [(thf)6Sr]2+ in 10 and for
[(thf)7Sr]2+ in 5. The compounds 9 and 10 show isomorphous
solid state structures with the alkaline earth metals lying on
inversion centers. The bidentate 1,2-dimethoxyethane molecules
even enable an octa-coordinate calcium atom in [(dme)4Ca]2+
(6). In compound 4 potassium binds to two carbazolyl
p-systems and to two THF molecules showing that hard and
soft Lewis bases are accepted in nearly equal measure. The
flexibility is even shown from the two different molecules 4A
and 4B with an additional diethyl ether ligand in molecule A.
Fig. 10 Molecular structure and numbering scheme of
[Sr(thf)6][VMes4]2 (10). Symmetry-related atoms (ꢀx + 1, ꢀy + 1,
ꢀz + 2) are marked with an ‘‘A’’. The second symmetry-related anion
is not shown for clarity. Selected bond lengths (pm): Sr–O1 249.3(4),
Sr–O2 247.6(3), Sr–O3 252.8(4), V–C1 214.7(5), V–C10 214.8(5),
V–C19 213.3(5), V–C28 215.9(5). Angles (deg.): C1–V–C10 115.2(2),
C1–V–C19 118.2(2), C1–V–C28 96.9(2), C10–V–C19 97.0(2),
C10–V–C28 117.6(2), C19–V–C28 113.5(2).
leading to a broader variation of the C–Al–C angles.
Enhancement of steric pressure by substitution of the phenyl
groups by mesityl substituents leads to severe distortions of the
tetrahedral geometry. The difference between the two small
Table 1 Comparison of average structural parameters of solvent-separated [Ca(thf)6][BPh4]2 (1), [CaI(thf)5][BPh4] (2), [Li(thf)2(tmeda)][AlPh3(tmp)] (3),
[(thf)2K(N-carbazolyl)2AlMes2] (4), [Sr(thf)7][AlPh4]2 (5), [Ca(dme)4][GaEt3(carbazolyl)]2 (6), [Li(thf)4][VMes4] (7), [CaI(thf)5][VMes4] (8),
[Ca(thf)6][VMes4]2 (9), and [Sr(thf)6][VMes4]2 (10) with complex cations of the type [(L)nM]+ and tetrahedral anions of the type [ER4]ꢀ. [Bond lengths
(pm) and angles (1)].
1
2
3
4
5
6
7
8
9
10
M
C. No.a
E
Ca
6
B
Ca
6
B
Li
4
Al
K
Sr
7
Al
Ca
8
Ga
Li
4
V
Ca
6
V
Ca
6
V
Sr
6
V
4b
Al
M–O
M–N
M–I
E–C
E–N
C–E–C
C–E–Cmin
C–E–Cmax
233.6
—
—
165.0
—
109.5
107.7
110.5
235.5
—
306.6
164.6
—
109.5
107.4
111.0
193.6
208.6
—
202.3
189.1
109.4
100.7
116.7
275.6
—
0
202.3
191.8
109.5
95.7
114.3
256.6
—
—
200.9
—
109.5
107.3
112.2
246.5
—
—
200.8
202.6
109.4
102.5
116.1
192.8
—
—
214.8
—
109.7
96.7
117.1
235.6
—
302.9
214.8
—
109.7
97.7
116.0
235.1
—
—
214.5
—
109.7
97.0
118.2
249.9
—
—
214.7
—
109.7
96.9
118.2
a
b
Coordination number of the metal atom M. K binds to two THF molecules and side-on to two arene p-systems.
ꢁc
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3
3.62 (20H, m, CH2O, THF), 6.72 (4H, t, JHꢀH = 7.2 Hz,
Experimental section
3
p-H), 6.85 (8H, t, JHꢀH = 7.2 Hz, m-H), 7.26 (8H, m, o-H).
13C{1H} NMR (100.65 MHz, 25 1C, [D8]THF): d 26.3 (10C,
CH2, THF), 68.1 (10C, CH2O, THF), 121.7 (8C, m-C), 125.6
General
All manipulations were carried out in an argon atmosphere
under anaerobic conditions. Prior to use, all solvents were
thoroughly dried and distilled in an argon atmosphere. The
reported compounds (except 1 and 2) are extremely moisture-
and air-sensitive. In many cases it was not possible to weigh
out a definite amount because the weight of the substances
changed permanently during handling and weighing. There-
fore, the analysis is often limited to NMR and X-ray structure
determinations. 1H NMR and 13C NMR spectra were
recorded at [D8]THF solutions at ambient temperature on a
Bruker AC 200 MHz or a Bruker AC 400 MHz spectrometer.
All spectra were referenced to deuterated THF as an internal
standard. DEI-mass spectra were obtained on a Finnigan
MAT SSQ 710 system (2,4-(dimethoxy)benzyl alcohol as
matrix), IR measurements were carried out on a Perkin Elmer
System 2000 FT-IR. Decomposition points were measured
with a Reichert–Jung apparatus Type 302102. The aluminium
contents were determined by complexometric titration (0.05 M
EDTA, indicator Eriochrome Black T) of a hydrolysed aliquot
after treatment with HNO3. In the case of 5, strontium was
removed by precipitation as SrSO4 before titration.
1
(4C, p-C), 137.0 (8C, o-C), 165.1 (4C, q, JCꢀB = 49.3 Hz,
i-C). MS (FAB-, m/z, [%]): 320 (BPh4ꢀ + 1) [100]. IR (Nujol,
cmꢀ1) n: 1946, m; 1882, m; 1823, m; 1765, w; 1625, m; 1579, s;
1345, s, 1295, s; 1247, s; 1178, s; 1134, s; 1018, s (br); 915, s;
864, s (br); 734, s; 708, s; 667, s; 610, s.
Suitable crystals of 1 and 2 were obtained directly from the
reaction mixtures.
Synthesis of [Li(thf)2(tmeda)][Ph3Al(tmp)] (3)
A solution of Li(tmp) (14 mL, 2.98 mmol, 0.213 M) in toluene
was dropped into
a solution of (Et2O)AlPh3 (0.99 g,
2.98 mmol) in THF (5 mL) at ꢀ78 1C. After stirring for 2 h
at room temperature a yellow solid had formed which was
separated and redissolved in a mixture of THF (4 mL) and
tmeda (2 mL). Reduction of one quarter of the volume,
filtration and storage at ꢀ20 1C led to crystallization of
colourless crystals. Separation and gently drying in vacuum
gave 1.84 g (2.78 mmol, 93%) of 3.
Physical data for 3. Decomposition above 32 1C. Anal. Calc.
for C41H65AlLiN3O2 (665.92 g molꢀ1): C, 73.89; H, 9.83; N,
6.31. Found: C, 73.53; H, 9.71; N, 6.40. 1H NMR
(200.25 MHz, 25 1C, [D8]THF): d 1.12 (12H, s, CH3, tmp),
1.33 (4H, t, CH2, tmp), 1.65 (2H, m, CH2, tmp) 1.72 (8H, m,
CH2, THF), 2.28 (12H, s, CH3, tmeda), 2.40 (4H, s, CH2,
tmeda), 3.65 (8H, m, CH2O, THF), 7.22 (9H, m, p,m,m0-H),
7.78 (6H, o,o0-H). 13C{1H} NMR (50.32 MHz, 25 1C,
[D8]THF): d 18.2 (1C, CH2, tmp), 25.6 (4C, CH2, THF),
31.5 (4C, CH3, tmp), 38.6 (2C, CH2, tmp), 18.2 (1C, CH2,
tmp), 45.0 (2C, CH3, tmeda), 45.2 (2C, CH3, tmeda), 49.0 (2C,
C(CH3)2, tmp), 57.3 (2C, CH2, tmeda), 67.9 (4C, CH2O,
THF), 124.5 (6C, m,m0-C), 126.9 (3C, p-C), 139.6 (6C,
o,o0-C), 139.9 (3C, i-C). 27Al NMR (104.28 MHz, 25 1C,
[D8]THF): very broad (w1/2 4 4000 Hz). IR (Nujol, cmꢀ1) n:
2371, m; 1878, w; 1846, w; 1803, w; 1763, w; 1735, w; 1696, m,
1686, m; 1664, m; 1648; m, 1593; m, 1593, s; 1571, m; 1303, s;
1165, s; 1074, m; 1033, m; 973, m; 917, m; 889, m; 674, m;
611, m.
The starting materials [CaI(Ph)(thf)4],70 [AlPh3(Et2O)],20
[AlPh3(thf)],20 GaEt3,71 [Ca(dme)2(NPh2)2],72 [AlCl(Et2O)-
Mes2],73 Li(tmp),74 K(N-carbozolyl),75 [VMes3(thf)],76
62
[Li(thf)4][VMes4]28 and VMes4 were prepared according to
known literature procedures. For activation the alkaline earth
metals were dissolved in liquid ammonia and immediately
thereafter the ammonia was removed in vacuo in order to
avoid amide formation.70
Synthesis of [Ca(thf)6][BPh4]2ꢃ2THF (1) and [CaI(thf)5][BPh4]
(2)
Light was excluded by wrapping the apparatus in aluminium
foil throughout preparation. Solid, freshly prepared AgBPh4
(0.5 g, 1.17 mmol) was added to a rapidly stirred solution of
[CaI(Tolyl)(thf)4] in THF (14 mL, 0.075 M) at 0 1C. The
reaction mixture was stirred for 1 h at 0 1C and formed a
brownish solid, consistent with 1, and a small amount of
elemental silver was collected by filtration afterwards
(290 mg). Further crystalline crops of 1 were obtained by
stepwise cooling of the orange coloured mother liquor to
ꢀ20 1C, and finally to ꢀ40 1C overnight. The supernatant
solution was decanted and stored at ꢀ78 1C, but no further
crystallization occurred at this temperature within one week.
Therefore, the remaining reaction mixture was allowed to
slowly warm to room temperature over a period of 24 h and
kept at this temperature for another day. During this
procedure the original yellow-orange colour of the solution
faded and elemental silver formed in addition to colourless
crystals of 2. These crystals were isolated by decantation and
dried in a vacuum. Yield: 230 mg (0.27 mmol, 26%) of 2
(slightly contaminated by elemental silver).
Synthesis of [(thf)2K(N-carbazolyl)2AlMes2] (4)
Solid (Et2O)Mes2AlCl (1.20 g, 3.10 mmol) was dissolved in
diethyl ether (20 mL) and a solution of K(carbazolyl)
(11.48 mL, 6.20 mmol, 0.54 M) in THF was added dropwise
at ꢀ25 1C. The mixture was stirred at ambient temperature for
12 h. After filtration the pale yellow solution was stored at
ꢀ20 1C to obtain colourless crystals. Filtration, washing with
a few millilitres of cold n-pentane and drying in vacuum
resulted in loss of coordinated diethyl ether and yielded 4
(2.15 g, 2.75 mmol, 88.7%).
Physical data for 4. Decomposition above 145 1C. Anal.
Calc. for C50H54AlK2N2O2 (781.06 g molꢀ1): Al, 3.45 Found:
Al, 3.36. 1H NMR (400.25 MHz, 25 1C, [D8]THF): d 1.73 (8H,
m, CH2, THF), 2.13 (6H, s, p-CH3, mes), 2.33 (12H, s,
o,o0-CH3, mes), 3.59 (8H, m, CH2O, THF), 6.60 (4H, s,
Physical data for 2. Anal. Calc. for C44H60BCaIO5 (846.75 g
molꢀ1): C, 62.41; H, 7.14. Found: C, 60.69; H, 7.09.1H NMR
(400.25 MHz, 25 1C, [D8]THF): d 1.77 (20H, m, CH2, THF),
3
m,m0-CH, mes), 7.73 (4H, t, JHꢀH = 7.6 Hz, H4, carbaz.),
ꢁc
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3
3
7.12 (4H, t, JHꢀH = 7.2 Hz, H5, carbaz.), 7.59 (4H, d,
(dme)), 6.75-7.06 (m, PhMe), 7.14 (46H, t, JHꢀH = 6.8 Hz,
3JHꢀH = 7.6 Hz, H6, carbaz.), 8.00 (4H, d, JHꢀH = 7.2 Hz,
H4), 7.30 (4H, t, 3JHꢀH = 7.2 Hz, H5), 7.47 (4H, d, 3JHꢀH
=
3
H3, carbaz.). 13C{1H} NMR (100.65 MHz, 25 1C, [D8]THF):
d 21.3 (2C, p-CH3, mes), 25.3 (4C, CH2, THF), 26.4 (4C,
o,o0-CH3, mes), 67.6 (4C, CH2O, THF), 115.1 (4C, C6,
carbaz.), 116.5 (4C, C3, carbaz.), 118.9 (4C, C4, carbaz.),
123.9 (4C, C2, carbaz.), 125.2 (4C, C5, carbaz.), 127.9 (4C,
m,m0-C, mes), 137.7 (2C, p-C, mes), 141.2 (2C, i-C, mes), 146.5
(4C, o,o0-C, mes), 149.7 (4C, C1, carbaz.). 27Al NMR (25 1C,
[D8]THF): d 199.6 (w1/2 = 3848 Hz). IR (Nujol, cmꢀ1) n: 2725,
m; 2669, m; 1930, w; 1711, w; 1595, vs; 1508, vs; 1495, vs; 1417,
s; 1388, s; 1310, vs; 1243, m; 1173, m; 1155, m; 1083, m; 1028,
m; 995, w; 971, w; 934, w; 876, m; 745, vs; 690, s; 643, w.
7.2 Hz, H6), 7.92 (4H, d, 3JHꢀH = 7.6 Hz, H3). 13C{1H} NMR
(50.32 MHz, 25 1C, [D8]THF): d 5.2 (6C, MeCH2Ga), 10.1
(6C, MeCH2Ga), 21.4 (PhMe), 58.9 (8C, OCH3 (dme)), 72.7
(8C, CH2O (dme)), 111.3 (4C, C6), 119.5 (4C, C2), 120.8 (4C,
C3), 126.1 (4C, C4), 127.9, 128.4, 128.9 (PhMe), 128.7 (4C,
C5), 135.7 (PhMe, i-C), 141.1 (4C, C1). IR (Nujol, cmꢀ1) n:
2725, m; 2669, m; 2308, w; 1930, w; 1773, w; 1711, w; 1595, vs;
1508, vs; 1495, vs; 1417, s; 1338, s; 1310, s; 1261, m; 1243, m;
1173, m; 1115, m; 1063, m; 1074, m; 1028, m; 995, w; 971, w;
934, w; 876, m; 845, w; 819, m; 745, vs; 690, s; 643, m; 617,w;
568, m; 501, m.
Synthesis of [(thf)5CaI][VMes4]ꢃ2THF (8)
Synthesis of [Sr(thf)7][AlPh4]2(THF) (5)
A stirred solution of [CaI(Mes)(thf)4] (20 mL, 1.33 mmol,
0.0665 M) in THF was cooled to ꢀ40 1C and solid
[Mes3V(thf)] (0.63 g, 1.31 mmol) was added. The resulting
blue suspension was allowed to warm to 5 1C over a period of
3 h and a clear blue solution was formed. Storage at 5 1C
overnight resulted in a color change to dark violet. Afterwards
the solution was reduced to half of its original volume and
stored at ꢀ20 1C. After six hours the formed dark violet
crystals (380 mg) were collected on a Schlenk frit and dried
in a vacuum. Further storage of the mother liquor at ꢀ20 1C
resulted in crystallization of additional 7, contaminated by
[CaI2(thf)4] (colorless crystals) and [VMes3(thf)] (blue
crystals). Yield: 380 mg (0.32 mmol, 24%) violet crystals of
[CaI(thf)5][Mes4V]ꢃ2THF.
Solid (Et2O)AlPh3 (0.65 g, 1.96 mmol) was dissolved in THF
(10 mL) and {(thf)xSrPh2} (15.9 mL, 0.99 mmol, 0.062 M) in
THF was added at ꢀ50 1C. After stirring for 1 h at this
temperature the mixture was allowed to warm to room
temperature and stirred for an additional 12 h. After filtration
and storage of the mother liquor at ꢀ20 1C the formed
colorless prisms of 5 were collected on a cooled frit and dried
gently in vacuum. Yield: 0.96 g (0.76 mmol, 77%).
Physical data for 5. Decomposition above 83 1C. Anal. Calc.
for C76H96Al2O7Sr (1263.15 g molꢀ1): C, 72.26; H, 7.66;
Al, 4.27. Found: C, 71.98; H, 7.69; Al, 4.38. 1H NMR
(200.25 MHz, 25 1C, [D8]THF): d 1.77 (32H, m, CH2, THF),
3
3.63 (32H, m, CH2O, THF), 6.92 (8H, t, JHꢀH = 7.0 Hz,
3
p-H), 7.09 (16H, t, JHꢀH = 7.2 Hz, m-H), 7.65 (16H, dd,
3JHꢀH = 7.4 Hz, o-H). 13C{1H} NMR (50.32 MHz, 25 1C,
[D8]THF): d 26.3 (16C, CH2, THF), 68.1 (16C, CH2O, THF),
124.5 (16C, m-C), 126.9 (8C, p-C), 139.6 (16C, o-C), 139.9 (8C,
Suitable crystals for X-ray diffraction experiments were
obtained by cooling of a saturated solution in THF from
room temperature to 5 1C.
i-C). 27Al NMR (104.28 MHz, 25 1C, [D8]THF): d 132.9 (w1/2
=
Synthesis of [(thf)6Ca)][VMes4]2ꢃ4THF (9)
23 Hz). MS (Micro-ESIꢀ, m/z, [%]): 335 (AlPh4-) [30]. IR
(Nujol, cmꢀ1) n: 2724, s; 1591, w; 1377, vs; 1305, m; 1247, w;
1154, w; 1085, m; 1041, m; 935, m; 889, m; 847, m; 674, m.
[VMes3(thf)] (1.95 g, 4.06 mmol) was added to a cooled
suspension of activated calcium (0.38 g. 9.5 mmol) in THF
(40 mL) and cyclooctadiene (2 mL) at 0 1C. The reaction
mixture was shaken at this temperature until the blue color of
the starting material had disappeared. The resulting
yellow-brown suspension was filtered to remove the excess of
calcium and the mother liquor was stored at ꢀ20 1C overnight.
Afterwards the solution was reduced to half of the original
volume in a vacuum and stored again at ꢀ20 1C. Dark violet
crystals formed during one week. This solid was isolated by
decantation, washed with a few millilitres of cold THF and
dried in a vacuum. Yield: 210 mg (0.12 mmol, 6%).
Synthesis of [Ca(dme)4][Ga(N-carbazolyl)Et3]2ꢃPhMe (6)
Solid (dme)2Ca(NPh2)2 (0.45 g, 0.816 mmol) was suspended in
toluene (15 mL), and GaEt3 (0.86 mL, 0.81 mmol, 0.94 M) in
toluene was added at ꢀ10 1C. After stirring for 1 h at this
temperature a clear solution was formed. The mixture was
allowed to warm to room temperature and stirred for an
additional 12 h. The resulting cloudy solution was filtered
and the removed white solid (completely insoluble in common
organic solvents) was discarded. The mother liquor was stored
for 20 days at ꢀ20 1C and was repeatedly filtered during this
time to remove newly formed portions of a fine precipitate.
Afterwards, storage of the yellowish mother liquor at room
temperature yielded colorless needles of 6 within 14 days
which were collected on a Schlenk frit and dried gently in
vacuum. Yield: 0.37 g (0.35 mmol, 86%).
Suitable crystals for X-ray diffraction experiments were
obtained directly from the reaction mixture.
Synthesis of [Sr(thf)6][VMes4]2ꢃ4THF (10)
A solution of VMes4 (1.32 g, 2.50 mmol) in THF (30 mL) was
added to activated strontium at room temperature. The
resulting red suspension was shaken for two days, filtered
and the obtained solution was reduced to 5 mL in a vacuum
afterwards. Thereafter, diethyl ether (20 mL) was added,
resulting in a suspension which was stirred for 30 min at
ambient temperature. The formed solid was isolated by
filtration and extracted with boiling diethyl ether until the
Physical data for 6. Decomposition above 168 1C. Anal.
Calc. for C52H86CaGa2N2O8ꢃC7H8 (1138.91 g molꢀ1): C,
62.22; H, 8.32. Found: C, 61.53; H, 8.12. 1H NMR (400.15
3
MHz, 25 1C, [D8]THF): d 0.56 (12H, q, JHꢀH = 8.0 Hz,
3
MeCH2Ga), 1.31 (18H, t, JHꢀH = 7.0 Hz, MeCH2Ga), 2.16
(s, PhMe), 3.02 (24H, s, OCH3 (dme)), 3.21 (16H, s, CH2O
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solvent was no longer colored. Yield: 450 mg (0.24 mmol,
19.3%) violet powder.
18 P. S. Tanner, R. A. Williams and T. P. Hanusa, Inorg. Chem.,
1993, 32, 2234–2235.
19 O. Michel, C. Meermann, K. W. Tornroos and R. Anwander,
¨
Suitable crystals for X-ray diffraction experiments can be
obtained directly from the reaction mixture by cooling to
ꢀ40 1C after removal of the excess of strontium.
Organometallics, 2009, 28, 4783–4790.
20 S. Krieck, H. Gorls and M. Westerhausen, Organometallics, 2008,
27, 5052–5057.
¨
21 S. Aldridge and A. J. Downs, Chem. Rev., 2001, 101, 3305–3365.
22 M. J. Harvey, T. P. Hanusa and M. Pink, Chem. Commun., 2000,
489–490.
Structure determinations
23 A. Verma, M. Guino-o, M. Gillett-Kunnath, W. Teng and
K. Ruhlandt-Senge, Z. Anorg. Allg. Chem., 2009, 635, 903–913.
24 S. Krieck, H. Goerls and M. Westerhausen, Chem.–Asian J., 2010,
5, 272–277.
25 R. Fischer, H. Goerls and M. Westerhausen, Organometallics,
2007, 26, 3269–3271.
The intensity data for the compounds were collected on
a
Nonius KappaCCD diffractometer using graphite-
monochromated Mo-Ka radiation. Data were corrected for
Lorentz and polarization effects but not for absorption
effects.77,78
26 M. Westerhausen, C. Guckel, T. Habereder, M. Vogt,
M. Warchhold and H. No
¨
¨
th, Organometallics, 2001, 20, 893–899;
The structures were solved by direct methods (SHELXS79)
2
and refined by full-matrix least squares techniques against Fo
M. Westerhausen, C. Guckel and P. Mayer, Angew. Chem., 2001,
¨
Angew. Chem. Int. Ed., 2001, 40, 2666–2668; M. Westerhausen,
¨
113, 2736–2739; M. Westerhausen, C. Guckel and P. Mayer,
(SHELXL-9780). All hydrogen atoms were included at calculated
positions with fixed thermal parameters. All non-disordered,
non-hydrogen atoms were refined anisotropically with the
exception of the THF molecules in 5.80 Crystallographic data
as well as structure solution and refinement details are
summarized in Table 2. XP (SIEMENS Analytical X-ray
Instruments, Inc.) was used for structure representations.
C. Guckel, H. Piotrowski and M. Vogt, Z. Anorg. Allg. Chem.,
¨
2002, 628, 735–740.
27 J. Langer, S. Krieck, H. Goerls and M. Westerhausen, Angew.
Chem., 2009, 121, 5851–5854; J. Langer, S. Krieck, H. Goerls and
M. Westerhausen, Angew. Chem., Int. Ed., 2009, 48, 5741–5744.
28 W. Seidel and G. Kreisel, Z. Anorg. Allg. Chem., 1976, 426,
150–154.
29 G. Kreisel, P. Scholz and W. Seidel, Z. Anorg. Allg. Chem., 1980,
460, 51–55.
30 W. Ludwig and W. Seidel, Thermochim. Acta, 1985, 85, 59–62.
31 M. M. Olmstead, P. P. Power and S. C. Shoner, Organometallics,
1988, 7, 1380–1385.
32 R. Kirmse, J. Stach and G. Kreisel, Z. Chem., 1980, 20,
420–421.
Acknowledgements
We thank the Deutsche Forschungsgemeinschaft (DFG,
Bonn, Germany) for generous financial support of this
research initiative. We also gratefully acknowledge the funding
of the Fonds der Chemischen Industrie (Frankfurt, Main,
Germany). S. Krieck is very grateful to the Verband der
Chemischen Industrie (VCI/FCI) for a PhD grant.
33 K. Thiele, H. Gorls, W. Imhof and W. Seidel, Z. Anorg. Allg.
¨
Chem., 2002, 628, 107–118.
34 W. Seidel, P. Scholz and G. Kreisel, Z. Anorg. Allg. Chem., 1979,
458, 263–266.
35 K. Thiele, H. Gorls, W. Imhof and W. Seidel, Z. Anorg. Allg.
¨
Chem., 1999, 625, 1927–1933.
36 V. C. Gibson, C. Redshaw, L. J. Sequeira, K. B. Dillon, W. Clegg
and M. R. J. Elsegood, Chem. Commun., 1996, 2151–2152.
37 W. Seidel and G. Kreisel, Z. Chem., 1981, 21, 295–296.
References
38 M. Rost, H. Gorls, W. Imhof, W. Seidel and K. Thiele, Z. Anorg.
¨
1 W. Tochtermann, Angew. Chem., 1966, 78, 355–375;
W. Tochtermann, Angew. Chem., Int. Ed. Engl., 1966, 5, 351–371.
2 D. J. Linton, P. Schooler and A. E. H. Wheatley, Coord. Chem.
Rev., 2001, 223, 53–115.
Allg. Chem., 1998, 624, 1994–2000.
39 G. Kreisel and W. Seidel, Z. Anorg. Allg. Chem., 1981, 478,
106–110.
40 P. J. Alonso, J. Fornie
B. Menjon, Chem. Commun., 2001, 2138–2139.
41 P. J. Alonso, J. Fornies, M. A. Garcıa-Monforte, A. Martı
B. Menjon, Chem.–Eur. J., 2005, 11, 4713–4724.
´
s, M. A. Garcı
´
a-Monforte, A. Martı
´
n and
3 M. Westerhausen, Dalton Trans., 2006, 4755–4768.
4 H. Lehmkuhl, Angew. Chem., 1963, 75, 1090–1097; H. Lehmkuhl,
Angew. Chem., Int. Ed. Engl., 1964, 3, 107–114.
´
´
´
´
n and
´
5 G. Bahr and H.-O. Kalinowski, in Methoden der organischen
¨
vol. XIII/2a, pp. 533–551.
¨
Chemie, ed. E. Muller, Houben-Weyl/Thieme, Stuttgart, 1973,
42 R. Ferguson, E. Solari, C. Floriani, A. Chiesi-Villa and C. Rizzoli,
Angew. Chem., 1993, 105, 453–455; R. Ferguson, E. Solari,
C. Floriani, A. Chiesi-Villa and C. Rizzoli, Angew. Chem., Int.
Ed. Engl., 1993, 32, 396–397.
6 B. G. Gowenlock and W. E. Lindsell, J. Organomet. Chem. Libr.,
Organomet. Chem. Rev., 1977, 3, 1–73.
43 R. Ferguson, E. Solari, C. Floriani, D. Osella, M. Ravera, N. Re,
A. Chiesi-Villa and C. Rizzoli, J. Am. Chem. Soc., 1997, 119,
10104–10115.
7 W. E. Lindsell, in Comprehensive Organometallic Chemistry, ed.
G. Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon Press,
New York, 1982, ch. 4.2, vol. I, pp. 223–252.
44 S. Harder, F. Feil and T. Repo, Chem.–Eur. J., 2002, 8, 1991–1999.
45 L. L. Ivanov, S. Y. Zavizion and L. I. Zakharkin, Synth. React.
Inorg., Met.-Org., Nano-Met. Chem., 1973, 3, 323–327.
46 L. L. Ivanov, S. Y. Zavizion and L. I. Zakharkin, Zh. Obshchei
Khim., 1973, 43, 2254–2258.
8 M. Westerhausen, Z. Anorg. Allg. Chem., 2009, 635, 13–32.
9 M. P. Coles, Curr. Org. Chem., 2008, 12, 1220–1230.
10 M. Westerhausen, M. Gartner, R. Fischer, J. Langer, L. Yu and
¨
M. Reiher, Chem.–Eur. J., 2007, 13, 6292–6306.
11 M. Westerhausen, M. Gartner, R. Fischer and J. Langer, Angew.
¨
47 S. Krieck, H. Gorls and M. Westerhausen, Inorg. Chem. Commun.,
¨
2008, 11, 911–913.
Chem., 2007, 119, 1994–2001; M. Westerhausen, M. Gartner,
R. Fischer and J. Langer, Angew. Chem., Int. Ed., 2007, 46,
1950–1956.
¨
48 S.-O. Hauber, F. Lissner, G. B. Deacon and M. Niemeyer, Angew.
Chem., 2005, 117, 6021–6025; S.-O. Hauber, F. Lissner,
G. B. Deacon and M. Niemeyer, Angew. Chem., Int. Ed., 2005,
44, 5871–5875.
12 M. Westerhausen, Dalton Trans., 2006, 4755–4768.
13 J. S. Alexander and K. Ruhlandt-Senge, Eur. J. Inorg. Chem.,
2002, 2761–2774.
49 J. Langer, M. Gartner, R. Fischer, H. Goerls and
¨
M. Westerhausen, Inorg. Chem. Commun., 2007, 10, 1001–1004.
14 M. Westerhausen, Angew. Chem., 2001, 113, 3063–3065;
M. Westerhausen, Angew. Chem., Int. Ed., 2001, 40, 2975–2977.
15 T. P. Hanusa, Coord. Chem. Rev., 2000, 210, 329–367.
16 M. Westerhausen, Coord. Chem. Rev., 1998, 176, 157–210.
17 J. L. Atwood and G. D. Stucky, J. Am. Chem. Soc., 1969, 91,
2538–2543.
50 J. Langer, H. Gorls and M. Westerhausen, Organometallics, 2010,
29, 2034–2039.
¨
51 R. Benn, A. Runfinska, H. Lehmkuhl, E. Janssen and C. Kruger,
¨
Angew. Chem., 1983, 95, 808–809; R. Benn, A. Runfinska,
ꢁc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010
1676 | New J. Chem., 2010, 34, 1667–1677

View Article Online
H. Lehmkuhl, E. Janssen and C. Kruger, Angew. Chem., Int. Ed.
¨
Engl., 1983, 22, 779–780.
67 Holleman-Wiberg Lehrbuch der Anorganischen Chemie, de Gruyter,
Berlin, New York, 34th edn, 1995.
52 R. Benn and A. Runfinska, Angew. Chem., 1986, 98, 851–871;
R. Benn and A. Runfinska, Angew. Chem., Int. Ed. Engl., 1986, 25,
861–881.
53 R. Benn, E. Janssen, H. Lehmkuhl and A. Runfinska,
J. Organomet. Chem., 1987, 333, 155–168.
68 W. N. Setzer and P. v. R. Schleyer, Adv. Organomet. Chem., 1985,
24, 353–451.
69 V. H. Gessner, C. Daschlein and C. Strohmann, Chem.–Eur. J.,
2009, 15, 3320–3334.
¨
70 R. Fischer, M. Gartner, H. Gorls and M. Westerhausen, Organo-
¨
metallics, 2006, 25, 3496–3500.
¨
54 W. A. King, B. L. Scott, J. Eckert and G. J. Kubas, Inorg. Chem.,
1999, 38, 1069–1084.
71 G. Bauer, in Handbuch der Praparativen Anorganischen Chemie,
¨
Ferdinand Enke Verlag, Stuttgart, 1978, vol. 2.
55 K. Ren, A. Mejiritski, J. H. Malpert, O. Grinevich, H. Gu and
D. C. Neckers, Tetrahedron Lett., 2000, 41, 8669–8672.
56 A. H. Cowley, C. L. B. Macdonald, J. S. Silverman, J. D. Gorden
and A. Voigt, Chem. Commun., 2001, 175–176.
57 K. Ren, J. H. Malpert, H. Gu, H. Li and D. C. Neckers, Tetra-
hedron, 2002, 58, 5267–5273.
58 O. T. Beachley, Jr., M. R. Churchill, J. C. Pazik and J. W. Ziller,
Organometallics, 1986, 5, 1814–1817.
59 G. H. Robinson, Chem. Commun., 2000, 2175–2181.
72 M. Gartner, R. Fischer, J. Langer, H. Gorls, D. Walther and
¨
¨
M. Westerhausen, Inorg. Chem., 2007, 46, 5118–5124.
73 M. S. Lalama, J. Kampf, D. G. Dick and J. P. Oliver, Organo-
metallics, 1995, 14, 495–501.
74 M. F. Lappert, M. J. Slade and A. Singh, J. Am. Chem. Soc., 1983,
105, 302–304.
75 R. Dinnebier, H. Esbak, F. Olbrich and U. Behrens, Organo-
metallics, 2007, 26, 2604–2608.
60 V. Sridharan, M. A. Martin and J. C. Mene
2375–2378.
61 R. Fischer, M. Gartner, H. Goerls and M. Westerhausen, Angew.
´
ndez, Synlett, 2006, 15,
76 W. Seidel and G. Kreisel, Z. Chem., 1974, 14, 25.
77 B. V. Nonius, COLLECT, Data Collection Software, Netherlands,
1998.
¨
Chem., 2006, 118, 624–627; R. Fischer, M. Gartner, H. Goerls and
78 Z. Otwinowski and W. Minor, Processing of X-Ray Diffraction
Data Collected in Oscillation Mode’’, in Methods in Enzymology,
276, Macromolecular Crystallography, Part A, ed. C. W. Carter
and R. M. Sweet, Academic Press, San Diego, 1997, pp. 307–326.
79 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr.,
1990, 46, 467–473.
¨
M. Westerhausen, Angew. Chem., Int. Ed., 2006, 45, 609–612.
62 W. Seidel and G. Kreisel, Z. Chem., 1976, 16, 115–116.
63 R. G. Parr and R. G. Pearson, J. Am. Chem. Soc., 1983, 105,
7512–7516.
64 R. G. Pearson, Inorg. Chem., 1988, 27, 734–740.
65 R. G. Pearson, Coord. Chem. Rev., 1990, 100, 403–425.
66 R. G. Pearson, Acc. Chem. Res., 1993, 26, 250–255.
80 G. M. Sheldrick, SHELXL-97 (Release 97-2), University of
Gottingen, Germany, 1997.
¨
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