Synthesis and molecular structures of meta-substituted arylcalcium iodides

Article abstract of DOI:10.1021/om301087e

The reduction of meta-methyl-substituted iodobenzene with activated calcium in tetrahydrofuran (THF) yields [(3-MeC₆H₄)CaI(thf) ₄] (1) and [(3,5-Me₂C₆H₃)CaI(thf) ₄] (2). The reaction of 3-halo-1-iodobenzene with calcium powder leads to the formation of the corresponding post-Grignard reagents [(3-XC ₆H₄)CaI(thf)₄] [X = F (3), Cl (4), Br (5), and I (6)]. The synthesis of the thf adducts of 3-methoxyphenylcalcium iodide (7) and β-naphthylcalcium iodide (8) follows the same strategy. All post-Grignard reagents show a characteristic low-field shift for the calcium-bound carbon atoms in ¹³C NMR spectra. The molecular structures of 1, 2, 4, and 8 show distorted octahedral environments for the calcium centers with the aryl and halide anions in a trans arrangement.

Full text of DOI:10.1021/om301087e

Article
pubs.acs.org/Organometallics
Synthesis and Molecular Structures of Meta-Substituted Arylcalcium
Iodides
Mathias Kohler, Jens Langer, Helmar Gorls, and Matthias Westerhausen*
̈
̈
Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University Jena, Humboldtstrasse 8, D-07743 Jena, Germany
S
* Supporting Information
ABSTRACT: The reduction of meta-methyl-substituted iodobenzene with activated calcium in
tetrahydrofuran (THF) yields [(3-MeC6H4)CaI(thf)4] (1) and [(3,5-Me2C6H3)CaI(thf)4] (2). The
reaction of 3-halo-1-iodobenzene with calcium powder leads to the formation of the corresponding
post-Grignard reagents [(3-XC6H4)CaI(thf)4] [X = F (3), Cl (4), Br (5), and I (6)]. The synthesis
of the thf adducts of 3-methoxyphenylcalcium iodide (7) and β-naphthylcalcium iodide (8) follows
the same strategy. All post-Grignard reagents show a characteristic low-field shift for the calcium-
bound carbon atoms in 13C NMR spectra. The molecular structures of 1, 2, 4, and 8 show distorted
octahedral environments for the calcium centers with the aryl and halide anions in a trans
arrangement.
Despite the vastly growing knowledge of post-Grignard
reagents, the influence of the substitution pattern on reactivity
and molecular structures is mainly limited to ortho and para
substituents.12 Ortho-positioned halogen substituents drasti-
cally reduce the stability and durability of arylcalcium reagents
in solution.16 Fluoro functionalities in ortho positions require
special stabilization strategies in order to avoid formation of
intermediate arynes and precipitation of calcium dihalide.
Niemeyer and co-workers20 kinetically shielded the reactive
pentafluorophenylcalcium unit by π-bonding encapsulation
between bulky aryl groups, thus enabling the crystal structure
determination of this complex [Ca−C 249.9(11) pm]. Also,
methyl groups can be attacked, yielding benzylcalcium
derivatives.7 In addition, ortho-tert-butyl groups are also
involved in degradation reactions, finally yielding 2,5-
dimethyl-2,5-bis[3,5-di(tert-butyl)phenyl]hexane.10−12 In para
positions, many more functional groups are tolerated, such as
halo,15,16 dimethylamino,16 and silyl groups.21 Astonishingly,
para-phenyl-substituted arylhalides as substrates did not yield
the expected arylcalcium halides,22,23 whereas derivatives with
phenyl groups in ortho positions are easily accessible, probably
due to effective steric shielding of the formed Ca−C bond.23
It is likely that both the regioselectivity and the speed of
subsequent reactions of these calcium-substituted arenes will be
affected by the other substituents already attached to the
benzene ring. Since ortho- and para-functionalized derivatives
often show similar effects, for instance, in electrophilic aromatic
substitution reactions, the accessibility of hitherto unexplored
meta-functionalized arylcalcium compounds is highly desirable
for comparison reasons. Therefore, we investigated the meta-
substituted arylcalcium reagents to fill the knowledge gap with
respect to these post-Grignard derivatives.
INTRODUCTION
■
Grignard reagents represent widely used organomagnesium
compounds that were introduced into preparative organic and
organometallic chemistry more than a century ago.1−3 Because
of the importance of these reagents, Grignard was honored with
the Nobel Prize in 1912. Despite the fact that early attempts to
prepare arylcalcium halides also date back more than a 100
years,4 the first structurally characterized arylcalcium complexes
consisted of oxygen-centered oligonuclear arylcalcium clus-
ters.5,6 Nevertheless, this success of isolation of arylcalcium
derivatives intensified the efforts to also isolate and characterize
arylcalcium halides that can be considered as post-Grignard
reagents with mesitylcalcium iodide being the first structurally
characterized representative7 and entering the textbooks shortly
thereafter.8 Knowing the requirements to isolate crystalline
arylcalcium complexes, many of such derivatives were prepared
and investigated spectroscopically as well as via derivatization
reactions. Several recent review articles summarize this vastly
growing arylcalcium (post-Grignard) chemistry.9−12
The synthesis of arylcalcium complexes succeeds with high
yields if iodoarenes are reduced with activated calcium in Lewis
basic solvents, such as ethers.9−12 Amines were also used to
stabilize arylcalcium complexes.13 As also observed for classical
Grignard reagents, a Schlenk-type equilibrium converts
arylcalcium halides into homoleptic diarylcalcium and calcium
dihalides depending mainly on solvent and temperature.
Substitution of iodide by an alkoxide shifts this equilibrium
quantitatively to the side of the homoleptic complexes.14
Because of the high reactivity of the arylcalcium complexes,
degradation of ethers often was observed,7,15,16 as is also known
for organyllithium17 and, in minor extent, for Grignard
reagents,18 justifying to consider these organometallics as
superbases.19 On the basis of similar electronegativities of
lithium and calcium, a comparable reactivity can be envisioned
that should be higher than that of Grignard reagents due to a
larger ionic character of the metal−carbon bonds.
Received: November 13, 2012
Published: November 30, 2012
© 2012 American Chemical Society
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Article
cases, the conversion was above 50%, in many cases above 70%.
In comparison to the para-substituted congeners, the
conversion rates were only slightly lower. Attempts to isolate
crystalline material were successful, but the yields were
significantly lower. Recrystallization of meta-fluoro- and meta-
chlorophenylcalcium iodides was extremely challenging. The
fluoro-substituted post-Grignard reagent was extremely soluble,
and also, the chloro-substituted derivative showed poor
crystallization behavior. The isolation of literature-known
mesitylcalcium iodide was challenging for another reason
because the synthesis of this highly soluble post-Grignard
reagent is accompanied by ether degradation reactions, thus
yielding benzylcalcium derivatives and lowering the yield of
isolated crystalline material.7
RESULTS AND DISCUSSION
■
Synthesis. In a general procedure, finely divided calcium
powder (prepared via dissolution in liquid ammonia and
immediate complete removal of NH3 in vacuum) was reacted
with the respective iodoarene in THF solution at −20 °C.
During continuous shaking, the reaction mixture was warmed
stepwise to 0 °C and then to ambient temperature. The solid
material was removed by filtration, and the filtrate was stored at
low temperatures, yielding crystalline arylcalcium iodides
according to eq 1. These calcium-based organometallics were
NMR Investigations. The NMR parameters of the aryl
groups of these post-Grignard reagents strongly depend on the
meta substituent (Table 2); an assignment is in agreement with
the increment method of these substituents and was
unambiguous on the basis of 2D NMR experiments. Never-
theless, all arylcalcium organometallics show low-field shifted
resonances for the calcium-bound ipso-carbon atoms of
approximately δ = 190. A similar chemical shift of δ = 189.1
was also detected for β-naphthylcalcium iodide in a [D8]THF
solution. Another obvious trend pertains to the halogen-bound
carbon atoms; due to the heavy atom effect, these carbon atoms
show a strong high-field shift with increasing mass of the
halogen. Expectedly, the degree of electron-withdrawing nature
of the halogen also influences the other resonances, leading to a
low-field shift of the other resonances with increasing size of
the halogen atom.
collected on a cooled frit and dried in vacuo. They could be
recrystallized by cooling of a THF solution, saturated at
ambient temperature, to −40 °C. A solvent change and the use
of tetrahydropyran neither enhanced the yield nor improved
the crystallization behavior of these meta-substituted complexes
significantly. The thf adduct of β-naphthylcalcium iodide, [(β-
naphthyl)CaI(thf)4] (8), was synthesized in a similar manner
(eq 2).
Molecular Structures. Despite the fact that these meta-
substituted arylcalcium organometallics can be recrystallized
and purified, crystal structure determinations failed for most of
the derivatives. The thf adduct of meta-fluorophenylcalcium
iodide (3) was extremely soluble in ethereal solvents, and the
complex crystallized in flimsy needles that agglomerated,
looking like wool. The chlorine-substituted derivative [(3-
ClC6H4)CaI(thf)4] (4) precipitated as a microcrystalline
substance. Nevertheless, we were able to determine the
molecular structure at a very tiny crystal. The single crystals
of [(3-BrC6H4)CaI(thf)4] (5) exhibited extremely poor
diffraction properties, and we were unable to obtain a
reasonable data set. The data set of crystalline [(3-IC6H4)CaI-
(thf)4] (6) gave no meaningful solution with direct and heavy
atom methods. The crystal quality of [(3-MeOC6H4)CaI(thf)4]
(7) did not allow an X-ray crystal structure determination. In
THF solution, this complex forms a tetrakis(thf) adduct,
whereas in the solid state, the high calcium content hints
toward a tris(thf) complex, probably suggesting that the 3-
methoxy group kicks out a thf ligand on an adjacent calcium ion
to form a dimer. The ability of methoxy groups to act as a
donor ligand in competition to thf was already observed in
dinuclear [{2,6-(MeO)2C6H3}3Ca2(thf)3I].25
The molecular structures and numbering schemes of meta-
alkylated 3-methylphenyl- and 3,3′-dimethylphenylcalcium
derivatives 1 and 2 are depicted in Figures 1 and 2. The
molecular structures of phenyl-,24 4-methylphenyl-24 and 2,4,6-
trimethylphenyl- (mesityl) calcium iodide7 are dominated by
the enhanced steric strain, induced by the ortho-methyl
substituents, and are included in Table 3 for comparison
reasons. All of these molecular structures have a hexacoordinate
calcium atom in distorted octahedral environments in common.
The anionic ligands are trans-arranged due to electrostatic
The yields of the reduction of meta- and para-substituted
arenes are compared in Table 1. The conversion was
determined by titration of an aliquot of the reaction solution
after removal of all solids (such as excess of calcium). In all
Table 1. Yields (%) of [(3-RC6H4)CaI(thf)4] and [(4-
RC6H4)CaI(thf)4] Determined via Titration of an Aliquot of
the Solution and Yields (%) of Isolated Crystalline Material
Depending on Meta or Para Substitution
[(meta-aryl)CaI(thf)4]
[(para-aryl)CaI(thf)4]
aryl
C6H5
titrated
crystalline
titrated
crystalline
ref
93
60
86
75
81
70
38
16, 24
16, 24
7
Me-C6H4
Me2C6H3
F-C6H4
60
81
51
74
67
66
75
44
a
a
39
12
4.9
3.6
25.5
27.9
16
Cl-C6H4
Br-C6H4
I-C6H4
16
b
b
60.7
95
18.3
15
16
MeO-C6H4
89
15
a
b
Aryl = 2,4,6-Me3C6H2 (mesityl). Solvent: tetrahydropyran (thp).
Isolated complex: [(4-BrC6H4)CaI(thp)4].
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Table 2. 13C{1H} NMR Data of Meta-Substituted Arylcalcium Iodides (Chemical Shifts δ of Exclusively Aryl Carbon Atoms)
compound
C1
C2
C3
C4
C5
C6
[(3-MeC6H4)CaI(thf)4]
[(3,5-Me2C6H3)CaI(thf)4]
[(3-FC6H4)CaI(thf)4]
[(3-ClC6H4)CaI(thf)4]
[(3-BrC6H4)CaI(thf)4]
[(3-IC6H4)CaI(thf)4]
189.7
189.7
195.6
194.8
196.3
197.1
191.3
142.1
139.2
125.9
139.8
142.6
149.0
125.0
132.5
132.2
162.6
133.2
124.5
101.0
156.8
123.5
124.6
108.8
122.5
125.4
131.4
106.5
125.0
132.2
125.3
126.7
127.5
128.4
124.4
138.1
139.2
136.1
138.7
139.0
139.0
132.5
[(3-MeOC6H4)CaI(thf)4]
those in the thf adducts of phenylcalcium and para-tolylcalcium
iodide.24 The situation is much more complex for the Ca−I
distances because the large iodide ion is very soft and highly
polarizable. This fact leads to a flat energy surface with respect
to the variation of the Ca−I distance. Harvey and Hanusa27
demonstrated that a difference of 0.15 Å for the Ca−I bond
length in [CaI2(thf)4] only requires 7.1 kJ mol−1. Because of
this flat energy potential, packing effects and intermolecular
forces in the crystalline state gain on importance and
overcompensate small intramolecular effects. In light of this
consideration, the Ca−I bond length difference of 5 pm
between 1 and 2 becomes understandable. Intramolecular
strain as observed for mesitylcalcium iodide additionally
enhances the Ca−I distance.7
The meta-methyl-functionalized phenyl substituents of 1 and
2 show rather narrow endocyclic C2−C1−C6 bond angles of
114.5(5)° and 113.4(2)°, respectively. These small values result
from electrostatic repulsion between the anionic charge (sp2
hybrid orbital at C1) and the C1−C2/6 bonds and represent a
common feature for aryl groups coordinated at very electro-
positive metals, such as calcium. The Ca1−C1−C2/6 bond
angles in [(3,5-Me2C6H3)CaI(thf)4] (2) are very similar [Ca1−
C1−C2 122.15(19)°; Ca1−C1−C6 123.70(19)°], whereas
large differences between proximal [Ca1−C1−C2 115.3(4)°]
and distal angles [Ca1−C1−C6 130.1(5)°] are observed for
[(3-MeC6H4)CaI(thf)4] (1). However, an obvious dependency
of these flexible angles on the coligand (thf or thp) or the size
and substitution pattern of the aryl group cannot be recognized
(Table 3), thus supporting again the influence of packing effects
in the solid state.
Figure 1. Molecular structure and numbering scheme of [(3-
MeC6H4)CaI(thf)4] (1). Ellipsoids represent a probability of 40%,
and H atoms are omitted for the sake of clarity. Selected bond lengths
(Å): Ca1−C1 2.522(6), Ca1−I1 3.1425(12), Ca1−O1 2.396(4),
Ca1−O2 2.382(4), Ca1−O3 2.365(4), Ca1−O4 2.400(5). Angles
(deg): C1−Ca1−I1 176.89(15), C1−Ca1−O1 92.45(17), C1−Ca1−
O2 90.38(18), C1−Ca1−O3 91.45(17), C1−Ca1−O4 92.43(19), I1−
Ca1−O1 88.09(11), I1−Ca1−O2 86.55(10), I1−Ca1−O3 88.27(11),
I1−Ca1−O4 90.65(13).
The molecular structure and numbering scheme of [(3-
ClC6H4)CaI(thf)4] (4) is shown in Figure 3. The data set was
collected at a very tiny crystal, and therefore, rather large
estimated standard deviations limit the discussion of this data.
The rather similar size of methyl and chloro substitutents leads
to comparable distortions, especially with respect to the
proximal and distal Ca1−C1−C2/6 angles (Table 3), despite
the fact that the arylcalcium iodides 1 and 4 crystallize in
different space groups.
The molecular structure and numbering scheme of the thf
adduct of β-naphthylcalcium iodide is depicted in Figure 4.
Expectedly, the hexacoordinate calcium center exhibits a similar
environment as in meta-substituted phenylcalcium iodides. The
Ca−I distance is rather large; nevertheless, Ca−I and Ca−C
bond lengths fall in the common range. The rather large β-
naphthyl group leads to a slight bending of the C1−Ca1−I1
bond angle [173.08(11)°]. Intramolecular steric repulsion leads
to significantly different proximal and distal angles at the ipso-
carbon atom [Ca1−C1−C10 110.2(3)°, Ca1−C1−C2
136.9(4)°; see also Table 3].
Figure 2. Molecular structure and numbering scheme of [(3,5-
Me2C6H3)CaI(thf)4] (2). Ellipsoids represent a probability of 40%,
and H atoms are not drawn. Selected bond lengths (Å): Ca1−C1
2.540(3), Ca1−I1 3.1912(6), Ca1−O1 2.382(2), Ca1−O2
2.4178(19), Ca1−O3 2.3974(19), Ca1−O4 2.351(2). Angles (deg):
C1−Ca1−I1 175.28(6), C1−Ca1−O1 89.10(8), C1−Ca1−O2
91.92(8), C1−Ca1−O3 95.71(8), C1−Ca1−O4 92.02(8), I1−Ca1−
O1 86.30(5), I1−Ca1−O2 87.40(5), I1−Ca1−O3 88.94(5), I1−Ca1−
O4 88.89(5).
reasons. Selected structural data of substituted phenylcalcium
iodides are compared in Table 3. Obviously, methyl groups in
meta positions do not induce much intramolecular strain, and
the Ca−C bonds of 1 and 2 are very short, even shorter than
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Table 3. Comparison of Selected Structural Parameters of Arylcalcium Iodide of the Type [(Aryl)CaI(L)4] with Hexacoordinate
Calcium Atoms in Distorted Octahedral Environments (Bond Lengths [Å] and Angles [deg])
b
aryl
L
Ca−C
Ca−I
Cipso−Ca−I
Ca−Cipso−Cproximal
Ca−Cipso−Cdistal
C−Cipso−C
ref
a
Ph
Ph
thf
2.574(7)
2.510(6)
2.556(5)
2.647(5)
2.522(6)
2.540(3)
2.574(4)
2.550(4)
2.643(9)
2.573(13)
2.605(9)
2.565(4)
2.552(6)
2.528(5)
2.565(4)
3.178(3)
3.121(1)
3.173(1)
3.1571(9)
3.143(1)
3.1912(6)
3.2084(9)
3.1560(8)
3.136(2)
3.158(3)
3.060(2)
3.1512(8)
3.187(1)
3.1932(8)
3.1512(8)
177.4(2)
171.8(1)
174.6(1)
176.4(1)
176.9(2)
175.28(6)
177.4(1)
176.3(1)
175.0(2)
174.1(3)
174.5(2)
176.3(1)
177.7(2)
173.1(1)
176.3(1)
117.5(5)
123.5(4)
118.4(4)
112.6(3)
115.3(4)
122.2(2)
121.3(3)
122.3(3)
115.3(6)
115.6(10)
116.5(6)
117.1(3)
116.7(5)
110.2(3)
121.9(5)
124.5(4)
128.4(4)
129.5(3)
130.1(5)
123.7(2)
124.5(3)
125.1(3)
126.4(6)
128.7(9)
129.1(6)
130.0(3)
129.8(5)
136.9(4)
129.0(4)
120
24
26
24
15
thp
thf
111.6(6)
113.2(5)
117.6(4)
114.5(5)
113.4(2)
114.2(4)
112.5(4)
118.3(9)
115.6(12)
114.3(8)
112.5(4)
113.5(6)
112.9(5)
113.8(5)
4-MeC6H4
4-MeC6H4
3-MeC6H4
3,5-Me2C6H3
2,4,6-Me3C6H2
4-MeOC6H4
4-ClC6H4
thp
thf
this work
thf
this work
thf
7
thp
thp
thf
15
15
3-ClC6H4
this work
4-BrC6H4
thp
thp
thf
15
4-IC6H4
15
α-naphthyl
β-naphthyl
β-naphthyl
16
thf
this work
15
thp
117.1(4)
a
b
The phenyl ring was restrained to a regular hexagon with equal C−C bond lengths. Tetrahydrofuran, thf; tetrahydropyran, thp.
Figure 3. Molecular structure and numbering scheme of [(3-
ClC6H4)CaI(thf)4] (4). Ellipsoids represent a probability of 40%,
and H atoms are neglected for the sake of clarity. Selected bond
lengths (Å): Ca1−C1 2.573(13), Ca1−I1 3.158(3), Ca1−O1
2.344(9), Ca1−O2 2.398(10), Ca1−O3 2.371(10), Ca1−O4
2.365(9). Angles (deg): C1−Ca1−I1 174.1(3), C1−Ca1−O1
88.6(3), C1−Ca1−O2 87.8(4), C1−Ca1−O3 94.6(4), C1−Ca1−O4
91.8(4), I1−Ca1−O1 87.2(2), I1−Ca1−O2 88.3(2), I1−Ca1−O3
90.2(3), I1−Ca1−O4 92.3(2).
Figure 4. Molecular structure and numbering scheme of [(β-
naphthyl)CaI(thf)4] (8). Ellipsoids represent a probability of 40%,
and H atoms are omitted for clarity reasons. Symmetry-related atoms
(x, −y − 1, z) are marked with the letter “A”. Selected bond lengths
(Å): Ca1−C1 2.528(5), Ca1−I1 3.1932(8), Ca1−O1 2.386(2), Ca1−
O2 2.384(2). Angles (deg): C1−Ca1−I1 173.08(11), C1−Ca1−O1
87.87(9), C1−Ca1−O2 94.50(9), I1−Ca1−O1 87.42(5), I1−Ca1−
O2 90.51(5).
magnesium turnings to prepare the 2-fold magnesiated
derivative [2,4-(MeO)2C6H2-1,5-(MgI·LiCl)2].29
CONCLUSION
The arylcalcium complexes show a characteristic strong low-
field shift of the ipso-carbon atom in 13C NMR spectra
regardless of the substitution pattern. 2D NMR methods allow
an unambiguous assignment of the aryl resonances that is in
agreement with the increment method. In addition, it is well-
known that the heavy atom effect leads to a significant high-
field shift of the halogen-bound carbon atom with increasing
mass of the halogen.
The thf adducts of arylcalcium iodides crystallize as
monomeric molecules with hexacoordinate calcium centers in
distorted octahedral environments regardless of meta and para
substituents. The aryl groups and iodide ions prefer a trans
arrangement due to electrostatic reasons. Softness and
polarizability of the large iodide ion lead to variable Ca−I
bond lengths between 314 and 321 pm depending largely on
■
The direct synthesis of meta-substituted phenylcalcium iodides
via the reduction of iodoarenes with activated calcium succeeds
in moderate to good yields; however, isolation of pure
crystalline substances often proved to be challenging. Func-
tional groups, such as halogens or methoxy substituents, are
tolerated in para and meta positions as well. The reduction of 3-
halo-1-iodobenzene selectively gave the 3-halophenylcalcium
iodides in crystalline form; a second reduction step at the other
halogen functionality was not observed, even when 1,3-
diiodobenzene was employed. Contrary to this finding,
magnesium reacts twice with 1,3-diiodobenzene, yielding
[C6H4-1,3-(MgI)2].28 This reaction was recently rediscovered,
and in the presence of lithium chloride, 1,5-diiodo-2,4-
dimethoxybenzene was reacted with a large excess of
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consumption by a hydrolyzed aliquot) was stored at −40 °C for 2
days. Afterward, the formed crystalline solid was collected on a cooled
Schlenk frit and dried in vacuo (4.50 g). A second crop of the product
(0.95 g) was obtained from the mother liquor at −90 °C. Combined
yield: 5.45 g (9.72 mmol, 39%) of needle-shaped crystals. Suitable
crystals of the composition [(3,5-Me2C6H3)CaI(thf)4] for X-ray
diffraction experiments were obtained by cooling a saturated solution
in THF from ambient temperature to −40 °C. Elemental analysis
packing effects and intermolecular forces in the solid state. For
the same reason, the molecules often also show severe
differences between proximal and distal Ca−Cipso−Cortho bond
angles. In these mainly ionic organometallics with very
electropositive metals, tilting of the aryl group is provoked by
intermolecular forces and packing effects in the solid state.
These investigations establish a large group tolerance during
the reduction of substituted iodobenzene with activated
calcium. The maintenance of reaction temperatures at and
below ambient temperature allows the high-yield synthesis of
post-Grignard reagents with a wide variety of functional groups,
a precondition for fruitful and intense use of calcium-based
organometallics in organic and organometallic chemistry.
1
(C24H41CaIO4, 560.57): calcd, Ca 7.15; found, Ca 7.39%. H NMR
([D8]THF, 600 MHz): δ 1.78 (m, 16 H, CH2 thf), 2.12 (br, 6H, CH3
tolyl), 3.63 (m, 16H, OCH2 thf), 6.38 (br, 1H, p-CH tolyl), 7.29 (br,
2H, o-CH tolyl). 13C{1H} NMR ([D8]THF, 150.9 MHz): δ 22.1 (2C,
CH3 tolyl), 26.3 (8C, CH2 thf), 68.2 (8C, OCH2 thf), 124.6 (1C, C4),
132.2 (2C, C3 and C5), 139.2 (2C, C2 and C6), 189.7 (1C, C1).
Synthesis of [(3-FC6H4)CaI(thf)4] (3). Finely divided calcium
metal (1.2 g, 29.9 mmol) was suspended in THF (40 mL) and cooled
to −20 °C. 1-Iodo-3-fluorobenzene (5.55 g, 25 mmol) was added at
this temperature, and the resulting mixture was allowed to warm to 0
°C while shaking. Shaking was continued for 1 h at 0 °C and for an
additional 4 h at ambient temperature. The resulting brown
suspension was filtered, and the solid residue was discarded. The
THF solution (51% yield of organocalcium compounds, determined
by acid consumption by a hydrolyzed aliquot) was stored at −90 °C
for 3 days. Afterward, the formed crystalline solid was collected on a
cooled Schlenk frit and dried in vacuo. Yield: 0.67 g (1.22 mmol,
EXPERIMENTAL SECTION
■
General Remarks. All manipulations were carried out under an
inert argon atmosphere using standard Schlenk techniques. THF was
dried over KOH and distilled over sodium/benzophenone in an argon
atmosphere; deuterated THF was dried over sodium, degassed, and
saturated with argon. The yields given are not optimized. 1H and
13C{1H} NMR spectra were recorded on Bruker AC 200, AC 400, or
AC 600 spectrometers. Chemical shifts are reported in parts per
million relative to Me4Si as an external standard. The residual signals
of [D8]THF were used as an internal standard. Calcium was activated
by dissolution in liquid NH3 and subsequent reduction of the deep
blue solution to dryness, resulting in finely divided calcium powders.
The calcium content of the products was determined by
complexometric titration of a hydrolyzed aliquot with 0.05 M EDTA
using Eriochrome BlackT as an indicator.30
1
4.9%) of a violet solid (crude product). H NMR ([D8]THF, 200
MHz): δ 1.73 (m, 16 H, CH2 thf), 3.60 (m, 16H, OCH2 thf), 6.33 (m,
p-CH phenyl), 6.79 (m, 1H, m-CH phenyl), 7.33 (m, 2H, o-CH and o-
CH′ phenyl). 13C{1H} NMR ([D8]THF, 50.6 MHz): δ 26.4 (8C, CH2
thf), 68.3 (8C, OCH2 thf), 108.8 (d, JCF = 21,0 Hz, 1C, C4), 125.3 (d,
JCF = 5,0 Hz, 1C, C5), 125.9 (d, JCF = 2,9 Hz, 1C, C2), 136.1 (s, 1C,
C6), 162.6 (d, JCF = 251.9 Hz, 1C, C3), 195.6 (s, 1C, C1). 19F{1H}
NMR ([D8]THF, 188.3 MHz): δ −120.3 (s, 1F).
Synthesis of [(3-MeC6H4)CaI(thf)4] (1). A suspension of finely
divided calcium metal (1.2 g, 30 mmol) in THF (40 mL) was cooled
to −20 °C. 3-Iodotoluene (5.45 g, 25 mmol) was added at this
temperature, and the resulting mixture was allowed to warm to 0 °C
while shaking. Shaking was continued for 1 h at 0 °C and for an
additional 5 h at ambient temperature. The resulting brown
suspension was filtered. The solid residue was extracted with THF
(20 mL) and discarded afterward. The combined THF solutions (60%
yield of organocalcium compounds, determined by acid consumption
by a hydrolyzed aliquot) were stored at −90 °C for 5 days. Afterward,
the precipitated crystalline solid was collected on a cooled Schlenk frit
and dried in vacuo. Yield: 6.01 g of an off-white solid (crude product).
Suitable crystals of the composition [(m-tolyl)CaI(thf)4]·0.5thf for X-
ray diffraction experiments were obtained by cooling of a saturated
solution in THF from ambient temperature to −40 °C. Those crystals
were also used for NMR measurements. Elemental analysis
(C23H39CaIO4, 546.55): calcd, Ca 7.33; found, Ca 7.03. 1H NMR
([D8]THF, 600 MHz): δ 1.78 (m, 16H, CH2 thf), 2.15 (br, 3H, CH3
tolyl), 3.64 (m, 16H, OCH2 thf), 6.55 (br, 1H, p-CH tolyl), 6.72 (br,
1H, m-CH tolyl), 7.45 (br, 1H, o-CH tolyl), 7.52 (br, 1H, o-CH′ tolyl).
Besides this signal set, another one of low intensity (*) was observed:
δ 2.19 (s, CH3 * tolyl), 6.67 (pseudo-d, p-CH * tolyl), 6.84 (pseudo-t,
m-CH * tolyl), 8.29 (pseudo-d, o-CH * tolyl), 8.45 (s, o-CH′ * tolyl).
Additionally, three intensive and very broad signals were observed: δ
2.1−2.3, 6.6−7.0, 7.7−8.2. 13C{1H}NMR ([D8]THF, 600 MHz): δ
21.8 (1C, CH3 * tolyl), 22.2 (1C, CH3 tolyl), 26.3 (8C, CH2 thf), 68.2
(8C, OCH2 thf), 123.5 (1C, C4), 125.0 (1C, C5), 126.1 (1C, C4 *),
126.6 (1C, C5 *), 132.5 (1C, C3), 134.2 (1C, C3 *), 138.1 (1C, C6),
141.0 (1C, C6 *), 142.1 (1C, C2), 144.9 (1C, C2 *), 185.3 (1C, C1
*), 189.7 (1C, C1). Again, additional broad signals were obtained: δ
125−127, 139.4−140.4, 143.5−144.5.
Synthesis of [(3-ClC6H4)CaI(thf)4] (4). 1-Iodo-3-chlorobenzene
(5.96 g, 25 mmol) was added to a suspension of finely dispersed
calcium metal (1.2 g, 29.9 mmol) in THF (40 mL) at −20 °C. The
resulting mixture was shaken for 1 h at 0 °C and for an additional 4 h
without cooling. The unreacted calcium was removed by filtration
through a Schlenk frit and covered with diatomaceous earth, and the
residue on the filter was dried in vacuo, suspended in THF (40 mL),
and stirred for 2 h at ambient temperature. After filtration, the
obtained solution was combined with the mother liquor. An overall
conversion of 74% was determined by acidimetric consumption of an
aliquot. The purple solution was stored for 1 day at −40 °C, and the
formed precipitate was collected on a cooled Schlenk frit and dried in
vacuo. Yield: 1.93 g (3.40 mmol, 13.6%). Suitable crystals of the
composition [(3-ClC6H4)CaI(thf)4] for X-ray diffraction experiments
were obtained by cooling a saturated solution in THF from ambient
temperature to −40 °C. Elemental analysis (C22H36CaIClO4, 566.96):
1
calcd, Ca 7.07; found, Ca 7.52%. H NMR ([D8]THF, 200 MHz): δ
1.73 (m, 16H, CH2 thf), 3.60 (m, 16H, OCH2 thf), 6.65 (m, 1H, p-CH
phenyl), 6.75 (m, 1H, m-CH phenyl), 7.48 (m, 1H, o-CH′ phenyl),
7.56 (m, 1H, o-CH phenyl). 13C{1H} NMR ([D8]THF, 100.6 MHz):
δ 25.3 (8C, CH2 thf), 67.5 (8C, OCH2 thf), 122.5 (1C, C4), 126.7
(1C, C5), 133.2 (1C, C3), 138.7 (1C, C6), 139.8 (1C, C2), 194.8 (1C,
C1).
Synthesis of [(3-BrC6H4)CaI(thf)4] (5). Activated calcium metal
(1.2 g, 29.9 mmol) was suspended in THF (40 mL), and 1-iodo-3-
bromobenzene (7.07 g, 25 mmol) was added slowly at −20 °C. The
suspension was shaken for 1 h at 0 °C and for an additional 4 h
without cooling. The formed precipitate was removed by filtration
through a Schlenk frit and covered with diatomaceous earth, and the
residue on the filter was dried in vacuo, suspended in THF (40 mL),
and stirred for 2 h at ambient temperature. After filtration, the
obtained solution was combined with the mother liquor. By
acidimetric consumption of an aliquot of the combined solutions, a
conversion of 67% was determined. After 4 days of storage of the
brown solution at −40 °C, the formed precipitate was finally collected
on a Schlenk frit and dried in vacuo. Yield: 3.90 g (6.38 mmol, 25.5%)
of a brown solid (crude product). Elemental analysis (C22H36CaIBrO4,
Synthesis of [(3,5-Me2C6H3)CaI(thf)4] (2). A suspension of finely
divided calcium metal (1.2 g, 29.9 mmol) in THF (40 mL) was cooled
to −20 °C. 1-Iodo-3,5-dimethylbenzene (5.80 g, 25 mmol) was added
at this temperature, and the resulting mixture was allowed to warm to
0 °C while shaking. Shaking was continued for 1 h at 0 °C and for an
additional 4 h at ambient temperature. The resulting violet suspension
was filtered, and the solid residue was discarded. The THF solution
(81% yield of organocalcium compounds, determined by acid
8651
dx.doi.org/10.1021/om301087e | Organometallics 2012, 31, 8647−8653

Organometallics
Article
1
611.41): calcd, Ca 6.56; found, Ca 6.80%. H NMR ([D8]THF, 200
MHz): δ 1.73 (m, 16H, CH2 thf), 3.60 (m, 16H, OCH2 thf), 6,72 (m,
1H, m-CH phenyl), 6.82 (m, 1H, p-CH phenyl), 7.54 (m, 1H, o-CH′
phenyl), 7.73 (m, 1H, o-CH phenyl). 13C{1H} NMR ([D8]THF, 100.6
MHz): δ 25.3 (8C, CH2 thf), 67.6 (8C, OCH2 thf), 124.5 (1C, C3),
125.4 (1C, C4), 127.5 (1C, C5), 139.0 (1C, C6), 142.6 (1C, C2),
196.3 (1C, C1).
X-ray Crystal Structure Determination. The intensity data were
collected on a Nonius KappaCCD diffractometer, using graphite-
monochromated Mo Kα radiation. Data were corrected for Lorentz
and polarization effects, but not for absorption.31,32
The structures were solved by direct methods (SHELXS33) and
2
refined by full-matrix least-squares techniques against Fo (SHELXL-
9733). All hydrogen atoms were included at calculated positions with
fixed thermal parameters. All nondisordered, non-hydrogen atoms
were refined anisotropically.33 XP (SIEMENS Analytical X-ray
Instruments, Inc.) was used for structure representations.
Synthesis of [(3-IC6H4)CaI(thf)4] (6). Finely dispersed calcium
metal (1.2 g, 29.9 mmol) was suspended in THF (80 mL) and cooled
to −20 °C. 1,3-Diiodobenzene (8.25 g, 25 mmol) was added at this
temperature, and the resulting mixture was allowed to warm to 0 °C
while shaking. Shaking was continued for 1 h at 0 °C and for an
additional 4 h at ambient temperature. The resulting brown
suspension was filtered, and the solid residue was dried in vacuo.
The residue was twice extracted with THF (40 mL), and the filtrates
were combined. The combined solutions (66% yield of organocalcium
compounds, determined by acid consumption by a hydrolyzed aliquot)
were stored at −40 °C for 4 days. Afterward, the formed crystalline
solid was collected on a cooled Schlenk frit and dried in vacuo. Yield:
4.59 g (6.97 mmol, 27.9%) of a pale yellow solid. Elemental analysis
Crystal Data for 1. C23H39CaIO4, 0.5 C4H8O; Mr = 582.57 g mol−1;
colorless prism, size 0.06 × 0.06 × 0.06 mm3; monoclinic; space group
C2/c; a = 17.5880(3) Å, b = 18.9070(4) Å, c = 16.7740(3) Å, β =
90.123(3)°; V = 5577.95(18) Å3; T = −140 °C; Z = 8; ρcalcd = 1.387 g
cm−3; μ (Mo Kα) = 13.6 cm−1; F(000) = 2416; 5317 reflections in
h(−22/22), k(−24/24), l(0/21); measured in the range 3.16° ≤ Θ ≤
27.48°; completeness Θmax = 86.8%; 5319 independent reflections; Rint
= 0.0422; 4857 reflections with Fo > 4σ(Fo); 285 parameters, 0
restraints; R1obs = 0.0483, wR2 = 0.1074, R1all = 0.0552, wR2
=
obs
all
0.1131; GOF = 1.138; largest difference peak and hole = 1.087/−
0.813 e Å−3.
1
(C22H36CaI2O4, 658.42): calcd, Ca 6.09; found, Ca 6.34%. H NMR
Crystal Data for 2. C24H41CaIO4; Mr = 560.55 g mol−1; colorless
prism, size 0.56 × 0.55 × 0.53 mm3; monoclinic; space group P21/c; a
= 13.3143(9) Å, b = 12.0557(9) Å, c = 16.2773(12) Å, β = 91.975(3)°;
V = 2611.2(3) Å3; T = 23 °C; Z = 4; ρcalcd. = 1.426 g cm−3; μ (Mo Kα)
= 14.48 cm−1; F(000) = 1160; 5180 reflections in h(−16/16), k(0/
14), l(0/20); measured in the range 3.02° ≤ Θ ≤ 27.58°;
([D8]THF, 400 MHz): δ 1.73 (m, 16H, CH2 thf), 3.58 (m, 16H,
OCH2 thf), 6.63 (m, m-CH phenyl), 7.05 (m, 1H, p-CH phenyl), 7.56
(m, 1H, o-CH′ phenyl), 7.96 (m, 1H, o-CH phenyl). 13C{1H} NMR
([D8]THF, 100.6 MHz): δ 25.3 (8C, CH2 thf), 67.2 (8C, OCH2 thf),
101.0 (1C, C3), 128.4 (1C, C5), 131.4 (1C, C4), 139.0 (1C, C6),
149.0 (1C, C2), 197.1 (1C, C1).
Synthesis of [(3-MeOC6H4)CaI(thf)n] (7). 3-Iodo-anisole (5.85 g,
25 mmol) was added to a suspension of finely divided calcium metal
(1.2 g, 29.9 mmol) in THF (40 mL) at −20 °C. The resulting brown
mixture was allowed to warm to 0 °C while shaking. Shaking was
continued for 1 h at 0 °C and for an additional 4 h at ambient
temperature. The suspension was filtered, and the solid residue was
discarded. The THF solution (75% yield of organocalcium
compounds, determined by acid consumption by a hydrolyzed
aliquot) was stored at −90 °C for 1 week. Afterward, the formed
crystalline solid was collected on a cooled Schlenk frit and dried in
vacuo. Yield: 4.43 g of a pale yellow solid. Elemental analysis
(tetrakis(thf) adduct: C23H39CaIO5, 562.54): calcd, Ca 7.12; (tris(thf)
completeness Θmax = 99.7%; 5184 independent reflections; Rint
0.0677; 4592 reflections with Fo > 4σ(Fo); 274 parameters, 0
restraints; R1obs = 0.0296, wR2 = 0.0656, R1all = 0.0383, wR2
=
=
all
obs
0.0690; GOF = 0.992; largest difference peak and hole = 1.299/−
0.578 e Å−3.
Crystal Data for 4. C22H36CaClIO4; Mr = 566.94 g mol−1; colorless
prism; size 0.05 × 0.05 × 0.05 mm3; orthorhombic; space group
P212121; a = 7.9202(5) Å, b = 10.2280(7) Å, c = 31.556(2) Å; V =
2556.3(3) Å3; T = −140 °C; Z = 4; ρcalcd. = 1.473 g cm−3; μ (Mo Kα)
= 15.81 cm−1; F(000) = 1160; 9019 reflections in h(−9/9), k(−12/8),
l(−37/37); measured in the range 2.58° ≤ Θ ≤ 25.02°; completeness
Θmax = 94.7%; 3970 independent reflections; Rint = 0.0542; 3240
1
reflections with Fo > 4σ(Fo); 253 parameters, 0 restraints; R1obs
=
complex: C19H31CaIO4, 490.44): calcd, Ca 8.17; found, Ca 8.69%. H
0.0739, wR2obs = 0.1185, R1all = 0.1001, wR2all = 0.1291; GOF = 1.291;
Flack parameter = 0.09(6); largest difference peak and hole = 0.563/−
0.524 e Å−3.
NMR ([D8]THF, 400 MHz): δ 1.73 (m, 16H, CH2 thf), 3.58 (m,
19H, CH2 thf and OCH3 phenyl), 6.24 (m, 1H, p-CH phenyl), 6.72
(m, 1H, m-CH phenyl); 7,19 (m, 2H, o-CH and o-CH′ phenyl).
13C{1H} NMR ([D8]THF, 100.6 MHz): δ 25.3 (8C, CH2 thf), 67.2
(8C, OCH2 thf), 53.2 (1C, OCH3 phenyl), 106.5 (1C, C4), 124.4 (1C,
C5), 125.0 (1C, C2), 132.5 (1C, C6), 156.8 (1C, C3), 191.3 (1C, C1).
Synthesis of [(β-Naphthyl)CaI(thf)4] (8). A suspension of finely
divided calcium metal (1.2 g, 30 mmol) in THF (60 mL) was cooled
to −20 °C. β-Iodonaphthalene (5.00 g, 19.7 mmol) was added at this
temperature, and the resulting mixture was allowed to warm to 0 °C
while shaking. Shaking was continued for 1 h at 0 °C and for an
additional 5 h at ambient temperature. During this time, the color of
the suspension turned from dark green to violet. The resulting violet
suspension was filtered. The solid residue was extracted with THF
(140 mL) and discarded afterward. The combined THF solutions
(84% yield of organocalcium compounds, determined by acid
consumption by a hydrolyzed aliquot) were stored at −40 °C for 4
days. Afterward, the formed crystalline solid was collected on a cooled
Schlenk frit and dried in vacuo. Yield: 3.26 g (5.60 mmol, 22.4%) of a
colorless solid. Suitable crystals of the composition [(β-naphthyl)CaI-
(thf)4] for X-ray diffraction experiments were obtained by cooling of a
saturated solution in THF from ambient temperature to −10 °C.
Those crystals were used for NMR measurements. Elemental analysis
Crystal Data for 8. C26H39CaIO4; Mr = 582.55 g mol−1; colorless
prism; size 0.06 × 0.05 × 0.05 mm3; monoclinic; space group Cm; a =
12.1149(4) Å, b = 13.5272(3) Å, c = 8.3474(3) Å, β = 99.737(1)°; V =
1348.27(7) Å3; T = −140 °C; Z = 2; ρcalcd. = 1.435 g cm−3; μ (Mo Kα)
= 14.05 cm−1; F(000) = 600; 4152 reflections in h(−15/11), k(−17/
17), l(−8/10); measured in the range 3.01° ≤ Θ ≤ 27.51°;
completeness Θmax = 99.3%; 2419 independent reflections; Rint
0.0195; 2397 reflections with Fo > 4σ(Fo); 166 parameters, 2
restraints; R1obs = 0.0219, wR2 = 0.0484, R1all = 0.0223, wR2
=
=
all
obs
0.0486; GOF = 1.036; Flack parameter = −0.028(17); largest
difference peak and hole = 0.309/−0.424 e Å−3.
ASSOCIATED CONTENT
■
S
* Supporting Information
Crystallographic data in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
Crystallographic data deposited at the Cambridge Crystallo-
graphic Data Centre under CCDC-909485 for 1, CCDC-
909486 for 2, CCDC-910006 for 4, and CCDC-866605 for 8
contain the supplementary crystallographic data, excluding
structure factors; this data can be obtained free of charge via
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge CB2 1EZ, U.K.; Fax: (+44) 1223−336−033; or
deposit@ccdc.cam.ac.uk).
1
(C26H39CaIO4, 582.55): calcd, Ca 6.88; found, Ca 6.89%. H NMR
([D8]THF, 600 MHz): δ 1.73 (m, 16H, CH2 thf), 3.59 (m, 16H,
OCH2 thf), 7.02 (m, 1H), 7.10 (m, 1H), 7.28 (m, 1H), 7.47 (m, 2H),
7.90 (m, 1H), 8.10 (m, 1H). 13C{1H} NMR ([D8]THF, 100.6 MHz):
δ 25.3 (8C, CH2 thf), 67.5 (8C, OCH2 thf), 122.3 (1C), 122.5 (1C),
123.5 (1C), 127.5 (1C), 128.2 (1C), 132.9 (1C), 134.0 (1C), 139.5
(1C), 140.8 (1C), 189.1 (1C, C−Ca).
8652
dx.doi.org/10.1021/om301087e | Organometallics 2012, 31, 8647−8653

Organometallics
Article
(26) Langer, J.; Krieck, S.; Fischer, R.; Gorls, H.; Westerhausen, M. Z.
̈
AUTHOR INFORMATION
■
Anorg. Allg. Chem. 2010, 636, 1190−1198.
(27) Harvey, M. J.; Hanusa, T. P. Organometallics 2000, 19, 1556−
1566.
Corresponding Author
*Fax: +49 (0) 3641 948132. E-mail: m.we@uni-jena.de.
(28) Bruhat, G.; Thomas, V. C. R. Acad. Sci. 1926, 183, 297−299.
(29) (a) Piller, F. M.; Appukkuttan, P.; Gavryushin, A.; Helm, M.;
Knochel, P. Angew. Chem., Int. Ed. 2008, 47, 6802−6806;(b) Angew.
Chem. 2008, 120, 6907−6911.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(30) Jander, G.; Jahr, K. F.; Schulze, G.; Simon, J. Massanalyse;
Walter de Gruyter: Berlin, Germany, 1989.
■
We thank the German Research Foundation (DFG, Bonn-Bad
Godesberg, Germany) and the Fonds der Chemischen
Industrie (VCI/FCI, Frankfurt/Main, Germany) for financial
support. M.K. is grateful to the Fonds der Chemischen
Industrie (VCI, Frankfurt/Main, Germany) for a generous
Ph.D. stipend. We also acknowledge support by the Friedrich
Schiller University Jena and the European Fonds for Regional
Development (EFRE).
(31) COLLECT: Data Collection Software; Nonius B.V.: Delft, The
Netherlands, 1998.
(32) Otwinowski, Z.; Minor, W. Processing of X-Ray Diffraction Data
Collected in Oscillation Mode. In Macromolecular Crystallography. Part
A; Carter, C. W., Sweet, R. M., Eds.; Methods in Enzymology;
Academic Press: San Diego, CA, 1997; Vol. 276, pp 307−326.
(33) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122.
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