Hydrocarbon-Soluble Bis(trimethylsilylmethyl)calcium and Calcium-Iodine Exchange Reactions at sp2-Hybrized Carbon Atoms

Article abstract of DOI:10.1021/acs.organomet.7b00592

Hydrocarbon-soluble and highly reactive [(L)_xCa(CH₂SiMe₃)₂] (L = tetrahydropyran, x = 4 (2a); L = tmeda, x = 2 (2b)) is synthesized by the metathesis reaction of Me₃SiCH₂CaI (1-I) with KCH₂SiMe₃. The durability of 2a in tetrahydropyran solution at 0 °C is sufficiently high for subsequent chemical transformations. The reaction of ICH₂SiMe₃ with calcium in diethyl ether yields unique cage compound [(Et₂O)₂Ca(I)₂·(Et₂O)₂Ca(I)(OEt)·(Et₂O)Ca(I)(CH₂SiMe₃)] (3). We demonstrate that alkylcalcium complexes are valuable reagents for calcium-iodine exchange reactions at C_sp²-I functionalities.

Full text of DOI:10.1021/acs.organomet.7b00592

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX-XXX
Hydrocarbon-Soluble Bis(trimethylsilylmethyl)calcium and Calcium−
Iodine Exchange Reactions at sp2‑Hybrized Carbon Atoms
Alexander Koch,† Marino Wirgenings,‡ Sven Krieck,† Helmar Gorls,† Georg Pohnert,‡
̈
and Matthias Westerhausen*,†
‡
†Institute of Inorganic and Analytical Chemistry and Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University
Jena, D-07743 Jena, Germany
S
* Supporting Information
ABSTRACT: Hydrocarbon-soluble and highly reactive
[(L)xCa(CH2SiMe3)2] (L = tetrahydropyran, x = 4 (2a); L
= tmeda, x = 2 (2b)) is synthesized by the metathesis reaction
of Me3SiCH2CaI (1-I) with KCH2SiMe3. The durability of 2a
in tetrahydropyran solution at 0 °C is sufficiently high for
subsequent chemical transformations. The reaction of
ICH2SiMe3 with calcium in diethyl ether yields unique cage
compound [(Et2O)2Ca(I)2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)-
(CH2SiMe3)] (3). We demonstrate that alkylcalcium com-
plexes are valuable reagents for calcium−iodine exchange
2
reactions at Csp −I functionalities.
trimethylphenyl)calcium (dimesitylcalcium). However, the
yield was rather low, and it was impossible to generalize this
concept for the synthesis of homoleptic calcium-based
organometallics.1 (ii) The solvent exchange from tetrahydro-
furan (THF) to 1,4-dioxane (diox) of the intricate co-
condensation product of BrCH(SiMe3)2 and calcium vapor
gave crystals of [(diox)2Ca{CH(SiMe3)2}2] (no yield given);
presumably, heteroleptic {(Me3Si)2CHCaBr} was the initial
product.2 (iii) Arylcalcium halides were reacted with KOtBu to
shift the Schlenk equilibrium toward the homoleptic derivatives
due to the insolubility of potassium halide and {Ca(OtBu)2} in
common organic solvents.3,4 (iv) The most successful approach
to dialkylcalcium complexes involved salt metathesis. Thus, the
reaction of 2 equiv of KCH(SiMe3)2 with CaI2 in THF yielded
the envisioned compound, [(thf)2Ca{CH(SiMe3)2}2].5 Bis-
(trimethylsilyl)methylcalcium compounds exhibited good met-
alation strength and displayed powerful intermediates to
heteroleptic calcium compounds.6,7 Furthermore, coligand-
free [Ca{C(SiMe3)3}2] was only accessible if the reaction was
performed in benzene.8 In addition, stabilized calcium
methanides such as benzyl and propenyl (η1-allyl) compounds
were also prepared by this metathetical approach.7,9,10 (v) Up
to now, the alternative strategy of transmetalation was
unsuccessful for the preparation of homometallic dialkylcalcium
complexes. The established transmetalation of tin bis[bis-
(trimethylsilyl)amide] with calcium yielded [Ca{N-
(SiMe3)2}2],11 whereas the reaction of calcium with isoelec-
tronic [Sn{CH(SiMe3)2}2] led to the formation of the
INTRODUCTION
■
Calcium is globally abundant, easily available, and inexpensive.
Further beneficial properties include nontoxicity and a chemical
behavior combining the advantageous properties of alkali and
early transition metals. Hence, it is not surprising that a
plethora of inorganic calcium compounds is ubiquitous in our
daily life. However, the underdeveloped organometallic
chemistry of this element rests in the shadows of lighter s-
block metals such as lithium and magnesium. This can mainly
be attributed to their facile synthesis and, in some cases, even
the commercial availability of organic lithium and magnesium
compounds.
In contrast, until today no easy and scalable straightforward
synthesis of dialkyl calcium compounds has been developed.
Several promising strategies for the preparation of homoleptic
diorganylcalcium complexes are summarized in Scheme 1: (i)
Fractionated crystallization allowed the synthesis of bis(2,4,6-
Scheme 1. Strategies for the Synthesis of Homoleptic
Diorganylcalcium Complexes with Ca−C Bonds
a
a
Received: August 2, 2017
See text; R = CH2SiMe3, R′ = CH(SiMe3)2, R″ = N(SiMe3)2.
© XXXX American Chemical Society
A
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Article
stannanide Ca[Sn{CH(SiMe3)2}3]2.12 In a similar procedure
using bis(trimethylsilylmethyl)zinc and calcium metal, hetero-
bimetallic zincates were isolated.13 (vi) Lewis acid−base
reactions of tris(trimethylsilylmethyl)alane or triethylgallane
with [Ca{N(SiMe3)2}2] yielded heterobimetallic calcium
alanates and gallanates, respectively.14
Very recently, we developed a straightforward direct
synthesis of [(thp)4Ca(CH2SiMe3)X] (monosylcalcium hal-
ides; X = Br (1-Br), I (1-I), monosyl = CH2SiMe3, thp =
tetrahydropyran) via the atom-economic Grignard-type reac-
tion of calcium metal with ICH2SiMe3.15 The smaller steric
protection and reduced stabilization of the negative charge of
the methanide functionality due to the lack of the second
trimethylsilyl group enhanced the metalation power, as recently
demonstrated in the deprotonation of an ortho-substituted
benzene.16 The replacement of the halide ion by a second
monosyl group should increase the solubility in hydrocarbons
and now allows the usage of such solvents as reaction media.
Furthermore, the reactivity of monosyl calcium compounds
relating to calcium−halogen exchange was investigated
(Scheme 2).
THP). However, the salt metathetical approach gave no reliable
results. In benzene and pentane, a very slow reaction occurred,
and only unidentified products were obtained. In contrast, ether
degradation products were isolated from reactions in ethereal
solvents. CaI2 was only slightly soluble in ether, which
hampered a fast reaction and initially led to potassium calciate,
which easily degraded the ethereal solvent. Therefore, a new
innovative homogeneous approach had to be developed: An
equimolar amount of 1-I was added at 0 °C to a solution of
KCH2SiMe3 in THP, which instantaneously resulted in the
formation of insoluble KI and highly soluble [(thp)4Ca-
(CH2SiMe3)2] (2a) (Scheme 2). This strategy represents a
reliable, easily scalable, and straightforward protocol to this
hydrocarbon soluble dialkylcalcium complex 2a with yields
typically higher than 85%.
In order to study the stability of 2a, a 0.42 M solution of 2a
in 0.4 mL of a mixture of pentane/THP (5.5/8) and 0.1 mL of
benzene/[D6]benzene, serving as internal NMR standard, was
1
prepared. The integration of the methylene moiety in the H
NMR spectrum permitted monitoring the decay of 2a,
obtaining t50 values of approximately 4 and 30 h at r.t. and 0
°C, respectively (Figure 1). Since only slow degradation is
Scheme 2. Reactivity of Me3SiCH2CaX (X = Br and I)
Referring to the Formation of [Ca(CH2SiMe3)2] and
a
Calcium−Iodine Exchange Reactions
a
See text; R = aryl, Ph2CCPh, c-C3H5.
Figure 1. Degradation of 0.42 M solution of [(thp)4Ca(CH2SiMe3)2]
(2a) in THP/pentane/benzene (5.5:8:3) at room temperature
(circles) and at 0 °C (squares).
RESULTS AND DISCUSSION
■
Solvent exchange from THF solutions of 1-I/Br to
tetrahydropyran (THP) or 1,4-dioxane (diox) lead to neither
the formation of halide free solutions nor to the isolation of
pure [(L)4Ca(CH2SiMe3)2] (L = ligated ether base). The
reaction of 1-I with KOtBu in tetrahydrofuran in analogy to the
synthesis of diarylcalcium compounds3,4 was very challenging
due to time-consuming removal of insoluble {Ca(OtBu)2}. The
reaction had to be performed with very small amounts (up to 2
mmol), regaining 86% of the monosyl groups as determined by
acidimetric titration of an aliquot of the reaction mixture.
Accompanying ether degradation reactions hampered an easy
scale-up and significantly lowered the yields of isolated product.
observed within the first hour at 0 °C, smooth reactions can be
carried out under inert conditions. At 0 °C, the degradation of
2a seems to decelerate, when ca. 60% of calcium-bound
trimethylsilylmethyl groups are still present. Taking this
concentration value as the initial value, a larger t50 value of
3.5 days is observed thereafter, which is more comparable to 1-I
with a t50 value of 1 week at r.t. in a THP/benzene (2/1)
mixture.15 This finding hints toward stabilization of alkylcal-
cium functionalities by formation of cage compounds
containing ether degradation products such as alkoxide and
oxide anions as observed earlier.17−19
1
The H NMR spectrum of the reaction mixture in [D8]THF
showed a resonance at −1.86 ppm for the calcium-bound
methylene group which is high-field-shifted by 0.08 ppm
compared to that of 1-I, indicating the formation of desired
[Ca(CH2SiMe3)2] (2), which is also soluble in pentane.15 The
Derivative 2a is a highly soluble compound even in saturated
hydrocarbons. Storage of a concentrated solution of 2a in
pentane at −40 °C commonly led to the separation of a second
oily phase, which sometimes crystallized and allowed the
determination of the molecular structure of 2a (Figure 2).
Complex 2a crystallized as a mononuclear complex. The
asymmetric unit consists of 1.5 molecules of A and B with an
inversion center located on the calcium atom of molecule B.
The coordination sphere is saturated by 4 thp ligands with
typical Ca1−Othp bond lengths (av. 242.0 pm), leading to a
distorted octahedral environment at the calcium atom with the
1
small coupling constant JC−H = 102.2 Hz is characteristic for
these trimethylsilylmethyl substituents as discussed previ-
ously.15
Due to these observations, alternative routes were studied. In
analogy to the syntheses of [(thf)2Ca{CH(SiMe3)2}2] and
[Ca{C(SiMe3)3}2],5,8 CaI2 was reacted with easily accessible
KCH2SiMe3 in various solvents (pentane, benzene, THF, and
B
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Scheme 3. Reaction between ICH2SiMe3 and Activated Ca in
Diethyl Ether Yielding [(Et2O)2Ca(I)2·(Et2O)2Ca(I)(OEt)·
(Et2O)Ca(I)(CH2SiMe3)] (3)
Figure 2. Molecular structures of [(thp)4Ca(CH2SiMe3)2] (2a, left)
and of [(tmeda)2Ca(CH2SiMe3)2] (2b, right). The thermal ellipsoids
represent a probability of 30%. Hydrogen atoms are omitted for clarity
reasons.
alkyl ligands in a trans arrangement. In contrast to the very
small Ca−C bond lengths in 1-I (252.7(3) pm) and 1-Br
(250.0(4) pm),15,19 the Ca−C bonds are elongated to an
average value of 258.2 pm, which can be explained by
intramolecular repulsion between the methyl groups of the
monosyl anions and the thp ligands leading to large Ca1−C1/5
−Si1/2 bond angles between 136.6(2) and 143.8(2)°. These
angles are quite comparable to those of 1-I (131.2(1)°) and 1-
Br (143.9(2)°), but there the thp ligands are pushed toward the
sterically less demanding halide anion. However, this is
impossible in [(thp)4Ca(CH2SiMe3)2] (2a) due to the
presence of another bulky trimethylsilylmethyl group, leading
to an elongation of the Ca−C bonds. This structural feature
explains the ease of ether degradation because intramolecular
strain is released by this side reaction. Substitution of ligated
thp by 1,2-bis(dimethylamino)ethane (tmeda) yielded mono-
nuclear [(tmeda)2Ca(CH2SiMe3)2] (2b, Figure 2) as colorless
cubes, whereas the diarylcalcium compounds form dinuclear
complexes.3,4 Similar to 2a, the Ca−C bonds are elongated to
an average value of 259.4 pm due to steric repulsion between
the trimethylsilyl moieties and the methyl groups of the tmeda
ligands.
Ether cleavage reactions start via a deprotonation step in α-
or β-position leading to alkoxide moieties.17−20 The solvent
exchange from THF to less strained THP enhances the
durability of organocalcium reagents. To prepare the
dialkylcalcium complex with volatile diethyl ether ligands and
to explore the reactivity of trimethylsilylmethylcalcium
complexes we reduced ICH2SiMe3 with activated calcium in
diethyl ether and discovered genuinely new and highly soluble
[(Et2O)2Ca(I)2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)(CH2SiMe3)]
(3) (Scheme 3). The molecular structure and numbering
scheme of 3 are depicted in Figure 3. Formation of ethoxide
ligands from diethyl ether degradation and incorporation in
molecular cage compounds have been observed earlier for
strongly Lewis acidic metals;20 due to the enormous basicity,
bridging positions are quite common. Due to severe ether
cleavage, [(Et2O)4Ca(CH2SiMe3)2] was not accessible via this
route. The yield of alkylcalcium moieties determined by
acidimetric titration was as low as 32%.
Figure 3. Molecular structure and numbering scheme of [(Et2O)2Ca-
(I)2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)(CH2SiMe3)] (3). Hydrogen
atoms are omitted for clarity reasons. Thermal ellipsoids represent a
probability of 30%.
chemistry. The Ca1−C1 distance is 245.3(8) pm, which is 5
pm shorter compared to that in 1-I and 1-Br,15,19 verifying a
reduced steric strain compared to dialkylcalcium complexes 2a
and 2b. The coordination of a further anion to Ca1 in contrast
to Ca2/3 leads to a reduced Lewis acidity of Ca1, shown by
elongated Ca1−O6, Ca1−I1/I3 and Ca1−I4 bond lengths.
Complex 3 combines the structural features of monosylcalcium
halide, ether degradation products (ethoxide moiety) and
calcium diiodide, an example combining organyl moieties and
ether cleavage products.10,15,19 The high solubility of such
complexes commonly leads to crystalline yields (2%) smaller
than the yield obtained by acidimetric titration of aliquots of
the reaction mixtures.19,21
Halogen−metal exchange reactions are equilibrium reactions,
controlled by the difference of the pKa values of the
participating reactants, and mainly a domain of alkyllithium
and Grignard reagents.22,23 Nevertheless, Bickelhaupt and co-
workers performed a calcium−bromine exchange at 2,6-
polyether-substituted bromobenzene with diphenylcalcium
and identified the products via conversion to tin derivatives.24
However, the general suitability of organocalcium compounds
for metal−halogen exchange reactions has never been shown.
Due to the high pKa value of the Si(CH3)4 (monosyl-H), 1-I
was combined with iodobenzene (4a) in [D8]THF, instantly
forming phenyl calcium iodide and ICH2SiMe3 as monitored by
NMR spectroscopy. Even after 1 week, no Wurtz-type coupling
to PhCH2SiMe3 was observed. To suppress Wurtz-type
coupling between newly formed ICH2SiMe3 and still existing
1-I, the reaction was performed at −20 °C.
The calcium triangle in 3 is doubly μ3-bridged by an ethoxide
and the iodide ion I4, giving a Ca3OI trigonal bipyramid with I4
and O6 in apical positions and resulting in a unique
coordination mode of iodide anions in calcium coordination
C
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To quantify the exchange, trimethylsilyl chloride was added,
and the product mixture was investigated by GC/MS, showing
83% yield of 5a (Table 1). However, bis(trimethylsilyl)methane
resulted in the exchange of only one iodine by a calcium atom
as monitored by NMR spectroscopy. Quenching of the reaction
mixture with Me3Si−Cl gave a mixture of 5g and 1,4-
bis(trimethylsilyl)benzene. The latter compound can be
explained by a fast calcium−iodine exchange of initially formed
5g in the presence of an excess of Me3Si−Cl. These findings are
in agreement with the previous results and underline that a
calcium−iodine exchange is much faster than the addition of
Me3Si−Cl to organocalcium compounds.
Table 1. Scope of Calcium−Iodine Exchange and
a
Subsequent Quenching with Me3Si−Cl
SUMMARY
■
An easily scalable straightforward synthesis of hydrocarbon-
soluble and highly reactive bis(trimethylsilylmethyl)calcium is
presented. The durability of [(thp)4Ca(CH2SiMe3)2] (2a) in
pentane/THP solutions allows the safe handling of this
organocalcium reagent making this organocalcium complex a
valuable heavy Grignard-type reagent. The reaction of
ICH2SiMe3 and calcium in diethyl ether allows the isolation
of [(Et2O)2Ca(I)2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)-
(CH2SiMe3)] (3), a unique trinuclear cage compound, beside
species with varying amounts of ethoxy and monosyl moieties.
These compounds clarify that classic Grignard reaction
conditions in diethyl ether do not represent valuable protocols
for the synthesis of dialkylcalcium compounds with small alkyl
substituents. Remarkably, (trimethylsilylmethyl)calcium deriva-
tives undergo calcium−iodine exchange reactions and show a
promising behavior as also observed for organolithium reagents
whereas organomagnesium compounds are less eligible for
metal−halogen exchange reactions.23 The full synthetic
potential of this novel class of Ca−Grignard-type reagents
will be explored to underline the competitiveness to organo-
lithium and organomagnesium (Grignard) reagents.
a
Yields are determined with GC/MS. Reaction conditions: 1) 4 (0.25
mmol), 1-I (0.275 mmol, added dropwise), 2 mL of THF, −40 °C, 10
min; 2) Me3Si−Cl (1 mmol), −40 °C, 10 min, then warming to r.t.
b
c
Aryl calcium iodide is observed by NMR spectroscopy; A 1 h
d
reaction time was used during step 1. Compound 4 (0.25 mmol),
Me3Si−Cl (1 mmol), 2 mL of THF, −40 °C, then dropwise addition
of 1-I (0.275 mmol). Yield was estimated by NMR spectroscopy via
integration of the resonances of ICH2SiMe3 and CH2(SiMe3)2; Yield
of 1,4 bis(trimethylsilyl)benzene; Addition of 0.55 mmol of 1-I (2.2
e
f
EXPERIMENTAL SECTION
g
■
Materials and Methods. All manipulations were carried out in an
inert nitrogen atmosphere using standard Schlenk techniques, if not
otherwise noted. THF, THP, benzene, and pentane were dried over
KOH and subsequently distilled over sodium/benzophenone in a
nitrogen atmosphere prior to use. TMEDA was dried over CaH2.
Deuterated solvents were dried over sodium, distilled, degassed, and
equiv).
was also obtained from the reaction of Me3Si−Cl with
Me3SiCH2CaI (1-I) still present, indicating an incomplete
conversion. Therefore, the reaction time was increased to 1 h,
and the same product distribution was found. Then, 1-I was
added to a mixture of iodobenzene (4a) and Me3Si−Cl at −40
°C, yielding 84% of 5a, indicating that the calcium−iodine
exchange is faster than the reaction of Me3Si−Cl with 1-I. If 1-
Br is employed instead of 1-I, then phenylcalcium bromide and
ICH2SiMe3 were formed, indicating that only the organyl
moiety was transferred, but halide scrambling was missing. The
use of iodo-pentafluorobenzene (4b) yields a larger amount of
5b, indicating that more electron-deficient aromatic compounds
enhance the efficiency of this calcium−iodine exchange. In
order to unravel the effect of ortho substitutions during the
calcium−iodine exchange, iodo-2,4,6-trimethylbenzene (4c)
was reacted with 1-I. However, no reaction occurred, whereas
the reaction of iodo-2,6-ditolylbenzene (4d) and 1-I in the
presence of Me3Si−Cl took place, yielding the expected silane
5d with 85%. The reaction of 1-I with iodo-triphenylethene
(4e) in the presence of Me3Si−Cl resulted in the formation of
5e with very good yields. However, the calcium organic
compounds were not stable under these conditions. Even
iodocyclopropane (4f) underwent an calcium−iodine exchange
with 1-I, yielding 31% of 5f after addition of Me3Si−Cl. The
reaction of 1,4-diiodobenzene (4g) with 2.2 equiv of 1-I
stored under nitrogen over sodium. H and 13C{1H} NMR spectra
1
were recorded on Bruker Avance 400 and Fourier 300 spectrometers.
Chemical shifts are reported in parts per million (ppm) relative to
SiMe4 as an external standard referenced to the solvents residual
proton signal. ClCH2SiMe3 and LiCH2SiMe3 were purchased from
ABCR. KOtBu was purchased from Fluka. NaI was purchased from
Lancaster. The yields given are not optimized unless noted otherwise.
KCH2SiMe3 was prepared by the metal-exchange reaction of
LiCH2SiMe3 with KOtBu in pentane. ICH2SiMe3 was prepared by
the reaction of ClCH2SiMe3 and NaI in acetone.25 Purity was
controlled by NMR spectroscopic measurements, by determination of
the alkalinity of an aliquot of the reaction solution and complexometric
titration of the Ca content with EDTA.
Large-Scale Synthesis of [(thp)4Ca(I)(CH2SiMe3)] (1-I). Acti-
vated calcium (4.20 g, 104 mmol, 1.1 equiv) was suspended in 150 mL
of THF. The suspension was cooled to −78 °C before 20.38 g of
ICH2SiMe3 (95 mmol, 1 equiv) were added. The reaction mixture was
shaken for 1 h at −78 °C. Then, all solids were removed by filtration,
yielding 125 mL of a 0.53 M solution of 1 THF (70% yield by
acidimetric titration). The solvent was removed, and the residue was
extracted with three portions of 30 mL of THP and a final portion of
60 mL of THP. Then, 130 mL of pentane were added. All solids were
removed by filtration and the solution was stored at −40 °C overnight,
initiating crystallization of 1. In the cold, additional 100 mL of pentane
were added to complete crystallization, yielding 28.26 g of [(thp)4Ca-
D
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(I)(CH2SiMe3)] (48 mmol, 50%). The analytical data are in
accordance with literature values.15
and addition of pentane yielded further crops of amorphous solids
with varying amounts of trimethylsilylmethyl and ethoxide groups. H
1
[(thp)4Ca(CH2SiMe3)2] (2a). A 0.274 M solution of [(thp)4Ca(I)-
(CH2SiMe3)] in THP (12.7 mL, 2.093 g, 3.5 mmol, 1eq) was slowly
added at 0 °C to a precooled solution of 442 mg of KCH2SiMe3 (3.5
mmol, 1eq) in 5 mL of THP. The white suspension was stirred for 30
min before the solvent was removed, leaving a slightly yellow residue,
which was extracted with 20 mL of pentane. The remaining solids (KI)
were removed, yielding 17 mL of a 0.18 M solution of [(thp)4Ca-
(CH2SiMe3)2] in pentane (87%), which is pure by NMR spectroscopy
as well as titrations and can be used without further purification.
Reduction of the volume to half of the original volume and storing at
NMR (400.13 MHz, 233 K, [D8]THF): δ −1.81 (2H, s), −0.14 (9H,
s), 1.13 (24 H, t, 3JH−H = 7.0 Hz), 1.22 (3H, br s), 3.40 (16H, t, 3JH−H
= 7.0 Hz), 3.88 (2H, br s). 13C{1H} NMR (100.6 MHz, 233 K,
[D8]THF): δ 5.3, 6.9, 15.6, 22.5, 59.2, 66.2. Crystal data for 3:
C28.5H72Ca3I4O6Si, M = 1166.79 g mol−1, colorless prism, size 0.112 ×
0.110 × 0.088 mm3, orthorhombic, space group Pbca; a = 13.3229(2),
b = 22.8513(2), c = 33.7872(3) Å; V = 10286.4(2) Å3, T = −140 °C, Z
= 8, ρcalcd. = 1.507 g cm−3, μ(Mo Kα) = 27.74 cm−1, multiscan,
transmin: 0.5720, transmax: 0.7456, F(000) = 4616, 108 250 reflections
in h(−17/16), k(−29/29), l(−43/43), measured in the range of 1.87°
≤ Θ ≤ 27.48°, completeness Θmax = 99.9%, 11 788 independent
reflections, Rint = 0.0418, 10949 reflections with F0 > 4σ(F0), 367
parameters, 0 restraints, R1obs = 0.0597, wR2obs = 0.1478, R1all = 0.0642,
wR2all = 0.1504, GOOF = 1.228, largest difference peak and hole:
2.462/−1.435 e Å−3.
General Method for the Calcium−Iodine Exchange Reac-
tions. Method A (for 4a, 4b, 4c, 4f, 4g). R-I (1 equiv) was dissolved
in 1 mL of THF and the solution was cooled to −40 °C. Then, 1.1
equiv of [(thp)4Ca(I)(CH2SiMe3)] were dissolved in 1 mL of THF
and added to the organyl iodide. This reaction mixture was stirred for
10 min. Then, 4 equiv of Me3Si−Cl were added at this temperature.
After stirring for another 10 min at −40 °C, the reaction suspension
was warmed to r.t., and 2 mL of H2O was added. The organic phase
was separated, dried over anhydrous Na2SO4, and directly used for
GC/MS measurements.
1
−40 °C yielded crystalline [(thp)4Ca(CH2SiMe3)2] (2a). H NMR
(400.13 MHz, 233 K, [D8]THF): δ −1.89 (4H, s), −0.15 (18H, s),
1.52 (16H, m), 1.63 (8H, m), 3.57 (16H, t, 3JH−H = 4.81 Hz). 13C{1H}
NMR (100.6 MHz, 233 K, [D8]THF): δ 5.6, 5.9, 24.5, 27.6, 69.0. 13
C
NMR (100.6 MHz, 233 K, [D8]THF): δ 5.6 (2C, t, 1JC−H = 102.2 Hz),
5.9 (6C, q, 1JC−H = 115.8 Hz), 24.5 (overlaid by [D8]THF), 27.6 (8C,
1
t, 1JC−H = 128.0 Hz), 69.0 (8C, t, JC−H = 142.0 Hz). 29Si NMR (79.5
MHz, 273 K, [D8]THF): δ −4.12 (m). Ca, calcd 7.17, found 7.24.
Crystal data for 2a: C28H62CaO4Si2, M = 559.04 g mol−1, colorless
prism, size 0.122 × 0.102 × 0.088 mm3, monoclinic, space group C2/c;
a = 31.8335(5), b = 17.2776(3), c = 24.1641(4) Å, β = 127.506(1)°, V
= 10 543.1(3) Å3, T = −140 °C, Z = 12, ρcalcd = 1.057 g cm−3, μ(Mo
Kα) = 2.73 cm−1, multiscan, transmin: 0.6473, transmax: 0.7456, F(000)
= 3720, 30375 reflections in h(−41/40), k(−22/15), l(−27/31),
measured in the range 2.05° ≤ Θ ≤ 27.48°, completeness Θmax
=
Method B (for 4a, 4d, 4e). R-I (1 equiv) and 4 equiv of Me3Si−Cl
were dissolved in 1 mL of THF, and this mixture was cooled to −40
°C. Then, 1.1 equiv of [(thp)4Ca(I)(CH2SiMe3)] dissolved in 1 mL of
THF was added. The reaction mixture was stirred for 10 min and then
warmed to r.t. After addition of 2 mL of H2O, the organic phase was
separated, dried over anhydrous Na2SO4, and directly used for GC/
MS experiments.
99.3%, 12009 independent reflections, Rint = 0.0631, 8419 reflections
with F0 > 4σ(F0), 563 parameters, 60 restraints, R1obs = 0.0787, wR2obs
= 0.1599, R1all = 0.1180, wR2all = 0.1797, GOOF = 1.079, largest
difference peak and hole: 0.939/−0.426 e Å−3.
[(tmeda)2Ca(CH2SiMe3)2] (2b). A 0.194 M solution of [(thp)4Ca-
(I)(CH2SiMe3)] in THP (9.0 mL, 1.046 g, 1.75 mmol, 1 equiv) was
added at 0 °C to a solution of 228 mg of KCH2SiMe3 (1.80 mmol,
1.025 equiv) in 3 mL of THP. The white suspension was stirred for 30
min before 0.5 mL of TMEDA were added. Afterward, all volatiles
were removed, leaving a slightly yellow residue, which was extracted
with 10 mL of pentane, yielding 8 mL of a 0.20 M solution of
[(tmeda)2Ca(CH2SiMe3)2] (2b) in pentane (91%). Purity was
controlled by NMR spectroscopy as well as by acidimetric titrations.
This solution can be used without further purification. Cooling of the
solution to −78 °C led to crystallization of big colorless cubes of
[(tmeda)2Ca(CH2SiMe3)2] (2b). 1H NMR (400.13 MHz, 233 K,
[D8]THF): δ −1.94 (4H, s), −0.18 (18H, s), 2.14 (24 H, s), 2.28 (8H,
s). 13C{1H} NMR (100.6 MHz, 233 K, [D8]THF): δ 5.6, 5.7, 46.3,
Crystal Structure Determinations. 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.26,27 The structure was
solved by direct methods (SHELXS)28 and refined by full-matrix least-
28,29
2
squares techniques against F0 (SHELXL-97 and SHELXL-2016).
All hydrogen atoms were included at calculated positions with fixed
thermal parameters. All nondisordered, non-hydrogen atoms were
refined anisotropically.28,29 XP30 was used for representations of
molecular structures.
58.6. 13C NMR (100.6 MHz, 233 K, [D8]THF): δ 5.6 (2C, t, 1JC−H
=
ASSOCIATED CONTENT
* Supporting Information
■
1
1
101.5 Hz), 5.7 (6C, q, JC−H = 115.6 Hz), 46.3 (8C, q, JC−H = 131.0
S
1
Hz), 58.6 (4C, t, JC−H = 131.1 Hz). 29Si NMR (79.5 MHz, 233 K,
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.7b00592.
[D8]THF): δ −4.12 (m). Ca, calcd 8.97, found 9.08. Crystal data for
2b: C20H54CaN4Si2, M = 446.93 g mol−1, colorless prism, size 0.122 ×
0.098 × 0.092 mm3, triclinic, space group P1; a = 15.2282(6), b =
̅
15.3310(6), c = 18.1514(7) Å; α = 89.694(2), β = 69.350(2), γ =
Structural details and NMR spectra (PDF)
67.551(2)°, V = 3623.7(2) Å3, T = −140 °C, Z = 5, ρcalcd = 1.024 g
cm−3, μ(Mo Kα) = 3.11 cm−1, multiscan, transmin: 0.6691, transmax
:
Accession Codes
CCDC 1548635−1548637 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
0.7456, F(000) = 1250, 35 300 reflections in h(−18/17), k(−18/18),
l(−22/20), measured in the range 1.57° ≤ Θ ≤ 25.68°, completeness
Θmax = 98.8%, 13604 independent reflections, Rint = 0.0378, 7998
reflections with F0 > 4σ(F0), 705 parameters, 0 restraints, R1obs
=
0.0890, wR2obs = 0.1529, R1all = 0.1482, wR2all = 0.1831, GOOF =
1.049, largest difference peak and hole: 0.961/−0.525 e Å−3.
[(Et2O)2CaI2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)(CH2SiMe3)] (3). Acti-
vated calcium (430 mg, 10.7 mmol, 1.1 equiv) was suspended in 20
mL of diethyl ether. The suspension was cooled to −78 °C, and 2.087
g of ICH2SiMe3 (9.7 mmol, 1 equiv) were added. The reaction
mixture was shaken for 1 h at −78 °C before 10 mL of pentane was
added. Then, all solids were removed by filtration, yielding 27 mL of a
0.118 M solution (33%, acidimetric titration). An additional 10 mL of
pentane was added, and the solution was stored at −40 °C, yielding
225 mg of crystalline [(Et2O)2CaI2·(Et2O)2Ca(I)(OEt)·(Et2O)Ca(I)-
(CH2SiMe3)] (3) (2%). Reduction of the volume of the mother liquor
AUTHOR INFORMATION
Corresponding Author
*E-mail: m.we@uni-jena.de. Web: http://www.lsac1.uni-jena.
de. Fax: +49 3641 9-48132.
■
ORCID
Alexander Koch: 0000-0003-1877-527X
Matthias Westerhausen: 0000-0002-1520-2401
E
DOI: 10.1021/acs.organomet.7b00592
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
metallics 2005, 24, 5506−5508. (c) Krieck, S.; Gorls, H.;
̈
Notes
Westerhausen, M. J. Organomet. Chem. 2009, 694, 2204−2209.
The authors declare no competing financial interest.
(18) (a) Westerhausen, M.; Gartner, M.; Fischer, R.; Langer, J.
̈
Angew. Chem., Int. Ed. 2007, 46, 1950−1956. (b) Westerhausen, M.;
ACKNOWLEDGMENTS
Gartner, M.; Fischer, R.; Langer, J.; Yu, L.; Reiher, M. Chem. - Eur. J.
̈
■
2007, 13, 6292−6306. (c) Westerhausen, M. Coord. Chem. Rev. 2008,
252, 1516−1531. (d) Westerhausen, M. Z. Anorg. Allg. Chem. 2009,
635, 13−32. (e) Westerhausen, M.; Langer, J.; Krieck, S.; Glock, C.
Rev. Inorg. Chem. 2011, 31, 143−184. (f) Westerhausen, M.; Langer, J.;
We appreciate the financial support of the Fonds der
Chemischen Industrie im Verband der Chemischen Industrie
e.V. (FCI/VCI, Frankfurt/Main, Germany, fund 510259). A.K.
thanks the Fonds der Chemischen Industrie im Verband der
Chemischen Industrie e.V. for a generous Ph.D. stipend. A.K.
also acknowledges the terminal grant of the Graduate Academy
of the Friedrich Schiller University.
Krieck, S.; Fischer, R.; Gorls, H.; Kohler, M. Top. Organomet. Chem.
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2013, 45, 29−72.
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DOI: 10.1021/acs.organomet.7b00592
Organometallics XXXX, XXX, XXX−XXX