Hydrocarbon-Soluble Bis(trimethylsilylmethyl)calcium and Calcium

Oct 11, 2017 - Hydrocarbon-soluble and highly reactive [(L)xCa(CH2SiMe3)2] (L = tetrahydropyran, x = 4 (2a); L = tmeda, x = 2 (2b)) is synthesized by ...
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Hydrocarbon-Soluble Bis(trimethylsilylmethyl)calcium and Calcium− Iodine Exchange Reactions at sp2‑Hybrized Carbon Atoms Alexander Koch,† Marino Wirgenings,‡ Sven Krieck,† Helmar Görls,† 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 complexes are valuable reagents for calcium−iodine exchange reactions at Csp2−I functionalities.

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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 sblock 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-

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 tetrahydrofuran (THF) to 1,4-dioxane (diox) of the intricate cocondensation 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 metalation strength and displayed powerful intermediates to heteroleptic calcium compounds.6,7 Furthermore, coligandfree [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 isoelectronic [Sn{CH(SiMe3)2}2] led to the formation of the

Scheme 1. Strategies for the Synthesis of Homoleptic Diorganylcalcium Complexes with Ca−C Bondsa

a

Received: August 2, 2017

See text; R = CH2SiMe3, R′ = CH(SiMe3)2, R″ = N(SiMe3)2. © XXXX American Chemical Society

A

DOI: 10.1021/acs.organomet.7b00592 Organometallics XXXX, XXX, XXX−XXX

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Organometallics stannanide Ca[Sn{CH(SiMe3)2}3]2.12 In a similar procedure using bis(trimethylsilylmethyl)zinc and calcium metal, heterobimetallic 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 halides; X = Br (1-Br), I (1-I), monosyl = CH2SiMe3, thp = tetrahydropyran) via the atom-economic Grignard-type reaction 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 prepared. The integration of the methylene moiety in the 1H 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 Calcium−Iodine Exchange Reactionsa

a

See text; R = aryl, Ph2CCPh, c-C3H5.

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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. The 1H 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 small coupling constant 1JC−H = 102.2 Hz is characteristic for these trimethylsilylmethyl substituents as discussed previously.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

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 alkylcalcium functionalities by formation of cage compounds containing ether degradation products such as alkoxide and oxide anions as observed earlier.17−19 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 B

DOI: 10.1021/acs.organomet.7b00592 Organometallics XXXX, XXX, XXX−XXX

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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 1Br (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 mononuclear [(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 αor 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%. 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

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 coworkers performed a calcium−bromine exchange at 2,6polyether-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. C

DOI: 10.1021/acs.organomet.7b00592 Organometallics XXXX, XXX, XXX−XXX

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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 1,4bis(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.

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 Table 1. Scope of Calcium−Iodine Exchange and Subsequent Quenching with Me3Si−Cla

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SUMMARY An easily scalable straightforward synthesis of hydrocarbonsoluble 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 [(Et 2 O) 2 Ca(I) 2 ·(Et 2 O) 2 Ca(I)(OEt)·(Et 2 O)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 derivatives 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 organolithium 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 Aryl calcium iodide is observed by NMR spectroscopy; cA 1 h reaction time was used during step 1. dCompound 4 (0.25 mmol), Me3Si−Cl (1 mmol), 2 mL of THF, −40 °C, then dropwise addition of 1-I (0.275 mmol). eYield was estimated by NMR spectroscopy via integration of the resonances of ICH2SiMe3 and CH2(SiMe3)2; fYield of 1,4 bis(trimethylsilyl)benzene; gAddition of 0.55 mmol of 1-I (2.2 equiv).

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EXPERIMENTAL SECTION

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 stored under nitrogen over sodium. 1H and 13C{1H} NMR spectra 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). Activated 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-

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 1Br 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 D

DOI: 10.1021/acs.organomet.7b00592 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

and addition of pentane yielded further crops of amorphous solids with varying amounts of trimethylsilylmethyl and ethoxide groups. 1H 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 Reactions. 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. 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. Crystal Structure Determinations. The intensity data were collected on a Nonius KappaCCD diffractometer, using graphitemonochromated 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 leastsquares techniques against F02 (SHELXL-97 and SHELXL-2016).28,29 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.

(I)(CH2SiMe3)] (48 mmol, 50%). The analytical data are in accordance with literature values.15 [(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 −40 °C yielded crystalline [(thp)4Ca(CH2SiMe3)2] (2a). 1H 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. 13C 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, t, 1JC−H = 128.0 Hz), 69.0 (8C, t, 1JC−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 = 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, 58.6. 13C NMR (100.6 MHz, 233 K, [D8]THF): δ 5.6 (2C, t, 1JC−H = 101.5 Hz), 5.7 (6C, q, 1JC−H = 115.6 Hz), 46.3 (8C, q, 1JC−H = 131.0 Hz), 58.6 (4C, t, 1JC−H = 131.1 Hz). 29Si NMR (79.5 MHz, 233 K, [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 P1̅; a = 15.2282(6), b = 15.3310(6), c = 18.1514(7) Å; α = 89.694(2), β = 69.350(2), γ = 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: 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). Activated 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

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.7b00592. Structural details and NMR spectra (PDF) Accession Codes

CCDC 1548635−1548637 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. 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

Article

Organometallics Notes

metallics 2005, 24, 5506−5508. (c) Krieck, S.; Gö r ls, H.; Westerhausen, M. J. Organomet. Chem. 2009, 694, 2204−2209. (18) (a) Westerhausen, M.; Gärtner, M.; Fischer, R.; Langer, J. Angew. Chem., Int. Ed. 2007, 46, 1950−1956. (b) Westerhausen, M.; Gärtner, 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.; Krieck, S.; Fischer, R.; Görls, H.; Köhler, M. Top. Organomet. Chem. 2013, 45, 29−72. (19) Westerhausen, M.; Koch, A.; Görls, H.; Krieck, S. Chem. - Eur. J. 2017, 23, 1456−1483. (20) (a) Burwell, R. L. Chem. Rev. 1954, 54, 615−685. (b) Bhatt, M. V.; kulkarni, S. U. Synthesis 1983, 1983, 249−282. (c) Maercker, A. Angew. Chem., Int. Ed. Engl. 1987, 26, 972−989. (21) Gärtner, M.; Görls, H.; Westerhausen, M. Organometallics 2007, 26, 1077−1083. (22) Elschenbroich, C. Organometallics, 3rd ed.; Wiley-VCH: Weinheim, 2016. (23) Dagousset, G.; François, C.; Leόn, T.; Blanc, R.; SansiaumeDagousset, E.; Knochel, P. Synthesis 2014, 46, 3133−3171. (24) Markies, P. R.; Nomoto, T.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.; Smeets, W. J. J.; Spek, A. L. Organometallics 1991, 10, 3826−3837. (25) Whitmore, F. C.; Sommer, L. H. J. Am. Chem. Soc. 1946, 68, 481−484. (26) Hooft, R. COLLECT, Data Collection Software; Nonius B.V.: The Netherlands, 1998. (27) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307− 326. (28) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (29) Sheldrick, G. M. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (30) XP; Siemens Analytical X-Ray Instruments Inc.: Madison, WI, 1994.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS 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.

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DOI: 10.1021/acs.organomet.7b00592 Organometallics XXXX, XXX, XXX−XXX