Reactivity Studies of [(thf)2Mg{Î¼-C(CH3)2C2H4C ... - ACS Publications

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Reactivity Studies of [(thf)2Mg{μ-C(CH3)2C2H4C(CH3)2}]2: Scrambling Reactions and Diverse Reactions with Dichlorophenylphosphane Reinald Fischer, Helmar Görls, and Matthias Westerhausen* Institute of Inorganic and Analytical Chemistry, Friedrich Schiller University Jena, Humboldtstrasse 8, D-07743 Jena, Germany S Supporting Information *

ABSTRACT: In THF solution [{(thf)2Mg{μ-C(CH3)2C2H4(CH3)2C}}2] (1) exchanges the alkanediide ligand with [{(thf)2Mg{μ-CH2)5}}2] in an equilibrium leading to the formation of [{(thf)2Mg}2{μ-C(CH3)2C2H4C(CH3)2}{μ-(CH2)5}] (2). Depending on the crystallization temperature, homoleptic 1 or heteroleptic 2 crystallizes from THF solutions, verifying a temperature-dependent Schlenk equilibrium. Irradiation of a solution of 1 in [D8]THF with UV light yields magnesium hydride and alkene via a β-hydride elimination reaction. In a metathetical approach dichlorophenylphosphane reacts with 1 in THF to give the intermediate “PhP(Cl){C(CH3)2C2H4(CH3)2CMgCl” (3MgCl), which forms three subsequent products. In order to ease handling and characterization of these compounds, hydrolysis and oxidation with sulfur has been performed. This product mixture was separated by column chromatography, yielding the chlorophosphane sulfide [Ph(S)P(Cl){C(CH3)2C2H4(CH3)2CH)}] (3-S), the cyclic phosphane sulfide [Ph(S)P{C(CH3)2C2H4(CH3)2C)}] (4-S), and the cyclic 1,1diphosphane disulfide [{(Ph(S)P}2{μ-C(CH3)2C2H4(CH3)2C}] (6-S2). Furthermore, traces of the acyclic 1,1-diphosphane disulfides [{PhP(S)(C(CH3)2C2H4CH(CH3)2)}{PhP(S)(C(CH3)2C2H4C(CH3)(CH2)}] (8-S2) and meso-[{Ph(S)P(C(CH3)2C2H4(CH3)2CH)}2] (7-S2) have also been isolated. Compounds 6−8 represent the phosphorus-containing products of indirect Grignard reductions.

1. INTRODUCTION

Scheme 1. Simplified Schlenk Equilibrium of Diorganylmagnesium in Diluted Ethereal Solutiona

The nature of the species in Grignard solutions has been repeatedly discussed since Schlenk and Schlenk Jr.1 formulated the basic Schlenk equilibrium in 1929 which was supplemented thereafter by additional components.2 Addition of 1,4-dioxane to Grignard solutions allows the nearly quantitative precipitation of the magnesium halides and, hence, to shift the Schlenk equilibrium in favor of the pure R2Mg organometallics.3 In the substance class of diorganylmagnesium compounds, magnesiacycles represent a special case. They aggregate in THF solution, and ring extension leads to different ring sizes depending on the concentration. Even the formation of organomagnesium polymers has been observed and described.4 This flexibility is possible because the ω-carbon atom is inter- or intramolecularly always in close contact to a magnesium atom. Thus, the 1H NMR spectrum of (CH3)2Mg in diethyl ether at −100 °C showed three resonances: one was assigned to a bridging methyl group, and the two other signals stem from terminally bound methyl groups.5 At higher temperatures coalescence was observed, and finally, a single resonance confirms that exchange reactions are fast on the NMR time scale. In general, diluted Grignard solutions show an equilibrium between mono- and dinuclear magnesium organometallics (Scheme 1; coordinating neutral Lewis bases are neglected). © XXXX American Chemical Society

a

Coordinated ether bases are not shown.

The exchange of carbanionic ligands strongly depends on the nature of the organic groups and on the solvent.6 Bridging organyl groups between magnesium atoms are also known from crystal structure determinations.7 The exchange rate of organic groups decreases if bulky carbanions are involved in this equilibrium. In the 13C NMR spectrum of a solution of (PhCH 2 CHI)Mg(iPr) in THF at −78 °C exclusively resonances of the heteroleptic complex are observed but no resonances of homoleptic (PhCH2CHI)2Mg and Mg(iPr)2 have been detected.8 The isolation of simple asymmetric diorganylmagnesium complexes has failed up to now because in most cases ethers were employed as solvents. Therefore, uncontrollable dismutation reactions led to organometallics interconvertible via Received: September 21, 2016

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DOI: 10.1021/acs.organomet.6b00743 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

(ii) Colorless crystalline 1 and its solutions turn dark if exposed to sunlight; therefore, we were interested in the photolysis products of 1. (iii) Finally, we investigated the possibility of synthesizing sterically shielded cyclic phosphanes via a metathesis reaction of 1 with dichlorophenylphosphane. The NMR spectra of 1 in [D8]THF solution show two temperature-dependent sets of resonances of the alkanediide ligand that can be interpreted as a chemical equilibrium between a mono- and dinuclear complex (see the Supporting Information). Thereafter, a solution containing equimolar amounts of 1 and [(thf)2Mg{μ-(CH2)5}]2 in THF (approximately 0.15 M of each compound) was prepared, heated under reflux, and immediately thereafter cooled to −40 °C in order to crystallize the heteroleptic complex. (At −20 °C pure compound 1 crystallized from this solution.) The colorless crystals grown at −40 °C were studied by X-ray diffraction experiments, verifying the heteroleptic nature of compound 2. The molecular structure and atom numbering scheme are depicted in Figure 1.

the Schlenk equilibrium, impeding the isolation of heteroleptic MgRR′ derivatives. This finding initiated diverse strategies to prepare such complexes: (i) crown ethers were applied to stabilize and coordinatively saturate the magnesium centers,9 (ii) hydrocarbons were applied to shift the Schlenk equilibrium,10 and (iii) chelate-forming organyls were investigated.11 Most commonly, Grignard reagents represent transfer reagents for carbanions/nucleophiles in diverse types of reactions such as addition reactions (to e.g. ketones for the synthesis of alcohols), metathesis reactions with metal halides (for e.g. the synthesis of d-block organometallics), transitionmetal-catalyzed cross-coupling reactions, and metalation reactions with H-acidic substrates. Largely unappreciated remained the reaction of the magnesium-based organometallics as reagents for Grignard reductions, as shown in Scheme 2, Scheme 2. Direct (Top) and Indirect (Bottom) Grignard Reduction Reactions via Initial Homolytic Mg−C Bond Cleavage and Subsequent Electron Transfer from the MgR Radical (Forming the Cation RMg+) as well as via β-Hydride Elimination from an Alkyl Group Yielding a Magnesium Hydride Species and an Alkene

Figure 1. Molecular structure and numbering scheme of [{(thf)2Mg}2{μ-C(CH3)2C2H4(CH3)2C}{μ-(CH2)5}] (2). The ellipsoids represent a probability of 30%. The asymmetric unit contains the two molecules A and B; only molecule B is drawn. H atoms are omitted for the sake of clarity. Selected bond lengths (pm) of molecule A [molecule B]: Mg1−C1 215.6(3) [215.3(3)], Mg1−C6 218.9(3) [219.7(3)], Mg1−O1 208.4(2) [209.2(2)], Mg1−O2 212.0(2) [210.9(2)], Mg2−C5 215.7(3) [216.0(3)], Mg2−C9 217.9(3) [218.2(3)], Mg2−O3 207.8(2) [208.3(2)], Mg2−O4 209.9(2) [209.6(2)]. Selected bond angles (deg) of molecule A [molecule B]: C1−Mg1−C6 132.38(11) [129.09(11)], C5−Mg1−C9 128.61(12) [131.95(12)], O1−Mg1−O2 87.98(8) [89.14(8)], O3−Mg2−O4 89.27(9) [88.65(8)].

even though some reports address this reaction behavior.12 The two reaction pathways consist of the direct reduction by the Grignard reagent (electron transfer from a Grignard reagent) and the indirect reduction via intermediate formation of magnesium hydride species. The homolytic magnesium− carbon bond cleavage leads to an organyl radical R• and RMg• species, the latter being a strong reducing agent with formation of [RMg+]. The pathway of the indirect reduction requires the presence of β-hydrogen atoms and the elimination of HMgR (or MgH2), which then acts as a reducing reagent via transfer of a hydride ion to a substrate molecule. The carbanionic group of compound 1, [C(CH3)2C2H4C(CH3)22−], exclusively contains β-hydrogen atoms, and therefore we were interested in the reaction patterns of this complex and studied the reaction of 1 with dichlorophenylphosphane in order to elucidate the scope of carbanion transfer in a metathetical approach and to study accompanying indirect Grignard reductions.

The heteroleptic complex [{(thf)2Mg}2{μ-C(CH3)2C2H4(CH3)2C}{μ-(CH2)5}] (2) crystallizes with two crystallographically independent molecules. The basic structures can be deduced from cycloundecane with the first and sixth methylene groups being replaced by Mg(thf)2 moieties; in addition, the hydrogen atoms of the second and fifth methylene units are substituted by methyl groups. Thus, compound 2 represents the ideal hybrid of the starting substrates. The Mg− C and Mg−O bond lengths of all three organometallics differ only marginally, and the C−Mg−C bond angles of 2 (132.38− 128.61°) are approximately the average values of the corresponding large C−Mg−C angles of [{(thf)2Mg(μ(CH2)5}2] (143.19°) and the small angles of the modifications of 1 (122.86(7), 121.7(1), and 123.7(1)°). The O−Mg−O bond angles between the donor atoms of the neutral Lewis bases differ only slightly (87.98(8)−89.27(9)°). The 1H and 13C{1H} NMR spectra of 2 at room temperature in [D8]THF show the resonances of both starting materials 1 (mono- and dinuclear compounds) and [(thf)2Mg{μ-CH2)5}]2.

2. RESULTS AND DISCUSSION 2.1. Ligand Exchange Reaction between 1 and [{(thf)2Mg(μ-(CH2)5}2] in THF Solution. The dinuclear compound [(thf)2Mg(μ-C(CH3)2C2H4C(CH3)2)]2 (1) was prepared via the reduction of 2,5-dichloro-2,5-dimethylhexane with magnesium turnings in THF and subsequent precipitation of magnesium chloride with 1,4-dioxane.4 Due to the lack of knowledge with respect to the chemistry of cyclic aliphatic diorganylmagnesium derivatives with tertiary carbon atoms, we studied the following three reactions of 1. (i) The reaction of 1 with [{(thf)2Mg(μ-CH2)5}2] should clarify if an intermolecular exchange of alkanediide ligands is observable in THF solution. B


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Organometallics Cooling of this sample to −40 °C leads to another set of resonances, and the signals of the dinuclear isomer of 1 vanish. Comparison of these NMR spectra with those of pure starting materials allows the assignment of the resonances of the heteroleptic complex 2, which is also in agreement with the results of the crystal structure determination. From this solution, pure 1 crystallizes at −20 °C; immediate cooling to −40 °C allows crystallization of pure derivative 2. Thus, in THF solution the temperature-dependent equilibrium shown in Scheme 3 is operative.

Scheme 4. Proposed Reaction during Photolysis of 1 with UV Light in [D8]THFa

a

For reasons of simplicity, a 1:1 ratio of both possible alkene moieties is shown bound at the same magnesium atom.

Scheme 3. Ligand Exchange Equilibrium of Homoleptic 1 and [{(thf)2Mg(μ-(CH2)5}2] in THF Solution Yielding Heteroleptic 2

oxidized the products of the metathesis reaction with sulfur, enabling convenient workup under ambient conditions (Figure 2).

Figure 2. 31P NMR spectra of the reaction of 1 with PhPCl2 (ratio 1:2) in THF solution: (a) reaction after 1 h at −50 °C; (b) reaction after 1 day at −40 °C; (c) reaction of solution (b) with sulfur for 1 day at 0 °C; (d) reaction of solution (b) with excess sulfur at 0 °C (the + symbols denote phosphorus-containing compounds that were not isolated).

2.2. Photolysis of 1. Complex 1 belongs to a class of organomagnesium compounds that has only hydrogen atoms in positions β to the alkaline-earth-metal atoms. In contrast to the case for nearly all magnesium-based organometallics, it was observed that the crystal surface of 1 showing toward the sunlight turned gray. As of yet very little is known with respect to photolabile Grignard reagents.13 Therefore, we irradiated a suspension of 1 in [D8]THF in an NMR tube with UV light. The initially colorless suspension turned brown rather quickly, and a gray solid precipitated from the solution. The soluble components were investigated by NMR spectroscopy. The NMR spectra showed in addition to the remaining 1 also the existence of two alkene moieties. The interpretation of these NMR spectra verified that the majority of the alkene units can be assigned to a terminal branched alkene, whereas significantly smaller amounts of inner branched alkene units formed. Consequently, a reaction as shown in Scheme 4 may be assumed for the photolysis of this Grignard reagent 1 (neglecting the different ratio of both possible alkene fragments). 2.3. Reaction of 1 with Dichlorophenylphosphane. In order to elucidate the synthetic potential of a sterically shielded magnesiacycle in metathetical applications, we reacted compound 1 with 2 equiv of dichlorophenylphosphane in THF at room temperature. This reaction allows the monitoring of the conversion by 31P NMR spectroscopy. Due to the fact that many phosphorus(III) derivatives are sensitive toward air, we

The 31P NMR spectrum shows after a reaction time of 1 h at −50 °C the immediate formation of the two chlorophosphanes 3-MgCl and 5 with chemical shifts of δ 108.3 and 107.6 as phosphorus-containing intermediates (Scheme 5). The relatively large stability of the primary product 3-MgCl at −50 °C shows that 1 initially reacts only with one halogen atom of the dichlorophenylphosphane, suggesting a graded reactivity of both P−Cl functionalities. Scheme 5. Initial Reaction of 1 with Dichlorophenylphosphane in THF at Room Temperature Yielding Substituted Chlorophenylphosphanes 3-MgCl and 5

C


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and the sulfide of 5, together 15%), 86.2 (60%, 4-S), and 37.4 (20%, 6-S2). The product 6-S2 obviously formed via the intermediate 1,2-diphosphane monosulfide 6-S, which shows doublets in the 31P{1H} NMR spectrum at δ −34.8 (1Jpp = 281 Hz) and 47.1 (1Jpp = 281 Hz). Column chromatographic separation allowed the isolation of three of these four products, which were additionally purified by recrystallization (3-S, 4-S, and 6-S2). Cyclic 1,6-diphosphanes were not observable under these reaction conditions. The 1H NMR spectrum of 3-S shows two doublets of diastereotopic methyl groups at the α-C atom of the aliphatic substituent. The doubling of the resonances of these methyl groups was also observed in the corresponding 13C{1H} NMR spectrum. This finding can be explained by a hindered rotation around the α-C−P bond at room temperature. The molecular structure and numbering scheme of this compound are depicted in Figure 3.

The intermediate 3-MgCl exhibits diverse reaction patterns in dilute solutions, as summarized in Scheme 6. (i) The Scheme 6. Subsequent Reactions of Intermediate 3-MgCl

Figure 3. Molecular structure and numbering scheme of [PhPCl(S){C(CH3)2C2H4CH(CH3)2}] (3-S). The crystal consists of a racemate of S and R isomers. The ellipsoids represent a probability of 30%. Selected bond lengths (pm): P1−S1 193.97(9), P1−Cl1 204.38(9), P1−C1 185.2(3), P1−C9 181.0(3). Selected bond angles (deg): S1− P1−C1 113.85(9), S1−P1−Cl1 112.62(4), S1−P1−C9 113.33(9), C1−P1−C9 102.72(9).

The central moiety of this compound is a chiral phosphorus atom with a distorted-tetrahedral environment containing the sulfur and chlorine atoms as well as the ipso-C of the phenyl substituent and the α-C atom of the aliphatic group at the corners of the tetrahedron. With the exception of the C1−P1− C9 bond angle of 102.72(9)°, the angles at P1 are larger than the tetrahedral angle. Due to the crystallographic inversion symmetry both enantiomers form a racemate in the crystalline state. The major product of the reaction of 1 with dichlorophenylphosphane is the cyclic 1-phenyl-2,2,5,5-tetramethyl-1phosphacyclopentane (4), which was oxidized with sulfur to give the corresponding phosphane sulfide 4-S. In the 1H as well as in the 13C{1H} NMR spectrum of 4-S resonances of the chemically and magnetically different methyl groups are observed. In the NOESY experiment a doublet at δ 0.95 can be assigned to the methyl groups, which are facing toward the phenyl group. The other doublet at δ 1.32 belongs to the methyl groups facing toward the sulfur functionality. The molecular structure and numbering scheme of 4-S are shown in Figure 4. The phosphorus atom is in a distorted-tetrahedral environment of the sulfur atom and three carbon atoms. The C1−P1− C4 bond angle of 96.65(9)° is very small due to the ring strain of the saturated five-membered phosphacycle.

intramolecular metathesis reaction leads to the formation of the cyclic sterically shielded 1-phenyl-2,2,5,5-tetramethyl-1-phosphacyclopentane (4). (ii) The reaction with another 1 equiv of dichlorophenylphosphane yields 1,6-dichloro-1,6-diphenyl2,2,5,5-tetramethyl-1,6-diphosphahexane (5), which again can react with 1 via a metathesis reaction or via intramolecular reduction to 1,2-diphenyl-3,3,6,6-tetramethyl-1,2-diphosphacyclohexane (6). (iii) The intermolecular Grignard reduction yields a phosphane that reacts with additional primary product to give the diphosphane 7. The 31P NMR spectrum of the reaction solution shows finally after 24 h at a temperature of −40 °C four resonances at δ 108.3 (16%), 107.6 (12%), 49.1 (45%), and −23.8 (28%). The signals of the first two substances are identical with those of the chlorophosphanes 3-MgCl and 5. The major product is the phosphane 4, and the fourth component is the 1,2diphosphane 6. In order to ease handling as well as isolation and characterization of these air-sensitive compounds, we performed an acidolysis and a subsequent oxidation with elemental sulfur. The 31P NMR spectrum of the reaction mixture after the oxidation with sulfur corresponds very well to the initial reaction solution. Again, the signals of four products can be recognized at chemical shifts of δ 115.5 and 114.9 (3-S D


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Figure 4. Molecular structure and numbering scheme of [PhP(S){C(CH3)2C2H4C(CH3)2}] (4-S). The ellipsoids represent a probability of 30%. Selected bond lengths (pm): P1−S1 196.40(6), P1−C1 187.21(18), P1−C4 187.65(18), P1−C9 182.34(18). Selected bond angles (deg): S1−P1−C1 115.36(6), S1−P1−C4 115.36(6), S1−P1− C9 110.35(6), C1−P1−C4 96.65(9).

Figure 5. Molecular structure and numbering scheme of (R,R)[{Ph(S)P}2{μ-C(CH3)2C2H4C(CH3)2}] (6-S2). Due to the centrosymmetric space group, the crystal also contains the S,S isomer. The ellipsoids represent a probability of 30%. Selected bond lengths (pm): P1−P2 225.41(8), P1−S1 196.34(8), P1−C1 186.9(2), P1−C9 182.5(2), P2−S2 196.34(8), P2−C4 187.3(2), P2−C15 183.0(2). Selected bond angles (deg): S1−P1−P2 111.95(3), C1−P1−P2 102.16(8), C9−P1−P2 107.03(7), S2−P2−P1 113.43(3), C4−P2− P1 102.16(8), C15−P2−P1 106.77(7).

The third isolated major component of the reaction of 1 with PhPCl2 is the derivative 6-S2. The 1H NMR spectrum shows the resonances of the phenyl groups and two signals for the methyl groups as well as two multiplets for the hydrogen atoms of the methylene fragments. The shape of the signals of the methyl and methylene units can be understood if fixed configurations are assumed on the NMR time scale. In the 13 C{1H} NMR spectrum the resonances of the P-bound carbon atoms exhibit an AA′X spin system. The 31P{1H} NMR spectrum of the compound 6-S2 in CDCl3 solution exhibits a singlet verifying the absence of the meso isomer in the product mixture. The molecular structure and atom-numbering scheme are shown in Figure 5. Due to the centrosymmetric space group the crystal of 6-S2 consists of a racemate of the R,R and S,S isomers, whereas the meso isomer is absent in the crystalline state. The molecular structure is a substituted cyclohexane ring with a chair conformation having two neighboring methylene units being replaced by phenylthiophosphanyl moieties. The P1−P2 bond length of 225.41(8) pm lies in the expected range of diphosphanes (226.3(4) pm)14 which are bonded to aromatic substituents and is significantly elongated in comparison to those in aliphatic diphosphane disulfides (approximately 221(1) pm).15 A special case within this substance class is tetramethyldiphosphane disulfide, because the determination of the crystal structure showed two molecules in the asymmetric unit with significantly different P−P bond lengths of 216.1(6) and 224.5(6) pm.16 The components of the reaction mixture were successfully isolated by column chromatography. The fraction before 3-S was eluted contained compound 7-S2, which was characterized by 31P NMR spectroscopy and single-crystal X-ray diffraction experiments. The molecular structure and atom-numbering scheme are depicted in Figure 6. The molecule of 7-S2 contains a center of symmetry between P1 and P1A and, hence, represents the meso isomer. Due to the inversion symmetry all heteroatoms, S1A, P1A, P1, and S1 lie on a plane. The P−P bond of 7-S2 with a value of 226.93(16) pm is slightly longer than those in the related cyclic 1,2diphosphane disulfide 6-S2 (225.41(8) pm).

Figure 6. Molecular structure of meso-[{PhP(S)(C(CH3)2C2H4CH(CH3)2)}2] (7-S2). The ellipsoids represent a probability of 30%. Symmetry-related atoms are marked with the letter “A”. Selected bond lengths (pm): P(1)−P(1A) 226.93(16), P(1)−S(1) 195.74(12), P(1)−C(1) 188.4(3), P(1)−C(9) 183.6(3). Selected bond angles (deg): S(1)−P(1)−P(1A) 110.48(6), C(1)−P(1)−P(1A) 110.04(11), C(9)−P(1)−P(1A) 106.43(12).

The low yield of the compound mixture 7-S2/8-S2 after chromatographic separation did not allow a complete characterization of these derivatives. Therefore, an alternative synthesis was developed consisting of the reduction of compound 3 with lithium sand and subsequent oxidation with sulfur. Very similar products formed in a 1:1 ratio and differed only by one terminal CC double bond of the derivative 8-S2. Attempts to separate this mixture by column chromatography or by fractional crystallization have failed up to now. The 1H NMR spectrum of the solution of 7-S2/8-S2 in CDCl3 shows that in these compounds the rotation of the bulky substituents at the phosphorus atoms is even more E


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Due to the fact that 3-S and the mixture of 7-S2 and 8-S2 only form in very minor amounts, another preparation was developed. The reaction of 1 with an excess of dichlorophenylphosphane yields compound 5 as the major product, which forms diastereoisomers. However, 5 quite easily eliminates dichlorophenylphosphane and forms 4 via a cyclization reaction. Therefore, we did not isolate 5 or its oxidation product 5-S2 but verified its structure by comparison of the corresponding 31P NMR resonances with those of the other reaction solutions (see Supporting Information).

hindered at room temperature than in derivative 3-S. Even at 50 °C the rotation of the phenyl groups remained restricted. Furthermore, also the demanding aliphatic groups, which are bound at the phosphorus atoms, are unable to freely rotate. Therefore, the 1H NMR spectrum of 7-S2/8-S2 showed at 50 °C well-separated resonances for the methyl groups at the α-C atoms of the aliphatic substituents. In addition the hydrogen atoms of the β-CH2 moieties remain diastereotopic in the 1H NMR spectrum at 50 °C. The presence of the three 1,2-diphosphanes 6−8 in the reaction mixture verifies that the reaction of the Grignard reagent 1 with chlorophosphanes yields not only the expected phosphanes and chlorophosphanes but also significant amounts of reduction products such as the 1,2-diphosphanes. In organic reactions it had been observed earlier that Grignard reagents with bulky substituents at the α-C atom but with β-hydrogen atoms at the organic substituent preferably transfer the small hydride ion to the substrate, especially in the absence of magnesium halide in the reaction solution (indirect Grignard reduction).17 Complex 1 is a typical representative of this substance class. This indirect Grignard reduction can proceed with both intermediately formed chlorophosphanes 5 and 3, as depicted in Scheme 7. In this type of reaction pattern, 5 forms

3. CONCLUSION AND PERSPECTIVE Grignard reagent 1 represents an organomagnesium compound that exclusively contains β-hydrogen atoms. Therefore, this complex tends to show unique reaction pathways. Thus, this reagent is photolabile and eliminates magnesium hydride and alkenes upon irradiation with UV light. This property offers the possibility of gently producing MgH2 under mild reaction conditions. The ease of β-hydrogen elimination is also observed during the reaction of PhPCl2 with 1, which leads to a significant extent to the reduction of phosphorus, yielding 6−8. The magnesiacycle 1 can be considered a mild potential reduction reagent. Oxidation of the phosphanes with sulfur leads to the formation of cyclic 1,2-diphosphane disulfide 6-S2 as a major product, and as side products, acyclic 1,2diphosphane disulfides 7-S2 and 8-S2 have been isolated. These compounds form due to an indirect Grignard reduction at the phosphorus atom of PhPCl2. The second major product of the reaction of PhPCl2 with 1 is the cyclic phosphane 4, which yields the corresponding phosphane sulfide 4-S after oxidation with sulfur. The sterically shielded cyclic phosphane 4 could represent a potential directing ligand for complexes in homogeneous catalysis. An interesting phenomenon is the exchange of the alkanediide anions between 1 and [(thf)2Mg{μ-(CH2)5}]2 in THF solution, which depends solely on the crystallization temperature. At −20 °C pure 1 precipitates from an approximately 1.5 M solution. However, at −40 °C [{(thf) 2 Mg} 2 {μ-C(CH 3 ) 2 C 2 H 4 (CH 3 ) 2 C}{μ-(CH 2 ) 5 }] (2) crystallizes from the same solution. To the best of our knowledge, this behavior is the first example that a crystalline MgRR′ complex can be isolated from a THF solution of MgR2 and MgR′2 via ligand dismutation without the use of additional chelating Lewis bases and exclusively via variation of the crystallization temperature. The reason for this unexpected finding could be that sterically overcrowded magnesium alkanediide derivatives undergo a very slow scrambling reaction and ligand exchange, leading to a decelerated adjustment of the Schlenk equilibrium in THF solution at −40 °C and, hence, allowing the crystallization of the heteroleptic complex 2.

Scheme 7. Indirect Grignard Reduction of Complex 1 with 5 and 3, Respectively, Yielding Alkenes and Acyclic (7) and Cyclic (6) Diphosphanes

4. EXPERIMENTAL SECTION 4.1. General Remarks. All manipulations were performed under strictly anaerobic and anhydrous conditions under an argon atmosphere using Schlenk techniques. Solvents were dried with standard methods and distilled under an argon atmosphere. The yields given were not optimized. 1H, 13C, and 31P NMR spectra were recorded on Bruker AC 400 and AC 600 spectrometers. The resonances of the solvents were used as internal references to assign chemical shifts.18 Magnesium complexes in [D8]THF were subject to ligand exchange reactions, and chemical shifts of free Lewis bases were observed due to a fast ligand exchange on the NMR time scale. Chemical shifts (δ values) are given in parts per million (ppm). Mass spectra (EI, 70 eV) were measured on an SSQ 710 spectrometer

“PhP(H){μ-C(CH3)2C2H4(CH3)2C}P(Cl)Ph”, which finally yields 6 after elimination of HCl and cyclization. In a similar reaction 3 is converted to “PhP(H){C(CH3)2C2H4(CH3)2CH}” which reacts in a similar way to give product 7. Compound 6 is oxidized in a two-step procedure to 6-S and finally to the isolated end product 6-S2; in a similar procedure compound 7 is oxidized to 7-S2. F


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Organometallics

overnight in a refrigerator at −40 °C. For the acidolysis 0.87 g (6.3 mmol) of (HNEt3)Cl was added and the solution stirred at 0 °C for 3 h. For the oxidation reaction, 0.25 g (7.8 mmol) of elemental sulfur was added and the solution stirred at 0 °C for 1 day. Thereafter, 25 mL of a saturated ammonium chloride solution was added and THF was removed in vacuo. The remaining aqueous solution was extracted three times with chloroform and the extract dried over anhydrous MgSO4. After removal of the drying agent all volatiles were removed and the compounds of the residue were separated on a silica gel column. With heptane, the excess sulfur was separated. With a heptane/toluene mixture (ratio 5/1) first 6-S2 was eluted and then a small amount of 7-S2 together with 3-S was eluted. Finally, the major product 4-S was obtained with toluene. Yield: 0.08 g (4.5%) of 3-S as colorless needles from heptane. Mp: 74−76 °C. Anal. Calcd for C14H22ClPS (288.8): C, 58.22; H, 7.68; S, 11.10; Cl, 12.27. Found: C, 58.29; H, 7.78; S, 10.05; Cl, 12.55. 1H NMR (600.1 MHz, CDCl3): δ 0.88 (6H, dd, J = 6.6 Hz, 6JHP = 1.8 Hz, CH3), 1.16 (2H, m, CH2), 1.21 (3H, d, 3JHP = 22.1 Hz, CH3), 1.26 (3H, d, 3JHP = 22.7 Hz, CH3), 1.49 (1H, m, J = 6.6 Hz, CH), 1.68 (2H, m, CH2), 7.53 (2H, m, m-CH), 7.59 (1H, m, p-CH), 8.05 (2H, m, oCH). 13C{1H} NMR (150.9 MHz, CDCl3): δ 20.9 (d, 3JCP = 15.1 Hz, CH3), 22.6 (d, 3JCP = 6.8 Hz, CH3), 28.6 (CH), 32.4 (d, JCP = 12.2 Hz, CH2), 32.9 (CH2), 45.4 (d, 1JCP = 52.3 Hz, C), 128.1 (d, 3JCP = 13.0 Hz, m-CH), 131.4 (d, 1JCP = 78.2 Hz, i-C), 132.3 (d, 4JCP = 3.2 Hz, pCH), 133.2 (d, 2JCP = 10.8 Hz, o-CH); 31P{1H} NMR (162.0 MHz, CDCl3): δ 116.4; MS (EI) m/e: 288# (M+, C14H22ClPS), 176#, 143#, 113, 71, 57 (# denotes signal with Cl isotope pattern). Some slightly contaminated crystals of 7-S2 were obtained as colorless platelets from heptane. 31P{1H} NMR (162.0 MHz, CDCl3): δ 49.5. Yield: 0.62 g (40.3%) of 4-S was obtained as colorless prisms from heptane/ether mixtures. Mp: 127−128 °C. Anal. Calcd for C14H21PS (252.3): C, 66.63; H, 8.39; S, 12.70. Found: C, 66.88; H, 8.68; S, 12.60. 1H NMR (600.1 MHz, CDCl3): δ 0.95 (6H, d, 3JHP = 15.2 Hz, CH3 Ph-facing side), 1.32 (6H, d, 3JHP = 16.1 Hz, CH3 S-facing side), 1.88−2.00 (4H, m, CH2), 7.36−7.45 (3H, m, m-CH, p-CH), 8.00− 8.05 (2H, m, o-CH). 13C{1H} NMR (150.9 MHz, CDCl3): δ 26.0 (d, 2 JCP = 1.1 Hz, CH3 Ph-facing side), 28.6 (d, 2JCP = 1.7 Hz, CH3 Sfacing side), 38.9 (d, 2JCP = 13.7 Hz, CH2), 39.8 (d, 1JCP = 47.7 Hz, C), 127.5 (d, 3JCP = 10.6 Hz, m-CH), 128.8 (d, 1JCP = 60.3 Hz, m-CH), 130.9 (d, 4JCP = 3.0 Hz, p-CH), 133.5 (d, 2JCP = 8.8 Hz, m-CH); 31 1 P{ H} NMR (162.0 MHz, CDCl3): δ 87.1; MS (EI) m/e: 252 (M+, C14H21PS), 237, 209, 196, 140. Yield: 0.14 g (11.7%) of 6-S2 as colorless prisms from heptane/ ether mixtures. Mp: 212−214 °C. Anal. Calcd for C20H26P2S2 (392.5): C, 61.20; H, 6.67; S, 16.34. Found: C, 61.62; H, 6.80; S, 15.84. 1H NMR (400.1 MHz, CDCl3): δ 1.20 (6H, m, CH3), 1.61 (2H, m, CH2), 2.02 (6H, m, CH3), 2.92 (2H, m, CH2, Ph-facing side), 7.38 (4H, m, m-CH), 7.45 (2H, m, p-CH), 8.62 (4H, m, o-CH). 13C{1H} NMR (100.6 MHz, CDCl3): δ 25.5 (CH3), 27.6 (CH3), 35.1 (2 × CH2), 43.0 (AA′X system, α-C), 126.9 (AA′X system, i-C), 127.7 (AA′X system, m-C), 132.1 (p-C), 134.9 (AA′X system, o-C). 31P NMR (162.0 MHz, CDCl3): δ 38.5. MS (EI) m/e: 392 (M+, C20H26P2S2,), 359, 329, 283, 252, 217, 196, 185, 140, 110, 69. 4.6. Synthesis of [PhPCl(S){C(CH3)2C2H4CH(CH3)2}] (3-S). A solution of 2.65 mmol of 1 in 30 mL of THF was combined at 0 °C with 0.73 g (5.30 mmol) of triethylammonium chloride. The suspension was stirred for 3 h in an ice bath and then stirred overnight without additional ice cooling. During this stirring crystalline triethylammonium chloride completely dissolved. At the same time the reaction mixture became viscous due to the precipitation of very thin small needles. The 31P NMR spectrum of a sample of the reaction mixture (with additional 20% of C6D6) showed that 81% of 3 and 18% of 5 formed. At this point 0.35 g (10.92 mmol) of elemental sulfur was added and the suspension was shaken overnight. The sulfur dissolved with reduction of the viscosity of the reaction mixture. A quantitative conversion was confirmed by 31P NMR spectroscopy. All volatiles were removed, and the compounds of the residue were separated on a silica gel column with heptane as the eluent.

(Finnigan MAT). Elemental analyses (C, H, S, Cl) were performed with a VARIO EL III (Elementar) elemental analyzer. The magnesium content and the alkalinity of the organomagnesium compounds were determined by common complexometric and acid/base titrations. The net weights of the samples were determined in thin-walled glass capillaries under an argon atmosphere. Melting points (not corrected) were determined with a melting point microscope from Kofler Boetius. Due to the sensitivity of the Grignard reagents, elemental analysis was not reliable. Therefore, we determined the metal content and the alkalinity. The purity of compounds was established by NMR spectroscopy because some substances gave unreliable elemental analyses (presumably due to sulfate formation during combustion). 4.2. Starting Materials. Dichlorophenylphosphane was purchased from Alfa Aesar. The magnesiacycles 1 and [{(thf)2Mg{μ-CH2)5}}2] were prepared according to literature protocols.4a 4.3. Synthesis of [{(thf)2Mg} 2{μ-C(CH 3) 2 C2 H4 (CH 3) 2 C}{μ(CH2)5}] (2). A solution of 1.63 g (2.90 mmol) of 1 and 1.55 g (3.25 mmol) of [{(thf)2Mg{μ-CH2)5}}2] in 20 mL of THF was prepared, heated under reflux, and then immediately cooled to −40 °C for crystallization purposes. Colorless rodlike crystals, which were partly grown together, precipitated overnight. These crystals were collected on a cooled frit, yield 1.6 g of 2 (53% with respect to 1), and used for characterization. Anal. Calcd for C29H58Mg2O4 (519.4): Mg, 9.36. Found: Mg, 9.30. Alkalinity: calcd, 377.7 mg of H2SO4/g; found, 377.4 mg of H2SO4/g. 1H NMR (400.1 MHz, [D8]THF, room temperature): δ −0.62 (4H, t, J = 5.8 Hz, MgCH2), 0.92 (12H, s, CH3), 1.05 (4H, s, β′-CH2), 1.28 (2H, br, γ-CH2), 1.63 (4H, br, βCH2), 1.79 (16H, m, thf), 3.62 (16H, m, thf). 13C{1H} NMR (100.6 MHz, [D8]THF, room temperature): δ 9.3 (MgCH2), 19.6 (C), 22.3 (C), 26.2 (CH2, thf), 31.9 (β-CH2), 33.4 (CH3), 34.2 (CH3), 46.2 (br, γ-CH2), 50.7 (β′-CH2), 53.7 (β′-CH2), 68.0 (CH2, thf). The NMR spectra recorded at −40 °C contain resonances of three compounds (2, dinuclear 1, and [{(thf)2Mg{μ-CH2)5}}2] with an intensity ratio of 3:1:1). In the 1H NMR spectrum all signals of [{(thf)2Mg{μ-CH2)5}}2] are covered by the resonances of 2. 1H NMR (400.1 MHz, [D8]THF, −40 °C): 2, δ −0.64 (4H, t, J = 6.4 Hz, MgCH2), 0.87 (12, s, CH3), 0.97 (4H, s, β′-CH2), 1.23 (2H, br, γCH2), 1.59 (4H, br, β-CH2), 1.79 (16H, m, thf), 3.62 (16H, m, thf); mononuclear 1, δ 9.01 (12, s, CH3), 1.02 (4H, s, β′-CH2). [{(thf)2Mg{μ-CH2)5}}2]: δ −0.64 (8H, t, J = 6.4 Hz, MgCH2), 1.23 (4H, br, γ-CH2), 1.59 (8H, br, β-CH2). 13C{1H} NMR (100.6 MHz, [D8]THF, −40 °C): 2, δ 8.8 (MgCH2), 22.0 (C), 26.2 (CH2, thf), 31.7 (β-CH2), 34.1 (CH3), 45.7 (γ-CH2), 53.3 (β′-CH2), 68.0 (CH2, thf); mononuclear 1, δ 19.5 (C), 33.3 (CH3), 50.3 (β′-CH2). [{(thf)2Mg{μ-CH2)5}}2]: δ 9.1 (MgCH2), 31.8 (β-CH2), 46.6 (γCH2). 4.4. Photolysis of [{(thf)2Mg(μ-C(CH3)2C2H4C(CH3)2)}2] (1). In an NMR tube a suspension of 160 mg (0.28 mmol) of 1 and 40 μL (0.29 mmol) of mesitylene as internal reference in [D8]THF were investigated by NMR spectroscopy before and after irradiation with a mercury vapor lamp (NU-8 KL, 2 × 8 W, 254 and 366 nm). For the photolysis reaction, the NMR tube was fixed with an elastic strap directly on the irradiation source and covered with aluminum foil. The solution was irradiated six times for 10 min. Between these irradiation periods the NMR tube was cooled with cold water. After these irradiation cycles the crystals of 1 dissolved and the solution turned brown with precipitation of a fine gray solid. After settling of the precipitate overnight, NMR spectra were recorded from the slightly dull solution. In addition to the signals of still present 1 new resonances could be assigned to the photolysis products. 1H NMR (600.1 MHz, [D8]THF): δ 1.18 (m, CH2), 1.57 (s, CH3), 1.64 (s, CH3), 1.69 (s, CH3), 4.53 (CH2), 4.60 (CH2), 4.66 (CH). 13 C{1H} NMR (150.9 MHz, [D8]THF): δ 18.2 (CH3), 21.9 (CH3), 26.1 (CH3, superimposed by THF resonances), 39.4 (CH2), 49.4 (CH2), 108.1 (CH2), 110.1 (C), 130.2 (CH), 149.1 (C). 4.5. Reaction of 1 with Dichlorophenylphosphane in a Molar Ratio of 1:2 and Oxidation with Sulfur. A solution of 2.77 g (3.15 mmol) of 1 in 100 mL of THF was cooled to −78 °C, and then 1.1 g (6.1 mmol) of dichlorophenylphosphane was added. This reaction mixture was stirred for 12 h at −78 °C and thereafter stored G


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Organometallics 4.7. Synthesis of a 1:1 Mixture of [{PhP(S)(C(CH3)2C2H4CH(CH3)2)}2] (7-S2) and [{PhP(S)(C(CH3)2C2H4CH(CH3)2)}{PhP(S)(C(CH3)2C2H4C(CH3)(CH2)}] (8-S2). A suspension of 3 (2.15 mmol) and 5 (0.48 mmol) in 30 mL of THF (see synthesis protocol for 3-S) was combined with 0.04 g (5.74 mmol) of lithium sand and the mixture stirred for 30 min. During this process, the very fine needles dissolved completely. Thereafter, excess lithium sand was removed with a Schlenk frit; then 0.35 g (10.92 mmol) of sulfur was added to the filtrate and the reaction mixture was shaken for 12 h on a mechanical shaker. In the 31P NMR spectrum of the reaction solution the resonances of 3 and 5 vanished and mainly the signals of two new compounds (31P NMR: δ 49.5 and 49.3) appeared. All volatiles were removed, and the compounds of the residue were separated on a silica gel column (eluent: (1) heptane, (2) toluene). Yield: 0.44 g (80%) of a 1:1 mixture of 7-S2 and 8-S2 as colorless prisms from diethyl ether. Anal. Calcd for C28H43P2S2 (505.7): C, 66.50; H, 8.57; S, 12.68. Found: C, 67.64; H, 8.69; S, 12.32. Data for 7-S2 are as follows: 1H NMR (600.1 MHz, CDCl3, 50 °C) δ 0.65 (12H, dd, J = 11.7 Hz, J = 6.7 Hz, CH3), 0.86 (4H, m, γ-CH2), 1.05 (6H, m, CH3), 1.15 (2H, m, δ-CH), 1.20 (6H, m, CH3), 1.27 (2H, m, β-CH2), 1.76 (2H, m, β-CH2), 7.52 (4H, br, m-CH), 7.55 (2H, br, p-CH), 8.94 (4H, br, o-CH); 13C{1H} NMR (150.9 MHz, CDCl3, 50 °C) δ 22.5 (3 CH3), 23.0 (CH3), 28.6 (δ-CH), 32.1 (m, γCH2), 34.6 (β-CH2), 49.4 (AA′X system, α-C), 127.8 (br, m-CH), 129.6 (AA′X system, i-C), 132.0 (p-CH), 135.5 (d, 2JCP = 4.5 Hz, oCH); 31P{1H} NMR (202.5 MHz, CDCl3, 50 °C) δ 49.5. Data for 8-S2 are as follows: 1H NMR (600.1 MHz, CDCl3, 50 °C) δ 0.65 (6H, dd, J = 11.7 Hz, J = 6.7 Hz, CH3), 0.85 (3H, m, CH3), 0.86 (2H, m, γ-CH2), 1.05 (3H, m, CH3), 1.15 (4H, m, δ-CH, CH3), 1.20 (3H, m, CH3), 1.27 (1H, m, β-CH2), 1.44 (1H, s, CH2), 1.48 (3H, s, ε-CH3), 1.69 (2H, m, γ-CH2), 1.76 (1H, m, β-CH2), 1.93 (1H, m, β-CH2), 4.35 (1H, s, CH2), 4.52 (1H, s, ε-CH2), 7.52 (4H, br, m-CH), 7.55 (2H, br, p-CH), 8.94 (4H, br, o-CH); 13C{1H} NMR (150.9 MHz, CDCl3, 50 °C) δ 22.6 (2 × CH3), 23.0 (CH3), 31.5 (m, γ-CH2), 35.2 (β-CH2), 49.3 (m, α-C), 110.0 (CH2), 127.8 (br, mCH), 129.6 (ABX system, i-C), 132.0 (p-CH), 135.5 (d, 2JCP = 4.5 Hz, o-CH), 145.5 (C); 31P{1H} NMR (202.5 MHz, CDCl3, 50 °C) δ 49.3 (ABX system). MS of the 1:1 mixture (EI, m/e): 506 (M+, C28H44P2S2), 393 (M+ − C8H17), 359, 281, 253 (M+/2), 251, 222, 185, 141, 113, 71, 57, 43. 4.8. Structure Determinations. The intensity data for the compounds were collected on a Nonius KappaCCD diffractometer using graphite-monochromated Mo Kα radiation. Data were corrected for Lorentz and polarization effects; absorption was taken into account on a semiempirical basis using multiple scans.19−21 The structures were solved by direct methods (SHELXS22) and refined by full-matrix least-squares techniques against Fo2 (SHELXL-9722). The hydrogen atoms of the compounds 3-S, 6-S2, and 7-S2 (with the exception of the methyl group of C5) were located by difference Fourier synthesis and refined isotropically. All other hydrogen atoms were included at calculated positions with fixed thermal parameters. All non-hydrogen and nondisordered atoms were refined anisotropically.22 Crystallographic data as well as structure solution and refinement details are summarized in the Supporting Information. XP (Siemens Analytical Xray Instruments, Inc.)23 and POV-Ray24 were used for structure representations. Crystallographic data (excluding structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publications CCDC-1504993 for 2, CCDC-1504994 for 3-S, CCDC-1504995 for 4-S, CCDC-1504996 for 6-S2, and CCDC-1504997 for 7-S2. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (e-mail: [email protected]).

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Crystallographic data of the crystal structure determinations (CIF) NMR and mass spectra of reported compounds and crystallographic and refinement details (PDF)

AUTHOR INFORMATION

Corresponding Author

*M.W.: e-mail, [email protected]; fax, +49 3641 948132. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Ms. Regina Suxdorf for the preparation of the Grignard reagents that were used. We also appreciate financial support by the Fonds der Chemischen Industrie (Verband der Chemischen Industrie, Frankfurt/M., Germany).

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REFERENCES

(1) Schlenk, W.; Schlenk, W., Jr. Ber. Dtsch. Chem. Ges. B 1929, 62, 920−724. (2) Ashby, E. C. Pure Appl. Chem. 1980, 52, 545−569. (3) Langer, J.; Krieck, S.; Fischer, R.; Görls, H.; Walther, D.; Westerhausen, M. Organometallics 2009, 28, 5814−5820. (4) (a) Fischer, R.; Suxdorf, R.; Görls, H.; Westerhausen, M. Organometallics 2012, 31, 7579−7585. (b) Fischer, R.; Görls, H.; Langer, J.; Enke, M.; Westerhausen, M. Organometallics 2016, 35, 587−594. (5) Ashby, E. C.; Parris, G. E. J. Am. Chem. Soc. 1971, 93, 1206− 1213. (6) House, H. O.; Latham, R. L.; Whitesides, G. M. J. Org. Chem. 1967, 32, 2481−2496. (7) (a) [(Et2O)(PhCH2)Mg(μ-CH2Ph)]2: Rochat, R.; Yamamoto, K.; Lopez, M. J.; Nagae, H.; Tsurugi, H.; Mashima, K. Chem. - Eur. J. 2015, 21, 8112−8120. (b) [(thf)(H3C)Mg(μ-CH3)]2: Michel, O.; Meermann, C.; Tornroos, K. W.; Anwander, R. Organometallics 2009, 28, 4783−4790. (8) Schulze, V.; Löwe, R.; Fau, S.; Hoffmann, W. J. Chem. Soc., Perkin Trans. 2 1998, 463−465. (9) (a) [PhMg(1,3-Xylyl[15]-crown-4]: Markies, P. R.; Nomoto, T.; Schat, G.; Akkerman, O. S.; Bickelhaupt, F.; Smeets, W. J. J.; Spek, A. L. Organometallics 1991, 10, 3826−2827. (b) [(4-t-BuC6H4)Mg(1,3xylyl[18]-crown-6)]: Markies, P. R.; Nomoto, T.; Akkerman, O. S.; Bickelhaupt, F.; Smeets, W. J. J.; Spek, A. L. Angew. Chem., Int. Ed. Engl. 1988, 27, 1084−1086; 1988, 100, 1143. (10) [(tmeda)Mg(CH3)(η3-L)] (L = Cp, Ind, fluorene): Viebrock, H.; Abeln, D.; Weiss, E. Z. Naturforsch., B: J. Chem. Sci. 1994, 49, 89− 99. (11) (a) [EtMg(μ-(CH2)2NMeR)] (R = Me, Cy) Bogdanovic, B.; Koppeltsch, G.; Krüger, C.; Mynott, R. Z. Naturforsch., B: J. Chem. Sci. 1986, 41, 617−628. (b) Bogdanovic, B.; Janke, N.; Krüger, C.; Schlichte, K.; Treber, J. Angew. Chem., Int. Ed. Engl. 1987, 26, 1025− 1026; Angew. Chem. 1987, 99, 1046−1047. (c) [BuMg{μC(SiMe3)2(SiMe2NMe2)}(thf)]: Al-Juaid, S. S.; Avent, A. G.; Eaborn, C.; El-Hamruni, S. M.; Hawkes, S. A.; Hill, M. S.; Hopman, M.; Hitchcock, P. B.; Smith, J. D. J. Organomet. Chem. 2001, 631, 76− 86. (d) [RMg{Cp-CH(t-Bu)C(1,3-Me2-pyrazole)2}] (R = Me, Et, CH2SiMe3): Honrado, M.; Otero, A.; Fernandez-Baeza, J.; SanchezBarba, L. F.; Garces, A.; Lara-Sanchez, A.; Martinez-Ferrer, J.; Sobrino, S.; Rodrigez, A. M. Organometallics 2015, 34, 3196−3208. (12) (a) Eschinasi, E. H.; Cotter, M. L. Tetrahedron Lett. 1964, 5, 3481−3485. (b) Warkentin, J. Can. J. Chem. 1970, 48, 1391−1393. (c) Lacout-Loustalet, M. B.; Dupin, J. P.; Métras, F.; Valade, J. J. Organomet. Chem. 1971, 31, 337−368. (d) Cabiddu, S.; Secci, M.; Maccioni, A. J. Organomet. Chem. 1975, 88, 121−128. (e) Holm, T. Acta Chem. Scand. 1987, 41b, 278−284. (f) Yuan, K.; Scott, W. J. J. Org. Chem. 1990, 55, 6188−6194. (g) Westerhausen, M.;

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00743. H


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Organometallics Makropoulos, N.; Wieneke, B.; Karaghiosoff, K.; Nöth, H.; SchwenkKircher, H.; Knizek, J.; Seifert, T. Eur. J. Inorg. Chem. 1998, 1998, 965−971. (h) Holm, T. J. Am. Chem. Soc. 1999, 121, 515−518. (13) Wagner, B. O.; Hammond, G. S. J. Organomet. Chem. 1975, 85, 1−14. (14) Blake, A. J.; Howie, R. A.; Mc Quillan, G. P. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1981, 37, 966−969. (15) (a) Sillanpaa, R.; Ergin, O.; Celebi, S. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1993, 49, 767−768. (b) Lee, J. D.; Goodacre, G. W. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1970, 26, 507−514. (16) Lee, J. D.; Goodacre, G. W. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1971, 27, 302−307. (17) See e.g.: (a) Reetz, M. T.; Weis, C. Synthesis 1977, 1977, 135− 136. (b) Cowan, D. O.; Mosher, H. S. J. Org. Chem. 1963, 28, 204− 206. (c) Foley, W. M.; Welch, F. J.; La Combe, E. M.; Mosher, H. S. J. Am. Chem. Soc. 1959, 81, 2779−2784. (18) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. Organometallics 2010, 29, 2176−2179. (19) Hooft, R. COLLECT, Data Collection Software; Nonius BV, Dordrecht, The Netherlands, 1998. (20) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C. W., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276, Macromolecular Crystallography, Part A, pp 307−326. (21) SADABS 2.10; Bruker-AXS Inc., Madison, WI, USA, 2002. (22) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122. (23) XP; Siemens Analytical X-ray Instruments Inc., Karlsruhe, Germany, 1990, Madison, WI, USA, 1994. (24) POV-Ray, Persistence of Vision Raytracer; Persistence of Vision, Victoria, Australia, 2007.

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Reactivity Studies of [(thf)2Mg{Î¼-C(CH3)2C2H4C ... - ACS Publications

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