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Mar 27, 2018 - ABSTRACT: A series of alkali-metal alkyl complexes containing a tridentate benzhydryl ligand, [2,2′-(4-MeC6H4NMe2)2CH]Li(TMEDA)...
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Article Cite This: Organometallics XXXX, XXX, XXX−XXX

Alkali-Metal Alkyl Complexes with the Tridentate Benzhydryl Ligand [2,2′-(4-MeC6H4NMe2)2CH]− Dmitry O. Khristolyubov,† Dmitry M. Lyubov,† Anton V. Cherkasov,† Georgy K. Fukin,† Andrey S. Shavyrin,† and Alexander A. Trifonov*,†,‡ †

Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinina str. 49, GSP-445, 630950 Nizhny Novgorod, Russia ‡ Institute of Organoelement Compounds of Russian Academy of Sciences, Vavilova str. 28, 119334 Moscow, Russia S Supporting Information *

ABSTRACT: A series of alkali-metal alkyl complexes containing a tridentate benzhydryl ligand, [2,2′-(4-MeC6H4NMe2)2CH]Li(TMEDA) (1TMEDA), [2,2′-(4-MeC6H4NMe2)2CH]Na(THF)3 (2THF), {[2,2′-(4MeC6H4NMe2)2CH]K(THF}2 (3THF), and [2,2′-(4-MeC6H4NMe2)2C(SiMe3)]K (5), were synthesized and structurally characterized. Smaller Li and Na ions form the monomeric complexes 1TMEDA and 2THF featuring η4-CCCN coordination of the [2,2′-(4-MeC6H4NMe2)2CH]− ligand, while the larger K affords the dimeric complex 3THF, in which two different types of metal−ligand bonding, μ-η5-pentadienyl-κ2-NN and μκ3-CNN:η6-arene are realized. Application of the Me3Si-substituited analogue [2,2′-(4-MeC6H4NMe2)2C(SiMe3)]− leads to the formation of the 1D coordination polymer {[2,2′-(4MeC6H4NMe2)2C(SiMe3)]K}∞ (5) with μ-η3:η6 bridging coordination of the ligands to potassium ions.

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INTRODUCTION Alkali-metal alkyls are key compounds in organic synthesis1 and have shown enormous utility in the preparation of a range of organometallic compounds through salt metathesis reactions. Formation of alkyl derivatives of heavier alkali metals as reactive intermediates is often assumed in superbase chemistry.2 These complexes present an intriguing object for investigation due to the variety of their structural features and peculiar bonding properties. Bulky silyl ([(R3Si)nCH3−n]−)3 and phenyl-substituted ([PhCH2]−)4 methanides, which were successfully used for the synthesis and isolation of a large number of lowcoordination and low-oxidation-state organometallic species, have been a special focus of interest.5 These types of carbanionic ligands allow exclusion of the β-hydrogen elimination pathway of decomposition, thus achieving kinetic stabilization of highly reactive organometallics. Steric demand, feasibility of negative charge delocalization within the conjugated benzylic π-system, and the possibility of nonconventional metal−ligand interactions provide additional means for stabilization.4b−d,6 A combination of the bulkiness of the silyl group and negative charge delocalization in the benzylic system at the central methanido carbon within aromatic system was applied for the synthesis of phenyl-silylsubstituted alkali-metal methanido complexes.7 Another approach to stabilization of the coordination center is “sidearm complexation”, where the cation is locked into position by pendant Lewis base groups with oxygen,8 nitrogen,9 phosphorus,10 and sulfur11 atoms. Thereby, M−C bonding is maintained and benzylic ligands bearing a side-arm donor © XXXX American Chemical Society

have been successfully used for the synthesis of alkali-metal complexes of various structures. Despite the large number of silyl-substituted benzylic alkalimetal complexes, diphenyl methanido derivatives remain scarce, and to date only benzhydryl (Ph2CH−)4b,12 and silylsubstituted (Ph2C(SiR3)−)13 complexes are known. Herein we report on the synthesis of new alkali-metal derivatives of 2,2′-methylenebis(N,N,4-trimethylaniline).14 Recently related tridentate pincer type alkyl ligands containing phosphino groups in ortho positions of the phenyl rings were successfully employed for the preparation of series of late d transition metal alkyls15 and Schrock-type carbene complexes.16 From this point of view the potentially tridentate benzhydryl ligand [2,2′-(4MeC6H4NMe2)2CH]− seems to be a suitable carbanionic ligand for the preparation of a wide range of pincer-type alkyl complexes.

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RESULTS AND DISCUSSION Metalation of 2,2′-methylenebis(N,N,4-trimethylaniline) (2,2′(4-MeC6H4NMe2)2CH2) with n-BuLi or Lochmann−Schlosser superbases (n-BuLi/t-BuOM, M = Na, K) affords the corresponding alkali-metal derivat ives [{2,2′-(4MeC6H4NMe2)2CH}M] (M = Li (1), Na (2), K (3)). When n-BuLi or a n-BuLi/t-BuOM mixture (M = Na, K) (1:1 molar ratio, hexane) are added at ambient temperature to a solution of 2,2′-(4-MeC6H4NMe2)2CH2 in hexane, the formation of yellow (Li) or orange (Na and K) amorphous precipitates of Received: March 27, 2018

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DOI: 10.1021/acs.organomet.8b00182 Organometallics XXXX, XXX, XXX−XXX

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It was found that the outcome of metalation of 4 depends on the reagent used and the manner in which the reaction was carried out. Thus, the reaction with Lochmann−Schlosser superbase (n-BuLi/t-BuOK) in hexane or Et2O proceeds nonselectively and affords a mixture of silylated ([2,2′-(4MeC6H4NMe2)2C(SiMe3)]K, 5) and nonsilylated (3) potassium alkyl complexes in approximately equimolar amounts. The same products were obtained when n-BuLi was added to an equimolar mixture of 4 and t-BuOK in hexane or Et2O. The formation of such a gamut of products can be rationalized by the competition of two reactions: metalation of the central carbon atom of 4 by n-BuLi/t-BuOK, which affords the target product 5, and the metathesis reaction with t-BuOK, resulting in 3 and t-BuOSiMe3 as a side product (Scheme 3). Previously

complexes 1−3 is observed. Complexes 1−3 are insoluble in aliphatic and aromatic hydrocarbons and Et2O, most likely due to their polymeric structures. However, these coordination polymeric structures can be readily split when compounds 1−3 are treated with Lewis bases such as THF and TMEDA. Monocrystalline samples suitable for single-crystal X-ray analysis were obtained by crystallization of complex 1 from a hexane/TMEDA mixture. For compounds 2 and 3 monocrystalline samples were obtained after cooling their concentrated solutions in THF at −30 °C. Complexes [2,2′-(4MeC6H4NMe2)2CH]Li(TMEDA) (1TMEDA, bright yellow), [2,2′-(4-MeC6H4NMe2)2CH]Na(THF)3 (2THF, orange), and {[2,2′-(4-MeC6H4NMe2)2CH]K(THF}2 (3THF, dark orange) were isolated in 72, 75, and 86% yields, respectively (Scheme 1).

Scheme 3. Reaction Pathways of 4 with t-BuOK and PhCH2K

Scheme 1. Synthesis of Complexes 1−3

cleavage of the C−SiMe3 bond of Ph2CHSiMe3 by heavy-alkalimetal alkoxides was successfully applied to the synthesis of [Ph2CH]M (M = Na, K, Rb, Cs) compounds.12c Interestingly the treatment of 4 with KCH2Ph in THF solution at ambient temperature also does not result in the deprotonation of central Ar2CHSiMe3 fragment but in C−SiMe3 bond cleavage leading to the formation of 3THF and PhCH2SiMe3 (Scheme 3). To the best of our knowledge this is the first example of C−SiMe3 bond cleavage by an alkali-metal alkyl complex. The C−SiMe3 bond cleavage products t-BuOSiMe3 and PhCH2SiMe3 were detected by NMR and GC-MS spectroscopy.17 To overcome this synthetic difficulty, the order of addition of reagents was changed. Deprotonation of 4 by an equimolar amount of n-BuLi (Et2O, 20 °C, 6 h) and subsequent addition of t-BuOK to the resulting yellow solid allowed for the synthesis of {[2,2′-(4-MeC6H4NMe2)2C(SiMe3)]K} (5) as an orange amorphous precipitate. Recrystallization of 5 from a THF/hexane mixture resulted in the isolation of the THF-free coordination polymer {[2,2′-(4-MeC6H4NMe2)2C(SiMe3)] K}∞ (5, Scheme 4) as a crystalline solid in 62% yield.

In order to increase both the steric demand of the ligand and the solubility of its derivatives in noncoordinating solvents, the 2,2′-(4-MeC6H4NMe2)2CH2 scaffold was modified by adding SiMe3 to the central benzhydryl carbon atom. The reaction of 3THF with an equimolar amount of ClSiMe3 was carried out in THF solution at 20 °C and afforded 2,2′-((trimethylsilyl)methylene)bis(N,N,4-trimethylaniline) 2,2′-(4MeC6H4NMe2)2CH(SiMe3) (4, Scheme 2). Compound 4 was isolated after separation of KCl and further recrystallization from hexane as colorless crystals in 70% yield and was identified by NMR, IR, GC-MS and microanalysis (see the Experimental Section).

Scheme 4. Synthesis of 5

Scheme 2. Synthesis of 4

The nuclearity of the alkali-metal derivatives of the [2,2′-(4MeC6H4NMe2)2CH]− ligand and its coordination fashion were found to be dependent on a number of factors: the nature of the alkali metal, the denticity of the Lewis base coordinated to the metal center, and the steric bulk of the benzhydryl ligand ([2,2′-(4-MeC6H4NMe2)2CH]− vs [2,2′-(4-MeC6H4NMe2)2C(SiMe3)]−). Thus, the lithium (1TMEDA) and sodium complexes B

DOI: 10.1021/acs.organomet.8b00182 Organometallics XXXX, XXX, XXX−XXX

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Organometallics (2THF) have monomeric structures (Figures 1 and 2), while the potassium derivative 3THF (Figured 3 and 4) and the SiMe3substituted analogue 5 (Figure 5) adopt dimeric or 1-D polymeric structures.

Figure 3. Molecular structure of {[2,2′-(4-MeC6H4NMe2)2CH]K(THF)}2 (3THFA). Thermal ellipsoids are drawn with 30% probability. Hydrogen atoms (except for KCH), Me groups of NMe2 fragments, and methylene carbons of THF molecules are omitted for clarity. Bond lengths (Å) and angles (deg): K1A−C1A 3.044(3), K1A−C20A 3.157(3), K2A−C20A 3.029(3), K2A−C1A 3.198(3), K1A−C2A 3.059(3), K1A−C7A 3.116(3), K1A−C11A 3.086(2), K1A−C16A 3.184(3), K2A−C21A 3.098(2), K2A−C26A 3.181(3), K2A−C30A 3.041(2), K2A−C35A 3.095(3), K1A−N3A 2.910(2), K1A−N4A 2.912(2), K2A−N1A 2.985(2), K2A−N2A 2.894(2), K1A−O1A 2.633(2), K2A−O2A 2.651(2); K1A−C1A−K2A 80.03(6), K1A− C20A−K2A 80.93(6), C1A−K1A−C20A 99.80(7), C1A−K2A−C20A 99.21(7), N1A−K2A−N2A 95.81(6), N3A−K1A−N4A 95.516), C2A−C1A−C11A 133.8(2), C21A−C20A−C30A 134.4(2).

Figure 1. Molecular structure of [2,2′-(4-MeC6H4NMe2)2CH]Li(TMEDA) (1TMEDA). Thermal ellipsoids are drawn with 30% probability. Hydrogen atoms except for LiCH are omitted for clarity. Bond distances (Å) and angles (deg): Li1−C7 2.253(2), Li1−N2 2.090(2), Li1−N3 2.115(2), Li1−N4 2.072(2), Li1−C8 2.461(2), Li1−C13 2.406(2); C7−Li1−N2 81.25(7), C7−Li1−N3 118.15(8), C7−Li1−N4 125.69(9), N3−Li1−N4 88.38(7), C8−C7−C6 130.92(8).

Figure 4. Molecular structure of {[2,2′-(4-MeC6H4NMe2)2CH]K(THF)}2 (3THFB). Thermal ellipsoids are drawn with 30% probability. Hydrogen atoms (except for KCH), Me groups of NMe2 fragments, and methylene carbons of THF molecules are omitted for clarity. Bond lengths (Å) and angles (deg): K1B−C1B 3.134(3), K1B−C20B 3.419(3), K1B−N1B 2.979(2), K1B−N2B 3.003(2), K1B−O1B 2.691(2), K1B−C21B 2.935(2), K1B−C22B 3.193(3), K1B−C23B 3.374(3), K1B−C24B 3.455(3), K1B−C25B 3.403(3), K1B−C26B 3.112(3), K2B−C20B 3.086(3), K2B−C1B 3.494(3), K2B−N3B 2.993(2), K2B−N4B 3.009(2), K2B−O2B 2.651(2), K2B−C11B 2.915(2), K2B−C12B 3.119(3), K2B−C13B 3.266(3), K2B−C14B 3.308(3), K2B−C15B 3.235(4), K2B−C16B 3.029(3); K1B−C1B− K2B 76.91(6), K1B−C20B−K2B 78.68(6), C1B−K1B−C20B 102.51(7), C1B−K2B−C20B 101.82(7), N1B−K1B−N2B 95.07(6), N3B−K2B−N4B 97.67(6), C2B−C1B−C11B 133.0(2), C21B− C20B−C30B 131.4(2).

Figure 2. Molecular structure of [2,2′-(4-MeC6H4NMe2)2CH]Na(THF)3 (2THF). Thermal ellipsoids are drawn with 30% probability. Hydrogen atoms except for NaCH are omitted for clarity. Bond distances (Å) and angles (deg): Na1−C7 2.596(2), Na1−N1 2.578(2), Na1−O1 2.329(2), Na1−O2 2.278(2), Na1−O3 2.313(2), Na1−C6 2.906(2), Na1−C1 2.933(2); N1−Na1−C7 66.87(4), O1− Na1−O2 109.70(5), O1−Na1−O3 95.92(5), O2−Na1−O3 89.03(5), C6−C7−C8 129.6(2).

X-ray diffraction studies revealed that the metal ions in all complexes are situated above or below the ligand planes. In the monomeric complexes 1TMEDA and 2THF the metal ions are bound to the [2,2′-(4-MeC6H4NMe2)2CH]− ligand in a nonsymmetric fashion: by a covalent M−C bond and a coordination M−N bond with one NMe2 group. The nitrogen atom of the second NMe2 group is not involved in the metal− ligand bonding. The central benzhydryl fragment Ar−CH−Ar in 1TMEDA and 2THF is not planar; one ofthe two Ph rings which does not interact with the metal center is twisted across the

CH−Cipso axis by 17.6° (1TMEDA) and 21.4° (2THF). The formal coordination numbers of Li and Na ions in 1TMEDA and 2THF are 4 and 5, respectively, due to coordination of one bidentate TMEDA molecule (for 1TMEDA) or three THF molecules (for 2THF). The bond lengths between alkali-metal ions and the C

DOI: 10.1021/acs.organomet.8b00182 Organometallics XXXX, XXX, XXX−XXX

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ion is coordinated by the central benzhydryl carbon (K1A− C20A 3.157(3) Å and K2A−C1A 3.198(3) Å) and two NMe2 groups (K1A−N 2.910(2) and 2.912(2) Å; K2A−N 2.894(2) and 2.985(2) Å) of the second ligand, thus forming a dimeric structure with a μ-η5-pentadienyl:κ3-CNN type of metal−ligand bonding. In the molecule 3THFB the K ions are bound with the benzhydryl carbon (K1B−C1B 3.134(3) Å and K2B−C20B 3.086(3) Å) and both NMe2 groups (K1B−N 2.979(2) and 3.003(2) Å; K2B−N 2.993(2) and 3.009(2) Å); moreover, η6 coordination of the same K ion with one of the phenyl rings (K1B−C Ar 2.935(2)−3.455(3) Å; K2B−C Ar 2.915(3)− 3.308(3) Å) of the second ligand leads to dimer formation. Finally the type of ligand coordination to the metal ion can be classified as μ-κ3-CNN:η6-arene. In contrast to 3THFA, in which the benzhydryl fragments of [2,2′-(4-MeC6H4NMe2)2CH]− ligands are nearly planar, unsymmetrical coordination of K ions in 3THFB leads to rotation of η6-coordination to the K ion phenyl ring along the CH−Cipso axis by 19.1°. Similar types of coordination of alkali-metal ions to diphenylmethanide anions in the crystalline state have been documented previously for potassium ([K(η5-CHPh2(THF)0.5]∞)12b and rubidium ((η6CHPh2)Rb(18-crown-6)(THF))12a complexes. Unlike dimeric 3THF, complex 5 containing the silylsubstituted ligand [2,2′-(4-MeC6H4NMe2)2C(SiMe3)]− in a crystalline state adopts a 1D polymeric structure (Figure 5). The potassium cation is bound with one [2,2′-(4MeC6H4NMe2)2C(SiMe3)] ligand in an η3 mode via the central benzhydryl carbon (K1−C1A 3.139(2) Å) and ipso and ortho carbons of one phenyl ring (K1−C5Aipso 2.979(2) Å and K1−C10Aortho 3.136(2) Å). η6 coordination of this K ion by the phenyl ring (K1−CAr 3.052(2)−3.251(2) Å) and one NMe2 group (K1−N2 2.889(2) Å) of the second [2,2′-(4MeC6H4NMe2)2C(SiMe3)]− ligand results in the formation of a 1D coordination polymer. Analogous μ-η3:η6-bridging coordination of the carbanionic ligand to potassium ions was previously documented for the disilyl-substituted benzyl complex {[(Me3Si)2CPh]K}∞.7b Unlike complexes coordinated by the [2,2′-(4-MeC6H4NMe2)2CH] ligand, in 5 only one NMe2 group is involved in the metal−ligand interaction. It is worth noting that in 5 the benzhydryl fragment is not planar; the phenyl ring, whose NMe2 group coordinates to the potassium cation, is nearly orthogonal to the plane of the second Ph ring (the dihedral angle between the planes is 88.3°). Despite this distortion of the benzhydryl fragment the central carbon retains its nearly planar sp2 configuration (the sum of bond angles is 359.5°). Short contacts between the potassium ion and methyl groups of SiMe3 and NMe2 fragments (K1−C4ASi 3.223(2) and K1−C12N 3.331(2) Å) are measured in 5; however, no distortion of the valence angles around Si and N atoms was detected. The 1H and 13C{1H} NMR spectra of 1TMEDA (C6D6), 2THF, and 3THF (THF-d8) recorded at ambient temperature present a single set of signals corresponding to the [2,2′-(4MeC6H4NMe2)2CH]− ligand, giving evidence for its symmetric coordination to the alkali-metal cation (see the Supporting Information). However, this contradicts the pattern observed in the crystalline state, featuring coordination of only one NMe2 group of the [2,2′-(4-MeC6H4NMe2)2CH]− ligand to the Li or Na ions. Most likely this reflects the existence of a rapid intramolecular dynamic process on the NMR time scale consisting of coordination−decoordination of the NMe 2 group to the metal center in solution. A variable-temperature NMR study for 1TMEDA (toluene-d8, 223−293 K) indicates

Figure 5. Molecular structure of {[2,2′-(4-MeC6H4NMe2)2C(SiMe3)]K}∞ (5). Thermal ellipsoids are drawn with 30% probability. Hydrogen atoms (except for KCH) and Me groups of NMe2 and SiMe3 fragments are omitted for clarity. Bond distances (Å) and angles (deg): K1B−C1A 3.139(2), K1B−C5A 2.979(2), K1B−C10A 3.136(2), K1A−C5A 3.052(2), K1A−C6A 3.071(2), K1A−C7A 3.157(2), K1A−C8A 3.251(2), K1A−C9A 3.208(2), K1A−C10A 3.064(2), K1A−N2A 2.889(2); C5A−C1A−C14A 115.3(2), C5A− C1A−Si1A 126.19(9), C14A−C1A−Si1A 118.01(9).

central benzhydryl carbons in complexes 1TMEDA (2.253(2) Å) and 2THF (2.596(2) Å) are comparable to the related distances in monomeric alkyl species of four-coordinated lithium (Li−C 2.202−2.315(8) Å)4g,9a,c,e−g,18 and five-coordinated sodium ions (Na−C 2.556(1)−2.568(2) Å).4d,6e,19 For both complexes 1TMEDA and 2THF interactions between alkali-metal ions and ipso and ortho carbons of one phenyl ring resulting in short M−C distances (Li1−C8 2.461(2) Å and Li1−C13 2.406(2) Å; Na1−C6 2.906(2) Å and Na1−C1 2.933(2) Å) were detected. Due to the presence of these interactions the metal ions are located above one of the halves of the ligand, and on the whole the coordination mode of [2,2′-(4-MeC6H4NMe2)2CH]− ligands in 1TMEDA and 2THF can be classified as η4-CCCN. A similar coordination mode of the carbanionic ligand was previously documented for a lithium complex with the α-silylsubstituted dimethylaminobenzyl ligand [2-Me2NC6H4CH(SiMe3)]Li (TMEDA).9f According to an X-ray analysis, in the crystalline state 3THF exists as the two different centrosymmetric dimeric molecules 3THFA and 3THFB. The asymmetric unit cell contains two molecules of each type, 3THFA and 3THFB: one crystallographically independent molecule and one molecule lying at an invertion center. 3THFA and 3THFB both contain two potassium cations sandwiched by two [2,2′-(4-MeC6H4NMe2)2CH]− ligands; however, they differ in the fashion of metal−ligand bonding. In the molecule 3 T H F A tw o [ 2,2 ′-(4MeC6H4NMe2)2CH]− ligands adopt an antiparallel orientation. Each K ion in 3 T H F A is bound to a [2,2′-(4MeC6H4NMe2)2CH]− ligand via the central benzhydryl carbon (K1A−C1A 3.044(3) Å; K2A−C20A 3.029(3) Å); moreover, short contacts with ipso and ortho carbons of both phenyl rings are detected as well (K1A−Cipso 3.059(3) and 3.086(2) Å; K2A−Cipso 3.041(2) and 3.098(2) Å; K1A−Cortho 3.116(3) and 3.184(3) Å; K2A−Cortho 3.095(3) and 3.181(3) Å), resulting in η5-pentadienyl type coordination. Interaction of the K ion with ipso and ortho carbons of the phenyl rings affects the planarity of benzhydryl fragment, which is slightly bent across the CH axis, and the dihedral angle between two Ph rings is 7.1°, while the maximum deviation of carbon atoms of phenyl rings from the Cipso−CH−Cipso plane is 0.3 Å. Simultaneously the same K D

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Organometallics

the metal.4i,23 Thus, a small Li cation featuring high charge density polarizes the negative charge on the benzylic carbon atom, while in the complexes of larger Na and K ions, which are much weaker Lewis acids, extensive charge delocalization was detected. The degree of charge delocalization can be estimated from the Cα−Cipso bond distances and the endocyclic Cortho− Cipso−Cortho bond angles in the solid state,4i,23 while the chemical shifts of para protons and carbons in the 1H and 13C NMR spectra are informative about the negative charge delocalization in the solution.4c,23 The Cα−Cipso bond distances (1TMEDA, 1.435(1) Å; 2THF, 1.427(2) Å; 3THF, 1.409(4)− 1.430(4) Å) and Cortho−Cipso−Cortho bond angles (1TMEDA, 114.0(1)°; 2THF, 114.6(2)°; 3THF, 114.2(2)−114.9(2)°) measured for the series of benzhydryl complexes 1TMEDA, 2THF, and 3THF have very close values regardless of the nature of the alkali-metal ion. Although the geometric parameters of complexes 1TMEDA, 2THF, and 3THF in the solid state turned out to be practically independent of the nature of the metal, the 1H and 13C NMR spectra of these complexes allowed for detection of a noticeable difference in the chemical shifts of the signals attributed to the para CH protons and carbons in solution. Thus, the transition from Li to K in the series of benzhydryl compounds leads to a strong field shift of the signals corresponding to the para CH protons and carbons (compare Li complex 1TMEDA, δH 6.40 ppm, δC 111.7 ppm; Na complex 2THF, δH 5.72 ppm, δC 108.6 ppm; K complex 3THF, δH 5.65 ppm, δC 108.0 ppm), indicating the highest charge density on the aromatic rings in K complex 3THF and the lowest in the Li congener 1TMEDA.

retention of the symmetrical coordination of the carbanionic ligand to the lithium ion even at low temperature (see Figures S5 and S6 in the Supporting Information). Cooling of a solution of 1TMEDA results only in broadening of the signal attributed to NMe2 groups of the [2,2′-(4MeC6H4NMe2)2CH]− ligand and its further splitting into two broad signals below 233 K caused by their slow rotation relative to the diphenylmethanido plane of the carbanionic ligand. At the same time aromatic protons and Me groups of both Ph rings remain equivalent even at 223 K. The central benzhydryl hydrogens appear in the 1H NMR spectra of 1TMEDA, 2THF, and 3THF at 3.91, 3.95, and 4.12 ppm, and the appropriate benzhydryl carbons in the 13C{1H} NMR spectra give rise to signals at 59.4, 63.1, and 69.2 ppm, respectively. The nature of the central alkali metal affects the chemical shifts of MCH fragments in 1H and 13C{1H} spectra which increase in the transition from lithium to potassium. The chemical shifts of the atoms of the central methanide fragment in both the 1H and 13C NMR spectra of 1TMEDA, 2THF, and 3THF are shifted substantially upfield in comparison to the unsubstituted benzhydryl anion,12 which can be associated with the electron-donating effect of Me and NMe2 groups incorporated into the Ph2CH scaffold. The LiCH benzhydryl proton in the 1H NMR spectrum of 1TMEDA exhibits very weak 7 Li−H coupling (2JLiH = 1.4 Hz), while the appropriate carbon appears in the 13C{1H} spectrum as a quartet with resolved 7 Li−C coupling (1JLiC = 4.9 Hz) due to splitting to one 7Li (spin 3/2, 92.41%), while the 6Li−13C splitting is hidden (see Figure S2 in the Supporting Information). The fact of Li−C splitting is indicative of significant covalent bonding, and the multiplicity of the signal (quartet) observed for the C−Li carbon indicates that 1TMEDA adopts a monomeric structure in solution. The Li−C coupling is due to the Fermi contact term involving s orbital contributions from both atoms; however, normally Li−C couplings are observed at low temperature.20 As was evidenced by X-ray analysis, the geometry around the central benzhydryl carbon in 1TMEDA, 2THF, 3THF, and 5 is indicative of its sp2 hybridization in the crystalline state, since the sum of bond angles around this carbon atom is very close to 360° (359.6° for 1TMEDA; 359.8° for 2THF; 359.9° for 3THF; 359.5° for 5). It is known that the value of 1JCH coupling constant correlates with the type of hybridization of the C−H bonding orbital.4d,i,21 The values are roughly proportional to the percent of s character and can be estimated from the empirical formula 1JCH = 500 × %s (%s = 0.25 for sp3, 0.33 for sp2).22 The 1JCH coupling constants measured for 1TMEDA (141 Hz), 2THF (146 Hz), and 3THF (149 Hz) are substantially larger than the values characteristic for sp3-hybridized CH bonds (1JCH = 125 Hz) but smaller than those that can be expected for sp2-hybridized CH bonds (1JCH = 167 Hz).4a The %s values calculated for 1TMEDA, 2THF, and 3THF (0.28−0.30) correspond to hybridization intermediate between sp2 and sp3 types. It is noteworthy that this value increases in the series Li−Na−K due to increasing polarization of the metal−carbon bond. Interestingly the related Li and K complexes with the Me3Sisubstituted dimethylaminobenzyl carbanion [2-Me2NC6H4CH(SiMe3)] feature substantially lower values of CH coupling constants (123.2 and 131.8 Hz for Li and K, respectively),9f while the 1JCH value for the parent 2,2′-(4-MeC6H4NMe2)2CH2 is 126 Hz. Formerly for the related benzyl alkali-metal complexes it was demonstrated that the degree of negative charge delocalization within the benzylic fragment is highly sensitive to the nature of

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CONCLUSIONS The tridentate benzhydryl ligand [2,2′-(4MeC6H4NMe2)2CH]− proved to be a useful platform for the synthesis of a series of isolable alkali-metal species featuring diverse structures and metal−ligand bonding modes. It was demonstrated that the nuclearity of the alkali-metal complexes coordinated by [2,2′-(4-MeC6H4NMe2)2CH]− ligand and the coordination mode of the latter are strongly affected by the nature of the alkali metal (ion size, electropsitivity), denticity of the Lewis base coordinated to the metal center, and steric bulk of the benzhydryl ligand ([2,2′-(4-MeC6H4NMe2)2CH]− vs [2,2′-(4-MeC6H4NMe2)2C(SiMe3)]−). For Li and Na ions having a smaller ion size monomeric complexes 1TMEDA and 2THF featuring a η4-CCCN coordination mode were isolated. In the case of the larger K the complexation with the tridentate [2,2′-(4-MeC6H4NMe2)2CH]− ligand leads to the formation of dimeric complex 3THF, in which the metal ions are sandwiched by two ligands. Two different types of metal−ligand bonding, μ-η5-pentadienyl:κ3-CNN and μ-κ3-CNN:η6-arene, were detected in 3THF. Attachment of an Me3Si group to the methanide carbon provokes the rotation of the phenyl rings and changes the mutual arrangement of the pendant Lewis base groups of [2,2′-(4-MeC6H4NMe2)2C(SiMe3)], leading to the formation of the 1D polymer {[2,2′-(4-MeC6H4NMe2)2C(SiMe3)]K}∞ with a μ-η3:η6 bridging coordination mode of the ligand to potassium ions.

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EXPERIMENTAL SECTION

All experiments were performed under an inert atmosphere, using standard Schlenk-tube and glovebox techniques. After they were dried over KOH, THF and TMEDA were purified by distillation from sodium/benzophenone ketyl. Hexane and toluene were dried by distillation from sodium/triglyme benzophenone ketyl prior to use. nE

DOI: 10.1021/acs.organomet.8b00182 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Synthesis of {[2,2′-(4-MeC6H4NMe2)2CH]K(THF)}2 (3THF). tBuOK (0.272 g, 2.43 mmol) and then a hexane solution of n-BuLi (2.5 mL, 1.0 M, 2.5 mmol) were added to a solution of 2,2′-(4MeC6H4NMe2)2CH2 (0.685 g, 2.43 mmol) in hexane. The reaction mixture was stirred at ambient temperature for 12 h. The orange amorphous precipitate of complex 3 was washed with hexane three times (30 mL) and then was dissolved in THF (10 mL). Cooling the resulting dark red solution to −30 °C overnight afforded dark orange crystals of 3THF. The mother liquid was decanted, and the crystals were washed with cold THF and dried under vacuum for 30 min. Complex 3THF was isolated in 86% yield (0.819 g, 1.04 mmol). Anal. Calcd for C46H66K2N4O2 (785.24 g/mol): C, 70.36; H, 8.47; N, 7.14. Found: C, 70.59; H, 8.25; N, 6.96. 1H NMR (400 MHz, THF-d8, 293 K): 1.78 (m, 8H, β-CH2 THF), 2.05 (s, 12H, C6H3CH3), 2.60 (s, 24H, NMe2), 3.62 (m, 8H, α-CH2 THF), 4.12 (s, 2H, KCH; 1JCH = 149 Hz), 5.65 (dd, 3JHH = 7.5 Hz, 4JHH = 1.5 Hz, 4H, H4), 6.73 (d, 3JHH = 7.5 Hz, 4H, H3), 7.30 (d, 4JHH = 1.5 Hz, 4H, H6) ppm. 13C{1H} NMR (100 MHz, THF-d8, 293 K): 21.2 (s, C6H3CH3),43.4 (s, NMe2), 69.2 (s, KCH), 108.0 (s, CH, C4), 114.7 (s, CH, C3), 116.2 (s, CH, C6), 131.1 (s, C5), 138.8 (s, C1), 139.2 (s, C2) ppm. IR (KBr, suspension in Nujol; cm−1): 2820 (m), 2780 (s), 1570 (s), 1550 (m), 1490 (s), 1405 (m), 1400 (m), 1340 (w), 1330 (m), 1310 (w), 1280 (s), 1270 (s), 1190 (w), 1175 (w), 1170 (w), 1150 (s), 1135 (m), 1090 (s), 1040 (s), 970 (s), 950 (w), 920 (s), 815 (s), 770 (s), 730 (s), 690 (w), 595 (m), 570 (w), 530 (m), 505 (m). Synthesis of [2,2′-(4-MeC6H4NMe2)2CH(SiMe3) (4). 3 (0.550 g, 1.72 mmol) was dissolved in THF (20 mL), and ClSiMe3 (0.190 g, 1.72 mmol) was added. The reaction mixture was stirred at 20 °C for 1 h. The solvent was removed under vacuum, and the reaction product was extracted with hexane. Cooling a concentrated hexane solution at −30 °C afforded colorless crystals of 4 in 70% yield (0.425 g, 1.20 mmol). Anal. Calcd for C22H34N2Si (354.60 g/mol): C, 74.52; H, 9.66; N, 7.90. Found: C, 74.70; H, 9.88; N, 7.86. 1H NMR (200 MHz, CDCl3, 293 K): 0.00 (s, 9H, SiMe3), 2.30 (s, 6H, C6H3CH3), 2.63 (s, 12H, NMe2), 5.08 (s, 1H, CH(SiMe3)), 6.93 (dd, 3JHH = 8.0 Hz, 4JHH = 1.2 Hz, 2H, H4), 7.06 (d, 3JHH = 8.0 Hz, 2H, H3), 7.20 (d, 4JHH = 1.2 Hz, 2H, H6) ppm. 13C{1H} NMR (50 MHz, CDCl3, 293 K): −0.4 (s, SiMe3), 21.2 (s, C6H3CH3), 30.3 (s, CH(SiMe3)), 45.7 (s, NMe2), 120.4 (s, CH, C3), 126.0 (s, CH, C4), 131.1 (s, CH, C6), 132.5 (s, C5), 138.9 (s, C1), 150.4 (s, C2). IR (KBr, suspension in Nujol; cm−1): 3020 (s), 2980 (s), 2930 (s), 2860 (s), 2820 (s), 2780 (s), 1995 (m), 1930 (w), 1875 (m), 1745 (w), 1720 (w), 1605 (s), 1570 (w), 1495 (s), 1475 (w), 1455 (m), 1440 (w), 1405 (w), 1375 (w), 1300 (s), 1260 (m), 1245 (s), 1190 (m), 1160 (s), 1135 (w), 1095 (s), 1075 (m), 1045 (s), 1005 (m), 950 (s), 925 (m), 885 (s), 855 (s), 840 (s), 820 (s), 780 (s), 745 (s), 690 (s), 620 (s), 570 (s) 535 (s), 525 (m), 500 (w). MS (EI): m/z 354.1 [M+]. Synthesis of {[2,2′-(4-MeC6H4NMe2)2C(SiMe3)K}∞ (5). To a solution of 4 (0.286 g, 0.81 mmol) in Et2O was added a hexane solution of n-BuLi (0.8 mL, 1.0 M, 0.8 mmol). The reaction mixture was stirred at ambient temperature for 6 h, and a yellow amorphous solid precipitate formed. Then t-BuOK (0.091 g, 0.81 mmol) was added, and the resulting mixture was stirred at ambient temperature for 12 h. An orange amorphous precipitate of complex 5 formed. To remove t-BuOLi from the reaction product, the orange precipitate was washed with hexane three times (30 mL) and then was dissolved in THF (5 mL). Layering of hexane onto the resulting solution at room temperature allowed isolation of orange crystals of 5. The mother liquid was decanted, and the crystals were washed with hexane and dried under vacuum for 30 min. Complex 5 was isolated in 62% yield (0.819 g, 0.50 mmol). Anal. Calcd for C22H33KN2Si (392.69 g/mol): C, 67.29; H, 8.47; N, 7.13. Found: C, 67.40; H, 8.54; N, 6.87. 1H NMR (200 MHz, THF-d8, 293 K): −0.18 (s, 9H, SiMe3), 1.96 (s, 6H, C6H3CH3), 2.56 (s, 12H, NMe2), 5.87 (dd, 3JHH = 7.6 Hz, 4JHH = 2.0 Hz, 2H, H4), 6.19 (d, 4JHH = 2.0 Hz, 2H, H6), 6.58 (d, 3JHH = 7.6 Hz, 2H, H3) ppm. 13C{1H} NMR (50 MHz, THF-d8, 293 K): 3.0 (s, SiMe3), 20.6 (s, C6H3CH3), 44.7 (s, NMe2), 71.1 (s, KC(SiMe3)), 111.2 (s, CH, C4), 117.5 (s, CH, C3), 125.6 (s, CH, C6), 131.4 (s, C5), 145.1 (s, C1), 147.2 (s, C2) ppm. IR (KBr, suspension in Nujol; cm−1): 2825 (m), 2780 (s), 1640 (m), 1605 (s), 1570 (m), 1500 (s), 1410

BuLi solution (1.0 M in hexane), t-BuOM (M = Na, K) and 4,N,Ntrimethylaniline were purchased from Acros. 2,2′-Methylenebis(N,N,4trimethylaniline) (2,2′-(4-MeC6H4NMe2)2CH2) was prepared according to the literature procedure.14 1H and 13C{1H} NMR spectra were recorded on either a Bruker Avance-II 400 MHz NMR spectrometer or Bruker DPX 200 MHz NMR spectrometer. Chemical shifts (δ) are reported in ppm relative to tetramethylsilane, referenced to the chemical shifts of residual solvent resonances (1H and 13C). IR spectra were recorded as Nujol mulls on a Bruker Vertex 70 spectrophotometer or as otherwise stated. The N, C, H elemental analyses were carried out at the microanalytical laboratory of the IOMC by means of a Carlo Erba Model 1106 elemental analyzer with an accepted tolerance of 0.4 unit on carbon (C), hydrogen (H), and nitrogen (N). Synthesis of [2,2′-(4-MeC6H4NMe2)2CH]Li(TMEDA) (1TMEDA).

To a solution of 2,2′-(4-MeC6H4NMe2)2CH2 (0.750 g, 2.66 mmol) in hexane (30 mL) was added at 20 °C a hexane solution of n-BuLi (2.7 mL, 1.0 M, 2.70 mmol). The reaction mixture was stirred at ambient temperature overnight. A bright yellow amorphous precipitate of 1 formed. After the addition of TMEDA (5 mL) to the reaction mixture the suspension slowly dissolved and further concentration of the solution at ambient temperature gave bright yellow crystals of 1TMEDA. The mother liquid was decanted, and the crystals were washed with cold hexane and dried under vacuum for 30 min. Complex 1TMEDA was isolated in 72% yield (0.792 g, 1.91 mmol). Anal. Calcd for C25H41LiN4 (404.56 g/mol): C, 74.22; H, 10.21; N, 13.85. Found: C, 74.43; H, 10.35; N, 13.60. 1H NMR (400 MHz, C6D6, 293 K): 1.41 (br s, 4H, CH2 TMEDA), 1.68 (br s, 12H, CH3 TMEDA), 2.40 (s, 6H, C6H3CH3), 2.58 (s, 12H, C6H3N(CH3)2), 3.91 (br q, 2JLiH = 1.4 Hz, 1H, LiCH; 1JCH = 141 Hz), 6.40 (dd, 3JHH = 7.7 Hz, 4JHH = 1.5 Hz, 2H, H4), 6.88 (d, 3JHH = 7.7 Hz, 2H, H3), 8.01 (d, 4JHH = 1.5 Hz, 2H, H6) ppm. 13C{1H} NMR (100 MHz, C6D6, 293 K): 21.9 (s, C6H3CH3), 44.0 (s, C6H3N(CH3)2), 44.7 (s, CH3 TMEDA), 55.6 (br s, CH2 TMEDA), 59.4 (q, 1JLiC = 4.9 Hz, LiCH), 111.7 (s, CH, C4), 117.3 (s, CH, C3), 117.4 (s, CH, C6), 132.6 (s, C5), 138.3 (s, C1), 139.7 (s, C2) ppm. 7Li{1H} NMR (155.54 MHz, C6D6, 293 K): −0.22 (s) ppm. IR (KBr, suspension in Nujol; cm−1): 2880 (m), 2775 (s), 1610 (m), 1575 (w), 1400 (m), 1300 (s), 1265 (m), 1225 (w), 1190 (m), 1160 (s), 1090 (s), 1045 (m), 1030 (s), 950 (s), 930 (m), 870 (w), 815 (s), 720 (m), 690 (m), 570 (m). Synthesis of [2,2′-(4-MeC6H4NMe2)2CH]Na(THF)3 (2THF). tBuONa (0.215 g, 2.23 mmol) and then a hexane solution of n-BuLi (2.3 mL, 1.0 M, 2.3 mmol) were added to a solution of 2,2′-(4MeC6H4NMe2)2CH2 (0.630 g, 2.23 mmol) in hexane (15 mL), and the reaction mixture was stirred at ambient temperature for 12 h. The orange amorphous precipitate of complex 2 was washed with hexane three times (30 mL) and then was dissolved in THF (10 mL). Cooling a concentrated THF solution at −30 °C resulted in the formation of orange crystals of 2THF. The mother liquid was decanted, and the crystals were washed with cold THF and were dried under vacuum for 30 min. Complex 2THF was isolated in 75% yield (0.871 g, 1.67 mmol). Anal. Calcd for C31H49N2NaO3 (520.72 g/mol): C, 71.50; H, 9.48; N, 5.38. Found: C, 71.82; H, 9.76; N, 5.20. 1H NMR (400 MHz, THF-d8, 293 K): 1.78 (m, 12H, β-CH2 THF), 2.07 (s, 6H, C6H3CH3), 2.60 (s, 12H, NMe2), 3.62 (m, 12H, α-CH2 THF), 3.95 (s, 1H, NaCH; 1JCH = 146 Hz), 5.72 (dd, 3JHH = 7.7 Hz, 4JHH = 2.0 Hz, 2H, H4), 6.48 (d, 3 JHH = 7.7 Hz, 2H, H3), 7.39 (d, 4JHH = 2.0 Hz, 2H, H6) ppm. 13C{1H} NMR (100 MHz, THF-d8, 293 K): 21.1 (s, C6H3CH3), 43.7 (s, NMe2), 63.1 (s, NaCH), 108.6 (s, CH, C4), 115.5 (s, CH, C3), 116.1 (s, CH, C6), 131.2 (s, C5), 139.1 (s, C1), 139.4 (s, C2) ppm. IR (KBr, suspension in Nujol; cm−1): 2820 (m), 2780 (s), 1610 (m), 1595 (w), 1570 (m), 1500 (s), 1450 (s), 1405 (m), 1305 (s), 1280 (m), 1260 (w), 1190 (s), 1160 (s), 1145 (m), 1090 (s), 1070 (s), 1070 (s), 1045 (s), 950 (s), 915 (s), 820 (s), 785 (w), 765 (s), 725 (s), 695 (m), 675 (w), 655 (m), 630 (w), 595 (s), 575 (s), 535 (s), 520 (m). F

DOI: 10.1021/acs.organomet.8b00182 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

metallic Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier: Oxford, U.K., 2006; Vol. II, pp 1−65. (f) Rathman, T. L.; Schwindeman, J. A. Org. Process Res. Dev. 2014, 18, 1192−1210. (g) Carl, E.; Stalke, D. Structure-Reactivity Relationship in Organolithium Compounds. In Lithium Compounds in Organic Synthesis: From Fundamentals to Applications; Luisi, R., Capriati, V., Eds.; Wiley-VCH: Weinheim, Germany, 2014; pp 1−31. (h) Mulvey, R. E.; Robertson, S. D. Angew. Chem., Int. Ed. 2013, 52, 11470−11487. (2) (a) Lochmann, L.; Trekoval, J. J. Organomet. Chem. 1987, 326, 1−7. (b) Schlosser, M. Pure Appl. Chem. 1988, 60, 1627−1634. (c) Lochmann, L. Eur. J. Inorg. Chem. 2000, 2000, 1115−1126. (d) Lochmann, L.; Janata, M. Cent. Eur. J. Chem. 2014, 12, 537−548. (e) Schlosser, M. Superbases as Powerful Tools in Organic Syntheses. In Modern synthetic methods; Scheffold, R., Ed.; VHCA: Basel, Switzerland, 1992; Vol. 6, pp 227−271. (f) Seyferth, D. Organometallics 2009, 28, 2−33. (g) Gessner, V. H.; Däschlein, C.; Strohmann, C. Chem. - Eur. J. 2009, 15, 3320−3334. (h) Benrath, P.; Kaiser, M.; Limbach, T.; Mondeshki, M.; Klett, J. Angew. Chem., Int. Ed. 2016, 55, 10886−10889. (3) For silyl-substituted methanides see: (a) Eaborn, C.; Smith, J. D. Coord. Chem. Rev. 1996, 154, 125−149. (b) Davidson, P. J.; Lappert, M. F.; Pearce, R. Acc. Chem. Res. 1974, 7, 209−217. (c) Davidson, P. J.; Lappert, M. F.; Pearce, R. Chem. Rev. 1976, 76, 219−242. (d) Eaborn, C.; Izod, K.; Smith, J. D. J. Organomet. Chem. 1995, 500, 89−99. (e) Lappert, M. F.; Liu, D. S. J. Organomet. Chem. 1995, 500, 203−217. (f) Eaborn, C.; Smith, J. D. J. Chem. Soc., Dalton Trans. 2001, 1541− 1552. (4) For phenyl-substituted methanides see: (a) Zarges, W.; Marsch, M.; Harms, K.; Boche, G. Chem. Ber. 1989, 122, 2303−2309. (b) Corbelin, S.; Lorenzen, N. P.; Kopf, J.; Weiss, E. J. Organomet. Chem. 1991, 415, 293−313. (c) Arnold, J.; Knapp, V.; Schmidt, J. A. R.; Shafir, A. J. Chem. Soc., Dalton Trans. 2002, 3273−3274. (d) Davidson, M. G.; Garcia-Vivo, D.; Kennedy, A. R.; Mulvey, R. E.; Robertson, S. D. Chem. - Eur. J. 2011, 17, 3364−3369. (e) Tatic, T.; Hermann, S.; Stalke, D. Organometallics 2012, 31, 5615−5621. (f) Bildmann, U. J.; Müller, G. Organometallics 2001, 20, 1689−1691. (g) Tatic, T.; Hermann, S.; John, M.; Loquet, A.; Lange, A.; Stalke, D. Angew. Chem., Int. Ed. 2011, 50, 6666−6669. (h) Langer, J.; Köhler, M.; Fischer, R.; Dündar, F.; Görls, H.; Westerhausen, M. Organometallics 2012, 31, 6172−6182. (i) Hoffmann, D.; Bauer, W.; Hampel, F.; van Eikema Hommes, N. J. R.; Schleyer, P. v. R.; Otto, P.; Pieper, U.; Stalke, D.; Wright, D. S.; Snaith, R. J. Am. Chem. Soc. 1994, 116, 528−536. (5) (a) Hitchcock, P. B.; Lappert, M. F.; Smith, R. G.; Bartlett, R. A.; Power, P. P. J. Chem. Soc., Chem. Commun. 1988, 1007−1008. (b) Eaborn, C.; Hitchcock, P. B.; Izod, K.; Smith, J. D. J. Am. Chem. Soc. 1994, 116, 12071−12072. (c) Eaborn, C.; Hitchcock, P. B.; Izod, K.; Lu, Z. R.; Smith, J. D. Organometallics 1996, 15, 4783−4790. (d) Eaborn, C.; Hawkes, S. A.; Hitchcock, P. B.; Smith, J. D. Chem. Commun. 1997, 1961−1962. (e) Qi, G.; Nitto, Y.; Saiki, A.; Tomohiro, T.; Nakayama, Y.; Yasuda, H. Tetrahedron 2003, 59, 10409−10418. (f) Harder, S.; Müller, S.; Hübner, E. Organometallics 2004, 23, 178− 183. (6) (a) Yan, K. K.; Upton, B. M.; Ellern, A.; Sadow, A. D. J. Am. Chem. Soc. 2009, 131, 15110−15111. (b) Yan, K. K.; Schoendorff, G.; Upton, B. M.; Ellern, A.; Windus, T. L.; Sadow, A. D. Organometallics 2013, 32, 1300−1316. (c) Pindwal, A.; Ellern, A.; Sadow, A. D. Organometallics 2016, 35, 1674−1683. (d) Pindwal, A.; Patnaik, S.; Everett, W. C.; Ellern, A.; Windus, T. L.; Sadow, A. D. Angew. Chem., Int. Ed. 2017, 56, 628−631. (e) Armstrong, D. R.; Davidson, M. G.; Garcia-Vivo, D.; Kennedy, A. R.; Mulvey, R. E.; Robertson, S. D. Inorg. Chem. 2013, 52, 12023−12032. (f) Avent, A. G.; Bonafoux, D.; Eaborn, C.; Hill, M. S.; Hitchcock, P. B.; Smith, J. D. J. Chem. Soc., Dalton Trans. 2000, 2183−2190. (7) For phenyl-silyl methanides see: (a) Engelhardt, L. M.; Leung, W.-P.; Raston, C. L.; Twiss, P.; White, A. H. J. Chem. Soc., Dalton Trans. 1984, 321−330. (b) Feil, F.; Harder, S. Organometallics 2000, 19, 5010−5015. (c) Schumann, H.; Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg. Chem. 2008, 634, 1334−1338.

(m), 1300 (m), 1250 (s), 1185 (s) 1160 (s), 1130 (w), 1090 (m), 1045 (m), 1020 (m), 950 (s), 885 (w), 855 (w), 840 (s), 820 (s), 770 (m), 740 (s), 690 (w), 660 (m), 630 (m), 575 (w), 540 (m). X-ray Crystallography. The X-ray data for 1TMEDA, 2THF, 3THF, and 5 were collected on Agilent Xcalibur E (1TMEDA) and Bruker D8 Quest (2THF, 3THF, 5) diffractometers (Mo Kα radiation, ω-scan technique, λ = 0.71073 Å) using CrysAlis PRO24 and APEX225 software packages. The structures were solved by direct and dual-space methods26a and were refined by full-matrix least squares on F2 for all data using SHELX.26b SADABS27 and CrysAlis PRO were used to perform area-detector scaling and absorption corrections. All nonhydrogen atoms were found from Fourier syntheses of electron density and were refined anisotropically. The central benzhydryl hydrogen atoms in 1TMEDA, 2THF, and 3THF were also found from Fourier syntheses of electron density and were refined isotropically. Other hydrogen atoms in 1TMEDA, 2THF, 3THF, and 5 were placed in calculated positions and were refined in the “riding” model with U(H)iso = 1.2Ueq of their parent atoms (U(H)iso = 1.5Ueq for methyl groups). CCDC files 1830975 (1TMEDA), 1830976 (2THF), 1830977 (3THF), and 1830978 (5) contain supplementary crystallographic data for this paper. These data are provided free of charge by The Cambridge Crystallographic Data Centre: ccdc.cam.ac.uk/structures. The crystallographic data and structure refinement details for 1TMEDA, 2THF, 3THF, and 5 are given in Table S1 in the Supporting Information.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00182. Crystal data and structure refinement detalis for complexes 1TMEDA, 2THF, 3THF, and 5 and NMR spectroscopic data of complexes 1TMEDA, 2THF, 3THF, and 5 and compound 4 (PDF) Accession Codes

CCDC 1830975−1830978 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 for A.A.T.: [email protected]. ORCID

Dmitry M. Lyubov: 0000-0001-8472-3764 Alexander A. Trifonov: 0000-0002-9072-4517 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the Russian Science Foundation (grant 17-73-20262). The X-ray study has been carried out using the equipment of The Analytical Center of The G. A. Razuvaev IOMC RAS.

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REFERENCES

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DOI: 10.1021/acs.organomet.8b00182 Organometallics XXXX, XXX, XXX−XXX