Methyllithium, structure

In a similar manner, treatment of anhydrous rare-earth chlorides with 3 equivalents of lithium 1,3-di-ferf-butylacetamidinate (prepared in situ from di-ferf-butylcarbodiimide and methyllithium) in THF at room temperature afforded LnlMeCfNBuOils (Ln = Y, La, Ce, Nd, Eu, Er, Lu) in 57-72% isolated yields. X-ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions (Figure 20, Ln = La). The new complexes are thermally stable at >300°C, and sublime... 

As documented in detail for organolithium species, ligand and donor play a key role in determining the degree of aggregation. Methyllithium adopts a hexameric structure in hydrocarbon solvents.13,15 In the presence of monodentate, donors such as THF or diethyl ether tetramers are observed, while the increase in donor denticity to 2 (1,1-Dimethoxyethane (DME), N,N,N, N -Tetramethylethylenediamine (TMEDA)) affords monomeric structures. Further documenting the differences between solution and solid states, [CH3Li]4 adopts a tetrameric structure in the latter.15,15a-15c... 

FIGU RE 12.1 The structure of the tetramer of methyllithium. Only two of the four methyl groups are shown. 

The methylenetriimido sulfite dianion [CH2S(NtBu)3]2 is prepared by the treatment of [CH3S(NtBu)3] with methyllithium in the presence of TMEDA (A,A,A, A -tetramethyl ethylene diamine).177 The structure of [(TMEDA)2 Li2 H2CS(NtBu)3 ] (63) resembles that of 61 with the TMEDA ligands replacing the two THF ligands on each Li centre. 

The treatment of 23 with methyllithium in the presence of furan gave rise to the tetracyclic product 26, which is obviously a [4 + 2]-cycloadduct of furan to the 1,2-cyclopentadiene derivative 25 [27]. The feature that the oxanorbornene system of 26 carries its saturated substituent in the endo-position is analogous to the [4 + 2]-cycloadducts of furan to all six-membered cyclic allenes (see Section 6.3). Balci et al. [36] also provided evidence for the generation of l-phenyl-l,2-cyclopentadiene. They postulated this species to be an intermediate in the reaction of l-phenyl-2-iodocydo-pentene with potassium tert-butoxide in benzene at 240 °C, which resulted in the formation of 1-phenyl- and 1,2-diphenylcyclopentene. Both products were considered as evidence in favor of the diradical nature rather than the allene structure of 1-phe-nyl-1,2 -cyclopentadiene. 

Scheme 6.82 Treatment of 6,6-dibromo-3-thiabicyclo[3.1.0]hexane (398) with methyllithium, trapping ofthe resulting l-thia-3,4-cyclo-hexadiene (399) by styrene, 1,3-butadiene and furan and the structure ofthe dimer404 of 399.

De Meijere, StaUce and coworkers were able to generate dilithiated 111, where the tricyclic non-metalated form can be considered as a subunit of the smallest possible fullerene By a two-fold tin-lithium exchange of the bis(trimethylstanno) derivative 110 with methyllithium, the dilithium compound 111 was cleanly obtained (Scheme 39) its solid-state structure could be clarified by means of X-ray crystallography. 

Introduction of the allene structure into cycloalkanes such as in 1,2-cyclononadiene (727) provides another approach to chiral cycloalkenes of sufficient enantiomeric stability. Although 127 has to be classified as an axial chiral compound like other C2-allenes it is included in this survey because of its obvious relation to ( )-cyclooctene as also can be seen from chemical correlations vide infra). Racemic 127 was resolved either through diastereomeric platinum complexes 143) or by ring enlargement via the dibromocarbene adduct 128 of optically active (J3)-cyclooctene (see 4.2) with methyllithium 143) — a method already used for the preparation of racemic 127. The first method afforded a product of 44 % enantiomeric purity whereas 127 obtained from ( )-cyclooctene had a rotation [a]D of 170-175°. The chirality of 127 was established by correlation with (+)(S)-( )-cyclooctene which in a stereoselective reaction with dibromocarbene afforded (—)-dibromo-trans-bicyclo[6.1 0]nonane 128) 144). Its absolute stereochemistry was determined by the Thyvoet-method as (1R, 87 ) and served as a key intermediate for the correlation with 727 ring expansion induced... 

The first W—W quadruply bonded complexes characterized were [W2Me Cl8 ]4- prepared by treatment of WC14 with methyllithium. Crystal structure analysis has established the short W—W distances of 2.264 and 2.263 A for the methyl and the mixed chloromethyl derivatives respectively. In addition, these compounds have the expected eclipsed stereochemistry.327,328... 

Various bimolecular assemblies that have been proposed for the transition state are shown in Scheme 13 (14, 19a, 20g). Bicyclic transition state A involves transfer of bridging alkyl group (R) to the terminally located aldehyde, while transition structure B involves reaction between terminal R and bridging aldehyde. The reaction may proceed via mono-cyclic, boat-like six-membered transition state C. Transition structures of types B and C were originally proposed for the reactions of orga-noaluminum compounds and carbonyl substrates (26, 27). Ab initio calculations suggest that methyllithium dimer reacts with formaldehyde through a bicyclic transition state related to A (28). The dinuclear Zn... 

Organometallic derivatives have been synthesized from monomeric molybdenum precursors, as well as from tetraacetatodimolybdenum (114). The reaction of MoC13 3THF with methyllithium in ether produced Li4Mo2(CH3)8 -2Et20 (152), which was structurally similar to the Mo2 Clf ion. The ionic Li3 Mo(C6 H5)6 reacted with M0CI3 3THF to produce a compound of... 

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