Tetram hexane

Methyllithium. MethyUithium [917-54 ] CH Li, crystallizes from benzene or hexane solution giving cubic crystals that have a salt-hke constitution (128). Crystalline methyllithium molecules exist as tetrahedral tetramers (129). Solutions of methyllithium are less reactive than those of its higher homologues. Methyllithium is stable for at least six months in diethyl ether at room temperature. A one-molar solution of methyllithium in tetrahydrofuran (14 wt %) and cumene (83 wt %) containing 0.08 M dimethyknagnesium as stabilizer loses only 0.008% of its activity per day at 15°C and is nonpyrophoric (117). 

Phosphonitrilic chloride (tetramer) [1832-07-1 ] M 463.9. Purified by zone melting, then crystd from pet ether (b 40-60°) or n-hexane. [van der Huizen et al. J Chem Soc, Dalton Trans 1317 1986.]... 

The pentafluorophenylcopper tetramer is usually analytically pure as isolated and melts at 200° with decomposition. If any significant decomposition occurs during the final drying, the product can be purified by dissolution in ether, filtration to remove copper metal, and precipitation by addition of hexane. It can also be recrystallized from benzene. When kept in a sealed container under nitrogen at room temperature, pentafluorophenyl copper tetramer appears to be stable for reasonable periods. It can be stored indefinitely at -78° under an atmosphere of carbon dioxide. 

Tetrameric [MeLi]4 (1), [EtLi]4 (2) and [t-BuLi]4 (3) are white pyrophoric powders. While methyllithium is soluble only in polar solvents like diethyl ether, the two others are soluble even in non-polar hydrocarbons like hexane. In non-donating solvent the tetrameric aggregation is retained. Each of the four U3 triangles is /ra-capped by a Ca atom above the center of the equilateral metal triangle. Even in the solid-state none of the three tetramers adopts ideal symmetry (Figure 6). 

Wen and Grutzner used, among other NMR parameters, the QSC of the lithium enolate of acetaldehyde to deduce that it exists as tetramers of different solvation in THF and THF/n-hexane solvent systems . However, the most thorough study of Li QSC and the most interesting in the present context was reported by Jackman and coworkers in 1987167 -pjjg effects on the QSC values of both aggregation and solvation in a number of organolithium systems was studied in this paper, i.e. different arylamides, phenolates, enolates, substituted phenyllithium complexes and lithium phenylacetylide. 

In solution lithium alkyls are extensively associated especially in non-polar solvents. Ethyllithium in benzene solution exists largely as a hexamer (9, 43) in the concentration range down to 0.1 molar and there is no evidence for a trend with concentration so presumably the hexamers persist to even lower concentrations. Indeed even in the gas phase at high dilution it exists as hexamer and tetramer in almost equal amounts (3). In a similar way n-butyllithium in benzene or cyclohexane is predominantly hexameric (62, 122). t-Butyl-lithium however is mostly tetrameric in benzene or hexane (115). In ether solution both lithium phenyl and lithium benzyl exist as dimers (122) and it has been suggested that butyllithium behaves similarly in ether (15) although this does not agree with earlier cryoscopic measurements (122). It is however certain that more strongly basic ethers cause extensive breakdown of the structure. 

This reaction type, known as directed ortho metalation reaction, requires strong bases, normally an alkyllithium reagent (most lithium dialkylamides are of insufficient kinetic basicity). Alkyllithium bases show high solubility in organic solvents due to association into aggregates of defined structure, typically as hexamers in hydrocarbon solvents e. g. hexane or tetramers-dimers in polar solvents e. g. THF (see Chapter 5). 

Phenyllithium dissolves in hexane by addition of TMEDA. Hie phenyllithium TMEDA adduct subsequently crystallizes out of solution as the dimer (113) corresponding to general structural type (16)." With diethyl ether solvation, phenyllithium exists as a solid tetramer (114). In ether solution PhLi is known to be either dimeric or tetrameric. Monomeric phenyllithium was successfully crystallized with PMDETA as the ligand. This monomer is depicted as (115). Note the difference in the coordination number of the carbanionic center in the monomer (115), the dimer (113), and the tetramer (114), i.e. one, two and three, respectively. 

Pairwise Cu-Cu distances of 242 pm are found in the [Cu(CN)(NH3)] sheet polymer formed from Cu(CN) power in aqueous NH3. Phosphine adducts of [RCsCCu] yield yellow crystals of [RC=CCuPR3] with n = 4 for R = Ph, R = Me, and a zigzag CU4 chain displaying Cu-Cu distances of 245 and 269 pm with bridging acetylides . A square-planar Cu4 tetramer (Cu-Cu 242 pm) with bridging trimethyl-silylmethyl groups is prepared from Cu(I) iodide and alkyllithium in hexane-ether °. 

Cyclohexa-1,2-diene (76), generated by debromination of 6,6-dibromobicyclo[3.1.0]hexane (75) with methyllithium in the absence of a trapping agent, gave the analogous dimer 77 and a tetramer. ... 

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