Methide anion

In an attempt to demonstrate the existence of pentavalent nitrogen, Schlenk and Holtz studied the reaction of triphenylmethyl sodium with tetramethylammonium chloride (52). The highly colored material was strongly conducting in polar solvents and could be identified as a salt, the stability of which is due to the resonance stabilization of the triphenyl-methide anion. In the absence of such stabilizing substituent effects (53), as with n-butyl or another alkyllithium reagent, a metalation of the tetramethylammonium cation occurs, which leads to type I products (18) ... 

In addition to the transfer reactions already discussed, propagating carbe-nium ions also react with nucleophilic hydride and methide anions. This reaction may be bimolecular, or it may occur by an intramolecular hydride shift to form a more stable carbenium ion. The activation energy of hydride transfer is usually higher than that of propagation, and therefore occurs only at elevated temperatures. Nevertheless, hydride transfer is the dominant reaction when a-methylstyrene is initiated by triphenylcarbenium ions. That is, steric hindrance prevents initiation by direct electrophilic addition of the carbenium ion to a-methylstyrene. Instead, it occurs by hydride transfer from monomer to yield triphenyl methane and the primary carbenium ion of a-methylstyrene [cf., Eq. (40)]. 

Similarly, isomerized carbenium ions are formed in polymerizations of a-methylstyrene derivatives by either a 1,3-intramolecular or bimolecular methide anion shift, or by reaction of carbenium ion with an exo-unsatu-rated oligomer [cf., Eq. (10)] [13]. 

Thus Eq. (1) represents the dissociation of alkyl (aryl) halide by Me3Al and the formation of alkyl (aryl) cation and counter anioa Equation (2) shows the alkylation of the cation methide anion from the counter anion and the formation of a hydrocarbon. 

The methide anion (CH3 ) has been shown to be pyramidal in the gas phase, and other saturated carbanions are also pyramidal. Hybridization is essentially sp3, with the lone pair electrons occupying one of the tetrahedral positions. 

The product formed in second-highest yield, 1,1,1,2-tetramethyldi-silane, as well as methylsilane require transfer of a mediyl group for their formation. No neutral silicon species are known to abstract metliyl groups, but Lampe has found that cations of various kinds do abstract mediyl radicals and methide anions from methylsilanes (29-31),... 

The blue colour formed on oxidation of variegatic acid (73) by oxidases or by alkaline potassium ferricyanide is due to the formation of delocalised hydroxyquinone methide anions of type (77) (Scheme 10) (607). The electronic spectrum of anions such as (77) is in close accord with that of the blue anion (78) generated by oxidation of catechol in the presence of Meldrum s acid (700). Due to its nature as a vinylo-gous carboxylic acid a substantial proportion of the hydroxyquinone methide (77) is present in the form of its anion even at neutral pH. 

The interaction of Lewis acid metal centers in alumina has been studied using Cp2Zr( CH3)2. ° This study was consistent with a methide anion being transferred from Zr to a Lewis acid site on the surface forming a cation-like zirconium or zirconocenium surface species, Cp2Zr+(CH3) with the formation of an A1-CH3 anionic complex. 

Scheme 1.40 [3]Dendralene synthesis using (a) a trivinyi methide anion [190] and (b) an indium pentadienyl nudeophile [191, 192].

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