Sodium and potassium derivatives of diphenyl(trimethylsilyl)methane

Base-free sodium and potassium derivatives of Ph2(Me3Si)CH have been synthesised from the substituted diphenylmethane and a ‘superbase’ mixture of nBuLi/tBuOM (M=Na or K) in hexane. Multinuclear NMR studies have demonstrated that the resultant carbanions are highly delocalised in THF-d8 solution. Crystalline PMDETA (PMDETA=N,N,N′,N″,N″-pentamethyldiethylenetriamine) adducts of both the sodium and potassium diphenylmethyl anions have been isolated from toluene solution and the crystal structure of the sodium derivative has been determined. This exists as a monomeric molecular species with η3-coordination of sodium to the carbanion, which is almost planar (Σangles=358.6°) at the central methyl carbon.