Dearomatization and C−H Deprotonation with Heavier Group 2 Alkyls: Does Size Matter?

We report that reaction of group 2 dialkyl compounds, [M{CH(SiMe3)2}2(THF)n] [M = Mg, Ca, n = 2; M = Sr, Ba, n = 3] with a bis(imino)pyridine ligand ultimately results in deprotonation of both methyl groups attached to the imine carbon center. The resulting compounds are mononuclear for M = Mg or Ca, but assemble into cyclic hexameric arrays when M = Sr or Ba. In all four cases deprotonation appears to occur by a common pathway involving pyridine dearomatization and subsequent deprotonation of a single imine-bound methyl substituent. Monitoring of each reaction has revealed that the efficacy of the transformation, as well as the stability of each intermediate, is dependent upon the identity, ionic radius, and resultant charge density of the alkaline earth reagent employed.