Exploiting σ/π Coordination Isomerism to Prepare Homologous Organoalkali Metal (Li, Na, K) Monomers with Identical Ligand Sets

摘要

Tetraamine Me₆TREN has been used as a scaffold support to provide coordinative saturation in the complexes PhCH₂MMe₆TREN (M=Li, Na, K). The Li derivative displays a LiC σ interaction with a pyramidalized CH₂ both in the solid state and in solution, and represents the first example of η4 coordination of Me₆TREN to lithium. In the sodium derivative, the metal cation slips slightly towards the delocalized π electrons whilst maintaining a partial σ interaction with the CH₂ group. For the potassium case, coordinative saturation successfully yields the first monomeric benzylpotassium complex, in which the anion binds to the metal cation exclusively through its delocalized π system resulting in a planar CH₂ group.