Alkali metal complexes having sterically bulky bis-iminopyrrolyl ligands – control of dimeric to monomeric complexes

摘要

We report the syntheses and structural diversity of three different bis-iminopyrrole ligands and their alkali metal (Li, Na, K) complexes featuring a shift from dimeric to monomeric nature by a simple tuning of the steric control of the imine nitrogen substitutions. The bis-iminopyrrole ligands having the molecular formula [(ArNCH) _(2) C _(4) H _(2) NH] [Ar = CHPh _(2) ( 1-H ), Ad ( 2-H ), Ad = adamentyl, and CPh _(3) ( 3-H )], were prepared through the reaction of 2,5-pyrrole-dicarbaldehyde with corresponding amines (ArNH _(2) ) in a 1?:?2 molar ratio and under acidic conditions. Using ligand 1-H , the lithium [{Li(Ph _(2) CHNCH) _(2) C _(4) H _(2) N} _(2) ] ( 1-Li ), sodium [{Na(Ph _(2) CH–NCH) _(2) C _(4) H _(2) N} _(2) (THF)] ( 1-Na ) and potassium [{κ ~(3) -(Ph _(2) CHNCH) _(2) C _(4) H _(2) N}-K(THF) _(2) ] ( 1-K ) complexes were obtained through either alkane elimination (for Li) or amine elimination (for Na, K). The alkali metal complexes [{κ ~(2) -(Ph _(3) CHNCH) _(2) C _(4) H _(2) N}M(THF) _( n ) ] [ n = 2, M = Li ( 3-Li ), Na ( 3-Na ); n = 3, M = K ( 3-K )] were synthesized using the ligand 3-H . Molecular structures of ligands 1-3-H , and alkali metal complexes 1-Li , 1-Na , 1-K , 3-Li , 3-Na and 3-K , in the solid state were established. The complexes 1-Li and 1-Na were found to be dimeric in the solid state whereas the complexes 1-K , 3-Li , 3-Na and 3-K were all monomeric – either due to a larger ionic radius (for 1-K ) or because of the presence of the bulky triphenylmethyl group on the imine nitrogen.