N,N′-Bis-Silylated Lithium Aryl Amidinates: Synthesis, Characterization, and the Gradual Transition of Coordination Mode from σ Toward π Originated by Crystal Packing Interactions

Abstract

In this work nine lithium N,N′-bis(trimethylsilyl)amidinates−TMEDA complexes and the dimeric adduct of 2-ethylbenzonitrile lithium bis(trimethylsilyl)amide were synthesized and characterized. The later compound was found to be a kinetically stabilized intermediate in the amidinate formation. The solid state structures of the amidinates revealed several types of crystalline supramolecular structures, generated by the degree and nature of involvement of the amidinate π system in the intermolecular interactions. The π system was also found to play a significant role in the intramolecular bonding with the lithium atom. The π bonding is obtained at the expense of the σ bond, weakening it, while keeping the metal–ligand bond length almost invariable. This facile π interaction along with the Li−N σ-bond activation can imply that similar involvements of the π systems may take place in the salt metathesis reactions with these compounds.