Synthesis, molecular structure and solution dynamics of dimeric benzamidinates containing a double diazaallyl lithium bridge. A rapid interconversion of σ and π bonds

Abstract

Dimeric Li[N(SiMe₃)₂] reacted with the nitriles 4-XC₆H₄CN (X = H or Me) in diethyl ether–hexane (1:10) to yield dimeric complexes [4-XC₆H₄C(NSiMe₃)₂·Li(NCC₆H₄X-4)]₂(X = H 1 or Me 2). Complex 2 is dimeric in the solid state with two four-co-ordinated lithium cations bound in a N,N′-bidentate π fashion to one amidine anion (chelating), forming a double diazaallyl lithium bridge, in a monodentate σ fashion to a nitrogen lone pair of a substrate molecule, and monodentate to a nitrogen lone pair of a second amidine anion. In solution, rapid interconversion of the different lithium-amidine bonds (σ to π and vice versa)was observed by means of the NMR chemical shifts.