SYNTHESIS, MOLECULAR-STRUCTURE AND SOLUTION DYNAMICS OF DIMERIC BENZAMIDINATES CONTAINING A DOUBLE DIAZAALLYL LITHIUM BRIDGE - A RAPID INTERCONVERSION OF SIGMA-BOND AND PI-BOND

Dimeric Li[N(SiMe(3))(2)] reacted with the nitriles 4-XC(6)H(4)CN (X = H or Me) in diethyl ether-hexane (1:10) to yield dimeric complexes [4-XC(6)H(4)C(NSiMe(3))(2).Li(NCC(6)H(4)X-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 pi fashion to one amidine anion (chelating), forming-a double diazaallyl lithium bridge, in a monodentate a 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 (sigma to pi and vice verse) was observed by means of the NMR chemical shifts.