MIXED AGGREGATION BETWEEN LITHIUM DIISOPROPYLAMIDE AND LITHIUM-CHLORIDE - NMR, SOLID-STATE STRUCTURE AND AB-INITIO CALCULATIONS

An improved synthesis of ((Pr2NLi)-N-i)(2)LiCl(Me2NCH2CH2NMe2)(2) (1) is presented. The structural characterisation of 1 by single crystal X -ray diffraction (C24H60ClLi3N6, M=489.1, monoclinic P2(1)/n, a=9.126( 3), b=17.538(6), c=20.470(7) Angstrom, beta=98.02(4)degrees, V=3244.2( 19) Angstrom(3), Z=4) revealed a three-ranged Li-N, Cl-Li, Li-N ladder molecular structure. Cryoscopy in benzene indicated that 1 remained s ubstantially undissociated in that solvent. Multinuclear variable temp erature NMR in toluene revealed fluxionality; a mechanism of fluxion i n arene solution involving rupture of an R2N-Li bond followed by pseud orotation of all external ligands around a chloride fulcrum is propose d. Semi-empirical (MNDO) and ab initio (HF/6-31G) calculational studi es of the simplified model (LiNH2)(2)LiCl gave six-membered ring minim um energy geometries. While coordination of four water molecules to th e model resulted in only modest changes to the six-membered ring struc ture at MNDO level, coordination of four dimethyl ether molecules led to a preference for the three-ranged ladder structure as predicted by SCF calculations using a 6-31G basis.