Solid State Structures and Solution Dynamics of Unsolvated and Diethyl Ether Solvated Dilithium N,N'-Bis(trimethylsilyl)ethylenediamide Complexes.
The lithiation of N,N'-bis(trimethylsilyl)ethylenediamine, 1, by 2 equiv of methyllithium in diethyl ether yields the dimeric diethyl ether adduct [{Li[N(SiMe(3))CH(2)CH(2)NSiMe(3)]Li.OEt(2)}(2)], 2. Recrystallization of 2 from benzene gives quantitatively the unsolvated trimer [{Li[N(SiMe(3))CH(2)CH(2)NSiMe(3)]Li}(3)], 3. The solution dynamics of 2 and 3 in toluene have been investigated using variable temperature multinuclear NMR spectroscopy. In solution, 2 is undergoing a rapid exchange process involving an equilibrium between unsolvated and diethyl ether solvated dimers, whereas compound 3 exists in a temperature dependent equilibrium of dimeric and trimeric species, of which the trimer is fluxional and exchanges inequivalent ligands by an intramolecular distortion of the Li(6)N(6) cage structure. Crystals of 2 are monoclinic, of space group P2(1)/n (No. 14), with a = 10.692(9) Å, b = 16.192(2) Å, c = 24.04(4) Å, beta = 101.16(5) degrees, V = 4083(8) Å(3), and Z = 4. Crystals of 3 are trigonal, of space group R&thremacr;m(No. 166), a = 17.765(1) Å, c = 13.394(1) Å, V = 3660.5(5) Å(3), Z = 3.
Gardiner
Michael G.
MG
Department of Chemistry, Monash University, Clayton, Melbourne, Victoria 3168, Australia.
Raston
Colin L.
CL