Effect of Polydentate Donor Molecules on Lithium Hexamethyldisilazide Aggregation: An X-ray Crystallographic and a Combination Semiempirical PM3/Single Point ab Initio Theoretical Study

摘要: Addition of 1 equiv polydentate amine or ether donor solvent to hydrocarbon solutions lithium hexamethydisilazide (LHMDS) yields a variety complexes with different aggregation states. X-ray crystallographic analyses have been carried out on six new compounds revealing three- and four-coordinate monomers, η1-coordinated mono- disolvated dimers, polymers dimers. PM3 calculations were able locate minima for possible structures the ligands N,N,N‘,N‘-tetramethylethylenediamine 1,2-dimethoxyethane. However, heats formation from these are found be unreliable in predicting relative stabilities isomers. Single point ab initio at 6-31G* level optimized give energies which correspond well known states LHMDS species. Deaggregation dimers monomers appears driven by combination steric, electronic, chelate effects.