A DENSITY-FUNCTIONAL TREATMENT OF ORGANOLITHIUM COMPOUNDS - COMPARISON TO AB-INITIO, SEMIEMPIRICAL, AND EXPERIMENTAL RESULTS

Density functional calculations on several classes of organolithium co mpounds are described. The compounds studied include lithium bonds to carbon, oxygen, and nitrogen and are representative of most types of o rganolithium compounds that have appeared in the recent literature. Th e computational results are compared to those using MNDO, which has be en shown to have some serious deficiencies in compounds involving carb on-lithium bonds, and to PM3 results, which offer some improvement ove r MNDO for many organolithium compounds. Most of the density functiona l calculations with a large basis set are in good agreement with avail able ab initio and experimental data. Calculated carbon-lithium bond l engths were slightly shorter than those calculated by other ab initio methods and were substantially longer than those calculated by MNDO, w hich is known to underestimate carbon-lithium bond lengths severely. D imerization energies of methyllithium, calculated by DMol, were also i n good agreement with those of other ab initio calculations. Lithium-n itrogen bonds in lithium amides were calculated to be slightly shorter by DMol than by MNDO, although the two methods were in qualitative ag reement for this type of compound. (C) 1995 by John Wiley & Sons, Inc.