STRUCTURE AND DYNAMICS OF PHOSPHORUS(V)-STABILIZED CARBANIONS - A COMPARISON OF THEORETICAL, CRYSTALLOGRAPHIC, AND SOLUTION STRUCTURES

The rotational coordinates about the P-C bond in four different phosph orus(V)-substituted methyl anions have been studied in detail at the H F/3-21G() level, with stationary points characterized at levels equiv alent to MP3/6-31+G//HF/6-31+G*. The locations of local minima on the rotational coordinate were found to be dependent on opportunities for hyperconjugative stabilization. When amino substituents on phosphorus were geometrically unconstrained, two local minima were found. By con trast, when the amino groups were constrained to local geometries simi lar to those found in diazaphosphorinanes, the effects on the rotation coordinate were considerable. A single minimum and a higher rotation barrier were noted. Comparisons of static structure and rotational dyn amics are made to both solution and solid-phase experimental data. The single-crystal X-ray structure of thio-N,N,N',N'-tetramethyl-P-benzyl phosphondiamide Li+7- is reported.