SOLUTION-STATE, SOLID-STATE, AND CALCULATED STRUCTURES OF AN ALPHA-LITHIATED MONOPHOSPHAZENE

The structure of lithiated P-diphenyl(methyl) (N-phenyl)phosphazene (L i(+)1a(-)) has been determined. The crystal structure consists of mono meric units containing a four-membered ring with the lithium bonded to the nitrogen and methylene carbon atoms of the phosphazene. The coord ination sphere of the metal is completed by two molecules of THF. The carbon bonded to lithium has a pyramidal configuration. Short intermol ecular Li-phenyl-P distances (average 3.10 Angstrom) have been measure d in the crystal packing. In THF at -111 degrees C, a 93:7 mixture of two compounds was found. The structure of the major component was dete rmined by multinuclear H-1, Li-6, C-13, N-15 and P-31 NMR spectroscopy of isotopically labeled (6)Li(+)1a(-). From the (2)J(PLi)-coupling co nstant measured and the NOEs observed in 2D HOESY spectra, it was conc luded that the major component retained a structure similar to that fo und in the solid state. N-15 Characterization was carried out through P-31,N-15 triple resonance experiments. MNDO calculations reproduced w ell the main structural features of Li(+)1a(-). Two local minima inter connected by two transition states were located through MNDO calculati ons. The preference for the formation of the C-P-N-Li four-membered ri ng was considered to be of electrostatic nature. No P-Li bonding inter action was predicted, and the calculated dissociation energy for the C -Li was 30.8 kcal . nol(-1).