Intramolecular N⋯E interactions in N-functionalised alkyl complexes R′ECl₂ (E = P, As, Sb; R = 6-Me-2-Pyr(SiMe₃)₂C^-)

The metathetical exchange reactions of R′Li·Et₂O [R′ = 6-Me-2-Pyr(SiMe₃)₂C^-] with ECl₃ (E = P, As, Sb) give the neutral E(III) complexes, R′ECl₂. All complexes have been crystallographically characterised and exhibit extremely short intramolecular N⋯E dative bonds, with the phosphorus derivative exhibiting the shortest neutral N⋯P dative bond of 2.238(1) Å. Theoretical studies performed with approximate density functional theory successfully model the unusual structural features of compound R′PCl₂, although the magnitude of the effect is somewhat underestimated. Under the same conditions, the lithium complex of the less bulky ligand r′ [r′ = 6-Me-2-Pyr(SiMe₃)CH^-] affords a weakly associated, dimeric complex [r′SbCl₂]₂, (via Sb-Cl⋯Sb bridging) which is a consequence of less steric compression from the alkyl group around the metal centre; intramolecular N⋯Sb coordination is also present.