Ylidene→Iminophosphine Coordination Complexes and Reversible Dissociation of Dichlorophosphetidines

Chloro-, bromo-, iodo-, and trifluoromethylsulfonyloxy-(2,4,6-tri-tert-butylphenylimino)phosphines (Mes*NPX; X =
Cl, Br, I, OTf) react quantitatively with 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (Im) to give Lewis acid−base
complexes with the general formula Mes*NP(Im)X. The dichlorophosphetidine (DippNPCl)2 (Dipp = 2,6-diisopropylphenyl) represents a formal cyclodimer of an iminophosphine and reacts with Im to give a similar complex.
The process represents a ligand induced dissociation of the phosphetidine framework and is reversed by the
introduction of an appropriate Lewis acid. Solid state structures of RNP(Im)X complexes show that the closest
contact between acid and base occurs between phosphorus and carbon in all cases, highlighting them as compounds
that contain examples of C→P coordinate bonds. Association of Im with phosphorus also effects a substantial
increase in the P−X distance, but all derivatives maintain a short NP bond, indicating the presence of NP π-bonding.