Phosphoric carboxylic imides. Part 6. Structure and reactivity of 1,3,2-diazaphospholidine-4,5-diones; crystal structure of 1,3-dimethyl-2-methylamino-1,3,2-diazaphospholidine-2,4,5-trione

Abstract

1,3-Dimethyl-2-methylamino-1,3,2-diazaphospholidine-2,4,5-trione (1b) has been synthesized, and its solvolytic behaviour and X-ray crystal structure determined. Methanolysis of (1b) gives products of the cleavage of both imide P–N bonds, indicating that the ring opening in (1b) is much slower than the second P–N cleavage in the ring-opened intermediate. The low reactivity of (1b) is correlated with the small size (92.3°) of the endocyclic N–P–N angle, which suggests that not much energy is released upon the formation of the P^V trigonal bipyramidal adduct. The molecular structure of (1b) reveals a high degree of coplanarity of the phospholidine ring with both imide N-methyl groups and both carbonyl oxygen atoms. The geometry indicates that the endocyclic nitrogen atoms in (1b) are involved in the resonance interactions not only with the adjacent carbonyl groups, but also with the phosphoryl centre.

1,3-Dimethyl-2-phenoxy-1,3,2-diazaphospholidine-2,4,5-trione (1a) has been found to react with p-anisidine or ammonia exclusively at the phosphorus atom. In the reaction with p-anisidine both P–O bond cleavage (displacement of phenol) and ring P–N bond cleavage products were obtained; this is interpreted in terms of pseudorotation of the initially formed P^V intermediate. Ammonia reacts with (1a) giving exclusively the ring-retained, P–OPh bond cleavage products. Our aminolysis results for (1a) contrast with those reported in the literature.