A study of the phosphorus trihalide - 1, 2-dimethylhydrazine system

Abstract

A new class of compounds having the general formula XnP(NCH3NCH3)3-nPXn (where X = Cl or F, and n = 0 to 3) has been synthesized and characterized. Three members of this family, Cl2PNCH3NCH3PCl2, FP(NCH3NCH3)2PF, and F2PNCH3NCH3PF2 have not been prepared before. Payne, Nöth, and Henniger reported the preparation of P(NCHlCH3)l and C1P(NCH3NCH3)2PC1, but did not characterize them completely.(18) Chemically these compounds are quite similar to related amino-hydrazino-, and hydroxylaminophosphines. The general mode of preparation is basically the same except for P(NCH3NCH3)3P. The relative lability and reactivity of the phosphorus-halogen bonds are quite similar, with the P-Cl bonds being more labile and reactive than the P-F bonds. This is reflected in the greater stability of the fluorine-containing compounds and the great ease with which the chloro derivatives are converted from one to another. The reactions of this family with borane and boron trifluoride reflect the general trends of the acid-base chemistry of the aminophosphines in that the basicity of the phosphorus seems to exceed that of the nitrogen to all but very hard Lewis acids. In the case of the hard acids which may coordinate at the nitrogen, seemingly weak complexes form, indicating that the nitrogen's basicity is quite low. These compounds are also able to displace carbon monoxide from metal carbonyls and coordinate via the phosphorus. However, unlike the aminophosphines, these compounds are able to act as chelating or bridging ligands. This family of compounds and their derivatives were characterized by 1H and 19F nmr, mass, and infrared spectrometry. Structures for the compounds have been proposed and these are consistent with the spectroscopic evidence obtained. Three energy barriers were obtained from variable temperature 19F nmr data of F2PNCH3NCH3PF2. The largest, 10.2 kca1/mo1e, has been assigned to hindered rotation about the N-N bond. The others, 4.2 and 3.4 kcal/mole, have been assigned to hindered rotation about the P-N bond in cis-F2PNCH3NCH3PF2 and to hindered rotation about the P-N bond in trans-F2PNCH3NCH3PF2. This is the first f1uorophosphine in which a value of the P-N energy barrier has been obtained. moreover, this appears to be the first compound in which three rotational barriers have been observed and measured.