Transition-Metal Derivatives of Polyphosphazenes: Syntheses of Polyphosphazenes and Cyclic Model Compounds with Iron Cyclopentadienyl Carbonyl Side Groups

The first high polymeric phosphazenes with skeletal phosphorus-transition-metal covalent bonds are reported. These species have been synthesized via two routes: (a) by the interaction of an organometallic iron anion, [FeCp(CO)₂]~ with a mixed-substituent polyphosphazene bearing both chloro-and trifluoroethoxy side groups, and (b) by the reaction of an organometallic halide, FeCp(CO)₂I, with a polyphosphazene that bears anionic sites at skeletal phosphorus. The polymers have been characterized by³¹P and 1H NMR and infrared spectroscopy, gel permeation chromatography, and thermal analyses. Spectroscopic comparisons are made with cyclic trimeric model molecules that bear the same substituent groups. The molecular structural characteristics of the polymers have also been probed indirectly by means of a single-crystal X-ray structure study of the small molecule model species, N₃p3(OCH₂CF3)₅FeCp(CO)2. Crystals of N3P3(OCH₂CF3)5FeCp(CO)2 are monoclinic and have the following parameters: space group P2₁/n, a = 9.690 (4) A, b = 20.684 (4) A, c - 15.082 (2) A, /? = 101.15 (2)°, V = 2965.8 A³, Z = 4.