Chromium, molybdenum, and tungsten chlorophosphazenes: molecular structures of N3P3Cl5[Cr(CO)3(.eta.-C5H5)] and N3P3Cl4(C5H5)[Mo(CO)3(.eta.-C5H5)]

Abstract : Cyclopentadienylchromium tricarbonyl anion reacts with hexachlorocyclotriphosphazene, (NPCl2)3, to form a metallophosphazene of formula N3P3Cl5Cr(CO)3(n-C5H5 (5). The reactions of the analogous molybdenum and tungsten anions with (NPCl2)3 are more complex and lead to the formation of metallophosphazenes of formula N3P3Cl4(C5H5)M-(CO)3(n-C5H5) (6a, M = Mo; 6b, M = W) in which the chlorine atom geminal to the metal has been replaced by a cyclopentadiene group. A key requirement for the success of these reactions is the use of a tetra-n-butlammonium counterion. The products are among the first chlorophosphazenes to contain metal-phosphorus side-group bonds. The structures of 5 and 6a were examined in detail by spectroscopic and X-ray diffraction techniques. In both compounds the N-P-N bond angle at the metal-bearing phosphorus is unusually narrow, being 112.3 (3) deg in 5 and 111.0 (3) deg in 6a. Moreover, an alternation of longer and shorter bond lengths is found for the P-N bonds located at increasing distances from the metal.