METAL-ASSISTED FORMATION OF PHOSPHORUS OXYGEN HETEROCYCLIC COMPLEXES

Starting with bis(dialkylamino)phosphine oxides or triphosphoxane [R(2)NPO](3) rings, transition metal complexes containing P4O4, P5O5, and P6O6 heterocycles have been assembled. Specific products isolated were found to depend critically on reaction conditions, the metal, and its ancillary ligands, as well as the phosphorus substituent. While only monometallic products were obtained from divalent precursors of the nickel triad, bimetallic complexes were also produced from the group 6 metal carbonyls. In general, larger rings were obtained at higher temperatures. Only P3O3 and P4O4 products were formed around molybdenum, while P5O5 structures could also be assembled about chromium, nickel, palladium, and platinum centers. One of the iron carbonyl complexes was found to feature an unusual eta(1)-P[OP(O)]P-2 ring, the product of a double POP to PP(=O) rearrangement. In addition, a dichromium P6O6 cluster complex featuring the novel hexaphosphoxane ring was synthesized from bis(cis-2,6-dimethylpiperidino)phosphine oxide. Use of isolated monometallic PnOn complexes as ligands yielded heterobimetallic products as well as phosphoxane ring transfer reactions. The X-ray crystal structures of five representative complexes containing FeP4O4 (14), Cr2P4O4 (19a, 19b), Cr2P6O6 (21), and MoFeP4O4, (25) cores, respectively, are reported.