Synthesis, spectroscopy, and structures of the seven-coordinate complexes (CH3)2AsC(CF3)=C(CF3)As(CH3)2W(CO)2I2P(OC6H5)3 and [(CH3)2AsC(CF3)=C(CF3)As(CH3)2]2W(CO)Br2 and spectroscopy of related seven-coordinate complexes

(L-L)W(CO)(3)I-2(L-L = (CH3)(2)AsC(CF3)=C(CF3)As(CH3)(2)) reacts with the monodentate phosphite P(OC6H5)(3) and (L-L)W(CO)(3)Br-2 reacts with L-L to form new seven-coordinate complexes (L-L)W(CO)(2)I2P(OC6H5)(3) and (L-L)(2)W(CO)Br-2. Low-temperature X-ray diffraction analyses show the tungsten atom to be seven coordinate in both complexes, with the geometry most closely approximated by a monocapped octahedral environment, the capping group being a carbonyl in the dicarbonyl complex; the geometry is most closely approximated by a pentagonal bipyramidal environment in the monocarbonyl complex. The H-1, C-13, and F-19 NMR data indicate that the dicarbonyl complex is stereochemically nonrigid at 298 K and rigid at lower temperatures, while the monocarbonyl is nonrigid both at 298 K and at lower temperatures. Delta G values calculated at coalescence temperatures are consistent with an intramolecular rearrangement process for both complexes. The C-13 chemical shifts and (2)J(C-13-P-31) values provide important structural considerations in the assignment of a seven-coordinate geometry. Spectroscopic properties for the related seven-coordinate dicarbonyl complexes (L-L)W(CO)(2)PX2 (P = P(OC6H5)(3); X = Br; P = P(OCH3)(3), P(C6H5)(3); X = Br, I) and monocarbonyl complexes (L-L)(2)W(CO)I-2 and (L-L)W(Co)X-2[P(OCH3)(3)](2) (X = Br, I) are presented and compared to those of the two title complexes.