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

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(L-L)W(CO)3I2 (L-L = (CH3)2AsC(CF3)== C(CF3)As(CH3)2) reacts with the monodentate phosphite P(OC6H5)3 and (L-L)W(CO)3Br2 reacts with L-L to form new seven-coordinate complexes (L-L)W(CO)2I2P(OC6H5)3 and (L-L)2W(CO)Br2. 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 1H, 13C, and 19F 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. ΔG not equal values calculated at coalescence temperatures are consistent with an intramolecular rearrangement process for both complexes. The 13C chemical shifts and 2J(13C-31P) 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)2PX2 (P = P(OC6H5)3; X = Br; P = P(OCH3)3, P(C6H5)3; X = Br, I) and monocarbonyl complexes (L-L)2W(CO)I2 and (L-L)W(CO)X2[P(OCH3)3]2 (X = Br, I) are presented and compared to those of the two title complexes.