SYNTHESIS, SPECTROSCOPY, AND STRUCTURES OF THE 7-COORDINATE COMPLEXES)(2)ASC(CF3)=C(CF3)AS(CH3)(2)W(CO)(2)I2P(OC6H5)(3) AND [(CH3)(2)ASC(CF3)=C(CF3)AS(CH3)(2)](2)W(CO)BR-2 AND SPECTROSCOPY OF RELATED 7-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 wit h 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 sh ow the tungsten atom to be seven coordinate in both complexes, with th e geometry most closely approximated by a monocapped octahedral enviro nment, the capping group being a carbonyl in the dicarbonyl complex; t he geometry is most closely approximated by a pentagonal bipyramidal e nvironment in the monocarbonyl complex. The H-1, C-13, and F-19 NMR da ta indicate that the dicarbonyl complex is stereochemically nonrigid a t 298 K and rigid at lower temperatures, while the monocarbonyl is non rigid both at 298 K and at lower temperatures. Delta G values calculat ed at coalescence temperatures are consistent with an intramolecular r earrangement 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 propertie s for the related seven-coordinate dicarbonyl complexes (L-L)W(CO)(2)P X2 (P = P(OC6H5)(3); X = Br; P = P(OCH3)(3), P(C6H5)(3); X = Br, I) an d 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.