Seven coordination. 1. Synthesis, structure, and fluxionality of(CH3)2AsC(CF3)=C(CF3)As(CH3)2W(CO)2I2P(OCH3)3

(L—L)W(CO)4 (L—L = (CH3)2AsC(CF3)=C(CF3)As(CH3)2) is oxidized by I2 to yield the seven-coordinate complex (L—L)W(CO)3I2 which reacts with monodentate phosphines or phosphites to form (L—L)W(CO)2I2P (P = phosphine or phosphite). Crystals of (L—L)W(CO)2I2P(OCH3)3 are monoclinic, space group P21/c, a = 15.711(3), b = 13.134(2), c = 13.800(3) Å, β = 111.81(2)° with Z = 4. The structure was solved from a Patterson map and anisotropically refined by least squares to a conventional R value of 0.039 using 3737 independent reflections. The crystal structure showed the tungsten atom to be seven-coordinate with a geometry most closely approximated by a capped octahedral environment, the capping group being a carbonyl moiety ([W—C] = 1.95 (1) Å). The capped face consists of the carbon atom ([W—C] = 1.98(1) Å) of the remaining carbonyl, an arsenic atom ([W—As] = 2.556(1) Å), and the phosphorus atom ([W—P] = 2.466(3) Å). The W—As bond trans to a phosphite group is longer (by 0.050(2) Å) than the W—As bond trans to an iodine atom. 1H nmr data indicate the complex to be fluxional at 298 K and rigid at lower temperatures, the data at lower temperatures being consistent with the configuration found in the crystal. The nmr data at lower temperatures suggest two exchange processes are occurring; one which averages two sets of As—CH3 groups and another process which averages all four As—CH3 groups.