The synthesis and seven-coordinate structure of (CH 3 ) 2 AsC(CF 3 =C(CF 3 )As(CH 3 ) 2 W(CO)Br 2 [P(OCH 3 ) 3 ] 2

(L–L)W(CO) 4 (L–L = (CH 3 AsC(CF 3 )=C(CF 3 )As(CH 3 ) 2 ) is oxidized by Br 2 to yield the seven-coordinate complex (L–L)W(CO) 3 Br 2 , which reacts with monodentate phosphines or phosphites to form (L–L)W(CO)Br 2 P 2 (P = phosphine or phosphite). Crystals of (L–L)W(CO)Br 2 [P(OCH 3 ) 3 ] 2 are monoclinic, space group P2 1 /c, a = 19.110(5), b = 9.208(3), c = 17.845(6) Å, β = 108.93(2)° at 21 °C with Z = 4. The structure was solved from a Patterson map and refined by least squares to a conventional R value of 0.092 using 2330 independent reflections. The crystal structure indicated the tungsten atom to be seven-coordinate with the geometry most closely approximated by a capped trigonal prismatic environment, the capping group being a bromine atom (W—Br, 2.686(5) Å). The capped face consists of the remaining bromine atom (W—Br, 2.695(5) Å), a phosphorus atom (W—P, 2.465(9) Å), and the two arsenic atoms from the bidentate ligand (W—As, 2.619(3) and 2.526(4) Å). The W—As bond trans to a phosphite is significantly longer (by 0.093 Å) than the W—As bond trans to a bromine. The 1 H nmr data indicate that the complex is stereochemically rigid at 25 °C and nonrigid at higher temperatures; however, the data at 25 °C are not consistent with the configuration found in the crystal.