7-CO-ORDINATE DIBROMO COMPLEXES OF MOLYBDENUM(II) AND TUNGSTEN(II) DERIVED FROM [MBR(2)(CO)(3)(NCME)(2)] - CRYSTAL-STRUCTURES OF THE ISOSTRUCTURAL COMPLEXES [WX(2)(CO)(3)(NCME)(SBPH(3))]CENTER-DOT-CH2CL2 (X=BROR I)

Reaction of the complexes fac-[M(CO)(3)(NCMe)(3)] (M = Mo or W) (prepa red in situ) with an equimolar quantity of Br-2 at -78 degrees C affor ded high yields of the seven-co-ordinate complexes [MBr(2)(CO)(3)(NCMe )(2)]. The reaction of these complexes with an equimolar amount of L ( L = PPh(3), AsPh(3) or SbPh(3)) in CH2Cl2 at room temperature gave the new mixed-ligand complexes [MBr(2)(CO)(3)(NCMe)L]. The molecular stru cture of [WBr2(CO)(3)(NCMe)(SbPh(3))].CH2Cl2 and its diiodo analogue [ Wl(2)(CO)(3)(NCMe)(SbPh(3))].CH2Cl2 have been crystallographically det ermined. Crystals of the former are monoclinic of space group P2(1)/c, a = 8.302(3), b = 26.199(3), c = 13.020(4) Angstrom, beta = 97.53(2)d egrees, Z = 4. Crystals of the latter are also monoclinic of space gro up P2(1)/c, a = 8.450(2), b = 25.941(6), c = 13.042(4) Angstrom, beta = 96.47(2)degrees, Z = 4. The two complexes are isostructural and can best be described as distorted capped trigonal prismatic with one tria ngular face having three carbonyl ligands and the other triangular fac e having X(2), Sb and N. The X(1) atom caps the rectangular face defin ed by C(1), X(2), N and C(3). The low-temperature (-60 degrees C, CDCl 3) C-13 NMR spectrum of [Wl(2)(CO)(3)(NCMe)(SbPh(3))].CH2Cl2 was obtai ned and correlated with the solid-state structure. Reaction of [WBr2(C O)(3)(NCMe)(2)] with 2 equivalents of AsPh(3) in CH2Cl2 at room temper ature gave [WBr2(CO)(3)(AsPh(3))(2)].