Seven-co-ordinate dibromo complexes of molybdenum(II) and tungsten(II) derived from [MBr2(CO)3(NCMe)2]. Crystal structures of the isostructural complexes [WX2(CO)3(NCMe)(SBPh3)]·Ch2Cl2(X = Br or I)

Reaction of the complexes fac-[M(CO)3(NCMe)3](M = Mo or W)(prepared in situ) with an equimolar quantity of Br2 at –78 °C afforded high yields of the seven-co-ordinate complexes [MBr2(CO)3(NCMe)2]. The reaction of these complexes with an equimolar amount of L (L = PPh3, AsPh3 or SbPh3) in CH2Cl2 at room temperature gave the new mixed-ligand complexes [MBr2(CO)3(NCMe)L]. The molecular structure of [WBr2(CO)3(NCMe)(SbPh3)]·CH2Cl2 and its diiodo analogue [WI2(CO)3(NCMe)(SbPh3)]·CH2Cl2 have been crystallographically determined. Crystals of the former are monoclinic of space group P21/c, a= 8.302(3), b= 26.199(3), c= 13.020(4)A, β= 97.53(2)°, Z= 4. Crystals of the latter are also monoclinic of space group P21/c, a= 8.450(2), b= 25.941 (6), c= 13.042(4)A, β= 96.47(2)°, Z= 4. The two complexes are isostructural and can best be described as distorted capped trigonal prismatic with one triangular face having three carbonyl ligands and the other triangular face having X(2), Sb and N. The X(1 ) atom caps the rectangular face defined by C(1), X(2), N and C(3). The low-temperature (–6O °C, CDCl3)13C NMR spectrum of [WI2(CO)3(NCMe)(SbPh3)]·CH2Cl2 was obtained and correlated with the solid-state structure. Reaction of [WBr2(CO)3(NCMe)2] with 2 equivalents of AsPh3 in CH2Cl2 at room temperature gave [WBr2(CO)3(AsPh3)2].