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)

Abstract

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)Å, 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)Å, 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].