Crystal structure of [W(η-C 6 F 6 ) 2 ] synthesised together with other sandwich complexes of tungsten and molybdenum containing η 6 -C 6 F 6 or η 6 -C 6 H 3 F 3 -1,3,5 ligands, from atoms of the metals

Reaction of molybdenum or tungsten atoms with hexafluorobenzene or 1,3,5-trifluorobenzene or with mixtures of these ligands and benzene or 1,3,5-trimethylbenzene gave the new compounds [M(C6F6)2], [M(C6H3F3-1,3,5)2], [M(C6F6)(C6H6)], [M(C6F6)(C6H3F3-1,3,5)] and [M(C6F6)(C6H3Me3-1,3,5)](M = Mo or W) in yields ranging from <1 to 5% as stable crystalline solids. A single-crystal X-ray study of [W(C6F6)2] showed it to have the same symmetry as [Cr(C6H6)2] and the same W–C bond lengths as in [W(C6H5Me)2]. The 19F and 1H NMR spectra of the mixed-ligand products show interring coupling with large coupling constants which make some of the spectra exceptionally easy to interpret.