The chemistry of tungsten(II) halides that contain a saturated monoanionic tridentate (carbon,nitrogen,nitrogen') ligand

Chelate assisted oxidative addition of aromatic carbon-halogen bonds (X = I, Br, or Cl) to tungsten(0) affords seven-coordinate d{dollar}sp4{dollar} W(II) halides that contain a saturated monoanionic {dollar}etasp3{dollar}- (C,N,N{dollar}spprime{dollar}) ligand. These halides exhibit dynamic behavior on the nuclear magnetic resonance (NMR) time scale in solution at ambient temperatures, and variable temperature experiments have been performed to determine kinetic parameters of this fluxionality. Solid state structures have been determined for the tungsten(II) iodide and bromide, and the geometry around the metal center is found to be dependent on the nature of the halide atom. Two-electron reduction of these halides affords a W(0) anion in which the chelating tertiary amines of the (C,N,N{dollar}spprime{dollar}) ligand retain coordination to the metal center. Reaction of the anion with Ph{dollar}sb3{dollar}SnCl or Ph{dollar}sp3{dollar}PAuCl generates air-stable tungsten(II) stannyl and gold complexes which have been structurally characterized by X-ray diffraction studies. Reductive elimination of a C-Sn bond occurs when the tungsten stannyl complex is heated under CO(g). Addition of the resulting tetraorganotin complex to W(CO){dollar}sb3{dollar}(EtCN){dollar}sb3{dollar} regenerates the W(II) stannyl product. A reductive elimination/oxidative addition equilibrium results when this stannyl complex is subjected to the weaker coordinating ligands pyridine and acetonitrile.; Metathesis exchange of these tungsten(II) halides with silver trifluoromethanesulfonate affords an air-stable W(II) triflate. This labile triflate ligand can be replaced readily by anionic ligands such as halides, cyclopentadienyl, diethyldithiocarbamate as well as alkoxides and aryloxides. Carbonyl insertion into the W-O bond in a series of the tungsten(II) alkoxides and aryloxides results in the generation of carboalkoxy- and carboaryloxy-groups which readily reductively eliminate to form new C-C bonds. In contrast, carbon dioxide insertion into the W-OMe bond generates an {dollar}etasp1{dollar}-carbonate ligand which retains coordination to the metal center.; Carbonyl substitution by nucleophilic phosphines and phosphites in the saturated ligand tungsten(II) halides as well as those of the related Schiff base system affords dicarbonyl complexes that exhibit interesting properties that are dependent on the nature of the halide as well as the phosphorous nucleophile. A kinetic study on the substitution of a carbonyl ligand by triethylphosphine in the Schiff base tungsten(II) fluoride supports a dissociative mechanism for these reactions.