The chemistry of fluorinated 1,3,5-triazapentadienyl coinage metal complexes

Our interest in fluorinated triazapentadienyl ligands is due to the relevant results observed over the past years in catalysis by fluorous biphase chemistry, the increased stability of metal adducts supported by fluorinated ligands, and the utility of monoanionic, nitrogen based ligands such as beta-diketiminates (or 1,5-diazapentadienyls) and tris(pyrazolyl)borates in the synthesis and catalytic application of the corresponding metal complexes.;Fluorinated 1,3,5-triazapentadienyls, a relatively new class of monoanionic, bidentate, nitrogen based ligands in coordination chemistry, were successfully obtained starting with a modified method for the synthesis of fluorinated triazapentadienes. This modified method is cheaper than the classical method and provides a route to obtaining highly fluorinated triazapentadienes in good yields. Deprotonation of these triazapentadienes yielded the triazapentadienyl ligands.;Fluorinated triazapentadienyl ligands were highly effective in the isolation and full characterization of a variety of copper(I), silver(I) and gold(I) adducts which show quite interesting bonding and structural features as well as some catalytic properties.;Structural and spectroscopy data of triazapentadienyl-copper(I)-carbonyl and -ethylene complexes revealed that fluorinated triazapentadienyl ligands are weak sigma-donors. For example, in infrared spectroscopy the upsilon(CO) signals of triazapentadienyl-copper(I)-carbonyl adducts are close to the corresponding signal of free CO, and appear at higher values than the copper(I)-beta-diketiminate analogs. This suggests that triazapentadienyl ligands generate a more acidic metal center with poor M → CO pi-back-donation. Similarly, the 1H NMR signals of triazapentadienyl-copper(I)-ethylene compounds show upfield shifted values for the bonded ethylene moieties in comparison with a beta-diketiminate-copper(I) analog. Moreover, copper(I)-ethylene and -acetonitrile adducts supported by triazapentadienyl ligands effectively catalyzed carbene and nitrene transfer reactions to a variety of substrates in high efficiencies.;X-ray diffraction analyses of triazapentadienyl-silver(I) complexes showed that in the solid state fluorinated triazapentadienyl ligands can bind to silver(I) in up to three different modes of coordination. For example, triazapentadienyl ligands can be kappa2-donors via terminal nitrogen atoms or kappa1-donors via either a central or one terminal nitrogen atom. In addition, the ligands can adopt U- or W-shaped backbones. 19F NMR spectroscopy data offer a way to assign the structural configuration of the metal-triazapentadienyl interaction and to predict the conformation of the fluorinated ligand backbone.;Gold(I) adducts were isolated for the first time with beta-diketiminate ligands. These remarkably air and light stable compounds are dinuclear species and feature 12-membered metallacycles in the solid state. In addition, fluorinated triazapentadienyl-gold(I)-ethylene adducts were isolated as air and light stable monomers in the solid state. 1H and 13C NMR analyses show that there is a higher degree of pi-back-donation in gold(I)-ethylene complexes in comparison with the copper(I)-ethylene analogs. Gold(I)-ethylene adducts supported by fluorinated triazapentadienyl ligands also mediate carbene transfer reactions from ethyl diazoacetate to saturated and unsaturated hydrocarbons.