Approaches to Alkaline Earth Metal-Organic Chemical Vapor Deposition Precursors. Synthesis and Characterization of Barium Fluoro-β-ketoiminate Complexes Having Appended Polyether "Lariats"

The synthesis and characterization of a family of β-ketoimines derived from 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hfa) and the corresponding volatile barium β-keioiminate - polyether complexes having the general formula Ba[CF₃COCHC(NR)CF₃]₂ where R = (CH₂CH₂O)₂CH₃, (CH₂CH₂O)₂CH₂CH₃, and (CH₂CH₂O)₃CH₂CH₃ is reported. These complexes can be transported in the vapor phase at 160 °C/0.05 Torr without decomposition. The β-ketoiminate ligands are synthesized by condensation of the appropriate amine-terminated poly(ethylene oxide)s with the trimethylsilyl enol ether derivative of hfa and converted to barium β-ketoiminate - polyether complexes by reaction with BaH₂. The poly(ethylene oxide) amines are in turn synthesized by triphenylphosphine-mediated reduction of the corresponding poly(ethylene oxide) azides (synthesized via the tosylates) to afford the amines in good yields and analytical purity. The amines, β-ketoimines, and barium complexes were characterized by elemental analysis, ¹H, ¹⁹F, and ¹³C NMR spectroscopy, mass spectroscopy, and thermogravimetric analysis. The eight-and ten-coordinate Ba²⁺ complexes having the formula Ba[CF₃COCHC(NR)CF₃]₂ where R = (CH₂CH₂O)₂CH₂CH₃ [C₂₂H₂₈N₂F₁₂O₆Ba; space group = monoclinic, P2₁; a = 12.1175(2) Å, b = 14.9238(2) Å, c = 16.9767(3) Å, a = γ = 90°, β = 90.0840(10)°, Z = 4] and R = (CH₂CH₂O)₃CH₂CH₃ [C₂₆H₃₆N₂F₁₂O₈Ba; space group = triclinic, P1 (#2); a = 10.971(2) Å, b = 12.134(2) Å, c = 15.280(4) Å. α = 89.94(2)°, β = 110.00(2)°, γ = 116.75(2)°, Z=2] were characterized by single-crystal X-ray diffraction. Both analyses reveal monomeric structures with the β-ketoiminate ligands coordinated to the Ba²⁺ center through all available oxygen and nitrogen atoms. These complexes are substantially more volatile than Ba(2,2,6,6,-tetramethyl-3,5-heptanedionate)₂ but less so than the most volatile Ba(1,1,1,5,5,5-hexafluoro-2,4-pentanedionate)₂·polyether complexes.