The synthesis and structures of tantalum complexes that contain a triamido or a diamidoamine ligand

Article abstract of DOI:10.1016/s0020-1693(97)05869-6

Addition of (Me₃SiNHCH₂CH₂)₂NH (H₃[N₃(TMS)]) or (Me₃SiNH-o-C₆H₄)₂NH (H₃[ArN₃(TMS)]) to a solution of TaMe₅ yields [N₃(TMS)]TaMe₂ or [ArN₃(TMS)]TaMe₂, respectively. An X-ray study of [ArN₃(TMS)]TaMe₂ showed it to have an approximate trigonal bipyramidal structure in which the two methyl groups are in equatorial positions and the triamido ligand is approximately planar. Addition of (C₆F₅NHCH₂CH₂)₂NH (H₃[N₃(C₆F₅)]) to TaMe₅ yields first [(C₆F₅NCH₂CH₂) ₂NH]TaMe₃, which then decomposes to [(C₆F₅NCH₂CH₂) ₂N]TaMe₂. An X-ray study of [(C₆F₅NCH₂CH₂) ₂N]TaMe₂ shows it to be approximately a trigonal bipyramid, but the C₆F₅ rings are oriented so that they lie approximately in the TaN₃ plane and two ortho fluorines interact weakly with the metal. Trimethylaluminum attacks the central nitrogen atom in [N₃(TMS)]TaMe₂ to give [(Me₃SiNCH₂CH₂)₂NAlMe ₃]TaMe₂, an X-ray study of which shows it to be a trigonal bipyramidal species similar to the first two structures, except that the C-Ta-C bond angle is approximately 30° smaller (106.6(12)°). Addition of B(C₆F₅)₃ to [(C₆F₅NCH₂CH₂) ₂NH]TaMe₃ yields {[(C₆F₅NCH₂CH₂) ₂NH]TaMe₂}₊ {B(C₆F₅)₃Me}^-, the structure of which most closely resembles that of [(Me₃SiNCH₂CH₂)₂NAlMe ₃]TaMe₂ in that the C-Ta-C angle is 102.0(6)°. The C₆F₅ rings in {[(C₆F₅NCH₂CH₂) ₂NH]TaMe₂}⁺ are turned roughly perpendicular to the TaN₃ plane, i.e. ortho fluorines do not interact with the metal in this molecule.