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

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)2NAlMe3]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)2NAlMe3]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.