The chelating diamide complexes mer-TaCl3(BDPP) (2), mer-TaCl3(BDPP) (3), and (BDPP)Ta(eta(2)-RC=CR)Cl (4a, R = Pr; 4b, R = Et; 4c, R = Ph) (BDPP = 2,6-(ArNCH2)(2)-NC5H3; Ar = 2,6-Pr-i(2)-C6H3), have been prepared. Proton and carbon NMR data suggest that the alkynes in 4a-c rotate rapidly on the NMR time scale. An X-ray study of(BDPP)Ta(eta(2)-PrC=CPr)Cl (4a) revealed a distorted-square-pyramidal geometry with the chloride occupying the apical position.