The preparation and characterization of the diamido-arsine ligand [NAsN]Li₂(THF) (1) (where NAsN = PhAs(CH₂SiMe₂NPh)₂), the protonated ligand precursor [NAsN]H₂ (2), and its coordination chemistry with tantalum is presented. The complex [NAsN]TaMe₃ (3) can be synthesized from 1 and TaMe₃Cl₂. Hydrogenation of 3 did not produce the desired tetrahydride ([NAsN]Ta)₂(µ-H)₄, instead, activation of Ta–N bonds in the complex produced a modest yield of the free ligand 2. In an attempt to understand the unusual reactivity of 3, a density functional theory investigation of the model complexes 'NAsN'Li₂(OMe₂)₂ (4) and 'NAsN'TaMe₃ (5) (where 'NAsN' = MeAs(CH₂SiH₂NMe)₂) and their phosphine analogs 'NPN'Li₂(OMe₂) (7), 'NPN'TaMe₃ (8), and a related niobium complex 'NPN'NbMe₃ (10) (where 'NPN' = MeP(CH₂SiH₂NMe)₂) was undertaken. The difference between the chemistry supported by the As and P ligands originates from the poor binding of As to Ta in these systems and is likely due to a mismatch of the soft As donor and the hard Ta(V) metal centre.Key words: arsine ligand, tridentate, tantalum, hydrogenation, DFT calculations.