¹³C- and ²H-enriched bis((3,5-dimethylphenyl)aminomethyl) tert-butylphosphine (the natural abundance (NA) ligand ᴬʳBiAMPᵗᴮᵘ; the ²H- and ¹³C-labelled analogues are denoted as _d_₄ - ᴬʳBiAMPᵗᴮᵘ and ¹³C₂ - ᴬʳBiAMPᵗᴮᵘ, respectively), containing two secondary amines and a tertiary phosphine, was synthesized using a Kabachnik–Fields protocol. The coordination chemistry of the ligand isotopologues (including the NA derivative) was investigated with the paramagnetic lanthanides Ce and Nd and the paramagnetic actinide elements Np and Pu, furnishing MI(ᴬʳBiAMPᵗᴮᵘ)(thf)₃ (M = Ce(1), Nd(2), Np(3), Pu(4)), MI(_d_₄ - ᴬʳBiAMPᵗᴮᵘ)(thf)₃ (M = Ce(²H-1), Nd(²H-2)) and MI(¹³C₂ - ᴬʳBiAMPᵗᴮᵘ)(thf)₃ (M = Ce(¹³C-1), Nd(¹³C-2), Np(¹³C-3), Pu(¹³C-4)); each complex bears the metal in the 3+ oxidation state chelated by the amide groups and phosphorus atom of the ᴬʳBiAMPᵗᴮᵘ ligand. Multinuclear (¹H, ³¹P, ¹³C, and ²H) NMR characterization of the complexes revealed wide windows of paramagnetically shifted resonances; the isotopically enriched derivatives allowed for the unambiguous identification of the methylene environments, highlighting the utility of the ᴬʳBiAMPᵗᴮᵘ ligands for providing rich spectroscopic signatures of paramagnetic f-element coordination complexes. A combination of single-crystal X-ray diffraction and UV-vis-NIR spectroscopic techniques was also employed for the characterization of the compounds. Actinide complexes 3 and 4 possess rare examples of molecular transuranium element–phosphorus bonds and the first examples of transuranium element–phosphine interactions.