Reaction of YI₃(THF)_3.5 with one equivalent of the potassium β-diketiminate (BDI) complex [HC{C(CH₃)NAr}₂K] (1) (Ar = 2,6-Prⁱ₂C₆H₃) affords the monomeric, mono-substituted yttrium BDI complex [HC{C(CH₃)NAr}₂YI₂(THF)] (2) in good yield. Reaction of 2 with DME affords [HC{C(CH₃)NAr}₂YI₂(DME)] (3) in quantitative yield, which is monomeric also. Reaction of the primary terphenyl phosphane Ar*PH₂ (Ar* = 2,6-(2,4,6-Prⁱ₃C₆H₂)₂C₆H₃) with potassium hydride, and recrystallisation from hexane, affords the potassium primary terphenyl phosphanide complex [{Ar*P(H)K(THF)}₂] (4) in high yield. Compound 4 is dimeric in the solid state, constructed around a centrosymmetric K₂P₂ four-membered ring, the coordination sphere of potassium is supplemented with an η⁶ K⋯C_aryl interaction. The reaction of 2 with one molar equivalent of 4 in THF affords the THF ring-opened compound [HC{C(CH₃)NAr}₂Y{O(CH₂)₄P(H)Ar*}(I)(THF)] (5). Compound 5 is formed as a mixture of endo_OR (5a) and exo_OR (5b) isomers (5a : 5b = ∼2 : 1) which may be separated by fractional crystallisation from hexane–toluene to give pure 5a. Attempted alkylation of 3 with two equivalents of KCH₂Si(CH₃)₃ affords the potassium yttriate complex [Y{µ-η⁵:η¹-ArNC(CH₃)CHC(CH₂)NAr}₂K(DME)₂] (6) in moderate yield; 6 contains two dianionic dianilide ligands, which are derived from C–H activation of a backbone methyl group, each bonded η⁵ to yttrium in the solid state. The reaction of 3 with one equivalent of KC₈ affords [{HC(C[CH₃]NAr)₂YI(µ-OCH₃)}₂] (7), derived from C–O bond activation of DME, as the only isolable product in very low yield. Compounds 2, 3, 4, 5a, 6, and 7 have been characterised by single crystal X-ray diffraction, NMR spectroscopy and CHN microanalyses.