Ligand exchange reactions have been used for the synthesis of metallacyclic complexes of Ni and Pd of the type [M(CH₂CMe₂-o-C₆H₄)(P–N)], where P–N is the phosphinito-imine ligand P(iPr)₂OC(Me)N(2,6-C₆H₃(iPr)₂. The protic acid [H(OEt₂)(BAr′₄)] (Ar′ = 3,5-C₆H₃(CF₃)₂) selectively cleaves one of the two σ metal–carbon bonds, affording cationic monoalkyl complexes. Nickel monoalkyls stabilized with Et₂O or MeCN ligands are thermally unstable and spontaneously undergo a decomposition process that ultimately leads to the breakdown of the phosphinito-imine ligand. In contrast, cationic alkylpalladium derivatives are thermally very stable, allowing the isolation of a formally unsaturated monoalkyl complex stabilized by an intramolecular π-arene interaction. Although monoalkynickel and -palladium phosphinito-imine derivatives are inactive as ethylene polymerization or copolymerization catalysts, they readily experience migratory insertion reactions. A palladium chelate arising from the successive insertion of CO and ethylene has been isolated and characterized.