C _sp , C _sp ² , and C _sp ³ Hydrocarbyl Group Migration from Pd(II) to P(III): Accessing Metallophosphoranes via Nonspectator Ligand Reactivity

Migration of palladium-bound hydrocarbyl ligands to tricoordinate phosphorus ligand P(N(o-N(2-pyridyl)C₆H₄)₂) (L) is demonstrated across a series of Pd(II) organometallic complexes bearing C_sp, C_sp ², and C_sp ³ groups. Treatment of ligand L with cis-[(TMEDA)PdI(C₆H₅)], cis-[(TMEDA)PdBr(CH₂C₆H₅)], [(η³-C₃H₅)PdCl]₂, and trans-[PdBr(C≡C─C₆H₅)(PPh₃)₂], respectively, results in migration of the hydrocarbyl group from Pd to P, yielding isolable (σ⁴-P)─Pd palladaphosphoranes: L^Allyl•Pd^Cl, L^Bn•Pd^Br, L^Ph•Pd^I, and L^CCPh•Pd^Br. The mechanistic pathway of the palladaphosphorane formation was investigated by in situ NMR experiments and DFT calculations, suggesting an α-migration mechanism. Halide exchange with NaBr or NaI affords the corresponding bromide and iodide congeners without disrupting the palladaphosphorane connectivity. ³¹P NMR chemical shifts correlate systematically with the identity and hybridization of the hydrocarbyl group, and electronic structure analyses attribute observed trends to variations in the s/p hybrid compositions of the local P─C bond orbitals. This work establishes an underappreciated facet in the reactivity landscape of Pd complexes bearing tricoordinate phosphorus (σ³─P) ligands by demonstrating their ability to undergo nonspectator metal-to-ligand group transfer, with implications for designing bifunctional ligand architectures capable of cooperative catalysis.