Accessing Palladaphosphoranes via Nonspectator Behaviors of a Structurally Constrained P(III) Ligand

Tricoordinate phosphorus ligands (𝜎³-P) are fundamental to palladium chemistry, typically functioning as steric and electronic modulators while remaining chemically inert during palladium-catalyzed transformations. Nonetheless, sporadic reports have revealed substituent scrambling between Pd and 𝜎³-P ligands, indicating additional metal-phosphorus interaction beyond the donor-acceptor relationship. In addition to lower-coordinate palladium-phosphido (Pd-(𝜎²-P)) intermediates, the involvement of higher-coordinate intermediates, palladaphosphoranes (Pd-(𝜎⁴-P)), has also been suggested for such processes. However, direct observation of Pd-(𝜎⁴-P) complex from group migration between Pd and P is rare, potentially due to their transient nature. To investigate intermediate-like structures of group migration between Pd and P, a structurally constrained, tridentate 𝜎³-P ligand was employed to stabilize Pd-(𝜎⁴-P) structures. Geometric tuning of the 𝜎³-P site has been shown to promote nonspectator reactivity, including insertion and addition reactions of 𝜎³-P ligands with transition metal-ligand bonds. This approach enables the exploration of group migration between transition metals and phosphorus, providing new insights into the reactivity landscape of 𝜎³-P ligands. 

In this presentation, the following will be discussed: (1) Migration of alkyl, aryl, and alkynyl ligands from Pd(II) oxidative addition complexes to a 𝜎³-P ligand. (2) Migration of alkyl groups from Pd(II) dialkyl compounds to a 𝜎³-P ligand. (3) Structural and spectroscopic analysis of palladaphosphoranes. (4) Experimental and computational mechanistic insights of hydrocarbyl group migration between Pd(II) and 𝜎³-P ligands.

Lily Wang is a 4th-year Ph.D. candidate in the Radosevich Lab. She earned her B.Sc. in Chemistry from the Hong Kong University of Science and Technology, where she worked on redox-active Ce(IV) complexes with Kläui tripodal ligands. Lily joined Prof. Alex Radosevich’s Lab in the fall of 2022. Her research focuses on synthesizing late transition metal complexes with structurally constrained P(III) ligands and probing their reactivity to discover novel metal-phosphorus cooperativities.