Palladium Bisphosphine Mono-Oxide Complexes: Synthesis, Scope, Mechanism, and Catalytic Relevance

Recent studies in transition metal catalysis employing chelating phosphines have suggested a role for partial ligand oxidation in formation of the catalytically active species, with potentially widespread relevance in a number of cata-lytic systems. We examine the internal redox reaction of PdII(bisphosphine)X2 (X = Cl, OAc, etc.) complexes to reveal previously underexplored aspects of bisphosphine mono-oxides (BPMOs), including evaluation of ligand structure and development of general reaction conditions to access a collection of structurally diverse BPMO precatalysts based on organopalladium oxidative addition complexes. In particular, a series of PdII(BPMO)(R)(X) (R=Aryl, Alkyl; X=I, Br) oxidative addition complexes bearing 24 different BPMO ligands were characterized by NMR and X-ray crystallog-raphy. Comparison of the catalytic performance of the oxidative addition complexes of phosphine versus bisphos-phine mono-oxides as precatalysts is demonstrated to be an enabling diagnostic tool in Pd catalytic reaction develop-ment. Finally, the differences in catalytic behavior between bisphosphine and bisphosphine mono-oxide complexes were rationalized through solid-state parametrization and stoichiometric experiments.