The Synthesis and Reactivity of [PC(sp²)P] Complexes of Iron and Palladium

The reactivity and stability of homogenous transition metal catalysts largely depends on the supporting ligand system. Thus, ligand design is a crucial component to reactivity modulation and optimization of catalysts. In particular, the development of ligand systems capable of participating in metal ligand cooperativity (MLC) has become a popular area of research in the organometallic community. Complexes of this nature promote participation from the supporting ligand and the metal center throughout a chemical process. Credited for their tunability, tridentate, chelating pincer ligands are well-known for their ability to participate in MLC-type reactivity on a variety of different metal centers. More specifically, transition metal carbenes bearing the [PC(sp²)P] pincer framework exhibit unique reactivity, including cooperative 1,2-additions across the M-C_carbene bond when treated with polar substrates.

This work in mind, efforts towards expanding the [PC(sp²)P] ligand system to an iron metal center were explored and the optimal synthetic route was discovered. Reactivity studies of the resulting[{PC(sp²)P}Fe(PMe₃)(N₂)] complex with styrene and select alkynes were investigated. The reactivity displayed in the presence of substrates containing π character is not only novel to the reactivity exhibited by other [PC(sp²)P] complexes, but also, all previously synthesized iron carbene complexes.

Furthermore, the Iluc lab has extensively studied the reactivity of a nucleophilic palladium(II) carbene complex, [{PC(sp²)P}Pd(PMe₃)]. As a continuation of this work, [{PC(sp²)P}Pd(PMe₃)] was treated with H₂O to further elucidate its small molecule activation competencies. Results indicated that the second activation of water proceeded through µ-oxo species and prompted the synthesis of a µ-sulfide dimer through treatment of the palladium carbene with H₂S. Additional work with [{PC(sp²)P}Pd(PMe₃)] focused on the ancillary ligands effect on reactivity and stability of the 4-coordinate carbene system.