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Study of bifunctional imidazolylphosphine ligands on Pd and Pt

Abstract

A series of three new Imidazolylphosphine ligands was designed and synthesized to probe the effects of phosphorus and heterocycle substituents on coordination geometry and ligand hapticity in Pd(0) and Pd(II) complexes of these ligands. The X-ray diffraction and spectroscopic data for Pd(0) complex show that it is a two -coordinate,14-electron species. Oxidative-addition chemistry of the two coordinate Pd(0) complexes shows that isopropyl substituents not only allow rapid reaction but retention of both phosphine ligands. In contrast, phosphorus tert-butyl groups slow oxidative-addition and lead to phosphine loss and chelation by the remaining phosphine. in all of the di-tert-butylphosphino- substituted compounds in this study, the chelate remained closed when amines were added. Amine binding could be effected after halide ionization, but without opening of the chelate ring. Amine binding involving hydrogen bonding was seen in the isopropyl series. The results described in this dissertation show the interplay of ligand substituents in determining ligand hapticity, coordination of other ligands, and secondary hydrogen-bonding interactions, properties of interest in study structure and catalysis of complexes featuring hybrid ligands. Our ultimate goal is finding the catalyst for hydration and hydroamination of an unsaturated bond, resulting in terminal alcohols and amines or in a heterocyclic ring, respectively. In this dissertation, we report the syntheses of Pt complexes with various bifunctional imidazolylphosphines and look into their reactivities with small molecules which could represent the important steps in the catalysis. The reactivites of resulted Pt(0) and hydrido Pt(II) complex with RO-H compounds of acidity ranging from acids to water are very different. Pt(0) Complex reacted only with more acidic species whereas hydrido Pt(II) complex reacted with all O-H compounds tested, with O-H activation, and the product H-Pt-OR was stabilized by hydrogen bonding interactions between oxygen atom and N-H on the imidazole ring. Bidentate phosphine ligands containing imidazolyl substituents were synthesised and studied on Pd and Pt. The combination of our ligands and Pd(0) precursor generated a catalyst for coupling reaction of bromobenzene and morpholine at room temperature. Our imidazolylphosphine and pyridylphosphine ligands were also tried on the Pt-catalyzed intromolecular hydroamination of unactivated olefins and secondary alkylamines

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