Improved Synthesis, Separation, Transition Metal Coordination and Reaction Chemistry of a New Binucleating Tetraphosphine Ligand

by Ekaterina Kalachnikova

Institution: Louisiana State University
Department: Chemistry
Degree: PhD
Year: 2015
Keywords: tetraphosphine ligand synthesis; alkene oxydative cleavage; alkene hydration; bimetallic; phosphine complexes; nickel; catalysis
Record ID: 2058203
Full text PDF: http://etd.lsu.edu/docs/available/etd-01222015-004745/


The first chapter of this dissertation involves discussion of alkene hydration and oxidative cleavage reactions catalyzed by late transition metal complexes. Previously reported results are summarized here. Mechanistic aspects of alkene hydration catalyzed by late transition metal complexes are also explained. The second part of Chapter 1 focuses on motivation for using bimetallic nickel phosphine complexes as possible catalytic precursors for alkene hydration. Chapter 2 describes studies into alkene hydration in the presence of catalytic amounts of dinickel phosphine complexes based on linear tetraphosphine ligand, PEt2CH2CH2(Ph)PCH2P(Ph)CH2CH2PEt2, et,ph-P4. Under conditions tested no alcohol products were detected. However we have observed formation of a small amount of oxidative cleavage products. Results from studies of oxidative cleavage reactions are described in Chapter 3. It was established that only a substoichiometric conversion to corresponding aldehydes can be achieved in the presence of catalytic amounts of bimetallic nickel complexes or free et,ph-P4 ligand. Extensive NMR studies indicated that in the presence of water dinickel tetraphosphine complexes, rac- and meso-Ni2X4(et,ph-P4) (X = Br, Cl) are not stable and readily fall apart via phosphine arm dissociation. To address this problem new stronger chelating tetraphosphine ligand, PEt2(o-C6H4)P(Ph)CH2(Ph)P(o-C6H4)PEt2, et,ph-P4-Ph has been designed by Stanley group. Chapter 4 describes improved synthesis of et,ph-P4-Ph and chromatographic procedure developed for separation of rac- and meso-diastereomers. The racemic form of et,ph-P4-Ph reacts with 2 equiv of PtCl2(cod) or [Rh(nbd)2](BF4) to give bimetallic Pt2Cl4(rac-et,pt-P4-Ph), 4R and [rac-Rh2(nbd)2(et,ph-P4)](BF4)2, 6R, in which et,ph-P4-Ph acts as a bridging and chelating ligand. Heterobimetallic complex, NiPtCl4(rac-et,pt-P4-Ph), 5R has been prepared by reaction of rac- et,ph-P4-Ph with 1 equiv of Ni2Cl4∙6H2O, followed by dropwise addition of 1 equiv of PtCl2(cod). Complexes 4R, 5R, and 6R have been characterized by 31P{1H} NMR spectroscopy and single-crystal X-ray diffraction studies.