Synthesis, Characterisation, Reactivity and Computational Study of Cobalt and Palladium Complexes of bis(Diphenylphosphino)amines

Abstract

This thesis presents the synthesis and characterisation of a range of cobalt(I) and cobalt(II) complexes of narrow bite angle bis(diphenylphosphino)amine-type (‘PNP’) and associated ligands.
Chapter 1 outlines the importance of bite angle in the coordination chemistry and reactivity of cobalt complexes, with particular emphasis on ‘PNP’ and related ligands.
Chapter 2 describes the synthesis of an array of ‘PNP’ and associated ligands and their corresponding phosphine selenides.
Chapter 3 presents the coordination chemistry of ‘PNP’ and ‘PCNCP’ ligands with [(MeCN)2PdCl2]. The reactivity of [PdCl2] with MeOH (affording [(PhCH2CH2NHPPh2)(MeOPPh2)PdCl2]) and [PdCl2] with trifluoroacetic acid (affording [(H-Py-o-(CH2)2N(PPh2)2)PdCl2][CF3CO2]) as well as CoCl2 and [N(n-Pr)4]Cl (affording [N(n-Pr)4][(Py-o-(CH2)2N(PPh2)2)PdCl2]) is probed.
Chapter 4 discusses the coordination of ‘PNP’ ligands with CoX2 (X = Cl, Br, and I), in particular describing the formation of zwitterionic (e.g., [CoX(Py-o-(CH2)2N2)(Py-o-(CH2)2N2)]) or ionic (e.g., [CoX(Ph(CH2)2N2)2]2[Co2X6]) complexes. The pathway to zwitterionic cobalt(II) complexes via an ionic cobalt(II) complex formed in situ is verified through the synthesis of [CoBr(Ph(CH2)2N2)2][PyCoBr3] obtained from reacting [CoBr(Ph(CH2)2N2)2]2[Co2Br6] with pyridine.
Chapter 5 outlines the synthesis and zinc reduction of cobalt(II) complexes [CoBr(‘PNP’)2][BArF4] to afford cobalt(I) complexes of the form [Co(‘PNP’)2][BArF4]. Attempts at other strategies to access cobalt(I) complexes, as well as the reactivity of Py-o-(CH2)2N(PPh2)2 and Ph(CH2)2N(PPh2)2 with ZnBr2, are presented.
Chapter 6 explores the reactivity of [Co2][BArF4] with ethylene, CO and H2, and describes the formation of [Co2(η2-CH2CH2)][BArF4], [Co2CO][BArF4] and an equilibrium mixture of [Co2(η2-H2)][BArF4] and [Co2(cis-(H)2)][BArF4], respectively (primarily studied by 31P NMR and computational studies).
Chapter 7, Chapter 8 and the Appendices contain all experimental details, conclusions and future outlook, and supplementary information, respectively.