Iminophosphine ligands and their metal binding properties : a thesis presented in partial fulfilment of the requirements for the degree of Science in Chemistry at Massey University, Palmerston North, New Zealand
This work focuses on the complexes of two iminophosphine ligands, N-(2-diphenylphosphinobenzylidine)-aniline (NP) and N-(2-diphenylphosphinobenzylidine)-4'-(benzo-15-crown-5) (O₅NP), and their complexes with Cu(I), Ag(I), Au(I), Cr(0), Mo(0) and W(0). The cation binding properties of the complexes of O₅NP have been investigated. Chapter One describes the aims of this work and also provides a brief introduction to ligands containing phosphorus and nitrogen donor atoms as well as crown ethers and their inclusion in transition metal complexes. The analytical technique of electrospray mass spectroscopy (ESMS) is introduced and its use in the study of cation binding to crown ethers and cryptands discussed. Chapter Two looks at the Cu(I), Ag(I) and Au(I) complexes of NP and O₅NP, such as [M(L)₂][PF₆] (M = Cu, Ag, Au; L = NP, O₅NP), [M(NP)X]₂, [M(O₅NP)Cl]₂ (M = Cu, Ag), Au(NP)X and Au(O₅NP)Cl (X = Cl, Br, I). Reported in this chapter are the X-ray structural analyses of O₅NP, [Cu(NP)₂][PF₆], [Ag(NP)₂][PF₆], [Au(NP)₂][PF₆], [Cu(NP)Br]2, Au(NP)Cl and Au(NP)Br. Far and Near IR, ¹H and ³¹P NMR and ESMS were used to investigate the nature of the complexes. The [M(L)₂][PF₆] complexes displayed a clear trend in which the number of coordinated imines decreased as the soft nature of the metal centre increased. Both the Far IR and crystal structure analyses showed the Cu(I) and Ag(I) halo complexes to be dimeric with bridging halides and the Au(I) halo complexes to be monomeric with terminal halides. The ³¹P NMR signal was found to be dependent on the mass of the metal centre. In Chapter Three the Cr(0), Mo(0) and W(0) carbonyl complexes of NP and O₅NP are discussed. To characterise the complexes, IR, ESMS and ¹H, ³¹P and ¹³C NMR techniques were employed. X-ray structural analyses of Mo(CO)₄(NP) and Mo(CO)₄(O₅NP) were also used. It was found that the metal centres had an octahedral geometry with the ligands being bidentate via the P and N atoms and having a cis conformation. Upon coordination, the ¹H NMR signal of the imine proton moves to lower frequencies, whereas the ³¹P NMR signal moves to higher frequencies. It was also demonstrated that the presence of the crown ether has no significant effect on the structure of the metal centre. Cation binding to the complexes of O₅NP, the free ligand, and starting material, 4'-aminobenzo-15-crown-5 (O₅NH₂), is discussed in Chapter Four. Electrospray mass spectroscopy (ESMS) was used as a qualitative measure of the relative cation binding strengths. The X-ray structural analyses of the inclusion complexes W(CO)₄(O₅NP)Na(PF₆) and [Cu(O₅NP)₂]K.[PF₆]₂ were determined, and provided information on the coordination of alkali cations by these complexes. W(CO)₄(O₅NP) binds Na⁺ within the cavity of the benzo-15-crown-5 moiety which experiences significant change to its conformation. [Cu(O₅NP)₂][PF₆] binds K⁺ in a sandwich formation suggesting that rotation of the ligands occurs about the Cu(I) centre. The starting material, O₅NH₂, and free ligand, O₅NP, were selective towards K⁺, forming a 1:1 species. The complexes M(CO)₄(O₅NP) (M = Cr, Mo, W) and [M(O₅NP)₂][PF₆] (M = Cu, Ag, Au) were selective towards Na⁺ and K⁺ respectively with a 1:1 formation. The halide complexes, [Cu(O₅NP)Cl]₂, [Ag(O₅NP)Cl]₂ and Au(O₅NP)C1, displayed different selectivities from each other. Both [Cu(O₅NP)C1]₂ and [Ag(O₅NP)Cl]₂ dissociated in solution to give the monomers which selectively bound Li⁺ and K⁺ respectively in a 1:1 species. The Au(O₅NP)Cl complex was selective towards Na⁺.