Hyde, Timothy Ian

2018-01-31T11:45:47Z

2018-01-31T11:45:47Z

1987

CHAPTER 1 An introduction to the work in the thesis is given. A survey of the literature describes general methods of synthesis of transition metal macrocycles and porphyrins and their relevance to substrate binding and activation. The aims of this study are introduced.

CHAPTER 2 The synthesis and characterization of four neutral 14- membered tetraaza 2 ,6 -pyridyl macrocycles L 1- ! 1* with varying carbon and nitrogen alkylation is described. Extensive 1H and 1 3C n.m.r. studies in combination with a single X-ray crystal structure of the free ligand I^.E^O were undertaken. The free ligand was found to adopt a puckered arrangement in order to minimise nitrogen donor lone pair interactions.

CHAPTER 3 The insertion of the platinum metals Ru(II), Rh(III), Ir(III), Pd(II), and Pt(II) into the tetraaza macrocyclic ligands L¹ - L⁴ is described. All new compounds were fully characterized by n.m.r., infrared and mass spectral techniques and by the X-ray crystal structures of cis [RuL³ (CO) Cl] BPh₄, trans [RhL² Cl₂„ ] PF₆, cis[IrL⁴(H)Cl]PF₆, and [PdL¹](BPh₄)₂. The Rh(III) and Pd(II) structures both show the macrocyclic ligands bound to four equatorial sites around each metal centre. In contrast the Ir(III) and Ru(II) complexes display folded ligand structures with one nitrogen donor, N(7), bent away to occupy an apical position to give a-is coordination of the remaining two ligands. 1H and ¹³C n.m.r. studies indicated that in most cases several ligand isomers were present in solution.

CHAPTER 4 The X-ray crystal structure of the square planar [Pd (TMC) ] cation shows the macrocycle to adopt the R.S.R.S. conformation.

The complex shows a fully reversible one electron reduction process in acetonitrile at E,= -1.45V vs. A g / A g+, ΔEp=65mV at Pt electrodes. Controlled potential electrolysis of [Pd(TMC)]²+ at -1.50V in acetonitrile afforded a reduction product which was assigned as a d⁹, Pd(I) complex [Pd(TMC)]+, (g₁₁ = 2.302, g₁=2.076) with coupling to ¹⁰⁵Pd (22.2%, I = 5/2), A₁₁= 53 , A₁=40G. From an investigation of TMC and six other tetraaza macrocyclic complexes, the Pd(II)/(I) redox couple was found to occur at potentials on average 300mV more cathodic than the corresponding Ni(II)/(I) couples. No Pd(II)/(III) redox process was observed within the anodic range of the acetonitrile solvent; this contrasts with the corresponding nickel macrocyclic complexes which all show Ni(II)/(III) redox couples in the range +0.68—»+1.33V.

CHAPTER 5 A comparison of the redox chemistry of the square planar nickel diiminopyridyl macrocyclic complexes [Ni(n₃X)]²⁺ was investigated. (X = n,p where n₄, n₃p are respective tetraaza and triazaphosphorus donor sets) . Both complexes show two reversible one electron reductions. Characterization of the first reduction product by e.s.r. spectroscopy shows the reduction of [Ni(n₄)]²⁺ to be ligand based, whereas for [Ni (n₃p)]²⁺the reduction was found to be metal based. The binding of CO, phosphines and related ligands to the mono ­ valent complex is described. The single crystal X-ray structure of [Ni(n₃p)] (PF₆)₂ was determined confirming the square planar nickel geometry.

A structural investigation of the monohalo derivatives [Ni(n₃X)Cl]+, (X = p,s, where n^s is a triazathia donor set) was u n d e r t a k e n . [Ni (n₃p)Cl]+ shows a 5 coordinate square based pyramidal geometry around Ni(II) analogous to the previously reported [Ni(n4)Br]+ complex. In contrast a dimeric structure with dichloro bridges between octahedral nickel(II) centres is found for the sulphur analogue [Ni(n₃s)Cl]₂²+•

CHAPTER 6 Parallel studies were instigated into the isoelectronic reactions of [NiL]+ with dioxygen and [NiL]²+ with superoxide ion in acetonitrile at 230K (L = TMC, C-rac HMC).The product of the reactions was a reactive paramagnetic pale green solution with an anisotropic e.s.r. signal, g₁=2.195, g₁₁=2.056. ⁶¹Ni labelling experiments confirmed the predominantly metal based radical nature of the species of proposed stoichiometry [NiL(O₂)]+ . A respective one or two electron transfer from nickel to superoxide or dioxygen is proposed to form a reactive, formal nickel(III) - peroxo complex. A rhombic e.s.r. signal from a paramagnetic green solution for L=TMC is also assigned as a nickel (III) - peroxo species.

http://hdl.handle.net/1842/28273

The University of Edinburgh

Annexe Thesis Digitisation Project 2017 Block 16

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Studies on transition metal tetraaza macrocyclic complexes

Thesis or Dissertation

PhD Doctor of Philosophy