Design and Synthesis of Meso- and Macrocyclic Tripodal Triamine Ligands and Investigations into their Coordination Chemistry

Abstract

The ability to directly and selectively functionalise hydrocarbons is one of the greatest remaining challenges facing chemists. The development of catalytic systems capable of affecting these transformations under ambient conditions would be of great environmental and economic importance. In nature, enzymes have been shown to utilise metal-based oxidants, such as high-valent terminal metal-oxos (M=O) to carry out these reactions. A multitude of biomimetic Mn=O and Fe=O complexes have been reported which are capable of activating C-H bonds. In this thesis, we postulate that late transition metal-oxos (Co, Ni, Cu, Zn) will form more potent oxidants than their early transition metal counterparts. However, there are currently no examples of stable late transition metal-oxo species in the literature, owing to the concept of the oxo-wall. It has been postulated that the oxo-wall may be circumvented through the synthesis of pseudo-tetrahedral metal-oxos. Herein, we describe the design and synthesis of several meso- and macrocyclic ligands. These oxidatively robust ligands have been designed to bind metals in a pseudo-tetrahedral fashion, which we believe will provide access to unprecedented late transition metal-oxos. We describe the synthesis of two mesocyclic ligands 2 and 4 as well as a library of useful synthons containing the 1,5-diazamacrocycle moiety. We show that 2 tends to form square pyramidal metal complexes [Fe(2)Cl2)] (24), [Cu(2)(MeCN)2] (30) and [Zn(2)Cl2] (31) in the absence of bridging ligands. In the case of FeCl2, a diiron species [Fe2(2)2Cl2)] (25) was also observed by X-ray crystallography. We also report the synthesis of a trigonal planar complex of 4, [Cu(4)(MeCN)](PF6) (33). Finally, we report the synthesis of a unique tricyclic macrocycle, 5, and describe tentative evidence that supports the formation of CuI and lithium complexes of this ligand. The ability to directly and selectively functionalise hydrocarbons is one of the greatest remaining challenges facing chemists. The development of catalytic systems capable of affecting these transformations under ambient conditions would be of great environmental and economic importance. In nature, enzymes have been shown to utilise metal-based oxidants, such as high-valent terminal metal-oxos (M=O) to carry out these reactions. A multitude of biomimetic Mn=O and Fe=O complexes have been reported which are capable of activating C-H bonds. In this thesis, we postulate that late transition metal-oxos (Co, Ni, Cu, Zn) will form more potent oxidants than their early transition metal counterparts. However, there are currently no examples of stable late transition metal-oxo species in the literature, owing to the concept of the oxo-wall. It has been postulated that the oxo-wall may be circumvented through the synthesis of pseudo-tetrahedral metal-oxos. Herein, we describe the design and synthesis of several meso- and macrocyclic ligands. These oxidatively robust ligands have been designed to bind metals in a pseudo-tetrahedral fashion, which we believe will provide access to unprecedented late transition metal-oxos. We describe the synthesis of two mesocyclic ligands 2 and 4 as well as a library of useful synthons containing the 1,5-diazamacrocycle moiety. We show that 2 tends to form square pyramidal metal complexes [Fe(2)Cl2)] (24), [Cu(2)(MeCN)2] (30) and [Zn(2)Cl2] (31) in the absence of bridging ligands. In the case of FeCl2, a diiron species [Fe2(2)2Cl2)] (25) was also observed by X-ray crystallography. We also report the synthesis of a trigonal planar complex of 4, [Cu(4)(MeCN)](PF6) (33). Finally, we report the synthesis of a unique tricyclic macrocycle, 5, and describe tentative evidence that supports the formation of CuI and lithium complexes of this ligand.