Metal Complexes of 1,4,7-Triazacyclononane With Pendant Donor Arms

Lovatt, Paul Alexander (1997) Metal Complexes of 1,4,7-Triazacyclononane With Pendant Donor Arms. PhD thesis, University of Glasgow.

Abstract

This work is centred upon a series of novel N-functionalised macrocycles and their transition metal complexes. The macrocycles in question are derivatives of 1,4,7-triazacyclononane (TACN) and are functionalised at one, two or all three nitrogens. The pendant arms contain alkene, phosphine and activated aryl donor groups. In some cases the pendant arm acts as a bridge between two macrocyclic rings producing a potential dinucleating ligand. The single alkene pendant arm macrocycles L10 & L11 contain both hard N3 and soft olefin donor sets. Complexation of L10 to Cu(I) results in a complex that has a coordinated alkene and Ns donor set, this causes considerable strain in the short C4 pendant arm. Rapid oxidation of the Cu(I) to Cu(II) releases the co-ordinated olefin releasing strain on the pendant arm. The Cu(II) complex formed is Jahn-Teller distorted [Cu(L10)2]2+ and contains an elongated Cu-Nax bond length of 2.5A. The C5 pendant arm macrocycle L11 forms a more stable Cu(I) complex and has been studied by 1H and 13C NMR spectroscopy, results show that p-back bonding is present in the complex. The Ag(I) complex of L11 to silver(I) has been studied by NMR, the degree of p-back bonding is reduced in this complex. A series of dimers with a planar {Cu(mu-OH)2Cu}2+ core has been structurally characterised by X-ray crystallography, with the macrocyclic ligands bound to the copper centres having either one (L10), two (L14) or three (L12) alkene pendant arms. The dinucleating macrocyclic ligands (L4-6) also form a series of copper dimers in which the TACN units are linked by either ortho-, meta- or para-xylene, spacer units. The meta-xylene linked macrocycle was ideal for the spatial requirements for a {Cu(mu-OH)2Cu}2+ core, the dimeric complex [Cu2(mu-OH)2L5]2+ has been structurally characterised showing the complex to have a bent {Cu(mu-OH)2Cu}2+ core. The Cu(I) complex of can "activate" molecular CO2 in the presence of trace amounts of water to produce the dimeric Cu(II) oxalate complex [Cu(L12)(mu-C2O4)2Cu(L12)]2+. Results indicate that the mechanism of complexation is not simple and an intermediate copper(I) hydrogen carbonate complex [Cu(L12)(mu-HCO3)2Cu(L12)] is believed to be involved in oxalate formation. The novel phosphine pendant arm macrocycles were prepared by photolytic addition of diphenylphosphine across their olefm analogous. The potentially hexadentate ligand N,N',N''-tris(diphenylphosphinylethyl)-1,4,7-triazacyclononane (L22) was prepared from the addition reaction of TACN with vinyl diphenylphosphine oxide. The ligands have been complexed to several metals in low or zero valence states. The Zn(II) complex of has been structurally characterised and shows the complex to be an asymmetric dimer in which both zinc atoms are coordinated by the three amine groups and the phosphine. In both halves of the dimer each zinc atom is further coordinated by a chloride ion and an asymmetrically bridging chloride ion giving pseudo-octahedral geometry at each centre. L16 forms a pseudo- octahedral complex with Ni(II) in which die metal centre is further coordinated by a chloride ion and an ethanol molecule. The addition of KSCN to [NiL16Cl(EtOH)]+ displaced the coordinated chloride and ethanol to give a new Ni(II) complex which contained coordinated thiocyanate. Other complexes have been prepared and their spectroscopic studies are presented. Chirality has been introduced into the ligand system via the chiral alcohol pendant arm macrocycle N-(S)-2-methyl-l-propanol-1,4,7-triazacyclononane (L23). This macrocycle complexes to Co(II) forming an air sensitive tetrahedral complex that rapidly oxidises to a Co(III) species. Complexation of L23 with Cu(NO3)2 produces an octahedral complex with bound nitrate, the second nitrate ion is hydrogen bonded to the coordinated alcohol of the ligand. The Zn(II) complex of L23 has been studied by and NMR and the spectroscopic studies are presented. The C-functionalised triamine (5S)-6-methyl-3-azaheptane-1,5-diamine has been synthesised with the aim of being converted to a chiral triazamacrocycle using the Richmann-Atkins synthetic route. This would allow chirality to be introduced into all hexadentate ligand systems.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: Robert D Peacock
• Keywords: Organic chemistry
• Date of Award: 1997
• Depositing User: Enlighten Team
• Unique ID: glathesis:1997-75319
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 21:13
• Last Modified: 19 Nov 2019 21:13
• URI: https://theses.gla.ac.uk/id/eprint/75319