Catalysis of hydroelementation reactions using m-terphenyl complexes

South, Amy (2020) Catalysis of hydroelementation reactions using m-terphenyl complexes. PhD thesis, University of Nottingham.

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Abstract

Herein the synthesis and catalytic properties of low-coordinate m-terphenyl transition metal complexes are reported. Previous work in the group has shown that these complexes act as precatalysts for the cyclotrimerisation and hydrophosphination of isocyanates. This project builds on this work and aims to expand the scope of these precatalysts.

The diaryl complexes M(2,6-Mes2C6H3)2 (M = Fe, Co, Zn) are shown to catalyse the hydroamination of isocyanates forming urea derivatives. The use of aromatic isocyanates results in a formal diinsertion of the isocyanate into the N–H bond affording biuret derivatives. These products can be selectively formed by tuning the reaction conditions; performing the reaction in THF solvent results in the exclusive formation of the urea and the use of an excess of the isocyanate results in the exclusive formation of the biuret. The use of diisopropylamine resulted in the tri- and tetrainsertion of the isocyanate into the N–H bond. The hydrophosphination of carbodiimides to form phosphaguanidines, was also investigated. This transformation required higher temperatures compared to the catalysis with isocyanates and the diinsertion of the carbodiimide is only observed with very low conversions. Stoichiometric reactions and catalyst poisoning tests were carried out in order to investigate the mechanism of the catalysis.

The complexes M(2,6-Mes2C6H3)2 are precatalysts for the hydroboration of isocyanates and carbodiimides. The monohydroboration product was shown to be the major product for all the substrates although small amounts of the dihydroboration product were observed with the aromatic isocyanates. The use of tBuNCO resulted in the hydrodeoxygenation of the isocyanate forming tBuN(BPin)CH3 and O(BPin)2.

A series of transition metal complexes containing an m-terphenyl ligand and the bidentate ligand TMEDA, with the form M(2,6-Mes2C6H3)X(tmeda) (M = Mn, X = Br ; M = Fe, X = Cl; M = Co, X = Br; M = Zn, X = Cl) were synthesised. The DPPE and DME analogues for 4 M = Fe were also isolated. These complexes were characterised by X-ray crystallography, NMR spectroscopy and the magnetic moments were measured using Evans method.

The reduction of Mn(2,6-Mes2C6H3)Br(tmeda) with KC8 was attempted but resulted in the formation of the dimer [(tmeda)MnBr(μ-Br)]2. Attempts to abstract the halide ligand with halide abstracting agents were unsuccessful. A salt metathesis reaction was carried out between and Na[N(SiMe3)2] which afforded Zn(2,6-Mes2C6H3)[N(SiMe3)2] and Zn[N(SiMe3)2]2.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Kays, Deborah
Keywords: Hydroelementation reactions, M-terphenyl complexes
Subjects: Q Science > QD Chemistry > QD146 Inorganic chemistry
Faculties/Schools: UK Campuses > Faculty of Science > School of Chemistry
Item ID: 61195
Depositing User: South, Amy
Date Deposited: 08 Sep 2020 08:58
Last Modified: 31 Dec 2020 04:40
URI: http://eprints.nottingham.ac.uk/id/eprint/61195

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