Developing sustainable methods in polar main group chemistry

Student thesis: Doctoral Thesis

Abstract

Sustainability in polar main group organometallic chemistry was investigated in two approaches: the investigation of alternative, more sustainable, solvents rather the traditional VOCs for use in selected addition reactions of pyrophoric organolithium reagents in air and the use of s-block bimetallic cooperative catalysis in isomerisation reactions in which homometallic compounds struggle, as an alternative to less abundant and more expensive transition metal catalysts.The ultrafast addition of a range of aryllithium reagents to nitriles has been accomplished using glycerol and water as solvent in the presence of air. These occurred heterogeneously, being ‘on glycerol’ and ‘on water’, with the addition being faster than the competitive hydrolysis of the aryllithium species, therefore providing a convenient route to produce imines and onward to ketones for a range of nitriles and aryllithium reagents.2-MeTHF was used as a solvent in the amidation of esters under air. These reactions involved the homogeneous addition of lithium amide solutions to esters to form the product the carboxamides. The reactions occurred in 20 s, with the amidation occurring quicker than the competing hydrolysis. The lifetime of the lithium amide in air was also examined.Mixed s-block metal organometallic reagents have been successfully utilised in the catalytic intramolecular hydroalkoxylation of alkynols. This success has been attributed to the unique manner in which the two metals can work cooperatively to overcome the challenges of the reaction: namely OH activation and coordination to and then addition across a C≡C bond. Of a series of alkali metal magnesiates tested a combination of K2Mg(CH2SiMe3)4(PMDETA)2/18-crown-6 was found to be the best catalyst. After optimising the reaction substrate scope was examined to probe the range and robustness of the system. A series of alkynols, including terminal and internal alkynes which contain a variety of potentially reactive functional groups, were cyclised. In comparison to previously reported monometallic systems, bimetallic K2Mg(CH2SiMe3)4(PMDETA)2/18-crown-6 displays enhanced reactivity towards internal alkynol-cyclisation. Kinetic studies revealed an inhibition effect of substrate on the catalysts via adduct formation and requiring dissociation prior to the rate limiting cyclisation step. Following from this success the possibility of performing the isomerisation of terminal alkynes to internal alkynes was examined. Despite some successfully catalysed reactions the optimal conditions remained elusive.
Date of Award17 Jan 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)
SupervisorEva Hevia (Supervisor) & Charles O'Hara (Supervisor)

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