The palladium-catalysed aerobic oxidative homocoupling reaction of arylboronic acids in aqueous micellar medium: kinetic and mechanistic studies

Othman, Mazin Abdulkhaliq 2011. The palladium-catalysed aerobic oxidative homocoupling reaction of arylboronic acids in aqueous micellar medium: kinetic and mechanistic studies. PhD Thesis, Cardiff University.

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Abstract

This thesis is divided into five Chapters. The first Chapter introduces water and micellar solutions as reaction medium, catalysis, palladium catalysts, the Suzuki cross-coupling and the oxidative homocoupling of arylboronic acids. The second Chapter describes studies of the aerobic oxidative homocoupling reaction of arylboronic acids in aqueous micellar media using Pd(bimsulfide)Cl₂ as a (pre) catalyst. Our results, in particular a bell-shaped pH-rate profile, favour a reaction mechanism where the rate-determining step is transmetalation involving a palladium-hydroxo complex and the acidic form of the arylboronic acid, although an alternative mechanism involving a palladium- aqua complex reacting with the arylboronate cannot be excluded. The third Chapter presents the synthesis of Pd-CTAB nanoparticles and their use as catalysts for the aerobic oxidative homocoupling of phenylboronic acid in aqueous micellar solutions. Again, a bell-shaped pH dependence of observed rate constant (&0bs) was observed which, together with our other results, suggests that the reaction again involves pH-dependent Pd-hydroxo and Pd-aqua species. We cannot confirm whether catalysis occurs on the surface of the nanoparticles or through leached Pd atoms/ions. The fourth Chapter embraces bimetallic core-shell Au-Pd nanoparticles encapsulated in a shell of poly(7V-isopropylacrylamide) (pNIPAM) of different sizes and morphologies, as well as Pd-pNIPAM nanocomposites. Both systems were used to catalyse the aerobic oxidative homocoupling reaction of PBA in aqueous micellar medium. Our kinetic studies gave similar results as observed for the Pd-complex described in Chapter 2 and the nanoparticles described in Chapter 3. Hence, an analogous mechanism was proposed. The observed rate constant showed non-Eyring-like behaviour, highlighting the dependence of Abs on the state (swollen or collapsed) of the pNIPAM shell surrounding the nanoparticles. Finally, the fifth Chapter describes preliminary studies exploring aerobic oxidative cross-coupling reactions of arylboronic acids and their derivatives in aqueous micellar solutions. Conclusions, future outlooks, remarks and suggestions finish Chapter 5 and the thesis.

Item Type:	Thesis (PhD)
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
ISBN:	9781303223372
Date of First Compliant Deposit:	30 March 2016
Last Modified:	19 Mar 2016 23:32
URI:	https://orca.cardiff.ac.uk/id/eprint/55140

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