Covalent & Supramolecular Phosphorus Ligands for Linear-Selective Hydroformylations

Identifier:  TDX:4075

Handle: https://hdl.handle.net/20.500.11797/TDX4075

Authors:  Romero Navarro, Andrés

Abstract:
The hydroformylation of internal octenes or the terminal one, catalysed by cobalt and Xantphos as ligand, or by cobalt-Xantphos complexes, has displayed a high selectivity towards the formation of aldehydes. The constant ratio in the different aldehyde regioisomers, independently of the starting octene isomer, led us to hypothesise that a tandem isomerization-hydroformylation transformation was taking place under optimised conditions. Moreover, the hydroformylations of a mixture of octene, heptene or hexene isomers were reported with excellent aldehyde selectivity and diminished formation of side-products (up to 73% selectivity towards the linear aldehyde). The rhodium-catalysed hydroformylation of terminal alkenes was described employing bisphosphite ligands with a distal regulation site. The use of alkali metal BArF salts as regulation agents enhanced the formation of the linear aldehydes (up to 99:1 l/b ratio and 90% yield), demonstrating the efficacy of the supramolecular regulation approach. This approach was also applied to obtain high-value aldehydes for the fragrance industry. The supramolecular rhodium catalysts for hydroformylations were also combined with Pd(0) derivatives to obtain bimetallic catalysts, which led to the isomerization/hydroformylation tandem reaction for mixtures of alkenes. The catalytic species, which are present in the rhodium-based catalytic cycle, as well as conversion curves for the hydroformylations of selected substrates, have been studied by High-Pressure NMR complexation studies and by FlowNMR operando spectroscopy. A monophosphite ligand based on the carbazole scaffold was efficiently synthesised. The purpose of synthesising this ligand was to supramolecularly maximise the activity and regioselectivity of hydroformylation reactions employing anionic regulation agents. Thus, the preliminary studies on the hydroformylation of two benchmark alkenes and studies on anionic regulation were performed.