Exploring small bite-angle PNP and PCP ligands for the rhodium-catalysed intermolecular hydroacylation of b-s-substituted aldehydes with alkenes and alkynes

Thesis

This thesis discusses the intermolecular hydroacylation reaction using cationic rhodium bis- phosphine complexes as catalysts. A series of small bite-angle rhodium bis-phosphine complexes have been prepared and characterised. The reactivity of these complexes has been investigated in order to gather information about the effect of subtle changes in the ligand design and they are compared to the previously reported catalysts.

Chapter 2 presents the challenges involved in the synthesis of small bite-angle isopropyl and cyclohexyl PNP and PCP bis-phosphine ligand containing rhodium complexes. These complexes have been fully characterised and screened in intermolecular hydroacylation reaction using 2- (methylthio)benzaldehyde (E) and 1-octene or 1-octyne as substrates. The formed complexes were shown to be very efficient and regioselective alkyne hydroacylation catalysts. The mechanism of the hydroacylation reaction was investigated using the isopropyl PNP complex [Rh(ⁱPrPNMePⁱPr₂)(C₆H₅F)][BAr^F₄] (11b).

Chapter 3 concentrates on developing new rhodium bis-phosphine complexes that involve a ligand incorporating the small bite-angle motif with the one of hemilability. The PNP complex [Rh((2-OMe-C₆H₄)₂PNMeP(2-OMe-C₆H₄)2)(C₆H₅F)][BAr^F₄] (41) was synthesised and analytically characterised. 41 was shown to be an active alkyne hydroacylation catalyst with more stability towards the catalyst deactivation pathway, reductive decarbonylation, compared to the previously investigated 11b. Additionally mechanistic studies using 41 were carried out.

The final chapter moves on to study the C-S activation ability of small bite-angle rhodium bis- phosphine complexes to remove the sulfur tether from the hydroacylation products at the end of the hydroacylation reaction. A screening is conducted to compare the reactivity of different small bite-angle ligands. Additionally, a detailed investigation is carried out to see the effect the C-S activation has on the hydroacylation reaction.

Authors: Pernik, I

• Publication date: 2014
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: small bite-angle; hydroacylation; homogeneous catalysis; rhodium; phosphine
• Subjects: Catalysis; Organometallic Chemistry