Synthesis and Coordination of Narrow Bite Angle P^N, S^N and P^P Compounds

Abstract

This thesis presents studies on the synthesis and coordination of a range of narrow bite angle iminophosphine (P^N, (R)2PC(R′)N(R′′)), thiolated iminophosphine (S^N, (R)2P(S)C(R′)N(R′′)) and diphosphinoamine (P^P, (R2P)2N(R′′)) ligands.
Chapter 1 gives an introduction to reductive elimination and the various factors that control this fundamental process, specifically the impact of ligand-imposed steric and electronic factors, alongside ligand bite angle effects for bidentate ligands. The various mechanisms for reductive elimination are also described.
In Chapter 2, the synthesis of iminophosphine, thiolated iminophosphine and diphosphinoamine compounds is presented. A new synthetic method for the preparation of iminophosphines is described, using a “one-pot” synthesis. The success of this method was found to depend on the nature of the substituents at the backbone C centre, with a tBu substituent giving the greatest success: the synthesis occurred readily and the product was stable. Characterisation of these novel compounds focuses on NMR spectroscopic techniques.
The coordination of iminophosphines and thiolated iminophosphines with palladium(II) compounds was assessed and is presented in Chapter 3. Coordination of these ligands with a palladium dichloride fragment was found to give both [PdCl2(κ2-L^L′)] complexes and C–H activated Cl-bridged palladium dimers. To assess the effectiveness of the iminophosphine, thiolated iminophosphine and diphosphinoamine compounds in mediating reductive elimination, their coordination with a palladium dimethyl fragment was explored, with the resulting production of ethane being monitored by NMR spectroscopy. The iminophosphine metal scaffolds were found to induce reductive elimination more readily than thiolated iminophosphines, whereas diphosphinoamines did not promote reductive elimination. Of the iminophosphines used in this thesis, a dependence on steric bulk was found; iminophosphines containing substituents with greater bulk resulted in faster reductive elimination, as monitored by the appearance of ethane.