PhD conferral T. van Dijk
Aula, Vrije Universiteit Amsterdam
Iminophosphanes: Synthesis and Coordination Chemistry. Reviving the art of nitrilium ion chemistry
T. van Dijk
Prof. K. Lammertsma, copromotors Dr J.C. Slootweg and Dr A.W. Ehlers
Amsterdam Institute for Molecules, Medicines and Systems
In his thesis, Tom van Dijk describes the use of nitrilium ions as synthons for imine-groups in various structures, of which 1,3-iminophosphanes are the main focus.
Readily accessible nitrilium triflates are convenient imine building blocks for the expedient synthesis of a novel class of 1,3-P,N-ligands. Only a few 1,3-iminophosphanes have been described in the literature, which is surprising since these molecules are highly interesting hybrid ligands featuring both a nitrogen and phosphorus coordination site. Furthermore, these ligands display various coordination modes, such as monodentate via phosphorus or nitrogen or bidentate through both phosphorus and nitrogen atoms. In contrast to the related and often applied pyridyldiphenylphosphane (PyPh2P), the imine substituents of 1,3-iminophosphanes can be readily varied using nitrilium ion chemistry, allowing facile tuning of the properties of these ligands. The coordination chemistry with gold(I) and rhodium(I) of both anionic and neutral 1,3-iminophosphanes has been thoroughly studied, to probe the properties of these ligands.
All nitrilium ions are sensitive towards moisture (e.g. from air) and need to be handled under an inert atmosphere. Nitrilium triflates with a N-cyclohexyl or N-iso-propyl group and C-phenyl group are unstable at room temperature and also need to be handled at –20 °C. By addition of a weakly nucleophilic base, such as 4-dimethylaminopyridine, an adduct is formed, which is stable at room temperature and is significantly more stable towards hydrolysis under atmospheric conditions. These adducts still function as imine synthons as was shown by the reaction with diphenylphosphane to give 1,3-iminophosphanes and with various nitrogen based nucleophiles giving amidines.