Rigid, Dianionic Carbene Scaffolds for Phosphenium Catalysis

A viable synthetic method for the preparation of a novel imidazolium NHC precursor, 1,3-bis(2-methoxyphenyl)-4,5-dimethylimidazolium ([IAnisMeH]+), was developed, and several salts with different anions prepared. Said precursor was converted to another novel NHC precursor, 1,3-bis(2-hydroxyphenyl)-4,5- dimethylimidazolium ([IPhenolMeH]+), by demethylation of the o-anisole substituents and two different salts were prepared. Having synthesised the imidazolium precursors to two novel NHCs, deprotonation of both species proved to be challenging. The best methods for the in situ synthesis of the corresponding free NHCs were either the addition of NaH/tBuOK or LiHMDS depending on the precursor employed. The coordination of IAnisMe was explored with the transition metals such as copper, nickel, and silver and with the metalloid, selenium. Thus, several mono-NHC complexes were synthesised along with one homoleptic, cationic copper complex, to show the versatility of the ligand and gain an understanding of the ligand's electronic properties. All the metal complexes were characterised by multinuclear NMR, single crystal X-ray diffraction, and combustion analysis where possible. Furthermore, coordination of both IAnisMe and IPhenolateMe to phosphorus was attempted, however no conclusive proof of target complex formation was acquired. The formation of the desired phosphenium cation targets remains speculative as a result.