Doctor of Philosophy
Paul J. Ragogna
The chemistry of the main group elements with nitrogen based ligands has been an area that has received little attention in comparison to transition metals. The preliminary investigations have focused on groups 13 and 14 revealing new bonding motifs and interesting reactivity. This has motivated us to synthesize group 15 and 16 derivatives in new bonding arrangements capable of activating small molecules.
In pursuit of isolating such species, the reactivity of sulfur dichloride and “S(OTf)2” with a series of diazabutadiene (DAB) ligands was explored. The substitution on the ligand was extremely influential on the outcome of the reaction. Alkyl groups on the nitrogen atom resulted in the production of 1,2,5-thiadiazolium heterocycles by loss of an alkyl group whereas methyl groups on the backbone carbon atom led to reaction with the eneamine tautomer of the ligand to give N,C-bound heterocycles. This could be avoided with aryl groups or hydrogen atoms on the backbone carbons and aryl groups on the nitrogen centres. The latter reactions produced dicationic analogues of the N-Heterocyclic carbene, the first examples for sulfur.
The chemistry of the chalcogen halides and bistriflate synthons with the diiminopyridine (DIMPY) ligand showed similar trends. Methyl groups on the backbone carbon resulted in bonding through a methyl carbon whereas phenyl groups or hydrogen atoms in the same position produced N,N’,N’’-chelated cations or dications. The dicationic triflate salts are stable in the open atmosphere, a remarkable feature for highly charged cations. The chemistry was also extended to phosphorus. Collectively these species represent the first DIMPY complexes for phosphorus, sulfur, selenium and tellurium.
Sulfur(II) dications with amine donors, namely pentamethyldiethylenetriamine could also be prepared. The complex was highly unstable indicating imine and pyridine groups offer greater stabilization. In addition to the chelate complexes, monodentate pyridine ligands coordinate to a dicationic sulfur centre. The monodentate species displayed reactivity with a variety of unsaturated organic substrates. Altering the group on the para position of the pyridine proved to have a significant effect on the reactivity indicating potential tuneability for the system.
Martin, Caleb D., "Uncovering New Bonding Motifs: The Synthesis of Chalcogen and Phosphorus Complexes Supported by Nitrogen Based Ligands" (2011). Electronic Thesis and Dissertation Repository. 287.