Exploring the chemistry of soft scorpionate ligands

• Main Author: Rajasekharan Nair, Rajeev
• Published: University of Strathclyde 2013
• Subjects: 540
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.632673

Alkylation of the soft scorpionate anions, TmR, Tbz and tzTtz have been successfully carried out. The resulting cationic species of TmMe were fully characterised. However, the formation of the cationic species is not always favourable and the alkylated products of Tbz and tzTtz were found to be unstable. The structures and degradation pathways of the three species were interrogated using ab-initio DFT calculations. This suggested that the B-N bond can lengthen when the scorpionate is alkylated and that this leads to thio-imidazole elimination. This work was extended to the synthesis of cyclic ring system initially by linking two sulphurs in the anion using dihalo-alkane species. Ring formation can also be effected using mild oxidising agents and treatment of TmMe and TmPh with NO+ and I₂ leads to the synthesis of a series of unique polycyclic heterocycles. The importance of B-N bond elongation to complex stability is investigated further using the Tbz anion. As expected Tbz is unable to form complexes with the hard metals e.g. cobalt. Treatment with soft metals (mercury, antimony and bismuth) does produce complexes but these are not stable. These metal complexes rearrange to form a new class of polycyclic rings. Studies using NO+ are extended to its chemistry of soft scorpionate metal complexes. A study was conducted which sought to use ruthenium complexes as nitric oxide scavengers. This chemistry failed to materialise and NO+ acts as a mild oxidising agent rather than a π acceptor with these species. % Buried volume analysis is performed using a series of soft scorpionates (TmR R = Me, iPr, tBu, and Ph) to calculate the steric demand of the ligands at the central metal atom. The study reveals that there is a modest effect when the scorpionate is supporting a four coordinated metal (e.g. zinc). However, for six coordinated metals (e.g. manganese as its tricarbonyl) the scorpionate has minimal influence.