Influence of the basicity of internal bases in diiron model complexes on hydrides formation and their transformation into protonated diiron hexacarbonyl form

Reaction of 2-(1-(pyridin-2-yl)ethyl)propane-1,3-dithiol with tri-iron dodecacarbonyl afforded a diiron pentacarbonyl complex, [Fe2L(CO)5] (A and H2L = 2-methyl-2-(1,2,5,6-tetrahydropyridin-2-yl)propane-1,3-dithiol). In the reaction, the pyridinyl ring of the original ligand was partially hydrogenated during the reaction. This complex was fully characterised by using crystallographic, infrared, and NMR spectroscopic techniques. Formation reaction of its bridging hydride and subsequent conversion into its protonated diiron hexacarbonyl complex, [Fe2L(CO)6] (ACOH+ in which the N atom of L is decoordinated and protonated), were experimentally and theoretically investigated. Results for this complex alongside with theoretic investigations into other diiron pentacarbonyl analogues revealed positive correlation of basicity of the internal bases of these investigated complexes to bridging hydrides formation. But subsequent conversion of these bridging hydrides into protonated diiron hexacarbonyl complexes was not solely dictated by the basicity. Protophilicity of the internal base and lability of its coordination with the diiron centre play also an important role as revealed by experimental and theoretic investigations.

Basicity of the internal base of the model complexes correlates positively to their protonation chemistry. But the conversion of their bridging hydride into their corresponding protonated hexacarbonyl complexes via intramolecular migration mechanism was not solely dictated by this basicity. Instead, behaviours of the bridging hydrides in solution were concertedly governed by basicity, protophilicity, and lability of the coordination between the diiron centre and the base as revealed by experimental and theoretic investigations.Figure optionsDownload as PowerPoint slide