| Summary: | This work aims to expand the library of low-coordinate m-terphenyl metal complexes suitable for electronic investigation. Herein, the synthesis of a series of para-substituted m-terphenyl ligands is reported, featuring a range of different electron-donating and -withdrawing groups. The effects of ligand architecture are then studied with respect to the structural, electronic and magnetic properties of the metal complexes.
The synthesis of a series of para-functionalised m-terphenyl iodide ligand precursors, R-Ar-I, 3.2 – 3.8, is first described, with characterisation by X-ray crystallography and NMR spectroscopy. Lithiation of these compounds affords a series of para-substituted m-terphenyl lithium complexes [R-Ar-Li]2, 3.9 – 3.13, which, despite being structurally similar, possess different electronic environments at their lithium ions, as evidenced by 7Li NMR spectroscopy. From these lithium precursors, a number of two-coordinate m-terphenyl metal complexes is prepared, including the Group 12 diaryls (R-Ar)2M (M = Zn, Cd, Hg), 4.1 – 4.12, and the iron diaryls (R-Ar)2Fe, 5.1 – 5.5. For each metal series, X-ray crystallography shows that the complexes are structurally invariant, with little change in C–M–C bond lengths and angles as the para-group is varied. However, a combination of 1H, 13C, 113Cd and 199Hg NMR spectroscopies reveals electronic differences both on the ligand framework and at the Group 12 metal centre. For the iron complexes, additional electronic analysis is performed by IR, UV/Vis and X-ray photoelectron spectroscopies, as well as cyclic voltammetry. Furthermore, the magnetic properties of 5.1 – 5.5 are examined by SQUID magnetometry to determine their single-molecule magnet behaviour. Finally, the reactivity of the iron diaryls towards small molecules is probed, with attempts to bind an infrared-active handle to the metal centre to study its electronic properties via analysis of the IR stretching frequencies.
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