Amido and Chloro Ti and Zr complexes coordinated by ansa bis(amidinate) ligands with a rigid o-phenylene linker

Bis-amido and bis-chlorine TiIV and ZrIV complexes stabilized by ansa bis(amidinate) ligands were prepared in fairly good yields by reacting a (bis)amidine ligand [C6H4-1,2-{NC(tBu)N(2,6-R2C6H3)H}2 [R = Me (1), iPr (2)] with an equimolar amount of the appropriate metal precursor. The ligands coordination mode to MIV ions was found to be strongly affected by the steric hindrance of the amidinate ligands as well as by the nature of the ancillary groups bound to the metal center (NMe2 vs. Cl). Bis(amido) ligands with the 2,6-Me2C6H3 substituents at the amidinate nitrogens coordinate the zirconium ion in a tetradentate fashion both in solution and in the solid state. Compounds containing the bulkier 2,6-iPr2C6H3 units prefer a tridentate coordination mode. With the smaller TiIV ion, all the bis(amidinate) ligands from this series are tridentate in the solid state while they reversibly switch their denticity from tridentate to tetradentate in solution depending on the temperature. The ZrIV complex featuring with the bulkier bis(amidinate) ligand 2, shows a similar behavior to that of its TiIV analogue, with a tridentate ligand coordination at the solid state and a temperature induced denticity change in solution as a temperature function. Thermodynamic standard parameters for such a coordination change have been measured from the respective linear van't Hoff plots fitting. Finally, ZrIVbis(chloride) complexes show an unique coordination mode with both the bis(amidinate) ligands.

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