(Amido)- and (Chlorido)titanium and -zirconium Complexes Coordinated by ansa-Bis(amidinate) Ligands with a Rigid o-Phenylene Linker: (Amido)- and (Chlorido)titanium and -zirconium Complexes Coordinated by ansa-Bis(amidinate) Ligands with a Rigid o-Phenylene Linker

Bis(amido)-Ti-IV and -Zr-IV complexes stabilized by the bis(amidinate)ligands {C6H4-1,2-[NC(tBu)N(2,6-R2C6H3)](2)}M(NMe2)(2) [M = Zr-IV, R = Me (3), R = iPr (4); M = Ti-IV, R = Me (5), R = iPr (6)] and {C6H4-1,2-[NC(tBu) N(2,6-Me2C6H3)](2)}Zr(NMe2)(3)H (3 center dot HNMe2) were prepared in fairly good yields by treating 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 metal precursor M(NMe2)(4) (M = ZrIV, TiIV). The salt metathesis reactions between equimolar amounts of the sodium amidinates C6H4-1,2-[NC(tBu) N(2,6-R2C6H3)](2)Na-2 and ZrCl4(thf)(2) were also scrutinized to synthesize the corresponding ZrIV bis(amidinate) dichlorides {C6H4-1,2-[NC(tBu)N(2,6-R2C6H3)](2)}ZrCl2 [R = Me (7), iPr (8)]. The coordination mode of the ligand to the MIV ions was strongly affected by the steric hindrance of the amidinate ligand (Mevs. iPr-substituted aniline moieties) as well as by the nature of the ancillary groups bound to the metal center (NMe2 vs. Cl). The bis(amido) ligand with the 2,6-Me2C6H3 substituents at the amidinate nitrogen atoms coordinates to the zirconium ion in a tetradentate fashion both in solution and in the solid state (3 and 3 center dot HNMe2). The compounds containing the bulkier 2,6-iPr(2)C(6)H(3) units prefer a tridentate coordination mode (4). With the smaller Ti-IV ion, the bis(amidinate) ligands from this series are tridentate in the solid state (5 and 6), whereas they reversibly switch their denticity from tridentate to tetradentate (kappa(3) vs. kappa(4)) in solution depending on the temperature. The Zr-IV complex 4, featuring the bulkier bis(amidinate) ligand 2, shows a behavior similar to that of its Ti-IV analogue, that is, a tridentate ligand coordination in the solid state and a temperatureinduced denticity change in solution. The standard thermodynamic parameters for the kappa(3)/kappa(4) interconversions of the two model compounds 4 and 5 in [D-8]toluene solution were determined from the respective linear van't Hoff plots. Finally, the Zr-IV bis(chloride) complexes 7 and 8 invariably show a tetracoordinate mode for their bis(amidinate) ligands (1 and 2) in solution and in the solid state.