(Amido)‐ and (Chlorido)titanium and ‐zirconium Complexes Coordinated by ansa‐Bis(amidinate) Ligands with a Rigid o‐Phenylene Linker. Issue 20 (31st May 2017) - Tolpygin, Aleksei O.
Abstract : Bis(amido)–Ti IV and –Zr IV complexes stabilized by the bis(amidinate) ligands {C6 H4 ‐1, 2‐[NC( t Bu)N(2, 6‐R2 C6 H3 )]2 }M(NMe2 )2 [M = Zr IV, R = Me (3 ), R = i Pr (4 ); M = Ti IV, R = Me (5 ), R = i Pr (6 )] and {C6 H4 ‐1, 2‐[NC( t Bu)N(2, 6‐Me2 C6 H3 )]2 }Zr(NMe2 )3 H (3· HNMe2 ) were prepared in fairly good yields by treating a (bis)amidine ligand C6 H4 ‐1, 2‐[NC( t Bu)N(2, 6‐R2 C6 H3 )H]2 [R = Me (1 ), i Pr (2 )] with an equimolar amount of the metal precursor M(NMe2 )4 (M = Zr IV, Ti IV ). The salt metathesis reactions between equimolar amounts of the sodium amidinates C6 H4 ‐1, 2‐[NC( t Bu)N(2, 6‐R2 C6 H3 )]2 Na2 and ZrCl4 (thf)2 were also scrutinized to synthesize the corresponding Zr IV bis(amidinate) dichlorides {C6 H4 ‐1, 2‐[NC( t Bu)N(2, 6‐R2 C6 H3 )]2 }ZrCl2 [R = Me (7 ), i Pr (8 )]. The coordination mode of the ligand to the M IV ions was strongly affected by the steric hindrance of the amidinate ligand (Me‐ vs. i Pr‐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‐Me2 C6 H3 substituents at the amidinate nitrogen atoms coordinates to the zirconium ion in a tetradentate fashion both in solution and in the solid state (3 and3· HNMe2 ). The compounds containing the bulkier 2, 6‐ i Pr2 C6 H3 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 and6 ), whereas they reversibly switch their denticity from tridentate to tetradentate (κ 3 vs. κ 4 ) in solution depending on the temperature. The Zr IV complex4, featuring the bulkier bis(amidinate) ligand2, shows a behavior similar to that of its Ti IV analogue, that is, a tridentate ligand coordination in the solid state and a temperature‐induced denticity change in solution. The standard thermodynamic parameters for the κ 3 /κ 4 interconversions of the two model compounds4 and5 in [D8 ]toluene solution were determined from the respective linear van't Hoff plots. Finally, the Zr IV bis(chloride) complexes7 and8 invariably show a tetracoordinate mode for their bis(amidinate) ligands (1 and2 ) in solution and in the solid state. Abstract : A series of Ti IV and Zr IV complexes stabilized by o ‐phenylenebis(amidinate) ligands are synthesized and characterized. A rather complex balance of different steric features, which spans from the nature of the substituents at the amidinate nitrogen atoms to the ionic radius of the metal ion and the type of ancillary ligands, affects the final coordination mode of the ligands.