(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 {C 6 H 4 ‐1,2‐[NC( t Bu)N(2,6‐R 2 C 6 H 3 )] 2 }M(NMe 2 ) 2 [M = Zr IV , R = Me ( 3 ), R = i Pr ( 4 ); M = Ti IV , R = Me ( 5 ), R = i Pr ( 6 )] and {C 6 H 4 ‐1,2‐[NC( t Bu)N(2,6‐Me 2 C 6 H 3 )] 2 }Zr(NMe 2 ) 3 H ( 3· HNMe 2 ) were prepared in fairly good yields by treating a (bis)amidine ligand C 6 H 4 ‐1,2‐[NC( t Bu)N(2,6‐R 2 C 6 H 3 )H] 2 [R = Me ( 1 ), i Pr ( 2 )] with an equimolar amount of the metal precursor M(NMe 2 ) 4 (M = Zr IV , Ti IV ). The salt metathesis reactions between equimolar amounts of the sodium amidinates C 6 H 4 ‐1,2‐[NC( t Bu)N(2,6‐R 2 C 6 H 3 )] 2 Na 2 and ZrCl 4 (thf) 2 were also scrutinized to synthesize the corresponding Zr IV bis(amidinate) dichlorides {C 6 H 4 ‐1,2‐[NC( t Bu)N(2,6‐R 2 C 6 H 3 )] 2 }ZrCl 2 [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 (NMe 2 vs. Cl). The bis(amido) ligand with the 2,6‐Me 2 C 6 H 3 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· HNMe 2 ). The compounds containing the bulkier 2,6‐ i Pr 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 (κ 3 vs. κ 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 temperature‐induced denticity change in solution. The standard thermodynamic parameters for the κ 3 /κ 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.