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Amido [ButC(NC6H4‐2‐OMe)2]2LnN(SiMe3)2 (Ln = Y (3), Nd (4)) and borohydrido complexes [ButC(NC6H4‐2‐OMe)2]2LnBH4 (Ln = Y (5), Nd (6)) coordinated by new amidinate ligand bearing two pendant anisolyl groups are synthesized. According to X‐ray analysis in complexes 3 and 4 one amidinate ligand is coordinated to the Ln3+ cation in a bidentate fashion (κ2‐NN), while the second one is tetradentate (κ4‐NNOO). At the same time in borohydrido neodymium complex 6 the amidinate ligands demonstrate κ4‐NNOO and κ3‐NNO coordination modes. Complexes 3–6 proved to be efficient initiators for ring‐opening polymerization of rac‐lactide and allow for achieving quantitative conversion of 500 equivalents of monomer into polymer in 0.3–4.5 h at 25 °C. The polymerization of ε‐caprolactone initiated by 3–6 proceeds much faster under similar conditions. [ABSTRACT FROM AUTHOR]

Bis(amido)–TiIV and –ZrIV complexes stabilized by the bis(amidinate) ligands {C6H4-1,2-[NC(tBu)N(2,6-R2C6H3)]2}M(NMe2)2 [M = ZrIV, R = Me (3), R = iPr (4); M = TiIV, R = Me (5), R = iPr (6)] and {C6H4-1,2-[NC(tBu)N(2,6-Me2C6H3)]2}Zr(NMe2)3H (3·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)]2Na2 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 (Me- vs. 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·HNMe2). The compounds containing the bulkier 2,6-iPr2C6H3 units prefer a tridentate coordination mode (4). With the smaller TiIV 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 (κ3 vs. κ4) in solution depending on the temperature. The ZrIV complex 4, featuring the bulkier bis(amidinate) ligand 2, shows a behavior similar to that of its TiIV 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 κ3/κ4 interconversions of the two model compounds 4 and 5 in [D8]toluene solution were determined from the respective linear van't Hoff plots. Finally, the ZrIV 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. [ABSTRACT FROM AUTHOR]