Synthetic, structural and catalysis studies of Ni(II) and Cu(II) complexes of a series of phenoxy-ketimine ligands with controlled variations of sterics, namely 2-[1-(2,6-diethylphenylimino)ethyl]phenol (
1a), 2-[1-(2,6-dimethylphenylimino)ethyl]phenol (
1b) and 2-[1-(2-methylphenylimino)ethyl]phenol (
1c), are reported. Specifically, the ligands
1a,
1b and
1c were synthesized by the TiCl
4 mediated condensation reactions of the respective anilines with
o-hydroxyacetophenone in 21–23% yield. The nickel complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}
2Ni(II) (
2a) and {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}
2Ni(II) (
2b), were synthesized by the reaction of the respective ligands
1a and
1b with Ni(OAc)
2 · 4H
2O in the presence of NEt
3 as a base in 71–75% yield. The copper complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}
2Cu(II) (
3a), {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}
2Cu(II) (
3b) and {2-[1-(2-methylphenylimino)ethyl]phenoxy}
2Cu(II) (
3c) were synthesized analogously by the reactions of the ligands
1a,
1b and
1c with Cu(OAc)
2 · H
2O in 70–87% yield. The molecular structures of the nickel and copper complexes
2a,
2b,
3a,
3b and
3c have been determined by X-ray diffraction studies. Structural comparisons revealed that the nickel centers in
2a and
2b are in square planar geometries while the geometry around the copper varied from being square planar in
3a and
3c to distorted square planar in
3b. The catalysis studies revealed that while the copper complexes
3a,
3b and
3c efficiently catalyze ring-opening polymerization (ROP) of l-lactide at elevated temperatures under solvent-free melt conditions, producing polylactide polymers of moderate molecular weights with narrow molecular weight distributions, the nickel counterparts
2a and
2b failed to yield the polylactide polymer.
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