Zinc(II) complexes containing <i>N′</i>-aromatic group substituted <i>N</i>,<i>N</i>′,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)amines: Synthesis, characterization, and polymerizations of methyl methacrylate and <i>rac</i>-lactide
Creators: name: Sujin Shin
name: Hyungwoo Cho
name: Hyosun Lee
name: Saira Nayab
name: Younghak Kim
Publisher: name: Taylor & Francis
Year: 2018
Subjects: subject: Biophysics
subject: Biochemistry
subject: Medicine
subject: Genetics
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: Molecular Biology
subject: Neuroscience
subject: Pharmacology
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Sociology
subject: FOS: Sociology
subject: FOS: Sociology

description: A novel series of Zn(II) complexes <b>[L</b><sub><b>n</b></sub><b>ZnCl</b><sub><b>2</b></sub><b>]</b> (L<sub>n</sub> = L<sub>A</sub> − L<sub>F</sub>) based on <i>N</i>,<i>N</i>′,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)amine bidentate ligands, <i>N,N</i>-bis((1H-pyrazol-1-yl)methyl)-3,5-dimethylaniline [<b>L</b><sub><b>A</b></sub>], <i>N</i>,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)-2,6-dimethylaniline [<b>L</b><sub><b>B</b></sub>], <i>N</i>,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)-2,6-diethylaniline [<b>L</b><sub><b>C</b></sub>], <i>N</i>,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)-2,6-diisopropylaniline [<b>L</b><sub><b>D</b></sub>], <i>N</i>,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)-4-bromoaniline [<b>L</b><sub><b>E</b></sub>] and <i>N</i>,<i>N</i>-bis((1H-pyrazol-1-yl)methyl)benzhydrylamine [<b>L</b><sub><b>F</b></sub>], has been synthesized and characterized. X-ray structures of these Zn(II) complexes showed a distorted tetrahedral geometry. No interaction exists between the N<sub>amine</sub> and the Zn(II) center in the <b>[L</b><sub><b>n</b></sub><b>ZnCl</b><sub><b>2</b></sub><b>]</b> (L<sub>n</sub> = L<sub>A</sub> − L<sub>F</sub>) complexes, resulting in formation of an eight-membered chelate ring. <b>[L</b><sub><b>F</b></sub><b>ZnCl</b><sub><b>2</b></sub><b>]</b> exhibited the highest catalytic activity (3.95 × 10<sup>4</sup> g PMMA/mol·Zn·h) for the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60 °C and yielded high molecular weight (<i>M</i><sub>w</sub>) (11.0 × 10<sup>5</sup> g/mol) of poly(methylmethacrylate) (PMMA). All the complexes resulted in syndiotactic enriched PMMA with high <i>T</i><sub>g</sub> (125–131 °C). The steric bulk of ligand architecture plays an influential role in controlling the catalytic activity and stereoregularity of the resultant PMMA. Further, alkyl derivatives <b>[L</b><sub><b>n</b></sub><b>ZnMe</b><sub><b>2</b></sub><b>]</b> (L<sub>n</sub> = L<sub>A</sub> − L<sub>F</sub>) of synthesized Zn(II) complexes, generated <i>in situ</i>, showed moderate to high activities toward ring opening polymerization (ROP) of <i>rac</i>-lactide (<i>rac</i>-LA) and yielded heterotactic polylactide (PLA) with <i>P</i><sub>r</sub> up to 0.95 at −50 °C. The activity and stereoselectivity toward ROP of <i>rac</i>-LA by these dimethyl Zn(II) complexes should be considered as a combined effect of steric hindrance and electronic density around the metal center.