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Unbridged bidentate aluminum complexes supported by diaroylhydrazone ligands: Synthesis, structure and catalysis in polymerization of ε ‐caprolactone and lactides
Author(s) -
Nie Kun,
Wang Changan,
Cheng Xueli,
Li Jikun,
Han Yinfeng,
Yao Yingming
Publication year - 2020
Publication title -
applied organometallic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.53
H-Index - 71
eISSN - 1099-0739
pISSN - 0268-2605
DOI - 10.1002/aoc.5627
Subject(s) - chemistry , denticity , trigonal bipyramidal molecular geometry , catalysis , polymerization , stereochemistry , caprolactone , crystallography , monomer , crystal structure , metal , ring opening polymerization , square pyramid , medicinal chemistry , organic chemistry , polymer
A series of novel diaroylhydrazone aluminum complexes have been synthesized and well‐defined structurally, and their catalytic performance in the polymerization of ε ‐caprolactone and lactides have also been evaluated. Complexes [(L 1–4 ) 2 AlMe] ( 1 – 4 ) {[L 1 = (3,5‐ t Bu 2 –2‐OMe‐C 6 H 2 )CH=NNCOC 6 H 5 ], [L 2 = (3,5‐ t Bu 2 –2‐OMe‐C 6 H 2 )CH=NNCO(C 6 H 4 –4‐OCH 3 )], [L 3 = (3,5‐ t Bu 2 –2‐OMe‐C 6 H 2 )CH=NNCO(C 6 H 4 –4‐Br)] and [L 4 = (2‐OMe‐C 6 H 4 )CH=NNCO(C 6 H 4 –4‐ t Bu)]} were prepared through treatment of AlMe 3 with the corresponding proligands L 1–4 H in molar ratios of 1: 1 or 1: 2. Chemical structures of all the complexes were well‐defined by elemental analysis, NMR spectra as well as single‐crystal X‐ray study. Complexes [(L 1–4 ) 2 AlMe] ( 1 – 4 ) in this work represent the first examples of aluminum complexes of aroylhydrazone ligands with crystallographic characterization. Specifically, they are all in monomeric form with a penta‐coordinated aluminum center, including two approximately co‐planar five‐membered metallacycles with aluminum. Introduced bulky tert ‐butyl substituents in aroylhydrazone ligands could affect the geometry around the central metal which is a distorted square‐based pyramid in complexes 1 – 3 while being a trigonal bipyramidal in complex 4 , thus affecting their catalytic behaviors. The complexes can successfully catalyze the ring‐opening polymerization of ε ‐caprolactone and L ‐lactide under mild conditions without any activator. In addition, complexes 1 – 4 could also polymerize rac ‐lactide, affording atactic polylactides with high conversions and good controllability in relatively short reaction time.