Issue 41, 2009

Neutral and cationic aluminium complexes containing a chiral (OSSO)-type bis(phenolato) ligand: synthesis, structures and polymerization activity

Abstract

Reaction of trimethylaluminium with the linked bis(phenol) trans-1,4-dithiocyclohexanediyl-2,2′-bis(4,6-di-tert-butylphenol) (cydtbpH2, 1a) led to the chiral methyl aluminium complex [Al(cydtbp)Me] (2a) as both racemate and resolved enantiomers, which were characterized by multinuclear NMR spectroscopy and elemental analysis. Rac-{trans-1,2-dithiocyclohexanediyl-2,2′-bis(6-tert-butyl-4-methylphenol)} (cytbmpH2, rac-1b) similarly gave rac-2b. Single-crystal X-ray diffraction of (S,S)-2a and rac-2b showed a strongly distorted trigonal bipyramidal geometry with significantly differing Al–S distances. Reaction of rac-2b with (−)-borneol gave the alkoxy complex 5 as a mixture of two diastereomers. Methyl abstraction from the neutral metal complex rac-2a using B(C6F5)3 gave the cationic complex [rac-Al(cydtbp)(THF)2]+[MeB(C6F5)3] (rac-6·(THF)2) that according to X-ray crystallography adopts an octahedral coordination geometry. Upon reacting trimethylaluminium with a bis(phenol) with a longer link, 3,4-trans-butanediyl-1,6-dithiahexanediyl)-2,2′-bis(6-tert-butyl-4-methylphenol), (cmtbmpH2, 3, a dinuclear compound 4 was obtained that contains two square pyramidal aluminium centers with two “fly-over” bis(phenolate) ligands. The neutral methyl aluminium complexes are active in the polymerization of methyl methacrylate (MMA) and in the ring-polymerization of rac-lactide (LA), producing PMMAs and PLAs in a controlled fashion. The cationic aluminium complexes were active in the cationic polymerization of isoprene and benzofuran.

Graphical abstract: Neutral and cationic aluminium complexes containing a chiral (OSSO)-type bis(phenolato) ligand: synthesis, structures and polymerization activity

Supplementary files

Article information

Article type
Paper
Submitted
11 May 2009
Accepted
11 Aug 2009
First published
25 Aug 2009

Dalton Trans., 2009, 9033-9042

Neutral and cationic aluminium complexes containing a chiral (OSSO)-type bis(phenolato) ligand: synthesis, structures and polymerization activity

B. Lian, H. Ma, T. P. Spaniol and J. Okuda, Dalton Trans., 2009, 9033 DOI: 10.1039/B909287K

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