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Alcoholysis of Aluminum Alkyls Supported by Bulky Phenoxide Ligands: Synthesis, Characterization, and ϵ‐Caprolactone Polymerization Activity of Two Dimeric Aluminum Isopropoxides
Author(s) -
Taden Insa,
Kang HakChul,
Massa Werner,
Spaniol Thomas P.,
Okuda Jun
Publication year - 2000
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/(sici)1099-0682(200003)2000:3<441::aid-ejic441>3.0.co;2-m
Subject(s) - chemistry , polymerization , monomer , dimer , alkyl , alkoxide , toluene , polymer chemistry , caprolactone , crystal structure , aluminium , molecule , crystallography , stereochemistry , polymer , catalysis , organic chemistry
Reaction of trialkylaluminum Al 2 R 6 (R = Me, Et) with 2,2′‐methylenebis(6‐ tert ‐butyl‐4‐methylphenol) (mbmpH 2 ) gives the dimeric mono(alkyl) complex [Al(mbmp)R] 2 with bridging oxygen atoms. Reaction of [Al(mbmp)R] 2 with one equiv. of 2‐propanol results in the formation of the dimeric isopropoxide [Al(mbmp)(μ‐O i Pr)] 2 . Single‐crystal X‐ray analysis shows a C 2h ‐symmetric structure with a planar Al 2 O 2 core. Monomeric methylbis(2,6‐di‐ tert ‐butyl‐4‐methylphenolato)aluminum, AlMe(OC 6 H 2 ‐2,6‐ t Bu 2 ‐4‐Me) 2 (MAD), was found to react with one equiv. of 2‐propanol to give a dimeric isopropoxide [AlMe(OC 6 H 2 ‐2,6‐ t Bu 2 ‐4‐Me)(μ‐O i Pr)] 2 in which the bulky phenolate, instead of the methyl group, has been displaced. According to the single‐crystal X‐ray structure analysis, the molecule contains a similar Al 2 O 2 core, but the two 2,6‐di‐ tert ‐butyl‐4‐methylphenolato ligands are cis ‐ and orthogonally arranged to each other. ϵ‐Caprolactone is polymerized at 50 °C in toluene in a controlled manner by [Al(mbmp)(μ‐O i Pr)] 2 , to give poly(ϵ‐caprolactone) with high molecular weights and narrow molecular weight distributions ( M w / M n < 1.50). The low efficiency values (number of polymer chains initiated per aluminum atom) imply that [Al(mbmp)(μ‐O i Pr)] 2 exists in a monomer–dimer equilibrium. The polymerization of ϵ‐caprolactone by [AlMe(OC 6 H 2 ‐2,6‐ t Bu 2 ‐4‐Me)(μ‐O i Pr)] 2 is faster, but somewhat less controlled.