Neutral Methyl and Cationic Aluminum Complexes Supported
by a trans-1,2-Cyclooctanediyl-Bridged [OSSO]-Type Bis(phenolato) Ligand: Synthesis, Structures, and Use in Catalysis for Propylene Oxide Polymerization
posted on 2014-04-14, 00:00authored byNorio Nakata, Yusuke Saito, Akihiko Ishii
Treatment
of trans-1,2-cyclooctanediyl-bridged [OSSO]-type
bis(phenolate) 1 with Me3Al in hexane led
to the formation of methylaluminum 4 as colorless crystals.
X-ray diffraction analysis of 4 revealed that the aluminum
center adopts a distorted-trigonal-bipyramidal geometry which occupies
the axial positions with one phenoxide oxygen and one sulfur atoms.
The dealkylation reaction of 4 with 1 equiv of B(C6F5)3 in C6D6 afforded
the novel cationic aluminum species 52+ as
a dimeric structure, which was isolated in the form of a [MeB(C6F5)3]− salt. In the
crystal structure of 52+, one aluminum atom
has a distorted-trigonal-bipyramidal environment, in which phenoxide
and μ-bridging oxygen atoms are located at two axial positions,
whereas the other aluminum atom has a distorted-square-pyramidal geometry,
which occupies the axial position with a nonbridged oxygen atom. The
cationic species 52+ promoted the ring-opening
polymerization (ROP) of propylene oxide to give an atactic polymer
in 44% yield with a low molecular weight (Mn = 2500) and a very narrow molecular weight distribution (PDI = 1.04).