The
synthesis and characterization of dinuclear aluminum complexes
bearing multidentate aliphatic aminoethanol-based ligands are presented.
Single-crystal X-ray analyses, NMR data, and mass data reveal that
four aluminum complexes synthesized are all dimeric in the solid,
solution, and gas states. Especially, 27Al NMR spectra
have demonstrated that they exist as both five-coordinate Al(III)
species in benzene-d
6 solution. All aluminum
complexes are effective catalysts for the cycloaddition of CO2 to propylene oxide in the presence of n-Bu4NI as a cocatalyst. Complexes 1 and 3, which have two methyl groups per aluminum center, are better catalytic
systems than the corresponding complexes 2 and 4 with a mono methyl group per aluminum. In addition, complexes 3 and 4 containing a pendant −CH2CH2NMe2 group attached to nitrogen showed
the higher activity than those 1 and 2 with
a pendant −CH2CH2OMe group did.
As expected, the catalytic activity for 3 increases as
the reaction temperature increases up to 130 °C. In addition,
compound 3 showed the highest activity for the cycloaddition
of CO2 with propylene oxide in the presence of tetrabutylphosphonium
bromide as a cocatalyst.
A series of new half-sandwich titanocene
[(η5-C5H5)Ti
L
Cl2] (1) and nonorganometallic titanium
complexes [Ti
L
Cl3(THF)] (2) and
[Ti
L
2Cl2] (3) containing 5-(2-hydroxyphenyl)tetrazole (
LH) were synthesized in high yield and fully characterized
by various spectroscopic methods and X-ray crystallography. In all
complexes, the ligand
L
acted as a monoanionic
bidentate ligand and hydrogen bonding between the oxygen of the tetrahydrofuran
and hydrogen of the tetrazolyl unit was observed. In the cycloaddition
of CO2 to propylene oxide, complex 3 showed
the highest activity among the reported Ti complexes.
First structurally characterized dimeric alumatranes with tricyclic five-membered rings were determined by single-crystal X-ray analysis and DFT calculations. New alumatranes were used as catalysts for trimethylsilycyanation reaction of aldehydes.
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