Abstract: Using stable nitroxyl radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) as a spin probe, Lewis acidic sites of methylaluminoxane (MAO) were identified. It was found that MAO contains two types of acidic sites. TEMPO, coordinated to the sites I and II, exhibits in the EPR spectra triplet (go=2.0047, aN=18.6 G) and triplet of sextets (go=2.0045, aN=19.6 G and aAl=1.7 G), respectively (aN and aAl are constants of hyperfine structure from the corresponding nucleus). According to EPR measurements, concentration of sites I is close to that of sites II, and MAO contains one site of each type per 100±30 aluminium atoms. The adducts of TEMPO with sites I are less stable than those with sites II. Based on the values of aAl and relative stabilities of the adducts with TEMPO, the acidic sites I and II were attributed to coordinatively unsaturated aluminium atoms in AlOMe2 and AlO2Me environment, respectively. From the EPR spectra of coordinated TEMPO, the average radius of MAO oligomers (AlOMe)n was evaluated to be 5.8 Å at 20°C, which corresponds to the value of n=15–20. Thus, the major part of MAO contains not more than one Lewis acidic site per one oligomeric (AlOMe)n molecule.

Cite: Talsi E.P. , Semikolenova N.V. , Panchenko V.N. , Sobolev A.P. , Babushkin D.E. , Shubin A.A. , Zakharov V.A.
The Metallocene/Methylaluminoxane Catalysts Formation: EPR Spin Probe Study of Lewis Acidic Sites of Methylaluminoxane
Journal of Molecular Catalysis A: Chemical. 1999. V.139. N2-3. P.131-137. DOI: 10.1016/S1381-1169(98)00194-0 WOS Scopus РИНЦ ANCAN OpenAlex

Dates:

Submitted:	Jan 26, 1998
Accepted:	May 18, 1998
Published online:	Jan 26, 1999
Published print:	Mar 5, 1999

Identifiers:

Web of science:	WOS:000078361700003
Scopus:	2-s2.0-0033525378
Elibrary:	13315771
Chemical Abstracts:	1999:45709
Chemical Abstracts (print):	130:223628
OpenAlex:	W2065997654

Citing:

DB	Citing
Web of science	71
Scopus	74
Elibrary	73
OpenAlex	69

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