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Volumn 86, Issue 7, 2013, Pages 800-812

Tetranuclear hafnium(IV) and zirconium(IV) cationic complexes sandwiched between Two Di-Lacunary species of α-keggin polyoxometalates: Lewis acid catalysis of the mukaiyamaaldol reaction

Author keywords

[No Author keywords available]

Indexed keywords

ANTI-SELECTIVITY; CATIONIC COMPLEXES; CLUSTER CATIONS; HIGH STEREOSELECTIVITIES; LEWIS ACID CATALYSIS; MUKAIYAMA ALDOLS; POLYOXOMETALATES; ROOM TEMPERATURE;

EID: 84880567307     PISSN: 00092673     EISSN: 13480634     Source Type: Journal    
DOI: 10.1246/bcsj.20130016     Document Type: Article
Times cited : (12)

References (76)
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    • Complete elemental analysis and TG/DTA data of powder sample of Cs-1, abbreviated as Cs-1pow, suggested its formula and composition to be Cs8[{Hf4(H2O)5(OH)6}(¡-1, 2-PW10O37)2]¢ 11H2O (Cs-1pow), The number of coordinated water molecules in Cs-1pow, 5, is different from that of the crystalline sample Cs-1, 6 (see Preparation of Cs-1 in Experimental section), The crystalline sample (Cs-1) was obtained by crystallization of the powder sample (Cs-1pow) under HCl-acidic conditions (pH 2.0
    • Complete elemental analysis and TG/DTA data of powder sample of Cs-1, abbreviated as Cs-1pow, suggested its formula and composition to be Cs8[{Hf4(H2O)5(OH)6}(¡-1, 2-PW10O37)2]¢ 11H2O (Cs-1pow). The number of coordinated water molecules in Cs-1pow, 5, is different from that of the crystalline sample Cs-1, 6 (see Preparation of Cs-1 in Experimental section). The crystalline sample (Cs-1) was obtained by crystallization of the powder sample (Cs-1pow) under HCl-acidic conditions (pH 2.0).
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    • Brønsted acidity of the water molecules coordinated to Hf atoms may be different in the two samples, i.e. the crystalline sample Cs-1 and the powder sample Cs-1pow, Silyl enol ether is more hydrolyzed by the stronger Brønsted acid. By passing Cs-1 and Cs-1pow through a cation-exchange resin column in the Na+ form, they have been changed to Na-1 and Na-1pow, respectively. As a matter of fact, the HPLC analysis suggested that silyl enol ether is much more hydrolyzed by Na-1 than by Na-1pow, indicating that Na-1 is a stronger Brønsted acid than Na-1pow. This is the reason why the activity of Lewis acid catalysis by Na-1 is much lower than that by Na-1pow, Thus, the catalytic data by Na-1pow are presented as the results
    • 11 Brønsted acidity of the water molecules coordinated to Hf atoms may be different in the two samples, i.e., the crystalline sample Cs-1 and the powder sample Cs-1pow. Silyl enol ether is more hydrolyzed by the stronger Brønsted acid. By passing Cs-1 and Cs-1pow through a cation-exchange resin column in the Na+ form, they have been changed to Na-1 and Na-1pow, respectively. As a matter of fact, the HPLC analysis suggested that silyl enol ether is much more hydrolyzed by Na-1 than by Na-1pow, indicating that Na-1 is a stronger Brønsted acid than Na-1pow. This is the reason why the activity of Lewis acid catalysis by Na-1 is much lower than that by Na-1pow. Thus, the catalytic data by Na-1pow are presented as the results.


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