Sterically Shielded Titanocene Enolates – Synthesis, Structure and Their Exceptional Stability towards Hydrolysis

Autor:	Michael Schmittel, Rolf Söllner, Helmut Werner, Olaf Gevert
Rok vydání:	1997
Předmět:	Steric effects chemistry.chemical_classification Double bond chemistry.chemical_element Photochemistry Medicinal chemistry Inorganic Chemistry Hydrolysis chemistry.chemical_compound Deprotonation Reaction rate constant chemistry Moiety Acetonitrile Titanium
Zdroj:	Chemische Berichte. 130:195-199
ISSN:	1099-0682 0009-2940
DOI:	10.1002/cber.19971300209
Popis:	The reaction of various sterically congested sodium enolates, generated by quantitative deprotonation of stable enols (of diphenylacetaldehyde in the case of 5), with dichlorotitanocene afforded a series of novel titanium enolates 1-5. The crystal structure of 1 could be determined. Due to the considerable steric shielding of the β,β-diaryl moiety, all the titanium enolates exhibit an oustanding stability towards hydrolysis, which increases with the higher steric demand of the substitutents at the C-C double bond. The kinetics of the hydrolysis, which is pseudo-first-order in THF/water (1 : 1) and acetonitrile/water (1 : 1), was investigated by UV spectroscopy. The pseudo-first-order rate constants measured in these solvent mixtures are in the range 6.4 · 10−4 s−1 < k1 < 1.1 · 10−3 s−1. For comparison, the hydrolysis of 6, which should exhibit the usual sensitivity of titanium enolates towards hydrolysis, is about 1000 times faster.
Databáze:	OpenAIRE
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