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Sterically Shielded Titanocene Enolates – Synthesis, Structure and Their Exceptional Stability towards Hydrolysis
Author(s) -
Schmittel Michael,
Söllner Rolf,
Werner Helmut,
Gevert Olaf
Publication year - 1997
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19971300209
Subject(s) - chemistry , steric effects , hydrolysis , moiety , deprotonation , solvent , acetonitrile , reaction rate constant , medicinal chemistry , photochemistry , organic chemistry , kinetics , ion , physics , quantum mechanics
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 < k 1 < 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.