Effects of the alkyl substituent in the -donor heteroatom on the kinetic and thermodynamic acidities of Fischer thiocarbene complexes.

MARTÍN E. ZOLOFF MICHOFF; DIEGO M. ANDRADA; ALEJANDRO M. GRANADOS; RITA H. DE ROSSI

NEW JOURNAL OF CHEMISTRY

Royal Society of Chemistry

Año: 2008 vol. 32 p. 65 - 72

1144-0546

Rate constants for the proton transfer reaction from Fischer thiocarbene complexes(CO)5MQC(SR1)CH3 (M = Cr or W; R1 = n-butyl, isopropyl, tert-butyl, cyclohexyl) to OHand various primary and secondary amines were determined in 50% acetonitrile?50% water at25 1C. These measurements allowed the determination of the thermodynamic and kinetic aciditiesfor these substrates. The results obtained show that there is a slight effect of the substituent onthe thermodynamic acidity, which is governed by its hydrophobicity; whereas the effect on thekinetic acidity is more noticeable and is due to the steric effect of the substituent.