Role of the hydrophobicity of the alkyl substituent in the -donor heteroatom on the thermodynamic and kinetic acidity of Fischer thiocarbene complexes. New insights into the physical chemistry of Fischer carbene complexes.

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

ROYAL SOC CHEMISTRY

Lugar: Londres; Año: 2010 vol. 12 p. 6616 - 6616

ate constants for the reversible deprotonation of (CO)5W=C(SR)CH3 (W-SR) by OH,water and a number of primary aliphatic and secondary alicyclic amines, have been determinedin 50% MeCN:50% water at 25 1C. In addition, solvation energy and proton affinities valuesfor M-SR (M = Cr and W) in the gas phase and in acetonitrile have been computed at DFTlevel. Although there is not a linear correlation between the calculated proton affinities andthe measured pKas, the calculations reveal that when solvent effects are taken into accountthe substituted compounds studied show differences in their proton affinities. There is a goodcorrelation between the change in cavitation energy (DGcav) for the Fischer carbene complexesand log P of the thioalkyl substituents. In proton transfer reactions with amines, steric effectsare more important for W complexes with respect to their Cr analogues as a consequence ofdifferences in transition state pr