Abstract
Benzoic acids 4-XC6H4CO2H and 3-XC6H4CO2H , bearing the (CO)5Cr:CN(CH3)2 group in the p- and m-position, and the corresponding benzoic acids XC6H3-2-Me-4-CO2H and XC6H3-2-Me-5-CO2H, in which the rotation of the aminocarbene moiety was blocked by the presence of a Me group, were prepd. together with the corresponding N,N-dimethylamido acids. The measurement of pKa values in EtOH and DMF revealed that the (CO)5Cr:CN(CH3)2 group is a very weak electron acceptor.
The restriction of the rotation of the aminocarbene moiety did not significantly influence its electronic properties. The obtained results are in accordance with earlier findings that the relatively strong acidity of carbene complexes bearing hydrogens at the alpha-position to the carbene atom is due to the resonance stabilization of the anion.