Two new aromatic organonitrile complexes of pentaamminecobalt(III) have been synthesized, the complexes of 2- and 4-nitrobenzonitrile. The kinetics of their base hydrolysis to coordinated carboxamides have been measured and found to follow a simple second order rate law with rate constants of 180 ± 4 M-1 s-1 and 510 ± 90 M-1 s-1 at 25°C and ionic strength 1.0 for the ortho and para isomers respectively. Rate constants for the hydrolysis of eleven coordinated substituted aromatic nitriles have been found to follow a Hammett type correlation where log k = 1.93σ + 1.30 at 25 °C and ionic strength 1. Carbon-13 NMR studies indicate that the variation in the slope of these Hammett plots for free and coordinated nitrile hydrolysis rates is a transition state effect rather than a ground state phenomenon.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry