The Organometallicfac-[(CO)3Mn(H2O)3]+Aquaion: Base-Hydrolysis and Kinetics of H2O-Substitution

Abstract
The novel organometallic aqua complex [(CO)3Mn(H2O)3]+ (1+) was obtained through hydrolysis of the analogous acetone complex. IR [νCO = 2051, 1944 cm-1] and 17O NMR spectroscopy revealed the presence of a fac tricarbonyl unit. Potentiometric titrations established that the trimer [(CO)3Mn3(OH)4]- was the principal condensation product in the pH range >6 prior to slow formation of the tetramer [{(CO)3Mn}(OH)]4. Water exchange in 1+, determined by NMR line broadening as kex = 19 ± 4 s-1 at 298 K, is four orders faster than with the analogous Re complex. The activation volume ΔV = −4.5 ± 0.4 cm3 mol-1 is indicative of an associatively activated (Ia) process.

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