KINETICS AND MECHANISM OF NUCLEOPHILIC SUBSTITUTION IN NICKEL TETRACARBONYL

The rate of the substitution reaction (1) of nickel carbonyl with triphenylphosphine or carbon monoxide has been measured over a 30° temperature range, in solution in n-hexane and toluene (Ph3P only), and in the gas phase (CO only). The reactions were followed by infrared spectrophotometry in the C-O stretching region, using C18O for the CO exchange reactions. The rates are independent of concentration or type of nucleophile, but first order with respect to Ni(CO)4 concentration. Rates of reaction in the gas phase or in toluene are ca. twice those in n-hexane, but activation parameters for all reactions are similar (ΔH* from 22 to 24 kcal mol-1, ΔS* from +7 to +14 eu). In particular, and contrary to earlier results, CO and Ph3P in the same solvent react with indistinguishable rates and activation parameters and compete for the same activated complex. Taken in conjunction with the results for the thermal decomposition of Ni(CO)4, in the following paper, the dissociative (SnI) mechanism (eq 9 and 10) is suggested for the reaction. © 1968, American Chemical Society. All rights reserved.