Reaction rate constants and mechanistic detail of the Ni+ + butanone reaction

Submerged Barriers in the Ni(+) Assisted Decomposition of Propionaldehyde

The reaction dynamics of the Ni(+) mediated decarbonylation of propionaldehyde was assessed using the single photon initiated decomposition rearrangement reaction (SPIDRR) technique. The exothermic production of Ni(+)CO was temporally monitored and the associated rate constants, k(E), were extracted as a function of activating photon energy. In addition, the reaction potential energy surface was calculated at the UCCSD(T)/def2-TZVP//PBEPBE/cc-pVDZ level of theory to provide an atomistic description of the reaction profile. The decarbonylation of propionaldehyde can be understood as proceeding through parallel competitive reaction pathways that are initiated by Ni(+) insertion into either the C-C or C-H bond of the propionaldehyde carbonyl carbon. Both paths lead to the elimination of neutral ethane and are governed by submerged barriers. The lower energy sequence is a consecutive C-C/C-H addition process with a submerged barrier of 14 350 ± 600 cm(-1). The higher energy sequence is a consecutive C-H/C-C addition process with a submerged barrier of 15 400 ± 600 cm(-1). Both barriers were determined using RRKM calculations fit to the experimentally determined k(E) values. The measured energy difference between the two barriers agrees with the DFT computed difference in rate limiting transition-state energies, 18 413 and 19 495 cm(-1).

Co(+)-assisted decomposition of h6-acetone and d6-acetone: acquisition of reaction rate constants and dynamics of the dissociative mechanism

Reaction rate constants have been acquired for the gaseous unimolecular decomposition reaction of the Co(+)(OC(CH(3))(2)) cluster ion and its deuterium labeled analog. Each rate constant is measured at a well resolved cluster internal energy within the range 12,300-16,100 cm(-1). The weighted, averaged kinetic isotope effect (KIE), k(H)/k(D) = 1.54 ± 0.05, is about three times smaller than the KIE measured for the rate-determining rate constants in the similar Ni(+)(OC(CH(3))(2)) decomposition reaction. These reactions likely follow the same oxidative addition-reductive elimination mechanism. Thus, this unexpected change in the KIE magnitudes is not due to differences in the dissociative reaction coordinates. Rather, we propose that the unique dissociation dynamics of these two similar systems is due to differences in the low-lying electronic structure of each transition metal ion.