No abstract

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 .

For several decades, the influence of Two State Reactivity (TSR) has been implicated in a host of reactions, but has lacked a stand-alone, definitive experimental kinetic signature identifying its occurrence....

The study of gas-phase ion-molecule reactions has been influential in the investigation of transition metal mediated bond activation and catalysis. We have furthered this field by developing a new technique capable of measuring the microcanonical kinetics for reactions between transition metal cations and neutral organic molecules. This novel method has been designated as single photon initiated dissociative rearrangement reaction (SPIDRR) technique and provides a nearly direct measurement of microcanonical reaction rate constants. For this reason, SPIDRR offers unique insight into reaction mechanisms and dynamics by assessing the energy dependence of the microcanonical rate constant, as well as measuring product branching fractions and kinetic isotope effects. The following paper provides a detailed overview of SPIDRR and its advantages in the field of gas-phase catalysis research.

The decomposition of ethyl acetate catalyzed by Ni­(I) has been investigated in the gas phase both experimentally and computationally. This approach allows us to determine what is the bare effect of the metal center in the catalytic process, without the intervention of environmental factors such as solvent, ligands, counterions, etc. This reaction is found to exhibit three competitive channels affording different products: ketene or ethanol, two units of acetaldehyde, and acetic acid or ethylene. Interestingly, each of these channels involves a characteristic hydrogen shift as the key step on the catalytic process: an inner-sphere H shift, an outer-sphere shift, and a peculiar orbital-like motion that merits careful characterization.