Density Functional Studies on Dicobalt Octacarbonyl Mediated Urea Formation from Primary Amine

Synthesis and Reactivity of Propargylamines in Organic Chemistry

Propargylamines are a versatile class of compounds which find broad application in many fields of chemistry. This review aims to describe the different strategies developed so far for the synthesis of propargylamines and their derivatives as well as to highlight their reactivity and use as building blocks in the synthesis of chemically relevant organic compounds. In the first part of the review, the different synthetic approaches to synthesize propargylamines, such as A³ couplings and C-H functionalization of alkynes, have been described and organized on the basis of the catalysts employed in the syntheses. Both racemic and enantioselective approaches have been reported. In the second part, an overview of the transformations of propargylamines into heterocyclic compounds such as pyrroles, pyridines, thiazoles, and oxazoles, as well as other relevant organic derivatives, is presented.

Density Functional Studies of Dicobalt Octacarbonyl-Mediated Azobenzene Formation from 4-Ethynylaniline

Two adiabatic potential-energy surfaces are employed for probing the processes of [Co2(CO)8]-mediated C6H5N=NC6H5 formation from NH2C6H5. Elementary steps, including oxidative addition of the coordinated amine proton to the cobalt center, reductive elimination of H2, CO association, and the coupling process of the diamino fragments, are modeled and examined by using DFT methods at the B3 LYP/631 LAN level. The formation of C6H5N=NC6H5 from NH2C6H5 through reductive coupling is a thermodynamically unfavorable process. Three hydride-migration processes, from the proton of N-H to the cobalt center, are established as the most energy-demanding steps. The activation energies (deltaG*) are calculated as 49.4, 55.4, and 33.3 kcal mol(-1), respectively, for the proposed reaction route 1. These large activation energies might be reduced slightly by purposely adding small protic molecules, such as H2O, or by changing the active metal from Co to a heavier metal, such as Rh or Ir. An alternative pathway, route 2, is also proposed, in which transition states with four-membered rings are formed. By this route, severe strain caused by the formation of three-membered rings during the hydride-migration processes in route 1 can be avoided. Route 2 is established as the more energy-feasible reaction pathway.