Abstract
AbstractThe hydroaminomethylation (HAM) reaction converts alkenes into N‐alkylated amines and has been well studied for rhodium‐ and ruthenium‐based catalytic systems. Cobalt‐based catalytic systems are able to perform the essential hydroformylation reaction, but are also known to form very active hydrogenation catalysts, therefore we examined such a system for its potential use in the HAM reaction. Thus, we have quantum‐chemically explored the hydrogenation activity of [HCo(CO)3] in model reactions with ethene, methyleneamine, formaldehyde, and vinylamine using dispersion‐corrected relativistic density functional theory at ZORA‐BLYP‐D3(BJ)/TZ2P. Our computations reveal essentially identical overall barriers for the catalytic hydrogenation of ethene, formaldehyde, and vinylamine. This strongly suggests that a cobalt‐based catalytic system will lack hydrogenation selectivity in experimental HAM reactions. Our HAM experiments with a cobalt‐based catalytic system (consisting of Co2(CO)8 as cobalt source and P(n‐Bu)3 as ligand) resulted in the formation of the desired N‐alkylated amine. However, significant amounts of hydrogenated starting material as well as alcohol (hydrogenated aldehyde) were always formed. The use of cobalt‐based catalysts in the HAM reaction to selectively form N‐alkylated amines seems therefore not feasible. This confirms our computational prediction and highlights the usefulness of state‐of‐the‐art DFT computations for guiding future experiments.
Highlights
The hydroaminomethylation (HAM) reaction is an atomeconomical transformation of an alkene, amine, CO, and H2 into an N-alkylated amine by consecutive hydroformylation (HF), condensation, and hydrogenation reactions (Scheme 1)
We computationally studied the hydrogenation according to the mechanism in Scheme 3 with [HCo(CO)3] as the active catalytic species for four substrates: ethene (X = CH2), formaldehyde (X = O), methyleneamine (X = NH), and vinylamine (X = CHNH2)
For each of the substrates, with exception of the symmetrical ethene, we studied the hydride transfer to either atom of the double bond: the carbon or the nitrogen or oxygen atom for methyleneamine and formaldehyde respectively, and the α- or β-atom for vinylamine
Summary
Extensively using rhodium-[2,3,4,5,6,7] and ruthenium-based homogeneous catalysts.[2,8,9,10,11,12,13,14,15]. It is attractive to use homogeneous cobalt-based catalysts since cobalt is a more abundant and less toxic metal than rhodium and ruthenium, and, in contrast to rhodium-based catalysts, cobalt-based catalysts generally have a very high isomerization activity.[24] This high isomerization activity opens up the possibility of the use of internal alkenes as the substrate, which prevents the arduous separation of the terminal alkene from the industrial mixture of isomeric internal alkenes.[25] cobalt forms very active hydrogenation catalysts in combination with phosphine ligands, even in the presence of carbon monoxide.[24,26,27] Steering the hydrogenation selectivity of the catalytic system is of paramount importance: hydrogenation of the intermediate enamine is necessary to yield the desired amine, but the alkene as well as the intermediate aldehyde may be hydrogenated to yield the undesired alkane and alcohol (Scheme 2). The motivation for this effort is the attractiveness of a cobalt alternative for the HAM reaction in combination with the fact that our computational exploration is based on a simplified model system, leaving room for the assumption that an in-vitro catalyst might have more favorable behavior
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
