Computational investigation of cobalt and copper bis (oxothiolene) complexes as an alternative for olefin purification

Dušan N Sredojević,Rajesh K Raju,Edward N Brothers,Salvador Moncho,Milivoj R Belić

doi:10.1007/s00894-020-04445-x

Dušan N Sredojević, Rajesh K Raju + Show 3 more

Open Access

https://doi.org/10.1007/s00894-020-04445-x

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Abstract

Considering that olefins present a large volume feedstock, it is reasonable to expect that their purification is industrially critical. After the discovery of the nickel bis (dithiolene) complex Ni(S2C2(CF3)2)2 that exhibits electro-catalytic activity with olefins but tends to decompose by a competitive reaction route, related complexes have been explored experimentally and theoretically. In this paper, a computational examination is performed on differently charged cobalt and copper bis (oxothiolene) complexes [M (OSC2(CN)2)2] to test their potential applicability as the catalysts for olefin purification, using the simplest olefin, ethylene. Possible reaction pathways for ethylene addition on these complexes were explored, to determine whether some of these candidates can avoid the reaction route that leads to decomposition, which is distinctive from the nickel complex, and to form stable adducts that can subsequently release ethylene by reduction. Our calculations suggest that the neutral cobalt complex might be an alternative catalyst, because all its forms can bind ethylene to produce stable interligand adducts with moderate to low activation barriers, rather than to form intraligand adducts that lead to decomposition. The calculations also predict that these interligand adducts are capable of releasing ethylene upon reduction. In addition, it can produce the desired interligand adducts following two different reaction pathways, assigned as the direct and the indirect, with no need for anion species as co-catalysts, which is crucial for the nickel complex. Thus, the olefin purification process could be much simpler by using this catalyst.

Highlights

Separation of olefins from petrochemical feedstock is an important process in the chemical industry and has attracted considerable attention for decades [1, 2]
In the absence of the reduced complex, the main products of the reaction between [NiL2] (1) and olefins are a series of decomposition species such as substituted dihydrodithiin (DHD) and metalcontaining products (MD)
The first remark was that the reaction of 1 with ethylene, in the absence of anion 1−, leads to the formation of the intraligand adduct, which further decomposes to produce experimentally detected DHD and MD species

Summary

Introduction

Separation of olefins from petrochemical feedstock is an important process in the chemical industry and has attracted considerable attention for decades [1, 2]. A direct pathway that leads to the formation of the desired cisinterligand adduct is symmetry-forbidden, which is in line with the Woodward-Hoffman addition rules [20]. Otherwise, this adduct can be formed through a twisted (pseudotetrahedral) intermediate, which is formed in the first step of the reaction, avoiding constraints imposed by orbital symmetry. This adduct can be formed through a twisted (pseudotetrahedral) intermediate, which is formed in the first step of the reaction, avoiding constraints imposed by orbital symmetry This was proposed in 2002 by Fan and Hall and summarized as a two-step mechanism that begins with the olefin addition followed by isomerization [20]

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Conclusion