Hindawi
Journal of Chemistry
Volume 2021, Article ID 7931956, 11 pages
https://doi.org/10.1155/2021/7931956
Research Article
Quantum Mechanistic Studies of the Oxidation of Ethylene by
Rhenium Oxo Complexes
Emmanuel Adu Fosu,1 Collins Obuah ,1 Louis Hamenu,1 Albert Aniagyei ,2
Michael Kojo Ainooson,1 and Krishna K. Govender 3,4
1Department of Chemistry, University of Ghana, Legon, Accra, Ghana
2School of Basic and Biomedical Sciences, University of Health and Allied Sciences, Ho, Ghana
3Department of Chemical Sciences, University of Johannesburg, P. O. Box 17011, Doornfontein Campus,
Johannesburg 2028, South Africa
4Council for Scientific and Industrial Research, National Integrated Cyber Infrastructure,
Centre for High Performance Computing, 15 Lower Hope Road, Rosebank, Cape Town 7700, South Africa
Correspondence should be addressed to Collins Obuah; cobuah@ug.edu.gh
Received 11 May 2021; Revised 28 July 2021; Accepted 10 August 2021; Published 23 August 2021
Academic Editor: Marcelino Maneiro
Copyright © 2021 Emmanuel Adu Fosu et al. %is is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is
properly cited.
Transition-metal-mediated oxygen transfer reactions are of importance in both industry and academia; thus, a series of rhenium
oxo complexes of the type ReO3L (L =O−, Cl−, F−, OH−, Br−, I−) and their effects as oxidation catalysts on ethylene have been
studied. %e activation and reaction energies for the addition pathways involving multiple spin states (singlet and triplet) have
been computed. In all cases, structures on the singlet potential energy surfaces showed higher stability compared to their
counterparts on the triplet potential energy surfaces (PESs). Frontier Molecular Orbital calculations show electrons flow from the
HOMO of ethylene to the LUMO of rhenium for all complexes studied except ReO −4 where the reverse case occurs. In the reaction
between ReO − −3L (L =O , Cl , F−, OH−, Br−, and I−) and ethylene, the concerted [3 + 2] addition pathway on the singlet PES leading
to the formation of dioxylate intermediate is favored over the [2 + 2] addition pathway leading to the formation of a metal-
laoxetane intermediate and subsequent rearrangement to the dioxylate. %e activation and the reaction energies for the formation
of the dioxylate on the singlet PES for the ligands studied followed the order O−>OH−> I−> F−>Br−>Cl− and
O−>OH−> F−> I−>Br−>Cl−, respectively. Furthermore, the activation and the reaction energies for the formation of the
metallaoxetane intermediate increase in the order O−>OH−> I−>Br−>Cl−> F− andO−>Br−> I−>Cl−>OH−> F−, respectively.
%e subsequent rearrangement of the metallaoxetane intermediate to the dioxylate is only feasible in the case of ReO −4 . Of all the
complexes studied, the best dioxylating catalyst is ReO3Cl (singlet surface) and the best epoxidation catalyst is ReO3F
(singlet surface).
1. Introduction industrial and academic field, organometallic-mediated
oxygen transfer processes, or reactions, have shown great
One of the primary goals in chemical research is to develop relevance over the past years [3]. %e catalytic oxidation of
novel catalytic reactions that increase the selectivity and olefinic bonds to form vicinal diols by the osmium tetroxide
efficiency of chemical processes [1, 2]. Exploring chemical catalyst is a typical and well-known example of oxygen
systems at the fundamentals of matter has led to the rational transfer processes or reactions [4, 5].
formulation and understanding of novel chemical catalytic %e osmium tetroxide catalytic oxidation of prochiral
processes or reactions, understanding transient properties, olefinic substrates together with asymmetric amine ligands
and identification of key intermediates due to the uncon- as chiral auxiliaries shows a very high enantioface selectivity
trollable nature of chemical reactions or processes [3]. In the [6]. Experimental and theoretical works over the past year
2 Journal of Chemistry
have shown the stability of epoxide formation via the cat- insertion of the ReO3L oxo complex (L =O−, Cl, and Cp)
alyzed oxidation pathways by early transition metals such across the olefinic bond and the interconversion of the
titanium, vanadium, and chromium [7–9] whereas oxo oxetane intermediate to its dioxylate, at the B3LYP [18] level
complexes such as ruthenium tetroxide [9], osmium te- using relativistic small-core ECPs with a valence basis set
troxide [4], and permanganate [10] tend to prefer cis- splitting (441/2111/21) for Re and 6-31G(d) all-electron basis
dihydroxylate olefinic substrates [11]. Exploring and un- sets for all other atoms. Findings from the theoretical
derstanding the mechanistic channels of olefinic catalyzed simulations by Deubel and Frenking [19] showed stability
substrates, especially osmium tetroxide, has been a subject of for the [3 + 2] mechanistic pathway over the [2 + 2] pathway.
interest and study due to the relevance of their cis-dihy- %e [3 + 2] pathway was found to be lower in energies
droxylate and epoxide products. relative to that of the rearrangement of the oxetane inter-
Early suggestions about the catalytic oxidation of the mediate to a dioxylate intermediate. By employing knowl-
ethylene by OsO4 complex was that the additionmechanistic edge from frontier orbital and charge transfer models,
pathway is energetically favorable for the formation of Deubel and Frenking [19] rationalized the reactivity dif-
dioxylate via a [3 + 2] insertion of the O�Os�O moiety ferences of the complexes.
across the olefinic bond which forms a dioxylate interme- Gisdakis and Rösch [20], in auxiliary to the computa-
diate which has been experimentally characterized with its tions performed by Pietsch et al. [11] and Deubel and
hydrolysis forming diols [6]. However, Sharpless et al. [9] Frenking [19], assigned charges (q=−1, 0, 1) to the ReO3L
raised arguments about the [3 + 2] mechanistic route and molecule such that themolecular systems are isoelectronic to
made a case for the [2 + 2] pathway due to the primary OsO4. %ey explored the mechanism of the [3 + 2] cyclo-
products (dichlorides, epoxides, and chlorohydrins) from addition of ReO3L (L =O−, CH3, Cl, and Cp) to ethylene
the chromyl chloride catalyzed oxidation of olefins. A new using the hybrid DFT model B3LYP, with (ECP) effective
proposal was then made by Sharpless et al. [9] where they core potentials and double-zeta basis sets, LANL2DZ, for the
suggested that the oxidative mechanism was via a [2 + 2] Re atom and 6-311G (d, p) basis sets for other atoms.
addition route or stepwise mechanism which results in Gisdakis and Rösch [20] did not study the formation of the
metallaoxetane intermediate before rearranging through dioxylate intermediates from the metallaoxetane along the
another transient to form a dioxylate complex. Arguments [2 + 2] addition pathway.
on the mechanistic details of the osmium tetroxide catalytic Aniagyei et al. [16] furthered the theoretical works by
oxidation of olefins, however, have been settled after im- Pietsch et al. [11], Deubel and Frenking [19], and Gisdakis
proved quantum simulations over the past years predicted and Rösch [20] by using a hybrid density functional theory at
both kinetic and thermodynamic stability via the [3 + 2] the B3LYP [18]/LACVP∗ level of theory to study the con-
pathway over the [2 + 2] pathway [1, 5, 6, 12–15]. Osmium certed and stepwise addition pathways for the oxidation of
tetroxide has been one of the best catalysts for most oxygen ethylene by ReO3L (L =O−, Cl−, Cp, CH , −3 OCH3, and
transfer reactions, but due to its volatility, toxicity, scarcity, NPH3) on several spin PES (spin multiplicity = 1, 2, 3, and 4,
and expensive nature, these factors demerit the use of os- where applicable).
mium tetroxide as a catalyst and urge researchers to in- Aniagyei et al. [16] concluded that the catalytic oxidation
vestigate alternative metal oxo complexes or substrate of ethylene by the ReO L complex (L =OCH , O−3 3 , CH3,
catalysts to replace osmium tetroxide. NPH Cl−3 , and Cp) shows both kinetic and thermodynamic
Rhenium is next to osmium on the periodic table. favorability on the [3 + 2] pathway leading to the formation
Catalytic oxidation of olefinic substrates by ReO3L oxo of a metallacycle over the [2 + 2] mechanistic pathway which
complexes has mainly been focused on the [3 + 2] and [2 + 2] forms an oxetane intermediate before rearranging into a
addition pathway [11, 13, 14, 16] using different levels of dioxylate intermediate on the singlet PES. %e rearrange-
theory with only Aniagyei et al. [16] investigating an epoxide ment of the oxetane intermediate into the dioxylate inter-
formation plausibility. However, Herrmann et al. [13] re- mediate was kinetically hindered except for the reaction
ported rhenium oxo complexes are good oxygen-transfer between ethylene and the perrhenate ion on the singlet PES.
catalysts [13, 17]. %e formation of an epoxide precursor was plausible in the
Using a hybrid DFT model, B3LYP [18], and the case of ReO3L (L =Cl−, CH3, −OCH3, NPH3) reaction with
Hay–Wadt relativistic effective core potential (ECP) for Re ethylene although these reaction modes showed ender-
(LANL2) and a double zeta basis set, 6-31G∗, for other gonicity in all cases on the singlet PES [16].
atoms, Pietsch et al. [11] studied the [3 + 2] and [2 + 2] %is work reports on the extended works by Aniagyei
mechanistic pathways by aiming at the thermodynamic et al. [16], Pietsch et al. [11], Deubel and Frenking [19], and
properties for the ethylene-catalyzed oxidation by ReO3L Gisdakis and Rösch [20] by employing a hybrid DFTmodel,
complexes (L�Cp∗, Cp, Cl, CH , −OH, −3 OCH3, and O−). B3LYP, at the B3LYP [18]/LACVP∗ level of theory to in-
Pietsch et al. [11] used qualitative molecular orbital diagrams vestigate all the concerted mechanistic channels. %is report
and concluded that the π-donor strength of the ligands (L) also confirms results by Aniagyei et al. on ReO −4 and ReO3Cl
accounts for the reactivity differences of this type of complex as well as a new derivative of ReO3L (L = F−, Br−, I−, and
[16]. OH−). Multiple spin states (singlet and triplet) have also
Deubel and Frenking [19] continued the theoretical been considered in the calculations due to the nature of
works by Pietsch et al. [11] and verified these claims by organometallic reactions which tend to show spin multi-
reporting the calculated PES for the [3 + 2] and [2 + 2] plicity flips on the PES. Furthermore, a change of spin
Journal of Chemistry 3
multiplicity affects the molecular geometry and spin mul- observed that the oxo complexes on the triplet surfaces had a
tiplicity crossing effects can dramatically affect reaction higher dipole moment compared to their counterparts on
mechanisms of organometallic transformations [21, 22]. the singlet PES. %is is accounted for by the change in the
molecular structure or geometry; that is, the oxo complexes
2. Computational Details have their tetrahedron geometry either completely or
slightly distorted on the triplet surface (Figure S10). %e
%e density functional/Hartree–Fock hybrid [23–25] model dipole moment calculated on a singlet potential surface
B3LYP [18] as implemented in Spartan’16 V.2.0.7 [26] has shows an increase in polarity for the ligand order
been used throughout this study together with the basis set O−<Cl−< F−<Br−< I−<OH−. %ese values also suggest
of LANL2DZ for rhenium and iodine atoms and the split that ReO3OH is the most polar catalyst and, hence, will have
valence double-ξ (DZ) [27] 6-31G (d) for the other nonmetal high solubility when used as a catalyst for the oxidation of
atoms (O−, Cl−, F−, Br−, and OH−). ethylene in polar solvents.
Starting geometries of the molecular systems were %e energy profile diagrams obtained from Frontier
modeled using Spartan’s graphical model builder and Molecular Orbital calculations are presented in
minimized interactively using the Sybyl force field [28]. All Figures S3–S8, and the results are presented in Table 2.%ese
geometries were fully optimized without any symmetry diagrams show the nature of electron transfer between the
constraints. A normal mode analysis was performed to verify Highest Occupied Molecular Orbital (HOMO) and Lowest
the nature of the stationary points. Equilibrium geometries Unoccupied Molecular Orbital (LUMO) of rhenium com-
were characterized by the absence of imaginary frequencies. plexes and ethylene. In all the rhenium complexes studied,
%e transition state structures were located by a series of electrons require more energy to move from the HOMO of
constrained geometry optimizations in which the forming, the rhenium complexes to the LUMO of the ethylene. In the
and breaking, of bonds was fixed at various lengths while the reverse case, electrons require lesser energy to travel from
remaining internal coordinates were optimized. the HOMO of ethylene to the LUMO of the rhenium
%e approximate stationary points located from such a complex for oxidation to occur. It is, therefore, concluded
procedure were then fully optimized using the standard that the oxidation of ethylene catalyzed by rhenium-oxo
transition state optimization procedure in Spartan. All first- complexes proceeds with the flow of electrons from the
order saddle points were shown to have a Hessian matrix HOMO of the ethylene to the LUMO of the oxo complexes
with a single negative eigenvalue, characterized by an except in the case of ReO −4 where the electron flow is from
imaginary vibrational frequency along the reaction the HOMO to the LUMO ethylene (Figure S8 and Table 2:
coordinate. entry 1).
%is study reports all Gibbs free-energy values unless
otherwise noted, at a temperature of 298.15K and pressure
of 1 atm using unscaled frequencies. 3.1. Reaction of Ethylenewith ReO3F. %e relative energies of
the main stationary points (reactants, transition states, in-
3. Results and Discussion termediates, and products) and some optimized structures
involved in the reaction between ethylene and ReO3F are
%e recomputed density functional theory (DFT) optimized shown in Figures 1(a) and 1(b), respectively. %e singlet
structures of ReO −4 and ReO3Cl on a singlet potential energy ReO3F species has its three Re�O bond lengths at 1.704 Å
surface are shown in Figures S1 and S2. %e energetics and while the Re-F bond equals 1.804 Å.%e triplet ReO3F has its
the nature of stationary points agree with those computed Re-F bond length at 1.845 Å and its three Re�O bond
previously by Aniagyei et al. [16]. As shown in the energy lengths at 1.808 Å, 1.695 Å, and 1.845 Å. %e triplet rhenium
profile diagrams (Figures S1 and S2), the addition of eth- oxo complex is 65.62 kcal/mol less stable than its singlet
ylene across the O�Re�O shows both kinetic and ther- structure.
modynamic preference for the [3 + 2] pathway over the %e concerted [3 + 2] insertion of the C�C bond across
[2 + 2] pathway leading to the formation of an oxetane. It is the O�Re�O functionality of ReO3F to form a dioxylate has
also evident from the profile diagrams (Figure S2) that an an activation barrier of 35.73 kcal/mol and shows an
epoxide is formed through a rearrangement of the oxetane endergonicity of 18.25 kcal/mol. %ese energies are lower
when the oxidation of ethylene is catalyzed by ReO3Cl. In all compared to the same reaction for ReO −4 (Figure S1). %e
cases, there were no triplet transition states observed. triplet dioxylate is found to be 5.87 kcal/mol less stable than
Mulliken and natural population analysis were per- its singlet dioxylate.
formed to estimate the partial atomic charges of each atom %e calculated transition state (structure TS 1A,
of the oxo complexes, and the results are shown in Table 1. Scheme S1 and Figure 1) shows high symmetry and is
%e results show that there are general higher natural synchronous to the newly forming C-O bonds (1.876 Å). In
charges compared to the Mulliken charges. For example, in the singlet product, Re�O and Re-F spectator bond lengths
Table 1, entry 1 is for ReO3F, the Mulliken partial charge of are 1.686 Å and 1.851 Å, respectively. Both Re-O bond
Re is +2.207, O is −0.544, and F is −0.395 while for the lengths are 1.899 Å. Although no transition state was ob-
natural charge, Re is +2.637, O is −0.702, and F is −0.530. served on the triplet PES, the triplet product had Re�O and
%e dipole moments of each oxo complex on both singlet Re-F bond lengths equal to 1.700 Å and 1.868 Å, respectively,
and triplet reaction surfaces are shown in Table 1. It was with both Re-O being 1.892 Å.
4 Journal of Chemistry
Table 1: Mulliken and natural population analysis as well as the dipole moments of rhenium oxo complexes.
Mulliken Re O L Natural Re O L Dipole
Entry population electronic electronic electronic population electronic electronic electronic moment Dipole
analysis charge charge charge analysis charge charge charge singlet moment triplet
1 ReO3F +2.207 −0.544 −0.395 +2.637 −0.702 −0.530 0.83 1.41
2 ReO3Cl +1.709 −0.520 −0.151 +2.364 −0.664 −0.372 0.75 0.81
3 ReO3Br +1.594 −0.521 −0.031 +2.318 −0.667 −0.319 1.20 1.66
4 ReO3I +1.558 −0.521 −0.003 +2.251 −0.669 −0.224 1.72 2.98
5 ReO3OH +2.004 −0.561 −1.260 +2.597 −0.720 −0.456 2.72 3.32
6 ReO −4 +1.834 −0.502 −0.502 +2.530 −0.882 −0.882 0.70 0.52
On the singlet PES, the formation for the metallaoxetane %e concerted [3 + 2] addition of the C�C bond across
intermediate via the [2 + 2] pathway has an activation energy the O�Re�O functionality of ReO3Br to form a dioxylate
of 45.55 kcal/mol and 19.65 kcal/mol endergonic. Again, no intermediate has an activation barrier of 34.87 kcal/mol and
triplet transition state was observed. %e calculated transi- shows an endergonicity of 16.60 kcal/mol. No transition
tion state (TS 1C in Scheme S1 and Figure 1) has its newly state was located on the triplet PES. %e triplet dioxylate, in
formed C-O and Re-C bond lengths as 1.904 Å and 2.299 Å, this case, was found to be 4.61 kcal/mol less stable than its
respectively. In the singlet product, the two Re�O bond singlet. %e transition state structure is highly symmetrical
lengths were 1.708 Å, while the Re-F bond length was and has its C-O bond lengths as 1.883 Å.
1.862 Å and the Re-O bond length was 1.908 Å. %e [2 + 2] singlet pathway has an activation barrier of
%e activation energy for the rearrangement of the 48.96 kcal/mol and shows an endergonicity of 21.52 kcal/
rhenaoxetane (singlet surface) into the dioxylate is mol. No triplet transition state was observed for the for-
61.81 kcal/mol relative to the energetics of the reactants. No mation of the metallaoxetane intermediate.%e formation of
transition state was found for the rearrangement on the the dioxylate intermediate via the [2 + 2] pathway has an
triplet surface. Since the activation barrier for the rear- activation of 63.17 kcal/mol relative to the energetics of the
rangement of the oxetane to form dioxylate is kinetically reactants on a single PES. No triplet transition state was
hindered due to its high activation barrier, and the direct found for the rearrangement.
[3 + 2] addition forming the dioxylate is the most favored %e [3 + 2] pathway was the most plausible route in
mechanistic pathway. forming diols. However, the formation of an epoxide is not
%e formation of an epoxide from the rearrangement of plausible on both the singlet and triplet surfaces because no
the singlet oxetane (TS 1D in Scheme S1) has an activation such saddle point structures (TS 1B and TS 1D in
energy of 67.47 kcal/mol and showed an endergonicity of Scheme S1) were found. %is means that no side reactions
41.54 kcal/mol. %e triplet epoxide product is found to be are competing with the formation of the dioxylate and
13.65 kcal/mol less stable than the singlet epoxide product. metallaoxetane intermediates.
%e energetics for the ReO3Cl catalyzed epoxidation is fa-
vored compared to the ReO3F. %e potential energy surface
of the reaction of ReO3F with ethylene was further explored 3.3. Reaction of Ethylene with ReO3I. %e relative energies
to locate an epoxide precursor (FO2–Re–OC2H4) (TS 1B in and optimized structures involved in the reaction between
Scheme S1) from the [2 + 1] pathway. However, no mini- ethylene and ReO3I are shown in Figure 3(a) and 3(b),
mum was found, implying that the most favored pathway respectively. %e singlet optimized ReO3I structure has its
leading to the formation of the epoxide is the [2 + 2] three Re�O bond lengths at 1.706 Å, while the Re-I bond
pathway. As observed in the mechanism for both ReO −4 and length is 2.625 Å.%e triplet ReO3I has a Re-I bond length of
ReO3Cl, the reaction involving ReO3F in the [3 + 2] pathway 1.845 Å, and the three Re�O bond lengths are 1.705 Å,
is both kinetically and thermodynamically favorable con- 1.845 Å, and 1.706 Å. %e triplet rhenium oxo complex is
cerning dioxylation. 52.86 kcal/mol less stable than its singlet structure.
%e oxidation of the C�C bond by ReO3I to form a
dioxylate intermediate has an activation barrier of
3.2. Reaction of Ethylenewith ReO3Br. Shown in Figures 2(a) 35.78 kcal/mol and showed an endergonicity of
and 2(b) are the energetics and optimized structures of the 17.34 kcal/mol. No transition state was located on the
reactants, transition states, intermediates, and products triplet PES. A triplet dioxylate intermediate was found to
involved in the reaction between ethylene and ReO3Br, be 3.63 kcal/mol less stable than its singlet dioxylate. %e
respectively. %e singlet ReO3Br-optimized species has three transition state is symmetrical, and the newly forming
Re�O bond lengths equal to 1.705 Å while the Re-Br bond C-O bond length is 1.880 Å. %e spectator bonds (Re�O
length equals 2.409 Å. %e optimized triplet ReO3Br has a and a Re-I) of the dioxylate intermediate have bond
Re-Br bond length of 2.404 Å, and its three Re�O bond lengths of 1.682 Å and 2.620 Å, respectively, and the Re-O
lengths were 1.808 Å, 1.692 Å, and 1.808 Å, respectively. %e bond length was 1.901 Å. %e formation of a metal-
triplet rhenium oxo complex is 65.009 kcal/mol less stable laoxetane has an activation barrier of 49.10 kcal/mol with
than its singlet structure. an endergonicity value of 21.30 kcal/mol. No transition
Journal of Chemistry 5
Table 2: %e Frontier Molecular Orbitals calculation for the rhenium oxo complexes.
Entry Singlet HOMO/ LUMO/ HOMO/eV LUMO/eV
HOMO-LUMO/eV HOMO-LUMO/eV
reactants eV eV ethene ethene metal-ethylene ethylene-metal Nature of bondingbonding bonding
1 ReO −4 −2.99 3.47 −7.26 0.51 10.70 3.50 Reverse
2 ReO3F −9.75 −3.70 −7.26 0.51 3.56 10.26 Normal
3 ReO3Cl −9.82 −3.97 −7.26 0.51 3.97 10.33 Normal
4 ReO3Br −9.41 −3.91 −7.26 0.51 3.35 9.92 Normal
5 ReO3I −8.61 −3.87 −7.26 0.51 3.39 9.12 Normal
6 ReO3OH −9.30 −3.39 −7.26 0.51 3.87 9.81 Normal
E/kcal/mol 67.47
TS 1Ds
61.81
TS 2Cs
45.55 O
TS 1Cs O F
1.712 Re 1.882
O 2.299 1.798 41.54 O
1.700 F [2+2] O 1Ds O
Re 1.853 35.73 1.425 1.904
F
1.861 Re 1.693
1.778
1.876O O TS 1As 2.346
1.410 [3+2] O 1.456
1.469
19.65
1Cs
18.25
O F O 1AsO F
1.708 1.686Re 1.862 1.851
2.160 1.908 O Re 1.899
O 1.453 O
0.00 1.516 1.450 1.451
1.513
O
O
1.331
1.704 Re 1.841F
O reaction pathway
(a)
Figure 1: Continued.
6 Journal of Chemistry
TS 2Cs TS 1As
TS 1Cs TS 1Ds
(b)
Figure 1: (a) Gibbs free-energy profile diagram for the reaction between ReO3F and ethylene at the B3LYP/LACVP∗ level of theory. (b)
Optimized transition states involved in the reaction between ReO3F and ethylene at the B3LYP/LACVP∗ level of theory.
state for the formation of the metallaoxetane was found %e formation of a dioxylate (structure 1A in Scheme S1)
on the triplet PES. %e calculated transition state (TS 1C through the insertion of the C�C bond across the O�Re�O
in Scheme S1) has its newly forming C-O and Re-C bonds of ReO3OH functionality has an activation barrier of
at 2.321 Å and 1.907 Å, respectively. In the metallaxetane, 38.20 kcal/mol and shows an endergonicity of 20.82 kcal/
the two Re�O and Re-I spectator bond lengths are mol. No transition state was located on the PES. A triplet
1.708 Å, and 2.719 Å, respectively, and the Re-O bond dioxylate was found to be 4.70 kcal/mol less stable than its
length is 1.811 Å. %e activation energy for the rear- singlet. %e calculated transient (structure TS 1A in
rangement of the metallaoxetane (singlet surface) into the Scheme S1) shows high symmetry, and it is synchronous to
dioxylate is 63.40 kcal/mol relative to the energetics of the the newly forming C-O bond with a bond length of 1.870 Å.
reactants. No transition state was found for the rear- %e Re�O and Re-OH spectator bond lengths were 1.690 Å
rangement on the triplet PES. As observed with ReO3Br, and 1.882 Å, respectively, and the Re-O bond length was
the formation of epoxide is not plausible with ReO3I. 1.905 Å. In the triplet product, however, the Re�O and Re-
OH spectator bond lengths were 1.706 Å and 1.903 Å, re-
spectively, and the Re�O bond length was 1.930 Å.
3.4. Reaction of Ethylene with ReO3OH. %e relative energies %e [2 + 2] pathway has an activation barrier of
of the main stationary points (reactants, transition states, 49.25 kcal/mol and shows an endergonicity of 20.05 kcal/
intermediates, and products) and some optimized structures mol. No triplet transition state for the formation of the
involved in the reaction between ethylene and ReO3OH are metallaoxetane was observed on the triplet PES. %e cal-
shown in Figures 4(a) and 4(b), respectively. %e singlet culated transition state (TS 1C in Scheme S1) has its C-O and
ReO3OH optimized species has all its three Re�O bond Re-C bond lengths as 2.331 Å and 1.779 Å, respectively. In
lengths equal to 1.709 Å, while the Re-OH bond length the singlet product, the two Re�O and Re-OH spectator
equals 1.878 Å. %e triplet ReO3OH has a Re-OH bond bond lengths are 1.731 Å and 1.908 Å and the Re-O bond
length of 1.870 Å, and its three Re�O bond lengths were length is 1.961 Å. %e rearrangement of the singlet oxetane
1.813 Å, 1.699 Å, and 1.843 Å, with a slightly distorted tet- has an activation energy of 62.88 kcal/mol relative to the
rahedron geometry. %e triplet rhenium oxo complex is energetics of the reactants. No transition state was found for
64.65 kcal/mol less stable than its singlet structure. the rearrangement on the triplet PES. In this case, the [3 + 2]
Journal of Chemistry 7
E/kcal/mol
63.17
TS 2Cs
1.714 O
48.96 O BrRe 2.539
TS 1Cs 2.315 1.795O O
1.697 Br2.421 1.916
Re
1.776 34.87
1.414
O
1.883 O TS 1As
[3+2]
1.409
[2+2]
21.52
1Cs O
O Br
1.708 2.480
16.60
Re
2.179 1.908 1As O
O 1.682 Br2.411
1.516 1.448 O Re 1.900
1.449 O
1.451
0.00 1.516
O
O
1.331
1.705 Re 2.409Br
O
reaction pathway
(a)
TS 2Cs
TS 1As
TS 1Cs
(b)
Figure 2: (a) Gibbs free-energy profile diagram for the reaction between ReO3Br and ethylene at the B3LYP/LACVP∗ level of theory. (b)
Optimized transition states involved in the reaction between ReO3Br and ethylene at the B3LYP/LACVP∗ level of theory.
8 Journal of Chemistry
E/kcal/mol
63.40
TS 2Cs
1.714 O I
49.10 O Re 2.780
TS 1Cs 2.321 1.797
O O
1.697 I
Re 2.634 [2+2]
1.425 1.907
35.78
1.777
1.880O O TS 1As
[3+2]
1.410
21.38
1Cs O
O I
0.00 1.708 2.719 17.34Re
2.182 1.811 1As
O
O 1.517 1.441
O
1.682 I
O 2.620Re
1.331 O 1.9011.706 Re 2.625I 1.450 O
O 1.448
reaction pathway 1.518
(a)
TS 1As
TS 2Cs
TS 1Cs
(b)
Figure 3: (a) Gibbs free-energy profile diagram for the reaction between ReO3I and ethylene at the B3LYP/LACVP∗ level of theory. (b)
Optimized transition states involved in the reaction between ReO3I and ethylene at the B3LYP/LACVP∗ level of theory.
Journal of Chemistry 9
E/kcal/mol
71.69
TS 1Ds
62.88
TS 2Cs
1.727 O
49.25 O OH
Re 1.913
TS 1Cs 2.331 1.804
O
O 1.779 44.46
1.703 OH [2+2]
1.887 1Ds
O1.702
1.427 O
Re 38.20 Re
O 1.783 HO
TS 1As 1.889 2.3341.870 O
1.456 O 1.451
1.410 [3+2]
1.469
20.05 20.82
1As
1Cs O
O OH
O
1.690 OH
1.731 1.908Re O Re
1.882
2.175 1.961 1.905
O 1.450 O
1.530 1.427
1.448
1.513
0.00
O
O
1.331
1.709 Re 1.878OH
O reaction pathway
(a)
TS 1Cs TS 1As
TS 2Cs TS 1Ds
(b)
Figure 4: (a) Gibbs free-energy profile diagram for the reaction between ReO3OH and ethylene at the B3LYP/LACVP∗ level of theory. (b)
Optimized transition states involved in the reaction between ReO3OH and ethylene at the B3LYP/LACVP∗ level of theory.
10 Journal of Chemistry
mechanistic pathway is the most plausible route to form the to use the Spartan cluster, and the Centre for High-Per-
dioxylate. In the exploration of the formation of an epoxide formance Computing (CHPC-South Africa) for allowing to
precursor (TS 1D in Scheme S1) from the rearrangement of use the cluster.
the oxetane, an activation barrier of 58.55 kcal/mol was
observed with an equivalent endergonicity value of
71.69 kcal/mol. A triplet epoxide was found to be 12.19 kcal/ Supplementary Materials
mol less stable than the singlet epoxide. Scheme S1: the proposed concerted addition mechanistic
%e potential energy surface of the reaction of ReO3OH pathway for the reaction of ReO3L (L =O−, Cl–, F−, Br, I−,
with ethylene was then explored to locate an epoxide pre- and OH−) with ethylene. Figure S1: energy profile diagram
cursor (HOO2–Re–OC2H4) [TS 1B in Scheme S1] from the for the reaction between ReO −4 and ethylene using B3LYP/
direct addition of the ethylene to the oxo complex [2 + 1], LACVP∗ level of theory. Figure S2: energy profile diagram
but no such minima were found on the reaction surface for the reaction between ReO3Cl and ethylene using B3LYP/
making the [2 + 2] pathway themost favorable one leading to LACVP∗ level of theory. Figure S3: the energy diagram for
the formation of the epoxide. the movement of electrons between the HOMO and LUMO
%e optimized singlet and triplet structures of for the of ReO3Cl and ethylene using B3LYP/LACVP∗ level of
involved reaction mechanism are shown in Figure S9 to theory. Figure S4: the energy diagram for the movement of
Figure S15. electrons between the HOMO and LUMO of ReO3F and
ethylene using B3LYP/LACVP∗ level of theory. Figure S5:
4. Conclusions the energy diagram for the movement of electrons between
the HOMO and LUMO of ReO3Br and ethylene using
%e results of this study show that the [3 + 2] mechanistic B3LYP/LACVP∗ level of theory. Figure S6: the energy di-
pathway is both kinetically and thermodynamically favored agram for the movement of electrons between the HOMO
for the formation of dioxylate. Comparing the catalysts and LUMO of ReO3I and ethylene using B3LYP/LACVP∗
studied in the manuscript to ReO −4 and ReO3Cl studied by level of theory. Figure S7: the energy diagram for the
Aniagyei et al. [16], the ReO3Cl catalyst is the best for the movement of electrons between the HOMO and LUMO of
dioxylate transformation. %e activation energies for the ReO3OH and ethylene using B3LYP/LACVP∗ level of the-
formation of the dioxylate follow the ligand order ory. Figure S8: the energy diagram for the movement of
O−>OH−> I−> F−>Br−>Cl−. %e hydroxylation ability of electrons between the HOMO and LUMO of ReO −4 and
the catalysts decreases down the group of the halogens ethylene using B3LYP/LACVP∗ level of theory. Figure S9:
except for the fluorine ligand. In the case where epoxide optimized singlet structures of the reactants involved be-
formation is possible, it goes through the [2 + 2] mechanistic tween ReO3L (L =O−, Cl−, F−, OH−, Br−, and I−) and ethene.
pathway. Among the catalyst studied, only ReO3F, ReO3Cl Figure S10: optimized triplet structures of the reactants
and ReO3OH showed potential epoxidation catalytic ability, involved between ReO
− − − − − −
3L (L =O , Cl , F , OH , Br , and I )
with ReO3F being the best. %e electron flow for the oxi- and ethene. Figure S11: optimized dioxylate involved in the
dation reactions occurs from the HOMO of ethylene to the reaction between ReO L (L =O−, Cl−, F−3 , OH−, Br−, and I−)
LUMO of the rhenium oxo complexes in all cases except for and ethene on the singlet PES. Figure S12: optimized
ReO −4 where vice versa occurs. For the ReO −4 , ReO3I, and dioxylate of the reaction involved between ReO3L (L =O
−,
ReO3Br reaction surfaces, no side reactions are competing Cl
−, F−, OH−, Br−, and I−) and ethene on the triplet PES.
with the formation of the dioxylate and metallaoxetane Figure S13: optimized oxetane involved in the reaction
intermediates. %e polarity of the complexes studied shows between ReO L (L =O−, Cl−, F−, OH−, Br−3 , and I−) and
that ReO3OH is the most polar with ReO3I having the ethene on the singlet PES. Figure S14: optimized oxetane
highest polarity for the halogen ligands. %at means, involved in the reaction between ReO3L (L =O−, Cl−, F−,
ReO3OH when used as a catalyst to oxidize ethylene to OH
−, Br−, and I−) and ethene on the triplet PES. Figure S15:
vicinal diols will show high catalytic activity in polar solvents optimized epoxide structures involved in the reaction be-
due to its high solubility. tween ReO L (L =O−, Cl−, F−3 , OH−, Br−, and I−) and ethene
on the singlet PES. Figure S16: optimized epoxide structures
Data Availability involved in the reaction between ReO L (L =O
−, Cl−, F−3 ,
OH−, Br−, and I−) and ethene on the triplet PES. (Supple-
%e data are given in the supplementary document attached mentary Materials)
to the manuscript for submission.
References
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