A computational study of the addition of ReO3L (L = Cl−, CH3, OCH3 and Cp) to ethenone

The periselectivity and chemoselectivity of the addition of transition metal oxides of the type ReO3L (L = Cl, CH3, OCH3 and Cp) to ethenone have been explored at the MO6 and B3LYP/LACVP* levels of theory. The activation barriers and reaction energies for the stepwise and concerted addition pathways involving multiple spin states have been computed. In the reaction of ReO3L (L = Cl−, OCH3, CH3 and Cp) with ethenone, the concerted [2 + 2] addition of the metal oxide across the C=C and C=O double bond to form either metalla-2-oxetane-3-one or metalla-2,4-dioxolane is the most kinetically favored over the formation of metalla-2,5-dioxolane-3-one from the direct [3 + 2] addition pathway. The trends in activation and reaction energies for the formation of metalla-2-oxetane-3-one and metalla-2,4-dioxolane are Cp < Cl− < OCH3 < CH3 and Cp < OCH3 < CH3 < Cl− and for the reaction energies are Cp < OCH3 < Cl− < CH3 and Cp < CH3 < OCH3 < Cl CH3. The concerted [3 + 2] addition of the metal oxide across the C=C double of the ethenone to form species metalla-2,5-dioxolane-3-one is thermodynamically the most favored for the ligand L = Cp. The direct [2 + 2] addition pathways leading to the formations of metalla-2-oxetane-3-one and metalla-2,4-dioxolane is thermodynamically the most favored for the ligands L = OCH3 and Cl−. The difference between the calculated [2 + 2] activation barriers for the addition of the metal oxide LReO3 across the C=C and C=O functionalities of ethenone are small except for the case of L = Cl− and OCH3. The rearrangement of the metalla-2-oxetane-3-one–metalla-2,5-dioxolane-3-one even though feasible, are unfavorable due to high activation energies of their rate-determining steps. For the rearrangement of the metalla-2-oxetane-3-one to metalla-2,5-dioxolane-3-one, the trends in activation barriers is found to follow the order OCH3 < Cl− < CH3 < Cp. The trends in the activation energies for the most favorable [2 + 2] addition pathways for the LReO3–ethenone system is CH3 > CH3O− > Cl− > Cp. For the analogous ethylene–LReO3 system, the trends in activation and reaction energies for the most favorable [3 + 2] addition pathway is CH3 > CH3O− > Cl− > Cp [10]. Even though the most favored pathway in the ethylene-LReO3 system is the [3 + 2] addition pathway and that on the LReO3–ethenone is the [2 + 2] addition pathway, the trends in the activation energies for both pathways are the same, i.e. CH3 > CH3O− > Cl− > Cp. However, the trends in reaction energies are quite different due to different product stabilities. The formation of the acetic acid precursor through the direct addition pathways was unsuccessful for all the ligands studied. The formation of the acetic acid precursor through the cyclization of the metalla-2-oxetane-3-one is only possible for the ligands L = Cl−, CH3 whiles for the cyclization of metalla-2-oxetane-4-one to the acetic acid precursor is only possible for the ligand L = CH3. Although there are spin-crossover reaction observed for the ligands L = Cl−, CH3 and CH3O−, the reactions occurring on the single surfaces have been found to occur with lower energies than their spin-crossover counterparts.


Background
Reactive intermediates are employed in increasingly diverse ways for synthetic purposes, and understanding of the underlying chemistry has become an essential part of synthesis. The development of new catalytic reactions that enhance chemical transformations with high selectivity and efficiency is a grand challenge in chemical research.
Ethenone, the simplest member of the ketene family, is a reactive intermediate with many useful synthetic applications in chemical industry. Ketenes are widely applied in synthetic chemical processes such as ketene dimers for conversion to 1,3-cyclobutanediols as replacements for bisphenol A in the preparation of polyesters and polycarbonates, manufacture of acetic acid and in vital pharmaceutical applications such as the preparation of β-lactam antibiotics (Ulrich 1967(Ulrich , 2009. Experimental and theoretical studies focusing on the mechanism of addition of transition metal-oxo species of the type LReO 3 to the C=C double bonds addition to ketene has been reported (Deubel et al. 2001;Middleditch et al. 2007;Herrmann et al. 1985Herrmann et al. , 1986Herrmann et al. , 1994. Middleditch et al. (2007) in an experimental study of the reaction of rhenium (VII) trioxo complexes containing the ligand sets scorpionate, [HB(pz) 3
In another experimental study, Herrmann et al. (1985) reported that the stable mononuclear complex Cp* ReO 3 can be reacted with an excess of diphenyl ketene in THF at room temperature to yield the corresponding [3 + 2] cycloaddition product. The isolated five membered [3 + 2] product was characterized by X-ray analysis. Herrmann et al. (1994) in an experimental study, also showed that when methyltrioxorhenium (VII), MTO was coordinated with a bipyridyl ligand, the resulting octahedral complex could be reacted with an excess of diphenyl ketene in THF to yield the corresponding [3 + 2] cycloaddition product. Herrmann et al. reported that when MTO‚4-tert-butylpyridine was reacted with diphenyl ketene in the presence of an excess of 4-tert-butylpyridine base, an instantaneous [3 + 2] cycloaddition product was formed. Deubel et al. (2001) reported a theoretical studies on the periselectivity, chemoselectivity, stereoselectivity and regioselectivity of the addition of the transition metaloxide OsO 4 and LReO 3 (L = O − , NPH 3 , CH 3 , Cp and Cp*) to ketenes. In the reaction of LReO 3 , L = O − , NPH 3 , CH 3 , Cp and Cp* with ketenes, Deubel et al. found the activation barrier for the [2 + 2] addition across the C=O moiety of the ketene to be the lowest for the ligands, L = (O − and NPH 3 ) and the [2 + 2] addition across the C=C moiety to be the lowest for the ligands, L = CH 3 and Cp. However, the differences between the calculated [2 + 2] activation barriers were calculated to be small.
Recently, Ahmed et al. (2015) reported density functional theory calculation at the MO6/LACVP* and B3LYP/LACVP* levels of theory on the peri-, chemoand regio-selectivity of the addition of transition metal oxo complexes of the type ReO 3 L (L = Cl − , O − , OCH 3 , CH 3 ) to substituted ketenes O=C=C (CH 3 ) (X) [X = CH 3 , H, CN and Ph] with the aim of elucidating the effect of substituents on the mechanism of the reactions. They reported the [2 + 2] addition pathway across the C=C or C=O (depending on the ligand) to be the most preferred pathway in the reactions of dimethyl ketene with all the metal complexes studied. The [2 + 2] addition pathway is also the most preferred in the reactions of ReO 3 Cl with all the substituted ketenes studied except for when X = Cl where the [3 + 2] addition pathway is preferred. The order in the activation energies of the reactions of dimethyl ketenes with the metal complexes ReO 3 L with respect to changing ligand L is O − < CH 3 O − < Cl − < CH 3 while the order in reaction energies is CH 3 < CH 3 O − < O − < Cl − was reported by Ahmed et al. (2015).
In contrast to ketenes, experimental and theoretical investigations on the mechanism of addition of transition metal-oxide of the type LMO 3 (M = Mn, Tc and Re) across the C=C double bonds of olefins has been extensively reported (Sharpless and Akashi 1975;Wiberg 1965;Aniagyei et al. 2013a, b, c;Adei 2009, 2011;Nelson et al. 1997;Corey and Noe 1997;Haller et al. 1997;Houk and Strassner 1999;Torrent et al. 1998;Del Monte et al. 1997;Tia and Adei 2011;Pietsch et al. 1998;Deubel and Frenking 1999;Gisdakis and Rösch 2001). Ketenes are related to olefins by the presence of the C=C double bonds but ketenes constitute activated double bonds due to the presence of the C=O double bond directly bonded to the C=C double bond. Therefore the chemistry of the addition of transition metal oxo complexes of the type LReO 3 to ketenes is much expected to be the same as olefins periselectivity.
In this work, the chemoselectivity and periselectivity of the addition of LReO 3 (L = Cl, Cp, CH 3 and OCH 3 ) to ethenone is carried out by employing hybrid density functional theory at the MO6 and B3LYP/LACVP* level of theory to calculate the energetics of the concerted and stepwise [3 + 2] and [2 + 2] addition pathways. Also the possible mechanistic channels to the formation of the ethanoic acid precursor (Schemes 1, 2, 3, 4) is explored. The singlet and triplet spin states have been considered in this work. The addition of the metal oxides LReO 3 across the C=O moiety of the ethenone leading to the [2 + 2] products such as metalla-2-oxolanes and metalla-2,3-dioxolane and also the [3 + 2] products such as metalla-2,3,5-trioxolane which were not explored in the previous works of Deubel et al. (2001) and Ahmed et al. (2015) are fully explored in this studies. Also the nucleophilic attack of both the carbonyl carbon and the adjacent carbon atom on an oxo ligand of the metal oxide is explored in this studies which was partially explored in the work of Ahmed et al. (2015) and not explored in the work of Deubel et al. (2001). Knowledge of the mechanistic details of these kinds of reactions might open new methods for efficient activation of double bonds by readily accessible transition metal-oxides, beyond the common methods of cis-hydroxylation using metal-oxides.

Details of calculation
We performed all the computations with the Spartan (2010) computational chemistry package developed by Wavefunction, Inc., versions 2008V1.2.0 and 2010V1.2.0, using the Becke-three-parameter Lee-Yang-Parr (B3LYP) hybrid exchange-correlational functional and the MO6 hybrid functional. The B3LYP functional, a Hartree-Fock DFT hybrid functional, is made up of the exchange-correlation energy from the local spin-density approximation (LSDA) method, 20 % of the difference between the Hartree-Fock exchange energy (Kohn-Sham exchange energy) and the LSDA exchange energy, 72 % of the Becke exchange potential (which includes the 1988 correction) (Becke 1988(Becke , 1996, 81 % of the Lee-Yang-Parr correlation potential (Lee et al. 1988) and 19 % of the Vosko-Wilk-Nusair potential (Vosko et al. 1980) and is one of the most widely used exchange-correlation functionals in organometallic chemistry. The MO6 functional (Zhao and Truhlar 2008) is a global hybrid metageneralized gradient approximation (meta-GGA) with 27 % of Hartree-Fock exchange, leading to a well-balanced functional for overall good performance for chemistry. It has thus been recommended for application in organometallic and inorganometallic chemistry (Peverati and Truhlar 2014). The atoms hydrogen-chlorine were described with the 6-31G (d) basis set while the metal Re was described with the LANL2DZ basis set (Dunning and Hay 1976;Wadt 1985a, 1985b;Wadt and Hay 1985;Roy et al. 2008). The MO6/LANL2DZ and B3LYP/LANL2DZ are the two most popular DFT levels of theory for organometallic and inorganic chemistry to date. The latest review article on DFT methods for computational studies of synthetically relevant homogeneous organometallic catalysis (Sperger et al. 2015) indicates that between the period 2009-2014 geometry optimization calculations are dominated by the LANL2DZ as ECP for the transition metal. Table 1d of that review shows that for the period 2013-2014, 51 % of all reviewed studies employed the LAN2DZ basis set for geometry optimization. The same review indicates that currently, the first choice of functional for energy calculations of TM systems is M06, followed by B3LYP, DFT-D3, and M06L, whereas the choice of basis set for the description of the transition metal is dominated by LANL2DZ and SDD (the Stuttgart-Dresden ECP with double zeta basis set).
Spartan uses a graphical model builder for input preparation. Molecules were constructed and minimized interactively using an appropriate molecular mechanics force field. All structural optimizations were done without symmetry restrictions. Normal mode analysis was performed to verify the nature of the stationary points located. Minima, representing reactants, intermediates and products were shown to have no imaginary frequencies.
Guess structures for transition state calculations were obtained by first constraining specific bonds along the reaction coordinates at fixed lengths while the remaining internal coordinates were fully optimized. This procedure gives an approximate transition state guess which is then submitted for transition state calculation using the standard transition state optimization procedure in Spartan. All transition state structures were subjected to full normal mode analyses to ensure that they have a Hessian matrix with a single negative eigen-value, characterized by an imaginary vibrational frequency along the reaction coordinate. An intrinsic reaction coordinate (IRC) calculation was carried out to ensure that transition states smoothly connect reactants and products. Figure 1 shows the relative energies of the main stationary points (reactants, transition states, intermediates and products) involved in the reaction between ReO 3 Cl and ethylene as well as some of the optimized structures.

Reaction of ReO 3 Cl with ethenone
The singlet ReO 3 Cl has all the Re-O bonds equal at 1.70 Å and the Re-Cl bond at 2.27 Å. The singlet structure is 62.7 kcal/mol more stable than the triplet structure.
On the singlet potential energy surface (PES), the concerted [3 + 2] addition of the C=C bond of ethenone (C=C=O) across the O=Re=O bond of singlet ReO 3 Cl to form metalla-2,5-dioxolane-3-one, A2/s ( Fig. 1) has an activation barrier of 27.4 kcal/mol and an exothermicity of 10.8 kcal/mol through the singlet transition state TS-[A1-A2]/s. At the M06 level of theory, the activation barrier and exothermicity are calculated to be 28.2 and 17.9 kcal/mol.
On the triplet PES, the formation of A2/t proceed in a stepwise manner as depicted in Schemes 3 and 4. In of ReO 3 Cl is the favorable and leads to the formation of A2/t. The species A2/s has been found to be 10.7 kcal/ mol more stable than the triplet counterpart A2/t. The rearrangement of the metalla-2,5-dioxolane-3-one intermediate, A2 to the acetic acid precursor on both the singlet and triplet PES could not located.
The formation of metalla-2-oxetane-3-one, A4/s ( Fig. 1) resulted from the direct [2 + 2] addition of the The calculated activation and reaction energies for the [2 + 2] addition of the C=C moiety of ketene across the Re=O functionality of ReO 3 Cl is about 4 and 6.8 kcal/ mol lower at the M06 level than at the B3LYP level of theory. Since the difference in energy barrier for the [3 + 2] addition pathways at the B3LYP and MO6 level of theory is similar, the remaining calculations were performed at the B3LYP/LACVP* level of theory. The MO6 results do not change the preferred addition pathway.

Reaction of ReO 3 CH 3 with ethenone
The optimized geometries and the energy profile of the reaction of ReO 3 (CH 3 ) with ethenone is shown in Fig. 2. The singlet reactant is calculated to be 68.0 kcal/mol more stable than the triplet reactant.
On the singlet PES, the formation of metalla-2,5-dioxolane-3-ones, species B2/s by the concerted [3 + 2] addition of the C=C functionality of ethenone across the O=Re=O bonds of singlet ReO 3 (CH 3 ) has activation barrier of 38.1 kcal/mol and endothermicity of 4.5 kcal/mol. Deubel et al. (2001) calculated the activation barrier and reaction energy for this route to be 44.5 and 16.3 kcal/mol respectively at the B3LYP/III+// B3LYP/II level with relativistic small-core ECPs and a (441/2111/21) valence-basis set.
On the triplet PES, the formation of B2 which was not reported in the work of Deubel and co-workers (  On the singlet PES, the formation of metalla-2-oxetane-4-one, B10/s (Fig. 2) is concerted. The activation barrier and endothermicity of the process are 44.8 and 4.7 kcal/mol. On the triplet surface, the carbon atom adjacent the carbonyl carbon of the C=C=O attacks an oxo ligand of ReO 3 CH 3 to form the intermediate X/t through a triplet transition state TS-[B1-X]/t. The activation and reaction energy for the formation of this intermediate are 57.9 and 30.6 kcal/mol respectively. B10/t could then be formed from the triplet intermediate X/t, through the triplet transition state TS-[X-B10]/t with an activation barrier of 32.5 kcal/mol and endothermicity of 3.3 kcal/mol. B2/s could also be formed from B10/s through the singlet transition state TS-[B10-B2]/s. The activation barrier for this route is 30.5 kcal/mol. On the triplet surface, the activation barrier is 50.2 kcal/mol. The acetic acid precursor B3/s is formed from B10/s through the transition state TS-[B10-B3]/s. The activation barrier for the process is 55.2 kcal/mol. The formation of metalla-2,4-dioxolane, B12/s on the singlet PES by the direct [2 + 2] addition of C=O functionality of ethenone across the Re=O bond of singlet ReO 3 CH 3 has activation barrier of 20.6 kcal/mol and exothermicity of 2.2 kcal/mol. Deubel et al. (2001) reported values of 23.3 and 0.5 kcal/mol for the activation and reaction energy respectively at the B3LYP/III+// B3LYP/II level with relativistic small-core ECPs and a (441/2111/21) valence-basis set.
On the triplet surface and not explored in Deubel et al. (2001) work, the concerted addition leading to the formation of B12/t has activation barrier of 49.1 kcal/mol and endothermicity of 9.9 kcal/mol. The singlet species B12/s has been found to be 7.7 kcal/mol more stable than B12/t. Figure 3 shows the optimized geometries and relative energies of the main stationary points involved in the reaction between ReO 3 (OCH 3 ) and ethenone. The singlet reactant C1/s is 63.8 kcal/mol more stable than the triplet C1/t.

Reaction of ReO 3 (OCH 3 ) with ethenone
On the singlet PES, the concerted [3 + 2] addition of the C=C bond of ethenone (C=C=O) across the O=Re=O bond of singlet ReO 3 OCH 3 to form metalla-2,5-dioxolane-3-one, C2/s (Fig. 3) has an activation barrier of 28.8 kcal/mol and an endothermicity of 2.5 kcal/ mol through the singlet transition state TS-[C1-C2]/s. On the triplet PES, the formation of C2/t proceed in a stepwise manner as depicted in Schemes 3 and 4. In one route, the carbon atom adjacent the carbonyl carbon of the C=C=O attacks an oxo ligand of ReO 3 OCH 3 to form the intermediate X/t through a triplet transition state TS-[C1-X]/t. The activation and reaction energy for the formation of this intermediate are 60.1 and 32.4 kcal/ mol respectively. The triplet intermediate X/t, then rearranges to C2/t through a triplet transition state TS-[X-C2]/t with an activation barrier of 6.5 kcal/mol and reaction energy of −35.7 kcal/mol. Alternatively, C2/t could be formed by direct attack of the carbonyl carbon of ethenone (C=C=O) on an oxo ligand of ReO 3 Cl to form the intermediate K/t through a triplet transition state TS-[C1-K]/t. The activation and reaction energy for the formation of this triplet intermediate are 51.4 and 17 kcal/mol respectively. The triplet intermediate K/t, then re-arranges to C2/t through a triplet transition state TS-[K-C2]/t with an activation barrier of 14.6 kcal/mol and reaction energy of −20.3 kcal/ mol. Though both stepwise routes leads to the formation of C2/t, the attack of the carbonyl carbon on the oxo ligand of ReO 3 Cl is the favorable and leads to the formation of C2/t. The species C2/t has been found to be 0.8 kcal/mol more stable than C2/s. The rearrangement of the metalla-2,5-dioxolane-3-one intermediate, C2 to the acetic acid precursor on both the singlet and triplet PES could not located.
The formation of metalla-2-oxetane-3-one, C4/s (Fig. 3) resulted from the direct [2 + 2] addition of the C=C bond of ethenone across the Re=O bond of singlet ReO 3 OCH 3 . The activation barrier and exothermicity of the process are 14.2 and 7.3 kcal/mol respectively. Species C2/s could be formed from C4/s through the transition state TS-[C4-C2]/s. The activation barrier for the rearrangement process is 37.8 kcal/mol. On the triplet surface, the activation barrier for the rearrangement process is 40.5 kcal/mol. A search for the formation of the acetic acid precursor, 3 whether through the direct addition pathway or rearrangement of the metalla-2-oxetane-3-one intermediate both on the singlet and triplet surfaces proved unsuccessful.
The formation of metalla-2-oxetane-4-one, C10/s (Fig. 3) by the direct [2 + 2] addition of the C=C bond of ethenone across the Re=O bond of singlet ReO 3 OCH 3 through the singlet transition state TS-[C1-C10]/s has an activation barrier and endothermicity of the process are 13.2 and 4.9 kcal/mol respectively. C10/s could rearrange to C2/s through the transition state TS-[C10-C2]/s to form the five membered metallacycle C2/s. The activation barrier for the rearrangement process is 29.5 kcal/mol. On the triplet surface, the activation barrier for the rearrangement process is 42.6 kcal/mol. An exhaustive attempt to locate the triplet counterpart of C2/s and the acetic acid precursor through the direct and rearrangement route proved futile.
The concerted [3 + 2] addition of the C=O bond of ethenone(C=C=O) across the O=Re=O bond of singlet ReO 3 OCH 3 to form metalla-2,3,5-trioxolane, C11/s has Fig. 3 Energetics of the reaction of ReO 3 OCH 3 with ethenone on the singlet and triplet PES at B3LYP/LACVP* an activation barrier of 17.4 kcal/mol and an exothermicity of 2.8 kcal/mol through the transition state TS-[C1-C11]/s. No triplet species was obtained. Also an attempt to locate an acetic acid precursor through the rearrangement of C11/s intermediate did not yield any results. The formation of metalla-2,4-dioxolane C12/s (Fig. 3) on the singlet PES by the direct [2 + 2] addition of the C=O moiety of C=C=O across the Re=O bond of singlet ReO 3 OCH 3 has activation and reaction energies of 19.9 and 1.38 kcal/mol respectively. The triplet counterpart of C12/s was computed to be 9.9 kcal/mol. No acetic acid precursor is located on both the singlet and triplet PES explored.
The formation of metalla-2,3-dioxolane C15/s on the singlet PES by the direct [2 + 2] addition of the C=O moiety of C=C=O across the Re=O bond of singlet ReO 3 OCH 3 has activation and reaction energies of 92.9 and 82.1 kcal/mol respectively. No triplet counterpart of C15/s and acetic acid precursor were located on the surface. Figure 4 shows the optimized geometries and relative energies of the main stationary points involved in the reaction between ReO 3 Cp and ethylene. In the singlet reactant, the cyclopentadienyl ligand (Cp) is bonded to the metal center in a η 5 -fashion i.e. Re-C (Cp) = 2.49, 2.51, 2.52, 2.49 and 2.46 Å, in agreement with work of Deubel and Frenking (Wiberg 1965;Pietsch et al. 1998). No triplet species could be located for the reactant.

Reaction of ReO 3 Cp with ethenone
On the singlet PES, the formation of metalla-2,5-dioxolane-3-ones, species D2/s by the concerted [3 + 2] addition of the C=C functionality of ethenone across the O=Re=O bonds of singlet ReO 3 Cp has activation barrier of 17.6 kcal/mol and exothermicity of 38.9 kcal/mol. Deubel et al. (2001) reported the activation barrier and reaction energy for this route to be 24.8 and −29.2 kcal/ mol respectively at the B3LYP/III+//B3LYP/II level with relativistic small-core ECPs and a (441/2111/21) valencebasis set.
An attempt to locate the acetic acid precursor through the direct addition pathway and the rearrangement of species D2/s proved unsuccessful.
Also, the formation of metalla-2-oxetane-4-one, D10/s on the singlet surface is concerted. The activation barrier and exothermicity of the process are 48.9 and 5.90 kcal/ mol. D10/s rearranges to D2/s through the transition state TS-[D10-D2]/s. The activation barrier for this route is 26.2 kcal/mol. On the triplet surface, the activation barrier is 47.8 kcal/mol. An attempt to locate the acetic acid precursor either from the direct addition pathway or the rearrangement of D10/s proved futile.
The formation of metalla-2,4-dioxolane, D12/s on the singlet PES by the direct [2 + 2] addition of C=O functionality of ethenone across the Re=O bond of singlet ReO 3 Cp has activation barrier of 9.6 kcal/mol and exothermicity of 11.9 kcal/mol. Deubel et al. (2001) reported values of 12.9 and −5.3 kcal/mol for the activation and reaction energy respectively at the B3LYP/III+// B3LYP/II level with relativistic small-core ECPs and a (441/2111/21) valence-basis set. On the triplet surface not explored in Deubel et al. (2001) work, the concerted addition leading to the formation of D12/t has a reaction energy of 7.3 kcal/mol. Species D12/s has been found to be 19.2 kcal/mol more stable than D12/t. The rearrangement of the singlet and triplet D2 intermediate to the acetic acid precursor proved unsuccessful.
The formation of metalla-2,3-dioxolane D15/s on the singlet PES by the direct [2 + 2] addition of the C=O moiety of C=C=O across the Re=O bond of singlet ReO 3 Cp has activation and reaction energies of 78.7 and 60.9 kcal/mol respectively. No triplet counterpart of D15/s and acetic acid precursor were located on the surfaces.
The formation of the acetic acid precursor 3 through the direct addition pathways was unsuccessful for all the ligands studied. The activation barriers for the formation of the acetic acid precursor through the cyclization of the metalla-2-oxetane-3-one, 4 is only possible for the ligands L = Cl − , CH 3 whiles for the cyclization of metalla-2-oxetane-4-one, 10 to the acetic acid precursor is only possible for the ligand CH 3 . The formation of the metalla-2,3,5-trioxolane, 11 from the direct [3 + 2] addition of ReO 3 L (L = Cl − ) to the C=O bond of ethenone is competitive to the direct [2 + 2] addition to form metalla-2,4-dioxolane, 12 when L = Cl − and also kinetically most favored over the direct [3 + 2] addition of ReO 3 L (L = Cl − ) to form metalla-2,5-dioxolane-3-one, 2. The formation of metalla-2,3-dioxolane, 15 for the ligand, (L = Cl − , Cp and CH 3 O − ) studied are uncompetitive in terms of higher activation and reaction energies. The trends in activation and reaction energies are found to follow the order Cp < CH 3 O − < Cl and Cp < Cl < CH 3 O − . Although there are spin-crossover reaction observed for the ligands (L = Cl − , CH 3 and CH 3 O − ), the reactions occurring on the single surfaces have been found to occur with lower energies than their spin-crossover counterparts.