158
A. Ibdah, H. B. Bakar, and S. Alduwikat
O
O
O
Me
Me
O
S
Me
S
S
Re
Re
Re
ϩ
N
X
O
N
O
S
S
S
N
X ϭ Me, H, NO2
X
X
Scheme 10. The small reaction model for the DFT calculation.
by DFT (M11-L) for the proposed oxidation step using the small
reaction model (Scheme 10)
Supplementary Material
P-NMR spectra, UV repeating scan experiments, kinetic data,
MacMolplt drawing of half-open structure, coordinate and
absolute energy of the computational study, and derivation of
rate law are available on the Journal’s website.
All the optimized transition states and intermediates were
verified through calculating the vibrational frequency (Hessian
calculation) of the optimized geometries. The transition state
structures were confirmed through intrinsic reaction coordi-
nate (IRC) calculations. The enthalpy of activation of the
nitropyridine release step is DHz ¼ 11.7 kcal molꢁ1 [23]
.
The
Conflicts of interest
enthalpy of activation (DHz) for pyridine oxide and picoline
oxide is 11.5 and 11.9 kcal molꢁ1 respectively. The DFT
calculation shows that the oxidation of ReVO to ReVIIO2
and pyridine release step are independent of the nature of the
substituent on the pyridine. The enthalpy of the reaction (DH)
for an NO2 substituent (ꢁ26.7 kcal molꢁ1[23]) is more exother-
The authors declare no conflicts of interest.
Acknowledgements
This work was supported by the Deanship of research at Jordan University of
Science and Technology, Irbid, Jordan.
mic than for H (ꢁ22.7 kcal molꢁ1) and Me (ꢁ21.7 kcal molꢁ1
)
References
substituents. The enthalpy with the nitro group is more
negative than with a methyl and hydrogen substituent because
the aromatic ring gains further stability on reduction with the
electron-withdrawing effect of the nitro substituent. The Re–O
and N–O bond length of the ReVO intermediates and the
transition states along with Mulliken charges on ReV, O, N,
and ReVII were also analysed (Supplementary Material). In the
transition state (TS) structures, the Re–O length decreases
and the N–O bond length increases. The Mulliken charges on
Re increase as a result of oxidation and the negative charges on
the N increase as a result of reduction. It also shows that the
substituent on the pyridine ring does not have a substantial
effect on the N charges for both the intermediates and the
transition state. The substituents on the pyridine oxide do not
have a considerable effect on the N–O bond length and the
charges on both N and O. The above calculation supports that
the rate-determining step is insensitive to the nature of the
pyridine oxide substituent.
In summary, DFT calculations and kinetics show that the
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monomerization shows that {MeReO(edt)}2 dimer has a lower
enthalpy than the {MeReO(pdt)}2 dimer. The reactivity differ-
ence between the two dimers was traced to the higher angle
strain on the bridging sulfur of {MeReO(edt)}2 than of the
{MeReO(pdt)}2 dimer.
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