The poster that I presented at the 253rd American Chemical Society National Meeting and Exposition in San Francisco, CA. It highlights some of my REU research at North Carolina State University under the mentorship of Dr. Elon Ison.

1. The strength of aluminum Lewis acid is best manifested in its stabilization of MTO molecule via
the coordination through the Re=O bond (∆Go= -17.5 kcal/mol). For comparison, the
stabilization provided by B(C6F5)3 is much smaller (∆Go= +2.3 kcal/mol). In order to evaluate the
catalytic competency of these molecules, we carried out hydrogenation reaction of our model
substrate, cyclooctene under conditions outlined below:
Computational and Experimental Studies of MTO Catalyzed Olefin Hydrogenation
Karam B. Idrees, Nikola Lambic, and Elon A. Ison*
North Carolina State University, Department of Chemistry, Raleigh, NC 27695-8204
Hydrogenation reactions is the conversion of alkenes(olefins) to alkanes by adding hydrogens
across the double bond. The reaction is usually carried out in the presence of metal catalysts:
However, we discovered that MTO can catalyze the hydrogenation reaction by itself after a
lengthy induction period of 20 h.
In the absence of B(C6F5)3, the reaction catalyzed by MTO proceeds to completion via the
formation of a putative Re-H analog capable of inserting the substrate to yield a rhenium alkyl,
which is then cleaved by H2 activation to regenerate the Re-H and achieve turnover.
TS1 TS2
Introduction
Olefin Hydrogenation Using FLPs
Mechanistic Considerations of MTO Activation
Catalytic Cycle of Pathway A
Energy Diagram of Pathway A
Transition States Analysis
Conclusions and Future Work
-REU at the Interface of Computations and
Experiments coordinators: Dr. Elon Ison, Dr. Elena
Jakubikova, and Dr. Reza Ghiladi.
DFT Calculations
B(C6F5)3
Al(C6F5)3
Increasing Lewis acidity
LA= Al(C6F5)3
∆Go= -17.5 kcal/mol
Optimized Lewis Acid/Base Adducts Structures:
MTO/ B(C6F5)3
Acid/Base adduct
MTO/ Al(C6F5)3
Acid/Base adduct
Lewis Acidity:
-40
-20
0
20
40
60
80
GibbsFreeEnergy(kcal/mol)
ReactionCoordinate
∆Go= 0.0 kcal/mol ∆G‡= 58.6 kcal/mol ∆Go= -7.2 kcal/mol
Imaginary frequency: -1284.4 cm-1
Imaginary frequency: -547.6 cm-1
∆Go= -7.2 kcal/mol ∆G‡= 30.9 kcal/mol ∆Go= -29.6 kcal/mol
∆Go= -29.6 kcal/mol ∆G‡= 30.5 kcal/mol ∆Go= -34.7 kcal/mol
Imaginary frequency: -1259.6 cm-1
Olefin Hydrogenation Using MTO
TS1 TS2 TS3
∆G‡ (kcal/mol) 58.6 30.9 30.5
Re-H (Å) 1.853 1.756 1.854
Re-C (Å) 2.323 2.339 2.351
C-H (Å) 1.354 1.512 1.364
Conditions: MTO (0.0046 mmol) and cyclooctene (0.092 mmol) were dissolved In toluene in a J-Young tube. The tube was then
subjected to 3 freeze pump thaw cycles and pressurized with H2. Conversion was determined by 1H NMR spectroscopy by integrating
the ratios of olefinic peak of the product with respect to the reactant peak. Product formation was also confirmed using GC-MS.
Olefin hydrogenation using MTO is only observed after an induction period of 20 hrs. The first calculated step agrees with the experimental data with
the high ∆G≠ of the first transition state. Methane formation was observed experimentally when carrying out a reaction in the absence of olefin.
• Olefin hydrogenation catalyzed by MTO is observed after a 20 h induction
period. The active catalyst in this reaction is thought to be Re-H, based on
1H NMR spectroscopy.
• Studies aimed to identify the nature of the active catalyst in the reaction
are currently underway in the Ison lab.
• Further computational studies regarding other pathways of MTO activation
and olefin hydrogenation.
Acknowledgment
Computational details: Calculations were done using M06 functional implemented in Gaussian 09. Basis set used was
SDD with added f polarization on Re and 6-31G (d,p) on all other atoms except Re. Energy calculations were carried out
in PCM solvation model (benzene) with 6-311G++ (d,p) basis set on all atoms except Re and was SDD with added f
polarization on Re.
∆Go= 4.8 kcal/mol
∆Go= 13.0 kcal/mol
∆Go= -7.2 kcal/mol
Pathway A
Pathway B
Pathway C
Computational details: Calculations were done using M06 functional implemented in Gaussian 09. Basis set used was SDD with added f
polarization on Re and 6-31G (d,p) on all other atoms except Re. Energy calculations were carried out in PCM solvation model (benzene)
with 6-311G++ (d,p) basis set on all atoms except Re and was SDD with added f polarization on Re.
Active Catalyst Generation
TS1
TS2
TS3
Our lab recently reported the hydrogenation reaction catalyzed by oxorhenium complexes in
the presence of a Lewis acid B(C6F5)3. While the reaction proceeded smoothly for many
catalysts, an induction period was observed when MTO (methyltrioxorhenium) was used .
J. Am. Chem. Soc., 2016, 138 (14), pp 4832–4842
In order to gain a better understanding of the induction period for the MTO/Borane system, we
carried out a joint experimental and computational studies.
The mechanism proposed by Ison and coworkers involves the formation of a frustrated Lewis
pair (FLP) between rhenium oxo and the Lewis acid. The unquenched nature of the B-O bond
leads to facile olefin activation and subsequently, hydrogenation. Since there is some evidence
for the Lewis acid effect on hydrogenation, we also aimed to evaluate a much stronger
aluminum analog of B(C6F5)3 commonly known as tris(pentafluorophenyl)alane.
LA= B(C6F5)3
∆Go= 2.3kcal/mol
Hydrogenation of Cyclooctene in the Presence of Lewis Acids
When boron was utilized as a Lewis acid, the hydrogenation product was observed after the
induction period, which is consistent with the results reported previously. However, when
aluminum was used as a Lewis acid, mostly polymerization product is observed.
MTO Catalyzed Hydrogenation
MTO
Active catalyst
Product release and
catalyst regeneration
TS3
When MTO was pressurized with hydrogen and heated for 3 d before adding
cyclooctene, hydrogenated product was observed without an induction
period. However, when MTO was heated with cyclooctene for 3 d before
pressurizing with hydrogen, the induction period was observed.