Authors: Vincent N. Cavaliere, Marco G. Crestani, Balazs Pinter, Maren Pink, Chun-Hsing Chen, Mu-Hyun Baik, and Daniel J. Mindiola
Journal: Journal of the American Chemical Society
Affiliation: Department of Chemistry and Molecular Structure Center, Indiana University
Chemists are interested in new, easier ways to obtain useful chemicals. Although ethane makes up the second largest proportion of natural gas it can be difficult to use as a feedstock for other C2 compounds (such as ethene aka ethylene), because of how unreactive it is. The current industrial method to convert ethane to ethene involves temperatures over 800 °C and creates 1.5 – 3 tons of carbon dioxide for every ton of ethene made. Less energy intensive and polluting methods for creation of ethene from ethane would be very useful.
In this paper the authors report the conversion of ethane to ethene using a titanium complex. First the complex A shown in Figure 1 was converted to 1 by addition of ethane. Using a pressure of 400 psi ethane a yield of 45% was obtained. The authors were unable to obtain crystals that could be used for X-ray diffraction; however they were able to deduce the structure using 1H, 13C, Heteronuclear Single Quantum Coherence (HSQC), and Correlation Spectroscopy (COSY) NMR. The researchers were also able to create a spectroscopically identical complex by reaction of (PNP)Ti=CHtBu(OTf) (PNP = N[2-PiPr2-4-methylphenyl]2-) with ClMgC2H5.
Figure 1. Formation of complex 1
Using computational models, the authors also investigated the pathway by which 1 is formed. Figure 2 describes the pathway the authors determined to be most likely. Due to the calculated stability of B the authors thought they should be able to isolate and characterize it. Despite great effort they have thus far they have been unsuccessful.
Figure 2. Reaction pathway for the formation of 1
The authors found complex 1 to be thermally stable up to 60 °C, but it forms products over the course of a few days. Ethene was not found to be one of these products. However through two electron oxidation of 1 using N3R (R = SiMe3 or 1-adamantyl) or by exposure of 1 to an atmosphere of N2O the authors were able to produce ethene. The authors also completed similar studies using n-pentane and n-hexane and were able to isolate 1-pentene and 1-hexene respectively.
This work represents new and exciting research into the production of useful chemicals under more mild conditions with the formation of less waste.