Regioselectivity In Catalytic Transfer Dehydrogenation And Mechanism Of 1 Alkene Isomerization

Download or read book Regioselectivity in Catalytic Transfer Dehydrogenation and Mechanism of 1-Alkene Isomerization written by Soumik Biswas and published by . This book was released on 2010 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bisphosphine and bisphohinite ligated pincer iridium complexes of the type (tBuPCP)IrHn (tBuPCP = C6H3-2,6-(CH2PtBu2)2, n=2, 4) and (tBuPOCOP)Ir(L) (tBuPOCOP = C6H3-2,6-(OPtBu2)2, L = H2, C2H4) are recognized to be outstanding catalyst precursors for transfer dehydrogenation of alkane. Catalytic regioselective dehydrogenation of alkane has a vast prospect. The catalytic transfer dehydrogenation property of these two pincer-iridium catalysts have been exploited in a tandem process known as Alkane Metathesis (AM), a process with enormous potential to transform lower hydrocarbons to higher hydrocarbons suitable for transportation fuel. Our studies here determine the difference between (tBuPCP)IrHn vs. (tBuPOCOP)Ir(L) in catalytic dehydrogenation of n-alkane to give regioselective alkenes is quite considerable. Hence we propose that this difference largely affects AM in the tandem system to result a product distribution of different molecular selectivity. We have found enormous disparity between these two complexes in terms of reactivity in different catalytic transfer dehydrogenation system. Kinetic, mechanistic and DFT (DFT by Prof. K.K.J et al.) studies predict that the subtle difference recognized in sterics exert major differences in the catalytic dehydrogenation. The sterics indicated here are mostly controlled by the alkyl groups attached to two phosphorous atom and the linkage in the pincer arm [-CH2- in (tBuPCP)Ir or -O- in (tBuPOCOP)Ir]. Catalytic 1-alkene isomerization is also another important reaction to study in this context as it has been well recognized to happen in parallel with n-alkane transfer dehydrogenation. All our different mechanistic, kinetic and DFT (DFT by Prof. K.K.J et al.) studies strongly indicate that the operative mechanism of 1-alkene isomerization is not previously presumed hydride-insertion pathway, which is very common in metal-hydride system. Although iridium-hydride plays a major role in catalytic transfer dehydrogenation, evidences indicate n-allyic mechanism of 1-alkene isomerization to be operative in this case. In addition our studies have gone in details to look into the elementary steps for n-allyic pathway. Besides these studies the transfer dehydrogenation technique has been exploited to determine different thermodynamic parameters of cycloalkanes of different ring sizes. In addition we have also investigated the regioselectivity in dehydrogenation of branch alkanes.