Uniform TitleIridium catalyzed alkane dehydrogenation, olefin isomerization and related chemistry
NameRay, Amlan (author), Goldman, Alan (chair), Krogh-Jespersen, Karsten (internal member), Uhrich, Kathryn (internal member), Sheridan, John (outside member), Rutgers University, Graduate School - New Brunswick,
SubjectChemistry and Chemical Biology,
DescriptionExcellent alkane dehydrogenation activity exhibited by the pincer-ligated iridium complexes of the type -- (X-RPCP)IrH2 (X-RPCP = 4-X-C6H2-2,6-(CH2PR2)2 with X = H, MeO; R = tBu, iPr) was exploited to functionalize a variety of aliphatic polyolefins via catalytic dehydrogenation. Of the two (MeO-RPCP)IrH2 complexes (2 : R = tBu and 3 : R = iPr) used for the study, 3 was found to be an extremely active system for dehydrogenation of poly(1-hexene), giving 100% conversion with respect to the initial concentration of norbornene (acceptor) used. The catalysts exhibited selectivity for dehydrogenation of polymer branches over the backbone, with a kinetic selectivity for terminal position of the branches.
Isomerization of 1-octene conducted with iridium-pincer complexes 1 ((H-tBuPCP)IrH2) 2 and 3, having different steric and electronic tuning, suggested that a larger alkyl group (R) on the phosphines along with a stronger [pi sign]-donating group on the pincer aryl ring (X) resulted in lower rate and higher selectivity for isomerization. In a related study, insertion of an olefin into the Ir-H bonds of the complexes (H-tBuPCP)Ir(H)(Y) were investigated using cis-1,2-dideutero-1-octene as the substrate. In presence of the substrate octene, some (H-tBuPCP)Ir(H)(Y) complexes (Y = Ph, NHPh etc) showed labile behavior in solution, being present in equilibrium with a (H-tBuPCP)Ir(H)(1-octene) complex. Results of kinetic experiments suggested that [pi sign]-donating Y groups enhanced the rate of olefin insertion. DFT calculations carried out on the systems predicted a slight preference for a pathway in which olefin binds to the metal center in between H and Y with a trans arrangement to the PCP-aryl ring. The olefin bound 14-electron complex (PCP)Ir(1-octene) was characterized by low temperature 1H and 31P NMR.
A new pincer complex (Me2N-tBuPCP)IrH2 (4d), having [pi sign]-electron rich iridium center, was synthesized and investigated for catalytic dehydrogenation. Complex 4d, was found to exhibit better selectivity and rate, as compared to the previously reported systems 1 and 2, for transfer dehydrogenation of branched and n-alkanes. It was also found to be a robust, slightly more stable and highly efficient catalyst for acceptorless dehydrogenation of cyclodecane.
NoteIncludes bibliographical references.
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.