Synthesis, characterization and catalytic evaluation of a Ziegler-type model iridium hydrogenation catalyst plus a novel tetrairidium tetrahydride complex

Date
2013
Authors
Hamdemir, Isil Kayiran, author
Finke, Richard G., advisor
Bernstein, Elliot R., committee member
Chen, Eugene Y.-X., committee member
Elliott, C. Michael, committee member
Wang, David, committee member
Journal Title
Journal ISSN
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Abstract
Following a critical review of the pertinent literature of Ziegler-type hydrogenation catalysts, the research presented herein is primarily focused on the synthesis, characterization and catalytic properties of a model Ziegler-type hydrogenation catalyst system made from [Ir(1,5-COD)(μ-O2C8H15)]2 plus AlEt3. The studies include: (i) a critical review of the relevant literature, (ii) ranking the activity, lifetime and thermal stability of the resulting Ir(0)n Ziegler nanoparticles; (iii) characterization of the true stabilizer species for Ir(0)n Ziegler nanoparticles as a function of the initial Al/Ir ratio; and (iv) the synthesis and characterization of a novel [Ir(1,5-COD)(μ-H)]4 complex considered as a plausible intermediate en route to Ir(0)n Ziegler nanoparticles. Studies evaluating and ranking the catalytic properties of Ziegler-type catalysts in the test reaction of cyclohexene hydrogenation reveal that the catalyst made with [Ir(1,5-COD)(μ-O2C8H15)]2 plus AlEt3 is a highly catalytically active, long-lived and thermally unusually stable nanoparticle catalyst. The catalytic lifetimes of the Ir(0)n Ziegler nanoparticles are higher than any known Ir(0)n nanoparticles in the extant literature. The nature of the stabilizer species in the Ziegler-type catalyst system made with [Ir(1,5-COD)(μ-O2C8H15)]2 plus AlEt3 at Al/Ir ratios 1-3 is then investigated by comparing 1H, 13C, 27Al NMR and IR data of the catalysts with those of individually-synthesized standards such as AlEt2(O2C8H15), [(n-Bu)4N][AlEt3(O2C8H15)] and [(n-Bu)2Al(µ-OH)]3. The results of the study shows that (i) AlEt2(O2C8H15) (Al/Ir=1, 2 and 3) and (iii) free AlEt3 (Al/Ir=3) are present in the catalyst solution in this model Ziegler-type hydrogenation catalyst system made from [Ir(1,5-COD)(μ-O2C8H15)]2 plus AlEt3. The spectroscopic and catalytic evidence provided in this study helps to rule out the initial hypotheses (iii) that anionic [AlEt3(O2C8H15)]- stabilizer exists and provides DLVO-type, Coulombic-repulsion stabilization. Also ruled out is (iv) that the AlEt3-derived stabilizers are Al-O-Al containing alumoxanes. In a separate study, a novel [Ir(1,5-COD)(μ-H)]4 complex is synthesized and characterized with the goal of (i) obtaining information on formation and stabilization mechanisms of Ziegler-type industrial hydrogenation model catalysts prepared from [Ir(1,5-COD)(μ-O2C8H15)]2 plus AlEt3; and with the goal of (ii) understanding the stabilization efficacies of various Al-based cocatalysts in the absence of any added carboxylate.
The synthesis of the previously unavailable [Ir(1,5-COD)(μ-H)]4 complex in 55% recrystallized yield was accomplished starting with commercially available LiBEt3H and [Ir(1,5-COD)(μ-Cl)]2 in the presence of excess 1,5-COD in THF. The resultant [Ir(1,5-COD)(μ-H)]4 was fully characterized by single-crystal XRD, XAFS, ESI-MS, UV-visible, IR, and NMR. In addition to the four main chapters, two appendix chapters (in which Isil K. Hamdemir has significant contributions) are included in the current dissertation due to their relevancy to the research presented herein. The characterization studies showing the presence of Ir~4-15 subnanometer clusters and Ir~40-150 nanoparticles, before and after catalytic hydrogenation, respectively, in the Ziegler-type catalyst system made from [Ir(1,5-COD)(μ-O2C8H15)]2 plus AlEt3 catalyst solution has been published (William M. Alley, Isil K. Hamdemir, Qi Wang, Anatoly Frenkel, Long Li, Judith C. Yang, Laurent D. Menard, Ralph G. Nuzzo, Saim Özkar, Kimberly Johnson, Richard G. Finke, "Iridium Ziegler-Type Hydrogenation Catalysts Made from [(1,5-COD)(μ-O2C8H15)]2 and AlEt3: Spectroscopic and Kinetic Evidence for the Irn Species Present and for Nanoparticles as the Fastest Catalyst"). Additionally, a broad distribution of metal cluster sizes from subnanometer to nanometer scale particles was observed in industrial Ziegler-type hydrogenation catalysts made with Co(neodecanoate)2 or Ni(2-ethylhexanoate)2 plus AlEt3 (William M. Alley, Isil K. Hamdemir, Qi Wang, Anatoly I. Frenkel, Long Li, Judith C. Yang, Laurent D. Menard, Ralph G. Nuzzo, Saim Özkar, Kimberly Johnson, Richard G. Finke, "Industrial Ziegler-type Hydrogenation Catalysts made from Co(neodecanoate)2 or Ni(2-ethylhexanoate)2, and AlEt3: Evidence for Nanoclusters and Sub-Nanocluster or Larger Ziegler-Nanocluster Based Catalysis"). These two studies were published as two chapters in the dissertation of, graduate student co-worker, William M. Alley, a dissertation which acknowledges Isil Kayiran Hamdemir's (I.K.H.) contributions.
Description
2013 Summer.
Includes bibliographical references.
Rights Access
Subject
Ziegler-type catalysts
characterization
tetrairidium
tetrahydride
hydrogenation
Citation
Associated Publications