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19499.pdf (3.79 MB)
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Hydrogen Transfer Reaction Involving Nickel POCOP-Pincer Hydride Complexes
Author Info
Wilson, Gleason
ORCID® Identifier
http://orcid.org/0000-0001-6006-7475
Permalink:
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447688935
Abstract Details
Year and Degree
2015, PhD, University of Cincinnati, Arts and Sciences: Chemistry.
Abstract
The development of efficient and low-cost catalysts from Earth abundant metals with an objective to replace expensive and precious metal-based catalysts is important for the affordability of commodity chemicals in the future. Therefore, study of nickel based POCOP-pincer hydride complexes as catalysts is of interest due to the use of an abundant metal and the known benefits of the POCOP-pincer ligand such as rigid backbone, high thermal stability and easy to tune the electronic and steric properties. Extensive research of the structure and reactivity of these nickel POCOP-pincer hydride complexes is of great importance to the understanding and development of relatively inexpensive nickel-based catalysts. Progress has been made in three research projects with a unifying theme of hydrogen transfer either from or to nickel POCOP-pincer hydride complexes. Nickel POCOP-pincer hydride complexes react with phenylacetylene to generate two insertion products. The 2,1-insertion is more favorable than the 1,2-insertion and both pathways involve cis addition of Ni–H across the C=C bond. Unlike the palladium case, alkynyl complexes and H2 are not produced in the nickel system. The more bulky hydride complex [2,6-(
t
Bu
2
PO)
2
C
6
H
3
]NiH shows no reactivity towards phenylacetylene. Catalytic hydrogenation of phenylacetylene with [2,6-(
i
Pr
2
PO)
2
C
6
H
3
]NiH and [2,6-(
c
Pe
2
PO)
2
C
6
H
3
]NiH takes place at an elevated temperature (70-100 °C) and proves to be heterogeneous. The structures of the insertion products have been studied by X-ray crystallography. Nickel POCOP-pincer hydride complexes have been found to be active catalysts for dehydrogenation of dimethylamine borane, a viable solid chemically stored hydrogen source. The intermediates and products have been determined by spectroscopic techniques. The homogeneous nickel POCOP-pincer hydride complexes catalyze the dehydrogenation of dimethylamine borane, and heterogeneous nickel particles leached from the POCOP-pincer complexes are believed to also act as a catalyst. Hydride transfer is an essential step in a vast array of stoichiometric and catalytic transformations. Although metal-hydride complexes formally deliver a hydride in those reactions, it may proceed
via
direct hydride transfer or single electron transfer (SET) followed by hydrogen atom transfer. Reactions between trityl cation and nickel POCOP-pincer hydrides support that hydride transfer proceeds solely
via
direct hydride transfer for [2,6-(
t
Bu
2
PO)
2
C
6
H
3
]NiH. The complexes [2,6-(
i
Pr
2
PO)
2
C
6
H
3
]NiH and [2,6-(
c
Pe
2
PO)
2
C
6
H
3
]NiH transfer hydride by direct hydride transfer (major pathway) and SET followed by hydrogen transfer (minor pathway), supported by
1
H NMR spectroscopy. Upon these findings, the reaction of N-(1-phenylethylidene) pyrrolidinium tetrafluoroborate with nickel POCOP-pincer hydrides was also studied in efforts to broaden the scope of hydride transfer reactions of the nickel POCOP-pincer hydrides. Stoichiometric reactions confirm that the hydride complex [2,6-(
i
Pr
2
PO)
2
C
6
H
3
]NiH reduces the iminium cation to a tertiary amine completely while the complexes [2,6-(
t
Bu
2
PO)
2
C
6
H
3
]NiH and [2,6-(
c
Pe
2
PO)
2
C
6
H
3
]NiH show evidence of partial iminium cation reduction.
Committee
Hairong Guan, Ph.D. (Committee Chair)
William Connick, Ph.D. (Committee Member)
James Mack, Ph.D. (Committee Member)
Pages
105 p.
Subject Headings
Chemistry
Keywords
Inorganic
;
Organometallic
;
Chemistry
;
nickel catalyst
;
hydrogenation
;
dehydrogenation
Recommended Citations
Refworks
EndNote
RIS
Mendeley
Citations
Wilson, G. (2015).
Hydrogen Transfer Reaction Involving Nickel POCOP-Pincer Hydride Complexes
[Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447688935
APA Style (7th edition)
Wilson, Gleason.
Hydrogen Transfer Reaction Involving Nickel POCOP-Pincer Hydride Complexes.
2015. University of Cincinnati, Doctoral dissertation.
OhioLINK Electronic Theses and Dissertations Center
, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447688935.
MLA Style (8th edition)
Wilson, Gleason. "Hydrogen Transfer Reaction Involving Nickel POCOP-Pincer Hydride Complexes." Doctoral dissertation, University of Cincinnati, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1447688935
Chicago Manual of Style (17th edition)
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Document number:
ucin1447688935
Download Count:
338
Copyright Info
© 2015, all rights reserved.
This open access ETD is published by University of Cincinnati and OhioLINK.
Release 3.2.12