THESIS
2022
1 online resource (xiv, 96 pages) : illustrations (some color)
Abstract
The development of catalysts relying on earth-abundant
st-row transition metals is highly
desirable. The unique electronic properties of 1
st-row transition metal would give rise to more
unexpected and surprising reactivities for homogeneous hydrogenation reactions. In addition,
novel hydrogenation mechanisms distinguished from the classical “inner-sphere” and “outer-sphere”
mechanisms are needed for the hydrogenation of some challenging substrates. In this
thesis, we focus on the understanding of Co chemistry and the chemoselective issues related
to the hydrogenation of C=C and C=O catalyzed by Co complexes (Chapters 2-5).
Furthermore, we discussed two interesting examples of hydrogenation including
(NHC)Cu(I)H-guanidine bifunctional catalysis for hydrogenation of esters (Chapter 6) and...[
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The development of catalysts relying on earth-abundant
st-row transition metals is highly
desirable. The unique electronic properties of 1
st-row transition metal would give rise to more
unexpected and surprising reactivities for homogeneous hydrogenation reactions. In addition,
novel hydrogenation mechanisms distinguished from the classical “inner-sphere” and “outer-sphere”
mechanisms are needed for the hydrogenation of some challenging substrates. In this
thesis, we focus on the understanding of Co chemistry and the chemoselective issues related
to the hydrogenation of C=C and C=O catalyzed by Co complexes (Chapters 2-5).
Furthermore, we discussed two interesting examples of hydrogenation including
(NHC)Cu(I)H-guanidine bifunctional catalysis for hydrogenation of esters (Chapter 6) and
ionic hydrogenation of oxocarbenium ions (Chapter 7).
Co(I), as one of the 1
st-row transition metals with a d
8 electron configuration, prefers 5-coordinated Co (I) complexes due to its relatively smaller d-p gap when compared to other
heavier d
8 transition metal centers. When Co(I) combines with a carbene ligand, it was found
that trans-dihydride complexes could be stabilized, which are important intermediates
frequently proposed in transition metal catalyzed hydrogenation reactions.
Our theoretical studies indicate that via an “inner-sphere” mechanism, the Co(I) catalyst
[Co(I)(H
2)(PR
3)] was able to selectively hydrogenate C=C but not C=O, while the
Co(I)/tetraphosphine catalyst [(P
4N
2)Co(I)H] catalyzed selective reduction of C=O rather than
the C=C via an “outer-sphere” mechanism.
Besides the classical “inner-sphere” and “outer-sphere” mechanisms, novel hydrogenation
mechanisms are interesting and can give surprising results and have the potential for the
hydrogenation of challenging substrates. Related to this aspect, this thesis also covers two
novel hydrogenation mechanisms: (1) a combination of a super hydride donor NHCCu(I)H
and an organic guanidine pendant in the ligand is powerful to reduce the relative inert ester
group (Chapter 6) and (2) a far less explored ionic hydrogenation mechanism was reported for
the enantioselective hydrogenation of oxocarbenium ions (Chapter 7).
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