Development of Selective Hydrogenation of Chemically Inert Carbonyl Compounds using (PNNP)Ir Complexes

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論文題目
Development of Selective Hydrogenation of Chemically Inert
Carbonyl Compounds using (PNNP)Ir Complexes
((PNNP)Ir錯体触媒を用いた化学的に不活性なカルボニル化合物の
選択的水素化反応の開発)
氏

名

GROEMER Bendik

論 文 内 容 の 要 旨
The three chapters as outlined in this thesis accounts for the development of
systems applicable for the selective reduction of carbonyl compounds to alcohols
utilizing (PNNP)Ir complexes. Within each of the three chapters of these thesis,
key challenges in the hydrogenation of carbonyl compounds were undertaken and
overcome utilizing new strategies for clean reduction of carbonyl compounds in
conjunction with sterically robust and multi-functional (PNNP)Ir complexes.
The first chapter of this thesis accounts for the development of a highly
efficient and selective system generally applicable to the selective reduction of
carboxylic acids to terminal alcohols. In previous works for the development of
systems for reduction of carboxylic acids, the challenges regarding the inherent
stability and tendency of carboxylic acids to undergo a wide range of side
reactions have limited the achieved selectivity and substrate scope. In chapter 1
of this thesis, is presented a novel approach to the selective reduction of
carboxylic acids to alcohols. In the presence of a Lewis acid additive and excess
amount of alcohol, smooth esterification of parent carboxylic acid was achieved
to yield ester intermediates. In the presence of the (PNNP)Ir complexes, the ester

intermediates were smoothly hydrogenated to yield their corresponding terminal
alcohols in high yield. This method was also applicable to a wide range of
dicarboxylic acids, which are highly challenging substrates due to their tendency
to undergo oligomerization and polyesterification. Our methodology allowed for
the selective hydrogenation of linear dicarboxylic acids of various carbon chainlength, achieving by far the largest substrate scope for dicarboxylic acid
hydrogenaiton when comparing to state-of-the-art systems. Furthermore, the
methodology allowed for the one-pot reduction of oxalic acid and glycolic acid to
ethylene glycol, thus paving the way for a novel production method for the
generation of ethylene glycol from biomass-derived chemicals.
In the second chapter of this thesis are presented the results of
investigation into utilization of (PNNP)Ir complexes for direct hydrogenation of
CO2 to MeOH. The hydrogenation of CO 2 to MeOH has attracted significant
attention in the past decades due to the possibility of directly transforming waste
CO2 into the valuable commodity chemical MeOH. Previous works for
homogeneous hydrogenation of CO 2 to MeOH have suffered from low catalyst
stability, and particularly, catalyst deactivation in presence of in situ generated
CO is well reported. In order to overcome these issues, we pursued a strategy of
hydrogenation in alcohol solvent in the presence of catalytic amounts of base
additive NaH. This strategy proved fruitful, as unprecedented catalytic stability
was obtained under these conditions, as the (PNNP)Ir complexes were found to
achieve high turnover numbers reaction temperatures of ~200 ºC and pressures
of 7–10.4 MPa for prolonged reaction time of >72 hours. To better understand the
impact of the reaction conditions for the selectivity for MeOH in this system,
gaseous products were quantified, and it was discovered that NaH had a highly
beneficial impact on increasing selectivity of MeOH over CO in this system.
Based on mechanistic studies, it was concluded that NaH served a duel role in
this system, firstly in increasing the concentration of catalytically active Irspecies for hydrogenation, and secondly, in catalyzing carbonylation of solvent
EtOH with in situ formed CO. By tweaking the reaction conditions in regards to
concentration of NaH and total pressure, the highest TON of any homogeneous
system for CO2 to MeOH hydrogenation, in the absence of amine additives, was

achieved, at high catalyst concentrations.
In the third chapter of this thesis, the development of a system for ketone
and ester hydrogenation utilizing (PNNP)Ir complexes in presence of
photoirradiation is accounted for. Generally peaking, hydrogenation of carbonyl
compounds is an energy intensive process requiring harsh conditions regarding
temperature and pressure, and one the main drawbacks of the (PNNP)Ir
complexes utilized in chapters 1 and 2 of this thesis is their requirement for high
reaction temperature and pressure. In addition to their properties for thermal
hydrogenation, the (PNNP)Ir complexes also exhibit useful photo-chemical
properties, and can act as photosensitizers, stabilizing charges spurred on by
photonic energy by metal-to-ligand charge-transfer. In chapter three, these
properties were successfully utilized to achieve photo-induced hydrogenation of
ketones, aldehydes and esters at mild conditions. In the presence of
photoirradiation, the (PNNP)Ir complexes underwent activation, likely through
partial hydrogenation of their ligands, to generated catalytically active species
which were found to be efficient for carbonyl compound hydrogenation at far
milder conditions compared to when the hydrogenation was conducted in absence
of photo-irradiation. Mechanistic studies utilizing a combination of electrospray
ionization mass spectroscopy and UV-Vis absorption spectroscopy supported a
proposed pathway for catalyst activation, and thus, not only was a system for
very mild hydrogenation of carbonyl compounds developed, but additionally, new
mechanistic insight generally applicable to homogeneous catalysts for carbonyl
compound hydrogenation was elucidated, with potential applications for new
catalyst design.
In conclusion, the utilization of (PNNP)Ir complexes in conjunction with
the development of new strategies for carbonyl compound reduction was found to
be highly fruitful, and the methodologies as presented in this thesis allowed for
unprecedented substrate scope for the general reduction of carboxylic acids to
alcohols, remarkable catalyst turnover in selective hydrogenation of CO 2 to
MeOH, as well as very mild reduction of esters to alcohols, while simultaneously
providing new mechanistic evidence with implication to next-generation design
of carbonyl reduction catalysts.