Browsing by Author "Ong, Tiow-Gan"

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Au-BINOL Hybrid Nanocatalysts: Insights into the Structure-Based Enhancement of Catalytic and Photocatalytic Performance
(2019-04-10)
Patolla, Shashank Reddy
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Kao, Chen-Rui
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Chen, Guan-Wei
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Huang, Yu-Cheng
;
Chuang, Yu-Chun
Advances in new systems of organic-inorganic hybrid nanocomposites are less prevalent, owing to a lack of facile strategies for precise control of their structures, compositions, and, hence, their properties. In this work, Au-BINOL hybrid nanocomposites with eccentric and concentric nanostructures were produced. The hybrid nanocomposites containing two distinct moieties of inorganic Au nanocrystals and organic BINOL nanospheres were applied to the catalytic hydrogenation of 4-nitrophenol with NaBH4 in the aqueous phase with and without the illumination of visible light. Here, we demonstrate that the existence of Au-BINOL interfaces offers benefits to their performance. The eccentric nanostructures made with CTAC show the superior activity from large Au-BINOL interfaces formed between the BINOL nano spheres and the faces of Au nanoplates. They further exhibit a high Au localized surface plasmon resonance (LSPR)-enhancement effect on the photoreduction of 4-nitrophenol, which is attributed to the strong LSPR absorption of exposed Au nanocrystals unaffected by the coverage of BINOL shells.
Carbodicarbenes and their Captodative Behavior in Catalysis
(2018-04-09)
Liu, Shu-kai
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Shih, Wei-Chih
;
Chen, Wen-Ching
;
Ong, Tiow-Gan
;
交大名義發表
That of carbones is a new family member in the class of low-valent carbon compounds. Unlike its cousin, the conventional carbene, the carbone possesses two free electron lone pairs. In combination with their unique allene-type structure, they possess stronger sigma-donating ability than conventional carbenes such as NHCs or CAACs. Because of this property, they have a huge potential to become a new class of ligands in organometallic chemistry and catalysis. Although carbodiphosphoranes (CDP) were initially discovered in 1961, nearly 50years were needed to attract the attention of the chemical community with the synthesis of the carbodicarbene (CDC). This Concept paper summarizes developments over the last 10years and future outlooks for this new class of sigma-donors, particularly carbodicarbenes.
Carbodicarbenes or Bent Allenes
(2017-02-01)
Wang, Ting-Hsuan
;
Chen, Wen-Ching
;
Ong, Tiow-Gan
;
應用化學系
;
Department of Applied Chemistry
The pursuit of unusual bonding environments of carbon species with non-octet electronic configurations has been quite active in fundamental organic and theoretical chemistry for many decades. In this respect, a distinct carbone species has been successfully isolated recently and defined as "carbodicarbene" or "bent allene." This neutral two-coordinated central carbon atom possesses two electron lone pairs, while its octet deficiency is overcome by sigma donation of N-heterocyclic carbenes (NHCs) bound to the central carbon. The present review is focused on the rich chemistry of carbodicarbenes in the aspects of synthesis, characterization, and ligand science of metal complex as well as their intrinsic reactivities.
Carbodicarbenes: Unexpected pi-Accepting Ability during Reactivity with Small Molecules
(2017-09-13)
Chen, Wen-Ching
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Shih, Wei-Chih
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Jurca, Titel
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Zhao, Lili
;
Andrada, Diego M.
An investigation of carbodicarbenes, the less explored member of the carbenic complex/ligand family has yielded unexpected electronic features and concomitant reactivity. Observed 1,2-addition of E-H bonds (E = B, C, Si) across the carbone central carbon and that of the flanking N-heterocyclic carbene (NHC) fragment, combined with single-crystal X-ray studies of a model Pd complex strongly suggests a significant level of pi-accepting ability at the central carbon of the NHC moiety. This feature is atypical of classic NHCs, which are strong sigma-donors, with only nominal pi-accepting ability. The unanticipated pi-acidity is critical for engendering carbodicarbenes with reactivity more commonly observed with frustrated Lewis pairs (FLPs) rather than the more closely related NHCs and cyclic (alkyl)(amino)carbenes (CAACs).
Expanding the Ligand Framework Diversity of Carbodicarbenes and Direct Detection of Boron Activation in the Methylation of Amines with CO2
(2015-12-07)
Chen, Wen-Ching
;
Shen, Jiun-Shian
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Jurca, Titel
;
Peng, Chun-Jung
;
Lin, Yen-Hsu
A simple and convergent synthetic strategy used to increase the diversity of the carbodicarbene ligand framework through incorporation of unsymmetrical pendant groups is reported. Structural analysis and spectroscopic studies of ligands and their Rh complexes are reported. Reactivity studies reveal carbodicarbenes as competent organocatalysts for amine methylation using CO2 as a synthon. A unique B-H-activated boron-carbodicarbene complex was isolated as a reaction intermediate, providing mechanistic insight into the CO2 functionalization process.
Expanding the Ligand Framework Diversity of Carbodicarbenes and Direct Detection of Boron Activation in the Methylation of Amines with CO2
(2015-12-07)
Chen, Wen-Ching
;
Shen, Jiun-Shian
;
Jurca, Titel
;
Peng, Chun-Jung
;
Lin, Yen-Hsu
A simple and convergent synthetic strategy used to increase the diversity of the carbodicarbene ligand framework through incorporation of unsymmetrical pendant groups is reported. Structural analysis and spectroscopic studies of ligands and their Rh complexes are reported. Reactivity studies reveal carbodicarbenes as competent organocatalysts for amine methylation using CO2 as a synthon. A unique B-H-activated boron-carbodicarbene complex was isolated as a reaction intermediate, providing mechanistic insight into the CO2 functionalization process.
Interface-Controlled Synthesis of Au-BINOL Hybrid Nanostructures and Mechanism Study
(2018-11-13)
Patlolla, Shashank Reddy
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Kao, Chen-Rui
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Yeh, Ai-Hsuan
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Lin, Hung-Min
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Chuang, Yu-Chun
The combined functionality of components in organic inorganic hybrid nanomaterials render them efficient nanoreactors. However, the development in this field is limited due to a lack of synthetic avenues and systematic control of the growth kinetics of hybrid structures. In this work, we take advantage of an ionic switch for regio-control of Au-BINOL(1,1'-Bi-2-naphthol) hybrid nanostructures. Aromatic BINOL molecules assemble into nanospheres, concomitant with the growth of the Au nanocrystals. The morphological evolution of Au nanocrystals is solely controlled by the presence of halides in the synthetic system. Here we show that quaternary ammonium surfactants (CTAB or CTAC), not only bridging Au and BINOL, but also contributing to the formation of concentric or eccentric structures when their concentrations are tuned to the range of 10(-5) to 10(-3) M. This facile strategy offers the potential advantage of scalable production, with diverse functional organic inorganic hybrid nanocomposites being produced based on the specific archetype of Au-BINOL hybrid nano composites.
Mechanistic Study of a Switch in the Regioselectivity of Hydroheteroarylation of Styrene Catalyzed by Bimetallic Ni-Al through C-H Activation
(2014-06-23)
Chen, Wen-Ching
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Lai, Ying-Chieh
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Shih, Wei-Chun
;
Yu, Ming-Shiuan
;
Yap, Glenn P. A.
We previously reported a highly efficient protocol for bimetallic Ni-Al-catalyzed hydroheteroarylation of styrene with benzimidazole based on C-H bond activation. We have now delineated the mechanism of this process, providing a rationale for an observed switch in regioselectivity in the presence of the Lewis acid, AlMe3. The present mechanistic study gives insights for the rational development of catalysts that exhibit required linear/branched selectivity.
Nickel Carbodicarbene Catalyzes Kumada Cross-Coupling of Aryl Ethers with Grignard Reagents through C-O Bond Activation
(1970-01-01)
Ambre, Ram
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Yang, Hsuan
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Chen, Wen-Ching
;
Yap, Glenn P. A.
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Jurca, Titel
The development of a cross-coupling reaction protocol between aryl ethers and Grignard reagents catalyzed by carbodicarbene (CDC) nickel complexes to afford biaryl compounds through C-O cleavage is reported. Aromatic substrates featuring a broad range of electron neutral, donating, or withdrawing groups are introduced at the desired position. The method has proven effective over a wide range of naphthyl methyl ethers, anisoles, and Grignard reagents. The robustness of the protocol is validated by performing multiple cleavage reactions, gram scale synthesis, and arylation of a dimethoxy esterdiol derivative.
Nickel promoted switchable hydroheteroarylation of cyclodienes via C-H bond activation of heteroarenes
(2015-07-01)
Lee, Wei-Chih
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Shih, Wei-Chin
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Wang, Ting-Hsuan
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Liu, Yuhua
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Yap, Glenn P. A.
We demonstrated Ni-catalyzed switchable hydroheteroarylation of cyclic dienes via C-H bond activation of heteroarenes. In the presence of an N-heterocyclic carbene (NHC) ligand, hydroheteroarylation of cyclic diene with azole afforded alpha-alkenyl-azole, forging a Heck-like product without using any external oxidant. Conversely, changing the ligand to PCy3 would switch this reaction manifold to afford the other isomeric beta-alkenyl substituted azole. (C) 2015 Elsevier Ltd. All rights reserved.
Nickel-catalysed para-CH activation of pyridine with switchable regioselective hydroheteroarylation of allylarenes
(2015-01-01)
Lee, Wei-Chih
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Chen, Chien-Hung
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Liu, Cheng-Yuan
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Yu, Ming-Shiuan
;
Lin, Yung-Huei
para-CH activation of pyridine with allylbenzene is described by Ni/Al cooperative catalysis in combination with a bulkier NHC ligand and a Lewis acid, leading to linear hydroheteroarylation products. Interestingly, the branch selectivity can be achieved by using the combination of a less sterically hindered amino-NHC ligand and AlMe3 through tandem reaction of facile alkene isomerization followed by a slow CH bond activation process.
Nickel-mediated cross-coupling via C-O activation assisted by organoaluminum
(1970-01-01)
Liu, Cheng-Yuan
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Wititsuwannakul, Taveechai
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Hsieh, Chu-Han
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Tsai, Chung-Yu
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Wang, Ting-Hsuan
We report the alkylation and arylation cross-coupling of aryl ethers based on C-O bond activation using a nickel catalyst and organoaluminum reagents. Ni(cod)(2) in combination with 1,2-bis(dicyclohexylphosphino)ethane ligand in toluene solution at 130 degrees C are the best conditions. The naphthyl ether or methoxy pyridine derivatives are suitable substrates for alkylation and arylation reaction with a wider scope of aluminum reagents in good yields. Computational analysis on the pyridine substrate is provided to help delineate the mechanistic pathway and demonstrate the important aspects of the cooperative interaction bimetallic catalysis. First, the coordination of AlMe3 to the O atom of pyridine is essential for C-O activation. Second, the beta-H transfer from methoxy to pyridine could be discouraged through the use of bidentate phosphine as a ligand. Finally, excess AlMe3 reagent is critical for facilitating a reductive elimination process.
One-Pot Tandem Photoredox and Cross-Coupling Catalysis with a Single Palladium Carbodicarbene Complex
(2018-04-16)
Hsu, Yu-Cheng
;
Wang, Vincent C. -C.
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Au-Yeung, Ka-Chun
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Tsai, Chung-Yu
;
Chang, Chun-Chi
The combination of conventional transition-metal-catalyzed coupling (2e(-) process) and photoredox catalysis (1e(-) process) has emerged as a powerful approach to catalyze difficult cross-coupling reactions under mild reaction conditions. Reported is a palladium carbodicarbene (CDC) complex that mediates both a Suzuki-Miyaura coupling and photoredox catalysis for C-N bond formation upon visible-light irradiation. These two catalytic pathways can be combined to promote both conventional transition-metal-catalyzed coupling and photoredox catalysis to mediate C-H arylation under ambient conditions with a single catalyst in an efficient one-pot process.
Selective C(8)-H Activation of Imidazopyridines Mediated by Cooperative Nickel-Aluminum Catalysis
(2016-09-01)
Liu, Cheng-Yuan
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Chen, Ying-Ho
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Chen, Chih-Hao
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Yu, Ming-Shiuan
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Tsai, Fu-Yu
A catalytic paradigm is described featuring a synergistic interaction between nickel, aluminum and different ligands to impart a rather remote C-H alkenylation of imidazo[1,5-a] pyridines at the C-8 position without the necessity of installing a directing group. The scope of the direct C-H activation reactions of various 5-aryl- and 3-arylimidazopyridines is established using different sterically hindered alkynes.
Synthesis and Isolation of an Acyclic Tridentate Bis(pyridine)carbodicarbene and Studies on Its Structural Implications and Reactivities
(2015-02-16)
Hsu, Yu-Chen
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Shen, Jiun-Shian
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Lin, Bo-Chao
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Chen, Wen-Ching
;
Chan, Yi-Tsu
The simple synthetic development of acyclic pincer bis(pyridine)carbodicarbene is depicted herein. Presented is the first isolated structural pincer carbodicarbene with a C-C-C angle of 143 degrees, larger than the monodentate framework. More importantly, theoretical analysis showed that this carbodicarbene embodies a more allene-like character. Palladium complexes supported by this pincer ligand are active catalysts for Heck-Mizoroki and Suzuki-Miyaura coupling reactions.
Synthesis and Structure of Carbodicarbenes and Their Application in Catalysis
(2018-01-01)
Liu, Shukai
;
Chen, Wen-Ching
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Ong, Tiow-Gan
;
交大名義發表
;
應用化學系
Carbodicarbenes are a special class of bisylidic CL2 compounds, the so-called carbones. Carbones are divalent carbon compounds, in which a four-electron carbon atom in the oxidation state of zero is bound by two sigma-donor ligands L via donor-acceptor interactions, resulting in the formulation L -> C(0)<- L. In carbodicarbenes (CDCs), the L ligand is a N-heterocyclic carbene (NHC) or any other singlet carbene species. Comparable to "classical" bisylides, CDCs possess two lone pairs of electrons at the central carbon atom, thus making them stronger sigma-donors than conventional carbenes like NHCs. These unusual donor properties make CDCs unique and highly potent ligands for transition metals and catalysis. This chapter summarizes the exciting developments of the last 10 years in CDC chemistry. A concise overview of this new class of carbone compounds is given by summarizing the synthesis of different CDC frameworks as well as their application in transition metal chemistry and homogenous catalysis.
Synthetic Modification of Acyclic Bent Allenes (Carbodicarbenes) and Further Studies on Their Structural Implications and Reactivities
(2013-04-22)
Chen, Wen-Ching
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Hsu, Yu-Chen
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Lee, Ching-Yu
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Yap, Glenn P. A.
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Ong, Tiow-Gan
The paper describes the synthetic development of Bertrand-type acyclic carbodicarbene scaffolds derived from an unsymmetrical bis(benzimidazol-2-yl)methane bearing two sterically demanding pendant arms, isopropyl (6a) or cyclohexyl (6b). X-ray crystallographic analysis shows that the impact of these pendant arms on the overall structural parameters of carbodicarbenes is minimal. The chemical reactivity of the carbodicarbenes was evaluated with iodomethane to afford compound 7, illustrating its nudeophilic properties. Finally, experiments were also undertaken to investigate the coordination ability of carbodicarbene toward the formation of rhodium carbonyl (10) and palladium allyl complexes (11). The crystal structures of the metal complexes have been determined, revealing that their metal-carbene distances are elongated only slightly, this fact was rationalized on the basis of geometrical steric considerations with regard to the ligand.
Tandem Isomerization and C-H Activation: Regioselective Hydroheteroarylation of Allylarenes
(2013-10-18)
Lee, Wei-Chih
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Wang, Chun-Han
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Lin, Yung-Huei
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Shih, Wei-Chun
;
Ong, Tiow-Gan
The first Ni-promoted prototype reaction based on the tandem C-H activation of heteroarenes with alkene isomerization is demonstrated, leading to the branched hydroheteroarylation products. Simultaneously, the reaction selectivity can be chemically switched to linear adducts through Ni-Al tandem catalysis.
The Elusive Three-Coordinate Dicationic Hydrido Boron Complex
(2014-01-22)
Chen, Wen-Ching
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Lee, Ching-Yu
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Lin, Bo-Chao
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Hsu, Yu-Chen
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Shen, Jiun-Shian
The formation of a hitherto unknown three-coordinate dicationic hydrido boron complex is described. Interestingly, supporting ligand carbodicarbene gave unprecedented reaction with BH3 without using more highly electrophilic Lewis acid precursors. Spectroscopic, crystallographic, and computational analysis was performed to understand the electronic features of these species.