Browsing by Author "Yap, Glenn P. A."

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Carbodicarbenes: Unexpected pi-Accepting Ability during Reactivity with Small Molecules
(2017-09-13)
Chen, Wen-Ching
;
Shih, Wei-Chih
;
Jurca, Titel
;
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
;
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.
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
;
Lai, Ying-Chieh
;
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
;
Yang, Hsuan
;
Chen, Wen-Ching
;
Yap, Glenn P. A.
;
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
;
Shih, Wei-Chin
;
Wang, Ting-Hsuan
;
Liu, Yuhua
;
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.
One-Pot Tandem Photoredox and Cross-Coupling Catalysis with a Single Palladium Carbodicarbene Complex
(2018-04-16)
Hsu, Yu-Cheng
;
Wang, Vincent C. -C.
;
Au-Yeung, Ka-Chun
;
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.
Synthesis and Isolation of an Acyclic Tridentate Bis(pyridine)carbodicarbene and Studies on Its Structural Implications and Reactivities
(2015-02-16)
Hsu, Yu-Chen
;
Shen, Jiun-Shian
;
Lin, Bo-Chao
;
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.
Synthetic Modification of Acyclic Bent Allenes (Carbodicarbenes) and Further Studies on Their Structural Implications and Reactivities
(2013-04-22)
Chen, Wen-Ching
;
Hsu, Yu-Chen
;
Lee, Ching-Yu
;
Yap, Glenn P. A.
;
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.
The Elusive Three-Coordinate Dicationic Hydrido Boron Complex
(2014-01-22)
Chen, Wen-Ching
;
Lee, Ching-Yu
;
Lin, Bo-Chao
;
Hsu, Yu-Chen
;
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.