Tiow-Gan Ong Lab
Our Research
目前我們實驗室發展的研究主題是利用過渡金屬錯合物或有機金屬為材料，尋找這些分子於催化反應中新的應用，以發展出新的催化化學，並將有利於綠色化學的發展。這些研究在 (i) 用於綠色分子合成的 C-H/C-O 鍵活化、(ii) 非八位碳物種（卡賓、碳和碳二卡賓）的化學和 (iii) 小分子活化方面帶來了新的關鍵創新。
(1) Reactive Dicarbon as a Flexible Ligand for Transition-Metal Coordination and Catalysis
Dicarbon is a reactive carbon allotrope that naturally exists only in the high-temperature medium of stellar space. We report the successful preparation of a series of bottleable phosphine-stabilized dicarbon (PDC) molecules. We explore the use of these molecules as a new complementary class of carbenelike ligands featuring strong σ-donor (>NHCs and CAAcs) but weak π-acceptor properties. Steric map analysis of PDC based on Cavallo’s SambVca program reveals comparable steric volume bulk of 32.5%, similar to the conventional IMes carbene. However, our PDCs exhibit dynamic steric flexibility modulated by the nature of the metal complexes and catalytic reaction environment. We demonstrate the catalytic utility of the PDC framework by its successful implementation for Suzuki−Miyaura cross-coupling and the reductive coupling reaction of an aldehyde and alkyne. Detailed investigations of the reductive coupling reaction reveal an important secondary interaction between PDC and metal complexes, which plays a critical role in the catalytic system.
(2) Synergistic Catalysis by Brønsted Acid/Carbodicarbene Mimicking Frustrated Lewis Pair-Like Reactivity for Metal-free Polymerization Process.
A new class of reactive non-metallic chemistry, namely Frustrated Lewis Pair (FLP) is based on a long-range attractive force between two components of Lewis acid and base that are sterically prevented from forming the classical Lewis acid-base adducts. FLP possesses unique property as it undergoes small molecule activation and metal-free catalysis like hydrogenation, CO2 reduction, hydrosilylation, borylation, amination, etc. Owing to its wide applications, FLP has become an emerging science in sustainable catalysis that reduces the dependency on fossil fuels and costly and toxic transition metal. Parallelly, carbodicarbene, a new class of carbon family, bearing two opposite reactive sites (nucleophilic and electrophilic) working simultaneously as a single component can also emulate FLP-like character for catalytic applications. Recently, the research team had employed alcoholic co-modulator to regulate the catalytic activity of carbodicarbene. The synergistic proof-of-concept using carbodicarbene/alcohol system successfully scores unprecedented results in dehydrosilylation, isocyanate cyclotrimerization, L-lactide (LA) and methyl methacrylate (MMA) polymerization (Angew. Chem., Int. Ed. 2021, 60, 19949-19956).
(3) Unconventional Chemical Bonding in Chemistry Theory & Future Advanced Carbon Material Synthesis.
Carbon, the smallest diatomic molecule with a carbon–carbon bond, which only detected in the blue flame and in interstellar atmosphere. The nature and strength of the bond in dicarbon (C2) has proven controversial and there have been numerous failed experimental attempts to stabilize C2. Our work is manifestation of the most state-of-the-art synthetic ingenuity approaches using special custom-made bulky and rich phosphine ligand to stabilize dicarbon as R3P→C2. The broad impact of our work will have paradigm-shifts on the fundamental understanding of the chemical bonding and reactivities of unstable carbons and silicon (Nat. Chem. 2021, 13, 89-93).
(4) Green Catalytic Process for Making Value-Adding Chemicals via C-O Bond Activation. A Chemical Journey toward Fossil Fuel-Free.
Our lab demonstrated nickel-catalyzed cross coupling reactions of inert methoxyarenes with heteroarene derivatives based on a tandem strategy of C−O/C−H bond activations, which is unprecedented. The protocol is an effective and greener molecular synthesis technology, which could be applied to a wide variety scope of organic substrates. Ultimately, our method based on C–O/C-H activation using on phenolic biomass as coupling partners would relied less on petroleum feedstocks. (ACS Catal. 2018, 8, 11368-11376).
(5) One-Pot Tandem Photoredox and Cross-Coupling Catalysis with a Single Pd-Carbodicarbene Complex: Incorporation of 1 and 2-electron Manifold in Single-Pot Reaction for the First-Time
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 conditions. We report a Pd-carbodicarbene (CDC) complex that mediates both 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 (Angew. Chem. Int. Ed. 2018, 57, 4622-4626).
(6) Carbodicarbenes: Unexpected π-Accepting Ability during Reactivity with Small Molecules and New Discovery of Frustrated Lewis Pair-Like within Framework
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 NHC fragment, combined with single-crystal X-ray studies of a model Pd complex strongly suggests a significant level of π-accepting ability at the central carbon of the NHC moiety. This feature is atypical of classic NHCs, which are strong σ-donors, with only nominal π-accepting ability. The unanticipated π-acidity is critical for engendering carbodicarbenes with reactivity more commonly observed with frustrated Lewis-pairs (FLPs) rather than the more closely related NHCs and CAACs (Journal of the American Chemical Society, 2017, 139,12380-12836).