Ka Wing Chan

Last Name

Chan

First Name

Ka Wing

ORCID

0000-0002-8069-0325

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Publications 1 - 10 of 16

Understanding the Structure, Activity and Initiation of Active Sites in Tungsten Oxo Based Olefin Metathesis Catalysts
Chan, Ka Wing (2019)
Silica-Supported Mn-II Sites as Efficient Catalysts for Carbonyl Hydroboration, Hydrosilylation, and Transesterification
Ghaffari, Behnaz; Mendes-Burak, Jorge; Chan, Ka Wing; et al. (2019)
Chemistry - A European Journal
C–H Activation and Proton Transfer Initiate Alkene Metathesis Activity of the Tungsten(IV)–Oxo Complex
Chan, Ka Wing; Lam, Erwin; D’Anna, Vincenza; et al. (2018)
Journal of the American Chemical Society
Bridging the Gap between Industrial and Well-Defined Supported Catalysts
Copéret, Christophe; Allouche, Florian; Chan, Ka Wing; et al. (2018)
Angewandte Chemie. International Edition
Molecular and Silica‐Supported Mo and W d0 Imido‐Methoxybenzylidene Complexes: Structure and Metathesis Activity
Zhizhko, Pavel A.; Tóth, Flórián; Gordon, Christopher; et al. (2019)
Helvetica Chimica Acta
Multiple Surface Site Three-Dimensional Structure Determination of a Supported Molecular Catalyst
Jabbour, Ribal; Renom-Carrasco, Marc; Chan, Ka Wing; et al. (2022)
Journal of the American Chemical Society
The structural characterization of supported molecular catalysts is challenging due to the low density of active sites and the presence of several organic/organometallic surface groups resulting from the often complex surface chemistry associated with support functionalization. Here, we provide a complete atomic-scale description of all surface sites in an N-heterocyclic carbene based on iridium and supported on silica, at all stages of its synthesis. By combining a suitable isotope labeling strategy with the implementation of multinuclear dipolar recoupling DNP-enhanced NMR experiments, the 3D structure of the Ir-NHC sites, as well as that of the synthesis intermediates were determined. As a significant fraction of parent surface fragments does not react during the multistep synthesis, site-selective experiments were implemented to specifically probe proximities between the organometallic groups and the solid support. The NMR-derived structure of the iridium sites points to a well-defined conformation. By interpreting EXAFS spectroscopy and chemical analysis data augmented by computational studies, the presence of two coordination geometries is demonstrated: Ir-NHC fragments coordinated by a 1,5-cyclooctadiene and one Cl ligand, as well as, more surprisingly, a fragment coordinated by two NHC and two Cl ligands. This study demonstrates a unique methodology to disclose individual surface structures in complex, multisite environments, a long-standing challenge in the field of heterogeneous/supported catalysts, while revealing new, unexpected structural features of metallo-NHC-supported substrates. It also highlights the potentially large diversity of surface sites present in functional materials prepared by surface chemistry, an essential knowledge to design materials with improved performances.
Low Temperature Activation of Supported Metathesis Catalysts by Organosilicon Reducing Agents
Mougel, Victor; Chan, Ka Wing; Siddiqi, Georges; et al. (2016)
ACS Central Science
Well-Defined Silica-Supported Tungsten(IV)−Oxo Complex: Olefin Metathesis Activity, Initiation, and Role of Brønsted Acid Sites
Chan, Ka Wing; Mance, Deni; Safonova, Olga V.; et al. (2019)
Journal of the American Chemical Society
Silica-Supported Pentamethylcyclopentadienyl Ytterbium(II) and Samarium(II) Sites: Ultrahigh Molecular Weight Polyethylene without Co-Catalyst
Allouche, Florian; Chan, Ka Wing; Fedorov, Alexey; et al. (2018)
Angewandte Chemie
Promoting active site renewal in heterogeneous olefin metathesis catalysts
Gani, Terry Z.H.; Berkson, Zachariah J.; Zhu, Ran; et al. (2023)
Nature
As an atom-efficient strategy for the large-scale interconversion of olefins, heterogeneously catalysed olefin metathesis sees commercial applications in the petrochemical, polymer and speciality chemical industries1. Notably, the thermoneutral and highly selective cross-metathesis of ethylene and 2-butenes1 offers an appealing route for the on-purpose production of propylene to address the C3 shortfall caused by using shale gas as a feedstock in steam crackers2,3. However, key mechanistic details have remained ambiguous for decades, hindering process development and adversely affecting economic viability4 relative to other propylene production technologies2,5. Here, from rigorous kinetic measurements and spectroscopic studies of propylene metathesis over model and industrial WOx/SiO2 catalysts, we identify a hitherto unknown dynamic site renewal and decay cycle, mediated by proton transfers involving proximal Brønsted acidic OH groups, which operates concurrently with the classical Chauvin cycle. We show how this cycle can be manipulated using small quantities of promoter olefins to drastically increase steady-state propylene metathesis rates by up to 30-fold at 250 °C with negligible promoter consumption. The increase in activity and considerable reduction of operating temperature requirements were also observed on MoOx/SiO2 catalysts, showing that this strategy is possibly applicable to other reactions and can address major roadblocks associated with industrial metathesis processes.

Publications 1 - 10 of 16

Ka Wing Chan

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