Metal–Ligand Bifunctional Catalysis: The “Accepted” Mechanism, the Issue of Concertedness, and the Function of the Ligand in Catalytic Cycles Involving Hydrogen Atoms

Journal Article · Mon Aug 21 00:00:00 EDT 2017 · ACS Catalysis

DOI:https://doi.org/10.1021/acscatal.7b01791· OSTI ID:1409775

Dub, Pavel A. ^[1]; Gordon, John C. ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

For years, following the ideas of Shvo and Noyori, the core assumption of metal–ligand bifunctional molecular catalysis has relied on the direct involvement of the chelating ligand in the catalytic reaction via a reversible proton (H⁺) transfer through cleavage/formation of one of its X–H bonds (X = O, N, C). A recently revised mechanism of the Noyori asymmetric hydrogenation reaction (Dub, P. A. et al. J. Am. Chem. Soc. 2014, 136, 3505) suggests that the ligand is rather involved in the catalytic reaction via the stabilization of determining transition states through N–H···O hydrogen-bonding interactions (HBIs) and not via a reversible H⁺ transfer, behaving in a chemically intact manner within the productive cycle or predominantly in a chemically intact manner within productive cycles. By reexamining selected examples of computational mechanistic studies involving bifunctional catalysts from the literature in the years between 2012–2017, the purpose of this paper is to point out common misconceptions in modeling concerted reactions and show that the actual stepwise nature of key transition states unveils a more complicated catalytic reaction pool (all conceivable catalytic pathways and their crossovers). Such a realization can not only potentially result in a reconsideration of the “accepted” mechanism but also lead us to a new conceptual understanding of the role that the ligand plays in the reaction. Finally, the ultimate goal of this paper is, therefore, to encourage the reader to reconsider the function of the ligand in catalytic cycles of hydrogenation/dehydrogenation with bifunctional catalysts, which until recently has relied almost exclusively on a chemically noninnocent ligand.

• Research Organization: Los Alamos National Laboratory (LANL)
• Sponsoring Organization: LANL Laboratory Directed Research and Development (LDRD) Program; USDOE
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1409775
• Report Number(s): LA-UR-17-24272
• Journal Information: ACS Catalysis, Journal Name: ACS Catalysis Journal Issue: 10 Vol. 7; ISSN 2155-5435
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
Inorganic and Physical Chemistry