The rational development of catalytic reactions involving cooperative behavior between two catalytic reactive sites represents a frontier area of research from which novel reactivity and selectivity patterns emerge. Within this context, this Feature highlights the development of a cooperative system involving transition metal Lewis acid/base pairs. Bimetallic systems consisting of copper carbene Lewis acids and metal carbonyl anion Lewis bases, (NHC)Cu–[M CO ], are easily synthesized from readily available organometallic building blocks (NHC = N-heterocyclic carbene; [M CO ] − = metal carbonyl anion, e.g. [FeCp(CO) 2 ] − , [Mn(CO) 5 ] − , etc. ). Stoichiometric reactivity studies indicate that the dative Cu←M bonds in these systems are labile towards heterolysis under mild conditions, thus providing in situ access both to polar metal–metal bonds and to “frustrated” transition metal Lewis acid/base pairs as dictated by reaction conditions. Catalytic transformations ranging from C–C and C–B coupling reactions to hydrogenation and other reductions have been developed from both manifolds: bimetallic catalysis involving (a) binuclear intermediates engaging in cooperative bond activation and formation, and (b) orthogonal mononuclear intermediates that operate in either tandem or co-dependent manners. Preliminary indications point to the future emergence of novel reactivity and selectivity patterns as these new motifs undergo continued development, and additionally demonstrate that the relative matching of two reactive sites provides a method for controlling catalytic behavior. Collectively, these results highlight the fundamental importance of exploring unconventional catalytic paradigms.
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Catalyst-free transfer hydrogenation of activated alkenes exploiting isopropanol as the sole and traceless reductant
Both metal-catalyzed and organocatalytic transfer hydrogenation reactions are widely employed for the reduction of CO and CN bonds. However, selective transfer hydrogenation reactions of CC bonds remain challenging. Therefore, the chemoselective transfer hydrogenation of olefins under mild conditions and in the absence of metal catalysts, using readily available and inexpensive reducing agents ( i.e. primary and secondary alcohols), will mark a significant advancement towards the development of green transfer hydrogenation strategies. Described herein is an unconventional catalyst-free transfer hydrogenation reaction of activated alkenes using isopropanol as an eco-friendly reductant and solvent. The reaction gives convenient synthetic access to a wide range of substituted malonic acid half oxyesters (SMAHOs) in moderate to good yields. Mechanistic investigations point towards an unprecedented hydrogen bond-assisted transfer hydrogenation process.
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- Award ID(s):
- 2102462
- NSF-PAR ID:
- 10409397
- Date Published:
- Journal Name:
- Green Chemistry
- Volume:
- 25
- Issue:
- 2
- ISSN:
- 1463-9262
- Page Range / eLocation ID:
- 746 to 754
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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N ‐dentate ligands, dinuclear Rh complexes and Fe/Mn phthalocyanine catalysts. -
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Z ‐selective semihydrogenation of alkynes and selective hydrogenation of C=C bonds in α,β‐unsaturated aldehydes and ketones. Spectroscopic studies established the dinickel complex (bpy⋅−)NiII(μ 2‐H)2NiII(bpy⋅−) as the active catalyst. MOF‐NiH efficiently catalyzed selective hydrogenation reactions with turnover numbers of up to 192 and could be used in five cycles of hydrogenation reactions without catalyst leaching or significant decrease of catalytic activities. The present work uncovers a synthetic strategy toward solution‐inaccessible Earth‐abundant bimetallic MOF catalysts for sustainable catalysis. -
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A mechanistic investigation on the ethanol self-condensation reaction (Guerbet reaction) catalyzed by a bis(pyridylimino)isoindolate Ru( ii ) catalyst was performed using a specifically designed continuously-stirred tank reactor (CSTR). Leveraging vapor–liquid equilibrium, the homogeneous catalyst was maintained in the reactor at a constant concentration by dissolving it in a non-volatile solvent while volatile substrates were fed continuously. The activity of the catalyst was monitored by analyzing the vapor exiting the reactor (reagents and products) using an in-line gas chromatograph. The formation of C 6 products demonstrates the catalyst's reactivity towards butanol, and the detection of solely saturated products implies that hydrogenation is fast under the reaction conditions. These observations led us to perform a detailed study of the hydrogenation step that provided evidence for a hydrogen-transfer pathway. The corresponding reaction mechanism for the Guerbet reaction was established.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d2gc04315g
