Catalytic Semihydrogenation of the Triple Bond

Marvell, Elliot N.; Li, Thomas

doi:10.1055/s-1973-22234

“…[45,50,51,[84][85][86][87][88][89] Our group has previouslyr eported ac atalytic system that was proposed to proceed via an in situ generated molecular [Pd 0 (IMes)] speciesa st he active catalyst( IMes = 1,3-bis-mesityl-imidazol-2-ylidene) (Scheme 5). [46,[90][91][92] Sprengers et al reported that the in situ generated catalyst is significantly more active than the isolated catalyst. [93] One explanation for this higher activity is that less maleic anhydride (MA) ligand is appliedf or the in situ generated species.…”

Section: Pdmentioning

confidence: 99%

Pd‐Catalyzed Z‐Selective Semihydrogenation of Alkynes: Determining the Type of Active Species

Drost

¹

,

Rosar

²

,

Marta

³

et al. 2015

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A protocol was developed to distinguish between well‐defined molecular and nanoparticle‐based catalysts for the Pd‐catalyzed semihydrogenation reaction of alkynes to Z‐alkenes. The protocol applies quantitative partial poisoning and dynamic light scattering methods, which allow the institution of additional validation experiments. For the quantitative partial poisoning method, tetramethylthiourea (TMTU) was developed as an alternative for the standard poison ligand CS2, and was found to be superior in its applicability. The protocol and the TMTU poison ligand were validated using the well‐described [PdII(phenanthroline)]‐catalyzed copolymerization of styrene and CO, confirming that this system is clearly operating as a well‐defined molecular catalyst. The protocol was subsequently applied to three catalyst systems used for the semihydrogenation of alkynes. The first was proposed to be a molecular [Pd0(IMes)] catalyst that uses molecular hydrogen, but the data gathered for this system, following the new protocol, clearly showed that nanoparticles (NPs) are catalytically active. The second catalyst system studied was an N‐heterocyclic carbene (NHC) Pd system for transfer semihydrogenation using formic acid as the hydrogen source, which was proposed to operate through an in situ generated molecular [Pd0(IMes)] catalyst in earlier studies. The investigations showed that only a small fraction of the Pd added becomes active in the catalytic reaction and that NPs are formed. However, despite these findings, a clear distinction between catalytic activity of NPs versus a molecular catalyst could not be made. The third investigated system is based on a [PdII(IMes)(η3‐allyl)Cl] precatalyst with additive ligands. The combined data gathered for this system are multi‐interpretable, but suggest that a partially deactivated molecular catalyst dominates in this reaction.

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“…Although alternative homogeneous systems have been developed, none of these have replaced heterogeneous palladium catalysts for cisselective semihydrogenation which is still widely used in numerous total synthesis of natural products. [26][27][28] Transition metal nanoparticles typically of the size less than 10 nm in diameter are now emerging as an important family of catalysts for various reactions. [29][30][31][32] These metal nano colloids as sometimes called are usually obtained by the reduction of metal compounds in the presence of stabilizing agents such as polymers, surfactants, polyoximes etc.…”

Section: Introductionmentioning

confidence: 99%

Palladium Nanoparticles Suspended in an Ionic Liquid as Reusable Catalyst for Alkyne Semihydrogenation

Lee¹,

Kim²,

Cheong³

et al. 2010

Bulletin of the Korean Chemical Society

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The reaction of PdCl2 dispersed in tetra-n-butylammonium bromide with tributyl amine at 120 o C under argon leads to stable isolable nanometric particles. X-ray diffraction analysis of the material indicated that it is constituted of Pd(0). Transmission electron microscopy analysis of the particles dispersed in acetone shows the mean particle size distribution (4 ± 1 nm). The isolated palladium nanoparticles can be dispersed in an ionic liquid or in methanol or used in solventless condition for selective hydrogenation of 2-hexyne under mild reaction conditions(0.2 MPa and 20 o C). The commercial variety of the Lindlar catalyst was also studied for comparative investigations.

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“…Many studies have been carried out with transition metals as additives. The addition of additional modifiers such as sulfur compounds seems to have the effect of selectively blocking unselective sites [67]. The addition of lead seems to block certain active sites and thus to depress the activity and enhance the selectivity [65].…”

Section: E Catalyst Modifiersmentioning

confidence: 99%

Selective Hydrogenation of Functionalized Hydrocarbons

Blaser¹,

Schnyder²,

Steiner³

et al. 2008

Handbook of Heterogeneous Catalysis

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The sections in this article are Introduction Significance of Catalytic Methods in Organic Synthesis Guidelines for the Selection of a Catalytic Hydrogenation System Introduction General Approaches to Tuning Catalytic Processes A Selectivity in Catalytic Hydrogenation: a Challenge for Organic Chemists B Concepts and Tools Useful for Catalytic Hydrogenation General Strategy and Experiment Planning Catalyst Selection A Metal Selection B Catalyst Support C Catalyst Particle Size and Morphology D Porosity of the Support and Location of the Metal E Metal Dispersion and Metal Crystallite Size F Other Factors Selection of the Reaction Medium A Solvent B Acids and Bases C Catalyst Modifiers Reaction Conditions A Temperature B Hydrogen Pressure C Substrate Concentration D Catalyst Loading and Substrate to Catalyst Ratio E Degree of Conversion Chemoselectivity in Catalytic Hydrogenation Selective Hydrogenation of Functionalized Aromatic Nitro Compounds Introduction Mechanism of Nitroarene Reductions Practical Aspects A Catalysts B Reaction Medium and Conditions C Safety and Health Aspects a Hazards Related to Hydrogen b Hazards Related to the Catalyst c Hazards Due to the Hydrogenation Reaction d Hazards Due to the High Decomposition Energy of Aromatic Nitro Compounds and some Intermediates e Toxicity D Hydrogenation Equipment Selective Hydrogenation of Halogenated Nitroarenes A Introduction B Catalysts a Modified Catalysts b In Situ Modification New Catalyst Systems for the Hydrogenation of a Nitro Group in the Presence of Reducible Functional Groups A Lead‐Modified Platinum Catalysts: the “Lindlar Approach” B H 3 PO 2 ‐Modified Pt Catalysts in the Presence of Vanadium Promoters Hydroxylamine Accumulation Selective Semihydrogenation of Alkynes Introduction Chemical and Physical Background for Selectivity in Alkyne Hydrogenation Tools to Achieve Selectivity for Alkene Formation A Metal Selection B Chemical Composition of the Support C Metal Location D Metal Dispersion and Crystallite Size E Catalyst Modifiers F Solvent G Temperature H Hydrogen Pressure I Substrate Concentration J Catalyst/Substrate Ratio K Agitation L Degree of Conversion Selective Catalytic Debenzylation Introduction Catalysts Used for Selective Debenzylation Influence of Reaction Conditions A Hydrogen Source and Pressure B Solvent, Modifiers and Promoters Selective Removal of Benzyl Groups A Selective Removal of O ‐Benzyl Groups in the Presence of other O ‐Benzyl Groups B Selective Removal of O ‐Benzyl Groups in the Presence of N ‐Benzyl Groups C Selective Removal of O ‐Benzyl Groups in the Presence of other Reducible Functions D Selective Removal of N ‐Benzyl Groups in the Presence of other N ‐Benzyl Groups E Selective Removal of N ‐Benzyl Groups in the Presence of other Reducible Functions F New Protecting Groups Mechanism of Debenzylation and Mode of Action of Modifiers Stereoselective Reactions Diastereoselective Hydrogenation Enantioselective Hydrogenation Chemoselective Hydrogenation of Nitriles Primary Amine Formation Chemoselective Hydrogenation of Unsaturated Nitriles

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Catalytic Semihydrogenation of the Triple Bond

Cited by 113 publications

References 0 publications

Pd‐Catalyzed Z‐Selective Semihydrogenation of Alkynes: Determining the Type of Active Species

Pd‐Catalyzed Z‐Selective Semihydrogenation of Alkynes: Determining the Type of Active Species

Palladium Nanoparticles Suspended in an Ionic Liquid as Reusable Catalyst for Alkyne Semihydrogenation

Selective Hydrogenation of Functionalized Hydrocarbons

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