Pincer Catalyst Research Articles

Correction to "Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal-Ligand Cooperativity Enables Selective Alkyne Hydrogenation".

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to “Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal–Ligand Cooperativity Enables Selective Alkyne Hydrogenation”Kuei-Nin T. Tseng, Jeff W. Kampf, and Nathaniel K. Szymczak*Cite this: J. Am. Chem. Soc. 2017, 139, 49, 18122Publication Date (Web):November 27, 2017Publication History Published online27 November 2017Published inissue 13 December 2017https://doi.org/10.1021/jacs.7b09662Copyright © 2017 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2390Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (455 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information Get e-Alerts

Direct Hydrogenation of a Broad Range of Amides under Base‐free Conditions using an Efficient and Selective Ruthenium(II) Pincer Catalyst

AbstractThe ruthenium(II) complex, [fac‐PNHN]RuH(η1‐BH4)(CO) (B; PNHN=8‐(2‐diphenylphosphinoethyl)aminotrihydroquinoline), is a highly versatile and effective catalyst (loadings of 0.1–1 mol %) for the hydrogenation of a multitude of amides, which include primary, secondary, and tertiary amides, to give their corresponding alcohols and amines in high yields under base‐free conditions. All products were confirmed by using GC and GC–MS.

Facile Ruthenium(II)-Catalyzed α-Alkylation of Arylmethyl Nitriles Using Alcohols Enabled by Metal–Ligand Cooperation

A facile ruthenium(II)-catalyzed α-alkylation of arylmethyl nitriles using alcohols is reported. The ruthenium pincer catalyst serves as an efficient catalyst for this atom-economical transformation that undergoes alkylation via borrowing hydrogen pathways, producing water as the only byproduct. Arylmethyl nitriles containing different substituents can be effectively alkylated using diverse primary alcohols. Notably, using ethanol and methanol as alkylating reagents, challenging ethylation and methylation of arylmethyl nitriles were performed. Secondary alcohols do not undergo alkylation reactions. Thus, phenylacetonitrile was chemoselectively alkylated using primary alcohols in the presence of secondary alcohols. Diols provided a mixture of products. When deuterium-labeled alcohol was used, the expected deuterium transposition occurred, providing both α-alkylation and α-deuteration of arylmethyl nitriles. Consumption of nitrile was monitored by GC, which indicated the involvement of first-order kinetics....

Oxidative Transformations of Biosourced Alcohols Catalyzed by Earth‐Abundant Transition Metals

AbstractThe catalytic acceptorless dehydrogenative oxidation of biosourced alcohols into carboxylic acid salts was achieved using earth‐abundant Fe and Mn complexes that feature aliphatic PNP pincer ligands in good to excellent yields. The Fe derivatives were characterized by using 57Fe NMR spectroscopy. Mn pincer catalysts are catalytically more efficient than their Fe counterparts thanks to their robustness under basic conditions. Attempts to generate aldehydes from alcohols were not successful using the Fe and Mn species, but a commercially available Ru analogue achieves this transformation selectively under very mild conditions in the presence of a large excess of acetone as a hydrogen acceptor.

Selective Catalytic Hydrogenation of Arenols by a Well-Defined Complex of Ruthenium and Phosphorus–Nitrogen PN3–Pincer Ligand Containing a Phenanthroline Backbone

Selective catalytic hydrogenation of aromatic compounds is extremely challenging using transition-metal catalysts. Hydrogenation of arenols to substituted tetrahydronaphthols or cyclohexanols has been reported only with heterogeneous catalysts. Herein, we demonstrate the selective hydrogenation of arenols to the corresponding tetrahydronaphthols or cyclohexanols catalyzed by a phenanthroline-based PN3-ruthenium pincer catalyst.

Dehydrogenative coupling of alcohols to esters on a silica polyamine composite by immobilized PNN and PONOP pincer complexes of ruthenium

Heterogenization of catalytically important homogeneous catalysts on solid supports has become an expanding area of research. PNN and PONOP ruthenium pincer complexes were immobilized on a silica poly(allylamine) composite, BP-1 by a two-step Mannich reaction. The complexes on BP-1 were characterized by solid state NMR, FT-IR, elemental analysis, and metal digestion studies. Model solution experiments were carried out to determine the site of electrophilic substitution on the pyridine ring of the pincer complexes and revealed substitution in both the meta- and para-position. The catalytic reactivity of immobilized (PNN)RuH(Cl)(CO) and (PONOP)RuH(Cl)(CO) on BP-1 was studied for the dehydrogenative coupling of alcohols to esters with the liberation of H2. Moderate to good ester yields were realized with both immobilized systems without using the base required for the homogeneous reaction and also in the presence of KOH. The homogeneous model reactions required a base for ester formation. The amine functionality on BP-1 served as the base to generate the active pincer catalyst on the BP-1 surface. Both immobilized catalysts were recycled for multiple alcohol reaction cycles. Four-step control experiments were carried out using an alcohol and both immobilized systems. The results revealed the heterogeneity of the alcohol catalysis by both BP-1-Ru-PNN and BP-1-Ru-PONOP systems. This study has opened a new catalytic methodology for reactions where base is required for catalyst activation, by using a solid support with basic functionality.

Additive-Free Cobalt-Catalyzed Hydrogenation of Esters to Alcohols

Here, we report an additive-free catalytic system for hydrogenation of carboxylic acid esters to alcohols with a well-defined cobalt pincer catalyst precursor. Various substrates, including methyl, ethyl, and benzyl esters, have been evaluated under hydrogenation conditions; however, methyl esters have low reactivity compared to those of the corresponding ethyl and benzyl esters. The biomass-derived γ-valerolactone successfully formed 1,4-pentanediol with a turnover number of 3890 with this system. Metal–ligand cooperativity is probed with the related [PN(Me)P] derivative of the cobalt catalyst, and the results suggest a nonbifunctional hydrogenation mechanism.

Hydrogen autotransfer and related dehydrogenative coupling reactions using a rhenium(i) pincer catalyst.

A novel rhenium complex bearing a non-innocent PNP pincer ligand was prepared. This novel catalyst is active in hydrogen autotransfer reactions to form new C-C and C-N bonds. More specifically, valuable alkylations of ketones and sulfonamides with primary alcohols are herein presented. In addition, the first examples of rhenium-catalysed synthesis of pyrroles are described by dehydrogenative coupling of diols, amines and ketones.

A Stable Manganese Pincer Catalyst for the Selective Dehydrogenation of Methanol

AbstractFor the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long‐term stability was demonstrated for the Mn‐PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.

A Stable Manganese Pincer Catalyst for the Selective Dehydrogenation of Methanol.

For the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long‐term stability was demonstrated for the Mn‐PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.

ChemInform Abstract: Ru‐MACHO‐Catalyzed Highly Chemoselective Hydrogenation of α‐Keto Esters to 1,2‐Diols or α‐Hydroxy Esters.

A ruthenium pincer catalyst has been shown to be highly effective for the hydrogenation of a wide range of α-keto esters, affording either diols or hydroxy esters depending on the choice of reaction conditions. Strong base, high temperature, and pressure favor the formation of diols whilst the opposite is true for the hydroxy esters.

Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal–Ligand Cooperativity Enables Selective Alkyne Hydrogenation

A new series of bifunctional Ru complexes with pendent Lewis acidic boranes were prepared by late-stage modification of an active hydrogen-transfer catalyst. The appended boranes modulate the reactivity of a metal hydride as well as catalytic hydrogenations. After installing acidic auxiliary groups, the complexes become multifunctional and catalyze the cis-selective hydrogenation of alkynes with higher rates, conversions, and selectivities compared with the unmodified catalyst.

ChemInform Abstract: Recent Developments of Iron Pincer Complexes for Catalytic Applications

AbstractReview: 95 refs.

DFT Study of Acceptorless Alcohol Dehydrogenation Mediated by Ruthenium Pincer Complexes: Ligand Tautomerization Governing Metal Ligand Cooperation.

Metal ligand cooperation (MLC) catalysis is a popular strategy to design highly efficient transition metal catalysts. In this presented theoretical study, we describe the key governing factor in the MLC mechanism, with the Szymczak's NNN-Ru and the Milstein's PNN-Ru complexes as two representative catalysts. Both the outer-sphere and inner-sphere mechanisms were investigated and compared. Our calculated result indicates that the PNN-Ru pincer catalyst will be restored to aromatic state during the catalytic cycle, which can be considered as the driving force to promote the MLC process. On the contrary, for the NNN-Ru catalyst, the MLC mechanism leads to an unfavored tautomerization in the pincer ligand, which explains the failure of the MLC mechanism in this system. Therefore, the strength of the driving force provided by the pincer ligand actually represents a prerequisite factor for MLC. Spectator ligands such as CO, PPh3, and hydride are important to ensure the catalyst follow a certain mechanism as well. We also evaluate the driving force of various bifunctional ligands by computational methods. Some proposed pincer ligands may have the potential to be the new pincer catalysts candidates. The presented study is expected to offer new insights for MLC catalysis and provide useful guideline for future catalyst design.

Ru-MACHO-Catalyzed Highly Chemoselective Hydrogenation of α-Keto Esters to 1,2-Diols or α-Hydroxy Esters

A ruthenium pincer catalyst has been shown to be highly effective for the hydrogenation of a wide range of α-keto esters, affording either diols or hydroxy esters depending on the choice of reaction conditions. Strong base, high temperature, and pressure favor the formation of diols whilst the opposite is true for the hydroxy esters.

A self-catalytic role of methanol in PNP-Ru pincer complex catalysed dehydrogenation

Extracting hydrogen from methanol is a safe and cost-efficient strategy for fuel supply. This process was realized recently at a mild condition with excellent efficiency by ruthenium pincer catalysts. Despite the experimental success, the associated mechanism remains under debate. With the aid of density functional theory (DFT) calculations, an updated and self-consistent mechanism which involves MeOH-catalysed dehydrogenation of ruthenium hydride intermediate and pre-protonation of the pincer ligand was present herein. This mechanism is kinetically favoured over the previously-proposed water- or formicacid-participated ones and more consistent with the optimal experimental condition where strong base and neat methanol solvent are used.

ChemInform Abstract: Hydrogenation of Aliphatic and Aromatic Nitriles Using a Defined Ruthenium PNP Pincer Catalyst.

AbstractThis developed protocol for the efficient Ru‐catalyzed reduction of nitriles allows the conversion of aliphatic, aromatic, and heteroaromatic into the corresponding amines.

The synthesis and efficient one-pot catalytic "self-breeding" of asymmetrical NC(sp(3))E-hybridised pincer complexes.

Cyclopalladation of the pyridyl-substituted chiral phosphine sulfide (N-P=S) and oxide (N-P=O) compounds afforded the asymmetric N-C(sp(3))*-S and N-C(sp(3))*-O pincer complexes. When applied as catalysts in asymmetric hydrophosphination, the newly developed aliphatic pincer catalyst could be recycled over three runs and obtained in large quantities via a one-pot "self-breeding" catalytic protocol.

Correction to Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Correction to Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Dehydrogenation of pyrrolidine based liquid organic hydrogen carriers by an iridium pincer catalyst, an isothermal kinetic study

A previously known homogenous iridium POCOPtBu pincer catalyst and several pyrrolidine based liquid organic hydrogen carriers (LOHCs) were investigated under dehydrogenation conditions and analyzed in a pseudo first order kinetic fashion to determine various kinetic properties. Dehydrogenation onset temperatures (DOT) of 180, 160, and 140 °C; activation energies (EA) of 115, 142, and 166 (kJ/mol); and frequency factor (A) values of 3.56 × 108, 1.05 × 1011, and 2.17 × 1014 (s−1) were found for ethyl perhydro carbazole (EPHC, 2), methyl perhydro indole (MePHI, 3), and butyl pyrrolidine (BuPy, 4) respectively. The dehydrogenation onset temperatures correlate with collision frequency factors rather than the activation energies. This evidence suggests that it is a steric constraint approach of the LOHC rather than a barrier to C–H bond activation at the iridium center which limits the rate of reaction.