Toward a Practical Catalyst for Convenient Deaminative Hydrogenation of Amides under Mild Conditions

Amide bond reduction is a versatile transformation offering access to various alcohols and amines that could be used as valuable precursors in the chemical and pharmaceutical industries, e.g., for manufacturing plastics, textiles, dyes, agrochemicals, etc. Over the last two decades, catalytic amide hydrogenation employing homogeneous catalysis has gained more attention due to the atom efficiency and low environmental impact of this transformation. Owing to the inherent strength of amide bonds, amide hydrogenation procedures often involve high temperatures and pressures, which is why efforts are being channeled to finding protocols with lower-energy input. Here, we report a mild amide hydrogenation method involving commercially available precursors Ru(acac)3 and 1,2-bis(di-tert-butylphosphinomethyl)benzene (L4), which under basic conditions, at 80 °C and under 30 bar of H2, can selectively hydrogenate a series of 2°-benzamides to anilines and alcohols with yields of 36–98% and 29–92%, respectively. Additionally, 1°- and 3°-amides proved to be appropriate substrates; however, low to moderate yields were obtained. The catalyst is believed to operate via an inner-sphere mechanism with a hemiaminal being the likely intermediate during the hydrogenation process

Efficient and Regioselective Ruthenium-catalyzed Hydro-aminomethylation of Olefins

An efficient and regioselective ruthenium-catalyzed hydroaminomethlyation of olefins is reported. Key to success is the use of specific 2-phosphino-substituted imidazole ligands and triruthenium dodecacarbonyl as catalyst. Both industrially important aliphatic as well as various functionalized olefins react with primary and secondary amines to give the corresponding secondary and tertiary amines generally in high yields (up to 96%) and excellent regioselectivities (<i>n/iso</i> up to 99:1)

Selective Palladium-Catalyzed Aminocarbonylation of 1,3-Dienes: Atom-Efficient Synthesis of β,γ-Unsaturated Amides

Carbonylation reactions constitute important methodologies for the synthesis of all kinds of carboxylic acid derivatives. The development of novel and efficient catalysts for these transformations is of interest for both academic and industrial research. Here, the first palladium-based catalyst system for the aminocarbonylation of 1,3-dienes is described. This atom-efficient transformation proceeds under additive-free conditions and provides straightforward access to a variety of β,γ-unsaturated amides in good to excellent yields, often with high selectivities

Formation and Reactivity of a Co₄‑μ-Alkyne Cluster from a Co(I)-Alkene Complex

Highly reactive Co­(I) complex [CpCo­(H₂CCHSiMe₃)₂] (<b>1</b>) easily forms a tetranuclear Co₄ cluster in hydrocarbon solvents under mild conditions, possessing a bridging alkyne ligand stemming from an unusual C–H activation of the H₂CCHSiMe₃ ligand. The cluster was structurally characterized, and the catalytic reactivity in [2+2+2] cycloaddition, hydroformylation, and hydrogenation reactions investigated. Interesting differences were found and compared to the mononuclear complex <b>1</b>, which could be relevant for the real catalytically active species

Toward Green Acylation of (Hetero)arenes: Palladium-Catalyzed Carbonylation of Olefins to Ketones

Green Friedel–Crafts acylation reactions belong to the most desired transformations in organic chemistry. The resulting ketones constitute important intermediates, building blocks, and functional molecules in organic synthesis as well as for the chemical industry. Over the past 60 years, advances in this topic have focused on how to make this reaction more economically and environmentally friendly by using green acylating conditions, such as stoichiometric acylations and catalytic homogeneous and heterogeneous acylations. However, currently well-established methodologies for their synthesis either produce significant amounts of waste or proceed under harsh conditions, limiting applications. Here, we present a new protocol for the straightforward and selective introduction of acyl groups into (hetero)­arenes without directing groups by using available olefins with inexpensive CO. In the presence of commercial palladium catalysts, inter- and intramolecular carbonylative C–H functionalizations take place with good regio- and chemoselectivity. Compared to classical Friedel–Crafts chemistry, this novel methodology proceeds under mild reaction conditions. The general applicability of this methodology is demonstrated by the direct carbonylation of industrial feedstocks (ethylene and diisobutene) as well as of natural products (eugenol and safrole). Furthermore, synthetic applications to drug molecules are showcased

Ligand-Controlled Palladium-Catalyzed Alkoxycarbonylation of Allenes: Regioselective Synthesis of α,β- and β,γ-Unsaturated Esters

The palladium-catalyzed regioselective alkoxycarbonylation of allenes with aliphatic alcohols allows to produce synthetically useful α,β- and β,γ-unsaturated esters in good yields. Efficient selectivity control is achieved in the presence of appropriate ligands. Using Xantphos as the ligand, β,γ-unsaturated esters are produced selectively in good yields. In contrast, the corresponding α,β-unsaturated esters are obtained with high regioselectivity in the presence of PPh₂Py as the ligand. Preliminary mechanistic studies revealed that these two catalytic processes proceed by different reaction pathways. In addition, this novel protocol was successfully applied to convert an industrially available bulk chemical, 1,2-butadiene, into dimethyl adipate, which is a valuable feedstock for polymer and plasticizer syntheses, with high yield and TON (turnover number)

From Internal Olefins to Linear Amines: Ruthenium-Catalyzed Domino Water–Gas Shift/Hydroamino­methylation Sequence

A selective ruthenium-catalyzed water–gas shift/hydroformylation of internal olefins and olefin mixtures is reported. This novel domino reaction takes place through a catalytic water–gas shift reaction, subsequent olefin isomerization, followed by hydroformylation and reductive amination. Key to the success for the efficient one-pot process is the use of a specific 2-phosphino-substituted imidazole ligand and triruthenium dodecacarbonyl as precatalyst. Industrially important internal olefins react with various amines to give the corresponding tertiary amines generally in good yield and selectivity. This reaction sequence constitutes an economically attractive and environmentally favorable process for the synthesis of linear amines

Ruthenium-Catalyzed Hydroformylation/Reduction of Olefins to Alcohols: Extending the Scope to Internal Alkenes

In the presence of 2-phosphino-substituted imidazole ligands and Ru₃(CO)₁₂ or Ru­(methylallyl)₂(COD) direct hydroformylation and hydrogenation of alkenes to alcohols takes place. In addition to terminal alkenes, also more challenging internal olefins are converted preferentially to industrially important linear alcohols in high yield (up to 88%) and regioselectivity (n:iso up to 99:1)

Selective Palladium-Catalyzed Carbonylation of Alkynes: An Atom-Economic Synthesis of 1,4-Dicarboxylic Acid Diesters

A class of novel diphosphine ligands bearing pyridine substituents was designed and synthesized for the first time. The resulting palladium complexes of <b>L1</b> allow for chemo- and regioselective dialkoxycarbonylation of various aromatic and aliphatic alkynes affording a wide range of 1,4-dicarboxylic acid diesters in high yields and selectivities. Kinetic studies suggest the generation of 1,4-dicarboxylic acid diesters via cascade hydroesterification of the corresponding alkynes. Based on these investigations, the chemo- and regioselectivities of alkyne carbonylations can be controlled as shown by switching the ligand from <b>L1</b> to <b>L3</b> or <b>L9</b> to give α,β-unsaturated esters

Rh(I)-Catalyzed Hydroamidation of Olefins via Selective Activation of N–H Bonds in Aliphatic Amines

Hydroamidation of olefins constitutes an ideal, atom-efficient method to prepare carboxylic amides from easily available olefins, CO, and amines. So far, aliphatic amines are not suitable for these transformations. Here, we present a ligand- and additive-free Rh­(I) catalyst as solution to this problem. Various amides are obtained in good yields and excellent regioselectivities. Notably, chemoselective amidation of aliphatic amines takes place in the presence of aromatic amines and alcohols. Mechanistic studies reveal the presence of Rh-acyl species as crucial intermediates for the selectivity and rate-limiting step in the proposed Rh­(I)-catalytic cycle