Ivana Fleischer

Alternative Metals for Homogeneous Catalyzed Hydroformylation Reactions

Transition-metal-catalyzed hydroformylation reactions constitute one of the most powerful tools for C-C bond formation in organic synthesis and represent an outstanding example of the application of homogeneous catalysis on an industrial scale. This process allows for the straightforward conversion of inexpensive chemical feedstock into broadly applicable aldehydes, which serve as major building blocks for numerous chemical products. These products are highly valuable for the chemical industry and used as plasticizers, detergents, and surfactants on a million ton scale. Moreover, aldehydes serve as versatile chemical intermediates for the production of fine chemicals and pharmaceuticals. Currently, most of the bulk hydroformylation processes rely on rhodium-based catalysts. The increasing demand and resulting high cost of this precious metal has resulted in alternative transition-metal catalysts becoming highly desirable. The following Review summarizes the progress achieved utilizing Ru, Ir, Pd, Pt, and Fe catalysts in hydroformylation reactions.

Ruthenium-catalysed alkoxycarbonylation of alkenes with carbon dioxide

Alkene carbonylations represent a major technology for the production of value-added bulk and fine chemicals. Nowadays, all industrial carbonylation processes make use of highly toxic and flammable carbon monoxide. Here we show the application of abundantly available carbon dioxide as C1 building block for the alkoxycarbonylations of industrially important olefins in the presence of a convenient and inexpensive ruthenium catalyst system. In our system, carbon dioxide works much better than the traditional combination of carbon monoxide and alcohols. The unprecedented in situ formation of carbon monoxide from carbon dioxide and alcohols permits an efficient synthesis of carboxylic acid esters, which can be used as detergents and polymer-building blocks. Notably, this transformation allows the catalytic formation of C-C bonds with carbon dioxide as C1 source and avoids the use of sensitive and/or expensive reducing agents (for example, Grignard reagents, diethylzinc or triethylaluminum).

Enantioselective Michael Addition to α,β-Unsaturated Aldehydes: Combinatorial Catalyst Preparation and Screening, Reaction Optimization, and Mechanistic Studies

Shortcut to chiral catalysts: An efficient combinatorial strategy based on back reaction screening by ESI-MS allows rapid evaluation of organocatalysts for the asymmetric Michael addition to α,β-unsaturated aldehydes (see scheme). An unexpected nonlinear effect has been observed in this reaction, resulting from a double nucleophilic–electrophilic activation mechanism involving two catalyst molecules.

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).

A Unique Palladium Catalyst for Efficient and Selective Alkoxycarbonylation of Olefins with Formates

Forget about CO! Carbonylations are among the most important homogeneously catalyzed reactions in the chemical industry, but typically require carbon monoxide. Instead, straightforward and efficient alkoxycarbonylations of olefins can proceed with alkyl formates in the presence of a specific palladium catalyst. Aromatic, terminal aliphatic, and internal olefins are carbonylated to give industrially important linear esters at low catalyst loadings.

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 (n/iso up to 99:1).

Development of a Ruthenium/Phosphite Catalyst System for Domino Hydroformylation–Reduction of Olefins with Carbon Dioxide

An efficient domino ruthenium-catalyzed reverse water-gas-shift (RWGS)-hydroformylation-reduction reaction of olefins to alcohols is reported. Key to success is the use of specific bulky phosphite ligands and triruthenium dodecacarbonyl as the catalyst. Compared to the known ruthenium/chloride system, the new catalyst allows for a more efficient hydrohydroxymethylation of terminal and internal olefins with carbon dioxide at lower temperature. Unwanted hydrogenation of the substrate is prevented. Preliminary mechanism investigations uncovered the homogeneous nature of the active catalyst and the influence of the ligand and additive in individual steps of the reaction sequence.

Towards the Development of a Selective Ruthenium-Catalyzed Hydroformylation of Olefins

The ruthenium-catalyzed hydroformylation of 1- and 2-octene to give preferentially the corresponding linear aldehyde is reported. The catalyst system comprising of Ru3 (CO)12 and an imidazole-substituted monophosphine ligand allows for high chemo- and regioselectivity. The hydroformylation proceeds with unprecedented rates for a ruthenium-based catalyst.

Regioselective Thiocarbonylation of Vinyl Arenes

A palladium-catalyzed thiocarbonylation of styrene derivatives is reported for the first time. The combination of thiols as nucleophiles and a bidentate ligand ensures a unique reaction outcome with high regioselectivity toward the more valuable branched isomer and new reactivity. The ambient reaction conditions (temperature, catalyst loading) and the use of a CO surrogate render this transformation a useful method for the synthesis of thioesters from available feedstock. Various functional groups on arene and thiol substituents are tolerated by the system. Notably, challenging ortho-substituted styrenes are converted with unprecedentedly high regioselectivity.

Brønsted acid-catalyzed hydroarylation of activated olefins

A mild, regiospecific Bronsted acid-catalyzed hydroarylation of activated olefins, capable of the formation of quinone methide-like intermediates, has been investigated. Variously substituted 2- and 4-vinylphenols, 4-vinylaniline or 6-vinyl-naphthalen-2-ol were successfully implemented in a sequential protonation and Friedel–Crafts-type alkylation reaction of electron-rich arenes.