Andreas J. Vorholt

Towards resource efficient chemistry: tandem reactions with renewables

In an economically expanding world new sustainable concepts have to be developed in order to overcome growing problems of resource availability. Merging different “Green principles” is a promising concept in this respect, e.g. the combination of tandem reactions and renewables. This review summarizes the trends in this field and demonstrates advantages and future demands. Four reactions, namely metathesis, hydroformylation, defunctionalisation and isomerisation, have been identified for transforming renewables in tandem reactions. Every reaction yields a reactive intermediate or secures a tailored selectivity in order to use the natural molecular structure of renewables.

Telomerization of Myrcene and Catalyst Separation by Thermomorphic Solvent Systems

Telomerization of common petrochemical 1,3‐dienes such as butadiene and isoprene have long been successful with different nucleophiles; however, the telomerization of the C10 hydrocarbon myrcene was not known until now. Herein, the first telomerization of the monoterpene myrcene with diethylamine is discussed, which provides an atom‐economical way of generating C20 amines in a single step. Variation of the palladium precursors and phosphorous ligands and optimization of solvent and additives led to the optimum catalyst system [Pd(MeCN)4](BF4)2/PPh3. By using a thermomorphic solvent system, the Pd complex can be easily separated with low leaching values.

Enantioselective tandem reactions at elevated temperatures: one-pot hydroformylation/SN1 alkylation.

As model substrates for the desired tandemreaction, 1-hexene (1a) as active terminal olefin and alcohol2 as carbocation precursor were chosen. For the hydrofor-mylation, a rhodium precatalyst was selected and synthesisgas (1:1) with pressure of 30 bars was applied.Proline was selected as initial catalyst for the a-alkylationwith additional acid for carbocation generation. In a preced-ing solvent screening, DMF, THF, acetonitrile, and toluenedid not lead to significant conversion (see the Supporting In-formation), whereas the combination of chloroform with tri-fluoroacetic acid gave more encouraging results. Previousexperiments in the a-alkylation had shown Bronsted acidsto be beneficial in the organocatalytic reaction step(Table 1, entry 1).To accelerate the hydroformylation of 1-hexene (1a), sev-eral rhodium precursors were tested in this reaction. Al-though all rhodium precursors were active in this reaction,surprisingly, the frequently used [Rh(CO)

Hydroformylation and Related Reactions of Renewable Resources

Today, the increasing global population and the rising consumption of fossil resources for energy and material use are important issues for research activities in the field of transformation of renewable resources. In petrochemistry, well-established reactions like hydroformylation are performed in multiton plants all over the world and are important examples for processing new resources beyond fossil feedstocks. This chapter deals with the application of three important reactions with carbon monoxide, specifically hydroformylation, hydroaminomethylation, and hydroesterification with renewables which have a C–C-double bond in the starting material. In these reactions, unsaturated oleocompounds and a variety of terpenes can be employed because of their naturally available double bonds.

Recycling homogeneous catalysts simply via organic solvent nanofiltration: New ways to efficient catalysis

Organic solvent nanofiltration is a convenient method for the recovery of homogeneous transition metal catalysts. The long chain olefin 1‐dodecene is hydroformylated continuously, and the commercially available catalyst complex is separated efficiently using a commercially available nanofiltration membrane. An advantage of this method is that both reaction and separation take place in a single liquid phase. Only continuous operation shows interactions of reaction and separation in the long run. Low energy demand, high scalability as well as transferability to other reactions make this method promising for new industrial applications.

Palladium-Catalyzed Aminocarbonylation of Aliphatic Alkenes with N,N-Dimethylformamide as an In Situ Source of CO

The palladium‐catalyzed aminocarbonylation of aliphatic alkenes is presented for the first time without the need for external CO pressure. N,N‐dimethylformamide (DMF) is used as an in situ source of both the required carbon monoxide and the amine substrate. The applied palladium catalytic system is well‐known for a number of carbonylation reactions, including those with CO surrogates and tandem isomerizing carbonylations. The reaction pathway was investigated and proved to proceed by an acid‐catalyzed DMF decomposition to CO and dimethyl amine with subsequent aminocarbonylation of the alkene. Pressure‐versus‐time curves gave more insight into the correlation between acid concentration and aminocarbonylation activity. Aliphatic alkenes (terminal and internal) are transformed, also in commercial glassware, into the corresponding linear N,N‐dimethylamides with excellent selectivities. Hence, amide synthesis by aminocarbonylation moves closer to application in standard organic laboratories.

Direct Synthesis of an α,ω-Diester from 2,7-Octadienol as Bulk Feedstock in Three Tandem Catalytic Steps

A new tandem catalytic process was designed and developed as a tool for the direct conversion of the widely available feedstock 2,7-octadienol into an α,ω-diester. This innovative auto-tandem catalysis is atom efficient and consists of three consecutive palladium-catalysed reactions: ether formation, ether carbonylation and alkoxycarbonylation. By using the design of experiments (DoE) approach, significant parameters were determined and the yield of the desired α,ω-diester was optimised. Model substrates allowed deeper insight into the progress of the reaction to be gained and, as a result, the reaction sequence was uncovered. Furthermore, by simply applying other ligands, a different reaction path was followed, allowing other, new tandem catalytic sequences to be explored and enabling new compounds to be obtained.

Renewable Surfactants through the Hydroaminomethylation of Terpenes

A catalytic system was developed to enable the use of industrially available terpenes (e.g., β‐myrcene, β‐farnesene) in hydroaminomethylation to obtain renewable building blocks for surfactants in two steps. This homogeneously catalyzed tandem reaction includes both hydroformylation and enamine condensation steps, followed by hydrogenation. Under the optimized conditions, the Rh/1,2‐bis(diphenylphosphino)ethane catalytic system delivers products in high yields (70 %) after short reaction times (3 h) with unprecedentedly high turnover frequency (TOF) values for the hydroformylation of 1,3‐dienes of over 739 mol mol−1 h−1. This is the highest TOF reported to date for the hydroformylation of a 1,3‐diene. Furthermore, regioselectivities of 97 % and above were observed in the hydroformylation step, which is extraordinarily high for the conversion of 1,3‐dienes. The terpene‐derived amines obtained were further functionalized to quaternary ammonium compounds that were found to show surface activity quite similar to that of industrially available quaternary ammonium compounds. The hydroaminomethylation of terpenes achieves higher step efficiency than industrial means and makes use of an alternative, renewable feedstock to synthesize more environmentally friendly surfactants.

First efficient catalyst recycling for the iridium-catalysed hydroformylation of 1-octene

This paper describes the development of an efficient catalyst recycling concept for the iridium-catalysed hydroformylation of 1-octene through the investigation of biphasic systems, thermomorphic solvent systems and an ex situ extraction. Particularly high selectivities (>90%) towards the desired aldehydes as well as low rates of iridium leaching were observed using the monosulfonated triphenylphosphine ligand (TPPMS). In polar solvents such as propylene carbonate or N,N-dimethylformamide, low rates of catalyst leaching (0.2%) as well as high rates of product separation (nearly 80%) were achieved. High reaction rates and a long-term activity and stability of the catalyst were observed using the solvent N,N-dimethylformamide and the extraction with non-polar solvents.

Decreasing Side Products and Increasing Selectivity in the Tandem Hydroformylation/Acyloin Reaction

A highly selective catalyst system was developed for the recently discovered tandem hydroformylation/acyloin reaction by systematic investigations and changes of reaction conditions. This new catalyst system is characterized by an excellent selectivity of the desired reaction pathway with negligible amounts of side products. A successful application of the tandem hydroformylation/acyloin reaction to a variety of olefins is enabled with comparable excellent selectivities up to >99 % for the first and second reaction step, therefore a general synthesis for the conversion of olefins into acyloins is found. Furthermore, very good to excellent yields for the intermediates and final acyloin products were observed within two catalysed reactions in one preparative step. The acyloin product was applied as a nonpolar precursor for surfactants. After attaching a polar head group to the acyloin and determination of tensiometric data, the molecule showed industrial relevant surface‐active properties.