Solvent design for catalyst recycling of rhodium/amine catalysts via scCO2 extraction in the reductive hydroformylation of alpha olefins

Efficient transformation protocols to directly convert olefins to alcohols are highly sought after. Ethylene glycol based solvents have proved to support the reductive hydroformylation of linear alpha olefins to alcohols using [Rh(acac)(CO)(2)] in combination with tertiary amines as catalysts. Incorporation of the amine functionality into the solvent using 2-[2-(dimethylamino)ethoxylethanol allowed simplification of the reaction system to three components and a catalytic activity with a TOF of 280 h(-1) for the reductive hydroformylation of 1-octene to be achieved. To immobilize the rhodium catalyst in a recycling approach using scCO(2) as the extracting solvent for product alcohols, amine functionalized PEG derivatives have been synthesized as the stationary catalyst phase. Amide condensation of PEG(600)-diacid with trimethyldiaminoethane resulted in a diaminated PEG(600) in which the amine group is linked via an amide bridge to the PEG(600) backbone. During nine consecutive runs, in which this PEG(600-)diamine was used as the stationary catalyst phase and product alcohols have been extracted with scCO(2), no loss in activity or selectivity was observed. Leaching of the stationary phase was <= 3 wt% (<= 0.5 wt% after the first two runs) of the extracted mass per run and rhodium leaching was determined to be 0.1% of the initial rhodium over all nine runs combined.

Automated summary

Efficient transformation protocols using ethylene glycol as a solvent, along with rhodium catalysts and amines as catalysts, can convert linear alpha olefins to alcohols. By incorporating amine functionality into the solvent, the reaction system can be simplified and achieve high catalytic activity. Amine functionalized PEG derivatives are used to immobilize the rhodium catalyst, and supercritical CO(2) is used as the extracting solvent for product alcohol recycling, without any loss in activity or selectivity.