Catalytic Conversion of Carbon Dioxide to Long Chain Esters via Formate Hydroesterification

CO₂-based hydroesterification is an attractive route to produce value added ester compounds, which could replace widely used CO-based hydroesterification processes if sufficient catalytic technologies are developed. One path to CO₂-based hydroesterification could proceed through an organoformate intermediate, which is then used in olefin hydroesterification to generate the desirable esters. This route opens the possibility of creating a net CO₂-based hydroesterification process using tandem catalytic systems for CO₂ hydrogenation to organoformate paired with formate-olefin hydroesterification. The tandem use of tripodal phosphine ruthenium(II) and 1,2-bis(di-tert-butylphosphinomethyl)benzene palladium catalysts were found to successfully produce methyl nonanoate from CO₂, H₂, methanol and 1-octene in a single-stage batch process. The CO₂-based hydroesterification catalysis efficiency was found to be largely limited by the productivity of organoformate generation and competitive 1-octene reduction. Catalytic yields of methyl nonanoate can be enhanced by adjustments in reaction procedures, including the use of a two-stage batch reaction process or delayed introduction of 1-octene, achieving a yield of up to 32 %. Under select conditions, control experiments indicate yields of methyl nonanoate can be improved to ca 75 %. Preliminary studies indicate significant interplay between the two ligands employed in the molecular tandem catalytic systems and establish the first catalytic protocol for the selective CO₂-based hydroesterification of olefins via organoformates.