Our group has been exploring poly(α-olefin)s (PAOs) as alternative solvent systems for catalysis and synthesis. Such PAOs can be used as greener solvents and can substitute for conventional alkane solvents like pentane, hexanes, and heptane. PAOs that are hydrogenated dimers or trimers of 1-decene or 1-dodecene are inexpensive and commercially available. While these C20, C24, C30, or C36 hydrocarbons are more viscous than alkanes, we recently showed that they are safer solvents for organolithium reagents because of their low volatility and high flash point. This paper will discuss those results and describe further studies where these more sustainable solvents are used in a variety of organometallic reactions and as media to store organometallic species. In our prior work we showed that PAO like solid and liquid paraffin can be used to store reactive organometallics. In that prior work, we noted that &gt;50% of tert-butyllithium in PAO was still present after a solution was left in the open air overnight. Further studies show other organolithium reagents including triaryllithium reagents and polymer-supported diphenyllithium too have extended stability and these highly colored species are stable in PAO for months. We also examined alkylboranes. In this case, we showed that while trihexylborane solutions in PAO do catch fire on exposure to a torch, that the green flame due to the borane self-extinguishes after the borane is consumed. The PAO does not itself catch fire. We also showed that PAO is a recyclable solvent for hydroboration/oxidation chemistry. Dialklymagnesium reagents that are commercially available as heptane solutions can also be prepared as PAO solutions. In PAO, these dialkylmagnesium reagents behave in reactions such as carbonation, nucleophilic addition, and reduction the same as they do in heptane. Finally, we examined the recyclability and reactivity of PAO containing a polyisobutylene (PIB) bound-analog of LDA in enolate chemistry. Our results show that a PAO solution of PIB-tert-butylamide behaves like PIB-tert-butylamide in heptane or THF in formation of trimethylsilyl enol ethers with the difference being that a PAO solution of PIB-tert-butylamide is a fully recyclable reagent/solvent system.

Safer recyclable solvents for organometallic reactions

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.