Developing greener, more benign, and more sustainable systems for synthesis is essential to modern chemistry. Our group has found that synthetically useful catalysts can be attached to polyisobutylene (PIB) and phase anchored to highly recyclable alkane solvents such as (poly-α-olefin)s (PAO)s. These PAOs are non-toxic, non-volatile, and non-flammable alternatives to traditional alkane solvents, such as hexanes and heptane. Here, we describe the synthesis of a recyclable Hunig’s base analogue – a PIB-bound diisopropylethylamine. This PAO-anchored analogue of Hunig’s base (PIB-DIPEA) does not leach to any detectable level from PAO into other polar organic solvents and can be recycled along with a PAO phase through at least 10 cycles. This recyclable PIB-DIPEA catalyst behaves exactly like Hunig’s base and was used to catalyze a Knovanagel condensation. In this application, it was reused for five cycles without any leaching or loss of PAO solvent. Products were isolated by simple solid/liquid separation in excellent yield. In addition to exploring other applications of PIB-DIPEA as a recyclable catalytic or stoichiometric base, we have also shown that PIB-DIPEA can be used in Wolf and Lamb chemistry. In this work, we showed that PIB-DIPEA in PAO does not react with a polar phase-anchored sulfonic acid. Thus, it can be used in one pot reactions where the acid catalyzes one step and the base a second step. Examples where this recyclable PIB-DIPEA/PAO system is used in multistep acid/base-catalyzed process will be discussed.

Developing a recyclable analogue of Hunig's base in a reusable polymeric solvent for organocatalytic reactions

ACS Spring 2022

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