ROMP-Boranes as Moisture-Tolerant and Recyclable Lewis Acid Organocatalysts

Although
widely used in catalysis, the multistep syntheses and
high loadings typically employed are limiting broader implementation
of highly active tailor-made arylborane Lewis acids and Lewis pairs.
Attempts at developing recyclable systems have thus far met with limited
success, as general and versatile platforms are yet to be developed.
We demonstrate a novel approach that is based on the excellent control
and functional group tolerance of ring-opening metathesis polymerization
(ROMP). The ROMP of highly Lewis acidic borane-functionalized phenylnorbornenes
afforded both a soluble linear copolymer and a cross-linked organogel.
The polymers proved highly efficient as recyclable catalysts in the
reductive N-alkylation of arylamines under mild conditions
and at exceptionally low catalyst loadings. The modular design presented
herein can be readily adapted to other finely tuned triarylboranes,
enabling wide applications of ROMP-borane polymers as well-defined
supported organocatalysts.