# B‑Alkyl-borabicyclo[3.3.1]nonane Reagents Promote Closed-Shell Nickel-Catalyzed Alkylarylation Toward Encoded Cyclooctene Monomers

## TL;DR

A new nickel-catalyzed method enables alkylarylation of cyclooctene monomers using B-alkyl-borabicyclo[3.3.1]nonane reagents, leading to tunable polymers.

## Contribution

A novel two-electron redox pathway for nickel-catalyzed alkylarylation using alkyl-9-BBN reagents is introduced.

## Key findings

- B-alkyl-borabicyclo[3.3.1]nonane reagents enable polar transmetalation in nickel-catalyzed alkylarylation.
- 5,6-alkylarylated cyclooctenes are produced and suitable for ring-opening metathesis polymerization.
- Density functional theory calculations show alkyl-9-BBN is more reactive than alkylboronic esters in transmetalation.

## Abstract

Access to new tailored
monomers is essential to explore
unprecedented
polymer structures and modulate their properties. In previous work,
we disclosed an iteroselective diarylation of 1,5-cyclooctadiene as
an attractive platform for preparing diverse cyclooctene monomers;
however, it was limited to C­(sp2) coupling partners. Established
difunctionalization methods with C­(sp3) fragments rely
on carbon-based radical formation, which is incompatible with 1,5-cyclooctadiene.
This work describes a two-electron redox manifold for the nickel-catalyzed
alkylarylation of 1,5-cyclooctadiene and discloses B-alkyl-borabicyclo­[3.3.1]­nonane (alkyl-9-BBN) as an effective transmetalating
reagent for maintaining a polar reaction mechanism. The method provides
5,6-alkylarylated cyclooctenes suitable for ring-opening metathesis
polymerization to obtain new materials. The properties of these polymers
are benchmarked and fine-tuned by variation of coupling partners in
the nickel catalysis. Density functional theory calculations revealed
that destabilization of the pretransmetalation complex promotes the
reactivity of alkyl-9-BBN in transmetalation compared to alkylboronic
esters.