# Boron, Aluminum, and Gallium Fluorides as Catalysts for the Defluorofunctionalization of Electron-Deficient Arenes: The Role of NaBArF4 Promoters

## TL;DR

This paper explores how boron, aluminum, and gallium fluorides can act as catalysts in chemical reactions involving electron-deficient arenes, with a focus on how a specific additive improves their performance.

## Contribution

The novel contribution is the discovery that NaBArF4 enhances catalytic activity by interacting with metal fluorides through weak interactions.

## Key findings

- Metal fluorides [{(ArNCMe)2CH}MF2] catalyze defluorofunctionalization of electron-deficient arenes via a metathesis mechanism.
- Addition of NaBArF4 recovers catalytic activity by forming weak M–F---Na interactions and lowering reaction barriers.
- DFT calculations show that NaBArF4 polarizes the M–F bond, facilitating hydrido fluoride formation and catalytic turnover.

## Abstract

A series of boron, aluminum, and gallium difluoride complexes
[{(ArNCMe)2CH}MF2] (M = B, Al, Ga) are reported
as catalysts
for the defluorofunctionalization of electron-deficient arenes. Thiodefluorination
reactions between TMS–SPh and poly(fluorinated aromatics) proceed
under forcing conditions. Evidence is presented for the fluoride entering
the catalytic cycle through a metathesis reaction with TMS–SPh
to form metal thiolate intermediates, e.g., [{(ArNCMe)2CH}MF(SPh)], which are then nucleophiles for addition to the aromatic
substrate, likely through a concerted SNAr mechanism. Attempts
to expand the scope of reactivity to include the hydrodefluorination
of electron-deficient arenes met with limited success. Activity could,
however, be recovered through the addition of NaBArF4 as a catalytic additive (ArF = 3,5-C6H3(CF3)2). NMR titrations suggest
that NaBArF4 is capable of coordinating with
aluminum and gallium fluoride complexes, most likely through weak
M–F---Na interactions (M = Al, Ga), and can play a role in
lowering the barrier of metathesis between [{(ArNCMe)2CH}MF2] and Et3SiH to form the group 13 hydrido fluoride
[{(ArNCMe)2CH}M(H)F], facilitating catalytic turnover.
DFT calculations indicate that this weak interaction leads to a polarization
of the M–F bond. The discovery of this additive effect has
potentially broad implications in developing new reactivity and applications
of thermodynamically stable metal fluorides.

A series of boron, aluminum, and gallium difluoride complexes
[{(ArNCMe)2CH}MF2] (M = B, Al, Ga) are reported as catalysts for the
defluorofunctionalization of electron-deficient arenes.