# Facile Access to Chelating CAArC‐Phosphine (CAArCPhos) Palladium Complexes

## TL;DR

The paper introduces a new method to synthesize chelating palladium complexes using a protecting group strategy and phosphine directing groups.

## Contribution

A novel protecting group strategy enables the synthesis of chelating CAArCPhos palladium complexes via acetate-assisted CMD-like metalation.

## Key findings

- A protection group strategy using methoxyisoindolines allows late-stage functionalization of 4-bromo isoindolium salts.
- The phosphine group directs palladation of the CAArCPhos ligand through a six-membered transition state.
- The method produces the first examples of chelating cyclic amino(aryl) carbene complexes.

## Abstract

In this article, we present a synthetic route to 4‐(diphenyl‐phosphino) isoindolium salts based on a new protecting group strategy. Key to success is the use of hemi‐aminal methyl ether precursors, which serve as base‐stable iminium salt equivalents that enable halogen‐metal exchange and subsequent functionalization. After removal of the protecting group, the catalytically active palladium(II) complexes are formed of phosphine isoindolium salts by a CMD‐like metalation process, producing the first examples of chelating cyclic amino(aryl) carbene complexes. Calculations on the mechanism support an acetate‐assisted intramolecular palladation of the cyclic amino(aryl) carbene‐phosphine (CAArCPhos) ligand enabled by the phosphine directing group through a six‐membered transition state.

A protection group strategy using methoxyisoindolines as protected iminium equivalents was developed to allow late‐stage functionalization of 4‐bromo isoindoliumsalts, enabling the synthesis of 4‐(diphenylphosphino) isoindolium salts. The phosphine functionality acts as a directing group for the palladation of the cyclic amino(aryl) carbene‐phosphine (CAArCPhos) ligand by an acetate‐assisted concerted‐metalated deprotonation (CMD)‐like process.