# Direct metathesis of carbon–carbon σ-bonds at a versatile macrocycle-supported diiron platform

## TL;DR

Scientists achieved a direct and efficient way to swap carbon-carbon bonds using a diiron complex, offering a new method for molecular engineering.

## Contribution

The first direct C–C σ-bond metathesis using a diiron complex without relying on π-bond chemistry or external activation factors.

## Key findings

- A diiron complex enables direct C(sp)–C(sp2) σ-bond metathesis through oxidative addition and reductive elimination.
- Lewis acid catalysts facilitate aryl-group exchange between diiron sites, enabling bond reformation.
- The process was demonstrated between diphenylacetylene and various diarylacetylenes in a stoichiometric reaction.

## Abstract

The metathesis of C–C σ-bonds holds potential as an atom-economical strategy for molecular engineering. While this reaction has been achieved in industrial and research settings, the former is energy-intensive and the latter has only been reported to operate either indirectly, proceeding through well-known π-bond metathesis chemistry, or through the use of structural/electronic factors that assist in C–C bond activation (e.g. anchimeric effects, directing groups, photochemical effects, etc.). Herein, we report the first example of a direct, thermodynamically favored C–C σ-bond metathesis reaction in which the C(sp)–C(sp2) bonds of diarylacetylenes are selectively cleaved before their fragments are metathesized and C(sp)–C(sp2) linkages are re-formed. Building on a known macrocycle-supported diiron system that undergoes selective C–C σ-bond oxidative addition, Lewis acid catalysts are shown to reversibly abstract Fe-bound aryl groups and perform aryl group exchange between diiron sites. Oxidatively induced reductive elimination reactions then re-form the C(sp)–C(sp2) σ-bonds to generate metathesis products. These studies culminated in a stoichiometric process for C–C σ-bond metathesis between diphenylacetylene and various diarylacetylenes.

The first example of a direct C(sp)–C(sp2) σ-bond metathesis occurs at a diiron complex. Following σ-bond oxidative addition, catalytic aryl-group exchange by Lewis acids precedes oxidatively induced reductive elimination to yield the products.