# Sterically Stabilized Homoleptic Copper and Gold Allyl Complexes

## TL;DR

Researchers created stable copper and gold allyl complexes that remain intact at room temperature and can perform chemical reactions.

## Contribution

The paper introduces stable homoleptic copper and gold allyl complexes with unique structural and reactivity properties.

## Key findings

- The potassium bis(allyl)cuprate complex is stable in solid and solution states at room temperature.
- The complex enables conjugate (1,4)-allylation of α,β-unsaturated ketones in hexanes.
- Gold analogs of the complexes are structurally similar but show different addition chemistry compared to copper.

## Abstract

Well-defined allyl derivatives of the coinage metals
remain rare,
often owing to their thermal and redox sensitivity. We report the
isolation of a potassium bis­(allyl)­cuprate, [KCuA′2] (A′ = 1,3-(SiMe3)2C3H3), prepared with either solution or mechanochemical methods,
which is stable at room temperature in both the solid state and solution.
In the solid state, it crystallizes as a dimer ([{KCuA′2}2]), featuring a planar K2Cu2 core and η1-bound allyl ligands. In neat hexanes,
[{KCuA′2}2] enables conjugate (1,4)-allylation
of α,β-unsaturated ketones. It does not transmetallate
when treated with lithium or sodium salts but converts to the crystallographically
authenticated, but less stable neutral tetramer, [{CuA′}4], which possesses μ-η:1η2 allyl bridges and a puckered Cu4 ring. Gold analogs
of both the anionic and neutral complexes have also been prepared
([{KAuA′2}2] and [{AuA′}4], respectively) and are structurally similar to their copper counterparts.
However, the potassium bis­(allyl)­aurate does not perform the same
addition chemistry as its copper analogue. DFT calculations on the
unsubstituted di­(allyl) cuprates (i.e., [{(Li,K)­Cu­(C3H5)2}2]) suggest that both the trimethylsilyl
groups and the substitution of Li+ with K+ influence
the aggregation of potassium bis­(allyl)­cuprate. These findings provide
structural and reactive benchmarks for coinage-metal allyl complexes.