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.

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.

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