Sterically Stabilized Homoleptic Copper and Gold Allyl Complexes

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.