Structural diversity of pentafluorophenylcopper complexes. First evidence of π-coordination of unsupported arenes to organocopper aggregates

The binding behavior of arenes toward pentafluorophenylcopper was investigated. Crystallization of pentafluorophenylcopper from a mixture of 1,2-dichloroethane and cyclohexane affords the homoleptic tetrameric complex [Cu(C₆F₅)]₄, whereas a π-complex, [Cu(C ₆F₅)]₄(η²-toluene)₂, is obtained from toluene solution. The unique coordination of two toluene molecules in [Cu(C₆F₅)]₄(η ²-toluene)₂ leads to major structural changes as the regular square planar tetramer is distorted toward a butterfly structure with one short and one long diagonal Cu⋯Cu distance of 2.5935(3) and 3.955(1) Å, respectively. The toluene molecules are bound in an unsymmetrical η²-coordination mode with the shortest contacts observed between copper and the meta carbon atoms (d(Cu-C) = 2.271(2), 2.298(2) Å) and slightly longer distances to the para positions (d(Cu-C) = 2.339(2), 2.455(4) Å). Multinuclear NMR studies show that complexation to the intact tetrameric cluster species also occurs in neat solution of the aromatic species. Strongly coordinating solvents such as acetonitrile or DMSO, however, lead to aggregate breakdown.