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(C6F5)]4(η2-toluene)2, is obtained from toluene solution. The unique coordination of two
toluene molecules in [Cu(C6F5)]4(η2-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.